The Electrochemical Behavior of 4 , 4 ' - Azopyridine - l , l ' - Dioxide

The electroreduction of 4 ,4 ' -azobispyr idinel , l ' -d ioxide (APDO) in dimethyl formamide solutions was studied by polarography, cyclic vol tammetry, controlled potential coulometry, and electron spin resonance, Voltammetric reduction showed two well-defined, reversible one-elect ron transfers. Coulometric reduction at a potential corresponding to the plateau of the first wave gave evidence of chemical reactions following the ini t ial electron t ransfer producing intermediates which were also electroactive at the same potentials. Coulometry at the second wave gave an over-al l value of six Faradays per mole for the complete reduction of APDO to the dianion of azopyridine (A_P), identified by electrochemical and electron spin resonance techniques. A mechanism for the reduction process consistent with the exper imental evidence is presented. The polarographie behavior of a number of ter t iary amine oxides in aqueous systems has been reported (1-9). Kubota and Miyazaki (6a) performed a polarographic s tudy of pyr idine N-oxide and its alkyl derivatives followed by a s tudy (6b) of the effect of subst i tuents on the polarographic reduct ion of pyr idine N-oxide derivatives. Recently, Date (7a) reported a thorough polarographic invest igat ion of d imethylani l ine N-oxide, followed by an invest igat ion of the relat ionship between the El~2 values of a series of simi lar compounds and the pKa's of their parent amines (7b). Chambers (8) studied the polarographic and adsorption behavior of dimethyldodecylamine N-oxide and E1ving and Warner (9) have reported a s tudy of the polarographic behavior of adenine 1-N-oxide. In all of the above work, the amine oxide group gives a well-defined, i r reversible polarographic wave * E l e c t r o c h e m i c a l Society Act ive Member . between pH values of 1 to 6. Date proposed that the amine oxide group is reduced to the corresponding parent amine in a reaction involving two electrons, the first electron addit ion being rate controlling. This mechanism agrees quite well with his exper imental data and is fur ther supported by Chambers ' work on N,N-dimethyldodecylamine N-oxide. Recently Nasielski and co-workers (10) studied the polarographic reduct ion of pyr id ine N-oxide and other heterocyclic N-oxides in DMF solution. They proposed that the reduction involves a single, two-elect ron wave (composed of reduction to the anion radical, fast protonation, and fur ther reduction, protonation, and dehydra t ion) , leading to the free base. We report here a s tudy of the amine oxide 4 ,4 ' -azobispyr idinel , l ' -d i oxide (APDO) in DMF, in which a clear separation of the step leading to formation of the anion radical and to formation of the dianion is obtained. Downloaded 19 Feb 2009 to 146.6.143.190. Redistribution subject to ECS license or copyright; see http://www.ecsdl.org/terms_use.jsp 344 J. E lec t rochem. Sot . : E L E C T R O C H E M I C A L S C I E N C E April 1968