GB2248234A

GB2248234A - A process for preparing n-substituted amides of acrylic or methacrylic acid

Info

Publication number: GB2248234A
Application number: GB9118329A
Authority: GB
Inventors: Wolfgang Ruppert; Werner Hoess; Heinz Vetter; Joachim Knebel; Willi Ploesser
Original assignee: Roehm GmbH; Roehm GmbH Darmstadt
Current assignee: Roehm GmbH; Roehm GmbH Darmstadt
Priority date: 1990-09-03
Filing date: 1991-08-27
Publication date: 1992-04-01
Anticipated expiration: 2011-08-27
Also published as: FR2666334B1; FR2666334A1; DE4027843A1; GB9118329D0; GB2248234B; ES2036467A1; ES2036467B1; NL9101348A

Description

Process for preparing]a-substituted amides of acrylic or methacrylic acid

The invention relates to an improved process for preparing N-substituted acrylic acid amides and methacrylic acid amides by reacting alkylesters of acrylic or methacrylic acid with aliphatic or aromatic amines.

N-substituted amides of acrylic and methacrylic acid are of considerable technical interest since they are polymerisable monomers with a relatively hydrophilic and inert functional group. In their preparation, the lower esters of acrylic and methacrylic acid are preferred starting materials because of their ready availability; to produce the N- substituted amides, they are reacted with the corresponding primary or secondary amines.

Since the unsaturated carboxylic acid esters are able to react with the amine both at their carbon-carbon (C-C)-double bond and also by means of their ester group, this leads to the desired unsaturated, Nsubstituted carboxylic acid amides being obtained in admixture with greater or lesser amounts of amine addition products to the C-C-double bond, depending on the reaction conditions, especially the concentration, temperature and pressure conditions and the influence of catalysts.

DE-B-25 02 247 discloses a process for preparing N(tert.aminoalkyl)(meth)acrylamides by thermal cleaving at temperatures of from 180 to 300C of fl-aminopropinoamides or -isobutyramides obtained for example by reacting acrylic or methacrylic esters with a tert. aminoalkylamine in a molar ratio of I:! 2 below 200'C. The cleaving reaction is preferably carried out continuously under reduced pressures down to 2 mbar or at pressures greater than atmospheric pressure up to about 11 bar. By the two reaction steps, methacrylamide yields of up to about 80% of theory are obtained, relative to the (meth)acrylic ester components used as starting materials.

DE-A-28 09 102 describes a process for preparing Nsubstituted (meth)acrylamides, in which (meth)acrylic acid esters are heated with a quantity of an amine ranging from a deficiency to a slight excess, in a single step, under autogenous pressure (about 10 to 20 bar), in homogeneous phase to a temperature of above 150C, preferably 180 to 250C. The reaction products are obtained in pure form by fractional distillation. N-methylmethacrylamide is, for example, formed from methylamine and methylmethacrylate in amounts which are dependent on the quantity of methylamine added per mol of methylmethacrylate, i.e. in quantities of 81% of theory based on ester (1.1 mol methylamine) and 89% of theory based on amine (0.5 mol methylamine) or 97% of theory based on amine (0.25 mol methylamine).

According to DE-A-28 16 516, the reaction of the alkylesters of acrylic or methacrylic acid with amines at temperatures between 50 and 180'C is carried out in the presence of catalytic quantities of a dialkyl tin oxide. It is convenient to use an excess of ester. Amides of (meth)acrylic acid are then obtained in yields of up to 98% of theory, based on amine. An analogous process in which the reaction is carried out in the presence of catalytic quantities of compounds of metals of the IVth subsidiary group and/or compounds of the metals lead, zinc and tantalum, is described in DE-A31 23 970.

Using the methods described in the prior art it is not possible to obtain N-substituted (meth)acrylamides continuously on an industrial scale by reacting the alkylesters of acrylic or methacrylic acid with amines. In the procedure according to DE-B-25 02 247, the 0- amino-propionamide or P-amino-isobutylamide formed from 2 mols of amine and 1 mol of unsaturated ester over long reaction times (about 10 to 20 hours) is cleaved in a second step before it can be obtained in pure form.

