Investigation of the decomposition of compounds containing azo groups by EPR spectroscopy

In photochemically, electrochemically and thermally initiated decomposition, compounds containing the azo group ((RN)-R-1=(NR)-R-2) usually form reactive, short-lived radicals R-1(.) and R-2(.) which corresponds to synchronous splitting. As examples, aliphatic azo compounds, 1-aryl-2-alkylazo compounds, azophosphonates, azosulfonates, azosulfones, azosulfides, triazenes, pentazadienes, hexazadienes, acyl- and diacylazo compounds, diazonium salts and cyclic azo compounds have been studied. R-1(.) and R-2(.) Were characterized by means of the EPR spin trap technique. These reactive radicals may abstract hydrogen from the solvent or any neighborhood functions, or dimerize (R-1-R-2). Some azo compounds trap R-1(.) and R-2(.) and thus form the corresponding hydrazyl radicals. In cathodic reduction, prior to the initiation of decomposition, corresponding anion radicals centered on the azo group were observed which have considerable stability if R-1 and R-2 are conjugated structures. (C) 1998 John Wiley & Sons, Ltd.