有机电解质在胶束催化聚苯乙烯氯甲基化反应中的作用

在实施聚苯乙烯氯甲基化反应的胶束催化体系中加入四丁基溴化铵 ((Bu)₄NBr, TBAB), 研究了有机电解质TBAB对胶束催化反应的影响规律. 实验结果表明, 在非离子表面活性剂NP-10及阴离子表面活性剂SDS的胶束催化体系中, TBAB的加入使聚苯乙烯氯甲基化反应的速率明显增大, 前者尤为突出；而在阳离子表面活性剂CTAB的胶束催化体系中, TBAB的加入几乎对反应速率无促进作用. 这种结果一方面归因于加入电解质TBAB会降低SDS的临界胶束浓度, 从而增强对聚苯乙烯四氯化碳溶液的增溶能力；更主要的原因是TBAB的丁基与表面活性剂碳氢链间的疏水相互作用会使季铵离子(Bu)₄N⁺嵌入SDS的胶束之中, 结合到NP-10的胶束表面, 使SDS胶束的阴离子头基对亲核取代反应(控制步骤)的禁阻作用得以减缓, 使NP-10的胶束表面携带了正电荷, 显著促进亲核取代反应的进行, 而对于CTAB的胶束, 由于静电排斥作用, 季铵离子(Bu)₄N⁺不能接近CTAB的胶束, 故TBAB的加入对聚苯乙烯氯甲基化反应不产生作用.

Effect of Organic Electrolyte on Chloromethylation of Polystyrene in Micellar Catalytic System

Organic electrolyte tetrabutyl ammonium bromide ((Bu)4NBr, TBAB) was added into micellar catalysis system in which chloromethylation reaction of polystyrene was carried out, and the effect of TBAB on the catalytic reaction was investigated. The experiment results show that the adding of TBAB speeds up obviously the chloromethylation reaction of polystyrene in the micellar catalytic systems in which nonionic surfactant NP-10 and anionic surfactant SDS are used, especially in the system in which non-ionic surfactant NP-10 is used the acceleration is more distinct. On the contrary, in the micellar catalytic systems in which cationic surfactant CTAB is used, TBAB hardly influences the reaction rate. On one hand the reason for this may attribute to the decrease of critical micelle concentration of SDS and the increase of solubilization of polystyrene in the micellar solution because of adding electrolyte TBAB, on the other hand, a more primary reason is that organic cation (Bu)4N of TBAB may be embedded into micelles due to the synergistic effect of electrostatic attraction and hydrophobic interaction between butyl groups and the hydrocarbon chains of SDS , so that the inhibiting effect of anionic head groups of SDS for the nucleophilic substitution reaction that is a controlling step is weakened. Under hydrophobic interaction, organic cation (Bu)4N of TBAB may also be combined on the surface of NP-10 micelles, so that the surface of NP-10 micelles charged positively accelerates distinctly the nucleophilic substitution reaction. For CTAB system, the cation (Bu)4N can not be closed to the micelles of CTAB owing to electrostatic repellence, so the adding of TBAB can not speed up the rate of chloromethylation reaction of polystyrene.