The oxidation of liquid hydrocarbons II. The energy-chain mechanism for the thermal oxidation of tetralin

Abstract

The liquid-phase oxidation of hydrocarbons, where the point of the oxidative attack is a >CH₂ group, has been shown to proceed at a rate independent of the oxygen pressure and proportional to the square of the hydrocarbon concentration. This arises from a primary chain reaction which g’ves a hydroperoxide as the primary intermediate. Degenerate chain branching, resulting from the decomposition of the hydroperoxide, is responsible for a slow exponential increase in the reaction rate with tim e: it is less marked the higher the temperature. At the reaction temperatures employed (65-120° C) the hydroperoxide is the predominant oxidation product, and the major kinetic problem has been to determine the nature of the primary reaction chain. An examination of the kinetic characteristics of the inhibited oxidation has shown that the normal chain termination is a unimolecular reaction of the chain carrier, and further, that the chains are initiated in a unimolecular reaction of the hydrocarbon. These conclusions enable a unique choice to be made in favour of an energychain mechanism. In this case the process of inhibition must not only be regarded as an additional means of terminating the reaction chain, but as a competition between the hydrocarbon and the inhibitor for the chain carrier in which the reaction with the inhibitor is greatly favoured.