KINETICS AND MECHANISM OF ISATIN RING-OPENING IN AQUEOUS BINARY-MIXTURES OF METHANOL AND ACETONITRILE COSOLVENTS

Solvent effects on the kinetics of hydrolysis of isatin by sodium hydr oxide have been investigated within the temperature range (30-55 degre es C) in methanol-water and acetonitrile-water media of varying solven t compositions up to 70% (v/v) of the organic solvent component. The t hermodynamic activation parameters were calculated and discussed in te rms of solvation effects. The determined isokinetic temperatures, in b oth systems, revealed the existence of compensation effect arising fro m strong solute-solvent interactions; log k was correlated with both l og [H2O] and the reciprocal of the dielectric constant. The first corr elation was observed to be linear while the second was nonlinear. Fina lly a mechanism for the isatin ring opening was proposed, which accoun ts for the role and the effect of the solvent on the reaction rate. (C ) 1998 John Wiley & Sons, Inc.