KINETICS AND MECHANISM OF CATALYTIC HYDROXYLATION OF PHENOL BY HYDROGEN-PEROXIDE .4. REGULARITIES OF ACTIVE CATALYST FORMATION

The processes occurring at the initial stage of phenol oxidation by pe roxide catalyzed by FeSO4 are investigated. The duration of the stage of selective benzoquinone formation is found to be primarily a functio n of the pH of the medium. In the presence of the monohydrate of terva lent iron and catechol (CT) in the reaction solution, a [Fe2+(OH).CT] complex that is active in hydroxylation is rapidly formed, which resul ts in a complete change of the reaction pathway. The main regularities of this complex formation are established. A hypothesis on the nature of the catalyst species responsible for each pathway is put forward. Taking into account the UV and ESR spectroscopic data and the results of photochemical phenol oxidation by hydrogen peroxide, the likely mec hanism of the initial stage of phenol oxidation by peroxide is discuss ed. The effect of cerium sulfate additives on the duration of the indu ction period and on the hydroxylation rate is explained.