Ti/SiO_2催化H_2O_2氧化苯甲醇制苯甲醛反应机理的理论研究

采用密度泛函理论B3LYP方法研究了非贵金属Ti催化H2O2氧化苯甲醇为苯甲醛的反应机理.考察了6条可能的反应途径,优化得到了各个途径的过渡态和中间体结构,计算了气相和液相中的反应势垒.结果表明,无催化剂时,H2O2氧化苯甲醇的反应途径具有非常高的反应势垒,反应不能进行;以Ti/SiO2为催化剂时,标题反应在乙腈溶液中的反应势垒为123.8kJ/mol,反应可在约353K下发生.结果还表明,标题反应在极性较大的溶剂中有较高的反应势垒,而在气相或者极性较小的溶剂中的反应势垒较低.

Theoretical Study on the Mechanism of Benzyl Alcohol Oxidation to Benzaldehyde Catalyzed by Ti/SiO2

The mechanism of benzyl alcohol oxidation to benzaldehyde catalyzed by Ti/SiO2 in different solvents was studied by the density function theory B3LYP method.Total six possible reaction pathways and the corresponding optimal structures of reactants,transition states,intermediates,and products were located at the B3LYP/6-31G level of theory.The reaction barriers were then calculated at the B3LYP/6-311++G(d,p) level of theory both in gas phase and in solvents.The calculation results show that a very high reaction barrier exists for the pathways where no catalyst is involved,suggesting that the oxidation cannot occur,while when Ti/SiO2 is involved,a reaction barrier about 123.8 kJ/mol is found for that in the acetonitrile solvent,indicating that the oxidation of benzyl alcohol by H2O2 to benzyl aldehyde can happen at about 353 K in the acetonitrile solvent.It is also found that the title reaction has a relative lower barrier in non-polar or low-polar solvent but relative higher barrier in a high-polar solvent.