DE102015226830A1 - Process for the preparation of high-boiling (meth) acrylic esters - Google Patents

Abstract

The invention relates to a process for the preparation of (meth) acrylic esters of the general formulas Ia or I.b in which a) at least one compound of the general formula III is provided, b) the at least one compound III provided in step a) in the presence of at least one alcohol R 2 -OH or at least one di-, tri- or tetravalent alcohol HO-Z- (OH) m, in the presence of at least one catalyst, and in the presence of at least one stabilizer, to obtain a reaction mixture comprising at least one (meth) acrylic ester of the general formulas Ia or Ib, wherein the alcohol R3-OH formed during the reaction is continuously removed by distillation, c) the at least one compound III is distilled off by distillation from the reaction mixture obtained in step b), giving a compound Ia or Ib which the at least one stabilizer and the at least one catalyst-enriched bottoms product d) treating the bottom product obtained in step c) with an aqueous basic solution, for deactivating the catalyst and for deprotonating the at least one stabilizer, e1) subjecting the aqueous basic solution treated bottom product from step d) to an extractive separation for removal at least a portion of the deprotonated stabilizer contained in the treated bottoms product and at least a portion of the deactivated catalyst contained in the treated bottoms product, or e2) removes the volatile constituents contained in the treated bottoms product from step d) at least partially by distillation and removes the resulting solid from the liquid Product phase separated.

Description

The present invention relates to a process for the preparation of high-boiling (meth) acrylic esters in the presence of at least one catalyst and in the presence of at least one stabilizer.

BACKGROUND OF THE INVENTION

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

As a rule, high-boiling (meth) acrylic esters are obtained industrially by transesterification of lower (meth) acrylic esters. Since it is an equilibrium reaction in the transesterification, it is necessary to achieve high reaction conversions to use one of the starting materials in a large excess and / or continuously remove one of the reaction products (usually the liberated lower alcohol) from the reaction mixture.

Various processes for the preparation of (meth) acrylic acid esters by transesterification in the presence of acidic or basic catalysts are described in the prior art.

EP 145 588 B1 For example, a process for the preparation of higher (meth) acrylic esters by transesterification of lower (meth) acrylic acid esters in the presence of a titanium alkoxide catalyst, in particular tetra-n-butyl titanate, and in the presence of aminophenols or aminomethylphenols as polymerization inhibitors.

US 2006/0084823 A1 describes a process for the preparation of higher (meth) acrylic acid esters by transesterification of lower (meth) acrylic acid esters in the presence of a titanium alkoxide catalyst, in particular tetramethyl titanate, and in the presence of a polymerization inhibitor. Concretely, 4-acetamino-2,2,6,6-tetramethylpiperidine-N-oxyl is used as the polymerization inhibitor.

DE 2317226 A1 describes a process for the preparation of higher (meth) acrylic acid esters containing a low color number and a small amount of polymerization inhibitor, wherein the lower (meth) acrylic acid ester in the presence of a titanium alkoxide catalyst, in particular tetramethyl titanate, a polymerization inhibitor and with the addition of a larger amount Adsorbent to be transesterified. Specifically, a mixture of 2,6-di-tert-butyl-para-cresol and activated carbon is added to the transesterification reaction and the titanium alkoxide catalyst is hydrolyzed after the reaction with water. The resulting mixture containing the higher (meth) acrylic acid ester is then filtered off.

JP 2003/048866 A describes a process for purifying carboxylic acid esters prepared by transesterification or direct esterification in the presence of an organic titanium catalyst in which the carboxylic acid esters are contacted with a solid adsorbent after completion of the reaction to remove the catalyst. Specifically, silica gel and activated clay minerals are used as solid adsorbents, which are then removed by filtration.

(Meth) acrylic esters with long-chain ester groups and crosslinked (meth) acrylic acid esters, so-called high-boiling (meth) acrylic esters, are difficult or impossible to distill off from the reaction mixture obtained after the transesterification because of their high boiling points. As a rule, these remain after removal by distillation of the readily volatile constituents together with the catalyst used and the stabilizer (polymerization inhibitor) in the bottom. Therefore, in the production of high-boiling (meth) acrylic esters usually at the end of the transesterification reaction, the problem is to remove the catalyst used and at least part of the stabilizer from the crude ester products. The adsorptive processes described heretofore in the art using solid adsorbents have the disadvantage that the final concentration of the stabilizer in the final (meth) acrylic acid ester products can not be adjusted and, if appropriate, stabilizer must be added again after the purification. In addition, these adsorption and filtration based purification processes are usually very time consuming and also relatively expensive depending on the adsorbent used. These circumstances work adversely affect the efficiency and thus the economy of the known in the prior art manufacturing process.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved process for the preparation of high-boiling (meth) acrylic acid esters, whereby the abovementioned disadvantages can be avoided or at least reduced. The process according to the invention is thus intended to enable a more efficient and economical production of high-boiling (meth) acrylic acid esters.

In the production of high-boiling (meth) acrylic esters by transesterification, a bottom product which contains the high-boiling (meth) acrylic acid ester, the catalyst used in the transesterification and the stabilizer used in the transesterification is usually obtained after completion of the reaction and removal of all distillable constituents. It has now surprisingly been found that the catalyst remaining in the bottom product after the transesterification reaction and at least part of the stabilizer remaining in the bottom product, if it has a pK _s value of less than 14 in water at 25 ° C., can be removed from the bottom product in that the bottom product is treated with a basic solution and the bottom product thus treated is either subjected to an extractive separation or the volatile constituents contained in the treated bottom product are removed by distillation and the resulting solid is separated from the liquid product phase.

worin
m den Wert 1, 2, oder 3 aufweist,
Z falls m den Wert 1 aufweist, für einen unverzweigten oder verzweigten C₂-C₁₀-Alkylenrest oder einen bivalenten Rest der allgemeinen Formel II.a,

worin
n den Wert 1, 2, 3, oder 4 aufweist und
R¹ ausgewählt ist unter Wasserstoff oder Methyl, steht,
falls m den Wert 2 aufweist, für einen unverzweigten oder verzweigten trivalenten C₂-C₁₀-Alkantriylrest steht oder,
falls m den Wert 3 aufweist, für einen unverzweigten oder verzweigten tetravalenten C₂-C₁₀-Alkantetraylrest steht,
R¹ unabhängig voneinander für Wasserstoff oder Methyl steht,
R² für eine unverzweigte oder verzweigte C₇-C₃₀-Alkylgruppe, eine C₆-C₁₀-Cycloalkylgruppe, die unsubstituiert ist oder mit ein oder zwei C₁-C₁₀-Alkylresten substituiert sein kann, einen Rest II.b bis II.d

oder einen Rest der allgemeinen Formel II.e,

steht, worin
p den Wert 0, 1, 2, 3 oder 4 aufweist,
R^1' ausgewählt ist unter Wasserstoff oder Methyl und
R^2a für eine unverzweigte oder verzweigte C₁-C₃₀-Alkylgruppe steht, wobei * in den Resten II.a bis II.e den Anknüpfungspunkt zum Sauerstoffatom der jeweiligen Estergruppe bezeichnet,
bei dem man

• a) wenigstens eine Verbindung der allgemeinen Formel III
  
  bereitstellt, worin R¹ die oben genannte Bedeutung aufweist und R³ für eine unverzweigte oder verzweigte C₁-C₄-Alkylgruppe steht,
• b) die in Schritt a) bereitgestellte wenigstens eine Verbindung III in Gegenwart wenigstens eines Alkohols R²-OH oder wenigstens eines zwei-, drei oder vierwertigen Alkohols HO-Z-(OH)_m, wobei R², m und Z die oben genannten Bedeutungen aufweisen, in Gegenwart wenigstens eines Katalysators, sowie in Gegenwart wenigstens eines Stabilisators, der in Wasser bei 25 °C einen pK_s-Wert von weniger als 14 aufweist und ausgewählt ist unter phenolischen Verbindungen, Oximen, N-Oxylverbindungen, Hydroxylaminen, Thiolen und Thiophenolen, umsetzt, unter Erhalt eines Reaktionsgemisches, das wenigstens einen (Meth)acrylsäureester der allgemeinen Formeln I.a oder I.b enthält, wobei der während der Umsetzung gebildete Alkohol R³-OH kontinuierlich destillativ ausgeschleust wird,
• c) von dem in Schritt b) erhaltenen Reaktionsgemisch die wenigstens eine Verbindung III destillativ im Wesentlichen abtrennt, unter Erhalt eines an den Verbindungen I.a oder I.b, dem wenigstens einen Stabilisator und dem wenigstens einen Katalysator angereicherten Sumpfprodukts,
• d) das in Schritt c) erhaltene Sumpfprodukt mit einer wässrigen basischen Lösung behandelt, zur Deaktivierung des Katalysators und zur Deprotonierung des wenigstens einen Stabilisators,
• e1) das mit einer wässrigen basischen Lösung behandelte Sumpfprodukt aus Schritt d) einer extraktiven Auftrennung unterzieht, zur Entfernung wenigstens eines Teils des in dem behandelten Sumpfprodukt enthaltenen deprotonierten Stabilisators und wenigstens eines Teils des in dem behandelten Sumpfprodukt enthaltenen deaktivierten Katalysators, oder
• e2) die in dem behandelten Sumpfprodukt aus Schritt d) enthaltenen leichtflüchtigen Bestandteile zumindest teilweise destillativ entfernt und den entstandenen Feststoff von der flüssigen Produktphase abtrennt.

