EP2417098A1

EP2417098A1 - Method for continuously producing alkylamino(meth)acrylamides

Info

Publication number: EP2417098A1
Application number: EP10706252A
Authority: EP
Inventors: Bardo Schmitt; Wolfgang Klesse; Martina Ebert; Dirk BRÖLL; Guido Protzmann; Joachim Knebel; Thomas Kehr; Hans-Gerhard Stadler; Gerhard Kölbl; Benedikt Laux
Original assignee: Evonik Roehm GmbH
Current assignee: Evonik Roehm GmbH
Priority date: 2009-04-07
Filing date: 2010-03-03
Publication date: 2012-02-15
Also published as: US8674133B2; AU2010234280A1; ZA201107331B; KR101689905B1; CA2758115C; WO2010115666A1; TWI519506B; US20110313195A1; DE102009002239A1; JP5599453B2; CN102369181A; KR20120016049A; JP2012522817A; TW201102364A; RU2546670C2; BRPI1015290A2; TW201600496A; CA2758115A1; AU2010234280B2

Abstract

The invention relates to a method for continuously producing alkylamino(meth)acrylamides by reacting alkyl(meth)acrylates with high-boiling amines. A catalyst activation and special regeneration technique allow for product qualities that have not yet been achieved. Furthermore, very high space-time and total yields can be achieved.

Description

Process for the continuous production of alkylamino (meth) acrylamides

Field of the invention

The invention relates to a continuous process for the preparation of alkylamino (nneth) acrylannides (C) by continuous aminolysis of, for example, methyl (meth) acrylate (A with Ri = methyl) with amines (B) with liberation of methanol (D with Ri = methyl ) according to the following reaction equation:

R ³

H ₂ C = C - COOR ¹ (A) + R ² NH ₂ (B)

^RJ

H ₂ C = C - CONHR ² (C) + R ¹ OH (D)

where:

R ¹ = linear or branched alkyl radical having 3 to 10

Carbon atoms,

R ³ is hydrogen or the methyl group

R ² is a linear, branched or cyclic

Alkyl radical, an aryl radical which may also be substituted by one or more alkyl groups, the linear, cyclic or branched alkyl radical may have a length of 1-12 carbon atoms, and for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert. Butyl, pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, decyl, undecyl and may optionally be replaced by

- NR ³ R ⁴ or

- OR ⁵

mono- or polysubstituted, in which case either R ³ or R ⁴ can assume the meaning of hydrogen and where furthermore:

R ³ , R ⁴ or R ⁵ can either be the same or different and represent an alkyl group having 1-12 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert. Butyl, pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, decyl, undecyl or hydrogen.

R ² can also be used

[(R ⁶ -O) _n ] - R ⁷

mean, where:

- R ⁶ may be a Ci-C ₄ alkyl group, which may also be branched, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl or tert. Butyl.

R ⁷ may be the methyl group or the ethyl group.

Examples of suitable amines are the following compounds: Dimethylaminoethylamine, diethylaminoethylamine, Dipropylaminoethylamin, Düsopropylaminoethylamin, dibutylaminoethylamine, Disobutylaminoehtylannin, Dimethylaminopropylannin, diethylaminopropylamine, dipropylaminopropylamine, Düsopropylaminopropylamin, dibutylaminopropylamine, Disobutylaminopropylamin, dimethylaminobutylamine, diethylaminobutylamine, Dipropylaminobutylamin, Düsopropylaminobutylamin, Dibutylaminobutylamin, Disobutylaminobutylamin, methylamine, cyclohexylamine, Dimethylaminohexylannin, Diethylaminohexylamin, Dimethylaminoneopentylamin.

In addition to dimethylaminopropylannin, dimethylaminoethylamine, dimethylaminobutylamine, dimethylaminopentylamine and dimethylaminohexylamine is particularly preferred.

State of the art

The literature describes many intermittent transesterification processes (batch transesterification processes) in combination with different catalysts.

