A Novel Production Method of Methyl Thioglycolate

Methyl thioglycolate, also known as methyl thioglycolate, is an intermediate with a wide range of uses in the synthesis of medicines, pesticides, food and tobacco flavors. At present, the production and synthesis methods of methyl thioglycolic acid mainly use thioglycolic acid and methanol as raw materials, and use H2SO4, solid super acid, etc. as catalysts for esterification synthesis.

Background technique

There are many problems such as low yield, long reaction time, equipment corrosion and serious environmental pollution. Chloride-based catalysts are also used to catalyze the synthesis of methyl thioglycolate. These methods also have the disadvantages of low yield and high cost, which greatly limit their wide application. Chinese patent CN102477006A discloses a method for synthesizing methyl thioglycolate. The method uses methyl chloroacetate as a raw material to synthesize through the steps of salt formation, acidification, extraction, and separation. The process has the disadvantages of cumbersome process and high energy consumption.Chinese patent CN101580485A discloses a method for producing methyl thioglycolate. The method uses 70-96% thioglycolic acid and methanol as raw materials, and uses p-toluenesulfonic acid as the activator to carry out the esterification reaction. Although this patent reduces the main raw materials The purity of thioglycolic acid, but thioglycolic acid is extremely unstable. When the content is greater than 70%, it is prone to polymerization reaction, which will reduce the yield of the finished product.[1]

Details of the synthesis method

Thioglycolic acid is prone to oxidation reaction in the air, and when the concentration is high, polymerization reaction is prone to occur. Therefore, the ideal synthesis method of methyl thioglycolic acid is carried out at a low concentration, but low-concentration aqueous thioglycolic acid does not Conducive to the progress of the esterification reaction, high-temperature distillation separation can easily accelerate the occurrence of side reactions, thereby reducing the yield of methyl thioglycolate. The content of thioglycolic acid in the thioglycolic acid aqueous solution produced by the sodium hydrosulfide method is usually 10-15%, and a large amount of high-salt organic wastewater will be produced. This brings certain difficulties to the preparation of methyl thioglycolate.Therefore, finding a production process of methyl thioglycolate with simple production process, high yield, easy treatment of extraction tail wastewater, and low cost is the key to solving the current constraints on methyl thioglycolate products.

The purpose of the present invention is to provide a method for producing methyl thioglycolic acid with a simple process, which integrates the separation of thioglycolic acid, the treatment of the extraction tailing wastewater, and the esterification reaction, which greatly simplifies the production process and can Effectively separate water and solid salt, and the content of organic matter in water and solid salt is low, the separated water can be reused, and solid salt can also be used as a by-product, which greatly reduces the side reactions in the production process of methyl thioglycolate , The methyl thioglycolate separated by the reaction can be used as a product after simple distillation or without distillation, which improves the yield and reduces the production cost.The method for producing methyl thioglycolate based on the sodium hydrosulfide method of the present invention includes the following steps:(1)Take the thioglycolic acid acidified liquid synthesized by the sodium hydrosulfide method as the raw material, distill and concentrate, and centrifuge to separate the NaCl solid to obtain the distilled concentrated liquid;(2)Add CaCl2 to the distillation concentrate of step (1), continue to precipitate NaCl solids, and separate the precipitated NaCl solids; CaCl2 added in the distillation concentrates and water in the distillation concentrates form molten salt hydrates to obtain molten salt hydrates的distilled concentrate;(3)To the distillation concentrate containing molten salt hydrate, catalyst and methanol are added, and the molten salt hydrate is used as the reaction medium to carry out the esterification reaction;(4)After the esterification reaction is completed, the temperature is lowered, the sedimentation layer is separated, and the upper organic phase is methyl thioglycolate.

References

[1]SHANDONG ZHANHUA JINJIALI CHEMICAL TECH - CN112538036, 2021, A