The acid-catalysed decomposition of N-nitrotolazoline

Abstract

Reaction of tolazoline with N₂O₄ yields N-nitrotolazoline, the prototypical nitroamidine. N-Nitrotolazoline undergoes acid-catalysed hydrolysis of the nitroamidine function to form N-(2-hydroxyethyl)phenylacetamide. The observed pseudo-first-order rate constants, k₀, have a non-linear dependence upon acidity, displaying saturation at higher acid concentrations consistent with a mechanism involving equilibrium protonation of N-nitrotolazoline prior to subsequent decomposition of the protonated intermediate. Reactions are subject neither to general acid- or base-catalysis nor to catalysis by thiocyanate ion. The solvent deuterium isotope effect for protonation was found to be 0.3, and for decomposition of the protonated intermediate, 1.7. A value of (–100 ± 5) J K^–1 mol^–1 was determined for ΔS ^‡ for the decomposition step. Thus, hydrolysis of the protonated intermediate involves rapid attack of a molecule of water at the amidine carbon atom followed by a slow, intramolecular rearrangement involving proton transfer.