The present invention thus relates to a process for the preparation of (meth) acrylic esters of the general formulas Ia or Ib

wherein
m is 1, 2, or 3,
Z if m is 1, an unbranched or branched C ₂ -C ₁₀ -alkylene radical or a bivalent radical of the general formula II.a,

wherein
n has the value 1, 2, 3, or 4 and
R ^{1 is} selected from hydrogen or methyl,
if m is 2, is an unbranched or branched trivalent C ₂ -C ₁₀ alkanetriyl radical, or
if m is 3, is an unbranched or branched tetravalent C ₂ -C ₁₀ -alkanetetrayl radical,
R ^{1 is} independently hydrogen or methyl,
R ^{2 is} an unbranched or branched C ₇ -C ₃₀ -alkyl group, a C ₆ -C ₁₀ -cycloalkyl group which is unsubstituted or may be substituted by one or two C ₁ -C ₁₀ -alkyl radicals, a radical II.b to II .d

or a radical of the general formula II.e,

stands in which
p has the value 0, 1, 2, 3 or 4,
R ^{1 'is} selected from hydrogen or methyl and
R ^{2a represents} an unbranched or branched C ₁ -C ₃₀ -alkyl group, where * in the radicals II.a to II.e denotes the point of attachment to the oxygen atom of the respective ester group,
in which one

• a) at least one compound of general formula III
  
  in which R ^{1 has} the abovementioned meaning and R ^{3 is} an unbranched or branched C ₁ -C ₄ -alkyl group,
• b) the at least one compound III provided in step a) in the presence of at least one alcohol R ² -OH or at least one di-, tri- or tetravalent alcohol HO-Z- (OH) _m , where R ² , m and Z are those mentioned above Having meanings, in the presence of at least one catalyst, as well as in the presence of at least one stabilizer which has a pK _s value of less than 14 in water at 25 ° C and is selected from phenolic compounds, oximes, N-oxyl compounds, hydroxylamines, thiols and Thiophenolen, reacting to obtain a reaction mixture containing at least one (meth) acrylic ester of the general formulas Ia or Ib, wherein the alcohol formed during the reaction R ³ -OH is continuously removed by distillation,
• c) substantially distilling off at least one compound III from the reaction mixture obtained in step b) to obtain a bottoms product enriched in the compounds Ia or Ib, the at least one stabilizer and the at least one catalyst,
• d) treating the bottom product obtained in step c) with an aqueous basic solution, for deactivating the catalyst and for deprotonating the at least one stabilizer,
• e1) subjecting the bottom product treated with an aqueous basic solution from step d) to an extractive separation, for removing at least part of the deprotonated stabilizer contained in the treated bottom product and at least part of the deactivated catalyst contained in the treated bottom product, or
• e2) the volatile constituents contained in the treated bottom product from step d) are at least partially removed by distillation and the resulting solid is separated from the liquid product phase.

The inventive method is characterized by the following advantageous properties:
With the process according to the invention, it is possible to prepare high-boiling (meth) acrylic esters and crosslinked (meth) acrylic esters which contain no or only negligible traces of catalyst and the desired product-specific amounts of stabilizer.

The removal of the catalyst and the excess amount of stabilizer takes place in a single purification step. The cleaning can thus be done easily and quickly, which can be dispensed with expensive adsorbent.

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

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 ₃₀ -alkyl" refers to unbranched alkyl groups having 1 to 30 carbon atoms or branched alkyl groups having 3 to 30 carbon atoms. Preferably, "C ₁ -C ₃₀ -alkyl" is unbranched alkyl groups having 1 to 20 carbon atoms or branched alkyl groups having 3 to 20 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, n-nonyl, isononyl , 2-propylhexyl, n-decyl, isodecyl, 2-propylheptyl, n-undecyl, isoundecyl, n-dodecyl, isododecyl, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, isohexadecane, n-heptadecane, n Octadecane, n-nonadecane, n-decosan and the like. C ₁ -C ₃₀ -alkyl is particularly preferably unbranched C ₁ -C ₂₀ -alkyl groups.

The term "C ₁ -C ₃₀ -alkyl" also includes in its definition the terms "C ₁ -C ₁₀ -alkyl" and "C ₁ -C ₆ -alkyl".

In the context of the present invention, the term "C ₇ -C ₃₀ -alkyl" refers to straight or branched alkyl groups having 7 to 30 carbon atoms. Preferably, "C ₇ -C ₃₀ -alkyl" is unbranched or branched alkyl groups having 10 to 26 carbon atoms. These include, for example, n-decyl, isodecyl, 2-propylheptyl, n-undecyl, isoundecyl, n-dodecyl, isododecyl, n-tridecyl, n-tetradecyl, isotetradecyl, n-pentadecyl, n-hexadecyl, isohexadecyl, n-heptadecyl, isoheptadecyl , n-octadecyl, isooctadecyl, n-nonadecyl, n-eicosyl, isoeicosyl, n -docosyl, isodocosyl, n-tetracosyl, isotetracosyl, n-hexacosyl, isohexacosyl and the like. C ₇ -C ₃₀ -alkyl is particularly preferably unbranched or branched C ₁₀ -C ₂₂ -alkyl groups, in particular unbranched or branched C ₁₂ -C ₂₀ -alkyl groups.

In the context of the present invention, the term "C ₁ -C ₄ -alkyl" is methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl. "C ₁ -C ₄ -alkyl" is preferably methyl, ethyl, propyl, isopropyl or n-butyl, particularly preferably methyl, ethyl or propyl, in particular methyl or ethyl.

The term "C ₆ -C ₁₀ -cycloalkyl" for the purposes of the present invention comprises cyclic hydrocarbons having 6 to 10, preferably having 6 to 8 carbon atoms. These include, for example, cyclohexyl, cycloheptyl, cyclooctyl, adamantyl and bicyclo [2.2.1] heptyl. Particularly preferably "C ₆ -C ₁₀ -cycloalkyl" is cyclohexyl and cycloheptyl.

Substituted C ₆ -C ₁₀ cycloalkyl groups may, depending on their ring size, have one or more (eg 1, 2, 3, 4 or 5) C ₁ -C ₁₀ alkyl substituents. Examples of C ₆ -C ₁₀ -cycloalkyl groups are 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 and 2-, 3- and 4-tert-butylcyclohexyl.

In the context of the present invention, the term "C ₂ -C ₁₀ -alkylene" refers to divalent hydrocarbon radicals having 2 to 10 carbon atoms. The divalent hydrocarbon radicals may be unbranched or branched. These include, for example, 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, 1,5-pentylene, 1-methyl-1,4-butylene, 2-methyl-1,4-butylene, 1-ethyl-1,3-propylene, 2-ethyl 1,3-propylene, 1,1-dimethyl-1,3-propylene, 1,2-dimethyl-1,3-propylene, 2,2-dimethyl-1,3-propylene, 1,6-hexylene, 1 Methyl 1,5-pentylene, 2-methyl-1,5-pentylene, 3-methyl-1,5-pentylene, 1-ethyl-1,4-butylene, 2-ethyl-1,4-butylene, 2-propyl-1,3-propylene, 1,1-dimethyl-1,4- butylene, 1,2-dimethyl-1,4-butylene, 2,2-dimethyl-1,4-butylene, 2,3-dimethyl-1,4-butylene, 1,7-heptylene, 2-methyl-1, 6-hexylene, 3-methyl-1,6-hexylenes, 2-ethyl-1,5-pentylene, 3-ethyl-1,5-pentylene, 2,3-dimethyl-1,5-pentylene, 2,4- Dimethyl-1,5-pentylene, 1,8-octylene, 2-methyl-1,7-heptylene, 3-methyl-1,7-heptylene, 4-methyl-1,7-heptylene, 2-ethyl-1, 6-hexylene, 3-ethyl-1,6-hexylene, 2,3-dimethyl-1,6-hexylene, 2,4-dimethyl-1,6-hexylene, 1,9-nonylene, 2-methyl-1, 8-octylene, 3-methyl-1,8-octylene, 4-methyl-1,8-octylene, 2-ethyl-1,7-heptylene, 3-ethyl-1,7-heptylene, 1,10-decylene, 2-methyl-1,9-nonylene, 3-methyl-1,9-nonylene, 4-methyl-1,9-nonylene, 5-methyl-1,9-nonylene, and the like. "C ₂ -C ₁₀ -alkylene" is preferably straight-chain C ₂ -C ₆ -alkylene groups or branched C ₃ -C ₆ -alkylene groups, in particular unbranched C ₂ -C ₄ -alkylene groups or branched C ₃ -C ₄ alkylene.

