A process for the preparation of organic azide the addition of an azide fuction to an organic compound in which process a mixture is prepared by adding an epoxide-derivative of the organic compound and an alkali metal azide salt to a solvent is described. The mixture is heated to a reaction temperature at which the epoxide-derivative and the azide can react to form an azide derivative of the organic compound. An amount,near equimolar to the epoxide derivative,of a (1-6c)alky-(2-4c)carboxylic acid ester having a boiling point above the reaction temperature is added to the mixture before and/or during the reaction.