Coupled oxidation of alcohol

Abstract

We have seen previously that hydrogen peroxide is formed in several oxidation reactions catalysed by enzymes like xanthine oxidase, uricase, and amino acid oxidase. In all these reactions one molecule of hydrogen peroxide is formed for each molecule of substrate oxidized. It is known that the hydrogen peroxide formed in the primary oxidation reaction can be used in promoting secondary or coupled oxidations of some substances (Thurlow, 1925; Harrison and Thurlow, 1926). The study of secondary oxidations by hydrogen peroxide revealed an unsuspected fact, namely, that it can be used in the oxidation of alcohol to the corresponding aldehydes. In this paper we propose to examine the conditions under which the coupled oxidation of alcohol takes place, the properties of the peroxide formed in the primary reaction, and the mechanism of the secondary oxidation of alcohol promoted by this peroxide. II−Coupled Oxidation of Alcohol by Uricase System. The study of this reaction was carried out in Barcroft differential manometers in the usual manner but with a series of controls. For instance, in order to detect the oxidation of alcohol by the uricase system, the oxygen uptake of four mixtures was measured separately: (1) uricase + uric acid; (2) uricase + alcohol; (3) uricase + uric acid + alcohol; (4) uric acid + alcohol. The reactions were carried out in buffer solution of p H 8·9 at 39° C. The quantity of enzyme varied from 25 to 50 mg of dry acetone preparation of liver, that of uric acid varied from 2 to 5 mg, and of alcohol from 5 to 10 mg per flask. The CO 2 was absorbed in the usual way by rolls of filter paper soaked with 10% KOH. The substrate in these experiments was always added in small dangling tubes suspended from the KOH tubes. These tubes were dislodged and their contents mixed with that of the flask after equilibration of the temperature and closing the taps of the manometers. After the experiment the contents of the flasks were examined for aldehydes. In manometric experiments with uricase the presence of KOH is required for absorption of CO 2 , and most of the aldehyde is absorbed by the potash paper where it polymerizes to a dark brown substance. In this way, even a small amount of aldehyde formed from alcohol gives rise to a yellow fringe on the potash filter paper.