Kinetics of the hydrolysis of isatin in water and water + co-solvent

Hydrolysis of isatin by sodium hydroxide was followed spectrophotometrically in a wide range of water-n-propanol, and water-iso-propanol proportions at different temperatures (30-45 °C). A non-linear relation was observedfor the plot of log k versus the reciprocal of the dielectric constant for the solvent used which suggested that there is a selective solvation by higher polar solvent, i.e. by water molecules. The activation thermodynamic parameters were calculated and discussed in terms of solvation effects. The determined isokinetic temperatures, in both systems, revealed the existence of compensation effect arising from strong solute-solvent interactions.