The search for more economical processes led to the discovery of continuous transesterification processes, in which the reactants are continuously fed in and the products are continuously removed. The continuous transesterification processes have the following advantages over the discontinuous transesterification processes: The process is easier to automate and can be operated with reduced personnel requirements, the product quality is more reproducible and less variable, the plant capacity increases due to the elimination of the sequential execution of the individual production steps (filling, reaction , Low boiler removal, product separation, emptying). The process has a higher space-time yield than a batch process.

Continuous transesterification processes are known. EP 0 960 877 (Elf Atochem SA) describes a continuous process for the preparation of methacrylate esters of dialkylaminoalcohols. Dialkylamino alcohols are reacted with in general methyl (meth) acrylate and the dialkylaminoalkyl (meth) acrylate is obtained by the following process:

The mixture of the starting materials (methyl (meth) acrylate and dialkylaminoalcohol) is used together with a tetraalkyl titanate as catalyst (for example tetrabutyl, tetraethyl or tetra (2-ethylhexyl) titanate) and at least one polymerization inhibitor (for example phenothiazine, tert-butylcatechol, hydroquinone monomethyl ether or hydroquinone) continuously fed to a stirred reactor, where at a temperature of 90 ⁰ C - 120 ⁰ C, the reaction to dialkylaminoalkyl (meth) acrylate takes place with simultaneous continuous withdrawal of the azeotropic methyl (meth) acrylate / methanol mixture. The crude reaction mixture (crude ester) is fed to a first distillation column, wherein at reduced pressure at the top of the distillation column a substantially catalyst-free stream is withdrawn and withdrawn in the bottom of the distillation column of the catalyst and a little dialkylaminoalkyl (meth) acrylate. The top stream of the first distillation column is then fed to a second distillation column which comprises a stream of low-boiling products containing a little dialkylaminoalkyl (meth) acrylate under reduced pressure and a stream comprising mainly dialkylaminoalkyl (meth) acrylate and polymethylation inhibitor (s) in the bottom. withdrawn, which is fed to a third distillation column. In the third distillation column, a rectification is carried out under reduced pressure, in which the desired pure dialkylaminoalkyl (meth) acrylate ester is stripped off at the top and essentially the polymerization inhibitor or the polymerization inhibitors in the bottom. The bottom stream of the first distillation column is recycled after further purification using a film evaporator as well as the top stream from the second distillation column. This process dispenses with dehydration of the alcohols before use, which can lead to increased deactivation of the tetraalkyl titanate used as a result of hydrolysis up to the formation of undesired precipitation of solids. Furthermore, the process has the disadvantage that in the first distillation column, the catalyst in the sump is thermally stressed at relatively high temperatures. This can easily lead to decomposition of the catalyst.

In this process, both the unreacted starting materials and the product are rectified in total twice overhead. This requires very high energy costs and a total of 4 rectification columns, some of which must be very large. The process is therefore burdened with very high investment and operating costs.

EP 0 968 995 (Mitsubishi Gas Chemical Comp.) Describes a continuous process for the preparation of alkyl (meth) acrylic acid esters using a reaction column. The transesterification reaction is carried out directly in a distillation column (i.e., reactor and distillation column for withdrawing the methyl (meth) acrylate / methanol azeotrope form an apparatus) to which the starting materials (methyl (meth) acrylate and alcohol) are continuously fed. The necessary catalyst, here likewise preferably a titanium compound, is located in the distillation column. In the case of a homogeneous catalyst, the catalyst is continuously metered into the distillation column. However, the use of homogeneous catalysts in a distillation column leads due to a rinsing effect by the liquid reflux in the distillation column to an increased catalyst requirement and when a

Catalyst precipitate for contamination of column internals. In the case of a heterogeneous catalyst, the catalyst is in the reaction column. However, the positioning of the catalyst in the distillation column is disadvantageous because in the distillation column then an increased pressure loss occurs and in addition for the regular purification of the distillation column very high effort must be operated. Furthermore, heterogeneous catalysts can deactivate, for example due to undesired polymerization.

