Reduction with liquid amalgams

The most powerful reductant is therefore zinc amalgam, whilst bismuth amalgam is the least reducing. The final reduction products obtained with these amalgams for a few elements are collected in Table 10.10. 

Liquid Iron Titanium Molybdenum Vanadium Uranium Tungsten 

The silver reductor has a relatively low reduction potential (the Ag/AgCl electrode potential in 1M hydrochloric acid is 0.2245 volt), and consequently it is not able to effect many of the reductions which can be made with amalgamated zinc. The silver reductor is preferably used with hydrochloric acid solutions, and this is frequently an advantage. The various reductions which can be effected with the silver and the amalgamated zinc reductors are summarised in Table 10.11.  

Silver reductor hydrochloric acid solution Amalgamated zinc (Jones) reductor sulphuric acid solution 

The dark silver chloride coating which covers the silver of the upper part of the reductor when hydrochloric acid solutions are employed moves further down 

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Light filters for colorimeters, see Filters, optical Limiting cathode potential 509 see also Controlled potential electro-analysis Linear regression 145 Lion intoximeter 747 Liquid amalgams applications of, 412 apparatus for reductions, 413 general discussion, 412 reductions with, (T) 413 zinc amalgam, 413 Liquid ion exchangers structure, 204 uses, 204, 560... 

A number of other routes are available for the syntheses of diquaternary salts of 4,4 -bipyridines. One method that has been extensively studied involves reaction of a 1-alkylpyridinium salt with sodium amalgam (or sodium in liquid ammonia) to form the 1,1 -dialkyl-1,1, 4,4 -tetrahydro-bipyridine, which is readily oxidized to the corresponding l,l -dialkyl diquaternary salt. This reaction is analogous to the synthesis of 4,4 -bipyridine by the action of sodium on pyridine, followed by oxidation of the intermediate tetrahydrobipyridine. " The reduction may be achieved electrolytically or by reaction with zinc or magnesium. Various oxidizing agents have been used to assist the conversion to the di-quaternary Another synthesis of diquaternary salts of... 

Bicyclo[4.2.0]octanes wiLh carbonyl groups adjacent to each bridgehead carbon cleave the central bond on reduction with lithium in liquid ammonia,158,159 with sodium/potassium alloy in the presence of chlorotrimethylsilane,160 with zinc in acetic acid,37 or with zinc amalgam in hydrochloric acid.15 7... 

Reduction of 5-methyl-l-oxo-2,3,4,6,7,8-hexahydro-l//-pyrido[l,2-ajpyrazinium iodide, its 2-benzyl derivative and cis- and trans-5-methylperhydropyrido[l,2-a]pyrazin-l-ones with Li in liquid NH3 gave 1-methyldecahydro-l,5-diazecin-5-one (73CPB1248). Under the same conditions, 2-benzoyl-5-methylperhydro-pyrido[l,2-a]pyrazinium iodide afforded 2-benzylperhydropyrido[l,2-a]pyrazine. The 10-membered l-methyldecahydro-l,5-diazecin-5-one was also obtained from trans-5-methylperhydropyrido[l,2-fl]pyrazin-l-one by treatment with sodium amalgam in aqueous EtOH. 

Reduction of ketones. Xanthone is reduced to xanthhydrol by shaking a suspension of the ketone in 95% ethanol at 60-70° with the liquid amalgam from 9 g. of sodium and 55 ml. of mercury. ... 

Hydrolysis of dihydrothebaine methine [ix] affords dihydrocodeinone methine [xxi], which can be reduced catalytically to the dihydromethine [xix] or with aluminium amalgam to dihydrothebainone methine [xxn]. The nitrogen-free product of degradation of dihydrocodeinone methine [xxi] has not been isolated [3]. It was hoped to prepare the AB-enol methyl ether [xxm] of dihydrothebainone dihydromethine by the sodium and liquid ammonia reduction of dihydrothebaine methiodide, but only a complex mixture of products was obtained in this way. Sodium ammonia reduction of the methiodide of [vn] yielded only the original base, but [xxm] was finally obtained by the catalytic reduction of dihydrothebaine- dihydromethine [xxiv] [18]. 

Gold, silver, mercury, and platinum metals, as well as Se and Te, can be precipitated from acid solution in the elemental form by reduction with chemical reagents such as zinc, NH2OH, N2H4, SO2, or formic acid. In the trace analysis of high purity mercury the sample (about 100 g) is dissolved in HNO3 and the solution is warmed in the presence of formic acid. First of all, nitric acid, then mercury, is reduced. The mercury forms a separate liquid phase, and the impurities remain in the aqueous solution [102]. In the trace analysis of silver, the sample is dissolved in nitric acid, then formic acid and mercury are added. The silver liberated on reduction dissolves in the mercury to form an amalgam [102]. 

The first well-authenticated preparation of the [Cr(C0)5] anion was carried out by Behrens and Weber (41) and involved the reduction of chromium hexacarbonyl with elemental sodium, lithium, calcium, or barium in liquid ammonia solution. It is not surprising that such a powerful reducing agent is necessary to effect the reduction of the very stable hexacoordinate chromium hexacarbonyl to the less stable pentacoordinate [Cr(CO)s] anion. In a subsequent report by Podall and associates the reduction of chromium hexacarbonyl with sodium amalgam in tetrahydrofuran or diglyme solution (42) is described. The same report also describes the direct preparation of the [Cr(CO)s] anion from chromium trichloride by treatment with elemental sodium in diglyme solution under carbon monoxide pressure. 

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