Hydrolysis of N-p-nitrobenzylideneaniline: a quantitative study of specific and general catalysis

Abstract

The pa_H*–rate profile for the hydrolysis of N-p-nitrobenzylideneaniline was investigated in the pa_H* range 2·72–10·94, in buffered aqueous methanol solutions (20·0% w/w H₂O) at 25° and ionic strength 0·045_M. The dependence of rate coefficients on buffer concentration at constant pa_H*, constant ratio of buffer components at each pa_H*, and constant ionic strength was also studied in the pa_H* range 3·02–8·25. The observed rate coefficients show the influence of catalysis, obeying the expression K_obs=K_ext+K_cat[HA], in which the straight line parameters show a complex dependence on a_H*. Starting from the generally accepted mechanism for these reactions, a steady-state rate equation for specific and general catalysis was developed. An analysis of this rate equation has given not only the entire set of parameters but also the rate-determining steps and the values of some individual rate coefficients. The risk of making erroneous conclusions in the absence of a quantitative study of general catalysis is underlined.