Kinetics and reactivity of indole-2,3-dione ring towards alkali in dimethyl sulphoxide-water mixtures

Kinetics of alkaline hydrolysis of indole-2,3-dione (isatin) and indole-2,3-dione (N-methyl isatin) have been carried out at different percentages of DMSO-H2O mixtures and at different temperatures in the range 30-45 degrees C. The reaction proceeds according to pesudo first-ordcr kinetics. The presence of an electron releasing substituent methyl group attached to nitrogen atom accelerates the reaction rate. Thermodynamic activation parameters Delta H-#, Delta S-# and Delta G(#) have been determined. The negative values of entropy of activation and the non-linear relation between log rate constant and reciprocal of dielectric constant suggest selective solvation by the higher polar water solvent molecules.