Mercury anode reactions

With a metal ion having four coordination centers, binding of four molecules (39) can occur. The reaction of four molecules of (39) with Hg(II) perchlorate in CH3CN produced complex (212) with a high yield [Eq. (150)]. Electrochemical oxidation of some phosphines on a mercury anode has been shown to lead to their complexes with Hg(II). Following this method, complex 212 was synthesized in high yield (92MI1). The M—P bonds were shown to be in an equatorial position. 

Xanthine and xanthosine were investigated on HMDE, applying out-of-phase ac and dc voltammetries [74]. It has been shown that both compounds are strongly adsorbed and interact chemically. In the cathodic stripping process, one could determine both compounds at trace level. Naidu et al. [146] have performed polaro-graphic studies to show that the product of anodic reaction (prewave) of potassium isobutyl xanthate is strongly adsorbed at the mercury electrode. 

Since the products of the electrolysis of aqueous NaCl will react if they come in contact with each other, an essential feature of any chloralkali cell is separation of the anode reaction (where chloride ion is oxidized to chlorine) from the cathode reaction (in which OH- and H2 are the end products). The principal types of chloralkali cells currently in use are the diaphragm (or membrane) cell and the mercury cell. 

This equation has a standard electrode potential of -0.447 V. Thus, the solution containing mercuric and chloride ions in contact with iron forms a battery. The reduction of the complex ions to metallic mercury is the cathodic reaction. The dissolution of iron is the anodic reaction. The overall reaction in the battery is given by the addition of Equation (13.42) and Equation (13.43). Due to the high value of its reversible cell voltage under standard conditions (0.85 V), it is expected that a very low equilibrium concentration of the complex ion can be achieved. 

Section 2 (Fig. 1, curves A and B), usually performed at the rotating platinum electrode (anode reactions) or the dropping mercury electrode (cathode reactions), should ideally suffice to define the electroactive species and determine its half-wave potential. It may be that systems in which acid-base equilibria exist are somewhat more laborious to study due to the necessity of recording voltammetric curves over a wide pH range, but in most cases the task can be accomplished with some effort. Once the voltammetric characteristics are known, it remains to carry out preparative constant potential electrolysis (cpe) at a suitable potential in order to make sure that the electroactive species is connected with the reaction of interest. 

Reductive cleavage of 6-ketosulfones [166], RC0CHR S02R", in DMF at mercury is a practical way of preparing alkyl ketones the primarily formed radical anion cleaved to a radical RCOCHR and a sulfinate ion R"S02. Since the anodic reaction was the oxidation of R"S02" to R"S03, an undivided cell could be used. 

In most cylindrical carbon—zinc cells, the zinc anode also serves as the container for the cell. The zinc can is made by drawing or extrusion. Mercury [7439-97-6] has traditionally been incorporated in the cell to improve the corrosion resistance of the anode, but the industry is in the process of removing this material because of environmental concerns. Corrosion prevention is especially important in cylindrical cells because of the tendency toward pitting of the zinc can which leads to perforation and electrolyte leakage. Other cell types, such as flat cells, do not suffer as much from this problem The anode reaction depends on the electrolyte used, but the charge-transfer step is... 

When the mercury is brought to more positive values, the anodic reaction and the potential for current flow also differ from those observed when Pt is used as the electrode. 

Electrochemical sensors based on amperometric detection are popular small instruments that can be used to directly probe samples. The electrodes in these sensors do not always have to be made of metal, e.g. platinum or mercury, and do not always have to be bare. A commonly employed working electrode is the rotating disk electrode, which is preferred over the DME for easily reduced species and anodic reactions. It works by convection mixing of the solution so that fresh sample is constantly passed over the surface. 

The mercury process has a similar anode reaction producing chlorine gas, but the cathode reaction occurs on mercury flowing through the reactor cell [51]. Sodium and mercury form an amalgam that flows out of the reactor to a decomposer reactor. There the amalgam reacts with water to form NaOH, hydrogen, and mercury for recycHng back to the electrolysis cell. 

Initially, the electrolysis of aqueous brine was carried out in amalgam cells [4,10, 11]. Typical conditions employed were an electrolyte feed of 25% NaCl at pH 4, a temperature of 343 K, and a current density in the range of 0.7 -1.4 A cm . The desired anode reaction, the evolution of chlorine, was accompanied by corrosion of the carbon at a rather rapid rate. Sodium amalgam was formed at the mercury cathode, which was then reacted with water to give 50% sodium hydroxide and hydrogen gas in a catalytic reactor known as a denuder. 

I.M. KolthofiF and C. Bamum, The anodic reaction and waves of cysteine at the dropping mercury electrode and at the platinum micro wire electrode, J. Am. Chem. Soc., 1940, 62, 3061-3065. 

The controlled-potential oxidation of selenium and tellurium has been studied extensively by Lingane and Niedrach (222). Both selenium and tellurium (—II) undergo well defined two-electron oxidation processes at all pH values. For selenium (—II) the primary anodic reaction seems to involve oxidation of the mercury electrode followed by formation of HgSe while tellurium (—II) seems to be directly oxidized to tellurium metal. In strongly alkaline solution tellurium (—II) appears to undergo an additional incomplete oxidation to TeOs-... 

The reaction forming azomethine and indoaniline dyes has been investigated by generating quinonediimine at the dropping mercury anode and recording its amount as a cathode-ray oscillogram before and after addition of benzoylacetanilide and a-naphthol derivatives to the solution [77]. 

Anodic stripping voltammetry consists of two steps (Figure 11.37). The first is a controlled potential electrolysis in which the working electrode, usually a hanging mercury drop or mercury film, is held at a cathodic potential sufficient to deposit the metal ion on the electrode. For example, with Cu + the deposition reaction is... 

Chloiine is pioduced at the anode in each of the three types of electrolytic cells. The cathodic reaction in diaphragm and membrane cells is the electrolysis of water to generate as indicated, whereas the cathodic reaction in mercury cells is the discharge of sodium ion, Na, to form dilute sodium amalgam. 

In some cases, particularly with iaactive metals, electrolytic cells are the primary method of manufacture of the fluoroborate solution. The manufacture of Sn, Pb, Cu, and Ni fluoroborates by electrolytic dissolution (87,88) is patented. A typical cell for continous production consists of a polyethylene-lined tank with tin anodes at the bottom and a mercury pool (ia a porous basket) cathode near the top (88). Pluoroboric acid is added to the cell and electrolysis is begun. As tin fluoroborate is generated, differences ia specific gravity cause the product to layer at the bottom of the cell. When the desired concentration is reached ia this layer, the heavy solution is drawn from the bottom and fresh HBP is added to the top of the cell continuously. The direct reaction of tin with HBP is slow but can be accelerated by passiag air or oxygen through the solution (89). The stannic fluoroborate is reduced by reaction with mossy tin under an iaert atmosphere. In earlier procedures, HBP reacted with hydrated stannous oxide. 

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