The reactions of O(3P) with some carboxylic acids and esters

Abstract

The reactions of O(3P) with formic acid, acetic acid, methyl acetate, ethyl acetate, n-propyl acetate, and isopropyl acetate have been studied kinetically as a function of temperature. The rate constants were measured in a discharge-flow system under pseudo-first-order conditions with a large excess of the organic reagent. No reaction could be found between O(3P) and either formic acid or acetic acid in the temperature range 300-420 K. The acetate esters, on the other hand, reacted with O(3P) at readily measurable rates over the same temperature range. The temperature dependence of the rate constants for these reactions in the temperature range 300-580 K is given, in the units L mol-1 s-1, by: O + methyl acetate: In k = (19.46 ± 0.24) - (1740 ± 170)/T O + ethyl acetate: In k = (20.30 ± 0.35) - (1750 ± 310)/T O + n-propyl acetate: In k = (21.80 ± 0.41) - (1920 ± 400)/T O + isopropyl acetate: In k = (19.91 ± 0.36) - (1430 ± 250)/T The lack of measurable reaction with the carboxylic acids, the systematic increase in the preexponential factor with increasing size of the ester group, and the observation of a significant yield of acetic acid among the products of the reactions with the esters indicate that attack by O(3P) is predominantly at the ester function. Linear free energy correlations are used to compare the results for the esters with those for reactions of O(3P) with other organic compounds containing oxygen.