Electrochemical investigations of nitro 1-5 and nitroso s-~Β° compounds in water a. 2, 6.7 and non-aqueous solvents 1 2.6. 7 indicate formation of the intermediate compound, azoxybenzene 2'5"6"8 lO which is also found among products of electrolysis a'3"4. Formation of azoxybenzene during electroreduction of nitro and nitroso compounds is easily understood having in mind the ability of phenylhydroxylamine and nitrosobenzene to condense with each other and remembering that these compounds are formed as intermediates during electroreduction v' 11-13 Some suggestions referring to the mechanism of formation of azoxybenzene during polarographic reduction of nitrobenzene in DMF will be published 5.
Azoxybenzene is reduced in water with consumption of 4e, which is interpreted in terms of formation of hydrazobenzene ~4-18. Chronovoltammetric studies show in the second scan an additional redox system at potentials more positive than that of the 4e wave, assumed to be the hydrazobenzene-azobenzene system 18. Only a few papers deal with azoxybenzene in aprotic solvents, describing its reduction as a one step process8'9'19'ZΒ°. In methanol 2Β°, as well as in DMF, with 0.2 M NaNOB as supporting electrolyte 8' 9, only one, 4e, wave of reduction was observed.
The main purpose of this paper is to present a more detailed mechanism of electroreduction of azoxybenzene in DMF as studied polarographically and chronovoltammetrically in the presence of various supporting electrolytes.
EXPERIMENTAL
Reagents
Commercially available DMF was kept over molecular sieves type 4A (B.D.H.) and then distilled under reduced pressure (5 mmHg). Perclalorates of Li +, Na +, K +, Et4N + (tetraethylammonium cation) and But4N + (tetra-n-butylammonium cation) used as background electrolytes were prepared, recrystallized and dried under reduced pressure. Azoxybenzene was prepared El from nitrobenzene and dextrose and recrystallized from ethanol (m.p. 36Β°C). Solutions in the polarographic cell were purged of dissolved oxygen with oxygen-free dry nitrogen.