Oxidation of 4­brometylbenzene by ozone in acetic acid

Abstract

The kinetics and the mechanism of ozonation of 4-bromethylbenzene in acetic acid was studied. The constants of the rate of reaction of ozone with 4-bromethylbenzene and 4-bromacetophenone at different temperatures were determined. We showed the possibility of conducting the process not only by the aromatic ring of the substrate in accordance with the Krige mechanism, but also with the formation of 4-bromacetophenone, which will be used when creating new methods of synthesis of oxygen-containing derivatives of ethylbenzene. It was established that oxidation of 4-bromethylbenzene by ozone in acetic acid flows mainly by the aromatic ring with the formation of ozonides – peroxide products of aliphatic nature. Up to 35 % of 4-bromacetophenone and trace amounts of 1-(4-bromphenyl)ethanol were identified among the products of oxidation reaction by the side chain. The reaction of ozone with 4-bromethylbenzene in acetic acid at temperatures of up to30 °Chas the first order by initial components and the value of constant of reaction rate does not depend on the concentration of reactants. With increasing temperature, constant of reaction rate begins to depend on the concentration of reagents, and in this case, ozone consumption increases significantly. This indicates that under experimental conditions, ozone is consumed simultaneously at different stages of oxidation. It was proved that ozonation of 4-bromethylbenzene is a complicated process, in which the substrate is oxidized by the non-chain mechanism. Ozone is consumed in two directions: in the reaction with the substrate by non-chain mechanism and by the chain mechanism at the stage of chain continuation in the reaction with the products of thermal decomposition of ozonides. This fact gives grounds to argue that at an increase in temperature, unproductive consumption of ozone will grow rapidly and, vice versa, under conditions of prevention of ozonolysis, ozone will participate in the reaction with formation of the target aromatic product. Thus, the experimentally obtained data are the basis for the development of the process of oxidation of derivatives of ethylbenzene and creation of the foundations of technology of 4-bromacetophenone synthesis with the help of ozone. This will considerably simplify the apparatus design of the process, enhance the output of the target product and will contribute to subsequent improvement of the method of oxidative processing of reagents