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

Hydrazone formation from salicylaldehyde and phenylhydrazine has been studi ed in water-ethanol (60:40 volume) solution at 35 degrees C and ionic stren gth of 0.25 (with KCI). The reaction exhibits specific acid (in pH<4) and g eneral acid catalysis tin 4<pH<6.5). In pH<4 attack of phenylhydrazine to s alicylaldehyde, and in pH>4 dehydration of intermediate is rate determining step. Apparent catalytic rate constants of water and boric acid in the rea ction are in good agreement with predicted values from Bronsted relationshi p. The kinetic results, UV, IR and NMR spectroscopic analyses exhibit gener al acid catalysis by boric acid and water.