In the context of the present invention, the term "C ₂ -C ₁₀ alkanetriyl" refers to trivalent hydrocarbon radicals having 2 to 10 carbon atoms, preferably having 3 to 8 carbon atoms. These include, for example, n-propane-1,2,3-triyl, n-butane-1,2,3-triyl, trimethylene methane, n-butane-1,3,4-triyl, 2-methyl-propane-1,2 , 3-triyl, n-pentane-1,2,3-triyl, n-pentane-1,4,5-triyl, 2-methyl-butane-1,3,4-triyl, 1,2-dimethylpropane-1 , 2,3-triyl, 1,1,1-trimethyleneethane, n-hexane-1,2,3-triyl, n-hexane-1,2,6-triyl, n-hexane-2,3,5-triyl , n-heptane-1,2,3-triyl, 1,1,1-trimethylene propane, n-heptane-1,6,7-triyl, 1,1,1-trimethylene-butane, n-octane-1,2,3 triyl, n-octane-1,7,8-triyl and the like. In particular, "C ₂ -C ₁₀ alkanetriyl" is C ₃ -C ₆ alkanetriyl.

In the context of the present invention, the term "C ₂ -C ₁₀ -alkanetetrayl" refers to tetravalent hydrocarbon radicals having 2 to 10 carbon atoms, preferably having 4 to 6 carbon atoms. These include, for example, n-butane-1,2,3,4-tetrayl, n-pentane-1,2,3,4-tetrayl, tetramethylene methane, n-hexane-1,2,3,4-tetrayl and the like. In particular, "C ₂ -C ₁₀ alkanetrayl" is n-butane-1,2,3,4-tetrayl and tetramethylene methane.

worin
n den Wert 1, 2, 3, oder 4 aufweist und
R¹ ausgewählt ist unter Wasserstoff oder Methyl,
falls m den Wert 2 aufweist, für einen unverzweigten oder verzweigten trivalenten C₂-C₁₀-Alkantriylrest steht oder,
falls m den Wert 3 aufweist, für einen unverzweigten oder verzweigten tetravalenten C₂-C₁₀-Alkantetraylrest,
R¹ unabhängig voneinander für Wasserstoff oder Methyl,
R² für eine unverzweigte oder verzweigte C₇-C₃₀-Alkylgruppe oder einen Rest der allgemeinen Formel II.e,

worin
p den Wert 0, 1, 2, 3 oder 4 aufweist,
R^1' ausgewählt ist unter Wasserstoff oder Methyl und
R^2a für eine unverzweigte oder verzweigte C₁-C₃₀-Alkylgruppe steht, wobei * in den Resten II.a und II.e den Anknüpfungspunkt zum Sauerstoffatom der jeweiligen Estergruppe bezeichnet.Preferably in the compounds R ^{2 is} -OH or HO-Z- (OH) _m and in the compounds of the general formulas Ia or Ib
m for the value 1, 2, or 3,
Z if m is 1, an unbranched or branched C ₂ -C ₁₀ -alkylene radical or a bivalent radical of the general formula II.a,

wherein
n has the value 1, 2, 3, or 4 and
R ^{1 is} selected from hydrogen or methyl,
if m is 2, is an unbranched or branched trivalent C ₂ -C ₁₀ alkanetriyl radical, or
if m is 3, an unbranched or branched tetravalent C ₂ -C ₁₀ -alkanetetrayl radical,
R ^{1 is} independently hydrogen or methyl,
R ^{2 is} an unbranched or branched C ₇ -C ₃₀ -alkyl group or a radical of the general formula II.e,

wherein
p has the value 0, 1, 2, 3 or 4,
R ^{1 'is} selected from hydrogen or methyl and
R ^{2a is} an unbranched or branched C ₁ -C ₃₀ -alkyl group, wherein * in the radicals II.a and II.e denotes the point of attachment to the oxygen atom of the respective ester group.

worin
n den Wert 1, 2, 3, oder 4 aufweist und
R¹ ausgewählt ist unter Wasserstoff oder Methyl,
R¹ unabhängig voneinander für Wasserstoff oder Methyl,
R² für eine unverzweigte oder verzweigte C₇-C₃₀-Alkylgruppe oder einen Rest der allgemeinen Formel II.e,

worin
p den Wert 0, 1, 2, 3 oder 4 aufweist,
R^1' ausgewählt ist unter Wasserstoff oder Methyl und
R^2a für eine unverzweigte oder verzweigte C₁-C₃₀-Alkylgruppe steht,
wobei * in den Resten II.a und II.e den Anknüpfungspunkt zum Sauerstoffatom der jeweiligen Estergruppe bezeichnet.Particularly preferred in the compounds R ^{2 is} -OH or HO-Z- (OH) _m and in the compounds of the general formulas Ia or Ib
m for the value 1,
Z is an unbranched or branched C ₂ -C ₁₀ -alkylene radical or a bivalent radical of the general formula II.a,

wherein
n has the value 1, 2, 3, or 4 and
R ^{1 is} selected from hydrogen or methyl,
R ^{1 is} independently hydrogen or methyl,
R ^{2 is} an unbranched or branched C ₇ -C ₃₀ -alkyl group or a radical of the general formula II.e,

wherein
p has the value 0, 1, 2, 3 or 4,
R ^{1 'is} selected from hydrogen or methyl and
R ^{2a is} an unbranched or branched C ₁ -C ₃₀ -alkyl group,
where * denotes in the radicals II.a and II.e the point of attachment to the oxygen atom of the respective ester group.

In a very particularly preferred embodiment of the process according to the invention, the (meth) acrylic acid esters are selected from compounds of the general formula Ia, in which
R ^{1 is} hydrogen or methyl and
R ^{2 is} an unbranched or branched C ₇ -C ₃₀ alkyl group.

In particular, in the compounds R ² -OH and in the compounds of general formula Ia
R ^{1 is} hydrogen or methyl and
R ^{2 is} an unbranched or branched C ₁₀ -C ₂₆ alkyl group.

Specifically, in the compounds R ² -OH and in the compounds of general formula Ia
R ^{1 is} hydrogen or methyl and
R ^{2 is} an unbranched or branched C ₁₀ -C ₂₂ alkyl group.

Especially in the compounds R ² -OH and in the compounds of general formula Ia
R ^{1 is} hydrogen or methyl and
R ^{2 is} an unbranched or branched C ₁₂ -C ₂₀ alkyl group.

Step a)

The at least one compound of the general formula III provided in step a) of the process according to the invention can be present either pure or as a mixture of different esters.

The compounds of general formula III are preferably methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate or mixtures thereof.

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

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

Specifically, the compounds of general formula III are methyl acrylate or methyl methacrylate.

The compounds III can either be obtained commercially or synthesized by known methods known to the person skilled in the art.

Step b)

wobei R¹, R^2, R³, m und Z eine der zuvor genannten Bedeutungen aufweisen.The transesterification in step b) can be represented by the following reaction equations:

wherein R ¹ , R ^2, R ³ , m and Z have one of the meanings mentioned above.

The alcohols R ² -OH or the dihydric, trihydric or tetrahydric alcohols HO-Z- (OH) _m used in step b) of the process according to the invention can either be obtained from natural sources or synthesized by known methods known to the person skilled in the art.

The alcohol R ² -OH is, for example, n-heptanol, isoheptanol, n-octanol, 2-ethylhexanol, n-nonanol, isononanol, n-decanol, 2-propyl-heptanol, isodecanol, n-undecanol, isoundecanol, n-dodecanol, isododecanol, n-tridecanol, n-tetradecanol, isotetradecanol, n-pentadecanol, n-hexadecanol, isohexadecanol, n-heptadecanol, isoheptadecanol, n-octadecanol, isooctadecanol, n-nonadecanol, n-eicosanol, isoeicosanol, n- Docosanol, isodocosanol, n-tetracosanol, isotetracosanol, n-hexacosanol, isohexacosanol, n-octacosanol, n-triacontanol and the like, as well as mixtures thereof.

R ² -OH is preferably n-decanol, 2-propyl-heptanol, isodecanol, n-undecanol, isoundecanol, n-dodecanol, isododecanol, n-tridecanol, n-tetradecanol, isotetradecanol, n- Pentadecanol, n-hexadecanol, isohexadecanol, n-heptadecanol, isoheptadecanol, n-octadecanol, isooctadecanol, n-nonadecanol, n-eicosanol, isoeicosanol, n-docosanol, isodocosanol, n-tetracosanol, isotetracosanol, n-hexacosanol, isohexacosanol and mixtures from that.

R ² -OH is particularly preferably n-decanol, 2-propylheptanol, isodecanol, n-undecanol, isoundecanol, n-dodecanol, isododecanol, n-tridecanol, n-tetradecanol, isotetradecanol, n-pentadecanol, n Hexadecanol, isohexadecanol, n-heptadecanol, isoheptadecanol, n-octadecanol, isooctadecanol, n-nonadecanol, n-eicosanol, isoeicosanol, n -docosanol, isodocosanol and mixtures thereof.

