WO2017032699A1

WO2017032699A1 - Method for producing low-boiling (meth)acrylic acid esters

Info

Publication number: WO2017032699A1
Application number: PCT/EP2016/069674
Authority: WO
Inventors: Martin KALLER; Harald Roessler; Mathieu BLANCHOT; Thorsten Friese; Bolette Urtel
Original assignee: Basf Se
Priority date: 2015-08-21
Filing date: 2016-08-19
Publication date: 2017-03-02

Abstract

The invention relates to a method for producing low-boiling (meth)acrylic acid esters in the presence of at least one metal, metal oxide, organo-metal oxide or metal alkoxide or metal alkoxide catalyst.

Description

Process for the preparation of low-boiling (meth) acrylic esters

The present invention relates to a process for the preparation of low-boiling (meth) acrylic acid esters in the presence of at least one metal, metal oxide, organo-metal oxide or metal alkoxide catalyst.

BACKGROUND OF THE INVENTION

(Meth) acrylic esters are important synthesis building blocks which are required, inter alia, for the preparation of polymers. In particular, (meth) acrylic esters with short-chain ester groups, so-called low-boiling (meth) acrylic esters, are of great commercial interest because of the high demand. There is therefore a need for effective and economical processes for the preparation of low-boiling (meth) acrylic esters.

Among others, (meth) acrylic esters can be obtained industrially by transesterification of lower (meth) acrylic esters. Since the transesterification is an equilibrium reaction, in order to achieve high reaction conversions, it is necessary to use one of the starting materials in a large excess and / or to continuously remove one of the reaction products (generally the liberated lower alcohol) from the reaction mixture ,

Many processes for the preparation of (meth) acrylic esters by transesterification in the presence of acidic and basic catalysts are known in the prior art.

JP 01258642, for example, describes inter alia the preparation of allyl methacrylate by transesterification of methyl methacrylate with allyl alcohol in the presence of a polymerization inhibitor and tetraisobutyl titanate as a transesterification catalyst. JP1 12224661 describes a process for preparing (meth) acrylic esters by transesterification of methyl or ethyl (meth) acrylate with C3-C24 alcohols in the presence of tetramethyl titanate and a polymerization inhibitor with removal by distillation of an azeotropic mixture of the liberated lower alcohol and used in excess methyl or ethyl (meth) acrylate.

EP 2807141 B1 describes a process for the preparation of 2-octyl acrylate by transesterification of ethyl acrylate with 2-octanol in the presence of ethyl titanate or 2-octyl titanate, in which an azeotropic mixture of ethyl acrylate and ethanol is continuously discharged with the aid of a distillation column during the transesterification and the remaining bottoms product is then purified via two distillation columns. The continuously withdrawn during the transesterification reaction aze- Ototropic mixture of ethyl acrylate and ethanol, with a mass ratio of ethyl acrylate to ethanol of 35:65, is advantageously supplied directly to the factory for the preparation of the ethyl acrylate. EP 1399408 B1 describes a process for the continuous preparation of higher (meth) acrylic esters by transesterification of a lower (meth) acrylic ester with a higher alcohol in the presence of a metal alkoxide catalyst. The lower alcohol liberated in the reaction is separated off continuously by distillation together with part of the lower (meth) acrylic acid ester, the reflux ratio being 5-15: 1 and, as a rule, part of the condensate is applied as reflux to the column top , In addition, to stabilize the column, a solution of a polymerization inhibitor in the lower (meth) acrylic ester is applied to the column. The metal alkoxide catalyst used is prepared in advance of the reaction of a lower metal alkoxide and the higher alcohol used for transesterification. Specifically, dimethylaminoethanol is used as the higher alcohol in this process.

In particular, in the preparation of low-boiling (meth) acrylic acid ester, the selective distillative separation of the liberated in the transesterification alcohol (lower alcohol) designed difficult. Due to the low boiling point differences in the distillative separation of the liberated lower alcohol in addition to the usually used in excess lower (meth) acrylic acid ester always at least a small portion of the higher alcohol used (recyclable material) entrained. Both the higher alcohol used and the lower (meth) acrylic acid ester can then be separated from the distillate only at considerable expense and returned to the reaction. In order to prevent excessive entrainment of the higher alcohol, usually high reflux ratios must be used in the selective distillative separation of the liberated lower alcohol. This fact has a negative effect on the efficiency and thus on the economy of the manufacturing processes known in the prior art.

SUMMARY OF THE INVENTION

The present invention is based on the object, an improved process for the preparation of (meth) acrylic acid esters, in particular low-boiling

(Meth) acrylic acid ester to provide, whereby the above-mentioned disadvantages can be avoided or at least reduced. The process according to the invention is therefore intended to produce a more efficient and economical production of low-boiling

Allow (meth) acrylic acid esters. It has now surprisingly been found that in the separation of the mixture consisting of the lower (meth) acrylic acid ester used and the liberated lower alcohol, the entrainment of the higher alcohol can be suppressed in an efficient manner by at least one column used in the head area for the separation liquid stream containing at least one lower alcohol, which corresponds in particular to the liberated during the transesterification lower alcohol, is introduced continuously.

The present invention thus relates to a process for the preparation of

(Meth) acrylic acid esters of the general formula I.

wherein

R ^{1 is} hydrogen or methyl,

R ^{2 is} a straight or branched C 3 -C 10 -alkyl group, a C 5 -C 7

Cycloalkyl group, wherein the cycloalkyl group is unsubstituted or may be substituted by at least one Ci-Cio-alkyl radical, an unbranched or branched C2-Cio-alkenyl group containing 1, 2 or 3 double bonds, or a C ₂ -Cio-alkyl group, the is substituted with a -N (R ^{3 a} R ^3b ) ₂ group or a - (OR ⁴ ) _n -OR ⁵ - group, where n can assume the values 0, 1, 2, 3 or 4, and

R ^3a and R ^3b are independently hydrogen, a d-Cs-alkyl group, a C5-C7-cycloalkyl or phenyl, where the substituents R ^3a and R ^3b in -N (R ^{3 a} R ^{3 b),} together with the N Atom to which they are attached can also form a 5- to 7-membered ring,

R ^{4 is} a Ci-C4-alkylene group and

R ^{5 is} a Ci-Cs-alkyl group in which at least one compound of general formula II

provides in which

R ^{1 has} the abovementioned meaning and

R ^{6 is} methyl, ethyl, n-propyl, isopropyl or n-butyl, b) the at least one compound II provided in step a) in the presence of at least one alcohol R ² -OH and in the presence of at least one catalyst which is selected from Mineral acids, metals, metal salts, organometallic compounds or metal alkoxides, to obtain a reaction mixture containing at least one (meth) acrylic acid ester of the general formula I, wherein the alcohol formed during the reaction R ⁶ -OH together with a part of at least one compound II, a column is at least discharged continuously by distillation and a depleted R ⁶ -OH the reaction mixture is obtained, c) subjecting the product obtained in step b) depleted R ⁶ -OH the reaction mixture a DES tilla tive separation, thereby obtaining a to the at least one compound II enriched fraction which optionally contains alcohol R ² -OH, and one to the verbin In the compounds of the general formula II, the radical R ⁶ is selected such that the boiling point at 1013 mbar of the corresponding alcohol R ⁶ -OH is at least 15 ° C. below the boiling point of in Step b) used alcohol R ² -OH and wherein during the distillative removal in step b) a liquid stream containing methanol, ethanol, n-propanol, isopropanol or butanol or a mixture of these alcohols, in the region of the head of the at least one column is initiated continuously. The amount of methanol, ethanol, n-propanol, isopropanol or butanol or a mixture of these alcohols, which is contained in the continuously introduced during the distillative removal in step b) liquid stream, in this case is preferably at least 80 wt .-%, based on the total weight of the liquid stream.

The inventive method is characterized by the following advantageous properties:

By continuously introducing a liquid stream containing methanol, ethanol, n-propanol, isopropanol or butanol or a mixture of these alcohols, at least one column used for distillative removal of the liberated lower alcohol (R ⁶ -OH) in the head Entrainment of the higher alcohol used (R ² -OH) are completely avoided. This can be done at the distillative removal of the liberated lower alcohol (R ⁶ -OH) significantly lower reflux ratios are driven, which significantly increases the conversion rate of the esterification and thus the space-time yield. The fraction obtained after removal of the desired (meth) acrylic acid ester enriched in the at least one compound II, optionally containing the alcohol R ² -OH used, can be used for further reactions or, in the case of continuous process control, back into the reaction in step b). to be led back. As a result, an almost complete recovery of the valuable material used R ² -OH can be achieved.

The inventive method is characterized by its efficiency and cost-effectiveness and is thus advantageously suitable for the industrial production of low-boiling (meth) acrylic acid esters.

The catalyst used in the process of the invention can be reused after separation of the compounds of general formula I for further reactions or stored for a long time. DETAILED DESCRIPTION OF THE INVENTION

In the context of the present invention, the terms (meth) acrylic acid, (meth) acrylate or (meth) acrylate refer to acrylic acid or the corresponding acrylic esters or acrylates as well as to methacrylic acid or the corresponding methacrylic acid esters or methacrylates.

In the context of the present invention, the term "C ₁ -C 10 -alkyl" refers to unbranched alkyl groups having 1 to 10 carbon atoms or branched alkyl groups having 3 to 10 carbon atoms. Preferably, "Ci-Ci _0- alkyl" stands for unbranched alkyl groups having 1 to 8 carbon atoms or for branched alkyl groups having 3 to 8 carbon atoms. These include, for example, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 2-pentyl, 2-methylbutyl, 3-methylbutyl,

1, 2-dimethylpropyl, 1, 1-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 2-hexyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1, 2-dimethylbutyl,

1, 3-dimethylbutyl, 2,3-dimethylbutyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl,

3.3-dimethylbutyl, 1, 1, 2-trimethylpropyl, 1, 2,2-trimethylpropyl, 1-ethylbutyl,

2-ethylbutyl, 1-ethyl-2-methylpropyl, n-heptyl, 1-methylhexyl, 2-methylhexyl,

1-ethylpentyl, 2-ethylpentyl, 1-propylbutyl, 1-ethyl-2-methylbutyl, n-octyl, isooctyl,

2-ethylhexyl and the like. In particular, C ₁ -C ₀ -alkyl is unbranched C ₁ -C ₆ -alkyl groups or branched C 3 -C ₆ -alkyl groups.

The term "Ci-Ci ₀ alkyl", the terms _"C3-C1 0-alkyl" includes "d-Cs-alkyl" and "CC ₄ alkyl" includes within its definition. In the context of the present invention, the term "C 2 -C 10 -alkenyl" refers to unbranched alkenyl groups having 2 to 10 carbon atoms or branched alkenyl groups having 3 to 10 carbon atoms containing 1, 2 or 3 double bonds. "C2-Cio-alkenyl" preferably represents unbranched alkenyl groups having 2 to 8 carbon atoms or branched alkenyl groups having 3 to 8 carbon atoms containing 1, 2 or 3 double bonds. These include, for example, vinyl, 1-propenyl,

2-propenyl, isopropenyl, 1-butenyl, 2-butenyl, 1-pentenyl, 2-pentenyl, 2-methyl-1-butenyl, 2-methyl-2-butenyl, 3-methyl-1-butenyl, 1-hexenyl, 2-hexenyl, 1 -heptyl, 2-heptenyl, 1-octenyl, 2-octenyl and the like. It is preferable

"C2-Cio-alkenyl" to unbranched or branched alkenyl groups having 3 to 6 carbon atoms, containing 1 or 2 double bonds, in particular unbranched or branched alkenyl groups having 3 to 6 carbon atoms, containing a double bond.

The double bonds in the C ₂ -C ₀ alkenyl groups may be present independently in the E or in Z configuration or as a mixture of both configurations. The term "C5-C7-cycloalkyl" for the purposes of the present invention comprises cyclic hydrocarbons having 5 to 7, in particular having 5 or 6 carbon atoms. These include cyclopentyl, cyclohexyl or cycloheptyl.

Substituted Cs-Cz-cycloalkyl groups may, depending on their ring size, have one or more (eg 1, 2, 3 or 4) C 1 -C 10 -alkyl substituents. Examples of substituted Cs-Cz-cycloalkyl groups are 2- and 3-methylcyclopentyl, 2- and 3-ethylcyclopentyl, 2-, 3- and 4-methylcyclohexyl, 2-, 3- and 4-ethylcyclohexyl, 2-, 3- and 4 Propylcyclohexyl, 2-, 3- and 4-isopropylcyclohexyl, 2-, 3- and 4-butylcyclohexyl, 2-,

3- and 4-sec-butylcyclohexyl, 2-, 3- and 4-tert-butylcyclohexyl, 2-, 3- and 4-methylcycloheptyl and the like.

