Development on Selective Oxidation of Toluene in Homogeneous Liquid Phase System

The homogeneous catalysts for selective oxidation of toluene in liquid phase can be divided into five types: transition metal salt,heteropoly compound,transition metal complex,nonmetallic compound and combined catalyst.The reaction conditions,results and mechanisms were summarized.The conditions were mild,and high selectivities were obtained for benzaldehyde and benzayl alcohol,when the heteropoly compound or the metalloporphyrin was used.Usually,the combined catalyst displayed better catalytic properties,and the selectivities for products were depended on the metal catalysts components,when the catalysts were composed of nonmetallic compounds and transition metal complexes.In addition,the reaction mechanism focusing on the side-chain oxidation of toluene was discussed.It is a significant direction to develop more efficient composite catalysts and processes for crude toluene oxidation in the future.