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

Article abstract of DOI:10.1139/v96-056

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.