In the context of the present invention, the term "C 1 -C ₄ -alkylene" refers to unbranched bivalent hydrocarbon radicals having 1 to 4 carbon atoms or to branched bivalent hydrocarbon radicals having 1 to 4 carbon atoms. These include, for example, methylene, 1,2-ethylene, 1,2-propylene, 1,3-propylene,

1,2-butylene, 1,3-butylene, 1,4-butylene, 2-methyl-1,3-propylene, 1,1-dimethyl-1,2-ethylene and the like. Preferably, "C 1 -C ₄ -alkylene" is 1,2-ethylene, 1,2-propylene or 1,3-propylene, in particular 1,2-ethylene or 1,3-propylene. In the case of singly or multiply branched Ci-Ci ₀ alkyl, Ci-Ci ₀ alkenyl groups, -C ₄ alkylene or substituted C ₅ -C ₇ cycloalkyl groups, the carbon atom at the branching point or the carbon atoms at the respective can Branching points, independently of each other have an R- or an S-configuration or both configurations in equal or different proportions.

Preference is given in the compounds R ² -OH and in the compounds of general formula I.

R ^{2 is} a straight-chain or branched C 4 -C 8 -alkyl group, a C 5 -C 6 -cycloalkyl group, where the cycloalkyl group is unsubstituted or may be substituted by one or two C 1 -C 4 -alkyl radicals, an unbranched or branched C 2 -C 6 -alkenyl group containing 1 or 2 double bonds, or a C 2 -C ⁶ -alkyl group substituted by a -N (R ^3a R ^3b ) group or a - (OR ⁴ ) _n -OR ⁵ group, where n is 0, 1, 2 or 3, and

R ^3a and R ^3b are each independently hydrogen or a Ci-C4-alkyl group, wherein the substituents R ^3a and R ^3b in -N (R ^3a R ^3b ), together with the N-atom to which they are attached, also a 5 - can form up to 6-membered ring, R ⁴ for a C2-C3-alkylene group and

R ^{5 is} a d-Cs-alkyl group.

Particularly preferred is in the compounds R ² -OH and in the compounds of the general formula I.

R ^{2 is} an unbranched or branched C 4 -C 6 -alkyl group, a C 5 -C 6 -cycloalkyl group, where the cycloalkyl group is unsubstituted or may be substituted by a C 1 -C 4 -alkyl radical, containing a straight or branched C 3 -C 6 -alkenyl group 1 or 2 double bonds, or an unbranched C 2 -C 4 -alkyl group which is substituted by a -N (R ^3a R ^3b ) group or an -OR ⁵ group,

R3a is hydrogen, an unbranched C 1 -C 4 -alkyl group or a branched one

C3-C4 alkyl group,

R ^{3b represents} an unbranched C 1 -C 4 -alkyl group or a branched C 3 -C 4 -alkyl group and

R ^{5 is} an unbranched C 1 -C 4 -alkyl group.

Very particularly preferably in the compounds R ² -OH and in the compounds of general formula I.

R ^{2 is} an unbranched or branched C 4 -C 6 -alkyl group, a C 1 -C 6 -cycloalkyl group, a straight or branched C 3 -C 6 -alkenyl group, containing

1 or 2 double bonds, or an unbranched C 2 -C 4 -alkyl group which is substituted by a -N (R ^3a R ^3b ) group or an -OR ⁵ group,

R3a is hydrogen, an unbranched C 1 -C 4 -alkyl group or a branched one

C3-C4 alkyl group,

R ^{5 is} an unbranched C 1 -C ³ -alkyl group. In particular, in the compounds R ^{2 is} -OH and in the compounds of general formula I.

R ^{2 is} an unbranched or branched C ⁴ -C 6 -alkyl group, a straight-chain or branched C 3 -C 6 -alkenyl group containing one double bond, or an unbranched C ² -C ³ -alkyl group which is substituted by an -N (R ^3a R ^3b ) Group is substituted,

R3a is hydrogen or an unbranched Ci-C4-alkyl group and

R ^{3b represents} an unbranched C 1 -C 4 -alkyl group or a branched C 3 -C 4 -alkyl group.

Specifically, in R ² -OH and in the compounds of general formula IR ^{2 is} an unbranched or branched C ⁴ -C 6 -alkyl group or a straight or branched C 3 -C 6 -alkenyl group containing a double bond.

In a preferred embodiment of the present invention is in the compounds of general formula I.

R ^{1 is} hydrogen or methyl,

R ^{2 is} an unbranched or branched C 4 -C 6 -alkyl group, a C 5 -C 6 -cycloalkyl group, where the cycloalkyl group is unsubstituted or may be substituted by a C 1 -C 4 -alkyl radical, containing a straight or branched C 3 -C 6 -alkenyl group 1 or 2 double bonds, or an unbranched one

C ² -C 4 -alkyl group substituted by a -N (R ^3a R ^3b ) group or an -OR ⁵ group,

R3a is hydrogen, an unbranched C 1 -C 4 -alkyl group or a branched one

C3-C4 alkyl group,

R ^{5 is} an unbranched C 1 -C ³ -alkyl group.

In a particularly preferred embodiment of the present invention is in the compounds of general formula I.

R ^{1 is} hydrogen or methyl and

R ^{2 is} a straight or branched C ⁴ -C 6 -alkyl group, a straight or branched C 3 -C 6 -alkenyl group containing one double bond, or a straight-chain C ² -C ³ ^-alkyl group which is substituted by a -N (R ^3a R ^3b ) group is

R3a is hydrogen or an unbranched Ci-C4-alkyl group and

Step a)

The at least one compound of the general formula II provided in step a) of the process according to the invention can be present either pure or as a mixture of different esters. According to the invention, the compounds of general formula II are methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, methyl methacrylate, methacrylic acid ethyl ester, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate or mixtures thereof.

The compounds of the general formula II are preferably methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, or mixtures thereof.

In particular, the compounds of general formula II are methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate or mixtures thereof.

Specifically, the compounds of general formula II are methyl acrylate or methyl methacrylate. The compounds II can either be obtained commercially or synthesized by known methods familiar to the person skilled in the art.

Step b)

The transesterification in step b) can be represented by the following reaction equation:

II I wherein the radicals R ¹ , R ² and R ^{6 have} one of the meanings mentioned above.

According to the invention, the starting materials, ie the compound of the general formula II and the alcohol R ² -OH, are chosen so that the boiling point at 1013 mbar of the corresponding released alcohol R ⁶ -OH, ie methanol, ethanol, n-propanol, Isopro - Panol or n-butanol, at least 15 ° C below the boiling point of the alcohol used R ² -OH. The boiling point at 1013 mbar of the liberated alcohol R ⁶ -OH is preferably at least 20 ° C., in particular at least 25 ° C., below the boiling point of the alcohol R ² -OH used. The at least one alcohol R ² -OH used in step b) of the process according to the invention can either be obtained commercially or synthesized by known methods known to the person skilled in the art. The alcohol R ² -OH is, for example, to

1-butanol, 2-butanol, 2-methyl-1-propanol, tert-butanol, 1-pentanol, 2-pentanol,

2-methylbutanol, 3-methylbutanol, 2,2-dimethylpropanol, 1-hexanol, 2-hexanol, 2-methylpentanol, 3-methylpentanol, 4-methylpentanol, 1, 1-dimethylbutanol,

2,2-dimethylbutanol, 3,3-dimethylbutanol, 1, 2-dimethylbutanol, 1-heptanol,

2-heptanol, 2-methylhexanol, 3-methylhexanol, 4-methylhexanol,

1, 2-dimethylpentanol, 1, 3-dimethylpentanol, 1, 1-dimethylpentanol,

1, 1, 2,2-tetramethylpropanol, 1-octanol, 2-ethylhexanol, n-nonanol, isononanol, n-decanol, 2-propyl-heptanol, cyclopentanol, cyclohexanol, cycloheptanol, 2- and 3-methylcyclopentanol, 2- and

3-ethylcyclopentanol, 2-, 3- and 4-methylcyclohexanol, 2-, 3- and 4-ethylcyclohexanol, 2-, 3- and 4-tert-butylcyclohexanol, 2-, 3- and 4-methylcycloheptanol, 2-, 3- and

4-ethylcycloheptanol, 1-propenol, 2-propenol, 1-butenol, 2-butenol, 3-butenol, 2-methyl-1-propenol,

1-methyl-2-propenol, 2-methyl-2-propenol, 1-pentenol, 2-pentenol, 3-pentenol, 4-pentenol, 2-methyl-1-butenol, 2-methyl-2-butenol, 3 Methyl-1-butenol, 3-methyl

2-butenol, 2-methyl-3-butenol, 3-methyl-3-butenol, 1-hexenol, 2-hexenol, 3-hexenol, 4-hexenol, 5-hexenol, 4-methyl-3-pentenol, 2- Methyl 4-pentenol, 3-methyl-4-pentenol, 4-methyl-4-pentenol, 5-heptenol, 5-heptenol, 6-octenol, 7-octenol,

Methylamino) ethanol, 3- (methylamino) propanol, 4- (methylamino) butanol,

Methylamino) -pentanol, 6- (methylamino) -hexanol, 8- (methylamino) -octanol,

Ethylamino) ethanol, 3- (ethylamino) propanol, 4- (ethylamino) butanol,

Ethylamino) -pentanol, 6- (ethylamino) -hexanol, 8- (ethylamino) -octanol,

isopropylamino) ethanol, 3- (isopropylamino) -propanol, 4- (isopropylamino) -butanol, isopropylamino) -pentanol, 6- (isopropylamino) -hexanol, 8- (isopropylamino) -octanol, n -butylamino) -ethanol, 3 - (n-butylamino) propanol, 4- (n-butylamino) butanol, n-butylamino) -pentanol, 6- (n-butylamino) hexanol, 8- (n-butylamino) octanol, tert -butylamino ) -ethanol, 3- (tert-butylamino) -propanol, 4- (tert-butylamino) -butanol, tert-butylamino) -pentanol, 6- (tert-butylamino) -hexanol, 8- (tert. Butylamino) octanol, hexylamino) ethanol, 3- (hexylamino) propanol, 4- (hexylamino) butanol,

Hexylamino) pentanol, 6- (hexylamino) hexanol,

Dimethylamino) ethanol, 3- (dimethylamino) -propanol, 4- (dimethylamino) -butanol, dimethylamino) -pentanol, 6- (dimethylamino) -hexanol, 8- (dimethylamino) -octanol, diethylamino) -ethanol, 3- ( Diethylamino) -propanol, 4- (diethylamino) -butanol, diethylamino) -pentanol, 6- (diethylamino) -hexanol, 8- (diethylamino) -octanol, 2-di-n-propylamino) ethanol, 3- (di-n-propylamino) -propanol, 4- (di-n-propylamino) butanol, 5- (di-n-propylamino) -pentanol, 6- (di-n-propylamino) -butanol di-n-propylamino) hexanol,

8- (di-n-propylamino) octanol, 2- (di (isopropyl) amino) ethanol, 3- (di (isopropyl) amino) propanol, 4- (di (isopropyl) amino ) -butanol, 5- (di (isopropyl) amino) pentanol, 6- (di (isopropyl) amino) hexanol, 8- (di (isopropyl) amino) octanol, 2- (dibutylamino ) - ethanol, 3- (dibutylamino) -propanol, 4- (dibutylamino) -butanol, 5- (dibutylamino) -pentanol, 6- (dibutylamino) -hexanol, 8- (dibutylamino) -octanol, 2- (dihexylamino) - ethanol, 3- (dihexylamino) -propanol, 4- (dihexylamino) -butanol, 5- (dihexylamino) -pentanol, 6- (dihexylamino) -hexanol, 2- (methyl-ethyl-amino) -ethanol, 2- (methyl -propylamino) -ethanol, 2- (methyl-isopropyl-amino) -ethanol, 2- (methyl-butyl-amino) -ethanol, 2- (methyl-hexyl-amino) -ethanol, 2- (methyl-octyl -amino) -ethanol, 2- (ethyl-propyl-amino) -ethanol, 2- (ethyl-isopropyl-amino) -ethanol, 2- (ethyl-n-butyl-amino) -ethanol,

2- (ethyl-isobutyl-amino) -ethanol, 2- (ethyl-sec-butyl-amino) -ethanol, 2- (ethyl-tert-butyl-amino) -ethanol, 2- (ethyl-hexyl-amino ) -ethanol, 2- (ethyl-octyl-amino) -ethanol,

3- (methyl-ethyl-amino) -propanol, 3- (methyl-propyl-amino) -propanol, 3- (methyl-isopropyl-amino) -propanol, 3- (methyl-butyl-amino) -propanol, 3- (Methyl hexylamino) propanol, 3- (ethyl-propyl-amino) -propanol, 3- (ethyl-isopropyl-amino) -propanol,

