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The electrochemical reduction of a series of nitro-substituted benzenesulfonyl chlorides is investigated. The results of the electrochemical study are analysed with the assistance of theoretical calculations. The study shows that the electron transfer mechanism depends on the position of the nitro substituent on the phenyl ring. The 3-nitrobenzenesulfonyl chloride follows a stepwise mechanism where the reduction leads to an intermediate radical anion. For the 4-nitrobenzenesulfonyl chloride, 2-nitrobenzenesulfonyl chloride, and 2,4-nitrobenzenesulfonyl chloride, the reduction follows a "sticky" dissociative mechanism, where the electron transfer and S–Cl bond cleavage are concerted. The dissociation products (arylsulfinyl radical and chloride anion) show strong interactions. The difference in behaviour is associated with the overlap of the π* orbital and the S–Cl σ* orbital for the latter three compounds. The through resonance stability of the arylsulfinyl radicals for the para and ortho nitro-substituted compounds facilitates the dissociation of the reduced structures. Upon reduction, the 3-nitrobenzenesulfonyl chloride and 4-nitrobenzenesulfonyl chloride, also produce the corresponding diaryl disulfones, which are easier to reduce that the parent molecules and hence induce an interesting autocatalytic mechanism. Such a mechanism, which depends on the concentration and the scan rate, does not take place with the 2-nitrobenzenesulfonyl chloride and 2,4-dinitrobenzenesulfonyl chloride due to the sterical hindrance of the nitro substituent at the ortho position, as it prevents the formation of the disulfones. [ABSTRACT FROM AUTHOR]

A series of chemically and biologically relevant N‐(arylthio)phthalimides is synthesized and its electrochemical reduction investigated. The results of the electrochemical study are analysed through application of Savéant's dissociative electron transfer theory and with the assistance of theoretical calculations. Reduction of all investigated N‐(arylthio)phthalimides leads to the corresponding radical anions, followed by the ejection of the phthalimide anion resulting from the dissociation of the N−S chemical bond. This stepwise electron transfer mechanism is evidenced by the electrochemical data which allow determination of the standard reduction potentials of all compounds. In the formation of the N‐(arylthio)phthalimide radical anions, the theoretical calculations show that the incoming electron, is hosted by the phthalimidyl group indicating a homolytic dissociation mechanism. The dissociation rate constants of the radical anions are deduced and show that upon changing the substituent from the MeO, to Me, H, F, Cl and Br the dissociation becomes faster. A good correlation with the Hammett substituent constants is also obtained. Application of Savéant's theory through determination of the associated driving force and the intrinsic barrier energies help rationalize the observed results and show that the change in the dissociation rate constant depends mainly on the standard reduction potential of the parent compounds. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of a series of biologically relevant p‐substituted arylsulfonylphthalimides was investigated and the results were analysed using theoretical calculations and application of Savéant's dissociative electron transfer theory. The dissociation rate constants of the radical anion intermediates were calculated and showed that upon changing the substituent from the MeO, to Me, H, F, Cl and CN the dissociation became faster. A good correlation with the Hammett substituent constants was also obtained. With the NO2 substituent the trend was however inversed. These results and the electrolysis data showed that the dissociation involves the N−S chemical bond. Theoretical calculations showed that for all investigated compounds the extra electron was hosted by the phthalimidyl group except for the p‐NO2 substituted compound for which the extra electron was hosted by the nitrophenyl moiety. Thermodynamic considerations showed that the dissociation of the radical anion of the p‐NO2 compound followed a heterolytic cleavage whereas those of the rest of the investigated compounds followed a homolytic cleavage. The above intriguing result was rationalized through application of the extension of Savéant's dissociative electron transfer theory to the decomposition of radical anions. This study is important not only for understanding substituents' effect on the biological activity of these compounds but also on the formation and dissociation of radical anions in general. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of S-phenyl benzenethiosulfonate (1) was investigated by cyclic voltammetry at different scan rates (0.1–60 V/s) using glassy carbon electrodes in three different solvents; acetonitrile, dimethyl sulfoxide, and dimethyl formamide. The initial electron transfer (ET) to the investigated compound follows a concerted process with the formation of a radical/ion pair before complete dissociation (“sticky” dissociative ET mechanism). Application of classical and “sticky” dissociative electron transfer theories, as well as theoretical calculations supported the proposed ET mechanism. The theoretical calculations showed that the LUMO of S-phenyl benzenethiosulfonate and SOMO of its reduced form are homed on the S-SO2 chemical bond with a low contribution on the rest of the molecule. This indicates that the incoming electron is directly injected to the chemical bond causing its cleavage. The controlled potential electrolysis of the investigated compound, monitored by high performance liquid chromatography and cyclic voltammetry, indicated the consumption of one electron per molecule, and final formation of diphenyl disulfide and phenyl sulfinate. All experimental and theoretical findings were used to propose the full reduction mechanism. Also, a solvent effect was observed on certain parameters including reduction peak potentials, transfer coefficient values, the strength of the interaction between the ion/radical fragments, and the chemical reaction processes following the first ET. This solvent effect was rationalized by comparison of the solvent’s properties. [ABSTRACT FROM AUTHOR]

Important aspects of the electrochemical reduction of 4-iodophenyl sulfonyl phthalimide and 4-iodophenyl sulfonyl chloride are investigated in acetonitrile at a glassy carbon electrode. A change in both the electron transfer mechanism as well as in the global reduction process is observed upon changing the group attached to the 4-iodophenyl sulfonyl moiety. For 4-iodophenyl sulfonyl phthalimide, the initial ET follows a stepwise process involving the intermediacy of the corresponding radical anion, which is readily detected by increasing the scan rate to 100 V/s. With 4-iodophenyl sulfonyl chloride, a concerted ET mechanism, where the S-Cl chemical bond is cleaved upon injection of the first electron, is followed. For the latter compound, an interesting autocatalytic mechanism is encountered, where the 4-iodophenyl sulfonyl chloride is reduced both at the electrode and through homogeneous electron transfer from the resulting sulfinate anion. An electron transfer between the generated sulfinate anion and the parent molecule is the basis to the observed autocatalytic process. Consequently, the reduction process depends on both the concentration of the substrate and the scan rate. Theoretical calculations results help to rationalize the observed difference in the first electron transfer mechanism. [ABSTRACT FROM AUTHOR]