DE 4 027 843 (Röhm GmbH) describes a continuous process for preparing N-substituted (meth) acrylamides by aminolysis of alkyl esters of (meth) acrylic acid with aliphatic and aromatic amines. The reaction temperature is> 150 ⁰ C, the pressure is about 160 bar. It works without a catalyst.

CN 183 71 88 (Jiangsu Feixiang Chemical Co.) describes a process for preparing N - ((- 3-dimethylamino) propyl) methacrylamide (DMAPMA) by reacting methyl methacrylate with N, N-dimethyl-1,3-propanediamine to give N - (- 3 (-3-dimethylamino) propyl) -3 - ((dimethylamino) propyl) amino) -2-methylpropanamide (BDMAPA). BDMAPA is pyrolyzed in a second reaction step at 160 ⁰ C on the metal catalyst and yields in 70 wt .-% - yield a DMAPMA with a purity of> 97%. The process is described as a batch process. The content of crosslinkers is quite high.

WO 2004/103952 (Röhm GmbH) describes a process for the continuous preparation of alkylaminoacrylamides by reaction of alkyl acrylates with high-boiling amines. Thanks to a special processing technique, previously unachieved product qualities are achieved. Furthermore, very high space-time and overall yields can be achieved. task

The object of the present invention is to provide a continuous process for the aminolysis of (meth) acrylic acid esters, which avoids the disadvantages of the two processes described above. Furthermore, the new process should provide a product that is better in quality than the one currently on the market. A better quality is understood to mean a lower crosslinker content or a lower content of addition products of the amines to the double bond of the starting ester or to the double bond of the product amide.

Qualities of the alkylamino (meth) acrylamides available on the market to date, for example, have the following composition:

N-3-dimethylaminopropylmethacrylamide (Jiangsu Feixiang Chemical Co., obtained May 2008, batch number 2007/05/01) has a purity of 98.4% and a crosslinker content of 1730 ppm. The crosslinker found was N-allylmethacrylamide.

It was therefore the object to develop a process which leads to an alkylamino (meth) acrylamide having a significantly lower crosslinking agent content.

Furthermore, with the new process, amino (meth) acrylates are to be prepared with as little effort and energy as possible (ie more cost-effective). The personnel costs for operating the system should be reduced. solution

These and other in detail not detailed, but from the introductory discussion of the prior art readily explicable or derivable tasks by a method having the features of claim 1. Advantageous modifications of the method according to the invention are in the dependent claims on claim 1 below Protection provided.

process Description

The method is shown schematically in FIG.

Explanations of the reference numbers FIG. 1:

1st reactor

2. low boiler discharge distillation column

3. low boiler distillation column

4. crude column

5. clean column

6. Catalyst preactivation

10. Catalyst feed

11. (meth) acrylate feed

12. Amine feed

13. low boiler discharge

14. low boiler circulating stream

15. crude product

16. low boiler discharge

17th Niedersieder discharge

18. Pure product

19. High boiler discharge

DSV = thin film evaporator

The (meth) acrylate-feedstock (11) is fed continuously to a suitable reactor (1), wherein both a single reaction vessel and a cascade of a plurality of successively connected reaction vessels can be used. Such a cascade may consist, for example, of 2, 3, 4, 5, 6 or optionally a plurality of individual reaction vessels. In a preferred embodiment, a cascade of 3 consecutively operated stirred kettles is used.

The (meth) acrylate-feed educt (11) can be carried out in various ways. It is possible, for example, to supply the reactant stream (11) only to the first reaction vessel of the cascade or else to divide the reactant stream (11) into substreams and to supply these substreams to all or only some of the reaction vessels connected in series to the cascade. It is equally possible to carry out the feed of the feedstock stream (11) via the apparatus (2) and / or the reaction apparatuses (1). It may be advantageous to feed the educt stream (11) only into the apparatus (2) or, in another embodiment, to divide the educt stream (11) into partial streams which then both the apparatus (2) and the first or optionally a plurality of reaction vessels of the cascade be supplied.

It makes sense that all reaction vessels have a vapor withdrawal to the distillation column (2) to remove the liberated during the reaction alcohol.