3- (ethyl-butyl-amino) -propanol, 3- (ethyl-hexyl-amino) -propanol, 4- (methyl-ethyl-amino) -butanol, 4- (methyl-propyl-amino) -butanol, 4- (Methyl-isopropyl-amino) -butanol, 4- (methyl-butyl-amino) -butanol, 4- (methyl-hexyl-amino) -butanol, 4- (ethyl-propyl-amino) -butanol, 4- (ethyl -isopropyl-amino) -butanol, 4- (ethyl-butyl-amino) -butanol,

4- (ethylhexylamino) butanol, 2- (N-piperidinyl) ethanol, 3- (N-piperidinyl) propanol, 4- (N-piperidinyl) butanol, 5- (N-piperidinyl) - pentanol, 6- (N-piperidinyl) hexanol, 8- (N-piperidinyl) octanol, 2- (N-pyrrolidinyl) ethanol, 3- (N-pyrrolidinyl) propanol, 4- (N-pyrrolidinyl) - butanol, 5- (N-pyrrolidinyl) pentanol, 6- (N-pyrrolidinyl) hexanol, 8- (N-pyrrolidinyl) octanol,

2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-isopropoxyethanol,

2-butoxyethanol, 2-hexoxyethanol, 3-methoxypropanol, 3-ethoxypropanol,

3-propoxypropanol, 3-isopropoxypropanol, 3-butoxypropanol, 3-hexoxypropanol, 4-methoxybutanol, 4-ethoxybutanol, 4-propoxybutanol, 4-isopropoxybutanol,

4-butoxybutanol, 4-hexoxybutanol,

2- (2-methoxyethoxy) ethanol, 2- (2-ethoxyethoxy) ethanol, 2- (2-propoxyethoxy) ethanol, 2- (2-butoxyethoxy) ethanol, 2- (2-hexoxyethoxy) ethanol,

3- (3-methoxypropoxy) propanol, 3- (3-ethoxypropoxy) propanol,

3- (3-propoxypropoxy) propanol, 3- (3-butoxypropoxy) propanol,

3- (3-Hexoxypropoxy) propanol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether,

2- (2- (2-methoxyethoxy) ethoxy) ethanol, 2- (2- (2-ethoxyethoxy) ethoxy) ethanol, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether or mixtures thereof. Preferably, R ^{2 is} -OH

2-methylbutanol, 3-methylbutanol, 2,2-dimethylpropanol, 1-hexanol, 2-methylpentanol,

3-methylpentanol, 4-methylpentanol, 1, 1-dimethylbutanol, 2,2-dimethylbutanol, 3,3-dimethylbutanol, 1, 2-dimethylbutanol,

Cyclopentanol, cyclohexanol, 2- and 3-methylcyclopentanol, 2- and 3-methylcyclopentanol

3-ethylcyclopentanol, 2-, 3- and 4-methylcyclohexanol, 2-, 3- and 4-ethylcyclohexanol, 2-, 3- and 4-tert-butylcyclohexanol,

1-propenol, 2-propenol, 1-buteneol, 2-butenol, 3-butenol, 2-methyl-1-propenol,

1-methyl-2-propenol, 2-methyl-2-propenol, 1-pentenol, 2-pentenol, 3-pentenol,

4-pentenol, 2-methyl-1-butenol, 2-methyl-2-butenol, 3-methyl-1-butenol, 3-methyl

2-butenol, 2-methyl-3-butenol, 3-methyl-3-butenol, 1-hexenol, 2-hexenol, 3-hexenol, 4-hexenol, 5-hexenol, 4-methyl-3-pentenol, 2- Methyl 4-pentenol, 3-methyl-4-pentenol,

4-methyl-4-pentenol,

2- (methylamino) ethanol, 3- (methylamino) propanol, 4- (methylamino) butanol,

2- (ethylamino) ethanol, 3- (ethylamino) propanol, 4- (ethylamino) butanol,

2- (isopropylamino) ethanol, 3- (isopropylamino) propanol, 4- (isopropylamino) butanol, 2- (n-butylamino) ethanol, 3- (n-butylamino) propanol, 4- (n-butylamino ) -butanol, 2- (tert-butylamino) -ethanol, 3- (tert-butylamino) -propanol, 4- (tert-butylamino) -butanol,

2- (dimethylamino) ethanol, 3- (dimethylamino) propanol, 4- (dimethylamino) butanol, 2- (diethylamino) ethanol, 3- (diethylamino) propanol, 4- (diethylamino) butanol,

2- (di (isopropyl) amino) ethanol, 2- (di-n-propylamino) ethanol, 3- (di-n-propylamino) propanol, 4- (di-n-propylamino) butanol, 3- (di- (isopropyl) amino) propanol,

4- (di- (isopropyl) -amino) -butanol, 2- (dibutylamino) -ethanol, 3- (dibutylamino) -propanol, 4- (dibutylamino) -butanol, 2- (methyl-ethyl-amino) -ethanol, 2- (methyl-propyl-amino) -ethanol, 2- (methyl-isopropyl-amino) -ethanol, 2- (methyl-butyl-amino) -ethanol, 2- (ethyl-propyl-amino) -ethanol, 2- (Ethyl-isopropyl-amino) -ethanol, 2- (ethyl-butyl-amino) -ethanol, 3- (methyl-ethyl-amino) -propanol, 3- (methyl-propyl-amino) -propanol, 3- (methyl - isopropyl-amino) -propanol, 3- (methyl-butyl-amino) -propanol, 3- (ethyl-propyl-amino) -propanol, 3- (ethyl-isopropyl-amino) -propanol, 3- (ethyl-butyl amino) propanol,

4- (methyl-ethyl-amino) -butanol, 4- (methyl-propyl-amino) -butanol, 4- (methyl-isopropyl-amino) -butanol, 4- (methyl-butyl-amino) -butanol, 4- (Ethyl-propyl-amino) -butanol, 4- (ethyl-isopropyl-amino) -butanol, 4- (ethyl-butyl-amino) -butanol,

2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-isopropoxyethanol,

2-butoxyethanol, 3-methoxypropanol, 3-ethoxypropanol, 3-propoxypropanol,

3-isopropoxypropanol, 3-butoxypropanol, 4-methoxybutanol, 4-ethoxybutanol,

4-propoxybutanol, 4-isopropoxybutanol, 4-butoxybutanol or mixtures thereof. R ² -OH is particularly preferably 1-butanol, 2-butanol, 2-methyl-

1-propanol, tert-butanol, 1-pentanol, 2-pentanol, 2-methylbutanol, 3-methylbutanol, 2,2-dimethylpropanol, 1-hexanol, 2-hexanol, 2-methylpentanol, 3-methylpentanol, 4-methylpentanol , 1, 1-dimethylbutanol, 2,2-dimethylbutanol, 3,3-dimethylbutanol, 1, 2-dimethylbutanol, 1-propenol, 2-propenol, 1-butene, 2-butenol, 3-butenol,

2-methyl-1-propenol, 1-methyl-2-propenol, 2-methyl-2-propenol, 1-pentenol,

2-pentenol, 3-pentenol, 4-pentenol, 2-methyl-1-butenol, 2-methyl-2-butenol, 3-methyl

1-butenol, 3-methyl-2-butenol, 2-methyl-3-butenol, 3-methyl-3-butenol, 1-hexenol,

2-hexenol, 3-hexenol, 4-hexenol, 5-hexenol, 2-methyl-4-pentenol, 3-methyl-4-pentenol, 4-methyl-4-pentenol, 2- (methylamino) -ethanol, 3 (methylamino) propanol,

2- (ethylamino) ethanol, 3- (ethylamino) propanol, 2- (isopropylamino) ethanol,

3- (isopropylamino) propanol, 2- (n-butylamino) ethanol, 3- (n-butylamino) propanol,

2- (tert-butylamino) ethanol, 3- (tert-butylamino) propanol, 2- (dimethylamino) ethanol,

3- (dimethylamino) -propanol, 2- (diethylamino) -ethanol, 3- (diethylamino) -propanol, 2- (di-n-propylamino) -ethanol, 3- (di-n-propylamino) -propanol, 2- (Di (isopropyl) amino) ethanol, 3- (di (isopropyl) amino) propanol, 2- (dibutylamino) ethanol, 3- (dibutylamino) propanol or mixtures thereof.

In particular, R ² -OH is 1-butanol, 2-butanol, 2-methyl-1-propanol, 1-pentanol, 2-pentanol, 2-methylbutanol, 3-methylbutanol, 1-hexanol, 2-hexanol, 2-methylpentanol, 3-methylpentanol, 4-methylpentanol, 1-propenol,

2-propenol, 2-butenol, 3-butenol, 1-methyl-2-propenol, 2-methyl-2-propenol,

3-pentenol, 4-pentenol, 2-methyl-3-butenol, 3-methyl-3-butenol, 4-hexenol, 5-hexenol, 3-methyl-4-pentenol, 4-methyl-4-pentenol, 2- (Methylamino) ethanol, 3- (methylamino) propanol, 2- (ethylamino) ethanol, 3- (ethylamino) propanol, 2- (isopropylamino) ethanol, 3- (isopropylamino) propanol, 2- (n Butylamino) ethanol, 3- (n-butylamino) propanol,

3- (dimethylamino) propanol, 2- (diethylamino) ethanol, 3- (diethylamino) propanol,

2- (di-n-propylamino) -ethanol, 3- (di-n-propylamino) -propanol, 2- (dibutylamino) -ethanol, 3- (dibutylamino) -propanol or mixtures thereof.

Specifically, R ² -OH is 1-butanol, 2-methyl-1-propanol, 1-pentanol,

3-methylbutanol, 1-hexanol, 2-propenol, 3-butenol, 2-methyl-2-propenol, 2-methyl-3-butenol, 3-methyl-3-butenol, 4-pentenol, 5-hexenol, 2- (Methylamino) ethanol, 3- (methylamino) propanol, 2- (ethylamino) ethanol, 3- (ethylamino) propanol,

2- (isopropylamino) ethanol, 3- (isopropylamino) propanol, 2- (tert-butylamino) ethanol,

3- (tert-butylamino) -propanol, 2- (dimethylamino) -ethanol, 3- (dimethylamino) -propanol,

2- (diethylamino) ethanol, 3- (diethylamino) propanol, 2- (di-n-propylamino) ethanol,

3- (di-n-propylamino) -propanol or mixtures thereof.

In general, in step b) of the process of the invention, the at least one alcohol R ² -OH in the deficit, based on the amount of the at least one compound of the general formula II used. The molar ratio of the least a compound of general formula II for at least one alcohol R ² -OH in the reaction mixture is usually in the range of 1, 1: 1 to 10: 1, preferably in the range of 1, 2: 1 to 5: 1 and in particular in the range of 1, 3: 1 to 3: 1. The total amount of the at least one alcohol R ² -OH in the reaction mixture of the reaction in step b) of the process according to the invention is usually in the range from 0.1 to 0.99 mol, preferably in the range from 0.2 to 0.9 mol, in particular in the range from 0.3 to 0.8 mol, based on 1 mol of compound II used. As a rule, the reaction mixture of the reaction in step b) of the process according to the invention comprises at least one polymerization inhibitor, which is also referred to below as a stabilizer.

Suitable polymerization inhibitors are all stabilizers known to those skilled in the art. These are, for example, For example, in the earlier German patent application with the file number 10249507.6 and in DE-A 10258329, DE-A 198 56 565 and in EP-A 765856. Polymerization inhibitors are phenolic compounds,

N-oxyl compounds, aromatic amines, phenylenediamines, sulfonamides, oximes, hydroxylamines, phosphorus-containing compounds, sulfur-containing compounds and metal salts, and optionally mixtures thereof in question.

The phenolic compounds suitable as stabilizers are, for example,

Phenol;

Alkylphenols, e.g. o-, m- or p-cresol (methylphenol), 2-tert-butyl-4-methylphenol, 6-tert-butyl-2,4-dimethylphenol, 2,6-di-tert-butyl-4- methylphenol, 2-tert-butylphenol, 4-tert-butylphenol, 2-tert-butyl-6-methylphenol, 2,4,6-tris-tert-butylphenol, 2,6-di-tert-butylphenol , 2,4-di-tert-butylphenol, 4-tert-butyl-2,6-dimethylphenol, 2-methyl-4-tert-butylphenol, 2,2'-methylene-bis (6-tert. butyl-4-methylphenol), octylphenol, nonylphenol, 2,6-dimethylphenol or 2,6-di-tert-butyl-p-cresol;

1 .2-Dihydroxybenzenes, such as. Catechol (1, 2-dihydroxybenzene) or tert-butylcatechol;

1, 3-dihydroxybenzenes;

Bisphenol A;

Aminophenols, such as. For example, p-aminophenol;

Nitrophenols such as p-nitrophenol;

Tocopherols, such as. B. α, β, or γ-tocopherol;

Hydroxycumarans, e.g. 2,3-dihydro-2,2-dimethyl-7-hydroxybenzofuran (2,2-dimethyl-7-hydroxycoumaran);

2-alkoxyphenols, such as 2-methoxyphenol (guaiacol),

2-ethoxyphenol, 2-isopropoxyphenol;

3-alkoxyphenols, such as. 3-methoxyphenol or 3-ethoxyphenol; Hydroquinones, such as. Hydroquinone, 2-methylhydroquinone, 2-tert-butylhydroquinone or 2,5-di-tert-butylhydroquinone, and

Hydroquinone monoalkyl ethers, e.g. 4-methoxyphenol (hydroquinone monomethyl ether) or 2-tert-butyl-4-methoxyphenol or 2,5-di-tert-butyl-4-methoxyphenol.

