Reactions of nitrous acid with oxalic acid and with ketones

Abstract

The subject of this work has been the kinetics of oxidation of oxalic acid and some aliphatic ketones by nitrous acid in aqueous sulphuric and perchloric acid media. Oxidation of oxalic acid by nitrous acid has been studied in solutions containing a mixture of oxalic acid and sodium oxalate over an H concentration 0.007 to 0.17M, at an approximately constant ionic strength 0.9M and temperatures 35, 45 and 55°C. The order of the reaction and the effect of change of ionic strength on the reaction have been determined. An activation energy for the reaction has been calculated and a mechanism suggested. The ketones, methyl ethyl, methyl n-propyl, methyl iso-propyl, methyl iso-butyl, diethyl ketone and acetone have been used to follow the oxidation of ketones by nitrous acid. Most experiments have been carried out at 25° in aqueous perchloric acid solutions (0.1 to 3M) at a constant ionic strength of 3.0M by addition of sodium perchlorate. Some experiments have been carried out with methyl ethyl ketone in sulphuric acid media. The factors investigated for this reaction have included the effect of temperature on the reaction, from which activation energies have been calculated. The reaction has been found to be first order with respect to nitrous acid and to the ketone, and the effect of change of ionic strength has been studied. By varying the concentration of perchloric acid at constant initial nitrous acid and ketone concentrations, the variation of the second order velocity constant for the reaction with perchloric acid concentration has been determined. Spectroscopic investigations on the equilibrium between NO and HNO2 in aqueous perchloric acid from about 30% to 60% have been carried out and from the results the concentration of NO+ at very low acidities roughly determined. An estimate of the value for the equilibrium constant at low acidities has been made. Possible mechanisms for the reaction on the basis of these results have been discussed and a plausible mechanism suggested.