Process for the production of .alpha., .beta.-unsaturated carboxylic acid alkyl esters sulfonated in the .alpha.-position and compounds obtainable by this process

The title compounds are obtained by reacting compounds corresponding to the following formula: EQU R.sub.1 --CH.dbd.CH--CO.sub.2 R.sub.2 wherein R.sub.1 represents hydrogen or a methyl group and R.sub.2 represents a primary or secondary C.sub.1 to C.sub.4 alkyl group, with from 0.6 to 1.6 mol. equivalents of SO.sub.3 and, optionally, with from 0.1 to 10 mol. equivalents of an alkylating agent at temperatures in the range from -10.degree. to +25.degree. C., subsequently heating the resulting reaction mixture for 0.5 to 6 hours to 70.degree.-200.degree. C. and then working it up by distillation.

This invention relates to a process for the production of sulfonated 
.alpha.,.beta.-unsaturated carboxylic acid alkyl esters corresponding to 
the following general formula (I): 
##STR1## 
in which R.sub.1 represents a hydrogen atom or a methyl group, 
R.sub.2 represents a primary or secondary alkyl group containing from 1 to 
4 carbon atoms and 
X represents a hydrogen atom or a primary or secondary alkyl group 
containing from 1 to 4 carbon atoms, and to their sulfonic acid salts. 
The present invention also relates to compounds corresponding to the 
following formula (I) 
##STR2## 
in which R.sub.1 and R.sub.2 are as previously defined and X.sup..sym. 
represents a proton or a metal ion equivalent, preferred metals being 
alkali metal and alkaline earth metals, zinc and aluminium. 
It is already known that .alpha.,.beta.-unsaturated carboxylic acids can be 
converted into sulfonic acid derivatives by reaction with sulfonation 
reagents (Rec. Trav. Chim. 62, 46 (1943); U.S. Pat. No. 2,895,987; FR-PS 
No. 2,110,792, Bull. Soc. Chim. Fr. 1973, 2266). However, the 
2-sulfoacrylic acid has only ever been produced in dilute solution because 
it polymerises when the solution is concentrated. 
Attempts to isolate the 2-sulfoacrylic acid by sulfonation with pure sulfur 
trioxide were also unsuccessful. 
It is also known that the 3-chloro-2-sulfopropionic acid obtained from 
acrylic acid by sulfonation with chlorosulfonic acid gives 2-methoxy 
sulfonyl propenoic acid methyl ester by reaction with chloromethyl formate 
for 18 hours at 95.degree. C. (FR-PS No. 2,110,792). The highly 
hygroscopic, dimethyl lauryl ammonium salt of 2-sulfopropenoic acid methyl 
ester is obtained from 3-chloro-2-sulfopropionic acid by esterification 
with methanol, reaction with pyridine to form the pyridinium salt and 
subsequent elimination by dimethyl lauryl amine (Bull. Soc. Chim. Fr. 
1973, 2266). One of the disadvantages of these known processes is that the 
ester derivatives derived from the carboxylic acids and/or sulfonic acids, 
which are of particular commercial interest, can only be obtained--if at 
all--by elaborate multistage syntheses. These complicated processes cannot 
be worked on a commercial scale. 
A process for the production of compounds corresponding to formula (I) has 
now been found and is characterised in that .alpha.,.beta.-unsaturated 
carboxylic acid esters corresponding to the following general formula 
(II): 
EQU R.sub.1 CH.dbd.CH--CO.sub.2 R.sub.2 (II) 
in which R.sub.1 and R.sub.2 are as previously defined above, are reacted 
with from 0.6 to 1.6 mol. equivalents of sulfur trioxide and, optionally, 
with from 0.1 to 10 mol. equivalents of an alkylating agent, based in each 
case on the unsaturated ester, at temperatures in the range from 
-10.degree. C. to +25.degree. C., the reaction mixture is heated for 0.5 
to 6 hours to temperatures in the range from 70.degree. C. to 200.degree. 