In particular, R ² -OH is n-dodecanol, isododecanol, n-tridecanol, n-tetradecanol, isotetradecanol, n-pentadecanol, n-hexadecanol, isohexadecanol, n-heptadecanol, isoheptadecanol, n-octadecanol, isooctadecanol, n- Nonadecanol, n-eicosanol, isoeicosanol and mixtures thereof.

wobei R¹ und n eine der zuvor genannten Bedeutungen aufweist, wie beispielsweise Diethylenglycol, Triethylenglycol, Tetraethylenglycol, Di-1,2-propylenglycol, Tri-1,2-propylenglycol, Tetra-1,2-propylenglycol und dergleichen.The dihydric alcohols HO-Z-OH (m = 1) are, for example, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1 , 4-butanediol, 2-methyl-1,3-propanediol, 1,1-dimethyl-1,2-ethanediol, 1,5-pentanediol, 1-methyl-1,4-butanediol, 2-methyl-1,4 butanediol, 1-ethyl-1,3-propanediol, 2-ethyl-1,3-propanediol, 1,1-dimethyl-1,3-propanediol, 1,2-dimethyl-1,3-propanediol, 2,2 Dimethyl 1,3-propanediol, 1,6-hexanediol, 1-methyl-1,5-pentanediol, 2-methyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 1-ethyl-1 , 4-butanediol, 2-ethyl-1,4-butanediol, 2-propyl-1,3-propanediol, 1,1-dimethyl-1,4-butanediol, 1,2-dimethyl-1,4-butanediol, 2 , 2-dimethyl-1,4-butanediol, 2,3-dimethyl-1,4-butanediol, 1,7-heptanediol, 2-methyl-1,6-hexanediol, 3-methyl-1,6-hexanediol, 2 Ethyl 1,5-pentanediol, 3-ethyl-1,5-pentanediol, 2,3-dimethyl-1,5-pentanediol, 2,4-dimethyl-1,5-pentanediol, 1,8-octanediol, 2 -Methyl-1,7-heptanediol, 3-methyl-1,7-heptanediol, 4-methyl-1,7-heptanediol, 2-ethyl-1,6-hexanediol, 3-ethyl-1,6-hexanedi ol, 2,3-dimethyl-1,6-hexanediol, 2,4-dimethyl-1,6-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 3-methyl-1,8- Octanediol, 4-methyl-1,8-octanediol, 2-ethyl-1,7-heptanediol, 3-ethyl-1,7-heptanediol, 1,10-decanediol, 2-methyl-1,9-nonanediol, 3 Methyl-1,9-nonanediol, 4-methyl-1,9-nonanediol, 5-methyl-1,9-nonanediol, and the like, or an alcohol of general formula IV,

wherein R ¹ and n have one of the meanings mentioned above, such as diethylene glycol, triethylene glycol, tetraethylene glycol, di-1,2-propylene glycol, tri-1,2-propylene glycol, tetra-1,2-propylene glycol and the like.

Preferably, the dihydric alcohols HO-Z-OH are 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,1-dimethyl-1,2-ethanediol, 1,5-pentanediol, 1-methyl-1,4-butanediol, 2-methyl-1,4-butanediol, 1 Ethyl 1,3-propanediol, 2-ethyl-1,3-propanediol, 1,1-dimethyl-1,3-propanediol, 1,2-dimethyl-1,3-propanediol, 2,2-dimethyl-1, 3-propanediol, 1,6-hexanediol, 1-methyl-1,5-pentanediol, 2-methyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 1-ethyl-1,4-butanediol, 2-ethyl-1,4-butanediol, 2-propyl-1,3-propanediol, 1,1-dimethyl-1,4-butanediol, 1,2-dimethyl-1,4-butanediol, 2,2-dimethyl 1,4-butanediol or 2,3-dimethyl-1,4-butanediol, or an alcohol of general formula IV, as defined above.

In particular, the dihydric alcohols HO-Z-OH are 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol or 1,1-dimethyl-1,2-ethanediol.

The trihydric alcohols HO-Z- (OH) ₂ (m = 2) are, for example, n-propane-1,2,3-triol (glycerol), n-butane-1,2,3-triol, n Butane-1,3,4-triol, 2-methyl-propane-1,2,3-triol, 2- (hydroxymethyl) -propane-1,3-diol, n-pentane-1,2,3-triol , n-pentane-1,4,5-triol, 2-methylbutane-1,3,4-triol, 1,2-dimethylpropane-1,2,3-triol, 2- (hydroxymethyl) -2-methyl -propane-1,3-diol, n-hexane-1,2,3-triol, n-hexane-1,2,6-triol, n-hexane-2,3,5-triol, n-heptane-1 , 2,3-triol, 2- (hydroxymethyl) -2-ethyl-propane-1,3-diol, n-heptane-1,6,7-triyl, 2- (hydroxymethyl) -2-propyl-propane-1 , 3-diol, n-octane-1,2,3-triyl, n-octane-1,7,8-triyl, and the like.

The trihydric alcohols HO-Z- (OH) ₂ (m = 2) are preferably n-propane-1,2,3-triol (glycerol), n-butane-1,2,3-triol, n Butane-1,3,4-triol, 2-methyl-propane-1,2,3-triol, 2- (hydroxymethyl) -propane-1,3-diol, n-pentane-1,2,3-triol , n-pentane-1,4,5-triol, 2-methylbutane-1,3,4-triol, 1,2-dimethylpropane-1,2,3-triol, 2- (hydroxymethyl) -2-methyl -propane-1,3-diol, n-hexane-1,2,3-triol, n-hexane-1,2,6-triol, n-hexane-2,3,5-triol, 2- (hydroxymethyl) 2-ethyl-propane-1,3-diol, more preferably n-propane-1,2,3-triol (glycerol), n-butane-1,2,3-triol, 2-methyl-propane-1 , 2,3-triol, 2- (hydroxymethyl) -propane-1,3-diol, n-pentane-1,2,3-triol, 2- (hydroxymethyl) -2-methyl-propane-1,3-diol or n-hexane-1,2,3-triol, 2- (hydroxymethyl) -2-ethyl-propane-1,3-diol.

The tetrahydric alcohols HO-Z- (OH) ₃ (m = 3) are, for example, n-butane-1,2,3,4-tetrol, n-pentane-1,2,3,4-tetrol, 2,2-bis (hydroxymethyl) propane-1,3-diol, n-hexane-1,2,3,4-tetrol and like. The tetrahydric alcohols HO-Z- (OH) ₃ (m = 3) are preferably n-butane-1,2,3,4-tetrol or 2,2-bis (hydroxymethyl) -propane-1,3 diol.

In general, in step b) of the process according to the invention, the at least one alcohol R ² -OH or the at least one dihydric, trihydric or tetrahydric alcohol HO-Z- (OH) _m in stoichiometric excess, based on the amount of at least one Compound of general formula III, used.

For the monohydric alcohols R ² -OH, the molar ratio of the at least one compound of the general formula III to the at least one alcohol R ² -OH in the reaction mixture is usually in the range from 1.1: 1 to 10: 1, preferably in the range of 1.2 : 1 to 5: 1 and especially 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 of 0.3 to 0.8 mol, based on 1 mol of compound III used.

For the dihydric alcohols HO-Z-OH and the dihydric alcohols of the general formula IV, the molar ratio of the at least one compound of general formula III to at least one alcohol HO-Z-OH or to at least one alcohol of general formula IV in the reaction mixture is usually in the range of 2.1: 1 to 20: 1, preferably in the range of 2.2: 1 to 10: 1 and in particular in the range of 2.3: 1 to 6: 1.

The total amount of the at least one alcohol HO-Z-OH or of the at least one alcohol of the general formula IV in the reaction mixture of the reaction in step b) of the process according to the invention is usually in the range of 0.05 to 0.49 mol, preferably in the range of 0.1 to 0.45 mol, in particular in the range of 0.15 to 0.42 mol, based on 1 mol of compound III used.

For the trihydric alcohols HO-Z- (OH) ₂ , the molar ratio of the at least one compound of the general formula III to the at least one alcohol HO-Z- (OH) ₂ in the reaction mixture is usually in the range from 3.1: 1 to 30: 1 , preferably in the range of 3.3: 1 to 15: 1 and in particular in the range of 3.4: 1 to 9: 1.

The total amount of the at least one alcohol HO-Z- (OH) ₂ in the reaction mixture of the reaction in step b) of the process according to the invention is usually in the range of 0.033 to 0.33 mol, preferably in the range of 0.066 to 0.32 mol, in particular in the range of 0.1 to 0.31 mol, based on 1 mol of compound III used.

For the tetrahydric alcohols HO-Z- (OH) ₃ , the molar ratio of the at least one compound of the general formula III to the at least one alcohol HO-Z- (OH) ₃ in the reaction mixture is usually in the range from 4.1: 1 to 40: 1 , preferably in the range of 4.3: 1 to 20: 1 and in particular in the range of 4.5: 1 to 10: 1.

The total amount of the at least one alcohol HO-Z- (OH) ₃ in the reaction mixture of the reaction in step b) of the process according to the invention is usually in the range from 0.025 to 0.24 mol, preferably in the range from 0.05 to 0.23 mol , in particular in the range of 0.1 to 0.22 mol, based on 1 mol of compound III used.

