Anodic oxidation of Cr

On the other hand, when about 4 Fmol-1 of electricity is passed in the anodic oxidation of cr-thiomethylsilanes, both desilylation and desulfurization take place to give the corresponding acetals in good yields as follows. Since acetals are easily hydrolyzed to aldehydes, such an a-thiomethylsilane is a synthon of a formyl anion (equation 22). 

The following mechanism for the oxidation of Cr(III) to Cr(VI) on a Pb02 surface has been postulated. Pb02 operates as oxygen carrier anode... 

The anodic oxidation of silyl-substituted tetrahedranes was studied by cyclic voltammetry5. Tri-f-butyl(trimethylsilyl)tetrahedrane is oxidized more easily compared with tetra-t-butyltetrahedrane owing to the cr-donating silyl group (equation 2). 

Passive layers of various metals have semiconducting properties others have in-solating properties. As usual, this is a consequence of the band gap. The anodic oxides of metals like Fe, Cr, Ni, Co and Cu show semiconducting properties, whereas the valve metals like Al, Ta, Zr, Hf and Ti form electronically insolating... 

In all the examples given so far, the substrate carries at least one V-o -hydrogen atom. The anodic oxidation of fully substituted amides, like N, V-di-/cr/-butylformamide and V-formyl-2,2,6,6-tetramethylpiperidine, in MeOH would be expected to follow a different pathway. The products isolated after 12-14 F, methyl V-/cr/-butylcarbamate and V-methoxycarbonyl-2,2,6,6-tetramethylpiperidine, respectively [Eq. (37)] [102], indicated that the primarily formed substrate radical cation looses the formyl proton. Further oxidation of the neutral radical leads to the cation, which may either undergo cleavage, as in Eq. (38), or nucleophilic attack by the solvent, as in Eq. (39). 

Au(Cr)-covered crystals were used in nonaqueous solutions (e.g., butanol [111] or acetonitrile [158]), anodic oxidation of chromium was not observed. When Ti was used instead of Cr as the adhesion-promoting layer, dissolution of this metal through gold was very slow. Long-term use of Au(Ti) coatings shows that Ti also disappears, but the adhesion of gold to the resonator surface remains as before. 

Pamplin KL, Johnsrai DC (1996) Electrocatalysis of anodic oxygen-transfer reactirai oxidation of Cr(lII) to Cr(VI) at Bi(V)-doped Pb02-film electrodes. J Electrochem Soc 143 2119-2115... 

Here the role of the particle is to couple the anodic oxidation of the reduced relay with H2 generation from water. The choice of the catalytic material may be based on the same considerations which apply for electrocatalytic reagents used on macroelectrodes the exchange current densities for the anodic and cathodic electron transfer steps must be high. Colloidal platin xm would then appear to be a suitable candidate to mediate reaction (6o). This fact was recognized already at the end of the last century when numerous examples for the intervention of finely divided Pt in the process of water reduction by agents such as Cr and V appeared in the german colloid literature. ... 

Chromium plating from hexavalent baths is carried out with insoluble lead-lead peroxide anodes, since chromium anodes would be insoluble (passive). There are three main anode reactions oxidation of water, reoxidation of Cr ions (or more probably complex polychromate compounds) produced at the cathode and gradual thickening of the PbOj film. The anode current density must balance the reduction and reoxidation of trivalent chromium so that the concentration reaches a steady state. From time to time the PbOj film is removed as it increases electrical resistance. 

Environmental tests have been combined with conventional electrochemical measurements by Smallen et al. [131] and by Novotny and Staud [132], The first electrochemical tests on CoCr thin-film alloys were published by Wang et al. [133]. Kobayashi et al. [134] reported electrochemical data coupled with surface analysis of anodically oxidized amorphous CoX alloys, with X = Ta, Nb, Ti or Zr. Brusic et al. [125] presented potentiodynamic polarization curves obtained on electroless CoP and sputtered Co, CoNi, CoTi, and CoCr in distilled water. The results indicate that the thin-film alloys behave similarly to the bulk materials [133], The protective film is less than 5 nm thick [127] and rich in a passivating metal oxide, such as chromium oxide [133, 134], Such an oxide forms preferentially if the Cr content in the alloy is, depending on the author, above 10% [130], 14% [131], 16% [127], or 17% [133], It is thought to stabilize the non-passivating cobalt oxides [123], Once covered by stable oxide, the alloy surface shows much higher corrosion potential and lower corrosion rate than Co, i.e. it shows more noble behavior [125]. 