C. and then worked up by distillation, after which the components of the 
distillate are optionally separated. Working up by distillation, 
optionally after the separation of readily volatile constituents, for 
example unreacted alkylating agent, is carried out in particular by 
continuously distilling the reaction mixture in a tubular evaporator at 
temperatures in the range from 100.degree. C. to 250.degree. C. under a 
pressure of from 0.05 to 30 mbars, the throughput amounting to between 0.1 
and 10 kg/m.sup.2.h. The distillate, which predominantly consists of 5 to 
90% by weight of the sulfonic acid (I) (X.dbd.H) and 10 to 95% by weight 
of the sulfonic acid ester (I) (X.dbd.R.sub.2), is separated by 
precipitating the sulfonic acid with an organic precipitant or by salt 
formation. The residual sulfonic acid ester is isolated by distillation. 
The .alpha.,.beta.-unsaturated carboxylic acid alkyl esters used are, for 
example, acrylic acid methyl ester, acrylic acid ethyl ester, acrylic acid 
propyl ester, acrylic acid isopropyl ester, acrylic acid butyl ester, 
acrylic acid isobutyl ester, crotonic acid methyl ester, crotonic acid 
ethyl ester, crotonic acid propyl ester, crotonic acid isopropyl ester, 
crotonic acid butyl ester and crotonic acid isobutyl ester. It is 
preferred to use acrylic acid methyl ester, acrylic acid ethyl ester and 
crotonic acid methyl ester. 
The .alpha.,.beta.-unsaturated carboxylic acid alkyl ester is preferably 
reacted with from 0.8 to 1.2 mol. equivalents of sulfur trioxide which may 
be introduced while stirring either in gaseous or liquid form. The sulfur 
trioxide should be introduced as quickly as possible. However, it is 
important to ensure that the above-mentioned reaction temperature, 
preferably in the range from 0.degree. to +10.degree. C., is maintained. 
Accordingly, the addition time depends upon the size and cooling capacity 
of the batch. In general, addition of the SO.sub.3 takes from 0.1 to 2.0 
hours. In the case of highly exothermic reactions, for example where 
crotonic acid methyl ester is used, it may be advisable to carry out the 
reaction in the presence of an organic solvent, particularly a low-boiling 
chlorinated hydrocarbon, such as chloroform or methylene chloride, which 
is added in a quantity of up to 100% by weight, based on the carboxylic 
acid ester and sulfur trioxide used. In general, particularly where 
acrylic acid methyl ester is used, the sulfur trioxide is added in the 
absence of a solvent. 
Suitable alkylating agents are, for example, C.sub.1 -C.sub.4 -dialkyl 
sulfates, alkyl- and aryl alkyl ethers, alcohols, alkyl halides and 
diazomethane. Dimethyl sulfate is preferred, particularly where acrylic 
acid methyl ester is the .alpha.,.beta.-unsaturated carboxylic acid ester. 
It is preferred to use from 0.2 to 5 mol. equivalents of C.sub.1 -C.sub.4 
-alkyl sulfate, based on the unsaturated ester. 
The reaction is normally carried out in batches in a stirrer-equipped 
reaction, although it may also be carried out continuously in a reaction 
tube into which the reaction components are simultaneously introduced. 
The alkylating agent is added after or during the reaction with sulfur 
trioxide. Thereafter the reaction mixture is preferably heated for from 
1.5 to 3 hours to between 80.degree. and 160.degree. C. 
The continuous distillation process may be carried out in a tubular 
evaporator. It is preferred to use a thin-layer evaporator comprising a 
rotating wiper or a falling-film evaporator. In this continous 
distillation process, the temperature is preferably maintained in the 
range from 140.degree. C. to 200.degree. C. and the pressure preferably 
maintained in the range from 0.3 to 3 mbar. The residence time in the 
evaporator amounts to between 0.1 and 10 kg of product per square meter of 
exchange surface of the tubular evaporator per hour. 