As a rule, the reaction mixture of the reaction in step b) of the process according to the invention contains at least one stabilizer.

Usually, the stabilizers used in the process according to the invention are stabilizers which have a pK _s value of less than 14 in water at 25 ° C. and are selected from phenolic compounds, oximes, N-oxyl compounds, hydroxylamines, thiols and thiophenols ,

• – Phenol;
• – Alkylphenole, wie z. B. o-, m- oder p-Kresol (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'-Methylen-bis(6-tert.-butyl-4-methylphenol), Octylphenol, Nonylphenol, 2,6-Dimethylphenol oder 2,6-Di-tert.-butyl-p-kresol;
• – 1,2-Dihydroxybenzole, wie z. B. Brenzcatechin (1,2-Dihydroxybenzol) oder tert.-Butylbrenzcatechin;
• – 1,3-Dihydroxybenzole;
• – Bisphenol A;
• – Aminophenole, wie z. B. p-Aminophenol;
• – Nitrophenole, wie beispielsweise p-Nitrophenol;
• – Nitrosophenole, wie beispielsweise p-Nitrosophenol;
• – Tocopherole, wie z. B. α-, β-, oder γ-Tocopherol;
• – Hydroxycumarane, wie z. B. 2,3-Dihydro-2,2-dimethyl-7-hydroxybenzofuran (2,2-Dimethyl-7-hydroxycumaran);
• – 2-Alkoxyphenole, wie beispielsweise 2-Methoxyphenol (Guajacol), 2-Ethoxyphenol, 2-Isopropoxyphenol;
• – 3-Alkoxyphenole, wie z. B. 3-Methoxyphenol oder 3-Ethoxyphenol;
• – Hydrochinone, wie z. B. Hydrochinon, 2-Methylhydrochinon, 2-tert.-Butylhydrochinon oder 2,5-Di-tert.-butylhydrochinon; und
• – Hydrochinonmonoalkylether, wie z. B. 4-Methoxyphenol (Hydrochinonmonomethylether) oder 2-tert.-Butyl-4-methoxyphenol oder 2,5-Di-tert.-butyl-4-methoxyphenol.

The phenolic compounds used as stabilizer in the process according to the invention are, for example,

• - phenol;
• - Alkylphenols, such as. As 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-butyl catechol;
• - 1,3-dihydroxybenzenes;
• Bisphenol A;
• - Aminophenols, such as. For example, p-aminophenol;
• Nitrophenols, such as p-nitrophenol;
• Nitrosophenols, such as p-nitrosophenol;
• - Tocopherols, such as. B. α-, β-, or γ-tocopherol;
• - Hydroxycumarans, such as. For example, 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, such as. For example, 4-methoxyphenol (hydroquinone monomethyl ether) or 2-tert-butyl-4-methoxyphenol or 2,5-di-tert-butyl-4-methoxyphenol.

The oximes used as stabilizer in the process according to the invention are, for example, aldoximes, ketoximes or amidoximes, for example diethylketoxime, acetoneoxime, methylethylketoxime, cyclohexanone oxime, dimethylglyoxime, 2-pyridinaldoxime, salicylaldoxime or other aliphatic or aromatic oximes or their reaction products with alkyl transfer agents.

The N-oxyl compounds used as stabilizer in the process according to the invention are, for example, 4-carboxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-sulphanyl-2,2,6,6-tetramethylpiperidine -N-oxyl or 4-ammonium-2,2,6,6-tetramethyl-piperidine-N-oxyl.

The hydroxylamines used as stabilizer in the process according to the invention are, for example, N, N-diethylhydroxylamine.

The thiols used as stabilizer in the process according to the invention are, for example, duodecylmercaptan or cysteine.

The thiophenols used as stabilizer in the process according to the invention are, for example, thiophenol or thiocresol.

The at least one stabilizer used in step b) of the process according to the invention is preferably selected from alkylphenols, 2-alkoxyphenols, 3-alkoxyphenols, hydroquinones and hydroquinone monoalkyl ethers.

The stabilizers used in step b) of the process according to the invention particularly preferably have a pK _s value of less than 13, in particular less than 12, in water at 25.degree.

In a very particularly preferred embodiment of the process according to the invention, the at least one stabilizer used in step b) additionally at 25 ° C. and a pH of 14 has a water solubility of at least 5 g / L, more preferably of at least 15 g / L, in particular of at least 30 g / L.

Specifically, the at least one stabilizer used in step b) of the process according to the invention is 2-methoxyphenol, 3-methoxyphenol, 4-methoxyphenol, hydroquinone or 2-methylhydroquinone.

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 0.001 to 1 wt .-%, preferably in the range of 0.005 to 0.7 wt .-%, in particular in the range of 0 , 01 to 0.5 wt.%, Based on the amount of compound III 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 suitable as a catalyst are, for example, metal oxides, acetates, 2-ethylhexanoates, stearates, acetylacetonates, chlorides, sulfates, phosphates, hydroxides, dithiocarbamates or carbonates of Li, Na, K, Rb, Cs, Mg, Ca, Mn, Ti, Co, Ni, Cu, Zn, Zr, Ge, Hf, Al, Cr, Fe, Sb or Sn. Particularly suitable metal salts are, for example, metal oxides, acetates, acetylacetonates, chlorides or dithiocarbamates of Li, Mn, Ti, Cu, Zr, Ni, Zn, Sb or Sn, such as antimony (III) oxide, tin (II) oxide, tin ( IV) oxide, nickel (II) acetylacetonate, zinc (II) acetylacetonate, zirconium (IV) acetylacetonate, copper (II) chloride, copper (II) acetate, copper (II) acetylacetonate, manganese (II ) chloride, manganese (III) chloride, manganese (III) acetylacetonate or manganese (IV) chloride or mixtures thereof.

Preferably, the metal in the metals, metal salts, organometallic compounds or metal alkoxides is selected from lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, manganese, titanium, copper, zinc, zirconium, hafnium, aluminum, iron, antimony, tin and Mixtures thereof.

The at least one catalyst used in step b) is particularly preferably selected from organometallic compounds and metal alkoxides of the general formula M [O (C ₁ -C ₄ -alkyl)] _q , where M is a q-valent metal cation and q is the value 1 , 2, 3 or 4.

• – Dialkylzinnlaurate, z. B. Dimethylzinndilaurat oder Dibutylzinndilaurat,
• – Dialkylzinnhalogenide, z. B. Dimethylzinndichlorid, Dipropylzinndichlorid oder Dibutylzinndichlorid,
• – Dialkylzinndialkoxide, z. B. Dimethylzinndimethanolat, Dimethylzinndiethanolat, Dibutylzinndimethanolat oder Dibutylzinndiethanolat,
• – Dialkylzinndiacetate, z. B. Dimethylzinndiacetat oder Dibutylzinndiacetat,
• – Dialkylzinnoxide, z. B. Dibutylzinnoxid oder Dioctylzinnoxid,
• – Trialkylzinnalkoxide,
• – Monoalkylzinndioxide, z. B. Monobutylzinndioxid, oder Mischungen davon.

Organometallic compounds which are particularly preferred as catalyst are, for example, organotin compounds, such as

• - Dialkyltin laurates, z. B. dimethyltin dilaurate or dibutyltin dilaurate,
• - Dialkylzinnhalogenide, z. For example, dimethyltin dichloride, dipropyltin dichloride or dibutyltin dichloride,
• - dialkyltin dialkoxides, e.g. B. Dimethylzinndimethanolat, Dimethylzinndiethanolat, Dibutylzinndimethanolat or Dibutylzinndiethanolat,
• - Dialkyltin diacetates, z. Dimethyl tin diacetate or dibutyltin diacetate,
• - Dialkyltin oxides, eg. Dibutyltin oxide or dioctyltin oxide,
• - trialkyltin alkoxides,
• - Monoalkylzinndioxide, z. As monobutyltin dioxide, or mixtures thereof.

The dialkyltin dialkoxides used as catalyst in step b) can be produced, for example, during the reaction (in situ) from the corresponding dialkyltin chlorides and sodium alkoxides.

Metal alkoxides which are particularly preferred as catalyst are, for example, titanium alkoxides, such as titanium (IV) methanolate, titanium (IV) ethanolate, titanium (IV) isopropoxide or titanium (IV) butanolate, triethanolamine titanate, zirconium alkoxides, such as zirconium (IV) -propoxide, Zirconium (IV) butoxide or zirconium (IV) pentoxide, triethanolamine zirconate, alkali metal or alkaline earth metal alkoxides and mixtures of said metal alkoxides.

In particular, organotin compounds or metal alkoxides are used as catalysts in step b) of the process according to the invention.

In a specific embodiment of the reaction according to the invention in step b), metal alkoxides, more particularly titanium 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, in particular from 0.01 to 5% by weight, based on the components used in step b).

The reaction in step b) of the process according to the invention can be carried out in the absence or in the presence of an added solvent.

If the reaction in step b) is carried out in the presence of an added solvent, this is an inert under the reaction conditions, organic solvent. 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.

