Kinetics and Mechanism for the Reaction of 5-Nitroisatin with Morpholine in Water–Methanol and Water–Acetonitrile Mixed Solvents

The kinetics of the reaction of 5-nitroisatin with morpholine in water–acetonitrile and water–methanol solvents was followed spectrophotometrically in the ranges of solvent composition (10–90% v/v) over the temperature range from 25 to 45 °C. The reaction was measured under pseudo-first-order condition respect to 5-nitroisatin and the overall reaction is second-order rate. The rate constant of reaction decreased with increasing organic solvent ratios and strongly increased with increasing water ratios in both mixed solvents. The thermodynamic activation parameters were calculated and explained. Both linearity and non-linearity were observed between log k_N and reciprocal dielectric constant for both solvents suggesting that the reaction of 5-nitroisatin with morpholine depends on specific as well as non-specific solvation of the medium. The reactivity was analyzed in the light of various single, dual, and multiple-regression equations using Kamlet–Taft solvatochromic parameters which were applied successfully to the mixed aqueous–acetonitrile and aqueous–methanol mixtures. Finally, a mechanism for the reaction is proposed.