Substituent effects in the micellar hydrolysis of N-phenylbenzohydroxamic acid under acidic conditions

The rates of hydrolysis of some para-substituted N-phenylbenzohydroxamic acids (X.C6H4.(C=O).N(OH)C6H5; X=H, CH3, OCH3, F, NO2) under acidic conditions with cationic, anionic and nonionic surfactants have been measured. Substituent effects upon first order rate constants in water and at the micellar surface fitted Hammett equation, based on sigma, sigma(+), sigma(-) parameters. Values of 'rho' increase with increasing surfactant concentration. The substituent effects indicate specific micellar influences on the rates and a difference in mechanism between the bulk aqueous phase and the micellar phase. The lipophilicity and polar effects of the substituents have also been evaluated.