The flow guidance to and from the reactors does not necessarily have to be as shown in the flow chart. It has proved advantageous in particular embodiments to introduce the discharge of a boiler of the cascade into the respective subsequent boiler of the cascade from below. The amine (12) is continuously fed to the distillation column (2) for dehydration.

The tetraalkoxititanate required as catalyst (the tetraalkoxititanate content with respect to (meth) acrylic ester A used is preferably 0.2% by weight - 4% by weight) is likewise preferably continuously introduced into the reactor (as the polymerization inhibitor (s)). 1) added.

As aminolysis catalysts, however, it is also possible to use all transesterification catalysts known from the prior art. Examples of suitable catalysts are zirconium acetylacetonate and further 1,3-diketonates of zirconium; furthermore, mixtures of alkali metal cyanates or alkali metal thiocyanates and alkali metal halides can be used, furthermore tin compounds, for example dioctyltin oxide, alkaline earth metal oxides or alkaline earth metal hydroxides, for example CaO, Ca (OH) ₂ , MgO , Mg (OH) ₂ or mixtures of the abovementioned compounds, furthermore alkali metal hydroxides, alkali metal alkoxides and lithium chloride and lithium hydroxide, it is also possible to use mixtures of the abovementioned compounds with the abovementioned alkaline earth compounds and the Li salts, dialkyltin oxides, for example dioctyltin oxide , Alkali metal carbonates, alkali metal carbonates together with quaternary ammonium salts, such as tetrabutylammonium hydroxide or hexadecyltrimethylammonium bromide, further mixed catalysts of diorganyltin oxide and organyltin halide, see also ure ion exchangers, phosphomolybdenum heteropolyacids, Titanal koholate, such as isopropyl titanate, chelate compounds of the metals titanium, zirconium, iron or zinc with 1, 3-di-carbonyl compounds, lead compounds such as lead oxides, lead hydroxides, lead alkoxides, lead carbonates or lead salts of carboxylic acids. Particularly preferred is a catalyst mixture of dialkyltin oxide and alkyl titanate, for example dioctyltin oxide and isopropyl titanate in a ratio of about 2.5: 1 (wt .-% / wt .-%). The catalyst or the catalyst mixture is used in amounts of 0.1% by weight to 10% by weight, preferably 0.2% by weight to 7% by weight, in each case based on the (meth) acrylate used.

A pre-activation of the catalyst has proved to be advantageous (6). The catalysts are mixed or dispersed, heated to temperatures of 90 ⁰ C to 120 ⁰ C and stirred for 2 to 3 hours until a homogeneous, clear solution has formed.

Suitable alkyl (meth) acrylates are all (meth) acrylates having a linear or branched alkyl radical having 3 to 10, preferably 3 to 6 and particularly preferably 3 or 4 carbon atoms. Typical examples thereof are propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, 3-methylbutyl (meth) acrylate, amyl (meth) acrylate, neopentyl (meth) acrylate, Hexyl (meth) acrylate, cyclohexyl (meth) acrylate, heptyl (meth) acrylate, n-octyl (meth) acrylate, ethylhexyl (meth) acrylate or decyl (meth) acrylate.

As amines, it is possible to use all compounds R ² NH ₂ whose radical R ² consists of 1 to 12, preferably 2 to 8 or particularly preferably 2 to 4 carbon atoms. Examples of typical structures and concrete compounds are already listed at the beginning of this application.

It will be further understood by those skilled in the art that the choice of starting materials is particularly advantageously such that as the alcohol is removed from the reaction mixture, the equilibrium can be shifted to the side of the products. The removal of the alcohol can be carried out by distillation by its lower boiling point compared to the amine used and / or by the formation of an azeotrope.

As polymerization inhibitors are, for example, hydroquinone, 4-hydroxy-2,2,6,6-tetra-methylpiperidinooxyl or bis (2- methoxycarbonylpropyl) sulfide or hydroquinone monomethyl ether in combination with oxygen in question.