Stabilizer effective N-oxyl compounds, i. stable nitroxyl or N-oxyl radicals are z. 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-0x0-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-methoxy-2,2, 6,6-tetramethyl-piperidine-N-oxyl,

4-acetoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4,4 ', 4 "-tris (2,2,6,6-tetramethylpiperidine-N-oxyl) phosphite, 2, 2,6,6-tetramethyl-piperidine-N-oxyl, 3-0x0-2,2,5,5-tetramethyl-pyrrolidone-N-oxyl) or Uvinul® 4040P from BASF SE.

As stabilizer suitable aromatic amines are, for. N, N-diphenylamine,

N-nitrosodiphenylamine or nitrosodiethylaniline.

As a stabilizer suitable phenylenediamines z. B. N, N'-dialkyl-p-phenylenediamine, wherein the alkyl radicals may be the same or different and each independently of one another consist of 1 to 4 carbon atoms and may be straight or branched, for example N, N'-di-sec-butyl -p-phenylenediamine (Kerobit® BPD from BASF SE).

Suitable sulfonamides as stabilizer are, for example, N-methyl-4-toluenesulfonamide, N-tert-butyl-4-toluenesulfonamide, N-tert-butyl-N-oxyl-4-toluenesulfonamide, N, N'-bis (4 -sulfanilamide) piperidine or 3 - {[5- (4-aminobenzoyl) -2,4-dimethylbenzenesulfonyl] ethylamino} -4-methylbenzenesulfonic acid.

Examples of suitable oximes as stabilizers are aldoximes, ketoximes or amidoximes, for example diethylketoxime, acetone oxime, methylethylketoxime, cyclohexanone oxime, dimethylglyoxime, 2-pyridinaldoxime, salicylaldoxime or other aliphatic or aromatic oximes or their reaction products with alkyl transfer reagents.

As a stabilizer effective hydroxylamines are, for. N, N-diethylhydroxylamine.

As a stabilizer effective phosphorus compounds are, for. B. triphenylphosphine, triphenyl phosphite, hypophosphorous acid, trinonyl phosphite or triethyl phosphite.

As a stabilizer effective sulfur compounds are z. As diphenyl sulfide, phenothiazine and sulfur-containing natural products such as cysteine. As a stabilizer effective metal salts are, for. For example, copper, manganese, cerium, nickel, chromium, carbonate, chloride, dithiocarbamate, dialkyldithiocarbamate, in particular dibutyldithiocarbamate, stearate, sulfate, salicylate, acetate or ethylhexanoate. Further suitable polymerization inhibitors are complexing agents based on tetraazazene (TAA), for example dibenzotetraaza [14] annulenes and porphyrins, as described in Chem. Soc. Rev. 1998, 27, 105-1 15, imines, z. B. Methylethyli- min, (2-hydroxyphenyl) benzoquinone imine, (2-hydroxyphenyl) benzophenone imine, Ν, Ν-dimethylindoaniline, thionine (7-amino-3-imino-3H-phenothiazine), methylene violet (7-dimethylamino-3-phenothiazinon ) and urea derivatives such as urea or thiourea in question.

The polymerization inhibitors used in step b) of the process according to the invention are preferably selected from phenolic compounds, N-oxyl compounds, sulfonamides and sulfur-containing compounds, and mixtures thereof.

Particularly preferred polymerization inhibitors are phenothiazine, hydroquinone monomethyl ether, N, N'-di-sec-butyl-p-phenylenediamine and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl.

Usually, one or more, for example two or three, of the abovementioned polymerization inhibitors are used in the reaction in step b) of the process according to the invention. Two or more, in particular two, of the abovementioned polymerization inhibitors are preferably used in the reaction in step b) of the process according to the invention.

The total amount of the at least one stabilizer in the reaction mixture of the reaction in step b) of the process according to the invention is usually in the range of 0.005 to 5 wt .-%, preferably in the range of 0.01 to 2 wt .-%, in particular in the range from 0.02 to 1% by weight, based on the amount of compound II used.

Catalyst The reaction according to the invention in step b) is generally carried out in the presence of a catalyst. Suitable catalysts are the customary catalysts usually used for transesterification reactions, which are usually also used in esterification reactions. As a rule, the at least one catalyst used in step b) of the process according to the invention is mineral acids, metals, metal salts, organometallic compounds or metal alkoxides. Suitable as a catalyst mineral acids are, for. As sulfuric acid and phosphoric acid and organic sulfonic acids, such as methanesulfonic acid and p-toluenesulfonic acid.

Suitable catalysts for the reaction in step b) of the process according to the invention are also metals such as Sn, Ti or Zr. The metals are preferably used for this purpose finely divided in the form of powders.

Metal salts which are suitable as catalyst are, for example, metal oxides, acetates, acetyl acetonates, chlorides, hydroxides, phosphates or carbonates of Li, Na, K, Rb, Cs, Mg, Ca, Mn, Ti, Co, Ni, Zn, Zr, Ge, Hf, Al, Cr, Fe, Sb or Sn. Particularly suitable metal salts are, for example, metal oxides, acetates, acetylacetonates, of Li, Ti, Zr, Ni, Zn, Sb or Sn, such as antimony (III) oxide, tin (II) oxide, tin (IV) oxide, nickel ( II) acetylacetonate and zinc (II) acetylacetonate. Suitable organometallic compounds as catalyst are, for example, organotin compounds, such as

Dialkyltin laurates, e.g. B. dimethyltin dilaurate or dibutyltin dilaurate;

Dialkyltin halides, e.g. Dimethyldichloride, dipropyltin dichloride or dibutyltin dichloride;

- dialkyltin dialkoxides, e.g. B. Dimethylzinndimethanolat, Dimethylzinndiethanolat,

Dibutyltin dimethanolate or dibutyltin diethanolate;

Dialkyltin diacetates, e.g. Dimethyl tin diacetate or dibutyltin diacetate;

Dialkyltin oxides, e.g. Dibutyltin oxide or dioctyltin oxide;

trialkyltin alkoxides;

- Monoalkylzinndioxide, z. For example, monobutyltin dioxide;

or mixtures thereof.

Metal alkoxides suitable as catalyst are, for example, titanium alkoxides, such as titanium (IV) ethanolate, titanium (IV) isopropoxide or titanium (IV) butanolate; Triethanolamine titanates such as triethanolamine isopropyl titanate or diethanolamine di (isopropyl) titanate; Zirconium alkoxides, such as zirconium (IV) propoxide, zirconium (IV) butanolate or zirconium (IV) pentanoate; Triethanolaminzirkonat; Alkali or Erdalkalialkoxide and mixtures of said metal alkoxides. In step b) of the process according to the invention, organotin compounds or metal alkoxides are preferably used as catalysts.

In a specific embodiment of the reaction according to the invention in step b), metal alkoxides, as defined above and below, are used as catalysts. The amount of catalyst used is preferably from 0.001 to 15% by weight, more preferably from 0.005 to 10% by weight, based on the components used in step b). Solvent:

The reaction in step b) can be carried out in the absence or in the presence of an added organic solvent. If the reaction in step b) is carried out in the presence of an added organic solvent, these are at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, the alcohol R ² -OH and the compounds (II) various organic solvent LM. In a first preferred embodiment of the process according to the invention, step b) is carried out in the presence of another solvent LM other than methanol, ethanol, n-propanol, isopropanol, n-butanol, the alcohol R ² -OH and the compounds (II). The at least one solvent LM is preferably an organic solvent which is inert under the reaction conditions. These include, for example, aliphatic and alicyclic hydrocarbons, halogenated aliphatic and alicyclic hydrocarbons, aromatic and substituted aromatic hydrocarbons or ethers. The solvent is preferably selected from pentane, hexane, heptane, ligroin, petroleum ether, cyclopentane, cyclohexane, dichloromethane, trichloromethane, carbon tetrachloride, 1, 2-dichloroethane, benzene, toluene, xylene, chlorobenzene, dichlorobenzenes, diethyl ether, methyl tert. Butyl ether, dibutyl ether, THF, dioxane, acetonitrile and mixtures thereof. More preferably, the at least one further solvent LM is selected from aliphatic and alicyclic hydrocarbons containing 5 to 8 carbon atoms, in particular hexane, heptane and cyclohexane, and mixtures thereof.

In a second preferred embodiment of the process according to the invention, step b) is carried out in the absence of a solvent LM other than methanol, ethanol, n-propanol, isopropanol, n-butanol, the alcohol R ² -OH and the compounds (II).

Reaction parameters:

The reaction in step b) and the distillative removal of the alcohol R ⁶ -OH formed during the reaction are generally carried out at a temperature in the range from 30 to 175 ° C., preferably at a temperature in the range from 40 to 150 ° C and in particular carried out at a temperature in the range of 80 to 120 ° C.

The reaction in step b) and the distillative removal of the alcohol R ⁶ -OH formed during the reaction can generally be carried out at ambient pressure or reduced pressure. Preferably, the reaction takes place in step b) and the distillative discharge of the alcohol R ⁶ -OH, at least at the beginning of the reaction, at ambient pressure. The pressure can also be reduced stepwise or continuously during the reaction in step b) once or several times in order to accelerate the removal of the alcohol R ⁶ -OH formed during the reaction. Preferably, the pressure in the course of the reaction in step b) is reduced stepwise or continuously.

The reaction in step b) and the removal of the alcohol R ⁶ -OH by distillation at the beginning of the reaction at ambient pressure are particularly preferably carried out, the pressure being reduced stepwise or continuously in the course of the reaction in step b).

The reaction in step b) can be carried out in the absence or in the presence of an inert gas. An inert gas is generally understood to mean a gas which, under the given reaction conditions, does not react with the starting materials, reagents, solvents or the products formed. Preferably, the transesterification is carried out without the addition of an inert gas under the reaction conditions.

However, it may be advantageous to carry out the reaction in step b) in the presence of an oxygen-containing gas mixture. As a rule, the oxygen-containing gas mixture is introduced continuously into the reaction zone for this purpose. The oxygen-containing gas mixture is usually gas mixtures containing oxygen. The oxygen-containing gas mixture is preferably gas mixtures having an oxygen content in the range from 1 to 30% by volume, preferably from 2 to 15% by volume and particularly preferably from 3 to 10% by volume. In particular, the oxygen-containing gas mixture is lean air.

Extraction of the lower alcohol

According to the invention, the low-boiling alcohol R ⁶ -OH released in the reaction in step b) is continuously removed in order to shift the equilibrium of the transesterification reaction. Due to the formation of an azeotropic mixture, part of the at least one compound II is generally entrained in the distillative discharge of the liberated, low-boiling alcohol R ⁶ -OH. In the gel in the distillative removal of the lower alcohol R ⁶ -OH in the process according to the invention entrainment of the alcohol used in the reaction in step b) R ² -OH is not observed. By distillative removal of a depleted in R ⁶ -OH reaction mixture is obtained.

For distillative removal of the liberated in the reaction in step b), lower boiling alcohol R ⁶ -OH together with a portion of the at least one compound II are generally all devices for the distillative separation of reaction mixtures containing liquid components. Suitable devices include distillation columns, such as tray columns, which may be equipped with bubble cap trays, sieve plates, trays, packing or packing, or rotary belt column evaporators, such as thin film evaporators, falling film evaporators, forced circulation evaporators, Sambay evaporators, etc., and combinations thereof. For the removal by distillation, the lower-boiling alcohol R ⁶ -OH liberated in the reaction in step b) is particularly preferably used together with a part of the at least one compound II distillation columns and / or rotary column columns, in particular distillation columns. The distillation column required for distillative discharge is usually in direct contact with the transesterification reactor, preferably it is installed directly on this. In the case of using several transesterification reactors connected in series, each of these reactors may be equipped with a distillation column or, preferably from the last boilers of the transesterification reactor cascade, the evaporated alcohol mixture may be fed via one or more manifolds to a distillation column. During the removal by distillation of the lower-boiling alcohol R ⁶ -OH released in the reaction in step b) together with part of the at least one compound II, a vapor is first withdrawn from the reaction mixture obtained in step b) which is then at least partially condensed. For condensation or partial condensation of the vapor all suitable capacitors can be used. These can be cooled with any cooling media. Capacitors with air cooling and / or water cooling are preferred, with air cooling being particularly preferred. The condenser is usually at the top, ie at the top of the distillation column, or is integrated in the top of the column.

