Reduction of silicon halides

The low ability of a Si—X bond to react by a one-electron transfer process is also clearly indicated by the electrode potential data derived from the electrochemical reduction of silicon halides (Table 11) (110). 

The hydrogen reduction of the halides of nonmetallic elements, such as silicon (Reaction 8) and boron, is an essential process in the production of semiconductors and high-strength fibers. 

Generally, the two-electron reduction of organic halides produces carbanion species. In fact, cathodic reduction of organic halides under certain conditions gives the product derived from the corresponding carbanion intermediates. Silicon is known to stabilize the carbanion at the a position by dn-pn interaction. Therefore, we can expect that silicon promotes the electron transfer from carbon-halogen bonds and the formation of the carbanion at the a position. 

The reaction of thiyl radicals with silicon hydrides (Reaction 3.18) is the key step of the so called polarity-reversal catalysis in the radical-chain reduction of alkyl halides as well as in the hydrosilylation of olefins using silane-thiol couple (see Sections 4.5 and 5.1) [33]. The reaction is strongly endothermic and reversible (Reaction —3.18). 

Since a carbon-halogen bond is more easily reduced than a silicon-halogen bond, cathodic reduction of organic halides such as allyl, benzyl, aryl and vinyl halides in the... 

The formation of silicon nitride whiskers was observed in several different reactions, including vapor deposition, CVD, and growth from a melt. However, only the following techniques are considered to have commercial significance nitriding of metallic silicon or silicon-silica mixture, carbothermal reduction of silica with simultaneous nitridation, and thermal decomposition of silicon halides. 

Gurtner C, Wun AW, Sailor MJ (1999) Surface modification of porous silicon by electrochemical reduction of organo halides. Angew Chem hit Ed 38 1966-1967... 

The reductions of chlorosilanes by lithium aluminum hydride, lithium hydride, and other metal hydrides, MH, offers the advantages of higher yield and purity as well as flexibility in producing a range of silicon hydrides comparable to the range of silicon halides (59). The general reaction is as follows ... 

Generally, this accords with the data available on the nonstationary process [14]. Hence, the electrochenucal reduction of silicon (IV) species in halide— hexafluorosilicate melts is accompanied by formation of rather stable... 

Gurtner C, Wun AW, Sailor MJ (1999) Surface modification of porous silicon by electrochemical reduction of organo halides. Angew Chem Int Ed 38 1966-1968 Hamadache F, Duvail JL, Scheuren V, Piraux L, Poleunis C, Bertrand P, Belkaid MS (2002) Electrodeposition of Fe-Co alloys into nanoporous p-type silicon influence of the electrolyte composition. J Mater Res 17 1074-1084... 

In practice vapours of the hydrocarbon halide, e.g. methyl chloride, are passed through a heated mixture of the silicon and copper in a reaction tube at a temperature favourable for obtaining the optimum yield of the dichlorosilane, usually 250-280°C. The catalyst not only improves the reactivity and yield but also makes the reaction more reproducible. Presintering of the copper and silicon or alternatively deposition of copper on to the silicon grains by reduction of copper (I) chloride is more effective than using a simple mixture of the two elements. The copper appears to function by forming unstable copper methyl, CUCH3, on reaction with the methyl chloride. The copper methyl then decomposes into free methyl radicals which react with the silicon. 

Open-chain alkanes, alkyl halide reduction, 29-31 Organosilicon hydrides bond strengths, 5-6 hypervalent silicon species, 9-11 ionic hydrogenation, 5 trivalent silicon species, 7-9 Orthoesters, reduction of, 97-99 Oxime reduction, 102... 

Germanium hydrides (as well as silicon hydrides) can be obtained in high yields by reduction of the corresponding halides or alkoxides by LiAlFLt in the presence of phase-transfer catalysts244. 

Silica is reduced to silicon at 1300—1400°C by hydrogen, carbon, and a variety of metallic elements. Gaseous silicon monoxide is also formed. At pressures of >40 MPa (400 atm), in the presence of aluminum and aluminum halides, silica can be converted to silane in high yields by reaction with hydrogen (15). Silicon itself is not hydrogenated under these conditions. The formation of silicon by reduction of silica with carbon is important in the technical preparation of the element and its alloys and in the preparation of silicon carbide in the electric furnace. Reduction with lithium and sodium occurs at 200—250°C, with the formation of metal oxide and silicate. At 800—900°C, silica is reduced by calcium, magnesium, and aluminum. Other metals reported to reduce silica to the element include manganese, iron, niobium, uranium, lanthanum, cerium, and neodymium (16). 

Reduction of halides (X) with zinc and hydrochloric acid. bles carbon and tin resembles silicon Germanium resem-... 

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