The amine used may contain water. The amount of water in the amine used is between 50 and 500 ppm (0.05-0.005% by weight). The amine is preferably dewatered by distillation before entering the reactor, via the distillation column (2). The water contained in the amine is removed overhead. To avoid contamination of the low boiler discharge (13) with the amine used, the task of the amine is preferably carried out in the lower part of the distillation column (2). The amine used can also be dehydrated in other ways:

- By an upstream dewatering distillation column or

by treatment with a dehydrating agent, such as a molecular sieve, or

by a membrane separation process, such as pervaporation.

Dewatering is therefore important because the water in the amine can cause irreversible damage to the catalyst (e.g., tetraalkyl titanate) in the reactor. The water contained in the amine leads to the formation of by-products and should therefore be strictly avoided. This dewatering step avoids the hydrolysis of the catalyst and the associated costs due to increased catalyst use and problems with solid precipitates. In addition, the purity of the product is increased by a reduced proportion of by-products.

The reaction takes place in the reactor (1) at a temperature in the range between 80 ⁰ C and 180 ⁰ C Depending on the material system and operating pressure. Prefers is the temperature range between 110 ⁰ C and 160 ⁰ C. To increase the reaction rate of the liberated in the reaction alcohol via the distillation column (2) from the reaction mixture, optionally also withdrawn as an azeotrope with the alcohol (13). This can be done either at atmospheric pressure, at overpressure or under negative pressure. The reaction mixture, which consists largely of the product alkyl (meth) acrylamide, unreacted (meth) acrylate and amine and small amounts of alcohol, the catalyst, the polymerization inhibitors and a proportion of by-products, is about 0.5 to 3 hours Reactor residence time (preferably, a residence time of 1 - 2 hours) is fed to a continuously operated falling-film evaporator (5). The vapors of the falling film evaporator (5) are fed to a low boiler distillation column (3). There is carried out at reduced pressure, preferably in the range of about 1 mbar - 500 mbar, the separation of the low-boiling in relation to the product amide components, mainly product alcohol and unreacted reactant (meth) acrylate and amine. These are withdrawn via the top of the distillation column (3) and returned to the reactor area or into the distillation column (2) (14). This circulation stream results in a high conversion based on the reactants and the entire process.

The in the course of the falling film evaporator (5) obtained with catalyst, polymerization and high-boiling by-products still contaminated crude amide (15) preferably contains> 80 wt .-% product amide and is used to work up a further vacuum distillation stage, which in the preferred pressure range between 0.1 and 200 mbar works, fed. Here, the distillative separation of pure product amide takes place as a top product.

The by-products formed in the process are high-boiling components with respect to the reactant amine and the reactant (meth) acrylate and thus enter the product amide as an impurity, whereby the product quality is markedly lowered. This problem can be solved by separating the product amide from the catalyst and the Polymerization inhibitors and the high-boiling by-products use a device with gentle film evaporation such as (5). Suitable apparatuses for this fall film, thin film and short path evaporator are known.

The preparation of the alkylamino (meth) acrylamides may optionally be followed by a purifying distillation unit which can also be operated under reduced pressure, for example at 500-0.1 mbar. This is particularly necessary if a particularly good separation of the high-boiling secondary components formed in the process should take place. In the process according to the invention, a two-stage workup is used in order to achieve a low crosslinker content. In the pre-distillation, the crude product (15) is heated and dosed on a column in the head to separate low boilers (16). The degassed feed stream is applied to a second column (4) in the middle to separate low boiler (17). The low-boiling intermediate is applied in a third column (5) and the product (18) distilled overhead to separate the high boilers in the resulting sump (19).

The inventive method is explained in more detail by the following example, without being limited thereto.