If the reaction in step b) is carried out in the presence of an added solvent, this is preferably selected from solvents, as defined above, which additionally have the property of entraining the low-boiling alcohol R ³ -OH in the distillative discharge in step b), ie to form a low-boiling azeotrope with the alcohol R ³ -OH. These preferred solvents (LM) thus have the function of an entraining agent.

In a first preferred embodiment of the process according to the invention, the reaction in step b) is additionally carried out in the presence of a solvent (LM) which forms a low-boiling azeotrope with the alcohol R ³ -OH.

Preferably, the solvent (LM) is selected from aliphatic and alicyclic hydrocarbons containing 5 to 8 carbon atoms.

The solvent (LM) is particularly preferably selected from hexane, heptane, n-octane, petroleum ether, ligroin, cyclohexane and cycloheptane, and mixtures thereof.

In particular, the solvent (LM) is selected from hexane, heptane and cyclohexane and mixtures thereof.

In a second preferred embodiment of the process according to the invention, the reaction in step b) is carried out in the absence of an added solvent.

The reaction in step b) and the distillative removal of the alcohol R ³ -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 ³ -OH formed during the reaction can be carried out at ambient pressure or reduced pressure. Preferably, the reaction is carried out in step b) and the distillative removal of the alcohol R ³ -OH, at least at the beginning of the reaction, at ambient pressure. The pressure may also be reduced stepwise or continuously during the reaction in step b) once or several times in order to keep or accelerate the discharge of the alcohol R ³ -OH formed during the reaction. Preferably, the pressure in the course of the reaction in step b) is reduced stepwise or continuously.

Particularly preferably, the reaction takes place in step b) and the distillative discharge of the alcohol R ³ -OH at the beginning of the reaction at ambient pressure, wherein the pressure in the course of the reaction in step b) is reduced stepwise or continuously.

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 resulting products involved in the reaction. However, since the stabilizing effect of the stabilizers used in step b) can be impaired or even prevented by inert gases, the transesterification in step b) preferably carried out without the addition of an inert gas under the reaction conditions. In this context, 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 ³ -OH released in the reaction in step b) is continuously discharged in order to shift the equilibrium of the transesterification reaction.

For distillative removal of the liberated in the reaction in step b), low-boiling alcohol R ³ -OH 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 columns, evaporators, such as thin film evaporators, falling film evaporators, forced circulation evaporators, Sambay evaporators, etc., and combinations thereof. For the removal by distillation of the low-boiling alcohol, R ³ -OH distillation columns and / or rotary-belt columns are particularly preferably used, in particular distillation columns. The distillation column needed for distillative discharge is usually in direct communication with the transesterification reactor, preferably it is installed directly on this. In the case of using a plurality of 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.

For distillative removal of the low-boiling alcohol R ³ -OH, 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.

In general, the reflux ratio in the column in the distillative removal in step b) is in the range from 50: 1 to 1:50, preferably in the range from 20: 1 to 1:20 and in particular in the range from 10: 1 to 1: 10th

Due to the formation of an azeotropic mixture, part of the at least one compound III can be entrained in the distillative removal of the low-boiling alcohol R ³ -OH. In order to compensate for any resulting losses of compound III in the reaction mixture, optionally at least one compound III may be added for the reaction in step b). The feeding of the at least one compound III 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 preferably carried out in such a way that the amount of compound III in the reaction mixture remains as constant as possible during the distillative discharge of the alcohol R ³ -OH.

If a solvent (LM) is used for the removal by distillation of the low-boiling alcohol R ³ -OH released in the reaction in step b), a mixture comprising the alcohol R ³ -OH, the solvent (LM) and optionally a part containing at least one compound III, subtracted and at least partially condensed.

In order to keep the loss of the solvent (LM) and possibly of the at least one compound III as low as possible, it is preferable to separate them off after the condensation of the alcohol R ³ -OH and again in the reaction in step b).

For the separation of the alcohol R ³ -OH from the solvent (LM) as well as from the optionally entrained at least one compound III are the usual methods known in the art for the separation of liquid-liquid mixtures. Preferably, the separation of the solvent (LM) and optionally entrained at least one compound III of the alcohol R ³ -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 ³ -OH, the organic solvent (LM) and optionally the at least one compound III, mixed with water and passed into a phase separator (decanter), where this by mechanical settling in two phases (An aqueous phase containing the alcohol R ³ -OH, and an organic phase which predominantly contains the solvent (LM) and optionally the at least one compound III), which can be removed separately. The organic phase containing the solvent (LM) and optionally the at least one compound III is then, as described above, returned to the reaction in step b).

The separated solvent (LM) and optionally separated at least one compound III can either be pumped directly back into the reaction zone of the reaction in step b) or at least partially over the top of the at least one used for distillative removal of the lower alcohol R ³ -OH, at least be initiated a column.

Preferably, the separated solvent (LM) and optionally separated at least one compound III is pumped directly back into the reaction zone of the reaction in step b).

Step c)

From the reaction mixture obtained in step b), the at least one compound III is subsequently separated by distillation essentially, to obtain a bottoms product enriched in the compounds I.a or I.b., the at least one stabilizer and the at least one catalyst. For distillative removal of the at least one compound III, the devices mentioned in the embodiments for distillative removal are generally suitable.

In a preferred embodiment of the process according to the invention, the at least one compound III removed in step c) is recycled back into the reaction in step b).

"Recycling in the reaction in step b)" means that in step c) separated at least one compound III is passed back into the reaction zone of the reaction in step b).

Step d)

The bottom product obtained in step c), enriched in the compounds I.a or I.b, the at least one stabilizer and the at least one catalyst is then fed to a further work-up step (step d)).

Step d) involves treating the bottom product obtained in step c) with an aqueous basic solution, deactivating the catalyst and deprotonating the at least one stabilizer. For this purpose, the aqueous basic solution is added to the bottom product obtained in step c) and thoroughly mixed, whereupon a two-phase mixture is generally formed. By adding the aqueous basic solution, the catalyst is hydrolyzed, which may optionally form sparingly soluble metal salts and / or metal alkoxides, and increases the pH of the bottom product, resulting in a deprotonation of at least one stabilizer contained therein.

The aqueous basic solution is, for. B. a solution prepared by dissolving a suitable base in water. Suitable bases are especially inorganic bases, for. As alkali metal hydroxides such as NaOH or KOH, ammonium salts such as ammonium hydroxide and alkali metal carbonates such as sodium carbonate, for. B. in the form of soda. Preference is given to alkali metal hydroxides, in particular NaOH and KOH. The amount of the inorganic base in the aqueous basic solution is typically in the range of 0.1 to 50 wt .-%, preferably in the range of 1 to 40, in particular in the range of 10 to 35 wt .-%.

Step e1) and e2)

The further purification or workup of the bottoms product treated with an aqueous basic solution can then be carried out in two different variants (step e1) or step e2)).

In the first variant (step e1)), the bottom product from step d) is subjected to an extractive separation to remove at least a portion of the deprotonated stabilizer contained in the treated bottom product and at least a portion of the deactivated catalyst contained in the treated bottom product.

For this purpose, the bottom product treated with an aqueous basic solution from step d) is allowed to stand until it decomposes by mechanical settling into two phases which can be removed separately (an aqueous phase containing at least part of the stabilizer and the hydrolyzed catalyst , and an organic phase predominantly containing the compound Ia or Ib and a remaining residue of the stabilizer).

The treatment of the bottom product obtained in step c) with the aqueous basic solution (step d)) and the subsequent extractive separation (step e1)) may optionally also be carried out several times until at least a portion of the catalyst is removed from the bottom product and / or the desired amount of stabilizer is present in the bottom product.

To facilitate the phase separation in step e1), optionally before or after the addition of the aqueous basic solution in step d), the bottom product can be diluted by adding an organic solvent which is immiscible or only slightly water-miscible. The addition of an organic solvent which is immiscible or only to a small extent miscible with water preferably takes place before the addition of the aqueous basic solution in step d).

The organic solvents which are immiscible or only slightly water-miscible are, for example, aliphatic or alicyclic hydrocarbons, such as pentane, hexane, heptane, ligroin, petroleum ether or cyclohexane, halogenated aliphatic or alicyclic hydrocarbons, such as dichloromethane, trichloromethane, tetrachloromethane, or dichloroethane, aromatic hydrocarbons, such as benzene, toluene or xylene, halogenated aromatic hydrocarbons, such as chlorobenzene or dichlorobenzene, ethers, such as methyl tert-butyl ether, diethyl ether, dibutyl ether, tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, Carboxylic esters, such as methyl acetate or ethyl acetate, and the like, or mixtures of said solvents.

The organic phase obtained after the extractive separation, which contains predominantly the compound I.a or I.b and a remaining residue of the stabilizer, is optionally neutralized by washing once or several times with an acidic aqueous solution and / or with water.

The aqueous acidic solution is a solution prepared by diluting or dissolving a suitable acid in water. Suitable acids are, for example, organic sulfonic acids, such as methanesulfonic acid and p-toluenesulfonic acid and mineral acids, such as. H ₂ SO ₄ , H ₃ PO ₄ or HCl, and the like. The amount of acid in the aqueous acid solution is typically in the range of 0.01 to 10 wt%, preferably in the range of 0.05 to 5 wt%.

