Zinc amalgam preparation

Usually prepared by the action of NaCN on benzaldehyde in dilute alcohol. It is oxidized by nitric acid to benzil, and reduced by sodium amalgam to hydrobenzoin PhCHOHCHOHPh by tin amalgam and hydrochloric acid to des-oxybenzoin, PhCH2COPh and by zinc amalgam to stilbene PhCH = CHPh. It gives an oxime, phenylhydrazone and ethanoyl derivative. The a-oxime is used under the name cupron for the estimation of copper and molybdenum. 

An aluminium-mercury couple acts in the same way as zinc dust. This aluminium amalgam, prepared by the action of mercuric chloride on aluminium (preferably granulated), is also suitable for reducing substances dissolved in ether or alcohol the water which is required is slowly added drop by drop. (The method is that of H. Wislicenus.) The extent of the reduction varies according to the nitro-compound concerned, but corresponds approximately to the effect of zinc dust in a neutral medium. Consequently reduction usually does not proceed beyond the hydroxylamine stage. 

Preparation of the Zinc Amalgam. —Granulated zinc in thin pieces or, still better, zinc foil 0-15 to 0-25 mm. thick and cut into small strips, is left for one hour with frequent shaking in contact with an equal weight of 5 per cent aqueous mercuric chloride solution. The solution is then poured off and the metal washed once with fresh water. 

Another Zinc Reduction. Prepare or activate the zinc as follows 400 g of mossy zinc is treated with 800 ml of 5% aqueous solution of mercuric chloride for 1 hour. Decant the solution off and use the zinc right away. Add. 834 mole of compound to be reduced to the zinc amalgam, followed by as much HCl acid (.834 mole) diluted in as much water as is required to cover all the zinc. Reflux for 6 hours while adding small portions of dilute HCL acid. Cool, separate the upper, wash free of acid (a few portions of dilute sodium hydroxide), dry and distill to get about a 79% yield of product. 

ReCl3(PPh3)(benzil)] reacts with bipy and related ligands or terpy to form a number of rhe-nium(III) and rhenium(II) compounds which are useful precursors for the synthesis of lower-valent rhenium complexes. " Thus, reduction of [Re(bipy)3][PF6]2 with zinc amalgam results in the rhenium(I) compound [Re(bipy)3][PF6] in excellent yields. The corresponding terpyridyl bis-chelate [Re(terpy)2][PF6] has been prepared in a similar manner. " The electrochemistry of the products provides a convenient measure of the chemical reactivity associated with the redox processes. Thus, the one-electron oxidation of [Re(bipy)3]" is reversible at -0.33 V, whereas the Re"/Re" redox couple is irreversible and occurs at relatively low potentials (-1-0.61 V) which is consistent with the instability of [Re(bipy)3] + in solution. However, in the presence of a small coordinating molecule such as CNBu, oxidation to the rhenium(III) state is readily available by the formation of seven-coordinate complexes of the composition [Re(bipy)3(L)]. " ... 

Finally, in the recent patent literature, some further processes for the preparation of phosphine were described for example, the treatment of white phosphorus with steam in the presence of phosphoric acid at 275-285 °C. According to a British patent, phosphine is formed when white phosphorus, in aqueous acid, is brought into contact with mercury or zinc amalgam A Japanese patent recommends the treatment of a mixture of white phosphorus and granulated zinc with acids and a small amount of methanol for the preparation of highly pure phosphine. Other patents describe electrolytic processes. Finally, it is mentioned that phosphine is formed by the electrolysis of phosporous and hypophosphorous acid, especially at mercury or lead cathodes. ... 

The compound [(i7s-CsHs)Cr(NO)2] 2 was first prepared in low yields (<5%) by the reduction of (i75-CsHs)Cr(NO)2Cl with sodium tetrahydroborate in a two-phase water-benzene system.6 Recently, this complex was isolated in 75% yield from the zinc amalgam reduction of (i7s-C5Hs)Cr(NO)2Cl in tetrahydrofuran over a period of 21 hours.2 However, [07s-CsH5)Cr(NO)2]2 is synthesized most conveniently by the reduction of the above-mentioned chloro complex with sodium amalgam in benzene as outlined below. 

In 1984, Fried et al. reported the reaction of bromodifluoroacetate with carbonyl substrates in the presence of zinc. The a,a-difluoro /1-hydroxyester was obtained in good yield without isolation of the Reformatsky reagent [240, 241] (Scheme 80) Later, this zinc reagent has also been prepared via reaction of ethyl bromodifluoroacetate with zinc amalgam in triglyme [242] or reaction of methyl iododifluoroacetate with zinc in acetonitrile [243]. 

Preparation of Zinc Amalgam. (Perform the experiment on a tray with high sides ) Put two or three small pieces of pure granulated zinc into a 25-ml porcelain bowl and add 3-4 ml of a 2% mercu-ry(II) nitrate solution acidified with 0.3 ml of concentrated nitric acid. Stir the mixture during 10 minutes, then pour o0 the solution and wash the zinc with water by decantation until the liquid becomes absolutely transparent. Store the zinc amalgam in a jar under water. 

Zinc amalgam [Zn(Hg)] is prepared as follows A 5.00-g sample of Zn metal is added to 100-mL beaker containing 50 mL of a 6 N HC1 solution which was chilled in an ice bath. Solid HgCl2 (ca. 0.5 g) is quickly added to the solution until the evolution of H2(g) stops. The acid solution is decanted from the solid Zn(Hg) and the solids are rinsed with distilled H20 (3 x 50 mL). The solid is thoroughly air dried yields are variable. Waste should be appropriately disposed. 

Reduction by zinc amalgam of a dry and oxygen-free THF solution containing [VC12(TPTP)] (TPTP = raeso-tetra-p-tolylporphyrinato) and addition of elemental sulfur yields [VS(TPTP)].659 Similar thiovanadyl complexes were prepared with OEP, TPP and TMTP (TMTP = meso-tetra-ra-tolylporphyrinato). Analytical results and mass spectra agree with the formulation [VS(por)], and v(V=S) was at 550-565 cm-1 (see Section 33.5.6.1). FT-EXAFS of [VO(OEP)] and [VS(OEP)] were recorded and the difference FT spectrum yielded... 

Zinc amalgam (for Clemmensen reduction) may be prepared by either of the following two methods. 

The amalgamated zinc is prepared by adding ioo g. of mossy zinc to a solution of io g. of mercuric chloride in 200 cc. of water and shaking for one-half hour. The liquid is then poured off and the metal washed by decantation. 

Prepare zinc amalgam for use as follows Add 20- to 30-mesh zinc to a 2% mercuric chloride solution, using about 100 mL of the solution for each 100 g of zinc. After about 10 min, decant the solution from the zinc, then wash the zinc with water by decantation. Transfer the zinc amalgam to the reductor tube, and wash the column with 100-mL portions of 2 N sulfuric acid until 100 mL of the washing does not decolorize 1 drop of 0.1 N potassium permanganate. 

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