Electrooxidation products

Recently, the electrochemical behavior saturated alcohols, that is, propargyl alcohol (HCSCCH2OH, PA) [145], benzyl alcohol (C6H5CH2OH, BA) [146] andallylalcohol [147], has been studied at Pd electrodes in an acid medium by cyclic voltammetry, chronoamperometry, and on-line mass spectrometry. For BA, it was observed that the fragmentation of the molecules occurs at potentials in the hydrogen ad-sorption/absorption region of palladium, whereas for PA the adsorbates maintain the C3-chain. On the other hand, the yields of the electroreduction and electrooxidation products for both PA and BA differ from those obtained at Pt [146,148,149]. 

Instrumentation. A cell design employing reticulated vitreous carbon as the working electrode material that enables both UV-Vis absorption and luminescence measurements has been described [47]. A thin-layer cell with a platinum working electrode has been developed [69]. The luminescence of the electrooxidation products of o-tolidine as a function of electrode potential was studied. A simplified flow cell design has been reported [70]. Luminescence spectra and fluorescence intensity for various aromatic compounds and their electrochemical and photochemical reaction products were observed as a function of flow rate, current and time after the potential step. In the latter study the electrooxidation of p-phenylenediamine (PPD) was examined. The cyclic voltammogram showed two oxidation peaks the first one is assumed to be caused by the formation of the radical cation according to... 

Zhao W, Jusys Z, Behm RJ (2012) Complete quantitative online analysis of methanol electrooxidation products via electron impact and electrospray ionization mass spectrometry. Anal Chem 84 5479-5483... 

Iron(IV) porphyrins can be generated upon oxidation of a-bonded iron(III) porphyrins [7, 12, 62, 184, 188, 219] with the stability of the electrooxidized product, depending in large part on the porphyrin macrocycle and the type of cr-bonded axial ligand [12]. The chemical or electrochemical oxidation of a Hs-fluoro Fe(III) complex, [(T(p, m-F2)PP)Fe(F)2] , has been examined by Nanthakumar and Goff [220,221] and the iron oxidation state was assigned as Fe(III) or Fe(IV), on the basis of NMR and UV-visible spectroscopy. 

ESR spectra of a variety of electrooxidation products of thiophene oligomers, including orthogonally bridged dimers of... 

OS 30] [R 30] [P 22] The feasibility of generating a cation pool, i.e. of performing multiple reactions with various reactants, by means of electrooxidative micro flow processing was demonstrated [66,67]. The micro reaction system was consequently termed cation flow . By this means, various C-C bonded products were made from carbamates, having pyrrolidine, piperidine, diethylamine and trihydroisoquinoline moieties. These carbamates were combined with various silyl enol ethers, yielding nine products. 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

Gold is generally considered a poor electro-catalyst for oxidation of small alcohols, particularly in acid media. In alkaline media, however, the reactivity increases, which is related to that fact that no poisoning CO-hke species can be formed or adsorbed on the surface [Nishimura et al., 1989 Tremihosi-Filho et al., 1998]. Similar to Pt electrodes, the oxidation of ethanol starts at potentials corresponding to the onset of surface oxidation, emphasizing the key role of surface oxides and hydroxides in the oxidation process. The only product observed upon the electrooxidation of ethanol on Au in an alkaline electrolyte is acetate, the deprotonated form of acetic acid. The lack of carbon dioxide as a reaction product again suggests that adsorbed CO-like species are an essential intermediate in CO2 formation. 

Tremiliosi-Eilho G, Gonzalez ER, Motheo AJ, Belgsir EM, Leger JM, Lamy C. 1998. Electrooxidation of ethanol on gold Analysis of the reaction products and mechanism. J Electroanal Chem 444 31-39. 

Jusys Z, Kaiser J, Behm RJ. 2003. Methanol electrooxidation over Pt/C fuel cell catalysts— Dependence of product yields on catalyst loading. Langmuir 19 6759-6769. 

Petukhova RP, Stenin VF, Podlovchenko BI. 1977. About the composition of the products of methanol electrooxidation on smooth platinum. Elektrokhimiya 14 755-756. 

Wang H, Jusys Z, Behm RJ. 2004. Ethanol electrooxidation on a carbon-supported Pt catalyst Reaction kinetics and product yields. J Phys Chem B 108 19413-19424. 

On the other hand, the electrooxidation of norbornadiene or bicyclo[2.2.2]octa-2,5-diene shows a different electrochemistry (type B) and yields a mixture of some unique products as shown in equations 12 and 13. 

Owing to these nonelectrodic reactions, the apparent number of electron equivalents involved in the electrooxidation of Ph2SnH2 at —0.27 V is < 2. Reduction of the chloro-hydride Ph2SnHCl yields Ph2SnH2 as the main product ... 

Electrooxidation of a-alkoxystannanes on a preparative scale can therefore be carried out at lower potentials, with cleavage of the C—Sn bond. Nucleophilic attack, e.g. by methanol, butanol or an amine on carbon at that a position, gives the product in high yields, 90-95% diether or 55% aminoether. A number of examples have been given ... 

Studies on the electrochemical oxidation of silyl-substituted ethers have uncovered a rich variety of synthetic application in recent years. Since acetals, the products of the anodic oxidation in the presence of alcohols, are readily hydrolyzed to carbonyl compounds, silyl-substituted ethers can be utilized as efficient precursors of carbonyl compounds. If we consider the synthetic application of the electrooxidation of silyl-substituted ethers, the first question which must be solved is how we synthesize ethers having a silyl group at the carbon adjacent to the oxygen. We can consider either the formation of the C-C bond (Scheme 15a) or the formation of the C-O bond (Scheme 15b). The formation of the C Si bond is also effective, but this method does not seem to be useful from a view point of organic synthesis because the required starting materials are carbonyl compounds. 

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