After neutralization, the organic solvent which may or may not be present in the organic phase and which is only partially miscible with water and the water which may be contained therein are removed by distillation.

Finally, the organic phase is filtered to remove any resulting solids.

• d.1) gegebenenfalls die Zugabe eines nicht oder nur zu einem geringen Teil mit Wasser mischbaren organischen Lösungsmittels zu dem in Schritt c) erhaltenen Sumpfprodukt,
• d.2) Behandlung des in Schritt c) oder in Schritt d1) erhaltenen Sumpfprodukts mit einer wässrigen basischen Lösung zur Deaktivierung des Katalysators und zur Deprotonierung des wenigstens einen Stabilisators,
• e1.1) Abtrennung wenigstens eines Teils der wässrigen basischen Phase von der organischen Produktphase,
• e1.2) Behandlung der in Schritt e1.1) erhaltene organischen Produktphase mit Wasser und anschließende Abtrennung wenigstens eines Teils der erhaltenen wässrigen Phase von der organischen Produktphase,
• e1.3) gegebenenfalls die Behandlung der in Schritt e1.2) erhaltenen organischen Produktphase mit einer sauren wässrigen Lösung und anschließende Abtrennung wenigstens eines Teils der wässrigen Phase von der organischen Produktphase,
• e1.4) gegebenenfalls die Behandlung der in Schritt e1.3) erhaltenen organischen Produktphase mit Wasser und anschließende Abtrennung wenigstens eines Teils der erhaltenen wässrigen Phase von der organischen Produktphase,
• e1.5) gegebenenfalls die destillative Entfernung des in der organischen Produktphase enthaltenen Wassers und des gegebenenfalls in der organischen Produktphase enthaltenen nicht oder nur zu einem geringen Teil mit Wasser mischbaren organischen Lösungsmittels,
• e1.6) die Filtration der organischen Phase, wobei die Schritte d.2) und e1.1) auch mehrfach durchgeführt werden können.

In a preferred embodiment of the method according to the invention, steps d) and e1) comprise the following steps:

• d.1) optionally adding an organic solvent which is immiscible or only slightly water-miscible with the bottom product obtained in step c),
• d.2) treatment of the bottom product obtained in step c) or in step d1) with an aqueous basic solution for deactivating the catalyst and for deprotonating the at least one stabilizer,
• e1.1) separation of at least part of the aqueous basic phase from the organic product phase,
• e1.2) treatment of the organic product phase obtained in step e1.1) with water and subsequent separation of at least a portion of the resulting aqueous phase from the organic product phase,
• e1.3) if appropriate, the treatment of the organic product phase obtained in step e1.2) with an acidic aqueous solution and subsequent separation of at least a portion of the aqueous phase from the organic product phase,
• e1.4) if appropriate, the treatment of the organic product phase obtained in step e1.3) with water and subsequent separation of at least a portion of the resulting aqueous phase from the organic product phase,
• e1.5) if appropriate, the removal by distillation of the water present in the organic product phase and of the organic solvent which is optionally not present in the organic product phase or which is only slightly water-miscible,
• e1.6) the filtration of the organic phase, wherein steps d.2) and e1.1) can also be carried out several times.

In the second variant (step e2)), the volatile constituents contained in the treated bottom product from step d) are at least partially removed by distillation and the resulting solid is separated from the liquid product phase.

This second variant is particularly suitable when the at least partial removal of the deprotonated stabilizer contained in the treated bottom product and the catalyst contained in the treated bottom product are incomplete or difficult by extractive means, according to variant 1 (step e1)), can accomplish, for example, if the organic and aqueous phases can only be incomplete or impossible to separate.

The separation of the resulting solid from the liquid product phase is preferably carried out by means of sedimentation and / or filtration, particularly preferably by means of filtration.

Optionally, the separated solid is washed once or several times with a little or no water-miscible organic solvent. The organic solvent which is optionally present in the combined liquid product phases and is not or only to a small extent miscible with water is then removed by distillation.

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.

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 with continuous process control, it can be as complete as possible Implementation be useful to connect multiple 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, when using a reactor cascade, are preferably introduced into the first reactor of the cascade, which contains the catalyst and optionally the at least one stabilizer. 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 ³ -OH, optionally used solvent (LM) and the at least one compound III is continuously discharged. For this purpose, a vapor is withdrawn from the reactor or the individual reactors containing the lower alcohol R ³ -OH, the optionally used solvent (LM) and a part of the at least one compound III. The vapor withdrawn for discharging the lower alcohol R ³ -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 reaction mixture is transferred to a distillation apparatus in which the excess of the at least one compound III is removed (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 III. After condensation of the vapor, the at least one compound III is returned to the reactor or the reactor cascade of the reaction in step b). 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 III to be recycled back into the last reactor of the cascade of the reaction in step b). Preferably, the at least one compound III to be recycled is passed exclusively or predominantly into the first reactor of the cascade.

If steps d) and e1) of the process according to the invention are carried out continuously, a continuous aqueous extraction unit can be used for this purpose.

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;
MeHQ stands for methylhydroquinone;
MeOH is methanol;
GC stands for gas chromatography;
Ti (OiPr) ₄ is titanium (IV) isopropoxide.

BEISPI ELE

Example 1: Synthesis of stearyl methacrylate with isopropyl titanate and basic wash

In a 4 L Miniplant glass reactor equipped with a stirrer and a reflux condenser with 10 theoretical plates, a mixture of stearyl and cetyl alcohol (BASF Hydrenol grade, 1 eq.) Was added as a solid and melted at about 50 ° C. During the melting process, MMA (1.75 eq., Stabilized with MeHQ) and MeHQ (about 200 ppm) were added. The mixture was heated to about 90 ° C and the catalyst Ti (OiPr) ₄ (0.0025 eq.) Was added. The transesterification was carried out so that at 1013 mbar and a reflux ratio of 2: 2, the temperature at the top of the column distillation column not exceeded the boiling point of the azeotropic mixture of MMA / MeOH (64 ° C). As the MeOH formation slowed down, a vacuum was applied to ensure a uniform distillation stream. During the reaction, the temperature of the sump increased from 106 ° C to 110 ° C.

After complete reaction (> 98% methacrylate), determined by gas chromatography, the excess of MMA was distilled off under reduced pressure (about 105 ° C, 50 mbar, 1-2 hours).

After completion of the distillation, the reaction mixture was cooled to about 50 ° C and 420 g of a NaOH solution (10 wt .-% in water) was added to hydrolyze the catalyst. The aqueous phase had a pH of 14. After phase separation, 400 g of the aqueous phase was recovered while a small portion of it remained as an intermediate layer in the vessel. The mixture was washed with water (420 g), whereupon the intermediate layer increased. By phase separation, a further 320 g of the water phase with a pH of 13 could be recovered. Further washing with 300 g of H ₃ PO ₄ (0.35% in water) resulted in rapid phase separation without the formation of an intermediate layer. The recovered aqueous phase (440 g) had a pH of 2. Therefore, the mixture was again washed with water (440 g), resulting in phase separation without the formation of an intermediate layer. The recovered aqueous phase (450 g) was neutral. All in all, 98% of the aqueous phase could be recovered by phase separation - only 2% of it remained in the vessel. The remaining water was then removed by distillation (70 ° C, 10 mbar). The crude product was cooled to 70 ° C and filtered through a heated Seitz filter over paper (100 micron filter plate, <3 bar).
Yield: 95%, purity (GC): 99.1%, color number (Hazen): 50, MeHQ concentration: 60 ppm.

Comparative Example C1: Synthesis of stearyl methacrylate with isopropyl titanate without basic wash

The reaction was carried out as in Example 1. However, after completion of the removal by distillation of the excess of MMA, the reaction mixture was cooled to about 50 ° C. and 500 ml of water were added to hydrolyze the catalyst. By phase separation 50 to 60% of the aqueous phase could be separated, the remaining water was removed by distillation (80 ° C, 30 mbar, complete removal, 1 to 2 h). The crude product containing the solid decomposed catalyst was cooled to 70 ° C and filtered through a heated Seitz filter over paper (100 μm filter plate, <3 bar).
Yield: 94%, purity (GC): 99.2%, color number (Hazen): 17, MeHQ concentration: 780 ppm.

