WO1999028294A1 - Method for making methacrylic thioesters - Google Patents

Abstract

The invention concerns a method for making methacrylic thioesters of formula (I) in which R represents a primary linear alkyl radical containing 3 to 12 carbon atoms, characterised in that it consists in reacting methacrylic anhydride with a mercaptan of formula RSH, R being as defined above, the reaction being advantageously carried out in the presence of a cationic ion exchanger resin in H<+> form as catalyst.

Description

 PROCESS FOR THE MANUFACTURE OF METHACRYLIC THIOESTERS

The present invention relates to a process for the manufacture of methacrylic thioesters of general formula (I):

H2C O \\ // C — C / \ (I)

CHÇ S — R

in which R represents a linear primary alkyl radical containing from 3 to 12 carbon atoms.

Until now, these thioesters were mainly prepared from mercaptate: RSM (M = K, Na) and methacryloyl chloride: H-, C = C (CH ₃ ) C0C1. Methacryloyl chloride is, however, a delicate product to handle: it tends to form dimers; it is a tear gas product and it requires processing at low temperature. This is why, from an industrial point of view, it is preferable to react methacrylic anhydride with mercaptan, thereby producing, at the same time as the desired thioester, methacrylic acid, which can be recycled to the synthesis of methacrylic anhydride. In US patent US Pat. No. 5,384,379, a synthetic route is described starting from methacrylic anhydride and an alkali metal salt of the corresponding alkylthiol in solvent medium (such as methyl t-butyl ether) . This method was reproduced in the laboratory: decantation problems were encountered, accompanied by an average yield, mainly due to insufficient conversion of the starting materials.

The Depositing Company has developed an alternative route which overcomes all the drawbacks described above.

The subject of the present invention is in fact a process for the manufacture of a thioester of formula (I) such as defined above, characterized in that methacrylic anhydride is reacted with a mercaptan of formula RSH, R being as defined above.

According to a preferred embodiment, the reaction is carried out in the presence of an cation exchange resin in H form as catalyst.

The cationic resin is then advantageously used at a rate of 2 to 15% by weight relative to the total charge. Resins of interest are those obtained by sulfonating a copolymer of styrene and divinylbenzene.

Furthermore, the reaction according to the invention is generally carried out under a nitrogen atmosphere, at a temperature of 40 to 100 ° C, in particular from 50 to 70 ° C, and preferably in the absence of solvent.

The molar ratio of methacrylic anhydride to mercaptan RSH is preferably between 0.5 and 2, more particularly between 0.8 and 1.2.

The methacrylic anhydride is advantageously used by being stabilized by a stabilizer such as bis tert-butyl hydroxytoluene.

The following example illustrates the present invention without however limiting its scope.

EXAMPLE

50.1 g (1 equivalent) of methacrylic anhydride stabilized by 5000 are introduced into a 250 ml reactor equipped with a condenser, an addition funnel, a nitrogen sparge and an extension tube for sampling. ppm of bis tert-butyl hydroxytoluene, with 3.4 g of a cationic resin in H ⁺ form sold under the brand "AMBERLYST 15".

32.2 g of n-butanethiol (1.1 equivalent) are added dropwise, with stirring and bubbling with nitrogen at 60 ° C. (temperature obtained using a heated water bath). After 3 hours of reaction, all the methacrylic anhydride has disappeared. The reaction mixture is cooled, then filtered to recover the resins.

The filtrate, stabilized with 5000 ppm of copper dibutyldithiocarbamate, is distilled under reduced pressure to obtain thiobutyl methacrylate with 70% yield and a CPG purity greater than 98%.

Claims

1 - Process for the manufacture of methacrylic thioesters of formula (I):

in which R represents a linear primary alkyl radical containing from 3 to 12 carbon atoms, characterized in that methacrylic anhydride is reacted with a mercaptan of formula RSH, R being as defined above. 2 - Process according to claim 1, characterized in that the reaction is carried out in the presence of a cationic ion exchange resin in H form as a catalyst. 3 - Process according to claim 2, characterized in that the cationic resin is chosen from those obtained by sulfonating a copolymer of styrene and divinylbenzene. 4 - Method according to one of claims 2 and 3, characterized in that the cationic resin is used in an amount of 2 to 15% by weight relative to the total charge. 5 - Method according to one of claims 1 to 4, characterized in that the reaction is carried out under a nitrogen atmosphere at a temperature of 40 to 100 ° C, in particular from 50 to 70 ° C. 6 - Method according to one of claims 1 to 5, characterized in that the molar ratio of methacrylic anhydride to mercaptan RSH is between 0.5 and 2, in particular between 0.8 and 1.2. 7 - Method according to one of claims 1 to 6, characterized in that the reaction is carried out in 1 ^• absence of solvent. 8 - Method according to one of claims 1 to 7, characterized in that the methacrylic anhydride is used while being stabilized by a stabilizer such as bis tert-butyl hydroxytoluene.