Halide electrode

In the reductive dimerization of methyl cinnamate to a cyclopentanone [Eq. (5)], similar yields are found at the cathode [42] and with metals (sodium, THE, and TBAI, —78°C) [40]. Because of the potential selective conversion at the electrode, halides can be reduced at the cathode to carbanions in the presence of carbonyl compounds, which are reduced at more cathodic potentials. This way labile carbanions can be obtained and reacted under conditions in which the same species generated by a metalorganic route would decompose. Eor example, trichlorobromoalkane can be cathodically converted in the presence of aldehydes to a dichloromethyl anion 0°C [route a, Eq. (6)] and be trapped to form a dichlorotetrahydrofuran, but for the metallorganic route [route b, Eq. (6)] a reaction temperature of — 110°C is necessary [43]. 

Franke C, Piazza G and Kolb D M 1989 The influence of halide adsorption on the electronic surface states of silver electrodes Electrochim. Acta 34 67-73... 

Salaita G N, Lu F, Laguren-Davidson L and Flubbard A T 1987 Structure and composition of the Ag(111) surface as a function of electrode potential in aqueous halide solutions J. Electroanal. Chem. 229 1-17... 

Matsumoto H, Inukai J and Ito M 1994 Structures of copper and halides on Pt(111), Pt(IOO) and Au(111) electrode surfaces studied by in situ scanning tunneling microscopy J. Eiectroanai. Chem. 379 223-31... 

Copper electrodes Copper foil Copper fungicides Copper glycinate Copper-gold Copper halide Copper halide system... 

In practical terms, it is suggested that, in any application where the presence of halide ions may cause problems, the concentration of these be monitored to ensure the purity of the liquids. This may be achieved either by the use of an ion-sensitive electrode, or alternatively by use of a chemical method such as the Vollhard procedure for chloride ions [52]. Seddon et al. have reported that effectively identical results were obtained with either method [37]. 

Participation in the electrode reactions The electrode reactions of corrosion involve the formation of adsorbed intermediate species with surface metal atoms, e.g. adsorbed hydrogen atoms in the hydrogen evolution reaction adsorbed (FeOH) in the anodic dissolution of iron . The presence of adsorbed inhibitors will interfere with the formation of these adsorbed intermediates, but the electrode processes may then proceed by alternative paths through intermediates containing the inhibitor. In these processes the inhibitor species act in a catalytic manner and remain unchanged. Such participation by the inhibitor is generally characterised by a change in the Tafel slope observed for the process. Studies of the anodic dissolution of iron in the presence of some inhibitors, e.g. halide ions , aniline and its derivatives , the benzoate ion and the furoate ion , have indicated that the adsorbed inhibitor I participates in the reaction, probably in the form of a complex of the type (Fe-/), or (Fe-OH-/), . The dissolution reaction proceeds less readily via the adsorbed inhibitor complexes than via (Fe-OH),js, and so anodic dissolution is inhibited and an increase in Tafel slope is observed for the reaction. 

As early as 1937, Kolthoff and Sanders32) used silver halide discs as ion-sensitive membranes for the corresponding anion. They found that interferences through redox-systems were negligible with those membranes compared to electrodes of... 

The indicator electrode employed in a potentiometric titration will, of course, be dependent upon the type of reaction which is under investigation. Thus, for an acid-base titration, the indicator electrode is usually a glass electrode (Section 15.6) for a precipitation titration (halide with silver nitrate, or silver with chloride) a silver electrode will be used, and for a redox titration [e.g. iron(II) with dichromate] a plain platinum wire is used as the redox electrode. 

If the pellet contains a mixture of silver sulphide and silver chloride (or bromide or iodide), the electrode acquires a potential which is determined by the activity of the appropriate halide ion in the test solution. Likewise, if the pellet contains silver sulphide together with the insoluble sulphide of copper(II), cadmium) II), or lead) II), we produce electrodes which respond to the activity of the appropriate metal ion in a test solution. 