For the purposes of the present invention, the term "head of the column" or "column head" is understood to mean the region of a distillation column which is located at the upper end, ie. H. usually in the upper fifth, preferably in the upper tenth, of the distillation column is located.

In general, the reflux ratio in the column in the distillative discharge in step b) is in the range from 10: 1 to 1: 100, preferably in the range of 8: 1 to 1:50, more preferably in the range of 7: 1 to 1: 30 and especially in the range of 6: 1 to 1:25.

In a specific embodiment of the process according to the invention, the reflux ratio in the column in the distillative removal in step b) is in the range from 5: 1 to 1:20, in particular in the range from 4: 1 to 1:15.

Usually, the discharge of the liberated in the reaction in step b), lower boiling alcohol R ⁶ -OH is started as soon as the temperature at the top of the column after the start of the reaction in step b) does not change significantly. This is the case, for example, after a few minutes to a few hours, for example after 15 or 20 minutes.

During the distillative removal of the lower boiling alcohol R ⁶ -OH released in the reaction in step b), the reflux ratio, as defined above, is preferably adjusted so that the temperature at the top of the column remains as constant as possible. The term "as constant as possible" in this context means that the temperature at the top of the column varies by less than 10 ° C, for example by less than 5 ° C or 3 ° C.

According to the invention, during the distillative removal in step b), a liquid stream containing methanol, ethanol, n-propanol, isopropanol or butanol or a mixture of these alcohols is introduced continuously in the region of the head of the at least one column.

If a mixture of methanol, ethanol, n-propanol, isopropanol or butanol is used in the liquid stream, this is a mixture of at least two, preferably two or three, in particular two of these alcohols. The alcohol present in the liquid stream, which is selected from methanol, ethanol, n-propanol, isopropanol, n-butanol or a mixture of these alcohols, preferably corresponds to the at least one alcohol R ⁶ -OH released in the reaction in step b). The liquid stream continuously introduced during the distillative removal in step b) preferably contains at least 80% by weight, more preferably at least 90% by weight, in particular at least 95% by weight, based on the total weight of the liquid stream, of methanol, ethanol , n-propanol, isopropanol or butanol or a mixture of these alcohols.

In a particularly preferred embodiment of the process according to the invention, the liquid stream introduced at the top of the column during the distillative removal in step b) additionally comprises at least one stabilizer (polymerization agent). hibitor). With regard to suitable and preferred stabilizers, reference is made to the general statements made above on suitable and preferred stabilizers. The total amount of at least one stabilizer contained in the liquid stream is usually in the range of 0.001 to 15 wt .-%, preferably in the range of 0.002 to 12 wt .-%, in particular in the range of 0.002 to 10 wt .-%, based on the Total weight of the injected liquid stream. In a specific embodiment of the process according to the invention, the liquid stream continuously introduced at the top of the column during the distillative removal in step b) consists of methanol, ethanol, n-propanol, isopropanol or butanol or a mixture of these alcohols containing at least one stabilizer, as before Are defined.

In a very specific embodiment of the process according to the invention, a liquid stream of methanol or ethanol containing the at least one stabilizer, as defined above, is introduced continuously during the distillative removal in step b) at the top of the column.

In an even more specific embodiment of the process according to the invention, a liquid stream of methanol containing the at least one stabilizer, as defined above, is introduced continuously during the distillative removal in step b) at the top of the column.

Usually, the introduction of the liquid stream at the top of the column begins shortly after the beginning of the reaction in step b), more precisely 1 to 30 minutes, for example 2, 5 or 10 minutes, after the beginning of the reaction in step b). The introduction of the liquid stream at the top of the column preferably begins before the discharge of the lower-boiling alcohol R ⁶ -OH released in the reaction in step b).

The introduction of the liquid stream at the top of the column is usually carried out continuously over the entire course of the reaction in step b), in particular at least until the discharge of the liberated, low-boiling alcohol R ⁶ - OH is completed.

The amount of liquid stream introduced hourly at the top of the column during the distillative discharge in step b) of the process according to the invention is usually from 0.1 to 25% by weight.

If the reaction in step b), in the absence of a further solvent LM or other, different from methanol, ethanol, n-propanol, isopropanol, n-butanol, the alcohol R ² -OH and the compounds II or, according to the first described above preferred zugten embodiment, is carried out in the presence of such a solvent LM and the proportion of the distilled off together with the alcohol R ⁶ -OH solvent LM in the case of recovery, as described below, directly in the reaction in step b) is recycled, which is during the distillative discharge in step b) of the process according to the invention hourly at the top of the column introduced amount of liquid stream preferably 0.5 to 20 wt .-%, particularly preferably 1 to 15 wt .-% and in particular 2 to 10 wt .-%, based to the total amount of the alcohol used in the reaction in step b) R ² -OH. In a preferred embodiment of the method according to the invention, at least one compound II is additionally supplied for the reaction in step b), in order to compensate for the losses occurring at the at least one compound II during the reaction. The feeding of the at least one compound II for the reaction in step b) can be carried out stepwise or continuously, preferably continuously, over the entire course of the reaction. The feed is intended to compensate for the loss of compound II in the reaction mixture caused by the distillative removal of the low-boiling alcohol R ⁶ -OH. The feeding of the at least one compound II preferably takes place in such a way that the amount of compound II in the reaction mixture remains as constant as possible during the distillative removal of the alcohol R ⁶ -OH.

If the reaction in step b), according to the first preferred embodiment described above, carried out in the presence of another solvent LM other than methanol, ethanol, n-propanol, isopropanol, n-butanol, the alcohol R ² -OH and the compounds II is distilled off in the discharge of the low-boiling alcohol R ⁶ -OH, at least a portion of the solvent LM together with the alcohol R ⁶ -OH and a portion of the at least one compound II continuously. The solvent LM here has the function of an entraining agent, which should facilitate the discharge of the low-boiling alcohol R ⁶ -OH.

If desired, the discharged at least one solvent LM together with the at least one compound II can be separated from the alcohol R ⁶ -OH and recycled to the reaction in step b). In order to keep the loss of the solvent LM and possibly of the at least one compound II as low as possible, it is preferable to separate them at least partially from the alcohol R ⁶ -OH and to return them to the reaction in step b). To separate the discharged solvent LM and the discharged at least one compound II from the alcohol R ⁶ -OH, the customary methods known to those skilled in the art for the separation of liquid-liquid mixtures are suitable. Preferably, the separation of the solvent LM and the at least one takes place Compound II of the alcohol R ⁶ -OH on the way of liquid-liquid extraction. The separation is preferably carried out continuously.

Usually, this is the discharged mixture containing the alcohol R ⁶ -OH, the organic solvent LM and at least one compound II, mixed with water and passed into a phase separator (decanter), where this by mechanical settling in two phases (an aqueous Phase, which contains the alcohol R ⁶ -OH, and an organic phase which contains predominantly the solvent LM and the at least one compound II), which can be removed separately. The organic phase containing the solvent LM and the at least one compound II is then returned to the reaction in step b). The aqueous phase containing the alcohol R ⁶ -OH can be subjected to a purification, preferably a distillative purification, wherein the alcohol R ⁶ -OH is obtained as valuable material. The thus recovered alcohol R ⁶ -OH can be sold or used for the synthesis of compounds II.

If the reaction in step b) according to the first preferred embodiment described above is carried out in the presence of a solvent LM, the distillative removal of the low-boiling alcohol R ⁶ -OH preferably comprises the following steps: b1) continuous distillative removal of at least part of the Solvent LM together with the alcohol R ⁶ -OH and a part of the at least one compound II via at least one column;

b2) at least partially extractive separation of the solvent LM discharged in step b1) and the at least one compound II of the alcohol R ⁶ -OH and

b3) at least partial recycling of the solvent LM separated off in step b2) and of the at least one compound II in the reaction in step b).

The recycling of the separated solvent LM and the at least one compound II into the reaction in step b) can be carried out in several ways.

The separated solvent LM and the at least one compound II can either be pumped directly back into the reaction zone of the reaction in step b) or at least partially introduced via the top of at least one column used for distillative discharge of the lower alcohol R ⁶ -OH.

In the at least partial overhead recycling, the separated solvent LM and the at least one compound II can be introduced separately from or combined with the liquid stream containing the lower alcohol and the at least one stabilizer. In the case of the at least partial recycling via the top, the separated solvent LM and the at least one compound are preferred. tion II separated from the liquid stream containing the lower alcohol and the at least one stabilizer initiated.

If the separated solvent LM is at least partially passed over the top of at least one used for distillative removal of the lower alcohol R ⁶ -OH, at least one column in the reaction zone of the reaction in step b), which is during the distillative discharge in step b) of the process according to the invention hourly at the top of the column introduced amount of liquid stream preferably 0.1 to 10 wt .-%, particularly preferably 0.2 to 5 wt .-% and in particular 0.3 to 3 wt .-%, based to the total amount of the alcohol used in the reaction in step b) R ² -OH.

If the reaction in step b), according to the second preferred embodiment described above, carried out in the absence of another solvent LM other than methanol, ethanol, n-propanol, isopropanol, n-butanol, the alcohol R ² -OH and the compounds II , the at least one compound II also entrained in the removal by distillation of the low-boiling alcohol R ⁶ -OH can also be at least partially separated off from the alcohol R ⁶ -OH, analogously to the above-described procedure for the separation of liquid-liquid mixtures become.

In order to reduce losses of the at least one compound II by the discharge of the low-boiling alcohol R ⁶ -OH in step b), it is preferred that in the distillative discharge of the low-boiling alcohol R ⁶ -OH entrained, at least one compound II also , analogous to the procedure described above, from the alcohol R ⁶ -OH at least partially separate. The separation is preferably carried out continuously.

Even in the absence of a further solvent LM, the separation of the at least one compound II from the alcohol R ⁶ -OH is preferably carried out by liquid-liquid extraction. In this case, however, the aqueous phase obtained in the liquid-liquid extraction can contain significant amounts of compound II in addition to the alcohol R ⁶ -OH. The aqueous phase can be subjected to a separation, preferably a distillative separation, for the recovery of the alcohol R ⁶ -OH and the compound II.

The separated from the low-boiling alcohol R ⁶ -OH, at least one compound II may still contain residual amounts of water (residual water), especially if their separation was carried out by the extractive route. Depending on the purpose, z. B. a return to the reaction in step b), then the separated compound II must be separated from the residual water. The separation of the residual water is preferably carried out by distillation. The at least one compound II separated from the low-boiling alcohol R ⁶ -OH can, if appropriate after removal of the residual water, be recycled back into the reaction in step b) as defined above or be retained for later reactions. Preferably, the separated, at least one compound II, optionally after removal of the residual water, directly back into the reaction in step b), as defined above, recycled.

The recovered alcohol R ⁶ -OH can be sold or used for the synthesis of compounds II.

catalyst Preparation

Due to the degradation of the metal alkoxide catalysts commonly used in the transesterification reactions, their degradation products, eg. As butanol in the case of Ti (OBu) ₄ , and the resulting transesterification products, eg. B.

Butyl (meth) acrylate, as impurities in the purification by distillation of

(Meth) acrylic acid ester products are entrained. In the case of the use of metal alkoxide catalysts, it is therefore expedient to carry out a pretreatment of the catalyst before the beginning of the reaction and to remove the interfering degradation products of the catalyst, for example BuOH, from the system.

In a preferred embodiment of the process according to the invention, the at least one catalyst used in step b) is selected from metal alkoxides obtained by reacting at least one metal or by reacting at least one metal compound selected from metal oxides, alkylmetal oxides, metal salts such as metal hydroxides or metal alkoxides of the general formula M [0 (C 1 -C 8 -alkyl)] _m , where m has the values 1, 2, 3 or 4, with at least one alcohol R ² - OH. These metal alkoxides used as catalysts in step b) of the process according to the invention are also referred to below as metal alkoxide catalysts.

Preferably, the metal of the metal compound used to prepare the at least one metal alkoxide catalyst is selected from K, Na, Ca, Mg, Ti, Zr, Mn, Fe, Co, Zn, Cd, Al, Ge, Sn and Sb.

Metal oxides, metal hydroxides or metal alkoxides of the general formula M [O (C 1 -C 5 -alkyl)] _m are particularly preferably used for the preparation of the at least one metal alkoxide catalyst, the metal being selected in each case from K, Na, Ca, Mg, Ti, Zr and Zn. Particularly preferred metallic starting materials for preparing the at least one metal alkoxide catalyst are, for example, potassium hydroxide (KOH), sodium methoxide (NaOMe), calcium oxide (CaO), magnesium oxide (MgO), zinc oxide (ZnO), titanium tetrachloride, titanium (IV). methanolate, titanium (IV) ethanolate, titanium (IV) isopropoxide, titanium (IV) butoxide, titanium (IV) acetylacetonate, zirconium tetrachloride, Zirconium (IV) propoxide, zirconium (IV) butoxide, zirconium (IV) pentoxide, zirconium (IV) acetylacetonate, or mixtures thereof.

