On the Formation of Benzonitrile from Benzaldehyde and Ammonia. II. Iodine as an Oxidant

The present authors previously reported a method of synthesizing nitriles from aldehydes by using iodine as an oxidant (Bull. Chem. Soc. Japan, 39, 854 (1966)). The possible route and detailed conditions of this reaction have now been investigated in the case of benzaldehyde; the results will be described in this paper. Benzaldehyde, ammonia, and iodine in methanol react to form benzonitrile and methyl benzoate as the main products. A possible reaction mechanism is suggested by a consideration of the effect of the temperature and of the concentrations of the reactants, and of the effect of the addition of ammonium iodide and water, as well as by a consideration of the results of the reaction starting from hydrobenzamide. The mechanism may be as follows. Iodamine, which is in equilibrium with iodine and ammonia, oxidizes benzilideneimine, which arises from the reaction between benzaldehyde and ammonia to give hydrobenzamide, to produce benzonitrile. Methyl benzoate is produced by the oxidation of the hemiacetal which arises from the reaction between benzaldehyde and methanol. Gyaphenin (2, 4, 6-triphenyl-1, 3, 5-triazine) is found as a by-product, but it is shown not to be produced by the trimerization of benzonitrile.