Dawson结构钼钒磷杂多化合物催化乙苯选择氧化的活性研究

Selective Oxidation of Ethylbenzene over Molybdovanadophophoric Compounds with Dawson Structure

合成了系列Ｄａｗｓｏｎ结构钼钒磷杂多化合物，并将其用于乙苯的过氧化氢选择氧化研究．实验发现，对于该类反应，其最佳的工艺条件为：乙苯２．５ｍｍｏｌ、催化剂０．０２ｍｍｏｌ、溶剂１０ｍＬ、３０％Ｈ２Ｏ２２．５ｍｍｏｌ．乙酸为该类反应的最佳溶剂，而在与之性质相近的甲酸中则活性极低，即该反应过程与过氧酸的存在无关．讨论了反应过程中催化剂的状态及活性中间体，并运用ＵＶ－Ｖｉｓ、ＥＳＲ等手段进行了表征．实验结果表明，反应过程中处于乙酸介质中的杂多化合物不会发生降解，反应的活性中心为Ｐ－Ｍｏ－Ｖ－ｐｅｒｏｘｏ中间体．

A series of heteropoly compounds with Dawson structrue were synthesized and were used to catalyze the selective oxidation of ethylbenzene with hydrogen peroxide. The reaction parameters were investigated in deteil. The results indicated that the catalysts had excellent catalytic activity for the reaction. The optimal conditions of the reaction are that ethylbenzene is 2.5 mmol, catalyst is 0.02 mmol, solvent is 10 mL and 30% H 2O 2 is 2.5 mmol. It should be emphasized that the possible role of the peracid appears to be somewhat ambiguous. Although acetic acid is the preferred solvent indicating that peracetic acid may be the preferred primary oxidant, but when formic acid was used as solvent, where performic acid is easily formed, there was practically no reaction. In solvents such as acetonitrile and sulfolane there were significant conversions. The fact that the heteropoly acids with Dawson structure without vanadium do not significantly decompose hydrogen peroxide or oxidize ethylbenzene, clearly indicates that the reaction must proceed by homolytic cleavage at the vanadium atom. So V is considered to be the active component for the reaction. The intermediate material of the reaction is the P Mo V peroxo identified by means of UV Vis spectra and ESR.