The reaction mixture accumulating consists predominantly of the sulfonic 
acid and the sulfonic acid ester of formula (I). Where the reaction is 
carried out in the absence of an alkylating agent, the sulfonic acid is 
predominant. Where the reaction is carried out in the presence of an 
alkylating agent, it is the sulfonic acid ester which predominates. 
The yield of the reaction mixture, based on the quantity of the starting 
components used, amounts to between 50 and 100% by weight. 
The precipitant used for isolating the sulfonic acid of formula (I), in 
which X represents a hydrogen atom, from the mixture is an organic 
solvent, preferably an aromatic hydrocarbon, for example benzene, toluene 
or xylene. A particularly good purifying effect is obtained by briefly 
heating the mixture with the precipitant, followed by cooling, resulting 
in precipitation of the sulfonic acid. 
The filtrate which is left after separation of the sulfonic acid and which 
mainly contains the organic solvent and the sulfonic acid ester is freed 
from the organic solvent by distillation. Subsequent fractional 
distillation in a column at a temperature of from 70.degree. C. to 
200.degree. C. and preferably at a temperature of from 80.degree. C. to 
150.degree. C. under a pressure of from 0.05 to 40 mbar and preferably 
under a pressure of from 0.3 to 7 mbar gives the sulfonic acid ester 
corresponding to formula (I) in which X.dbd.R.sub.2. 
Another possible method of separating off the sulfonic acid comprises salt 
formation with the carbonates, oxides or acetates of alkali metals, 
alkaline earth metals, aluminium and zinc, preferably with ZnO, MgO, 
Na-acetate. Salt formation is carried out in polar organic solvents, 
preferably in acetonitrile or acetic acid. The sulfonic acid ester may be 
obtained from the filtrate by distillation using the procedure described 
above. 
The products obtained by the process according to the invention are 
valuable organic intermediate products. For example, surface-active 
substances as well as microbicidally and fungicidally active substances 
may be obtained by the addition of nucleophilic agents to the double bond.

EXAMPLE 1 
Reaction of acrylic acid methyl ester with SO.sub.3 : 
(a) Preparation of a mixture of 2-sulfopropenoic acid methyl ester and 
2-methoxy sulfonylpropenoic acid methyl ester: 
471 g of liquid sulfur trioxide are stirred at 0.degree. to 10.degree. C. 
into 506 g of acrylic acid methyl ester stabilised with 2 g of 
hydroquinone, a gentle stream of an inert gas being simultaneously 
introduced. After the mixture initially formed has been tempered for 2 
hours at 100.degree. C., readily volatile constituents, predominantly 
unreacted acrylic acid methyl ester and dimethyl sulfate accumulating 
during the reaction, are distilled off in vacuo. The crude mixture 
remaining is then introduced into a thin-layer evaporator under the 
following conditions: 
______________________________________ 
Temperature of the heating jacket: 
158.degree. C. 
Pressure adjusted: 0.5 to 1.0 mbar 
Throughput: 1.0 kg/m.sup.2 h 
______________________________________ 
The condensate obtained is a substantially colourless oil consisting of 
2-sulfopropenoic acid methyl ester and 2-methoxy sulfonyl propenoic acid 
methyl ester from which the acid precipitates partly in the form of a 
crystalline phase. 
Yield: 622 g (64% by weight, based on the components used, acrylic acid 
methylester and SO.sub.3), 
The following composition is established by NMR-spectroscopy: 60% by weight 
of 2-sulfopropenoic acid methyl ester and 40% by weight of 2-methoxy 
sulfonyl propenoic acid methyl ester. 
(b) Isolation of 2-sulfopropenoic acid methyl ester: 
The mixture consisting of sulfonic acid and sulfonic acid ester which 
accumulates during the thin-layer distillation process is stirred with 500 
g of benzene, accompanied by brief heating. After cooling, the 
2-sulfopropenoic acid methyl ester precipitates in the form of highly pure 
crystals. 
Yield: 200 g (19.5% by weight, based on the components used, acrylic acid 
methyl ester and SO.sub.3) 
Melting point: 66.degree. C. 
