Hydrogen atom abstraction and solvent involvement in the electrochemistry of haloaromatics

Synthesis of Graphene-like Films by Electrochemical Reduction of Polyhalogenated Aromatic Compounds and their Electrochemical Capacitor Applications

“…On the contrary, for HCB, the transfer coefficient is found to be 0.42, indicating the occurrence of a stepwise mechanism. These results are in good agreement with most current published research findings about the electrochemical reduction of aryl halides on electrocatalytic surfaces (Ag, Pd, Cu, Au and Hg). − It is well-known that aryl halides undergo the stepwise DET mechanism at inert electrodes, e.g., glassy carbon (GC). ,, However, the various driving forces such as the type of the halogen atom, the molecular structure of ArX, the morphology and surface structure of the electrode, and adsorption/desorption behavior of the halide ions can change their DET mechanism from stepwise to concerted. Electrochemical studies performed with Ag electrodes have revealed that, upon reduction of aryl bromides (ArBr), the nature of the electrode material promotes the radical mechanism due to the strong interaction between ArBr •– and Ag .…”

Polymerization Photoinitiators with Near-Resonance Enhanced Two-Photon Absorption Cross-Section: Toward High-Resolution Photoresist with Improved Sensitivity

“…Here again, the irreversibility of both CV waves reveals the unstable character of the electrogenerated anion radicals which could potentially be involved in hydrogen abstraction, radical−radical coupling reactions, or in the hydrogenolysis of the carbon−halogen bond. 88 From the spectroscopic data, ΔE 00 is found at 440 and 433 nm for V-Shape and Oct, respectively (2.82 and 2.87 eV). From eq 2, a standard Gibbs energy for the ET between two V-Shape or Oct molecules can be calculated, corresponding to −11.4 and −2.3 kJ/mol.…”

“…The distribution of spin densities obtained at the DFT/M06HF/6-31G­(d,p) shown in Figure S6 indicates a stronger delocalization of the radical anion, which is thus more stable. Here again, the irreversibility of both CV waves reveals the unstable character of the electrogenerated anion radicals which could potentially be involved in hydrogen abstraction, radical–radical coupling reactions, or in the hydrogenolysis of the carbon–halogen bond …”

Current electrochemical approaches to selective deuteration

“…The electrochemical reduction of aryl halides was in fact first studied several decades ago, with pioneering work by Murray, 36 Renaud 37 and Grimshaw 38 in the 1970's demonstrating the use of D 2 O in conjunction with an electrochemical reduction to affect deutero-dehalogenation (Scheme 9). These and latter works 39,40 examined the mechanistic distinction between either reduction to an aryl radical followed by deuterium atom transfer, or alternatively further reduction to an aryl carbanion reacting with D + , and the effect of the structure of the substrate on the preference for either of these possible pathways. In certain circumstances d 3 -MeCN or d 6 -DMSO were found to be superior than D 2 O as a deuterium atom transfer agent.…”

“…In certain circumstances d 3 -MeCN or d 6 -DMSO were found to be superior than D 2 O as a deuterium atom transfer agent. 39 Common electrochemical conditions at this time incorporated a mercury pool electrode, which is an unattractive option in modern electrochemical synthesis from a practical perspective. In the 1990's further work emerged from Sawaki, 41 who employed a lead cathode in DMF/D 2 O, but observed overincorporation of deuterium on certain aromatic substrates.…”