The other processes discussed in the prior art also require long reaction times - about 3 to 10 hours - in order to react the amine used (even if present in minor amounts) to obtain the unsaturated amide. It has also been found that in processes which use an excess of acrylic or methacrylic ester, deposits and blockages are produced in the apparatus as the result of the formation of various by-products, including polymerisation products; this means that continuous methods cannot be used. Accordingly, with these processes, the selectivities for the unsaturated amides as reaction products, based on the unsaturated esters used, are significantly lower than those based on the amine used.

The aim of the present invention is to provide a continuous process for preparing N-substituted amides of acrylic or methacrylic acid from esters of these acids by aminolysis thereof, preferably including the recovery of the unsaturated N-substituted amides in pure form.

According to one aspect, the present invention provides a process for preparing an N-substituted amide of acrylic or methacrylic acid of formula I R 1 0 R 2 1 11 - // H 2 k; - c N \1 R 3 1 (wherein R 1 represents H or CH 3 and R 2 and R 3 each represent C,_,- alkyl, aralkyl or aryl groups or R 2 represents H and R 3 represents C,_,- alkyl, aralkyl or aryl groups or Cl-6-alkylene groups which also have substituents in the terminal position), comprising reacting an alkylester of acrylic or methacrylic acid with an amine of formula II - 4 ..I HN R 2 R 3 II, (wherein R 2 and R 3 are as hereinbefore defined) at a temperature above 150C and a pressure exceeding 1 bar with the continuous admixture of said alkylester and said amine in a molar ratio of respectively 1:: 2, for a reaction time ranging from 5 to 40 minutes, with continuous removal of the reaction mixture.

If desired, the removed reaction mixture may be introduced into a column operating at temperatures above 160'C so as to complete the cleaving into unsaturated amide and amine, and then further separated by fractional distillation into said N-substituted amide, amine excess and by-products.

Using the invention it is possible for the first time to obtain Nsubstituted amides by transesterifying unsaturated esters with amines in a single process. Extensive trials with the reaction component methylmeth acrylate/methylamine, a preferred system according to the invention, for preparing N-methylmethacrylamide showed that the proportion of methylamine wasted when using the process according to the invention, e.g. with 2 to 3 mol of methylamine per mol of methylmethacrylate, was only about 0.1 mol per mol of N-methylmethacrylamide, as against a loss of 0.3 mol of amine per mol of N-methylmethacrylamide when using the starting components in an equimolar ratio.

The preferred acrylic or methacrylic esters are methylacrylate, ethylacrylate and methylmethacrylate, since they are readily obtainable on an industrial scale and the alcohol liberated during aminolysis can easily be eliminated from the reaction mixture. The suitability of the esters declines as the number of carbon atoms in the alcohol groups increases. From this aspect, alkylesters with more than 4 carbon atoms in the C alkyl group must be regarded as less suitable.

The aminolysis according to the invention is carried out with amines of formula II which may be primary or secondary amines with aliphatic, araliphatic and aromatic groups R 2 and/or R 3 each having 1 to 8 carbon atoms in the R 2 or R 3 group. Primary amines, especially primary aliphatic amines are preferred. Examples of aliphatic primary amines include, in particular, methylamine, ethylamine, n-propylamine, nbutylamine and sec.-butylamine, whilst examples of aliphatic secondary amines include dimethylamine, diethylamine, methyl-ethylamine and di-nbutylamine. An example of a suitable araliphatic amine is benzylamine and examples of aromatic amines are aniline and methylsubstituted anilines. of the primary amines, methylamine is particularly preferred.

The amines which are to be reacted may contain, in particular, in addition to the primary amino group, other functional groups such as ether, thioether or amino groups, whilst tertiary amino groups as such are preferred. Examples of amines of this kind having groups with tertiary nitrogen atoms are 3-dimethylaminopropylamine and 2- morpholinoethylamine.

The alkylester and the amine may be reacted in the presence of an aminolysis catalyst, e.g. in a reactor. Known aminolysis catalysts such as dialkyl tin oxides may be used, but their catalytic effect is not particularly important particularly at high reaction temperatures of above approximately 180C.

In order to avoid polymerisation losses it is advisable to carry out the reaction and working up of the reaction mixture in the presence of polymerisation inhibitors such as hydroquinone, hydroquinone monomethylether or phenothiazine, which may optionally develop their stabilising properties better in the presence of molecular-dissolved oxygen.

