Cathodes, aluminum mercury

Octachlorodibenzothiophene (88) has been formed by irradiation of a solution of pentachlorobenzenesulfenyl chloride in CCI4 in a low-pressure, cold cathode mercury arc (62%). A similar photolysis of bis-(pentachlorophenyl) sulfide, prepared by the action of sulfur monochloride and sulfuryl chloride on benzene in the presence of aluminum chloride, also yielded 88 (42%). Both routes are shown in Scheme 4. 

Trigeminal trihalides are completely reduced by catalytic hydrogenation over palladium [62] and Raney nickel [63], and partially reduced to dihalides or monohalides by electrolysis using mercury cathode [57 ], by aluminum... 

A term used to describe how easily a metal is oxidized is active. A more active metal is one that is more easily oxidized. A listing of metals in order of activity is known as an activity series. The activity series is used to determine which substances will be oxidized and reduced in an electrochemical cell the element higher on the list will be oxidized. For example, in a cell with aluminum and silver electrodes in their appropriate solutions, aluminum is oxidized and silver is reduced. Therefore, aluminum is the anode and silver is the cathode. If you have ever bitten a piece of aluminum foil and experienced discomfort, you had this electrochemical process occur in your mouth. Silver (or mercury) fillings and the aluminum serve as electrodes and your saliva serves as an electrolyte between the two. The resulting current stimulates the nerves in your mouth resulting in the discomfort. 

Numerous methods for the synthesis of salicyl alcohol exist. These involve the reduction of salicylaldehyde or of salicylic acid and its derivatives. The alcohol can be prepared in almost theoretical yield by the reduction of salicylaldehyde with sodium amalgam, sodium borohydride, or lithium aluminum hydride by catalytic hydrogenation over platinum black or Raney nickel or by hydrogenation over platinum and ferrous chloride in alcohol. The electrolytic reduction of salicylaldehyde in sodium bicarbonate solution at a mercury cathode with carbon dioxide passed into the mixture also yields saligenin. It is formed by the electrolytic reduction at lead electrodes of salicylic acids in aqueous alcoholic solution or sodium salicylate in the presence of boric acid and sodium sulfate. Salicylamide in aqueous alcohol solution acidified with acetic acid is reduced to salicyl alcohol by sodium amalgam in 63% yield. Salicyl alcohol forms along with -hydroxybenzyl alcohol by the action of formaldehyde on phenol in the presence of sodium hydroxide or calcium oxide. High yields of salicyl alcohol from phenol and formaldehyde in the presence of a molar equivalent of ether additives have been reported (60). Phenyl metaborate prepared from phenol and boric acid yields salicyl alcohol after treatment with formaldehyde and hydrolysis (61). 

A standard solution of B-5 fixative containing a concentration of mercuric chloride of 60 g/1 was plated for 8 hours and yielded 60% recovered mercury metal. Two liters of solution were plated, thus a total of 120 g of mercuric chloride were processed. The stoichiometric amount of mercury metal from the reduction of 120 g of mercuric chloride equals 88 g. The recovered mercury metal totaled 53 g, thus demonstrating a 60% recovery efficiency. During the eight hour process the aluminum cathodes were changed once. The solution pH was between 3.6-3.8. 10 g of calcium chloride were added in order to... 

Common procedures of qualitative mercury analysis, i.e. using aluminum foil hooked up to a battery to determine the presence of mercury in a solution (mercury metal forms on the surface of the aluminum foil), suggested the use of aluminum as a cathode. This principle was applied on a larger scale using aluminum wire which had to be flattened to a certain thickness for the voltage used. 

Several methods are employed for the reductive defluorination of 2-fluoro-l-phenyl-ethanones. Electrolytic reduction at a mercury cathode selectively replaces fluorine in 2-fluoro-l -phenylethanone by hydrogen.94 The hydrodefluorination of fluoroacetophenones, e.g. 7, to dithioacetals of the corresponding defluorinated ketones with aluminum chloride and ethanethiol take place readily by stirring the mixture in dichloromethane at 0°C under nitro-... 

Accidentally chewing on a stray fragment of aluminum foil can cause a sharp tooth pain if the aluminum comes in contact with an amalgam filling. The filling, an alloy of silver, tin, and mercury, acts as the cathode of a tiny galvanic cell, the aluminum behaves... 

Castner, Hamilton Young — (Sep. 11, 1858, Brooklyn, New York, USA - Oct. 11,1899, Saranac Lake, New York, USA) Castner studied at the Brooklyn Polytechnic Institute and at the School of Mines of Columbia University. He started as an analytical chemist, however, later he devoted himself to the design and the improvement of industrial chemical processes. He worked on the production of charcoal, and it led him to investigate the Devilles aluminum process. He discovered an efficient way to produce sodium in 1886 which made also the production of aluminum much cheaper. He could make aluminum on a substantial industrial scale at the Oldbury plant of The Aluminium Company Limited founded in England. However, - Hall and - Heroult invented their electrochemical process which could manufacture aluminum at an even lower price, and the chemical process became obsolete. Castner also started to use electricity, which became available and cheap after the invention of the dynamo by - Siemens in 1866, and elaborated the - chlor-alkali electrolysis process by using a mercury cathode. Since Karl Kellner (1851-1905) also patented an almost identical procedure, the process became known as Castner-Kellner process. Cast-... 

