碘仿电解合成的机理研究

Study on Mechanism of Iodoform Electrosynthesis

采用循环伏安法分别研究了铂电极在 0 .1 mol· L- 1 Na2 CO3+0 .0 5mol· L - 1 KI,0 .1 mol· L - 1Na2 CO3+0 .0 5 mol· L- 1 KI+0 .5mol· L- 1 乙醇 ,0 .1 mol· L- 1 Na2 CO3+0 .0 5 mol· L- 1 KI+0 .5 mol· L- 1丙酮溶液中的电化学行为 ,发现含 I- 体系的阳极氧化反应十分复杂 ,除了 I- 被电氧化为 I2 外 ,同时还发生生成 IO3- 等含碘高价化合物的电氧化反应 ,此外电氧化反应过程中还存在多个后续化学反应 ;电化学阴极还原反应则较为简单。中间产物 IO-的作用非常关键 ,IO-攻击甲基酮中 - CH3与 >C=O之间的 C- C键而生成碘仿 ,碘仿电解合成反应中存在着复杂的竟争反应现象。

The mechanism of iodoform electrosynthesis was investigated for the electrochemical reaction systems: 0.1 mol·L -1 Na 2CO 3+0.05 mol·L -1 KI,0.1 mol·L -1 Na 2CO 3+0.05 mol·L -1 KI+0.5 mol·L -1 alcohol and 0.1 mol·L -1 Na 2CO 3+0.05 mol·L -1 KI+0.5 mol·L -1 acetone. The technique adoped is repetitive triangular potential sweep.The obtained cyclic voltammograms indicates that the anodic reaction is quite complex, in which three anodic oxidation reactions take place. Firstly, iodide ion is oxidized to form iodine.Secondly, the new formed iodine will be electrooxidized further with the formation of iodate. Also iodine, which is formed by electrooxidation, will react with hydrooxyl ion in the basic electrolyte solution and hypoiodite ion is formed. When there is alcohol or acetone present in the solution, IO - will react with alcohol or acetone by chemical redox reaction and iodoform is formed. It was found that iodine could be oxidized to form iodate further by electrooxidation when the potential was polarized to be higher. Compared with electro-oxidation in the cyclic voltammogram ,the electroreduction reaction is relatively simple in which there is only the reduction of iodate ion to form iodine. So both in oxidation and reduction half cycle of potential sweep,iodoform is formed . The mechanism of iodoform formation by electrochemical chemical processes was also analysed in which IO - played particularly important role. The complex competation reactions of IO - took place during the process of iodoform formation. The cyclic voltammogram with different rate of potential sweep identified that the electrochemical reactions taking place on Pt electrode during potential sweep were not simple mass transportation controlled process.