Electrochemical reduction of benzyl bromide in the presence of carbon dioxide

none2The electrochemical reduction of benzyl bromide has been investigated in acetonitrile and CO2-saturated acetonitrile by cyclic voltammetry and controlled-potential electrolysis. Electroreduction of the halide in the absence of CO2 leads to a variety of products, the distribution of which depends on the electrode material, applied potential and proton availability in the medium. The electrocarboxylation processes have been carried out at Hg and graphite cathodes using both a two-compartment cell and an undivided cell with a sacrificial Al anode. The best results (87% phenylacetic acid yield) were obtained at Hg in the undivided cell. Catalysis by Co(salen) allows the process to be performed at potentials more positive than those required by direct reduction but gives only poor to moderate yields of acid. Results obtained from experiments carried out with benzyl chloride have been compared with those obtained in the case of benzyl bromide.noneISSE A.A.; GENNARO A.AHMED ISSE, Abdirisak; Gennaro, Armand

Electrochemical reduction of benzyl bromide in the presence of carbon dioxide

751-757The electrochemical reduction of benzyl bromide has been investigated in acetonitrile and CO2-saturated acetonitrile by cyclic voltammetry and contro lled-potential electrolysis. Electroreduction of the halide in the absence of CO2 leads to a variety of products, the distribution of which depends on the elec trode material, applied potential and proton availability in the medium. The electrocarboxylation process, have been carried out at Hg and graphite cathodes using both a two compartment cell and an undivided cell with dissolving Al anode. The best results (87% phenylacetic yield) are obtained at Hg in the undivided cell. Catalysis by Co(salen) allows the process to be performed at potentials more positive than those required by direct reduction but gives only poor to moderate yields of acid. Results obtained from experiments carried out with benzyl chloride have been compared with those obtained in the case of benzyl bromide

One-pot synthesis of benzoic acid by electrocatalytic reduction of bromobenzene in the presence of CO2

The electrocatalytic properties of Ag for the reduction of organic halides have been exploited for one-pot electrosynthesis of benzoic acid. Among various investigated dipolar aprotic solvents, only dimethylformamide gives good results. The process has been investigated both under potentiostatic and galvanostatic control. In both cases, the reaction smoothly proceeds under mild conditions and lasts in a few hours, giving benzoic acid yields of the order of 80%. Keywords: Electrocarboxylation, Benzoic acid, Electrocatalysi

Estimation of the standard reduction potentials of some 1-arylethyl radicals in acetonitrile

The redox properties of some arylethyl radicals, which are involved in the electrochemical synthesis of important anti-in\ufb02ammatory agents, have been investigated in CH3CN by an indirect electrochemical method based on the catalytic reduction of the corresponding arylethyl halides (RX) by electrogenerated aromatic or heteroaromatic anion radicals (D\ue001-). The reaction between RXand D\ue001- leads to aradical R\ue001, which can react with D\ue001- eitherbyradical coupling (k3) or by electron transfer (k4). Examination of the competition between these reactions, which can be expressed by a dimensionless parameter q =k4/(k3 + k4), as a function of E\ub0 D/D\ue001- allows estimation of the reduction potentials of the arylethyl radicals. The standard reduction potentials obtained for the radicals 1-(4-isobutylphenyl)ethyl, 1-(6-methoxy-2-naphthyl)ethyl, and 1-(4-biphenyl)ethyl are -1.64, -1.62, and -1.15 V vs. SCE, respectively

One-versus two-electron reaction pathways in the electrocatalytic reduction of benzyl bromide at silver cathodes

The electrocatalytic reduction of benzyl bromide at a silver cathode has been investigated in acetonitrile in the absence and presence of acids, using cyclic voltammetry (CV) and controlled-potential electrolysis (CPE). CV gives rise to two reduction waves, which represent the dissociative 1e- reduction of PhCH2Br to PhCH2\ue002 and Br-, followed by a further reduction of the benzyl radical to PhCH2- at more negative potentials. The charge stoichiometry (1e- vs 2e-/molecule) and product distribution depend on the applied potential and reaction medium. In the absence of added acids, the reduction of PhCH2Br at potentials of the \ufb01rst wave is a 1e- process mainly yielding bibenzyl, whereas toluene becomes the principal product at potentials beyond the second wave. The addition of acids strongly modi\ufb01es the dependence of selectivity on the applied potential. The presence of a strong acid changes the mechanism of the process, which now becomes a 2e- reduction to toluene, even at potentials corresponding to the \ufb01rst reduction wave

The influence of aluminium cations on electrocarboxylation processes in undivided cells with Al sacrificial anodes

The in\ufb02uence of Al cations on the electrochemical carboxylation of acenaphthylene (1), benzophenone (2), 6-methoxy-2-acetonaphthone (3), and benzyl chloride (4) has been investigated in dimethylformamide at a glassy carbon cathode. The Al(III) ions were either added at the beginning of the experiment or were released from the anode during electrocarboxylation. It has been found that when Al cations are added to the reaction medium, they strongly in\ufb02uence the reduction process, in most cases leading to a complete change of the mechanism. For example, in the case of 1, the radical anion (1\ue001-) formed upon 1e- reduction rapidly reacts with Al(III) to give an Al(III) adduct, which is further reduced either at the electrode or in solution by disproportionation. The rate constant of the adduct formation is ca. 3 orders of magnitude larger than that of the carboxylation reaction between 1\ue001- and CO2. By contrast, when Al(III) ions are supplied to the reaction medium in concomitance with carboxylate formation, hence by oxidation of the anode during electrocarboxylation, they show no e\ufb00ect on the cathodic process. This has been con\ufb01rmed by both voltammetric investigations and preparative scale experiments. It thus appears that whereas free Al(III) ions strongly in\ufb02uence the reduction process, the metal cations produced by the consumable anode in undivided cells are intercepted and complexed by the carboxylated products before they can reach the cathode. Therefore, the cathodic process occurs in a medium without free Al(III) ions

Silver nanoparticles deposited on glassy carbon. Electrocatalytic activity for reduction of benzyl chloride

A potentiostatic single-pulse technique was employed to prepare silver nanoclusters deposited on glassy carbon (GC) from CH3CN + 0.1 M LiCO4 plating solutions containing 1–2 mM AgClO4. The morphology of the particles, obtained at a constant voltage pulse of variable duration, was examined by scanning electron microscopy. Clusters with particle diameter of 100–400 nm, which are uniformly distributed over the GC surface, can be prepared on a time-scale of 30–90 s. The Ag clusters exhibit remarkable electrocatalytic activity for the reduction of benzyl chloride. The supported Ag nanoclusters and bulk Ag metal have comparable electrocatalytic activities, both anticipating the reduction potential of PhCH2Cl by ca. 0.5 V with respect to bare GC. The Ag-modified electrode was used in preparative scale electrocatalytic reduction of benzyl chloride in different experimental conditions. Good yields of toluene or phenylacetic acid were obtained, depending on experimental conditions, whereas no loss of catalytic activity could be observed, even when the electrode was repeatedly used over a period of several days. Keywords: Nanoparticles, Electrodeposition, Silver clusters, Electrocatalysis, Benzyl chlorid