提高硫氢化钠法合成巯基乙酸选择性的方法

来源期刊：中南大学学报(自然科学版)2002年第2期

论文作者：刘广义 冯其明 钟宏

文章页码：153 - 156

关键词：巯基乙酸;硫氢化钠法;热力学;选择性

Key words：thioglycolic acid; sodium hydrosulphide; thermodynamics; selectivity

摘    要：副反应多导致硫氢化钠法生产巯基乙酸过程中巯基乙酸收率低.利用热力学理论研究了发生这些副反应的原因,并提出予以防止的工艺条件,以提高硫氢化钠法的选择性.研究结果表明:HS^-,S^2-和-SCH2COO^-中硫原子取代氯乙酸中氯原子的反应是能自发进行的不可逆反应;降低溶液pH值可减少溶液中S^2-和-SCH₂COO^-的量,提高硫氢化钠法合成巯基乙酸选择性;增大反应体系中硫化氢气体的分压,有助于降低溶液pH值,并可提高反应产物巯基乙酸的收率与浓度;硫氢化钠法合成巯基乙酸的适宜工艺条件为:氯乙酸钠和硫氢化钠的量比为1∶(1.2~1.3),反应压力为0.8 MPa,反应温度为(55±1)℃,反应时间为12 min,此时巯基乙酸的收率在91%以上.

Abstract: The main matter that causes the lowratio of yield in synthesis of thioglycolic acid with sodiumhydrosulphide is that it has many auxiliary reactions during reaction course. This paper studies the causes that cause these side-reactions with thermodynamic methods, using relevant conditions of technology to prevent them from happening, thus improving the selectivity of synthesis with sodium hydrosulphide methods. The results show that: reaction of substituting sulfur atom in HS^-, S^2-or　-SCH2COO^-for chlorine atom in chloroactic acid is an irreversible one with spontaneity, and it can lessen the amount of S^2-and　-SCH₂COO^-in solution and improve selectivity of synthesis of HSCH₂COOHwithNaHS by depressing value of pH, and it can be helpful for depressing the value of pH in the aqueous solution and enhance the yield ratio and the concentration of thioglycolic acidwith higher pressure. The yield ratio of thioglycolic acid is over 91%under suchoptimal conditions as reaction temperature (55±1)℃, pressure 0.8MPa and time 12 min, withmolarreac-tantn(ClCH₂COONa)∶n(NaHS) ratio of 1∶(1.2~1.3).