The mercaptocarboxylic acid (mercaptopropionic acid) is suitable as a crosslinking agent for an acrylate polymer and a curing agent for an epoxy resin, and is used in a synthetic resin such as an optical lens. In particular, this is carried out by esterification with an alcohol, whereby a plurality of carboxylate compounds having a thiol group can be synthesized.
U.S. Patent No. 5,048,432 discloses the addition of hydrogen sulfide to an unsaturated compound such as methacrylate or acrylic acid to prepare 3-mercaptopropionic acid. When hydrogen sulfide is added, a basic catalyst selected from magnesium oxide and The basic anion exchange resin is carried out in an environment. Among them, a resin having a tertiary amine or a quaternary ammonium hydroxide as a functional group is selected as the resin. However, this method has a disadvantage that the process is very complicated because it is subjected to a step of converting hydrogen sulfide to acrylic acid to convert to 3-mercaptopropionic acid (HSCH2CH2COOH).
A method for synthesizing 3-mercaptopropionic acid based on an addition reaction of acrylic acid and hydrogen sulfide is disclosed in Korean Patent Laid-Open Publication No. 1998-024803. It is carried out in the presence of a solid support having a hydrazine functional group which does not contain hydrogen directly bonded to a nitrogen atom, similarly to the above-mentioned U.S. Patent No. 5,008,432.
In Korean Patent Publication No. 1998-024803, 3-mercaptopropionic acid is synthesized at a high conversion ratio and selectivity in the presence of a solid support having a basic functional group in accordance with an addition reaction of acrylic acid and hydrogen sulfide. However, there are still disadvantages in that the preparation process is complicated.
A method for converting thiodipropionic acid (dimer) to 3-sulfopropionate (polymer) is disclosed in Chinese Patent Publication No. CN 101125827A. This method has a problem that the composition and by-products of the product are not good under such conditions because of the relatively severe reaction conditions required for the acidic treatment based on iron and strong acid.
Further, a preparation method of 3-sulfonypropionitrile and 3-mercaptopropionic acid which is easy to handle is disclosed in Korean Patent No. 10-0350658. In the method of the present invention, thiomalononitrile is used as a starting material, and the above thiomalononitrile is reacted with a basic hydrosulfide (hydrogen sulfide basic) in the presence of an alkali hydroxide. A high yield of 3-sulfhydrylpropionitrile is produced. As a result, the obtained nitrile and the strong acid are subjected to an acidification treatment or a saponification treatment to obtain a preferable mercaptopropionic acid in a high yield. The present invention can obtain a high yield of 3-sulfhydrylpropionitrile and 3-mercaptopropionic acid in which no dithiomalononitrile or dithiodipropionic acid is mixed. However, this method requires the following steps: using acrylonitrile and sodium hydrosulfide to form thiomalononitrile (dimer), in which sodium hydrosulfide and caustic soda are added to form sodium 2-cyanoethanethiol (single) After the reaction, the sodium 2-cyanoethanethiolate is refluxed under strong acid (hydrochloric acid) to convert the nitrile to a carboxylic acid group. Therefore, the reaction step is complicated and difficult to prepare. Since the nitrile is converted into a carboxylic acid under the condition of hydrochloric acid which is not refluxed by separating 3-pyridylpropionitrile, the yield of the product is low, and the 3-sulfopropionitrile is not reacted. Excess problem.
In order to solve such a conventional problem, Korean Patent Publication No. 10-2013-0087447 provides that it is possible to obtain 3 from thiomalononitrile without using sodium hydrosulfide and caustic soda in thiomalononitrile (dimer). A method for producing 3-mercaptopropionic acid in the step of sulfhydrylpropionitrile. In this method, after reacting acrylonitrile with sodium hydrosulfide to obtain sodium 2-cyanoethanethiol, neutralizing with an acid, layer separation, obtaining 3-sulfhydrylpropionitrile, followed by addition of acid, reflux, conversion It is 3-mercaptopropionic acid, followed by distillation under reduced pressure to obtain 3-mercaptopropionic acid. This method is simple in process, economical, and yield superior to the conventional method from the viewpoint of preparation of 3-sodium pyrimonitrile having a small production of dimer. However, since the acid is added after conversion to 3-mercaptopropionitrile, it is converted to 3-mercaptopropionic acid, and a considerable yield loss and decomposition of the product due to high-temperature treatment are obtained in the process of performing vacuum distillation. Therefore, there is a need for an improved solution that not only distills the product under reduced pressure at a lower temperature but also improves the yield.