Cathodic electrolysis

Cathodic protection of an uncoated ship is practically not possible or is uneconomic due to the protection current requirement and current distribution. In addition, there must be an electrically insulating layer between the steel wall and the antifouling coating in order to stifle the electrochemical reduction of toxic metal compounds. Products of cathodic electrolysis cannot prevent marine growths. On the contrary, in free corrosion, growths on inert copper can occur if cathodic protection is applied [23]. 

Technetium metal can be electrodeposited from an acidic solution of pertechnetate using a platimun, nickel or copper cathode. Electrolysis of neutral, unbuffered solutions, alkaline solutions, and sulfuric acid solutions lower than 2 N yield a black deposit of hydrated TcOj The current efficiencies are generally poor but the deposition is reasonably quantitative. The deposition requires the application of relatively negative cathode potentials and is therefore non-selective. Polaro-graphy indicates that the overpotentials for the evolution of hydrogen on technetium are rather low hence, electrolysis from acidic media will always include concurrent discharge of hydrogen . ... 

Endo et al. investigated the reductive decomposition of various electrolytes on graphite anode materials by electron spin resonance (ESR). In all of the electrolyte compositions investigated, which included LiC104, LiBF4, and LiPFe as salts and PC, DMC, and other esters or ethers as solvents, the solvent-related radical species, which were considered to be the intermediates of reductive decomposition, were detected only after prolonged cathodic electrolysis. With the aid of molecular orbital calculation, they found that the reduction of salt anion species is very difficult, as indicated by their positive reduction enthalpy and that of free solvent (A/4 — 1 kcal mol ). However, the coordination of lithium ions with these solvents dramatically reduces the corresponding reduction enthalpy (A/ —10 kcal mol ) and renders the reaction thermodynamically favored. In other words, if no kinetic factors were to be considered, the SEI formed on carbonaceous anodes... 

The method was checked for the synthesis of [Au(Meso-DME)]OAc and [Au(Etio)][AuCl4] [99]. The [AuCl4] ion was destroyed by cathodic electrolysis and thus exchanged for [CI04]. AuCl(TPP) can also be made (see Sect. 2.5). 

Sodium perchlorate is prepared by electrolysis of concentrated solutions of sodium chlorate in cells without diaphragms using platinum anodes and iron cathodes. Electrolysis is continued until some 95 per cent of the initial chlorate... 

This phenomenon has been studied by different combined electrochemical techniques such as -> spectroelec-trochemistry, radioactive -> tracer method, -> electrochemical quartz crystal microbalance, conductivity etc. by varying the experimental parameters, e.g., film thickness, the composition and concentration of the electrolyte solutions, the wait-time at different waiting potentials, and temperature [iii-x]. Several interpretations have been developed beside the ESCR model. The linear dependence of the anodic peak potential on the logarithm of the time of cathodic electrolysis (wait-time) -when the polymer in its reduced state is an insulator -has been interpreted by using the concept of electric percolation [ix]. Other effects have also been taken into account such as incomplete reduction [vii], slow sorp-tion/desorption of ions and solvent molecules [iii-vi], variation of the equilibrium constants of -+polarons and - bipolarons [viii], dimerization [xi], heterogeneous effects [xii], etc. 

Regioselective Michael addition of imidazole to levoglucosenone 475 is effectively catalyzed by cathodic electrolysis. The electrochemical conditions are milder and provide higher yields as compared to the base-catalyzed reactions (Scheme 110) <1996JOC8786>. 

Deactivation of the Co plus Mo cathodes occurred during the first 1000 s of cathodic electrolysis, an effect that was tentatively attributed to sorption of H into the composite lattice by diffusion. However (cf. Ref 75), because H is codeposited anyway during electroforming of these composite cathode materials, this may not be the critical reason for this effect other impurity effects may be involved. 

The production of the 2-pyrrolidone anion by direct cathodic electrolysis of 2-pyrrolidone has been referred to [33,34] and examples of its use as an ex situ reagent presented (Scheme 2). Despite the early promise of this conveniently prepared strong base [pXa(2-pyrrolidone) = 24.1], it is only recently that its advantages have been exploited more widely. The 2-pyrrolidone anion is formed as an ex situ reagent by direct cathodic electrolysis at —2.5 V (VS.SCE) and a further example of its use is given in Scheme 8, in which reaction the tetraalkylammonium counterion was essential in preventing defluorination [35]. 

Cathodic electrolysis of pyridinium ions (404) causes an electron to be added to the ring. This electron is in an orbital very like the LUMO of pyridine (p. 68), which we know to have the largest coefficient on the 4-position. This is the site of dimerization.331... 

