SILANE

also called Silicon Hydride, any of a series of covalently bonded compounds containing only the elements silicon and hydrogen, having the general formula SinH2n + 2, in which n equals 1, 2, 3, and so on. The silanes are structural analogues of the saturated hydrocarbons but are much less stable. The term silane is extended to include compounds in which any or all of the hydrogen atoms have been replaced by other atoms or groups of atoms, as in tetrachlorosilane, SiCl4. Silanes have been prepared by the reaction of magnesium silicide (Mg2Si) with acids or by the reduction of silicon chlorides with lithium aluminum hydride. All the silanes burn or explode upon contact with air, and they are decomposed by alkaline solutions with formation of hydrogen and hydrous silica. Upon heating, the silanes decompose into hydrogen and silicon; they react with the halogens or hydrogen halides to form halogenated silanes, and with olefins to form alkylsilanes. The simplest silane, monosilane (SiH4), is also the stablest; it is a colourless gas that liquefies at -112 C (-170 F) and freezes at -185 C (-301 F). It decomposes slowly at 250 C (482 F), rapidly at 500 C (932 F). The instability of the silanes results from the lability of the silicon-hydrogen bond; derivatives in which all the hydrogen atoms have been replaced by organic groups, such as tetramethylsilane, Si(CH3)4, resemble the saturated hydrocarbons. The compound dimethyldichlorosilane, (CH3)2SiCl2, is important as the starting material for the dimethylpolysiloxanes, members of the silicone family of polymers. Chlorotrimethylsilane and vinyltrichlorosilane are used to impart water repellency to numerous materials such as cloth, paper, and glass.