The gaseous oxidation of aliphatic alcohols II. Ethyl alcohol: the products formed in the later stages of reaction

Abstract

In the slow oxidation of ethanol between 270 and 370° C there is an induction period during which a critical concentration of acetaldehyde accumulates without pressure change. This paper describes detailed analytical studies of the reaction following the induction period. Pressure increase in general provides a good measure of reactant consumption except in the late stages of reaction. The yields of acetaldehyde and hydrogen peroxide, which are initially high, fall off as the pressure rises, while those of methanol, formaldehyde, carbon monoxide and water increase. Formation of carbon monoxide closely parallels that of methanol at 295° C. In ethanol-rich mixtures oxygen consumption ceases abruptly after the maximum rate is reached, and is superseded by a pyrolytic reaction in which carbon monoxide and methane are formed in equivalent amounts. The maximum pressure of acetaldehyde is linearly dependent on initial ethanol concentration and is sensibly independent of oxygen; the same behaviour is shown by the maximum rate of pressure rise. Small quantities of added acetaldehyde markedly shorten the induction period, but have little effect on the subsequent stages of reaction; larger amounts of acetaldehyde increase the reaction rate. Added methanol retards the reaction, apparently by stabilizing radicals formed from acetaldehyde oxidation. The yields of peroxides are affected by temperature and, markedly, by changes in the nature and extent of the surface, but the essential features of the reaction mechanism persist under wide series of conditions. The analytical results are well accounted for by a mechanism in which acetaldehyde, formed (with hydrogen peroxide) in primary chains, is oxidized in a branching chain cycle; this process leads, through formation of CH 3 radicals, to the C 1 compounds observed.