Kinetics of the reaction between aromatic aldehydes and 1,5-diamino-4,8-dihydroxypyridazino[4,5-d]pyridazine

Abstract

Kinetic studies were performed to investigate the mechanism of Schiff base formation in the reaction between aromatic aldehydes and 1,5-diamino-4,8- dihydroxypyridazino[4,5-d]pyridazine (DDPP). The studies were conducted at different temperatures with ethanol as solvent and acetic acid as catalyst. It is proposed that the first step involves the reaction of the aldehyde with a solvated proton (i.e. specific acid catalysis). Depending on the acidity of the medium, free or mono-protonated (DDPP) attacks the carbonyl group to form a carbinol-amine intermediate which then dehydrates to form the product. Plot of Δ# versus ΔS# for the reaction gave a good straight line with isokinetic temperature of 343.15 K. Good linear relationship was obtained from the plot of log k against σ° values. The rate law derived from the proposed mechanism is in agreement with the experimental data and observations. The effects of meta and para substituents of benzaldehyde toward reactivity have been studied.