The reaction of the amine with the acrylic or methacrylic ester is advantageously carried out in a reactor with minimum possible remixing in the liquid phase. For this purpose, the mixture of the amine and the unsaturated ester, at a temperature of about 50 to 1OWC, is forced in liquid form out of a mixer into the reactor under a pressure of more than 1 bar. The first part of the reactor may also be constructed as a mixing area into which the reactants are metered separately.

The reaction is advantageously carried out in a tube reactor at temperatures above 150'C, particularly at temperatures from 180 to 25WC and also at temperatures from 250 to 30WC. Instead of a virtually isothermic reaction, the reaction may also be carried out within a sharper temperature gradient, from about 100'C at the entrance to the reactor to about 300C at the exit of the reactor. The advantage of this procedure is that, at most, there are only slight amineC-C-double bond products present in the reaction mixture, and the formation of the N- substituted acrylamide or methacrylamide is substantially complete.

The pressures in the reactor are preferably autogenous and are higher than 1 bar, preferably higher than 5 bar, e.g. from 10 to 30 bar, or higher. After retention times of from 5 to 40 minutes, particularly from 5 to 25 minutes, more especially from 10 to 20 minutes, the reaction mixture is, if desired, continuously passed from the reactor exit into a separation system consisting of columns.

Advantageously, the outflow from the reactor is conveyed into a first column in which the cleaving alcohol and excess amine are distilled off at the top and in which the temperature is still high enough to cleave any amine-C-C-double bond product still present. This means temperatures greater than 16WC and more particularly greater than 180'C, so that the Nsubstituted unsaturated amide and possibly higherboiling by-products are obtained in the expulsion part of the column. The mixture of amine and alcohol drawn off at the top is further separated under conventional conditions, advantageously by distillation, and the amine is recycled into the reaction. The N- substituted acrylamide or methacrylamide is recovered from the expelled fraction by high purification, particularly distillation, or from amides which crystallise at normal temperature, by crystallisation and possibly recrystallisation.

In a further aspect, the invention provides an Nsubstituted amide of acrylic or methacrylic acid of formula I as defined above when prepared by a process according to the invention.

The invention will now be illustrated by means of the following nonlimiting Examples and accompanying drawings in which:

Figure 1 is a schematic representation of the apparatus utilized in Example 1.

Ficrure 2 is a graph showing loss of mol (monomethylamine)/mol (Nniethylmethacrylamide) vs. Molar Ratio mol (monomethylamine)/mol (methylmethacrylate) (Example 3).

EXAMPLES

Exami)1e 1 Reaction of methylmethacrvlate with methvlamine in a molar ratio of 1:2 In an apparatus as shown in Figure 1, the reaction is carried out in an isothermically operated tube reactor (C501) at 21WC, with a retention time of 15 minutes and using a ratio of 1:2 = MMA:MA (methylmethacrylate:methylamine) [1,2] under a pressure of 160 bar. The MMA reactor feed is mixed with 300 ppm of hydroquinone monomethylether and saturated with oxygen from the air. The flow of product (3) leaving the reactor is conveyed to a distillation column (K501) (pressure approx. 1 bar absolute) in which the sump temperature is above 160'C, in order to remove the lower boiling fractions, namely methylamine, dimethylamine, trimethylamine, methanol, H 2 0 and methacrylic acid. In another column (K502) the methylamine, transferred from column K501 (4), is separated from the by-products mentioned above and recycled into the reaction (6). The other low boiling fractions are obtained in the sump of the columns (K502) (pressure approx. 10 bar) and are eliminated as waste products (7) (methanol, water, methacrylic acid, dimethylamine, trimethylamine).

The sump products from distillation column (K501) contain the desired product N-methylmethacrylamide and high boiling fractions. The addition products contained in the feed to column K501 (3), such as P-methyl- or Pdimethylaminoisobutyric acid methylamide, are cleaved almost entirely into the corresponding amines and Nmethylmethacrylamide in the expulsion part of the column.

In a third distillation column (K503) (pressure approx. 100-200 bar absolute) N-methylmethacrylamide (9) 4 C is separated from the higher boiling fractions (8) by distillation.

