Electrochemical oxidation applications

The electrochemical stability range determines the usefulness of nonaqueous electrolytes for electrochemical studies as well as for applications. It indicates the absence of electrochemical oxidation or reduction of solvent or ions, and of faradaic current... 

Electrochemical methods of protection rest on different precepts (1) electroplating of the corroding metal with a thin protective layer of a more corrosion-resistant metal, (2) electrochemical oxidation of the surface or application of other types of surface layer, (3) control of polarization characteristics of the corroding metal (the position and shape of its polarization curves), and (4) control of potential of the corroding metal. 

The field of electrochemical ion transfer reactions (EITRs) is relatively recent compared with that of electron transfer reactions, and the application of molecular dynamics simulations to study this phenomenon dates from the 1990s. The simulations may shed light on various aspects of the EITR. One of the key questions on this problem is if EITR can be interpreted in the same grounds as those employed to understand electron transfer reactions (ETRs). Eor example, let us consider the electrochemical oxidation reaction of iodine ... 

In this method the creation of defects is achieved by the application of ultrashort (10 ns) voltage pulses to the tip of an electrochemical STM arrangement. The electrochemical cell composed of the tip and the sample within a nanometer distance is small enough that the double layers may be polarized within nanoseconds. On applying positive pulses to the tip, the electrochemical oxidation reaction of the surface is driven far from equilibrium. This leads to local confinement of the reactions and to the formation of nanostructures. For every pufse applied, just one hole is created directly under the tip. This overcomes the restrictions of conventional electrochemistry (without the ultrashort pulses), where the formation of nanostructures is not possible. The holes generated in this way can then be filled with a metal such as Cu by... 

Different experimental approaches were applied in the past [6, 45] and in recent years [23, 46] to study the nature of the organic residue. But the results or their interpretation have been contradictory. Even at present, the application of modem analytical techniques and optimized electrochemical instruments have led to different results and all three particles given above, namely HCO, COH and CO, have been recently discussed as possible methanol intermediates [14,15,23,46,47]. We shall present here the results of recent investigations on the electrochemical oxidation of methanol by application of electrochemical thermal desorption mass spectroscopy (ECTDMS) on-line mass spectroscopy, and Fourier Transform IR-reflection-absorption spectroscopy (SNIFTIRS). 

R. Kotz reviews the application of the most powerful surface physics technique, photoelectron spectroscopy, for the elucidation of the composition of electrodes. He exemplifies the potential of this technique for materials which play a key role in electrochemical oxidation processes or are used in some other electrochemical process. 

Much of the study of ECL reactions has centered on two areas electron transfer reactions between certain transition metal complexes, and radical ion-annihilation reactions between polyaromatic hydrocarbons. ECL also encompasses the electrochemical generation of conventional chemiluminescence (CL) reactions, such as the electrochemical oxidation of luminol. Cathodic luminescence from oxide-covered valve metal electrodes is also termed ECL in the literature, and has found applications in analytical chemistry. Hence this type of ECL will also be covered here. 

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. 

Because the direct electrochemical oxidation of NAD(P)H has to take place at an anode potential of + 900 mV vs NHE or more, only rather oxidation-stable substrates can be transformed without loss of selectivity—thus limiting the applicability of this method. The electron transfer between NADH and the anode may be accellerated by the use of a mediator. At the same time, electrode fouling which is often observed in the anodic oxidation of NADH can be prevented. Synthetic applications have been described for the oxidation of 2-hexene-l-ol and 2-butanol to 2-hexenal and 2-butanone catalyzed by yeast alcohol dehydrogenase (YADH) and the alcohol dehydrogenase from Thermoanaerobium brockii (TBADH) repectively with indirect electrochemical... 

Other mediators which have been used in combination with diaphorase for the regeneration of NAD+ are riboflavin and Vitamin K3, which is 2,3-dimethyl-1,4-naphthoquinone. However, especially riboflavin is not stable enough for synthetic applications [40]. Better stability is exhibited by phenanthrolindiones as mediators. In combination with diaphorase, Ohshiro [41] showed the indirect electrochemical oxidation of cyclohexanol to cyclohexanone using the NAD+ dependent HLADH with a turnover frequency of two per hour. For an effective enzymatic synthesis, this turnover frequency, however, would be too small. In our own studies, we were able to accelerate the NAD(P)+ regeneration considerably by lowering the electron density within the... 

In the cation pool method organic cations are generated by low temperature electrochemical oxidation of their precursors. Because electrochemical reactions take place only on the surface of the electrode, the accumulation of cations usually takes several hours. Therefore, the applicability of the method strongly depends on the stability of the cation that is accumulated. In order to solve this problem, we have developed a sequential one-pot indirect method, in which an active reagent is generated and accumulated electrochemically (step 1), and is subsequently allowed to react with a precursor to generate a cation pool (step 2). The cation pool thus-generated is allowed to react with a nucleophile (step 3).36... 

The mechanism of the polymerization was discussed based on electrochemical measurements. Applications of the electro-oxidative polymerization were also described. 

Colbow, Zhang, and Wilkinson [128] showed that the performance of liquid feed fuel cells could be increased by oxidizing the carbon diffusion layer. The DL was electrochemically oxidized in acidic aqueous solution (impregnated in some cases with proton-conducting ionomer) prior to application of the electrocatalyst. 

In this chapter we describe the use of polyelectrolytes carrying redox-active centers on electrode surfaces with particular emphasis on organized layer-by-layer redox polyelectrolyte multilayers (RPEM). In redox-active polyelectrolyte multilayers the polyion-polyion intrinsic charge compensation can be broken by ion exchange driven by the electrochemical oxidation and reduction forming extrinsic polyion-counterion pairing. In this chapter we describe the structure, dynamics and applications of these systems. 

CNTs-nanoparticles composites have also been exploited for electrochemical sensing applications [17, 118, 119[. Incorporation of metal and oxide nanoparticles has been demonstrated to enhance the electrocatalytical efficiency. A wide range of particles have been used (Pt, Pd, Co, FeCo alloy, Co, Cu, Ag, Cu) and in some cases such CNT/nanoparticles have been combined together with charged polymers [17]. 

Baillie, C.. Bader, M.G. (1991). Chemical aspects of interfacial adhesion between electrochemically oxidized carbon fibers and epoxy resins. In Proc. ICCM-VIII, Composites Design. Manufacture and Application (S.W. Tsai and G.S. Springer, eds.), SAMPE Pub. Paper I IB. 

This electrochemical oxidation mediated by NHPI was applicable to benzylic carbons, allylic carbons, deprotection of acetals, oxidative cleavage of cyclic acetals and amide to afford benzoylated compounds, enones ", carbonyl compounds, -hydroxyethyl esters and imides, respectively (equations 31-35). 

Electrochemical oxidation is a means of generating reactive metabolites either in the absence of biological nucleophiles or through the addition of nucleophiles under controlled conditions. Mass spectrometric, NMR and IR evaluations can all be performed as described for amodiaquine [41] but recapitulation of microsomal metabolism under electrochemical conditions is not always possible and hence this technique is probably of limited applicability. 

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