Mechanism and Kinetics of the Reaction of Nitrate Radicals with Carboxylic Acids

Abstract

Rate constants for the reaction of nitrate radical (NO 3 * ) with several carboxylic acids (RCO 2 H) were measured in acetonitrile using laser flash photolysis, and found to be on the order of 10 5 -10 6 M À 1 s À 1 . No observable H/D kinetic isotope effect was observed at the carboxyl OÀ H group, α-CÀ H bond and (possibly) in the case of formic acid, the formylic CÀ H bond. This suggests that NO 3 * does not abstract hydrogen from any of these positions despite the fact that all these processes are thermodynamically favorable. Reactivity increases with increased length and/or branching of the alkyl side chain (R), and approaches, but does not quite reach, that of an alkane towards NO 3 * . The relative inertness of carboxylic acids towards NO 3 * can be explained by the polar effect.