The choice of cathode materials is less restricted by corrosion considerations than the choice of anodes so few metals react readily with the medium that their use is impractical. Some of the most popular electrode materials are mercury, lead, tin, copper, iron, aluminum, platinum, nickel, and carbon. 

Early workers [103] detected benzilic acid formed during the reduction of benzophenone in dimethylformamide in the presence of carbon dioxide. The carbon dioxide radical anion system is known to have E" = —2.2V (vs. SCE) [104] and will thus not be formed in preference to the ketone radical anion. Reaction occurs through trapping of aromatic carbonyl radical anions by carbon dioxide, and this has been developed into a convenient synthesis of aryllactic acids. The modern technological process uses constant current conditions. On a small scale, a divided cell with mercury cathode has been used to obtain benzilic acids from substituted benzophenones and carbon dioxide in 70-90% yields [105] and to convert 4-isopropylacetophenone to the corresponding phenyllactic acid in 85% yield [106]. On a technical scale, these reactions are best carried out in an undivided cell using a lead cathode and a sacrificial aluminum anode with dimethylformamide as solvent... 

The reduction products from triphenylsulfonium ions depend on the electrode material and the potential [116-118]. Electrolysis of tirphenylsulfonium bromide at a mercury electrode at the potential of the first wave quantitatively yields diphenylsulfide and diphe-nylmercury. No benzene or diphenyl is formed. At potentials more negative than the second reduction wave, diphenylsulfide and benzene are formed quantitatively, provided low substrate concentrations are used. With increasing substrate concentration the yield of diphenylmercury increases at the expense of benzene. Reduction in aqueous solution at an aluminum cathode produces diphenylsulfide and some benzene addition of DMF increases the yield of benzene, as DMF is as a better hydrogen atom donor than water [117]. 

The mercury cathode (page 648) has found wide application in the removal of many metal ions prior to the analysis of the residual solution. In general, metals more easily reduced than zinc are conveniently deposited in the mercury, leaving such ions as aluminum, beryllium, the alkaline earth metals, and the alkali metals in solution. The potential required to decrease the concentration of a metal ion to any desired level is readily calculated from polarographic data. 

The second type of cell is a mercury pool type. A mercury cathode is particularly useful for separating easily reduced elements as a preliminary step in an analysis. l or example, copper, nickel, cobalt, silver, and cadmium are readily separated from ions such as aluminum, titanium, the alkali metals, and phosphates. The precipitated elements dissolve in the mercury little hydrogen evolution occurs even at high applied potentials because of large overvoltage effects. A coulomet-ric cell such as that shown in Figure 24-5b is also useful for coulometric determination of metal ions and certain types of organic compounds as well. 

Selective defluorination of 1,3-difluorobenzene to fluorobenzene has been successfully carried out by use of cathodic reduction at mercury in diglyme containing Bu4NBp4and a catalytic amount of a dimethylpyrrolidinium (DMP ) salt. In this reaction, DMP is first reduced to form an amalgam, which reduces difluorobenzene catalyti-cally as shown in Scheme 1. Also, cathodic reduction of perfluoroben-zene at an aluminum cathode in aqueous DMF provides benzene in moderate yield (Eq. 4). 

Magnesium and zinc are the predominantly used galvanic anodes for the cathodic protection of pipelines [13—16]. The corrosion potential difference of magnesium with respect to steel is 1 V, which Umits the length of the pipeline that can be protected by one anode. Economic considerations have led to the use of aluminum and its alloys as anodes. However, aluminum passivates easily, decreasing current output. To avoid passivation, aluminum is alloyed with tin, indium, mercury, or gallium. The electrochemical properties of these alloys, such as theoretical and actual output, consumption rate, efficiency, and open circuit (corrosion) potential, are given in Table 15.1. 

So-called ultrafine metal powders below 1 i in diameter can be made by pyrogenic dissociation of the vapors of the carbonyls of iron, nickel, and cobalt. Aluminum of a particle size below the resolving power of the electron microscope has been formed by evaporation and condensation under vacuum in an inert atmosph e. Similarly, evaporated magnesium has been quenched by JP-4 fuel for directly making a slurry fuel. Also, long ball-milling fine magnesium powder in the presence of a surfactant can lead to particles below I n. Iron or nickel electrolytically deposited on a mercury cathode form very active, often pyrophoric, fine powdm that, however, can be stabilized in order to be handled in air. 

Ziegler and collaborators 162, 283) succeeded in the electrolytic preparation of tetraethyllead, a process which is also suitable for obtaining other ethyl metal compounds. The electrolysis of alkali aluminum (or boron) tetraethyl with a lead anode and a mercury cathode yields at the anode a... 

Platinum, grassy carbon, graphite, stainless steel, carbon fiber, silver, lead, mercury pool, and some other metals are reported to be usable as cathode materials in electrochemical carboxylation. Among them, platinum, stainless steel, carbon fiber, and graphite are frequently used for an efficient formation of carboxylic acid by electrochemical fixation of carbon dioxide with a sacrificial anode, such as magnesium and aluminum [1-4], as a couple in an undivided cell (one-compartment cell). 

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