Photochemical reactions of azo compounds. IX. Further studies related to the photochemical reactions of bisazo compounds

Abstract

The photochemical reactions of 4,4'-bis(pheny1azo)biphenyl and 4-phenylazoazobenzene in 98% sulphuric acid have been examined, for comparison with the corresponding reactions in 2 2~ acid. Photochemical cyclodehydrogenation of 4-phenylazoazobenzene to two benzo[c]cinnoline derivatives has thereby been effected for the first time. The observed course of the latter reaction has led, in turn, to studies of the benzidine rearrangement of 2-(2-phenylhydrazino)benzo[c]cinnoline, of the photochemical cyclodehydrogenation of 3-phenylazobenzene, and of the photochemical reaction of 2-phenylazobenzo[c]cinnoline. The results of these investigations are now recorded and discussed.It has been known for some time that azobenzene (I), on being irradiated in 2 2~ sulphuric acid, forms a mixture of benzo[c]cinnoline (11) and benzidine (111) in approximately equivalent quantities.l.2 Under these conditions the reaction appears to be largely an intermolecular disproportionation process, in which cyclodehydrogenation of a given quantity of azobenzene to benzo[c]cinnoline is accompanied by reduction of an equal quantity of the same compound to hydrazobenzene. Hydrazobenzene has not been detected, as such, in any of the reaction mixtures, but it is obviously the precursor of the isolated benzidine.

Mild Synthesis of a Family of Planar Triazinium Cations via Proton-Assisted Cyclization of Pyridyl Containing Azo Compounds and Studies on DNA Intercalation

“…The synthesis, to the best of our knowledge, is among the simplest ones of the available literature procedures for making cationic heterocyclic compounds. Literature search has revealed that 3-(phenylazo)pyridine in concentrated sulfuric acid (98%) undergoes photocyclization with C−C bond formation analogous to photocyclization of certain azobenzenes to benzo[ c ]cinnoline derivatives . It has been possible to isolate the different salts of the parent molecules by the use of common mineral acids as the proton source, and their characterization is made by different spectroscopic, electrochemical techniques, as well as single-crystal structure analysis of a representative compound.…”