Photochemical reactions of azo compounds. IV. Further photochemical cyclodehydrogenations

Abstract

1,1'-, 1,2'-, 2,2'-Azonaphthalenes, and 2-phenylazonaphthalene are not cyclized photochemically under conditions in which azobenzene is converted into benzo[c]cinnoline and benzidine; but 1-phenylazonaphthalene has been shown to give naphtho[1,2-c]cinnoline, and 4-phenylazobenzene gave 2-phenylbenzo[c]cinnoline. Although 4-styrylazobenzene showed some evidence of cyclization, the reaction was extremely slow and was accompanied by considerable decomposition. 4-Phenylezoazobenzene was cleaved by sulphuric acid, and no cyclized product was obtained. Irradiation of 4,4'-bis(phenylazo)biphenyl gave two cleavage products, and two benzo[c]cinnoline derivatives. Simultaneous reduction and oxidation apparently occurred within the same molecule.