The D.C. polarography of azobenzene in pyridine

The d.c. polarography of azobenzene, sulphuric acid, acetic acid and mixtures of azobenzene with each of these acids in pyridine is reported. Azobenzene reduces in two one-electron steps, as is thecase in acetonitrile and dimethylformamide. Sulphuric acid is reduced in two irreversible steps corresponding to the reduction of the solvated proton produced by the first and second dissociationsof sulphuric acid, respectively. Acetic acid exhibits a single irreversible proton reduction wave.On addition of acid, azobenzene is reduced to hydrazobenzene via azoniumbenzene formed by protonation of azobenzene. Two such azonium waves are recorded in the polarograms when sulphuric acid is present corresponding to the two-proton dissociation steps of sulphuric acid. With acetic acid only one azonium wave is noted. In pyridine the reduction of azobenzene in the presence of proton donors is similar to that observed in acetonitrile. The differences noted between thebehaviour in the two solvents arise from the different Lewis basicities of pyridine and acetonitrile.