Investigation of the decomposition of 1,3-diaryl-5-(3-chloro-2-quinoxalyl)-formazans by PMR and MASS spectrometry

Abstract

In contrast to triarylformazans, 1,3-diaryl-5-(3-chloro-2-quinoxalyl)formazans are unstable in ordinary organic solvents. When they are heated in chloroform, they undergo acidic cleavage, which leads to the formation of 3-chloro-2-quinoxalylhydrazones of p-substituted benzaldehydes and arenediazonium cations. These compounds, as a result of a redox reaction with the participation of the solvent, are converted to 4-chloro-1-(4-Y-phenyl)-1,2,4-triazolo[4,3-a]quinoxalines, substituted benzenes, nitrogen, and hydrogen chloride. The formation of the latter transforms the entire decomposition process into an autocatalytic process. Effects of chemical polarization of the nuclei (CPN), which unambiguously indicate the intermediate formation of diazoaryl radicals during the process, are observed in the PMR spectra of the final products. Such CPN effects, which were also observed in dimethyl sulfoxide (DMSO) and glacial acetic acid, indicate a process involving the oxidative formation of annelated triazoles from α-azahetarylhydrazones via a radical pathway within a solvent “cage.”