General acid catalysis of boric acid and water on dehydration step in formation of phenylhydrazone from salicylaldehyde

Abstract

976-978Hydrazone formation from salicylaldehyde and phenylhydrazine has been studied in water-ethanol (60:40 volume) solution at 35°C and ionic strength of 0.25 (with KCI). The reaction exhibits specific acid (in pH<4) and general acid catalysis (in 4pHpH<4 attack of phenylhydrazine to salicylaldehyde, and in pH>4 dehydration of intermediate is rate detennining step. Apparent catalytic rate constants of water and boric acid in the reaction are in good agreement with predicted values from Bronsted relationship. The kinetic results, UV, IR and NMR spectroscopic analyses exhibit general acid catalysis by boric acid and water.</span