Polarographic study of the kinetics and equilibria of the reaction of benzaldehydes with hydrazine

摘要

Whereas kinetics and mechanism of reactions of semicarbazide and hydroxylamine with carbonyl compounds has been studied in considerable detail, relatively little attention has been paid to equilibria involved, as well as to reactions with unsubstituted hydrazine. Polarographic current-voltage curves enable simultaneous determination of the aldehyde and hydazone. Anodic oxidation waves are used to prove absence of azine formation, variations in concentration of the intermediate carbinolamine can be determined. Preliminary investigation of the kinetics of the reaction of benzaldehydr with hydrazine indicated a decrease in the rate of establishment of the equilibrium with pH increasing from 2 to 6. The equilibrium constant increases in this pH-range. The shape of the dependence of K = [ArCH = NNH_2]/[ArCHO][NH_2NH_3~+] on pH indicates the presence of a rapidly established acid-base equilibrium, preceding the dehydration of carbinolamine, which is the rate determining step. Investigation of kinetics and substituent effects is in progress.