.sup.1 H-NMR-spectrum (in d.sub.3 -acetonitrile): .delta.3.85 (s), 6.85 
(d), 6.9 (d), 11.0 (s) ppm 
(c) Isolation of 2-methoxy sulfonyl propenoic acid methyl ester: 
The filtrate remaining after precipitation and separation of the sulfonic 
acid is concentrated by evaporating off the benzene. The residue is 
subjected to fractional distillation. The fraction distilling over at 
93.degree. C./0.4 mbar consists of 2-methoxy sulfonyl propenoic acid 
methyl ester. 
Yield: 108 g (10.5% by weight, based on the components used, acrylic acid 
methyl ester and SO.sub.3) 
Melting point: 25.degree.-30.degree. C. 
.sup.1 H-NMR-spectrum (in d.sub.3 -acetonitrile): .delta.3.85 (s), 3.9 (s), 
6.9 (d), 7.02 (d) ppm 
(d) Isolation of the Na-salt of 2-sulfopropenoic acid methyl ester; 
66.5 g of the condensate mixture obtained by thin-layer distillation in 
accordance with (a) are dissolved in 60 g of acetonitrile. 32.8 g of 
Na-acetate are then introduced in portions with stirring at room 
temperature. The white solid precipitating is separated off by filtration. 
After drying, the Na-salt of 2-sulfopropenoic acid methyl ester is left. 
Yield: 41.8 g (35 mole percent, based on the acrylic acid methyl ester 
used) 
Melting point: 219.degree. C. 
.sup.1 H-NMR-spectrum (in D.sub.2 O): .delta.3.85 (s), 6.65 (d) ppm 
The 2-methoxy sulfonyl propenoic acid methyl ester may be obtained from the 
filtrate by the method described in (c). 
EXAMPLE 2 (Comparison Example) 
154 g of sulfur trioxide are added dropwise over a period of 40 minutes to 
180 g of acrylic acid methyl ester stabilised with 2 g of hydroquinone, an 
increase in temperature to 55.degree. C. being allowed. The crude mixture 
accumulating is distilled entirely from a receiver with a short Vigreux 
column in between in such a way that fractions are separated off under an 
adjusted pressure of from 0.1 to 1.0 mbar and at temperatures increasing 
from 60.degree. C. to 180.degree. C. 26 g of a colourless liquid 
consisting of acrylic acid methyl ester and dimethyl sulfate initially 
distill over at 60.degree. to 100.degree. C. with vigorous foaming of the 
mixture initially introduced. Thereafter only a fraction distilling over 
at 108.degree. to 112.degree. C. can be separated off. Small quantities of 
a colourless oil identified by spectroscopy as 2-methoxy sulfonyl 
propenoic acid methyl ester are obtained. 
Yield: 27 g (8.1% by weight, based on the components used, methyl acrylate 
and SO.sub.3). 
EXAMPLES 3 to 11 
The Examples listed in the following Table represent possible variants of 
the process according to the invention based on changes to important 
parameters of the process and on the use of different ester components. 
The procedure is the same as described in Example 1. 
__________________________________________________________________________ 
Examples 3 4 5 6 7 8 9.sup.1 
10.sup.2 
11 
__________________________________________________________________________ 
Ester component 
R.sub.1 :H 
R.sub.1 :H 
R.sub.1 :H 
R.sub.1 :H 
R.sub.1 :H 
R.sub.1 :H 
R.sub.1 :H 
R.sub.1 CH.sub.3 
R.sub.1 :H 
formula II 
R.sub.2 :CH.sub.3 
R.sub.2 CH.sub.3 
R.sub.2 :CH.sub.3 
R.sub.2 :CH.sub.3 
R.sub.2 :CH.sub.3 
R.sub.2 :CH.sub.3 
R.sub.2 :CH.sub.3 
R.sub.2 :CH.sub.3 
R.sub.2 :C.sub.2 
H.sub.5 
Molar ratio 
1/0.65 
1/1 1/1.6 
1/1 1/1 1/1 1/1 1/1 1/1 
ester:SO.sub.3 
Process parameters 
after addition of 
the SO.sub.3 
Temperature [.degree.C.] 
