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Electrogenerated chemiluminescence in mechanistic investigations of electroorganic reactions: Part III. Reduction of some disulfides at the dropping mercury electrode
Authors:Fritz Pragst
Institution:Sektion Chemie, Humboldt-Universität Berlin, Hessische Strasse 1-2, D.D.R.-104 Berlin (G.D.R.)
Abstract:In the simultaneous cathodic reduction of diphenyl disulfide (Ph?S?S?Ph) or dibenzoyl disulfide (Ph?CO?S?S?CO?Ph) and a series of fluorescent aromatic hydrocarbons A at the dropping mercury electrode in dimethylformamide the emission of A is observed. This electrogenerated chemiluminescence (ECL) originates from the electron transfer between A? and the radicals Ph?S or Ph?COS, which are formed in a one-electron reductive cleavage of the disulfide bond by A?. As an intermediate the anion radical Ph?S?S?Ph? or Ph?CO?S?S?CO?Ph? is assumed. In the case of Ph?S?S?Ph the ECL intensity is enhanced by proton donors (water or benzoic acid), which increase the cleavage rate of Ph? S?S?Ph? in an electrophilic attack by the proton. The relatively negative threshold reduction potential of A (?1.4 to ?1.6 V) for the ECL in comparison with the half-wave potential (?0.85 V) supports a mercury-assisted heterogeneous reduction mechanism of Ph?S?S?Ph. The intensity-potential curves and the intensity—time curves at the mercury drop were measured for different concentrations of Ph?S?S?Ph and A and for different mercury pressures. No luminescence could be detected with o,o′-dinitrodiphenyl disulfide and diethyl disulfide.
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