Example: Continuous aminolysis to amino (meth) acrylamide

For the continuous production of N-dimethylaminopropylmethacrylamide, the first reaction vessel was charged with 200 kg / h of preactivated catalyst feed containing 2.0% by weight of isopropyl titanate, 5.0% by weight of dioctyltin oxide from the distillation column (2) and 144 kg / h N-dimethylaminopropylamine (DMAPA) added. The pre-activation was carried out at 110 ⁰ C for 2 h in a stirred tank. Furthermore, the 1st reaction vessel flowed via the distillation column (2) the recycle stream from the top of the low boiler Distillation column continuously to (400 kg / h with the composition 70 wt .-% Eduktmethacrylat and methanol, DMAPA and by-products The molar MMA: DMAPA ratio in the reactor feed was 1, 8: 1. Furthermore ran in the distillation column (2) from Methanol was used to liberate the stirred tank vapors via the bottom of the column to the 1st reaction vessel Under these reaction conditions (pressure about 500 mbar), a reaction temperature of 138 ^° C. was established in the 1st reaction vessel . 155 ⁰ C. the distillate takeoff of the distillation column (2) was 110 kg / h. the sequence of the first reaction vessel was running in the 2nd reaction vessel and the flow of the second reaction vessel was in the 3rd reaction vessel. at a residence time of For a total of about 150 minutes, the following proportions of the components were determined at the end of the third reaction vessel:

MMA 43% by weight

DMAPA 4.86% by weight

Aminoamide 35% by weight

The vapors of the individual reaction vessels were continuously fed to the distillation column (2).

The course of the third reaction vessel was continuous to the thin-film evaporator of a low-boiling column in which unreacted DMAPA, MMA and methanol were withdrawn as distillate (400 kg / h) and recycled as recycle stream of the distillation column (2). The bottom outlet of the low-boiling column thin-film evaporator was 240 kg / h and had the composition: about 90% by weight of product amide, 0.1% by weight of DMAPA, a higher proportion of high-boiling components and traces of the reactants. The crude product is then worked up in a two-stage distillation.

Ends distillation:

The crude product prepared (about 90 wt .-% product amide) is conveyed via a pipeline in batches in the feed tank. There stabilizers are added.

By means of a pump, the product, heated by a heater, reaches the top of the column. The separated low boilers (16) are, as far as possible condensed and fed to thermal utilization. Non-condensable fractions are absorbed in the gas scrubber in sulfuric acid.

The degassed feed stream is applied to the middle of the second column and freed there by an evaporator of low boiling points (17). The resulting low boiler are condensed and also thermally utilized.

Main run distillation:

The "low-boiling product" is collected and added to the third column via a preheater The pure product (18) is drawn overhead, almost completely condensed in the dephlegmator and transferred to the clean product tank.

Uncondensed fractions are liquefied in the downstream condenser and used thermally.

The high boilers are withdrawn in the bottom of the second evaporator and fed to thermal utilization (19). The process according to the invention leads to a product (N-3-dimethylaminopropyl methacrylamide) having a purity of> 98%, in the example 98.9%, and a content of less than 600 ppm, in particular 500 ppm, more preferably below 400 ppm, in Example 240 ppm crosslinker. The crosslinker found was N-allylmethacrylamide (analysis by GC).

polymerisation

Formulation: Solution polymer of N-3-dimethylaminopropylmethacrylannide, 15% by weight in n-butyl acetate Conditions: 0.30% by weight of 2,2'-azobis (isobutyronitrile), ext. on

Monomer, 18 h at 70 ⁰ C in a water bath Inventive product: already contains 240 ppm by weight of N-allyl methacrylamide

(Crosslinker); Comparison 1 to 4: by addition with N-allyl methacrylamide product of the invention is based on the corresponding

Crosslinker content adjusted,

The comparative experiments were used to find out what amount of crosslinking agent N-allylmethacrylamide in the monomer has significant effects in the application (polymerization).

The comparison with the commercially available product clearly shows that the crosslinker content of the product, obtainable by the process according to the invention, is substantially lower. Already at 600 ppm of crosslinking initiating gelation is observed in the polymerization, at 1000 ppm gels the approach completely.

