苯胺聚合反应中重铬酸盐的还原机理

应用红外光谱、X射线衍射、元素分析、焙烧实验等手段证明,重铬酸盐氧化聚合苯胺的产物是聚苯胺/Cr(OH)3复合物.这不同于文献中的一般观念.随反应介质酸性的增强,复合物中Cr(OH)3的含量从38.4％逐渐下降到1.3％.强酸性介质有利于重铬酸盐还原为易溶的Cr3＋,弱酸性介质有利于重铬酸盐还原为难溶的Cr(OH)3.基于该实验事实,提出了重铬酸盐还原过程的两步机理.

Mechanism for the Reduction of Dichromate in the Polymerization of Aniline

The product of oxidative polymerization of aniline using dichromate as oxidant was proved to be polyaniline/Cr(OH)3 composites by methods of IR, XRD, elemental analysis and pyrolysis experiment.This conclusion is different from the idea in the literature that when aniline is oxidized the product of the reduction of dichromate is soluble Cr3＋ that would not remain in the polyaniline product.The Cr(OH)3 content in the composites decreased from 38.4％ to 1.3％ along with the growth of solution acidity,as shown in Fig.1.The reduction Cr2O72－ of was supposed to be composed of two steps:the reduction of Cr2O72－ to Cr(OH)3 followed by the dissolution of Cr(OH)3 into acidic solution.The standard Gibbs free energy of the first step was calculated to be －582.11 kJ•mol－1,which is a very large negative value.The second step being the adsorption of polyaniline onto Cr(OH)3 retards its dissolution and leads to the formation of polyaniline/Cr(OH)3 composites.