Application of the dissociative electron transfer theory and its extension to the case of in-cage interactions in the electrochemical reduction of arenesulfonyl chlorides

Abstract

Important aspects of the electrochemical reduction of a series of substituted arene sulfonyl chlorides are investigated. An interesting autocatalytic mechanism is encountered where the starting material is reduced both at the electrode and through homogeneous electron transfer from the resulting sulfinate anion. This is due to the homogenous electron transfer from the two-electron reduction produced anion (arene sulfinate) to the parent arene sulfonyl chloride. As a result, the reduction process and hence the generated final products depend on both the concentration of the substrate and the scan rate. A change is also observed in the reductive cleavage mechanism as a function of the substituent on the phenyl ring of the arene sulfonyl chloride. With 4-cyano and 4-nitrophenyl sulfonyl chlorides a "sticky" dissociative ET mechanism takes place where a concerted ET mechanism leads to the formation of a radical/anion cluster before decomposition. With other substituents (MeO, Me, H, Cl, and F) a "classical" dissociative ET is followed, where the ET and bond cleavage are simultaneous. The dissociative electron transfer theory, as well as its extension to the case of strong in-cage interactions between the produced fragments, along with gas phase chemical quantum calculations results helped us to rationalize both the observed change in the ET mechanism and the occurrence of the "sticky" dissociative ET mechanism. The radical/anion pair interactions have been determined both in solution as well as in the gas phase. The study also shows that despite the low magnitude of in-cage interactions in acetonitrile compared to the gas phase their existence strongly affects the dynamics of the involved reactions. It also shows that, as expected, these interactions are reinforced by the existence of strong electron-withdrawing substituents. The occurrence of an autocatalytic process and the existence of the radical/anion interaction may explain the differences previously observed in the reduction of these compounds in different media.

pH dependent kinetic insights of electrocatalytic arsenite oxidation reactions at Pt surface

“…6. Note that D values determined by using equation (7) are closely matched with the reference values previously determined at variable pH by using diffusion cell method [25][26][27]. Remarkable fluctuations are seen in case of D values determined by equation (3), which might be due to inconstancy of  with scan rate at higher pH values as discussed earlier.…”

New Insights into the Substituents’ Effect on the Formation and Dissociation of Radical Anions: Dissociative Electron Transfer to Arylsulfonylphthalimides

“…Scanning towards more negative potentials, several additional peaks are observed (solid CV in Figure 5a). The first peak is followed by the reduction peak of p‐cyanobenzenesulfinate (Ep=−1.93 V vs SCE), which is preceded by a small peak corresponding to the reduction of its protonated form, as previously observed in the reduction of the p‐cyanbenzenesulfonyl chloride [35] . The peak corresponding to the reduction of the phthalimide anion, generated at the first reduction peak, is also observed at −2.19 V vs SCE.…”

“…It is important to note some important differences between the arylsulfonyl chlorides we studied previously [35] and the presently investigated arylsulfonylphthalimides ( 1 a – g ). The former compounds are all reduced following a concerted electron transfer mechanism, where the electron transfer and the S−Cl bon cleavage are simultaneous, and with strong in cage interaction between the fragments for the p‐cyano and p‐nitro compounds.…”

Photocatalytical and Photochemical Generation of Imidoyl Radicals: Synthetic Applications

“…[42] The salient features of the approach were broad substrate scope, high functional group tolerance, and good to excellent yields. In addition to 61, the authors also explored CH 3 [43] to give difluoromethyl radical 64, which undergoes an addition reaction with isocyanide 1 to generate imidoyl radical 65. The generated imidoyl radical 65 undergoes intramolecular cyclization, followed by oxidation to provide a cationic intermediate 67, which finally leads to the desired 6-difluoroalkylated phenanthridines 41 via deprotonation.…”

“…SCE] reduces the CF 2 HSO 2 Cl 61 [E 1/2 =−0.4 to −1.1 V vs . SCE] [43] to give difluoromethyl radical 64 , which undergoes an addition reaction with isocyanide 1 to generate imidoyl radical 65 . The generated imidoyl radical 65 undergoes intramolecular cyclization, followed by oxidation to provide a cationic intermediate 67 , which finally leads to the desired 6‐difluoroalkylated phenanthridines 41 via deprotonation.…”