Example 2: Synthesis of stearyl methacrylate with dimethyltin dichloride and basic wash

A mixture of stearyl and cetyl alcohol (BASF Hydrenol grade, 2068 g, 8 mol, 1 eq.), Dimethyl tin dichloride / Sodium methoxide in methanol (1: 1 molar, each 0.001 eq.), MeHQ (3000 ppm) and cyclohexane (10 wt .-% based on the total weight of the reaction mixture) was added. The reactor was heated to reflux temperature (about 104 ° C bottom temperature) while the temperature at the top of the column was kept at <65 ° C. The condensed distillate (a mixture of cyclohexane and methanol) was continuously mixed with water and passed into a phase separator. The aqueous phase containing methanol was drained while the organic phase containing cyclohexane and traces of MMA was continuously returned to the reactor. The amount of MeOH lost by the distillation was compensated by the addition of fresh MMA (every hour). After complete conversion (115 to 118 ° C bottom temperature), the low-boiling fractions (cyclohexane and excess MMA) were removed by distillation. Subsequently, cyclohexane (about 10% by weight based on the total amount of the reaction mixture) was added to the reaction mixture to facilitate the washing procedure. The crude product was washed with a 30% NaOH aqueous solution (16% by weight based on the total amount of the reaction mixture), followed by a washing step with water (about 14% by weight based on the total amount of the reaction mixture) and a Washing step with 0.35% H ₃ PO ₄ (7 wt .-% based on the total amount of the reaction mixture). The washing procedure serves to remove the hydrolyzed catalyst and the excess of MeHQ. After washing, the cyclohexane was removed under reduced pressure and the residue filtered.
Yield: quantitative, purity (GC): 99.2%, color number (Hazen): 16, MeHQ concentration: 180 ppm.

Example 3: Synthesis of ethylene glycol dimethacrylate with dimethyltin dichloride and basic wash

In the apparatus described in Example 2, ethylene glycol (708 g, 11.4 mol), methyl methacrylate (2849 g, 28.5 mol), hydroquinone monomethyl ether (8.99 g), hydroquinone (3.75 g), dimethyltin dichloride (12, 59 g, 0.057 mol as a 70 wt% solution in methanol), sodium methoxide (3.15 g, 0.057 mol as a 30 wt% solution in methanol) and cyclohexane (400 g) and heated to boiling. The reaction was carried out as indicated in Example 2, but the organic phase containing cyclcohexane and traces of MMA was recycled continuously to the top of the distillation column. The basic wash was carried out analogously to Example 2.
Yield: 94.6%, purity (GC):> 99.9%, color number (Hazen): 37. The concentration of stabilizer in the final product is usually less than 200 ppm.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 145588 B1 [0005]
• US 2006/0084823 A1 [0006]
• DE 2317226 A1 [0007]
• JP 2003/048866 A [0008]

Claims (15)

Process for the preparation of (meth) acrylic esters of the general formulas Ia or Ib

wherein m has the value 1, 2, or 3, Z if m is 1, an unbranched or branched C ₂ -C ₁₀ -alkylene radical or a bivalent radical of the general formula II.a,

wherein n is 1, 2, 3, or 4 and R ^{1 is} selected from hydrogen or methyl, if m is 2, is an unbranched or branched trivalent C ₂ -C ₁₀ alkanetriyl radical, or if m has the value 3, is an unbranched or branched tetravalent C ₂ -C ₁₀ -alkanetetrayl radical, R ^{1 is} independently of one another hydrogen or methyl, R ^{2 is} a straight-chain or branched C ₇ -C ₃₀ -alkyl group, a C ₆ -C ₁₀ -cycloalkyl group which is unsubstituted or may be substituted by one or two C ₁ -C ₁₀ -alkyl radicals, a radical II.b to II.d

or a radical of the general formula II.e,

in which p has the value 0, 1, 2, 3 or 4, R ^{1 'is} selected from hydrogen or methyl and R ^{2a is} a straight or branched C ₁ -C ₃₀ -alkyl group, where * in the radicals II. a to II.e denotes the point of attachment to the oxygen atom of the respective ester group, in which a) at least one compound of the general formula III

in which R ^{1 has} the abovementioned meaning and R ^{3 is} an unbranched or branched C ₁ -C ₄ -alkyl group, b) the at least one compound III provided in step a) in the presence of at least one alcohol R ² -OH or at least a dihydric, trihydric or tetrahydric alcohol HO-Z- (OH) _m , where R ² , m and Z have the abovementioned meanings, in the presence of at least one catalyst, and in the presence of at least one stabilizer which is dissolved in water at 25 ° C has a pK _s value of less than 14 and is selected from phenolic compounds, oximes, N-oxyl compounds, hydroxylamines, thiols and thiophenols, to obtain a reaction mixture containing at least one (meth) acrylic ester of the general formulas Ia or Ib in which the alcohol R ³ -OH formed during the reaction is continuously removed by distillation, c) the reaction mixture obtained in step b) contains at least one compound III essentially by distillation, giving a bottoms product enriched in the compounds Ia or Ib, the at least one stabilizer and the at least one catalyst, d) treating the bottom product obtained in step c) with an aqueous basic solution, for deactivating the catalyst and for deprotonating the at least one stabilizer, e1) subjecting the aqueous base solution treated bottoms product from step d) to an extractive separation to remove at least a portion of the deprotonated stabilizer contained in the treated bottoms product and at least a portion of the deactivated bottoms contained in the treated bottoms product Catalyst, or e2) the volatile constituents contained in the treated bottom product from step d) at least partially removed by distillation and the resulting solid is separated from the liquid product phase. The method of claim 1, wherein the at least one stabilizer has a water solubility of at least 5 g / L at 25 ° C and a pH of 14. Method according to one of claims 1 or 2, wherein in the compounds of the general formulas Ia or Ib m is 1, 2, or 3, Z if m is 1, is an unbranched or branched C ₂ -C ₁₀ alkylene radical or a bivalent radical of the general formula II.a,

wherein n is 1, 2, 3, or 4 and R ^{1 is} selected from hydrogen or methyl, if m is 2, is an unbranched or branched trivalent C ₂ -C ₁₀ alkanetriyl radical, or if m has the value 3, is an unbranched or branched tetravalent C ₂ -C ₁₀ -Alkantetraylrest, R ^{1 is} independently hydrogen or methyl, R ^{2 is} an unbranched or branched C ₇ -C ₃₀ alkyl group or a radical of the general formula II.e,

in which p has the value 0, 1, 2, 3 or 4, R ^{1 'is} selected from hydrogen or methyl and R ^{2a is} a straight or branched C ₁ -C ₃₀ -alkyl group, where * in the radicals II. a and II.e denotes the point of attachment to the oxygen atom of the respective ester group. A process as claimed in claim 1 or 2, wherein the (meth) acrylic esters are selected from compounds of the general formula Ia in which R ^{1 is} hydrogen or methyl and R ^{2 is} a straight or branched C ₇ -C ₃₀ -alkyl group. Process according to any one of claims 1 to 4, wherein the reaction in step b) is additionally carried out in the presence of a solvent (LM) which forms a low-boiling azeotrope with the alcohol R ³ -OH. A process according to claim 5, wherein the solvent (LM) is selected from aliphatic and alicyclic hydrocarbons containing 5 to 8 carbon atoms and mixtures thereof, in particular under hexane, heptane, cyclohexane and mixtures thereof. Method according to one of claims 1 to 4, wherein step b) is carried out in the absence of an added solvent. Method according to one of the preceding claims, wherein the compound III removed in step c) is at least partially recycled to the reaction in step b). Method according to one of the preceding claims, wherein steps d) and e1) comprise the following steps: d1) if appropriate, adding an organic solvent which is immiscible or only slightly water-miscible with the bottom product obtained in step c), d2) treatment of the bottom product obtained in step c) or in step d1) with an aqueous basic solution for deactivating the catalyst and for deprotonating the at least one stabilizer, e1.1) separation of at least part of the resulting aqueous phase from the organic product phase, e1.2) treatment of the organic product phase obtained in step e1.1) with water and subsequent separation of at least a portion of the resulting aqueous phase from the organic product phase, e1.3) if appropriate, the treatment of the organic product phase obtained in step e1.2) with an acidic aqueous solution and subsequent separation of at least a portion of the aqueous phase from the organic product phase, e1.4) if appropriate, the treatment of the organic product phase obtained in step e1.3) with water and subsequent separation of at least a portion of the resulting aqueous phase from the organic product phase, e1.5) if appropriate, the removal by distillation of the water present in the organic product phase and of the organic solvent which is optionally not present in the organic product phase or which is only slightly water-miscible, e1.6) the filtration of the organic phase, wherein the steps d.2) and e1.1) can also be performed several times. Method according to one of the preceding claims, wherein in the compounds of the general formula Ia R ^{2 stands} for a straight or branched C ₈ -C ₂₂ alkyl group. Method according to one of the preceding claims, wherein in the compounds of general formula III, R ^{1 is} hydrogen or methyl and R ^{3 is} methyl. A process according to any one of the preceding claims, wherein the at least one stabilizer is selected from alkylphenols, 2-alkoxyphenols, 3-alkoxyphenols, hydroquinones and hydroquinone monoalkyl ethers. Method according to one of the preceding claims, wherein the at least one catalyst used in step b) is selected from organic sulfonic acids, mineral acids, metals, metal salts, organometallic compounds and metal alkoxides. Method according to one of the preceding claims, wherein the at least one catalyst used in step b) is selected from organometallic compounds and metal alkoxides of the general formula M [O (C ₁ -C ₄ alkyl)] _q , where M is a q-valent metal cation and q has the values 1, 2, 3 or 4. A method according to any one of claims 13 or 14, wherein the metal in the metals, metal salts, organometallic compounds or metal alkoxides is selected from lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, manganese, titanium, copper, zinc, zirconium, hafnium, Aluminum, iron, antimony, tin and mixtures thereof.