It is so universally applied that it may be found in combination with metal oxide cathodes (e.g., HgO, AgO, NiOOH, Mn02), with catalytically active oxygen electrodes, and with inert cathodes using aqueous halide or ferricyanide solutions as active materials ("zinc-flow" or "redox" batteries). The cell (battery) sizes vary from small button cells for hearing aids or watches up to kilowatt-hour modules for electric vehicles (electrotraction). Primary and storage batteries exist in all categories except that of flow-batteries, where only storage types are found. Acidic, neutral, and alkaline electrolytes are used as well. The (simplified) half-cell reaction for the zinc electrode is the same in all electrolytes ... 

Some fluorine-ion conductors exhibit high ionic conductivities, even at room temperature [4], which are not equaled by other halide-ion conductors. However, there is a lack of known electrode materials. Further research on this topic is very worthwhile. 

Mercury cyanide, 5, 1062 Mercury electrodes potential range aqueous solution, 1, 480 Mercury fluoride, 5. 1059 Mercury fulminate, 2, 7, 12 5, 1063 Mercury halides, 5, 1049 Mercury iodate, 5,1068 Mercury iodide, 5. 1059 Mercury ions Hgf... 

Anions (e.g., halides) that form insoluble silver salts can be measured at a rotating silver disk electrode. In this, the deposition and stripping steps involve the reaction... 

Vitanov and Popov et al.156 660-662 have studied Cd(0001) electrolyti-cally grown in a Teflon capillary in an aqueous surface-inactive electrolyte solution. The E is independent of ce) and v. The capacity dispersion is less than 5%, and the electrode resistance dispersion is less than 3%. The adsorption of halides increases in the order Cl" < Br" < I".661 A comparison with other electrodes shows an increase in adsorption in the sequence Cd(0001) < pc-Cd < Ag( 100) < Ag(l 11). A linear Parsons-Zobel plot with /pz = 1.09 has been found at a = 0. A slight dependence has been found for the Cit a curves on ce, ( 5%) in the entire region of a. Theoretical C, E curves have been calculated according to the GCSG model. 

Unlike cations, the adsorption activity of CT, Br", and I at Pt electrodes is appreciable806 and increases in the given sequence of anions. At a 0, the <7, A curves for LiC104, NaCl,NaBr, and Nal coincide, which indicates that complete desorption of halide ions takes place at negatively charged surfaces. The values of Ea=0 for a renewed Pt electrode have been found to be -0.18, -0.24, and -0.33 V (SCE in H20) for NaCl, NaBr, and Nal in DMSO, respectively. 

Fewer examples are reported for organic electrode reactions some alkyl halides were catalytically reduced at electrodes coated with tetrakis-p-aminophenylporphy-rin carboxylate ions are oxidized at a triarylamine polymer and Os(bipy)3 in a Nafion film catalytically oxidizes ascorbic acid Frequently, modified electrodes fail to give catalytic currents for catalyst substrate combinations that do work in the homogeneous case even when good permeability of the film is proven... 

Ikezawa, Y. and Terashima, H. (2002) Influence of halide anions on the behavior of pyridine adsorbed on Au(lll) electrode. Electrochimica Acta, 47, 4407 412. 

In general, the electrolysis of a molten salt at inert electrodes produces the metal at the cathode, e.g., calcium from calcium chloride (melting point 774 °C). The anion is often a halide ion which, on discharge, yields the halogen, e.g., chlorine from calcium chloride. 

Homogeneous polycrystalline membrane electrodes [see Fig. 2.10 (3)J. The relatively high electrical conductance of monoclinic / -Ag2S and its extremely low solubility product led to the development of halide and other metal ISEs with addition of silver sulphide. 

The above equations have been derived under the condition that the mixture of halide sulphide is really polycrystalline, i.e., that no mutual compound has been formed between them, otherwise aCI and os2- (and so S0AgCi and S0Ag2s) would reflect considerable interaction. Further, the equations can be extended to any halide X instead of chloride. The aim that, in spite of the silver sulphide present, we can in fact deal with halide electrodes, can be fulfilled by the following conditions ... 

S0AgX must nevertheless be relatively low in order to provide the electrodes with sufficient sensitivity to lower halide concentrations and... 

According to the foregoing theory, any halide electrode can measure Ag+, but not a halide whose solubility product is lower than that of the halide in the membrane so, although an Agl electrode measures I, Br and Cl, an AgCl electrode measures only Cl". 

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