Anodic electrolysis

The electrolyte is made by in situ chlorination of vanadium to vanadium dichloride in a molten salt bath. Higher valent chlorides are difficult to retain in the bath and thus are not preferred. The molten bath, which is formed by sodium chloride or an equimolar mixture of potassium chloride-sodium chloride or of potassium chloride-lithium chloride or of sodium chloride-calcium chloride, is contained in a graphite crucible. The crucible also serves as an anode. Electrolysis is conducted at a temperature about 50 °C above the melting point of the salt bath, using an iron or a molybdenum cathode and a cathode current density of 25 to 75 A dnT2. The overall electrochemical deposition reaction involves the formation and the discharge of the divalent ionic species, V2+ ... 

Fig. 3.9. Cathodic and anodic electrolysis waves at very rapid electron transfer.

INCO [International Nickel Company] An electrolytic process for extracting nickel from nickel sulfide matte. The matte is melted and cast into anodes. Electrolysis with an aqueous electrolyte containing sulfate, chloride and boric acid dissolves the nickel and leaves the sulfur, together with precious metals, as an anode slime. Operated in Manitoba by International Nickel Company of Canada. 

Takimiya et al. (2001, 2003, 2006) have synthesized methylenedithiotetraselenafulvalene (MDT-TSeF) and ethylenethiotetraselenafulvalene (ET-TSeF), which were found to be soluble in organic solvents. Using anodic electrolysis supported by BU4NAUI2 in ethanol-chlorobenzene solution, the authors have obtained diiodoaurate cation-radical salts of the donors. The formulas of the salts are depicted in Scheme 8.11. At room temperature, both salts showed very high conductivities of 2 X 10 and 1.6 X 10 cm , respectively. However, these salts differ with respect to... 

The process is operated at a platinum electrode and a reduced efficiency due to side reactions is observed. A maximum yield of 55% is reported. The use of in situ generated NBS and bromine for the synthesis of nucleosides from silylated pyrimidines has been studied. Nokami etal. [125] suggest the use of only catalytic amounts of NBS or bromine and regeneration of the catalyst by anodic electrolysis in an undivided cell system. 

The polymerization of anions is a special type of irreversible anodic processes. Of these the oxidation of sulphate to persulphate ions has been studied in the deepest detail. In the production of pcrsulphuric acid the yield is increased to a certain limit by a higher concentration of the initial sulphuric acid and an increased current density at the anode of smooth platinum. In too concentrated sulphuric acid the pcrsulphuric acid is already hydrolysed to a considerable extent to monopersulphuric acid (Caro s acid), which then acts as a depolarizer and lowers the required high potential at the anode. Electrolysis of sulphate solutions also gives persulphates and in this reaction the current efficiency will depend on the nature of the cation the efficiency increasing in the order of Na+, K+ and NHj. 

Electrolytic oxidation of cyanide is carried out by anodic electrolysis at high temperatures. It has been more successful for wastes containing high concen-... 

The dimer reduction product of wave I, in turn, exhibited a polarographic anodic wave with E1/2 = —0.27 V in neutral aqueous medium. Anodic electrolysis at the crest of this wave led to regeneration of the parent pyrimidone-22). 

Preparation of Electrodes. The Ag/AgBr and Ag/AgI electrodes were prepared by anodic electrolysis of the appropriate sodium salt solution (IN) at 6.5 ma. per sq. cm. for 5 minutes. The two electrodes to be coated were connected and dipped into the solution a wire of pure silver was used as the cathode. In the case of the Ag/AgCl electrode IN HC1 was used. Just after preparation the electrodes were immersed in the appropriate halide solution (10-3 M). The Ag/Ag halide electrodes prepared in this manner showed a difference of potential of 0.3 to 0.5 mv. in the presence of 10 5 M solution of sodium halide. This potential will be referred to as rest or nonflow potential. 

Tin, in contrast to the other metals, deposited spontaneously onto Pt (that is, at open circuit, without the need for current flow in an external circuit) [51]. Auger spectra following spontaneous deposition showed a strong oxygen signal. Anodic electrolysis (oxidation) increased the oxidation state of the surface layer somewhat and rendered the surface passive except for evolution of H2 at very negative potentials and 02 at very positive potentials. Once immersion of Pt(lll) in Sn2+ (C1 or Br ) solution had taken place, the Sn deposit could not be removed from the surface by electrolysis in the same electrolyte. LEED patterns of the Sn layer were diffuse, indicating that the tin oxide layer was disordered. The pathway of spontaneous Sn deposition probably involves disproportionation, followed by oxidation of the metallic tin. 

Anodic electrolysis of urethanes in methanol gives a-methoxyurethanes, which have been used in reactions with nucleophiles or eliminated to give enamine derivatives. Yields from the electrolysis step are... 

The setup for this experiment is indicated in the block diagram of Fig. 1. The working-electrode compartment and the auxiliary-electrode compartments are physically separated (by a frit or other such device) to avoid unwanted mixing of cathode- and anode-electrolysis products. During the experiment either the electrolysis current, i, the... 

Silver selenite was prepared by addition of a selenious acid solution to a solution of silver nitrate. The product was recrystallised three times from nitric acid ( ). Sodium hydrogen selenite solution was prepared by neutralisation of recrystallised selenious acid by carbonate-free sodium hydroxide. The silver-silver selenite electrodes were obtained by first electroplating silver onto a platinum foil and then converting some of the silver to silver selenite by further anodic electrolysis. The procedure was apparently the same as used for the preparation of silver-silver chloride electrodes. The experiments were carried out in the dark or in subdued daylight. 

The anodizing process consists of 1) trim forming, 2) cleaning, 3) anodic electrolysis usually in sulfuric acid and, 4) sealing in an aqueous bath. Each of these steps are important, for example, the anodized oxide layer must be controlled to provide an optimum thickness. Sealing the anodized layer is also very important and must be complete. Corrosion problems associated with anodized aluminum trim include etching of the oxide film (known as "blush and bloom ) and pitting of the aluminum. 

Anodic electrolysis of enaminone 476 led to an isoquinoline 477 in a fair yield, Scheme 129 (84TL5023). 

Both PAn and PPy can be prepared only by anodic electrolysis at the electrode surface because anilines and pyrroles cannot be reduced within the potential limit of solvents such as water or acetonitrile. 

CF2-CF2-0-CF2-CF2-0.1 Application of the Kolb6 reaction to fluorocarbon acids has also continued to attract interest, and reports which have appeared indude (i) electrolysis of the mixture (CF3)2CH C02H-(CF3)2CH-CX>2K to give the compounds CF3-CH CF2, CF3-CH2-CFs, and the expected product (CFs)2CH-CH(CF8)2 (67 %), which is readily dehydrofluorinated to perfluoro-2,3-dimethylbuta-1,3-diene (39%) i" (ii) electrolysis of the add CF8 0-(CF2)2 C02H in MeOH-MeCN (10%) to give mainly the ether CF3-0 (CF2)4 0-CF3 (60%) and (iii) crossed anode electrolysis,i of CFs COsH-EtCXJaH-EtCXlsNa... 

Feedstuff, anodizing, electrolysis, copper winning 5.0 Sulphate, carbonate, hydroxide - ... 

FIGURE 14.15 Apparatus for electrolysis in which a direct current of electricity is passed through a reaction medium, in this case water with a dissolved salt to make it electrically conducting reduction occurs when electrons are added to the medinm at the cathode, and oxidation occurs when they are removed at the anode. Electrolysis is a reagent-free way of doing oxidation and reduction. 

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