Abstract: We have studied the Copper (II) Salt-Mediated Reaction of nucleophilic substitution of the azide group of acyl azide by secondary amine group. In the course of the reaction copper (II) azide, acetic acid and the corresponding amide are formed. On the basis of IR spectra of reaction products we have concluded that there is the absorption band shifts of the stretching vibrations of azide group, which explains the formation of an intermediate complex with copper (II) acetate. Characteristic to the Copper (II) acetate blue-green color of the solution changes to brown color of the Copper (II) azide solution. It can be used as a characteristic "color" or a quantitative test, to determine amount of acyl azide and the secondary aliphatic amines.