Four-electron Step Research Articles

Anodic voltammetry of codeine and dihydrocodeine at rotating disc electrodes of platinum and gold

Of the analgesics examined, phenylbutazone and oxyphenylbutazone showed neither anodic nor cathodic activity, while codeine is oxidised by a single four-electron step and dihydrocodeine by a six-electron step to the same products. Electrode kinetic parameters have been evaluated, and the reaction mechanisms elucidated. Determination of codeine and dihydrocodeine by anodic voltammetry is simple and rapid, and gives relative standard deviations of 2–3%, and is free from interference from adsorption on the electrodes in 0.1 mol l–1 sulphuric acid. The influence of pH in the range 0–11.5 has been examined.

Polarographic studies on 4,5-DIIODO-(R)-fluorescein

Polarographic examination of title compound (0.2 mol m −3) in 10% ethanolic Britton—Robinson universal buffers (ionic strength, 0.5 mol dm −3 with added KCl), using gelatin (0.004%) as maximum suppressor, and its millicoulometry reveal two two- and four-electron steps in acidic solutions, which merge into one wave at intermediate pH-values, and separate out again into two waves of varying heights in the alkaline pH-range. That the second four-electron step involves splitting of the two CI bonds has been prove by recording anodic waves for the liberated iodide ions (i) by using Kalousek commutator technique, and (ii) after carrying out cpe. The other product of cpe has been identified as fluorescin (leuco-fluorescein) by polarographic comparison of its aerial oxidation product with authentic fluorescein. The low negative halfwave potential of the first wave indicates that the title compound is reduced in the more readily reducible quinonoid form or as its ionic mesomer instead of in the difficultly reducible lactoid (furanoid) form as suggested by the earlier workers. Further, we did not obtain any significant evidence for the opening of the pyrone ring as suggested by them. The course of electrode process at various pH-values has been suggested.

Electrochemistry of α, α′-dibromoketones reduction of 2,4-dibromo-1,5-diphenyl-1,4-pentadien-3-one (α, α′-dibromo-dibenzylidene acetone) at the mercury electrode

2,4-Dibromo-1,5-diphenyl-1,4-pentadien-3-one (VIII (PhCH=CBrCOCBr=CHPh, α, ga'-dibromodibenzylidene acetone) is electroreduced in “aprotic” dimethylformamide at the mercury electrode; E1/2 of the first step is −0.97 V vs. SCE; two electrons/molecule of VIII were transferred (c.p.e.) and two Br−/molecule of VIII were released. The product was identified as cis-1,5-diphenyl-1-penten-4-yn-3-one(PhCH=CHCOC=CPh), which is the rearrangement product of an unstable dimethylenecyclopropanone. In MeOH solutions, electroreduction of VIII follows a different path, the first two-electron step being substituted by a four-electron step (c.p.e.), which furnishes 3,4-diphenyl-cyclopent-2-enone, XIII. XIII seems to be a rearrangement product of a cyclic precursor. Subsequent two-step reduction of this intermediate in MeOH affords finally 1,5-diphenylpentan-3-one(α, α'-dibenzylacetone).

Electrochemistry of α, α'-dibromoketones: Reduction of 2,4-dibromo-1,5-diphenyl-1,4-pentadien-3-one (α,α'-dibromo-dibenzylidene acetone) at the mercury electrode

2,4-Dibromo-1,5-diphenyl-1,4-pentadien-3-one (VIII (PhCH=CBrCOCBr=CHPh, α, ga'-dibromodibenzylidene acetone) is electroreduced in “aprotic” dimethylformamide at the mercury electrode; E 1/2 of the first step is −0.97 V vs. SCE; two electrons/molecule of VIII were transferred (c.p.e.) and two Br −/molecule of VIII were released. The product was identified as cis-1,5-diphenyl-1-penten-4-yn-3-one(PhCH=CHCOC=CPh), which is the rearrangement product of an unstable dimethylenecyclopropanone. In MeOH solutions, electroreduction of VIII follows a different path, the first two-electron step being substituted by a four-electron step (c.p.e.), which furnishes 3,4-diphenyl-cyclopent-2-enone, XIII. XIII seems to be a rearrangement product of a cyclic precursor. Subsequent two-step reduction of this intermediate in MeOH affords finally 1,5-diphenylpentan-3-one(α, α'-dibenzylacetone).

Polarographic determination of nitramide

Nitramide gives two cathodic polarographic waves with half-wave potentials varying with pH, and having minimum values − 1·22 V at pH 4·5 and − 1·58 V at pH 8·8. Nitramide is fist reduced to nitrosamine in a two-electron reduction. In the second step, hydroxy-hydrazine may be formed in a two-electron reduction, or hydrazine itself in a four-electron step. For the polarographic determination of nitramide the first wave is used, and the supporting electrolyte is a Britton—Robinson buffer 0·1 M in KCl, at pH < 5 and at 0–2°.