Silane

Silane is an inorganic compound with chemical formula, SiH₄. It is a colourless, flammable gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon.

Silane may also refer to many compounds containing silicon, such as trichlorosilane (SiHCl₃) , tetramethylsilane (Si(CH₃)₄) and silane methacrylate (H2C=C(CH3)CO2(CH2)3Si(OCH3)3).

Production

Commercial-scale routes

Industrially, silane is produced from metallurgical grade silicon in a two-step process. In the first step, powdered silicon is reacted with hydrogen chloride at about 300 °C to produce trichlorosilane, HSiCl₃, along with hydrogen gas, according to the chemical equation:

The trichlorosilane is then boiled on a resinous bed containing a catalyst which promotes the formation of silane and silicon tetrachloride according to the chemical equation:

The most commonly used catalysts for this process are metal halides, particularly aluminium chloride. This is referred to as a redistribution reaction, which is a double displacement involving the same central element. It may also be thought of as a disproportionation reaction even though there is no change in the oxidation number for silicon (Si has a nominal oxidation number IV in all three species). However, the utility of the oxidation number concept for a covalent molecule, even a polar covalent molecule, is ambiguous. The silicon atom could be rationalized as having the highest formal oxidation state and partial positive charge in SiCl₄ and the lowest formal oxidation state in SiH₄ since Cl is far more electronegative than is H.