Buffer Catalysis in the Hydrolysis of Picrylimidazole

Article abstract of DOI:10.1021/ja00396a040

The kinetics of the hydrolysis of picrylimidazole (S) was studied between pH 0.47 and 10.6 with different buffers at various concentrations.The reaction is strongly catalyzed by carboxylate and phosphate ions.Imidazole also catalyzes the reaction although it is a weak catalyst.At pH below 4 S starts to be protonated and the buffer-independent rate constant increases until it reaches a plateau.Rate constants for the base-catalyzed pathway are separated into the contribution of the rate for the protonated and unprotonated substrates.The Broensted plots give slopes of 0.5 and 0.58, respectively.The mechanism of catalysis is discussed.