Reduction by Metals

Lithium metal can also be produced by electrolysis in nonprotic solvents. Other methods based on reduction by metals, eg, aluminum or siHcon from the chloride or by magnesium from the oxide, have not had practical commercial appHcation. 

Although silver iodide is the least photosensitive of the three halides, it has the broadest wavelength sensitivity in the visible spectmm. This feature makes silver iodide particularly useful in the photographic industry. It resists reduction by metals, but is reduced quantitatively by zinc and iron in the presence of sulfuric acid. 

For a review of reductions by metal hydride-Lewis acid combinations, see Rerick, M.N. in Augustine Reduction, Marcel Dekker NY, 1968, p. 1. 

Reductions by metal ions are covered in Section 6 in terms of (/) electron-acceptance and ii) electron-acceptance concerted with homolytic fission. One group of reactions, which includes oxidations and reductions by metal ions, is that between a metal ion and a neutral free radical. These form a self-contained class which is treated separately in Section 7. 

As reductions by metals often occur by one-electron transfers, radicals are involved as intermediates. When the reaction conditions are adjusted so that coupling competes favorably with other processes, the formation of a carbon-carbon bond can occur. The reductive coupling of acetone to 2,3-dimethylbutane-2,3-diol (pinacol) is an example of such a reaction. 

Lithium aluminum hydride, LiAlH4 has been used as the reducing agent in the preparation of Cr(CO)6 from CrCl3. Reduction by metals such as Na, Mg, or A1 has also been used, as shown by the preparation of the V(CO)s ion ... 

S02 and NOx in flue gas from coal combustion contribute to smog and acid rain. Methods to remove these pollutants include alkaline wet scrubber systems that fix S02 to solid CaS04, and selective catalytic reduction by metal/metal oxide systems of NO/NOz to N2 and steam in the presence of ammonia. Particulate active carbons have also been used in flue gas decontamination, especially as they avoid costly scrubber processes and can operate at lower temperatures. The potential of active carbon fibers in this application has been explored by a... 

Crown ethers have also been found to lower the rate of reduction by metal hydrides. Wiegers and Smith (1978) reported that the rate of reduction of camphor by LiAlH4 in tetrahydrofuran was depressed by a factor of 6 on addition of one equivalent of crown ether [201]. They also concluded that, although the free cation shows a catalytic effect in metal hydride reduction, it is not indispensable. Dibenzo-18-crown-6 [11] was also found to lower the rate of... 

Reduction of dienes and polyenes 3. Reduction by metal hydrides and dissolving metals... 

Deng, B., Campbell, T.J., and Burris, D.R. Kinetics of vinyl chloride reduction by metallic iron in zero-headspace systems, in American Chemical Society - Division of Environmental Chemistry, Preprints of Extended Abstracts, 37(l) 81-83, 1997. 

Under the conditions which cause migration of the double bonds, e.g. treatment with sodium and especially potassium, the isolated double bonds can become conjugated, and thus they undergo reduction by metals. Some macrocyclic cycloalkadienes were reduced (predominently to trans cycloalkenes) by treatment with potassium on alumina in a hydrogen atmosphere [350]. 

Nitrosyidisulfonic acid, reaction mechanisms, 22 129, 130 Nitrous acid, 33 103 decomposition, rate constants, 22 157 as oxidizing agent, 22 133 reaction mechanisms, 22 143-156 electrophilic nitrosations, 22 144-152 with inorganic species, 22 148, 149 nitrite oxidation by metals, 22 152-154 oxidation by halogens, 22 154, 155 in solution, 22 143, 144 reduction by metals, 22 155, 156 Nitrous oxide reductase, 40 368 Nitroxyl, reaction mechanisms, 22 138 Nitrozation, pentaamminecobalt(III) complexes, 34 181... 

Electrocatalysis of proton reduction by metal complexes in solution has been widely studied [106-111] and confinement of molecular electrocatalysts for this process in polymeric films has also received some attention [111, 112]. This area has received much impetus from biochemical and structural studies of the iron-only... 

Twccdie Barron J. Org. Chem. 1960,25, 2023. See also Hutchins Learn J. Org. Chem. 1982, 47, 4380. ""For a review of reductions by metal hydride-Lcwis acid combinations, see Rerick, in Augustine Reduction-, Marcel Dekker New York, 1968, pp. 1-94. 

The reduction of unsaturated-ketohexosyl purines has been thoroughly studied.52 53 In particular, in the case of the unsaturated 2 -keto-nucleosides 61a, 61b, and 63, a mechanism of the reduction by metal hydride was established53 by study of the n.m.r. spectra of the different deoxynucleosides obtained by the action of sodium borohydride in deu-terated solvents and of sodium borodeuteride in nondeuterated solvents. The reduction of both 7-(3-0-acetyl-4,6-dideoxy-L-g(i/cm>-hex-3-eno-pyranosyl-2-ulose)theophylline (61a) and its 6-chloropurine relative 61b in methanol led, respectively, to 7-(2-0-acetyl-4,6-dideoxy-/ -L-xi/fo-hexopyranosyl)theophylline (90a) and (2-0-acetyl-4,6-dideoxy-/ -L-xi/fo-hexopyranosyl)-6-chloropurine (90b) having OH-2 equatorial,... 

Reduction by metal hydrides (LiAlH4, NaBH4) of these benzofuran-ones gives 3-hydroxy-2,3-dihydrobenzofurans which are dehydrated by distillation or by treatment with an acid or with P205 or treating the 3-acetoxy derivative with trifluoroacetic acid.39 The intermediates are more or less stable depending on their structures or their degree of purity 3-hydroxy-2,3-dihydrobenzofuran, described by Stoermer as... 

Electron transfer is typical for cathodic reduction in electrochemical methods as well as for reductions by metals and metallic reducing agents ... 

A. J. Birch and G. Subba Rao (1972). Reduction by metal-ammonia solutions and related reagents , in Advances in Organic Chemistry. Ed. E. C. Taylor, New York Wiley-Interscience, Vol. 8, p. 1. See also A. A. Akhrem, I. G. Reshetova and Y. A. Titov (1972). Birch Reduction of Aromatic Compounds. New York IFI/Plenum. 

Gould, 3.P., 1982. The kinetics of hexavalent chromium reduction by metallic iron. Water Res., 16 871-878. 

Birch AJ. Reduction by metal-amine solutions, applications in synthesis and determination of structure. Quart Rev (London) 1958 12 17. 

J. Malek, Reductions by Metal Alkoxyaluminum Hydrides, Org. React. 1985, 34, 1-317. 

---