Method for preparing azoiminoethers and azocarboxylic acid esters and novel azocarboxylic acid mixed esters

The invention concerns a method for preparing an azoiminoether hydrochloride which consists in reacting an azonitrile with an alcohol and hydrochloric acid in an aromatic solvent, wherein the molar ratio R=HCl/azonitrile is >2 when the alcohol is methanol and >3 when the alcohol is ethanol or a higher alcohol. The invention also concerns a method for preparing an azocarboxylic acid ester which consists in the synthesis of an azoiminoether hydrochloride by the inventive method and, hydrolysis in the presence of the resulting azoiminoether hydrochloride. Said methods enable to obtain liquid composition of azocarboxylic acid esters. The invention further concerns mixed azoiminoether salts of formula (II'). The invention also concerns mixed azoiminocarboxylic acid esters corresponding to the formula (III').