Figure 3: Formation of Hydrazone Bonds. a. General reaction scheme for the formation of a hydrazone bond from an aldehyde or ketone. b. A hydrazone bond formed from a hydrazine or hydrazide and an aldehyde has a fast reaction rate and has a higher degree of acid lability than a hydrazone bond formed from reaction with a ketone. c. To improve the stability of hydrazone bonds, sodium cyanoborohydride (Na+[BH3CN]–) can be used to reduce the Schiff base to a much more hydrolytically stable secondary amine.