The reaction is preferably carried out in a solvent such as benzene, toluene or dimethylformamide at temperatures between 80??? and 150??? C., preferably at 125??? C. Conveniently, either the hydrazoic acid is liberated during the reaction from an alkali metal azide, e.g. sodium azide, in the presence of a weak acid such as ammonium chloride or a tetrazolide salt obtained in the reaction mixture d