Very particular preference is given to preparing the at least one metal alkoxide catalyst, titanium alkoxides (Ti [0 (C 1 -C 8 -alkyl)] 4) and zirconium alkoxides

(Zr [0 (Ci-C5-alkyl)] 4), in particular titanium alkoxides (Ti [0 (Ci-Cs-alkyl)] 4) used.

Suitable and preferred alcohols R ² -OH used to prepare the at least one metal alkoxide catalyst are those as defined above.

Preferably, the alcohol used for the preparation of at least one metal alkoxide catalyst corresponds to the alcohol R ² -OH R ² -OH used in the reaction in step b). Usually, the alcohol R ² -OH used for the preparation of the at least one metal alkoxide catalyst is in a 1, 1 to 50-fold molar excess, preferably in a 1, 5 to 30-fold molar excess, in particular in a 2 to 15-fold molar excess, based on the amount of metal oxide, metal hydroxide or metal alkoxide M [0 (C 1 -C ₅ -alkyl)] _m used.

The preparation of the at least one metal alkoxide catalyst is generally carried out at a temperature of 10 to 200 ° C, preferably at a temperature of 20 to 150 ° C and in particular at a temperature of 30 to 130 ° C. The preparation of the at least one metal alkoxide catalyst can be carried out in the absence or in the presence of an inert gas as defined above.

The preparation of the at least one metal alkoxide catalyst can generally be carried out at ambient pressure or reduced or elevated pressure. Preferably, the preparation of the at least one metal alkoxide catalyst is carried out at ambient or reduced pressure.

The low-boiling components formed in the preparation of the at least one metal alkoxide catalyst are usually removed by distillation during and / or at the end of the preparation. The low-boiling components are usually water, a C 1 -C 8 alcohol, or other organic solvents.

The distillative removal of the low-boiling components formed during the preparation of the at least one metal alkoxide catalyst is preferably carried out under reduced pressure. The alcohol used in excess R ² -OH is also removed by distillation after completion of the reaction.

The preparation of the at least one metal alkoxide catalyst is preferably carried out in situ. In this context, the term "in situ" means that the preparation of the catalyst occurs immediately prior to the reaction in step b) and the metal alkoxide catalyst obtained directly, i. H. without further work-up or purification, in the reaction in step b) is used. The amount of the metal alkoxide catalyst used in step b) is 0.01 to 10 mol%, preferably 0.02 to 7 mol% and in particular 0.05 to 5 mol%, based on the total amount of the compound (II) in the reaction mixture.

Step c)

The R ⁶ -OH depleted reaction mixture obtained in step b) is then subjected to distillative separation to obtain a fraction enriched in the at least one compound II, which optionally contains alcohol R ² -OH, and one of the compounds I and at least a catalyst-enriched bottoms product.

For distillative separation of the reaction mixture which has been depleted in R ⁶ -OH and obtained in step b), the devices mentioned in the embodiments for distillative removal are generally suitable. For fractional distillation of the product fraction, fractional distillation is preferably carried out using distillation columns, in particular packing columns.

In a preferred embodiment of the process according to the invention, the fraction obtained in step c) which has been enriched in the at least one compound II and optionally contains alcohol R ² -OH is returned to the reaction in step b).

"Recycling into the reaction in step b)" means that the fraction enriched in the at least one compound II, which optionally contains alcohol R ² -OH, is passed back into the reaction zone of the reaction in step b).

Cleaning:

In general, the bottom product obtained in step c) and enriched in the compounds I and the at least one catalyst, which optionally contains at least one stabilizer, is subsequently subjected to a further purification. The bottom product obtained in step c) and enriched in the compounds I and the at least one catalyst, which optionally contains at least one stabilizer, is subjected to further distillative separation, in particular fractional distillation (fine distillation), to obtain a compound which is attached to the compound. fertilizing the general formula I enriched product fraction and a sump fraction enriched in the at least one catalyst and the at least one stabilizer.

For distillative separation of the enriched in the compounds I and the at least one catalyst bottom product, which optionally contains at least one stabilizer, are also the aforementioned distillation apparatuses.

The distillative separation of the bottoms product enriched in the compounds I and the at least one catalyst, which optionally contains at least one stabilizer, is preferably carried out in fractionated form. Usually fractions with a high content of compounds I, e.g. with a content of at least

95 wt .-%, for example, of at least 98 wt .-% or at least 99 wt .-%, and fractions having a lower content of compounds I obtained. Optionally, the product fractions enriched in the compounds of the general formula I are combined with a lower content of compounds I, for example a content of compounds I of less than 95% by weight, for example 85, 90 or 94% by weight, and as described above, purified by distillation. This procedure can also be repeated several times until the compounds I are present in the desired purity.

The content of compounds I in the product fraction thus obtained is usually above 95% by weight, frequently above 98% by weight or higher, for example above 99% by weight.

As a rule, the product fraction enriched in the compounds of general formula I contains no alcohol R ² -OH and no catalyst used in the reaction in step b). The sump fraction enriched in the at least one catalyst and the at least one stabilizer can then be stored for a longer time or used further directly for a further reaction in step b).

Reactors and continuous process control In the process according to the invention, the reaction zone may consist of a reactor or of an arrangement of several reactors. Several reactors are preferably connected in series. The process according to the invention can be carried out batchwise or continuously.

In a preferred embodiment of the process according to the invention, at least one of steps b), c) or the subsequent purification (fine distillation) is carried out continuously. The reactors used in the process according to the invention may be any reactors which are suitable for carrying out chemical reactions in the liquid phase.

Suitable reactors are non-backmixed reactors, such as tubular reactors or built-in residence time vessels, but preferably backmixed reactors, such as stirred tanks, loop reactors, jet loop reactors or jet nozzle reactors. However, combinations of successive backmixed reactors and non-backmixed reactors may also be used. Optionally, several reactors can be combined in a multi-stage apparatus. Such reactors are, for example, loop reactors with built-in sieve trays, cascaded vessels, tube reactors with intermediate feed or stirred columns. Preferably, stirred tank reactors are used. The stirred tank reactors are usually made of metallic materials, with stainless steel being preferred. The reaction mixture is preferably mixed intensively with the aid of a stirrer or a circulation pump. In a preferred embodiment, step b) of the process according to the invention is carried out in a single stirred tank. In a further preferred embodiment, step b) of the process according to the invention is carried out in at least two stirred tanks, which are connected to one another in the form of a cascade. Especially in the case of continuous process control, it may be expedient for the most complete reaction possible to combine several reactors in the form of a cascade. The individual reactors are passed through the reaction mixture in succession, wherein the outlet of the first reactor to the second reactor, the outlet of the second reactor to the third reactor, etc. is supplied. The cascade can z. B. 2 to 10 reactors, with 2, 3, 4 or 5 reactors are preferred. If a cascade of several reactors is used to carry out step b), all reactors of the cascade can be operated at the same temperature. In general, however, it is preferable to steadily increase the temperature from the first to the last reactor of a cascade, wherein a reactor is operated at the same or higher temperature than the upstream reactor in the flow direction of the reaction mixture. Conveniently, all reactors can be operated at substantially the same pressure.

When the process is carried out continuously in step b), streams of the educts and optionally of the organic solvent (LM) into the reactor or, if a reactor cascade is used, are preferably introduced into the first reactor of the cascade which contains the catalyst and optionally the at least one stabilizer (polymerization inhibitor). contains. The residence time in the reactor or the individual reactors is determined by the volume of the reactors and the flow rate of the reactants. At the same time, a stream of the lower alcohol R ⁶ -OH and the at least one compound II is continuously discharged. For this purpose, a vapor is withdrawn from the reactor or the individual reactors containing the lower alcohol R ⁶ -OH and a part of at least one compound II. The vapors drawn off for discharging the lower alcohol R ⁶ -OH from the respective reactors of a cascade can be combined and condensed together. Optionally, you can combine several reactors of the cascade to form a subunit, in each case then the subunits are coupled to a capacitor. There is also the possibility to couple each reactor of the cascade with a capacitor.

After completion of the reaction in step b) or at the end of the reactor cascade, the depleted R ⁶ -OH reaction mixture is transferred to a distillation apparatus in which the excess of the at least one compound II and the optionally still present alcohol R ² -OH is removed by distillation ( Step c)). The distillation in step c) of the process according to the invention is preferably carried out at reduced pressure. For this purpose, a vapor is withdrawn which contains the at least one compound II and optionally the remaining alcohol R ² -OH. After condensation of the vapor, the at least one compound II and optionally the alcohol R ² -OH in the reactor or the reactor cascade of the reaction in step b) is returned. If a cascade of a plurality of reactors is used to carry out step b), it is preferable not to pass the at least one compound II and the optionally attributable alcohol R ² -OH back into the last reactor of the cascade of the reaction in step b). Preferably, the at least one compound II to be recycled and the optional alcohol R ² -OH to be recycled are passed exclusively or predominantly into the first reactor of the cascade. Subsequent to step c), the bottom product enriched in the compounds I, the at least one catalyst and optionally the at least one stabilizer is transferred again into a distillation apparatus for further purification (purification step). The purification is preferably carried out by means of fractional distillation at reduced pressure, with fractions having different contents of compounds I being obtained. Fractions having a low content of compounds I, for example less than 95% by weight, as defined above, are recycled back to the reactor or reactor cascade of the reaction in step b) and / or to the distillation apparatus in step c). Fractions having the desired content of compounds I, for example having a content of compounds I of at least 95% by weight, as defined above, are discharged from the process.

The catalyst remaining in the bottom after the purification step and optionally remaining at least one stabilizer is then recycled back into the reactor in step b) or into the first reactor of the cascade of step b) or into a new batch process in a batchwise process Implementation to be used.

The invention will be explained in more detail with reference to the examples described below. The examples should not be construed as limiting the invention.

The following abbreviations are used in the following examples: MMA stands for methyl methacrylate;

EA stands for ethyl acrylate;

AMA stands for allyl methacrylate;

DMAE stands for dimethylaminoethanol;

DMAEMA stands for dimethylaminoethyl methacrylate;

TBAEMA is 2- (N-tert-butylamino) ethyl methacrylate;

MeHQ stands for methylhydroquinone;

PTZ stands for phenothiazine;

MeOH is methanol;

GC stands for gas chromatography;

GC area% is the percentage of the area of a substance peak in relation to the total area of the peaks in a gas chromatogram (GC area percent);

Ti (OiPr) ₄ is titanium (IV) isopropanolate;

Ti (OnBu) ₄ is titanium (IV) n-butoxide;

Tyzor (Tyzor TPT 20 B) stands for a mixture of tetraisopropyl titanate and

Tetra (n-butyl) titanate (80:20, 1 mol% based on the amount of allyl alcohol used).

EXAMPLES I) Construction of the apparatus:

The experiments were carried out in a 4 L jacketed stirred-tank reactor with closable opening, air inlet tube, separating column, sampling point, internal temperature measuring sensor and bottom outlet valve. The mixture was stirred with an anchor stirrer at 160 rpm.

As a separation column, a 50 cm long Oldershaw column with Sulzer packing (diameter 4 cm) made of stainless steel (10 theoretical plates) was used. On the top of the column it was possible to meter in a stabilizer solution continuously. The stabilizer solution is a solution of a suitable polymerization inhibitor in an organic compound, which may or may not be identical to one of the components in the stirred tank. On the separation column, a liquid distributor for adjusting the reflux ratio was attached.

For temperature control, thermostated oil was pumped continuously through the jacketed vessel. II) Preparation Examples

Example 11.1: Preparation of allyl methacrylate with addition of MMA to the reaction solution and a solution of PTZ in MeOH overhead

16.4 mL (15.75 g, 55.3 mmol) of titanium (IV) isopropanolate were placed in a one-necked flask and mixed with 40.5 mL (32 g, 0.55 mol) of allyl alcohol. The reaction mixture was stirred in a rotary evaporator for 30 min at 80 ° C and 500 mbar. All low-boiling components were then removed by increasing the vacuum. Tetraallyloxytitanium (IV) was obtained in quantitative yield (15.5 g) as a yellowish liquid.

transesterification:

The reactor was charged with 2635 mL (2477 g, 24.74 mol) MMA, 752 mL (639 g, 11 mol) allyl alcohol, 1.75 g MeHQ, and 0.7 g PTZ. During the heating, the catalyst represented in the preceding step was added tetraallyloxy titanium (IV) (62.8 g, 221 mmol, 2 mol% based on allyl alcohol) at a temperature of 96 ° C and atmospheric pressure in the reactor. The reaction mixture was heated to boiling while the temperature in the kettle was between 93 and 103 ° C. The distillation column was operated at the beginning of the reaction for 15 min with full reflux. To the top of the column was added a 0.01% by weight solution of PTZ in methanol (47 g per hour, total 140 g of solution). When the temperature stabilized at 62 to 64 ° C at the top of the column, the azeotropic mixture of MMA and methanol was withdrawn at a reflux ratio of 1: 1. In the course of the reaction, the vacuum was reduced from atmospheric pressure to 700 mbar to accelerate the decrease of the distillate. In order to keep the level of the reactor constant, the amount of distillate withdrawn was continuously balanced by addition of MMA (950 mL, 893 g, 8.92 mol in 5.00 hours). The reaction was monitored by GC and stopped after reaching 97.4% conversion based on allyl alcohol after 5.00 h. Excess MMA and allyl alcohol (2.6% of the amount used) were removed in vacuo; wherein the recovered amount of allyl alcohol can be reused in the next experiment. AMA was subsequently purified by distillation. There were obtained 605 g (4.76 mol, 44% yield) AMA with a purity of 99.3% (GC). [Another 588 g, 4.66 mol, 42% yield with a purity of 95.9%. Another 168 g, 1, 33 mol, 12% yield with lower purity. Total 98% yield]. Colorless product.

