Purification Of Thioglycolic Acid And Synthesis Of Ammonium Thioglycolate

Thioglyolic acid (TGA) which is an important fine chemical material is widely used in pharmacy, analysis, hairdressing and the production of PVC. The consumption of TGA is trending up year by year in and abroad. Though China has begun the synthesis of TGA since long ago, the technique for the synthesis of TGA is still coarse now. Especially the purification of TGA is lack of research. Most of the pure TGA used in China needs to be imported. In order to solve this problem, the purification of TGA was researched systematically on the basis of the Bunte Salt method for the synthesis of TGA and its electrical reduction. The research offered certain academic value and had a promising future in engineering.Dithiodiglyolic acid (DTDGA) was the byproduct of TGA. It was needed that the analysis method for DTDGA should be set up when doing the research of TGA purification. Thus, the reduction of DTDGA into TGA by zinc amalgam and the iodometric titration was utilized in the detection of DTDGA. Using the zinc amalgam reductor made by ourselves, the largest standard deviation for the detection og DTDGA was 0.37 %, and the average recovery rate of the samples was 100.58 %.This method was simple and nice with a good repeatability which satisfied the analysis in the purification of TGA.Extraction was an important unit in TGA purification which directly influence the further purification and the cost of product. Several extractants was compared by the distribution coefficient of TGA and the distillation effect of TGA. Ether was chosen as the extratant of TGA and its optimal operating conditions were as followed: keeping the volume ratio of organic layer and aqueous layer as 1:2, after extracting four times, the extraction percentage of TGA was 99.02 %.TGA was easily oxidated and self-estified under heat, but its boiling point was high. So the ordinary rectification of TGA resulted in low purity and great loss of product. Orthogonal experiments were carried out to investigate the heat sensitivity of TGA. It was found that the content of sulfuric acid in TGA was the most influencing factor, and with its increase the loss of TGA became larger. Temperature and time was the subordinate influencing factors. The loss of TGA increased with the rise of temperature and the lengthen of time.Based on these, the distillation conditions were optimized as followed: The organic layer after extracting should be washed with 20%(weight percent) sodium hydroxide water solution with the volume ratio of the aqueous layer and organic layer as 1:25 before distillation. Then the organic layer was distilled under atmospheric pressure, (35℃～80℃) to recover ether for the first step. Then the residue was vacuum distilled for no more than 150 minutes with a rotary evaporator under the vacuum of 0.099 Mpa, keeping the temperature under 147℃. Then the distillate was collected as the TGA production with the purity of 95.87 % (weight percent) and yield of 71.05%.In order to enlarge the application of TGA, the synthesis of ammonium thioglycolate which belonged to the TGA production series was investigated, and its optimal sythesis conditions were as followed: 30%(weight percent) ammonium hydrate were added dropwise into the organic layer after extracting keeping the molar ratio of ammonium hydrate and TGA as 1.16:1. The under pinky aqueous layer was separated as ammonium thioglycolate production with the purity of 54.25 and the yield of 92.9%. Then the product was further distilled under the vacuum of 0.095 Mpa with temperature no higher than 30℃to let off the volatilized ingredients. The purity of ammonium thioglycolate reached 74.27% and the yield of the distillation was 92.57%.