Purification of Thioglycolic Acid and Synthesis of Ammonium Thioglycolate
|Keywords||Thioglycolic acid Ammonium thioglycolate Extraction Purified by distillation|
Thioglycolic acid (TGA) is an important chemical raw material, widely used in medicine, analysis, beauty salons, PVC production field, at home and abroad, the growing consumption. Although domestic production of TGA has already begun, but the process backward, especially high purity TGA Production inadequacy, still need to import large quantities of products. In response to this situation, this combination of electricity in Bunte salt to restore production TGA technology based on further TGA purification process, the academic significance and prospects for engineering applications. TGA synthesis process byproducts dithiodimorpholine acid (DTDGA), study of the purification process of the TGA, simultaneously establishing of TGA and DTDGA, fast, accurate analysis method. Zinc mercury Qi efficiently DTDGA reduced to the characteristics of the TGA, using home-made zinc amalgam reduction column, to combined the iodometric method establishes a quantitative analysis method of DTDGA, measurement results, the maximum relative standard deviation of 0.37%, the average rate of 100.58% of the recoveries. The method is accurate, simple operation, has good repeatability and precision to meet the analytical requirements in the production process of purification. Extraction separation is an important part of the process of purification of thioglycolic acid, and is directly related to the level of the ease and cost of further purification. Herein by several representative extractants the distribution coefficient and the distillation results of the comparison, selected ether as the TGA extraction agent, is determined on this basis, the preferred extraction conditions: oil and water compared to 1:2, and extracted four times, in this condition, to TGA extraction rate of 99.02%. TGA itself relatively high boiling point, and heat is easily oxidized or self-esterification, using ordinary distillation operation for purification, the purity of the product is low, the loss rate. This paper uses orthogonal experimental design investigated the TGA's own heat-sensitive, the sulfate content is the most important factor to affect the TGA the loss rate, the higher the content the greater the loss rate; temperature and time as a secondary factor affecting the rate of loss, as the temperature the raising and the extension of the time, the TGA loss rate increases. On this basis, it is determined more suitable TGA purification process: first with w (NaOH) = 20% of the aqueous solution, maintaining the water and oil than 1:25, the organic phase was extracted and washed, and then distilling the organic phase. The distillation Early atmospheric pressure, at low temperature (35 ° C to 80 ° C) recovery ether, and then switch to a rotary evaporator and distilled under reduced pressure, the control within the operation time 150min, the degree of vacuum of 0.099Mpa tower reactor temperature below 147 ° C, the collected fractions can be obtained mass fraction of 95.87% of the TGA product, yield 71.05%. To expand the uses of the TGA product its downstream product ammonium thioglycolate synthesis process, a preliminary study, synthetic optimum conditions: in ether extraction TGA organic phase, added dropwise mass fraction of 30% of concentrated aqueous ammonia, the control NH 3 and the TGA molar ratio 1.16:1 reaction was carried out, separating the lower reddish aqueous phase solution, i.e., ammonium thioglycolate, purity of 54.25%, the yield of the product was 92.9%. Control the vacuum degree 0.095MPa, temperature 30 ℃, low purity products further distillation after removal of low-boiling materials, ammonium thioglycolate product purity of 74.27%, the distillation yield of 92.57%.