Electrochemical oxidation of 6- and 7-hydroxypteridine and 6,7-dihydroxypteridine at the pyrolytic graphite electrode

Abstract

Summary Over the pH range 2.3–10, 6-hydroxypteridine is oxidized electrochemically at the PGE by way of two voltammetric peaks. The first, least positive, peak is due to a 2 e –2H + oxidation to 6,7-dihydroxypteridine. In very acidic solution (2 M H 2 SO 4 ), 7-hydroxypteridine also gives two voltammetric peaks. Again the first, least positive, peak is a 2 e –2H + oxidation to 6,7-dihydroxypteridine. The second, more positive, peaks of both compounds are due to electrochemical oxidation of 6,7-dihydroxypteridine which occurs over the pH range of 2.3–9. Under voltammetric conditions this peak is due to a 2 e –2H + oxidation to a di-imine of 6,7-dihydroxypteridine that very rapidly hydrates to a diol. Under conditions of controlled potential electrolysis, however, the oxidation involves transfer of approximately 6 e . Under the latter conditions the initial electrode product, the bridgehead diol of 6,7-dihydroxypteridine under goes rearrangement, further oxidation and hydrolysis yielding as final products, tetraketopiperazine, oxamide, urea, oxamic acid, ammonia, formaldehyde, formic acid and CO 2 . The electrochemical and related chemical reactions were studied by d.c. polarography, cyclic and linear sweep voltammetry, coulometry, and macroscale electrolysis followed by product isolation and identification, and radioisotope tracer techniques.