Catalysis by onium salts on the monochromate oxidation of benzhydrols in non-polar media — A kinetic study

Kinetic studies on the oxidation of benzhydrols with phase transferred monochromate in non-polar media have been carried out using tricaprylmethylammonium chloride, tetrabutylammonium bromide and tetrabutylphosphonium bromide as phase transfer catalysts (PTC). The oxidation has been found to be selective with quantitative formation of benzophenone. The reaction is first order in the [oxidant] as well as the [substrate]. The specific rates and activation parameters have been evaluated. The oxidation takes place at fairly low activation energy with all the catalysts employed. Rates of oxidation decrease with increase in the dielectric constant of the non-polar media. A mechanism involving formation of a Huckel type transition state in the rate determining step is quite probable.