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在pH7.0~9.0和25℃下,用分光光度法研究了双子阳离子表面活性剂(16-2-16,2Br-)胶束及其相应的普通阳离子表面活性剂CTAB胶束对羧酸酯(对-硝基苯基α-吡啶甲酸酯(PNPP)和对-硝基苯基乙酸酯(PNPA))水解的催化作用.用胶束催化的相分离模型处理实验数据,得到了相关常数KS和km.结果表明:(1)用胶束催化相分离模型处理双子阳离子表面活性剂胶束催化反应是合理的;(2)在相同的反应条件下,双子阳离子表面活性剂(16-2-16,2Br-)胶束比CTAB胶束能更有效的催化羧酸酯水解反应;(3)PNPP和PNPA水解反应的表观速率常数kobsd及其在胶束相中的反应速率常数km均随反应体系pH增大而增加,水解剪切反应为酸-碱催化反应过程.
The effect of gemini cationic surfactant (16-2-16,2Br-) micelles and their corresponding common cationic surfactants CTAB micelles on carboxylate esterification was studied spectrophotometrically at pH 7.0-9.0 and 25 ℃. (P-nitrophenyl-α-picolinate (PNPP) and p-nitrophenyl acetate (PNPA)). The experimental data were obtained by the micellar catalysis phase separation model and the correlation Constants KS and km. The results show that: (1) It is reasonable to use micellar catalytic phase separation model to deal with micellar catalysis of gemini cationic surfactant; (2) Under the same reaction conditions, gemini cationic surfactant (16- 2-16,2Br-) micelles catalyze the hydrolysis of carboxylic acid esters more efficiently than CTAB micelles. (3) The apparent rate constant kobsd of PNPP and PNPA hydrolysis and its reaction rate constant in micelle phase km All increased with the increase of pH of the reaction system. The hydrolytic cleavage reaction was an acid-base catalysis reaction.