锌催化电还原脱氯合成2,3,5,6-四氯吡啶：反应机理和工艺优化

Electrochemical reduction of dechlorination of pentachloropyridine to 2,3,5,6-tetrachloropyridine over zinc-based catalyst: reaction mechanism and process optimization

采用循环伏安法和恒电位电解法,探讨了含有ZnCl_2的乙睛水混合溶液中五氯吡啶(PCP)在不锈钢阴极表面电还原脱氯生成2,3,5,6-四氯吡啶(2,3,5,6-TCP)的反应机理;采用恒电流电解法对该电还原脱氯过程的各种工艺条件进行了优化。结果表明:该体系中PCP电还原脱氯生成2,3,5,6-TCP主要遵循以Zn/Zn^(2+)为氧化还原媒介的间接电还原机理;优化工艺条件下(阴极液含0.025 mol·L^(-1)HCl+15%(体积分数)水+0.2 mol·L^(-1)苯磺酸钠+0.16 mol·L^(-1) ZnCl_2的乙腈溶液;电流密度为1.25 A·dm^(-2)),0.08 mol·L^(-1) PCP能高选择性地脱氯生成2,3,5,6-TCP,2,3,5,6-TCP的收率和电解电流效率分别可达88.7%和59.1%。

The electrochemical dechlorination mechanism of pentachloropyridine（PCP） to 2,3,5,6-tetrachloropyridine（2,3,5,6-TCP） on stainless steel cathodes in an acetonitrile/water mixed solution containing ZnCl_2 was investigated by cyclic voltammetry and constant potential electrolysis methods. Moreover, an optimization of various operating conditions under constant potential electrolysis for the dechlorination process was performed in an H-cell. It showed that indirect electrochemical dechlorination using Zn/Zn2＋ as the redox mediator is the main pathway of PCP to 2,3,5,6-TCP. The 0.08 mol·L^（-1） PCP could be selectively dechlorinated to 2,3,5,6-TCP with 88.7% yield and 59.1% of current efficiency under optimum conditions（catholyte： an acetonitrile solution containing 0.025 mol·L^（-1） HCl, 15%（vol） water, 0.2 mol·L^（-1） sodium benzenesulfonate and 0.16 mol·L^（-1） ZnCl_2, and 1.25 A·dm^（-1）of current density）.