Synthesis of Phosphoric Acids and their Derivatives. - Among various approaches to phosphate esters the phosphorylation of phenols with dialkyl cyanophosphonate and the synthesis of triaryl phosphates under phase-transfer conditions are worthy of mention. Mixed trialkyl phosphates are also reported to be formed by brief cathodic electrolysis of the reaction of dialkyl phosphonates with aromatic aldehydes and ketones, presumably by rearrangement of the initial a-hydroxy compounds. Further reports have appeared of the generation of metaphosphates by various methods. The synthesis of analogues 1 of famesyl pyrophosphate which incorporate photoactive esters has been reported both compounds are competitive inhibitors of farnesyl transferase. 

Kijima, M. Toyabe, T. Shirakawa, H. Kawata, S. Kyotani, H. Nakamura, Y. Endo, M, Synthesis of carbyne by cathodic electrolysis of hexachlorobutadiene, Synth. Metals 1997, 86, 2279-2280. 

Here I would like to mention attempts of synthesizing carbynoid structures by Kijima et al. [6,9] using electrochemical approach. Cathodic electrolysis of a solution of poly(vinylidene fluoride) (PVDF) in DMF containing tetrabutylammonium perchlorate, and tert-butyl alcohol as a mediator was found to produce -doped conjugated polymers consisting of 76% of poly(fluoro-acetylene) and 24% of carbynoid moieties [6] (Scheme 12.7) ... 

Mercury-cathode electrolysis allows small quantities of Al to be separated from large amounts of Fe, Ni, Co, Cu, Zn, Mn, Cr, Mo, Pb, etc., while Be, V, Ti, Zr, Mg, Ca, and the rare earths remain in solution together with the aluminium [4]. 

Anode Cathode Electrolysis Lead storage battery Potential Dry cell batteries Corrosion... 

The Pb9 ion has also been identified in ammonia solutions of K1 by the cathodic electrolysis of lead electrodes. 

The cathodic electrolysis of mixtures of alcohols and dialkyl methyl (or phenyl)phosphonates in the presence of tetraethylammonium perchlorate in acetonitrile yields mixed esters of the corresponding phosphonic acids. The yields and... 

Ugaz A, Puppah S, Gale RJ, Acar YB. (1994). Electrokinetic soil processing. Complicating features of electrokinetic remediation of soils and slurries saturation effects and the role of the cathode electrolysis. Chemical Engineering Communications 129 183-200. 

The synthesis of some 2,4-dioxahydrindans is illustrated in Scheme 6. Oxidation of 4-C-hydroxymethyl-2,3,4-trideoxy-D-cryfAro-hex-2-enopyranose with silver carbonate on Celite produced 4-C-hydroxymethyl-2,3,4-trideoxy-D-r/ireo-hex-2-eno-l,5-lactone together with the expected D-erythro lactone." Michael addition of various nitroalkanes to levoglucosenone under cathodic electrolysis conditions (circumstances that were found to be milder and higher yielding than the base-catalysed version) resulted in products 42. Phthalimide, succinimide and saccharin were also nucleophiles in this process. ... 

The carrier ampholytes adjacent to the electrodes must be protected from anodic oxidation or cathodic reduction. This is done by using special electrode solutions, which perform the function of a liquid lock. A dilute solution of an acid such as phosphoric or sulfuric acid is used at the anode. A dilute alkali such as sodium hydroxide is used at the cathode. Electrolysis attracts the acid and the base to the respective electrodes. The acid at the anode gives a positive charge to the carrier ampholytes there. Thus they are repelled from the anode. At the cathode, the base gives a negative charge to the carrier ampholytes nearby. They are then repelled from the cathode. 

Littauer and Jenningsexamined the cathodic electrolysis of seawater as a means of fouling prevention at various current densities, and obtained partial protection. However, at current densities greater than 1 mAcm , calcareous deposits formed on the electrode. 

A special purified grade of the diaphragm cell sodium hydroxide is made by extracting the 50% solution with liquid ammonia to remove chloride, chlorate, and carbonate. Metal ions, such as iron, nickel, cobalt, and copper, can be removed by electroplating them onto porous cathodes. Electrolysis also removes some anions such as sulfide. Iron and nickel are also removed by filtration using magnesium oxide filter aid after oxidation with hypochlorite. ... 

Konstantinov, V.I., Polyakov, E.G., and Stangrit, P.T. (1978) Cathodic electrolysis of chloride-fluoride and oxyfluoride melts-chloride melts of tantalum, ElectrochimActa 23,713-716. 

Copper, however, is used in applications where purity is important. Copper, when pure, is ductile and an excellent electrical conductor, so it needs to be refined to be used in electrical wiring. Copper anodes (blister copper) are suspended in a water solution containing sulfuric acid and copper sulfate with steel cathodes. Electrolysis results in dissolution of copper from the anode and migration of copper ions to the cathode, where purified metal is deposited. The result is copper of 99.9 percent purity. A similar procedure may be used in recycling copper. Other metals that are electrorefined include aluminum. 

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