The reaction was carried out several times in the manner described. Mixtures with a lower proportion of AMA were combined and distilled together again via a column to obtain AMA with a purity of 99.4%. Colorless product.

Example II.2: Preparation of allyl methacrylate without addition of MMA during the reaction

The reaction was carried out as in Example 11.1, but no MMA was added during the reaction. After 4.75 h, the composition in the reactor (GC area%, uncorrected) was: MMA 43.59, MeOH 0.09, allyl alcohol 0.89, allyl alcohol methylethacrylate 55.29, unknown 0.14 - this corresponds to a conversion of 98%. The reaction mixture was not further worked up.

Example II.3: Distillation of an AMA reaction mixture

From a reaction mixture obtained according to Example 11.1, the excess MMA was removed via a distillation column with 10 theoretical plates in vacuo. The resulting reaction mixture was composed as follows (GC area%): AMA 99.32, MMA 0.45. The still contained catalyst and the stabilizers were removed by distillation on a Sambay evaporator (heating surface 0.046 m ² , wiper made of V2A steel, speed 170 rpm, external temperature 95 ° C, 50 mbar). The purity of the product thus obtained was 99.67 GC area%. Colorless product.

Comparative Example 11.1: Preparation of allyl methacrylate with addition of an MMA PTZ solution overhead The reaction was carried out in the manner described in Example 11.1. However, a solution of PTZ in MMA was added at the top of the column. Within the first three hours of the reaction time, 3% of the amount of allyl alcohol used was lost via the distillates removed.

Comparative Example II.2: Preparation of Allyl Methacrylate Using Tyzor (Tyzor TPT 20 B) as Catalyst The reaction was carried out as in Example 11.1 except that a mixture of tetraisopropyl titanate and tetra (n-butyl) titanate (80:20, 1 mol% based on the amount of allyl alcohol used). 1276 g of AMA were obtained (10.1 mol, 92% of theory). Of these, only 206 g (1.63 mol, 15% of theory) had a purity of> 99%. Colorless product.

Example II.4: Preparation of dimethylaminoethyl methacrylate (DMAEMA) with addition of MMA to the reaction solution and a solution of PTZ in MeOH overhead

Catalyst Preparation:

66.3 ml (63.6 g, 224 mmol) of titanium (IV) isopropanolate were introduced into a one-neck flask and mixed with 108 ml (96 g, 1.10 mol) of dimethylaminoethanol. The reaction mixture was stirred in a rotary evaporator for 30 min at 80 ° C and 500 mbar. All low-boiling components were then removed by increasing the caudate. Tetrakis (dimethylaminoethyl) titanate was obtained in quantitative yield (89.9 g) as a yellowish liquid.

Transesterification: The reactor was charged with 2635 mL (2477 g, 24.74 mol) MMA, 10110 mL (980 g, 11 mol) dimethylaminoethanol, 3.50 g MeHQ, and 1.4 g PTZ. During the heating, the catalyst shown in the preceding step was added tetrakis (2-dimethylaminoethyloxy) titanium (IV) (89.9 g, 221 mmol, 2 mol% based on dimethylaminoethanol) at a temperature of 101 ° C and atmospheric pressure in the reactor given. The reaction mixture was heated to boiling while the temperature in the kettle was between 103 and 108 ° C. The distillation column was operated at the beginning of the reaction for 15 min with full reflux. To the top of the column was added a 0.01% by weight solution of PTZ in methanol (53 g per hour, total 160 g of solution). When the temperature stabilized at 60 to 63 ° C at the top of the column, the azeotropic mixture of MMA and methanol was withdrawn at a reflux ratio of 2: 2. In the course of the reaction, the vacuum was reduced from atmospheric pressure to 750 mbar to accelerate the decrease of the distillate. In order to keep the level of the reactor constant, the amount of withdrawn Distillate continuously equilibrated by addition of MMA (1550 ml, 1457 g, 14.6 mol in 7.33 hours). The reaction was monitored by GC and terminated after reaching 97% conversion based on dimethylaminoethanol after 7.33 h. Excess MMA and dimethylaminoethanol (3% of the amount used) were removed in vacuo; wherein the recovered amount of dimethylaminoethanol can be reused in the next experiment. DMAEMA was subsequently purified by distillation. There were 1428 g (9.09 mol, 83% yield) DMAEMA with a purity of> 99% (GC). [In fact, the DMAEMA yield was 90%, but only 83% reached> 99%]. Colorless product.

Comparative Example II.3: Preparation of dimethylaminoethyl methacrylate (DMAEMA) using Tyzor (Tyzor TPT 20 B) as catalyst

The reaction was carried out as described in Example II.4, but a mixture of Ti (0'Pr) 4 and Ti (0 ⁷ Bu) 4 (8: 2 molar) was used as the catalyst. Only after 15 h was a turnover of 95% achieved.

Example II.5: Preparation of isoamyl methacrylate with addition of MMA to the reaction solution and a solution of PTZ in MeOH overhead

Catalyst Preparation:

33.5 ml (31.8 g, 0.1 l mol) of titanium (IV) isopropanolate were placed in a one-necked flask and mixed with 58.6 ml (47.5 g, 0.54 mol) of isoamyl alcohol. The reaction mixture was stirred in a rotary evaporator for 30 min at 80 ° C and 500 mbar. All low-boiling components were then removed by improving the vacuum. Tetraisoamyl titanate was obtained in quantitative yield (43.6 g) as a yellowish liquid. transesterification:

As described in Example 11.1, methyl methacrylate (2253 g, 22.5 mol), isoamyl alcohol (882 g, 10 mol), and methylhydroquinone (3.20 g) and phenothiazine (1, 30 g) were introduced into the plant described and with the added in the previous step catalyst shown. At a reflux ratio of 2: 2 and a temperature of <65 ° C at the top of the column an azeotrope of methanol and methyl methacrylate was withdrawn. The losses by distillation were compensated by adding fresh methyl methacrylate (566 g, 5.64 mol in 3 h). Over the top of the column, a 0.01% by weight solution of PTZ in methanol was metered in (130 g in 2 hours). After 3 h, the conversion was 99% (determined from GC area%). Yield after distillation: 99% (GC purity: 98.7%), of which 82% with a purity of 99.7%. Example 11.6: Preparation of isoamyl acrylate with addition of EA to the reaction solution and a solution of PTZ in ethanol over head

Tetraisoamyl titanate was prepared as described in Example 11.5 and to a mixture of ethyl acrylate (2253 g, 22.5 mol), isoamyl alcohol (882 g, 10 mol), and methylhydroquinone (3.20 g) and phenothiazine (1.30 g ). At a reflux ratio of 5: 1 and a temperature of <77 ° C at the top of the column an azeotropic mixture of ethanol and ethyl acrylate was withdrawn. The losses by distillation were compensated by adding fresh ethyl acrylate (650 g, 6.49 mol in 6 h). Over the top of the column, a 0.01% by weight solution of PTZ in ethanol was metered in (160 g in 6 h). After 6 hours, the pressure was gradually reduced to 650 mbar and stopped the supply of ethanol at the top of the column. After 1 1, 5 h, the conversion was 99% (determined from GC area%). Yield after distillation: 91% (GC purity: 98.7%), of which 76% with a purity of 99.5%.

Example II.7: Preparation of isobutyl methacrylate with the addition of MMA to the reaction solution and a solution of PTZ in MeOH overhead

Catalyst Preparation:

A single-neck flask was charged with 21.4 ml (20.1 g, 71 mmol) of titanium (IV) isopropanolate and mixed with 58.6 ml (40.9 g, 0.55 mol) of isobutyl alcohol. The reaction mixture was stirred in a rotary evaporator for 30 min at 80 ° C and 500 mbar. All low-boiling components were then removed by improving the vacuum. Tetraisobutyl titanate was obtained in quantitative yield (24.1 g) as a yellowish liquid.

Transesterification: As described in Example 11.1, methyl methacrylate (2477 g, 24.7 mol), isobutyl alcohol (815 g, 11 mol), and methylhydroquinone (1.75 g) and phenothiazine (0.70 g) were introduced into the plant described and added to the catalyst shown in the previous step. At a reflux ratio of 2: 2 and a temperature of <65 ° C at the top of the column an azeotrope of methanol and methyl methacrylate was withdrawn. The losses by distillation were compensated by adding fresh methyl methacrylate (600 g, 5.99 mol in 3 h). Over the top of the column, a 0.01% by weight solution of PTZ in methanol was metered in (133 g in 3 hours). After 4 h, the conversion was 99% (determined from GC area%). The reaction mixture was not worked up further.

For the following examples, the plant described above under point I has been extended by further parts to allow the use of a solvent: mixing vessel with automatic dosing of water via dosing pump and dean ter. Return of the organic phase from the decanter into the reactor by pump.

Example 8: Preparation of dimethylaminoethyl methacrylate (DMAEMA) using a solvent and dibutyltin oxide as catalyst

The reactor was treated with dimethylaminoethanol (802 g, 9 mol), MMA (1694 g, 16.9 mol), heptane (253 g), dibutyltin oxide (17.9 g), MEHQ (2.5 g) and PTZ (1, 25 g) and the mixture is heated to boiling at atmospheric pressure. The reflux ratio was changed so that the temperature at the top of the column did not exceed 64 ° C. The azeotropic mixture of methanol and heptane separated off at the top of the column was mixed continuously with stirring in a mixing vessel with the same amount of water (50 to 250 ml / h) and then transferred to a decanter. The methanol-containing water phase was discarded while the organic phase was pumped back into the reactor. To keep the excess of MMA constant, a total of 186 g of MMA was added during the reaction. A 9% by weight solution of MEHQ in methanol was metered into the top of the column (30 ml / h). After 10 hours, 91% conversion based on the amount of dimethylaminoethanol used was achieved. Dimethylaminoethanol was not carried to the distillates.

Workup was omitted, but the low boilers contained can be easily separated by distillation and reused in the next batch. The remaining after the distillation of the product in the reactor stabilizers and the catalyst can also be used in other approaches.

Example 9: Preparation of allyl methacrylate using a solvent and dibutyltin oxide as a catalyst

The reactor was treated with allyl alcohol (799 g, 12.1 mol), MMA (1630 g, 16.3 mol), heptane (265 g), dibutyltin oxide (34.9 g), MEHQ (5 g) and PTZ (18 g ) and the mixture is heated to boiling at atmospheric pressure. The reflux ratio (R: D) was changed in such a way (6: 4 - 1:10) that the temperature at the top of the column did not exceed 58 ° C. The azeotropic mixture of methanol and heptane separated off at the top of the column was mixed continuously with stirring in a mixing vessel with the same amount of water (50 to 250 ml / h) and then transferred to a decanter. The methanol-containing water phase was discarded while the organic phase was pumped back into the reactor. In order to keep the excess of MMA constant, MMA was metered in continuously during the reaction (20 mL / h). A 9% by weight solution of MEHQ in methanol was metered into the top of the column (30 ml / h). After 5 h, 80% conversion based on the amount of allyl alcohol used was achieved. Allyl alcohol was not carried to the distillates. The crude product mixture thus obtained was vacuum-distilled to give allyl alcohol methacrylate (AMA) in a purity of 98% and a yield of 61 to 80%. The withdrawn low boilers could be reused in the next reactions.

The amount of catalysts and stabilizers left in the reactor were reused for three further reactions by the method described above. After 5 h, in each case 80% conversion based on the amount of allyl alcohol used was achieved. A loss of catalytic power could not be determined.

Comparative Example II.4: Preparation of allyl methacrylate with the addition of a solution of MeHQ in MMA overhead and dibutyltin oxide as catalyst

The reaction was carried out as in Example 9, except that a 9% by weight solution of MEHQ in MMA was metered onto the top of the column as stabilizer solution

(30 mL / h). The distillate removed in this experiment contained 10 to 15% allyl alcohol. The approach was rejected.

