Synthesis of Glyoxylic Acid by Glyoxal Oxidation in the Presence of Hydrohalic Acids

A procedure was developed for preparing glyoxylic acid by glyoxal oxidation with nitric acid in the presence of hydrohalic acids with selective isolation of glyoxylic acid from the reaction mixture in the form of magnesium and calcium salts. Specific features of the synthesis of glyoxylic acid were demonstrated, and optimum conditions for each step of the process were determined. The highest yield of glyoxylic acid was obtained in oxidation of glyoxal with an HNO3 : HCl mixture. Oxidation in the presence of HF and HBr is characterized by lower yields because of low dissociation constant of HF and side redox reactions with HBr. Dilute solutions of glyoxylic acid were obtained by an exchange reaction of its calcium salt with a hydrofluoric acid solution at room temperature. An increase in the reaction temperature leads to an increase in the content of glycolic and oxalic acids formed by disproportionation of glyoxylic acid in the initial step of the exchange reaction.