Claims

claims

A process for the continuous production of alkylamino (neth) acrylannide of the formula (C)

R ₃

I (C)

H ₂ C = C - CONHR ²

wherein R ^{2 is} a linear or branched or cyclic alkyl radical or aryl radical having 1 to 12 C atoms, by reaction of a compound of the formula (B),

R ² NH ₂ (B)

where R ^{2 has} the abovementioned meaning, with alkyl (meth) acrylate (A),

R ₃

(A) H ₂ C = C - COOR ¹

R ³ is hydrogen or the methyl group,

wherein R ^{1 is} a linear or branched alkyl radical having 3 to 10 carbon atoms, in the presence of a catalyst or a catalyst mixture which has been thermally activated and in the presence of at least one polymerization inhibitor in a continuous reaction apparatus,

characterized, that the reactants are fed continuously to a suitable reactor (1) and that the alcohol or an alcohol / alkyl (meth) acrylate mixture (13) formed in the reaction is withdrawn continuously with the aid of a distillation column (2) and also:

- The reaction mixture is continuously fed from the reactor into a distillation column (3) or an evaporator (5), wherein the highly volatile components (A, B, alcohol) and a very small proportion of product amide (C. By distillation under reduced pressure overhead ) are withdrawn and returned to the reactor and withdrawn from the bottom of the column the product amides (C) together with the catalyst and the polymerization inhibitors and high-boiling by-products;

- The bottom stream (15) from the distillation column (3) is fed continuously to a purifying distillation.

2. The method according to claim 1,

characterized,

that the vapor stream of the evaporator (5) is fed continuously to a further distillation column, the pure product amide (C) being removed by distillation under reduced pressure overhead, and via the bottom the catalyst and the polymerization inhibitors and the high-boiling by-products with a small portion of product amide ( C) are withdrawn, and that the resulting product amide is fed to a two-stage pure distillation, which consists of a preliminary distillation with low boilers and Niedersiederabzug and a main run distillation, which separates the high boilers consists.

3. The method according to any one of the preceding claims,

characterized,

the amine (B) is fed to the reactor for dehydration via the distillation column (2).

4. The method according to any one of the preceding claims,

characterized,

the molar ratio of alkyl (meth) acrylate to amine in the feed is between 1 and 2, preferably 1.05-1.15.

5. The method according to any one of the preceding claims,

characterized,

in that a tetraalkyl titanate is used as the catalyst and a pre-activation is carried out.

6. The method according to any one of the preceding claims,

characterized,

that the catalyst in an amount of 0.1 to 10 wt .-%, based on the (meth) acrylate used.

7. The method according to any one of claims 1 to 5,

characterized,

that the catalyst in an amount of 0.2 to 7 wt .-%, based on the (meth) acrylate used.

8. The method according to any one of the preceding claims,

characterized,

using as the catalyst mixture is a mixture of dioctyltin oxide and isopropyl titanate in a ratio of 2.5: (% /Gew.-% wt .-) applies 1, wherein the catalyst mixture was activated at 90 to 120 ⁰ C for 2 to 3 hours.

9. The method according to claim 8,

characterized,

the catalyst mixture is used in an amount of 0.1-10% by weight, based on the (meth) acrylate used.

10. The method according to any one of the preceding claims,

characterized,

in that the polymerization inhibitor used is either phenothiazine, tert-butyl catechol, hydroquinone monomethyl ether, hydroquinone or mixtures thereof, the amount of the inhibitor being between 10 and 5000 ppm, based on the reaction mixture.

11. The method according to any one of the preceding claims,

characterized,

that additionally oxygen is used as the polymerization inhibitor.

12. The method according to any one of the preceding claims,

characterized,

that dimethylaminopropylamine is preferably used as the amine.

13. The method according to any one of the preceding claims,

characterized,

the pressure in the first distillation column (3) is between 2 and 500 mbar.

14. The method according to any one of the preceding claims,

characterized,

the residence time in the reactor is between 0.5 and 3 hours.

15. The method according to any one of the preceding claims,

characterized,

the evaporator (5) is a film evaporator.

16. A monomer according to claim 1 with a crosslinker content less than 600 ppm, producible by a method according to the preceding claims.