Example 10: Preparation of 2- (N-tert-butylamino) ethyl methacrylate (TBAEMA) without addition of MMA during the reaction, addition of a stabilizer solution to the top of the column, addition of the extracted solvent to the top of the column, partial conversion and recycling with reuse of catalyst and stabilizer. In the plant described in Example 8, MMA (2012 g, 20.10 mol), 2- (N-tert-butylamino) ethanol (1341 g, 11.1, 45 mol), heptane (213 g), dibutyltin oxide (42 g , 0.17 mol), hydroquinone monomethyl ether (8.00 g) and phenothiazine (14.2 g) are added and the mixture is heated to boiling at atmospheric pressure. The placed on the reactor distillation column was operated under full reflux until the temperature was about 60 ° C. Thereafter, at a reflux ratio (R: D) = 5: 3 distillate was removed (50 to 250 mL r ¹ ). The resulting azeotropic mixture of methanol and heptane and traces of MMA were mixed with the same amount of water, transferred to a phase separation vessel, the aqueous, methanol-containing, phase removed from the system and the organic phase returned to the top of the distillation column. An 8% by weight solution of hydroquinone monomethyl ether in methanol (about 100 ml in 18 h) was metered onto the top of the distillation column. The temperature of the reaction mixture increased during the reaction from 100 ° C to 1 10 ° C. After reaching 95% conversion (about 17 h, determined by quantitative gas chromatography with n-dodecane as internal standard), the reaction was stopped and the resulting crude product subjected to purification by vacuum distillation, the following fractions were obtained: 1) heptane and Excess MMA, 2) traces of MMA, traces of heptane, unreacted alcohol and TBAEMA. The mixture of catalyst, stabilizers, TBAEMA, unreacted alcohol and polymers remaining in the reactor was mixed with fraction 1) obtained above. Further, fresh MMA and fresh alcohol were added to achieve the same composition as above. The reaction was again carried out as described above, the resulting crude product distilled to give the fractions 1) and 2) and a residue were obtained.

The residue thus obtained was admixed, as described above, with fraction 1) and with fresh MMA and fresh alcohol in order to achieve the desired composition. The reaction was again carried out as described above and the crude product was purified by distillation, again the fractions 1) and 2) and a distillation residue were obtained.

Fraction 1) was stored for use in later reactions and the entire unit was cleaned by boiling out with methanol, removing the distillation residue from the system and discarding it.

The fractions 2) obtained in the three reactions described above were combined and subjected to distillative purification (fine distillation) to give the following fractions: A) traces of heptane, MMA, alcohol, traces of TBAEMA (recycling in subsequent reactions), B) traces of MMA , Alcohol and TBAEMA (storage for recycling in further fine distillations) and C) pure TBAEMA with a purity> 99%. The yield of pure TBAEMA is by this method usually -75% (4772 g, 25.76 mol) of a colorless product (<20 Hazen, APHA).

Example 1 1: Preparation of 2- (N-tert-butylamino) ethyl methacrylate (TBAEMA) without addition of MMA during the reaction, metered addition of a stabilizer solution to the top of the column, metered addition of the solvent to the top of the column, full conversion and recycling under Discard catalyst and stabilizer, with residue work-up.

In the plant described in Example 8, MMA (2553 g, 25.50 mol), 2- (N-tert-butylamino) ethanol (1328 g, 11, 44 mol), heptane (359 g), dibutyltin oxide (42 g , 0.17 mol), hydroquinone monomethyl ether (8.00 g) and phenothiazine (14.2 g) are added and the mixture is heated to boiling at atmospheric pressure. The placed on the reactor distillation column was operated under full reflux until the temperature was about 60 ° C. Thereafter, at a reflux ratio (R: D) = 5: 3 distillate was removed (50 to 250 mL h-1). The resulting azeotropic mixture of methanol and heptane and traces of MMA were mixed with the same amount of water, transferred to a phase separation vessel, the aqueous methanol-containing phase removed from the system and the organic phase recycled to the top of the distillation column. At the top of the distillation column, an 8 wt .-% solution of Hydroquinone monomethyl ether in methanol (about 100 mL in 15 h). The temperature of the reaction mixture increased during the reaction from 100 ° C to 1 12 ° C. After reaching> 99% conversion (about 15 h, determined by quantitative gas chromatography with n-dodecane as internal standard), the reaction was stopped and subjected to purification of the resulting crude product by vacuum distillation, the following fractions were obtained: 1) heptane and excess MMA, 2) traces of heptane, MMA, TBAEMA and traces of unreacted or equilibriated or otherwise split off alcohol and 3) pure TBAEMA

(> 99 GC area%, <20 Hazen, APHA).

The remaining in the reactor mixture of catalyst, stabilizers, TBAEMA, unreacted or eliminated alcohol and polymers was removed from the reactor and stored. The reaction was carried out two more times as described above, whereby the fractions 1) and 2) obtained in the distillation can be used as starting material.

After the third run, the distillation residue remains in the reaction vessel and the distillation residues obtained from the two previous reactions are added and the mixture is purified by distillation again to give a further fraction of pure TBAEMA (> 99 GC area%, <20 Hazen, APHA) , The remaining residue may optionally be used in whole or in part in further reactions.

Overall, the yield of pure TBAEMA according to this method is -85% d. Theory, which advantageously dispenses with a separate fine distillation.

Claims

claims:

1 . Process for the preparation of (meth) acrylic acid esters of general formula I.

wherein

R ^{1 is} hydrogen or methyl,

R ^{2 is} an unbranched or branched C 3 -C 10 -alkyl group, a C 5 -C 7 -cycloalkyl group, where the cycloalkyl group is unsubstituted or may be substituted by at least one C 1 -C 10 -alkyl radical, an unbranched or branched C 2 -C 10 -alkenyl group, containing 1 , 2 or 3 double bonds, or a C 2 -C ¹⁰ -alkyl group substituted by a -N (R ^3a R ^3b ) group or a - (OR ⁴ ) _n -OR ⁵ group, where n is 0, 1 , 2, 3 or 4, stands and

R ^3a and R ^3b independently of one another represent hydrogen, a C 1 -C 5 -alkyl group, a C 5 -C 7 -cycloalkyl group or phenyl, where the substituents R ^3a and R ^3b in -N (R ^3a R ^3b ), together with the N- Atom to which they are attached can also form a 5- to 7-membered ring,

R ^{4 is} a Ci-C4-alkylene group and

R ^{5 is} a C 1 -C 8 -alkyl group in which a) at least one compound of the general formula II

provides in which

R ^{1 has} the abovementioned meaning and

R ^{6 is} methyl, ethyl, n-propyl, isopropyl or n-butyl, b) the at least one compound II provided in step a) in the presence of at least one alcohol R ² -OH and in the presence of at least one Catalyst selected from mineral acids, metals, metal salts, organometallic compounds or metal alkoxides, to obtain a reaction mixture containing at least one (meth) acrylic ester of the general formula I, wherein the formed during the reaction of alcohol R ⁶ -OH together with a part of the at least one compound II is continuously removed by distillation via at least one column and a depleted in R ⁶ -OH reaction mixture is obtained, c) the obtained in step b) to R ⁶ -OH depleted reaction mixture subjected to a distillative separation, to obtain a fraction enriched in the at least one compound II which optionally contains alcohol R ² -OH and a bottom product enriched in the compounds I and the at least one catalyst, wherein in the compounds of general formula II the radical R ⁶ is chosen such that the boiling point at 1013 mbar of the corresponding alcohol ls R ⁶ -OH is at least 15 ° C below the boiling point of the alcohol used in step b) R ² -OH and wherein during the distillative removal in step b) a liquid stream containing methanol, ethanol, n-propanol, isopropanol or Bu - Tanol or a mixture of these alcohols, in the region of the head of at least one column is continuously introduced.

2. The method of claim 1, wherein the during the distillative removal in step b) continuously introduced liquid stream at least 80 wt .-%, based on the total weight of the liquid stream, methanol, ethanol, n-propanol, isopropanol or butanol or a mixture contains these alcohols.

3. The method according to any one of claims 1 or 2, wherein for the implementation in step b) additionally compound II is supplied.

4. The method according to any one of the preceding claims, wherein the reflux ratio in the column in the distillative discharge in step b) in the range of 10: 1 to 1: 100.

5. The method according to any one of claims 1 to 4, wherein step b) in the presence of another, of methanol, ethanol, n-propanol, isopropanol, n-butanol, the alcohol R ² -OH and the compounds (II) different solvent LM is carried out.

6. The method of claim 5, wherein the at least one further solvent LM is selected from aliphatic and alicyclic hydrocarbons containing 5 to 8 carbon atoms, in particular hexane, heptane and cyclohexane, and mixtures thereof.

Method according to one of claims 5 and 6, wherein b1) continuously at least a portion of the solvent LM together with the alcohol R ⁶ -OH and a part of the at least one compound II via at least one column by distillation,

b2) the solvent LM, which has been discharged in step b1), and the at least one compound II is at least partially removed by extraction from the alcohol R ⁶ -OH and

b3) the solvent LM separated off in step b2) and the at least one compound II are at least partially recycled to the reaction in step b).

A process according to any one of claims 1 to 4, wherein step b) is carried out in the absence of a solvent LM other than methanol, ethanol, n-propanol, isopropanol, n-butanol, the alcohol R ² -OH and the compounds (II).

A process according to any one of the preceding claims, wherein the alcohol contained in the liquid stream corresponds to the at least one alcohol R ⁶ -OH released in the reaction in step b).

Method according to one of the preceding claims, wherein the introduced during the distillative discharge in step b) liquid stream contains at least one stabilizer.

Method according to one of the preceding claims, wherein the introduced during the distillative discharge in step b) continuously at the top of the column liquid stream of methanol, ethanol, n-propanol, isopropanol or butanol or a mixture of these alcohols containing at least one stabilizer consists.

Method according to one of the preceding claims, wherein the amount of liquid stream introduced hourly during the distillative removal in step b) 0.1 to 25 wt .-%, based on the total amount of the alcohol used in the reaction in step b) R ² - OH, is. 13. The method according to any one of the preceding claims, wherein the obtained in step c) enriched at least one compound II fraction, the optionally alcohol R ² -OH, is returned to the reaction in step b).

A process according to any one of the preceding claims wherein the bottom product obtained in step c) is further distilled to give a product fraction enriched in the compounds of general formula I and a bottoms fraction enriched in the at least one catalyst and the at least one stabilizer.

The process of claim 14, wherein the sump fraction enriched in the at least one catalyst and the at least one stabilizer is reused for re-conversion in step b).

Method according to one of the preceding claims, wherein in the compounds of general formula I,

R ^{1 is} hydrogen or methyl,

R ^{2 is} a straight or branched C 4 -C 6 -alkyl group, a C5-C6-

Cycloalkyl group, where the cycloalkyl group is unsubstituted or may be substituted by a C 1 -C 4 -alkyl radical, a straight-chain or branched C 3 -C 6 -alkenyl group containing 1 or 2 double bonds, or an unbranched C 2 -C 4 -alkyl group which N (R ^3a R ^3b ) group or an -OR ⁵ group is substituted,

R 3a is hydrogen, an unbranched C 1 -C ₄ -alkyl group or a branched C 1 -C ₄ -alkyl group,

R ^{5 is} an unbranched C 1 -C ³ -alkyl group. 17. The method according to any one of the preceding claims, wherein in the compounds of general formula I,

R ^{1 is} hydrogen or methyl and

R ^{2 is} an unbranched or branched C ⁴ -C 6 -alkyl group, a straight-chain or branched C 3 -C 6 -alkenyl group containing one double bond, or a straight-chain C ² -C ³ -alkyl group which is substituted by a -N (R ^3a R ^3b ) - Group is substituted,

R3a is hydrogen or an unbranched Ci-C4-alkyl group and

18. The method according to any one of the preceding claims, wherein in the compounds of general formula II, R ^{1 is} hydrogen or methyl and R ^{6 is} methyl.

Method according to one of the preceding claims, wherein the at least one stabilizer is selected from phenolic compounds, N-oxyl compounds, sulfonamides and sulfur-containing compounds, and mixtures thereof.

Method according to one of the preceding claims, wherein the at least one catalyst used in step b) is selected from metal alkoxides.

The process according to claim 20, wherein the at least one metal alkoxide catalyst used in step b) is prepared by reacting at least one metal or by reacting at least one metal compound selected from metal oxides, alkylmetal oxides, metal salts or metal alkoxides of the general formula M [O (C 1 -C 4) Alkyl)] _m , where m is 1, 2, 3 or 4, with at least one alcohol R ² -OH.

The method of claim 21, wherein the preparation of the at least one metal alkoxide catalyst is carried out prior to step b).

23. The method according to any one of claims 21 or 22, wherein the optionally resulting in the preparation of the at least one metal alkoxide catalyst, low-boiling components are removed by distillation.