It is quite often possible to prepare hydroxypyridinone complexes directly by one-pot synthesis from the appropriate hydroxypyranone, amine, and metal salt 90-92). They can also be prepared by reacting complexes such as P-diketonates with hydroxypyridinones (see e.g., Ce, Mo later). Several maltolate complexes, of stoichiometry ML2, ML3, ML4, or MOL2, have been prepared by electrochemical oxidation of the appropriate metal anode, M — a first-row d-block metal (Ti, V, Cr, Mn, Fe, Co, Ni), In, Zr, or Hf, in a solution of maltol in organic solvent mixtures 92). Preparations of, e.g., manganese(III), vanadium(III), or vanadium(V) complexes generally involve oxidation... 

Platinum-based catalysts are widely used in low-temperature fuel cells, so that up to 40% of the elementary fuel cell cost may come from platinum, making fuel cells expensive. The most electroreactive fuel is, of course, hydrogen, as in an acidic medium. Nickel-based compounds were used as catalysts in order to replace platinum for the electrochemical oxidation of hydrogen [66, 67]. Raney Ni catalysts appeared among the most active non-noble metals for the anode reaction in gas diffusion electrodes. However, the catalytic activity and stability of Raney Ni alone as a base metal for this reaction are limited. Indeed, Kiros and Schwartz [67] carried out durability tests with Ni and Pt-Pd gas diffusion electrodes in 6 M KOH medium and showed increased stability for the Pt-Pd-based catalysts compared with Raney Ni at a constant load of 100 mA cm and at temperatures close to 60 °C. Moreover, higher activity and stability could be achieved by doping Ni-Al alloys with a few percent of transition metals, such as Ti, Cr, Fe and Mo [68-70]. 

The configuration of the macrocyclic ligand affects the electrochemical properties of Ni(II) complexes (Table I) (56a, 54). For example, the oxidation and reduction potentials of CR,S,R,S)-[Ni(14)]2+ are shifted by +0.14and +0.13 V, respectively, compared with those of the Rfi,S,S isomer. Similar trends are also observed for a series of R,Sfi,S and Rfi,S,S isomers of -methylated cyclam derivatives (61a, 61b). The anodic shift of the redox potentials for the i ,S ,S-Ni(II) complex indicates that the complex is more difficult to oxidize to Ni(III) but easier to reduce to Ni(I), compared with the RJl,S,S complex. This may be related to the reduced ligand field strength of the R,Sfi,S complex, which stabilizes the antibonding -orbitals and thus makes addition of an electron more favorable while removal of an electron is less favorable. 

The M(DLD)3" complexes (M = Co, Rh, Cr) can be isolated as crystalline, x-ray isomorphous salts of the Me3PhN+ cation with two waters of hydration. The diamagnetism and electronic spectra of the Co(lII) complex are consistent with a d6 octahedrally coordinated ion. Cyclic voltametry shows quasi-reversible oxidation at +0.14 V (in CH2C12 versus Ag AgI). A separation between the anodic and cathodic waves of 0.60 V suggests that a reversible rearrangement occurs upon oxidation of the Co(DED)3 anion. An investigation of the oxidation product is currently underway. 

The anode of an electrolytic cell was constructed from (a) Cr (b) Pt (c) Cu (d) Ni. Determine whether oxidation of the electrode or oxidation of water will occur at the anode. 

The generation of cr-radical cations from saturated hydrocarbons requires very strong SET oxidizers. The oxidation reactions can be accomplished by chemical electron transfer (CET), photochemical electron transfer (PET), and anodic oxidation. The oxidation potentials of stable, organic CET oxidants, e.g., commercially available tris(4-bromophenyl)aminium hexachloroantimonate (TBA +SbCI<,) or tris(2,4-dibromo-phenyl)aminium hexachloroantimonate (TDA +SbCl6 ), are too low (1.06 and 1.50 V... 

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