M. Evers

Electrochemical behaviour of selenoorganic compounds—I. Dibenzo (b,d) selenopyrane and related compounds

The electrochemical properties of selenoxanthene, selenoxanthene-9-ol and selenoxanthone in non-aqueous and mixed media are investigated by voltammetry at rotating platinum and vitrous carbon disk electrodes, cyclic voltammetry, chronopotentiometry and constant potential coulometry. In “dry” acetonitrile selenoxanthene leads to selenoxanthylium cation. In the presence of water, selenoxanthene-9-ol is obtained. Further oxidation of selenoxanthene-9-ol gives the selenoxanthone which can be oxidized to the corresponding selenoxide. Influence of acids and bases is shown.

Electrochemical behaviour of seleno-organic compounds. Part 2 : Benzo(b) selenophene and dibenzo(b,d)selenophene

Abstract The electrochemical oxidation of benzo( b )selenophene and dibenzo( b,d )selenophene in non-aqueous media has been studied using platinum and glassy carbon electrodes. The selenoxide of dibenzo( b,d )selenophene has been isolated. A mechanism consistent with voltammetric measurements has been established. The electrochemical oxidation of dibenzo( b,d )thiophene was discussed and compared with its seleno analog.

Electrochemical study of dibenzo(c,e)-1,2-dithiin in acetonitrile medium

The electrochemical properties of dibenzo(c,e)-1,2-dithiin in acetonitrile solution are investigated by voltammetry at rotating platinum and vitrous carbon disk electrodes, and by cyclic voltammetry and constant potential coulometry. Attention is particularly devoted to the first charge transfer step and the subsequent chemical reactions. Evidence for an ECE process is given. Comparison of the chemical and electrochemical oxidation of dibenzo(c,e)-1,2-dithiin and related open-chain compounds is discussed.

Electrochemical oxidation of selenanthrene in acetonitrile at conventional electrodes and microelectrodes

Abstract The electrochemical oxidation of selenanthrene was studied by conventional and microelectrode techniques. The first signal was proved to follow an ECE mechanism: steady-state voltammetry at microelectrodes and cyclic voltammetry showed a monoelectronic transformation into the cation-radical, whereas controlled potential coulometry and electrolysis gave the corresponding 5-selenoxide with an exchange of 2F mol −1 . The electrochemical reversibility of the intermediary cation-radical was investigated and its stability compared with those of similar heterocyles. Further oxidation led to 5,10-selendioxide.

The electrochemical oxidation of thioselenanthrene in acetonitrile at conventional electrodes and microelectrodes

Abstract The electrochemical oxidation of thioselenanthrene (1c) in acetonitrile was studied by conventional and microelectrode techniques. Steady-state and cyclic voltammetry proved the occurrence of a DISP2 mechanism for the first oxidation signal. Controlled potential coulometry led to the formation of the corresponding selenoxide. The first electron transfer proceeds with a high heterogeneous rate constant (0.58 ± 0.10 cm s−1), whereas a pseudo-first-order apparent rate constant of 8.87 ± 1.11 s−1 was computed for the chemical step, giving a half-lifetime of 78 ± 10 ms for the cation-radical of 1c. In order to compare their cation-radical stabilities, similar measurements were also realized for phenoxathiine (1d) and phenoxaselenine (1e).

The electrochemical oxidation of dibenzo(c,e)-1,2-diselenine to its cation radical. A voltammetric study in acetonitrile at conventional electrodes and microelectrodes

Abstract The electrochemical oxidation of dibenzo(c,e)-1,2-diselenine ( 1a ) in dry acetonitrile was studied by conventional and microelectrode techniques. Steady-state voltammetry and cyclic voltammetry proved the occurrence of an electro-chemical-electronic (ECE)-type mechanism for the first oxidation signal. The chemical step involves the reaction of the cation radical with residual water. The first electron transfer proceeds with a heterogeneous rate constant of 0.14 ± 0.01 cm s −1 , whereas a pseudo-first-order kinetic rate constant of 20.7 ± 2.8 s −1 is computed for the chemical step, giving a half-life of 33 ± 4 ms for the cation radical of 1a . A comparison of these two rate constants with those of dibenzo(c,e)-1,2-dithiin ( 1b ), selenanthrene ( 2a ) and thianthrene ( 2b ) indicates that the electron transfer rate depends on the nature of the oxidized chalcogen, whereas the stabilization of the cation radical is also dependent on the geometry of the heterocycle.

Electrochemical oxidation of 2-phenyl-1,2-benzisothiazol-3(2H)-one and related open-chain compounds in acetonitrile

Abstract The electrochemical oxidation of 2-phenyl-1,2-benzisothiazol-3(2H)-ones and related compounds in acetonitrile solution was studied by voltammetry using a rotating platinum electrode, cyclic voltammetry, controlled potential coulometry and electrolysis. Further oxidation of studied compounds gave the corresponding sulfoxide. Comparison of the cyclic compound and related open-chain compounds was discussed.

Electrochemical behaviour of pharmacologically interesting seleno-organic compounds—part 3. Ortho methylseleno benzanilides

Abstract The electrochemical behaviour of 2-(methylseleno)benzanilide, one of the major metabolites of Ebselen, together with a series of 2-methylseleno-(4′-X-phenyl)benzamides were investigated by voltammetry using a rotating platinum electrode, cyclic voltammetry, controlled potential coulometry and electrolysis. The measurements were realized in acetonitrile solution. The influence of temperature and acid on the nature of the oxidized products is shown. Comparison with their thio analogs is discussed.

Electrochemical behaviour of seleno-organic compounds—part 3. Electrochemical study of dibenzo (c, e)-1,2-diselenine in acetonitrile medium

Abstract The electrochemical oxidation of dibenzo(c, e)-1,2-diselenine 1b has been investigated in acetonitrile medium by voltammetry at rotating platinum electrode, cyclic voltammetry and constant potential coulometry. The exhaustive oxidation of compound 1b exclusively leads to the formation of the monoxide of dibenzo(b, d)selenophene with concomitant extrusion of selenium dioxide. The influence of the duration and the temperature of the electrolysis is reported. Each step of the electrochemical oxidation is described in detail. Comparison with the chemical and electrochemical oxidation of dibenzo(c, e)-1,2- dithiine and the chemical oxidation of cyclic vic-diselenide is discussed.

Electrochemical oxidation of 2-phenyl-1,2-benzisothiazol-3(2H)-ones and related compounds in acetonitrile. A study using microelectrodes

Abstract The electrochemical oxidation of 2-phenyl-1,2-benzisothiazol-3(2H)-ones and related compounds was studied by conventional and microelectrode techniques. Hammett plots were drawn for a series of N-aryl substituted 2-phenyl-1,2-benzisothiazol-3-(2H)-ones and compared with those of the selenium analogues, 2-phenyl-1,2-benzisoselenazol-3(2H)-ones. Controlled potential electrolysis furnished the corresponding sulphoxides and the reaction pathway was shown to proceed through an ECE mechanism.