Electrocatalyzed organohalide reductions

A kinetic method was used to estimate standard reduction potentials (E{dollar}sp0spprime){dollar} for a series of PCBs and PBBs in N,N-dimethylformamide. The method involves electrochemical measurement of rate constants (k{dollar}sb1){dollar} for electron transfer between an electrochemically generated reductant and a halobiphenyl. Since the reverse rate constant is at the diffusion limit, (k{dollar}sb{lcub}rm d{rcub}{dollar}), k{dollar}sb1{dollar}/k{dollar}sb{lcub}rm d{rcub}{dollar} is the equilibrium constant for electron transfer. E{dollar}sp0spprime{dollar}-values for PCBs and PBBs were correlated with peak potentials obtained from simple voltammetric experiments. These correlations can be used to predict E{dollar}sp0{dollar}'s for halobiphenyls to within about {dollar}pm{dollar} 0.05 V.; Reductions of {dollar}alpha{dollar}-haloacetic acids are new examples of activated carbon-halogen cleavage by vitamin B{dollar}sb{lcub}12{rcub}{dollar} at its E{dollar}sp0{dollar} for Co(II)/Co(I). In aqueous acetonitrile pH 3, the catalytic reductions feature stepwise loss of halogen to give acetic acid. Electrocatalysis with vitamin B{dollar}sb{lcub}12{rcub}{dollar} decreased overpotentials for reduction of haloacetic acids by 0.75 to 1.4 V. Rate constants estimated by cyclic voltammetry were: chloroacetic acid 6 {dollar}times{dollar} 10{dollar}sp3{dollar} M{dollar}sp{lcub}-1{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar}; trichloroacetic acid 1.5 {dollar}times{dollar} 10{dollar}sp5{dollar} M{dollar}sp{lcub}-1{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar}; and bromoacetic acid 9 {dollar}times{dollar} 10{dollar}sp4{dollar} M{dollar}sp{lcub}-1{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar}. The large decreases in overpotential and the high catalytic rate constant suggest an inner-sphere mechanism.; 9-Amino-Co{dollar}alpha{dollar}-chloro-Co{dollar}beta{dollar}-cyanocob(III)yrinic acid c-lactam, a derivative of vitamin B{dollar}sb{lcub}12{rcub}{dollar} was synthesized with a 45% yield. The product contained six carboxylic groups on the corrin ring, but titration with acid showed only one pK{dollar}sb{lcub}rm a{rcub}{dollar}, at 4.95. In the presence of 7 mM cyanide ion (CN{dollar}sp-{dollar}) a direct two-electron reduction of Co(III) to Co(I) was found at a potential of {dollar}-{dollar}0.686 V (vs SCE). In the pH 2.5/HCN phosphate buffer solution, the apparent diffusion coefficient at polished glassy carbon electrode was 1.3 {dollar}times{dollar} 10{dollar}sp{lcub}-6{rcub}{dollar} cm{dollar}sp2{dollar} s{dollar}sp{lcub}-1{rcub}{dollar}. The catalyst was incorporated in a film of didodecyldimethyl-ammonium bromide (DDAB) on pyrolytic graphite electrode (PG) for electrocatalytic studies. The surface concentration ({dollar}Gammasb{lcub}rm t{rcub}{dollar}), 3.24 {dollar}times{dollar} 10{dollar}sp{lcub}-9{rcub}{dollar} mol cm{dollar}sp{lcub}-2{rcub}{dollar} and the apparent charge transfer coefficient (D{dollar}sb{lcub}rm ct{rcub}{dollar}), 5.9{dollar}times{dollar} 10{dollar}sp{lcub}-7{rcub}{dollar} cm{dollar}sp2{dollar} s{dollar}sp{lcub}-1{rcub}{dollar}, were obtained. The vitamin B{dollar}sb{lcub}12{rcub}{dollar} hexacarboxylate in DDAB films catalytically reduced trichloroacetic acid and ethylene dibromide in solution, and thus has similar catalytic activity to vitamin B{dollar}sb{lcub}12{rcub}{dollar}.; Expanded space grid digital simulation of second-order, two-electron homogeneous electrocatalysis was extended to slow scan voltammetry at hemispherical microelectrodes. Working curves of catalytic efficiency vs. log k{dollar}sb1{dollar} were generated assuming reacting species with equal diffusion coefficients. Simulations using hemispherical radii of (2/{dollar}pi){dollar}r{dollar}sb{lcub}rm d{rcub}{dollar} were used to predict catalytic efficiencies for microdisk electrodes with radii r{dollar}sb{lcub}rm d{rcub}{dollar}. Simulated working curves were used to estimate a log k...