Table 1 shows the molar currents established in the apparatus at the corresponding sampling points (1-9) (see Figure 1). Using the process described, methylinethacrylate was converted into N-methylmethacrylamide in yields of 95.2% of theory. 1.15 mol of methylamine were used up for each mol of N-methylmethacrylamide formed.

Example 2

Reaction of methylmethacrylate with methvlamine in a molar ratio of 1:3 When the reaction of MMA with RA in a molar ratio of 1:3 was carried out under reaction conditions which were otherwise identical to those described in Example 1, the consumption of monomethylamine was 1.11 mol per mol of N-methylmethacrylamide formed. The yield of unsaturated amide, based on methylmethacrylate, was 96% of theory.

Example 3 (Comparative Example) Reaction components in a molar ratio of 1:1 With the ratio of MMA to MA adjusted to 1:1, the other conditions being identical to those in Example 1, the experiment was made substantially more difficult by the formation of considerable amounts of polymer, in spite of stabilisation. The yields were reduced to 76.9% of theory. The loss of methylamine per mol of Nmethylmethacrylamide formed was 0.3 mol (see Figure 2 which shows the loss of amine as a function of the molar ratio of the starting components).

Under these conditions, other amines of general TABLE 1

Sampling points 1 2 3 4 1 5 1 6 1 7 8 Molar currents (mol/h) Methylmethacrylate 107 0.5 0.5 Methanol 81.2 81.2 81.2 Monomethylamine 214 30.5 82.0 82.0 Water 11.3 11.3 11.3 Dimethylamine 20.3 20.3 Methacrylic acid 0.6 0.6_ 0.6 Trimethylamine 1.5 1.5 1.5 N-methylmethacryl- 30.6 101.9 101.9 amide Methyl P-methylamino- 0.41 isobutyrate Methyl fl-dimethyl0.12 aminoisobutyrate fl-methylaminoiso- 51.0 butyric acid methyl amide fl-dimethylaminoiso- 20.3 butyric acid methyl amide High boiling 3.4 3.4 3.4 fractions Temp. 'C 197 12 216 -6 54 180 150 Molar mass of high boiling fractions 250 9/mol 0 M) j 0 (D l H H 0 m 0) 5:1 l.

P (D U) tr (D M 0 (D " 0) 0 bt) rt 0 (D 1 L PI rt F- 0 P) H 0 i.

rt ft r::r (D (D 0 P) m _ M (D m m r, C$ 0 0 0:1 (D P m -1.

(n j ka 1 -i 0 1

Claims

1. A process for preparing an N-substituted amide of acrylic or methacrylic acid of formula I R 1 0 R 2 H 2 C N R 3 I (wherein R 1 represents H or CH 3 and R 2 and R 3 each represent Cl_. _alkyl, aralkyl or aryl groups or R 2 represents H and R 3 represents C, _Calkyl, aralkyl or aryl groups or Cl-6-alkylene groups which also have substituents in the terminal position), comprising reacting an alkylester- of acrylic or methacrylic acid with an amine of formula II HN R,/' 2 II, (wherein R 2 and R 3 are as hereinbefore defined) at a temperature above 150C and a pressure exceeding 1 bar with the continuous admixture of said alkylester and said amine in a molar ratio of respectively 1: 2, for a reaction time ranging from 5 to 40 minutes, with continuous removal of the reaction mixture.

2. A process as claimed in claim 1 wherein said alkylester and said amine are reacted in the presence of an aminolysis catalyst.

3. A process as claimed in claim 1 or claim 2 wherein the removed reaction mixture is introduced into a column operating at temperatures above 1600C so as to complete the cleaving into unsaturated amide and amine, and then further separated by fractional distillation into said a N-substituted amide, amine excess and by-products.

4. A process as claimed in any one of the preceding claims wherein said amine is a primary amine.

5. A process as claimed in any one of the preceding claims wherein said amine is a primary aliphatic amine.

6. A process as claimed in any one of the preceding claims wherein said amine is methylamine.

7. A process as claimed in claim 1 substantially as herein described and with reference to the Examples.

8. An N-substituted amide of acrylic or methacrylic acid of formula I as defined in claim 1 when prepared by a process as claimed in any one of the preceding claims.