Antimony, electrochemical oxidation

Hydrocarbons undergo related reaction.s in the super-acid media, such as fluorosuiphuric acid and antimony pentachloride. It has been suggested that the initial one-electron processes during the electrochemical oxidation of alkanes in fluorosuiphuric acid involve a protonated carbon-hydrogen bond with formation of a carbon radical and release of two protons [15]. 

Radical cations that are produced by electrochemical oxidation are not stable in solvents with appreciable base character. This results because such radicals are subject to attack by available nucleophiles, and solvents that contain donor electron pairs are good nucleophiles. Cation radicals are most stable in solvents that are good Lewis acids and show negligible basic properties. Some of the solvent systems that have been employed to stabilize electrochemically produced cation radicals include nitromethane and nitrobenzene,21 dichloro-methane,22 trifluoroacetic acid-dichloromethane (1 9),23 nitromethane-AlCl3,24 and AlCl3-NaCl (1 l).25 Organic chemists should be familiar with the stabilization of carbonium ions by superacid media.26 These media usually contain fluorosulfuric acid, or mixtures of fluorosulfuric acid with antimony pen-tachloride and sulfur dioxide, and are potent solvents for the production and stabilization of organic cations. 

Similar forced-flow chromatography separation using anion-exchange chromatography and automatic detection is described for lead With a platinum coulo-metric detector the highly irreversible electrochemical oxidation of Sb(III) in dilute HCl was electrocatalyzed by 1 or I2 and specifically adsorbed at the electrode sur-face This detection system was used coupled with the ion-exchange separation of antimony. 

Russian workers have looked at acoustic waves produced during the electrochemical oxidation of antimony [ 147], almost a reverse application of sonoelectrochemistry. Antimony was anodized in aqueous H3B03 solutions galvanostatically (2.2 x 1(T3 A/cm2) and isothermally (292 K). The formation voltage increased to >200 V with time, which is characteristic of the valve metals. Acoustic waves were observed in this electrochemical oxidation with amplitudes that did not differ essentially from the very beginning of the oxidation. The energy of the acoustic wave had only one sharply distinct peak which coincided in time with the appearance of the electrochemical breakdown products. 

Electrochemical oxidation of biphenylene and a tetramethyl derivative have been shown to produce dications which have greater stability than the dication from biphenyl [185], Biphenylene and methyl derivatives have been converted into dications by the action of a mixture of antimony pentafluoride and sulphonyl chloride fluoride [186], Their H- and C-n,m.r, spectra indicate that these dications have delocalised lO-ir-electron systems [186],... 

Radical cations can be derived from aromatic hydrocarbons or alkenes by one-electron oxidation. Antimony trichloride and pentachloride are among the chemical oxidants that have been used. Photodissociation or y-radiation can generate radical cations from aromatic hydrocarbons. Most radical cations derived from hydrocarbons have limited stability, but EPR spectral parameters have permitted structural characterization. The radical cations can be generated electrochemically, and some oxidation potentials are included in Table 12.1. The potentials correlate with the HOMO levels of the hydrocarbons. The higher the HOMO, the more easily oxidized is the hydrocarbon. 

Concentrated hydrochloric acid will dissolve many metals (generally those situated above hydrogen in the electrochemical series), as well as many metallic oxides. Hot concentrated nitric acid dissolves most metals, but antimony, tin and tungsten are converted to slightly soluble acids thus providing a separation of these elements from other components of alloys. Hot concentrated sulphuric acid dissolves many substances and many organic materials are charred and then oxidised by this treatment. 

The hrst working lead cell, manufactured in 1859 by a French scientist, Gaston Plante, consisted of two lead plates separated by a strip of cloth, coiled, and inserted into a jar with sulfuric acid. A surface layer of lead dioxide was produced by electrochemical reactions in the first charge cycle. Later developments led to electrodes made by pasting a mass of lead oxides and sulfuric oxide into grids of lead-antimony alloy. 

Electrochemical detection has been achieved in a number of ways. The change in pH has been sensed with a traditional glass pH electrode antimony electrode or amperometrically via the pH sensitive oxidation of hydrazine... 

Electrochemical data have been collected for a selection of the antimony OEP and TPP complexes including [Sb(Por)Me2] and [Sb(Por)(R)(OH)] (R = Me, Et). The complexes show one-electron oxidations and reductions at the porphyrin rings. Spectroelectrochemistry indicated that small amounts of antimony(III) products may be formed through a chemical reaction following the first reduction. " ... 

Nitric acid reacts with practically all common metals. Such reactions, however, can vary, forming different products depending on the position of the metal in electrochemical series, the concentration of nitric acid, temperature, and pH. Very weakly electropositive metals such as arsenic, antimony, or tin are oxidized to oxides in higher valence states e.g.,... 

Metal and semiconductor materials (borides, carbides, nitrides, and silicides). Tin oxide-coated glass has been used as an electrode material in electrochemical spectroscopy. By doping of the tin oxide with antimony, an n-type semiconductor is formed. The surface is chemically inert and is transparent in the visible region of the spectrum. However, it is more useful for its optical transparency than as an electrode material. 

The redox properties of macrobicyclic iron(II) mono- and binuclear oximehydrazonates and a-dioximates formed by capping with antimony(V) and germanium(IV) triorganyles were studied by cyclic voltammetry [73, 74]. The electrochemical behaviour of these compounds is similar to that of analogous boron- and tin-capped clathrochelates. Oxidation of all mononuclear complexes involves a one-electron process, assigned to the oxidation of encapsulated iron(II) ion to iron(III) ion. This process is electrochemically... 

When the lead—antimony alloy commonly used for the positive grids of lead—acid batteries was substituted for lead—calcium alloy, the cycle life of the batteries decreased dramatically. Obviously, antimony influenced the electrochemical behaviour of Pb02- One of the hypotheses was that it affected the hydration of Pb02 PbO(OH)2 particles. This hypothesis was verified through oxidation of Pb—Sb alloys with different content of antimony and determining the water content in the anodic Pb02 layer formed. The obtained results of these investigations are presented in Fig. 10.27 [34]. 

The effects of antimony, tin, and lead additions to the palladium black catalyst was analyzed [110]. Accordingly, each adatom strongly promotes formic acid oxidatirai in an electrochemical cell and reduces the amount of CO poison that develops on the catalyst surface after 1 h of oxidation. The authors attributed this effect to the third body effect (steric effect) but did not discard an electronic effect regarding that a decrease in the CO binding energy on palladium due to the presence of the adatoms, using XPS technique, was observed. 

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