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

Rate constants for the reaction of nitrate radical (NO3 center dot) with several carboxylic acids (RCO2H) were measured in acetonitrile using laser flash photolysis, and found to be on the order of 10(5)-10(6) M(-1)s(-1). No observable H/D kinetic isotope effect was observed at the carboxyl O-H group, alpha-C H bond and (possibly) in the case of formic acid, the formylic C H bond. This suggests that NO3 center dot 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 NO3 center dot. The relative inertness of carboxylic acids towards NO3 center dot can be explained by the polar effect.

Automated summary

The study measured rate constants for the reaction of nitrate radical with carboxylic acids, finding that the reactivity of carboxylic acids towards NO3 center dot is relatively low. It was also observed that NO3 center dot does not abstract hydrogen from the carboxyl O-H group, alpha-C H bond, and possibly the formylic C H bond in formic acid. This suggests that the relative inertness of carboxylic acids towards NO3 center dot can be explained by the polar effect.