Solvolysis of Pyridoxal Hydrochloride in Alcohols

HPLC, ¹H-NMR, MS and product analysis showed that pyridoxal hydrochloride was solvolyzed in methanol to form pyridoxal monomethylacetal. The reaction followed first order kinetics with the rate constant of 1.45 x 10^-4 s^-1 at 40 °C. The rate was not appreciably enhanced in the presence of an excess amount of HC1. The reaction was greatly retarded by addition of an equimolar amount of KOH. The results showed that the pyridinium-phenol species of pyridoxal hemiacetal is reactive. The reaction is responsible for the “aging” of alcoholic solutions of pyridoxal, which has caused poor reproducibility of the kinetic data for the formation of Schiff bases with amino acids.