Oxidation of methylbenzenes by ozone in the liquid phase in the presence of a manganese(II) bromide catalyst

In this study, the selective oxidation of methylbenzenes by ozone in the liquid phase was investigated. It was established that the ozonation of methylbenzenes in acetic acid in the presence of Mn(II) acetate and NaBr is ineffective, as the reaction predominantly leads to the destruction of the aromatic system. The use of the "CH3COOH–H2SO4" system is shown to direct the process towards the oxidation of the methyl group, significantly increasing the rate and selectivity of the process. A notable feature of manganese(II) bromide catalysis is the absence of substantial amounts of aromatic alcohols among the oxidation products of methylbenzenes. The process proceeds through the formation of aldehydes as intermediate reaction products. The main stages of the catalytic cycle were examined, and the kinetic parameters of the interaction between O3 and the manganese(II) bromide catalyst, as well as between Mn3+ and methylarenes in the presence of sodium bromide, were established. A catalytic mechanism is proposed, wherein ozone reacts with the Mn(II)Br– complex, and selective oxidation occurs through the interaction of the substrate with Mn2+Br•. The maximum oxidation selectivity is achieved at a catalyst component ratio of [Br–]/[Mn2+]=1.1.