Photolysis of the tetrazole ring.

Abstract

The preparation of 5-ethoxycarbonyltetrazole, 5-phenyltetrazole, 1-methyl-5-phenyltetrazole, 2-methyl-5-phenyltetrazole, 5-p-nitrophenyltetrazole, 1-methyl-5-p-nitrophenyltetrazile, 2-methyl-5-p-nitrophenyltetrazole, 1-methyl-3,5-diphenyl-1,2,4-triazole and 2-methyl-4,5-diphenyl-1,2,3-triazole have been described. Photolysis of 5-phenyltetrazole produces 3,6-diphenyl-s-tetrazine and 1,4-dihydro-3,6-diphenyl-s-tetrazine, whereas the latter undergoes smooth oxidation with bromine producing 3,6-diphenyl-s-tetrazine. Several attempts were made to trap the possible nitrilimine intermediate by photolysing 5-phenyltetrazole in the presence of norbornene and ethyl acrylate, but in neither case was any pyrazoline derivative obtained. The production of 1-4-dihydro-3,6-diphenyl-s-tetrazine through the possible photodimer or free radicals formations has also been discussed. Photolysis of 2-methyl-5-phenyltetrazole produces 2-methyl-4,5-diphenyl-1,2,3-triazole in addition to some other yet unidentified products. The structure of 2-methyl-4,5-diphenyl-1,2,3-triazole has been confirmed by its independent synthesis starting from benzil. Several attempts were made to trap the possible C-phenyl-N-methyl-nitrilimine by photolysing 2-methyl-5-phenyltetrazole with benzonitrile, but no change in the total yield of 1,2,3-triazole derivative was observed. The formation of 2-methyl-4,5-diphenyl-1,2,3-triazole through a possible photodimer of 2-methyl-5-phenyltetrazole has also been assumed. As 2-methyl-4,5-diphenyl-1,2,3-triazole on heating up to 220-225° for 6 hours did not produce any 1-methyl-3,5-diphenyl-1,2,4-triazole, the idea of the formation of 1-methyl-3,5-diphenyl-1,2,4-triazole via 2-methyl-4,5-diphenyl-1,2,3-triazole during the thermolysis of 2-methl-5-phenyltetrazole was given up. It has been shown, by using the Vycor filter, that radiations above 2400 A are responsible for effecting the photolysis of 2-methyl-5-phenyltetrazole. Several attempts were made to effect the photolysis of 1-methyl-5-phenyltetrazole by direct irradiation and once with the sensitizer, benzophenone, but in all cases 1-methyl-5-phenyltetrazole was found to be stable towards ultraviolet irradiation. 2-methyl-5-p-nitrophenyltetrazole, which has been isolated in 93% yield by methylation of 5-p-nitrophenyltetrazole, has been found to be stable towards the direct ultraviolet irradiation. The magnetic anisotropy-effects on the ortho protons of the phenyl rings of 2-methyl-5-phenyltetrazole, 5-phenyltetrazole, 5-p-nitrophenyltetrazole, 2-methyl-5-p-nitrophenyltetrazole and 1-methyl-3,5-diphenyl-1,2,4-triazole and 3,6-diphenyl-s-tetrazine have been discussed. Infrared, ultraviolet and n.m.r. spectra were used extensively in the structure determinations of these compounds.