100 100 100 100 80 150 100 100 100 
Time [hours] 
1.0 0.5 1.0 5.0 1.0 3.0 2.0 2.0 2.0 
Yield of crude 
34.0 63.0 
47.0 59.0 46.0 64.0 61.0 45.0 40.0 
mixture.sup.3 
(after thin-layer 
evaporation) 
[% by weight] 
Yield of sulfonic.sup.4 
32.0 57.0 
55.0 44.0 41.0 50.0 57.0 38.0 34.0 
acid 
(calculated from 
percentage in the 
crude mixture) 
[mole percent] 
__________________________________________________________________________ 
.sup.1 SO.sub.3 added in the presence of methylene 
.sup.2 The sulfonic acid formed during the reaction and also the sulfonic 
acid ester are present in the form of a cis/trans-isomer mixture. 
Separation was not possible. 
.sup.3 The values indicated are based on the quantity by weight of the 
starting components 
.sup.4 The yields quoted in mole percent are based on the 
.alpha.,unsaturated carboxylic acid esters used. 
EXAMPLE 12 
Preparation of the magnesium salt of 2-sulfopropenoic acid methyl ester 
2 g of magnesium oxide are stirred at room temperature into 16.6 g of 
2-sulfopropenoic acid methyl ester dissolved in 30 g of acetonitrile. The 
white solid obtained after 4 hours is separated off by filtration and 
washed with acetonitrile, giving a salt corresponding to the following 
formula: 
##STR3## 
in a yield of 17.7 g (100%, based on the sulfonic acid used). 
.sup.1 H-NMR-spectrum (in D.sub.2 o): .delta.3.85 (s), 6.65 (d) ppm 
EXAMPLE 13 
Preparation of the zinc salt of 2-sulfopropenoic acid methyl ester: 
16.6 g of 2-sulfopropenoic acid methyl ester dissolved in 30 g of 
acetonitrile and 4.1 g of zinc oxide are reacted with stirring at 
15.degree. C. The white solid formed after 5 hours is separated off by 
filtration and washed with acetonitrile, giving a salt corresponding to 
the following formula: 
##STR4## 
in a yield of 18.8 g (95%, based on the sulfonic acid used). 
.sup.1 H-NMR-spectrum (in D.sub.2 o): .delta.3.85 (s), 6.65 (d) ppm 
EXAMPLE 14 
Reaction of acrylic acid methyl ester, SO.sub.3 and dimethyl sulfate. 
235 g of liquid sulfur trioxide are stirred at 0.degree. to 10.degree. C. 
into 253 g of acrylic acid methyl ester stabilised with 2 g of 
hydroquinone, a gentle stream of an inert gas being simultaneously 
introduced. The reaction mixture is left to come to room temperature, 
followed by the rapid addition of 740 g of dimethyl sulfate. After the 
mixture has been heated for 3 hours to 160.degree. C., 480 g of readily 
volatile constituents, predominantly dimethyl sulfate, are distilled off 
in vacuo. The crude mixture is then introduced into a thin-layer 
evaporator under the following conditions: 
______________________________________ 
Temperature of the heating jacket: 
145.degree. C. 
Pressure adjusted: 0.5 to 1.0 mbar 
Throughput: 1.0 kg/m.sub.2 h 
A colourless oil is obtained. 
______________________________________ 
Yield: 598 g. 
A product ratio of 20% of 2-sulfopropenoic acid methyl ester to 80% of 
2-methoxy sulfonyl propenoic acid methyl ester is established by 
NMR-spectroscopy. The product mixture is purified and separated in the 
same way as described in Example 1. 
Yield: 205 g of 2-methoxy sulfonyl propenoic acid methyl ester (42% by 
weight, based on the components used, methyl acrylate and SO.sub.3).