The relationship between redox potentials and substituent constants in biologically active arylazoxy compounds

Seven compounds containing the cyanoazoxy group were studied by cyclic voltammetry, in protic (aqueous/ethanolic phosphate buffer, pH 6.9) and aprotic (DMF + TBAP 0.1 mol L−1) media. In protic medium, all the arylazoxycyanides containing electrowithdrawing groups behaved similarly. A 4e−/4H+ reduction wave generating the hydrazo derivative is evident, as well as its counterpart for oxidation, in the reverse scan, to the azo derivative, which undergoes further reduction, in a successive scan. For the compounds with electrodonating substituents, slightly different reduction behaviour is evident, due to the instability of the electrogenerated azo compound. otic medium, all the arylazoxycyanides follow a similar and standard electrochemical reduction pathway, represented by two main waves, the first one reversible, corresponding to the uptake of one electron to form a stable anion-radical and a second one, much more intense and irreversible. In the case of the electrowithdrawing nitro and cyano derivatives, additional waves are observed, due to the reducibility of those groups. h media, linear relationships between EpIc (potential of first cathodic wave), Eredox (for aprotic) and Hammett substituent constants (σp, σ−) were observed. The reduction potentials correlate considerably better with (σp, σ−), showing the strong influence of resonance factors in the mechanism of reduction.