Kinetic and Mechanistic Studies on the Formation of Number of 2-Pyrazoline Derivatives

The kinetics of the addition of hydrazine to the double bond of some chalcones have been studied using UV-visible technique. The reaction is considered as a pseudo-first order process which includes a nucleophilic attack by hydrazine at the -carbon of the ,-unsaturated carbonyl system to afford the expected heterocycle pyrazoline.
The rate constants were found to depend on different variables such as variation of different substituents. Arrhenius parameters and entropy of activation for all reactions have been computed. A suitable mechanism which is consistent with the experimental results is suggested for the reactions