Estimation of Standard Reduction Potentials of Halogen Atoms and Alkyl Halides

Abstract

Standard reduction potentials, SRPs, of the halogen atoms have been calculated in water on the basis of an appropriate thermochemical cycle. Using the best up-to-date thermodynamic data available in the literature, we have calculated E(o)(X•/X-) values of 3.66, 2.59, 2.04, and 1.37 V vs SHE for F•, Cl•, Br•, and I•, respectively. Additionally, we have computed the SRPs of Cl•, Br•, and I• in acetonitrile (CH3CN) and dimethylformamide (DMF) by correcting the values obtained in water for the free energies of transfer of X• and X- from water to the nonaqueous solvent S and the intersolvent potential between water and S. From the values of E(o)(X •/X-) in CH(3)CN and DMF, the SRPs of a series of alkyl halides of relevance to atom transfer radical polymerization and other important processes such as pollution abatement have been calculated in these two solvents. This has been done with the aid of a thermochemical cycle involving the gas-phase homolytic dissociation of the C-X bond, solvation of RX, R•, and X•, and reduction of X• to X- in solution.

The solvent effect on the electrocatalytic cleavage of carbon-halogen bonds on Ag and Au

“…In all solvents E p of BAN on GC is 0.25-0.3 V more positive than that of CAN; this feature is consistent with the alkyl bromide reduction being both thermodynamically and kinetically more favoured than that of the corresponding chloride, owing to the weaker carbon-halogen bond in BAN than in CAN [47]. On Au and Ag, the effect of the halide leaving group still remains, but the reduction potentials are remarkably shifted in the positive direction with respect to GC, emphasizing the catalytic nature of the process at these metallic electrodes.…”

Characterization and photocatalytic behavior of 2,9-di(aryl)-1,10-phenanthroline copper(i) complexes

“…), and the strong reducing potential of *C, excited state complex *C may take part in an oxidative quenching cycle when the excitation involves populating the LUMO+1 and/or LUMO+2. 19a,36a,66 As *C is a strong reductant and sufficiently long-lived, fairly efficient outer sphere electron-transfer occurs from the complexed phenanthroline radical anion to the oxidative quencher, in this case, CBr 4 (E ox = -0.48 V), 76 except when the electron of the radical ion is populating the LUMO. This results in cleavage of one of the carbon-bromine bonds of CBr 4 and thus forms the tribromomethyl radical and a bromide anion as well as the ground state Cu(II) complex D. The Cu(II) in D is surrounded by the two encaging phenanthroline ligands that provide a tetragonally-distorted pseudo-tetrahedral ligand environment.…”

Direct C(sp3)–H Cross Coupling Enabled by Catalytic Generation of Chlorine Radicals

“…A photoredox catalyst was envisioned to promote the necessary single-electron oxidation and reduction of the Ni catalyst to facilitate the overall redox-neutral process. Importantly, whereas most photoredox catalysts do not have sufficient energy to oxidize chloride anion ( E ° = 2.03 V vs SCE in MeCN), 11 this strategy offers a visible-light-driven mechanism for halogen radical formation enabled by the sequential capture of two photons.…”