Commercial-scale routes Silane can be produced by several routes. Typically, it arises from the reaction of hydrogen chloride with
magnesium silicide: : It is also prepared from metallurgical-grade silicon in a two-step process. First, silicon is treated with
hydrogen chloride at about 300 °C to produce
trichlorosilane, HSiCl3, along with
hydrogen gas, according to the
chemical equation : The trichlorosilane is then converted to a mixture of silane and
silicon tetrachloride: : This
redistribution reaction requires a catalyst. 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 and the lowest formal oxidation state in , since Cl is far more electronegative than is H. An alternative industrial process for the preparation of very high-purity silane, suitable for use in the production of semiconductor-grade silicon, starts with metallurgical-grade silicon, hydrogen, and
silicon tetrachloride and involves a complex series of redistribution reactions (producing byproducts that are recycled in the process) and distillations. The reactions are summarized below: • • • • The silane produced by this route can be thermally decomposed to produce high-purity silicon and hydrogen in a single pass. Still other industrial routes to silane involve reduction of
silicon tetrafluoride () with
sodium hydride (NaH) or reduction of with
lithium aluminium hydride (). Another commercial production of silane involves reduction of
silicon dioxide () under Al and gas in a mixture of
NaCl and
aluminum chloride () at high pressures: :
Laboratory-scale routes In 1857, the German chemists
Heinrich Buff and
Friedrich Woehler discovered silane among the products formed by the action of
hydrochloric acid on aluminum silicide, which they had previously prepared. They called the compound
siliciuretted hydrogen. For classroom demonstrations, silane can be produced by heating
sand with
magnesium powder to produce
magnesium silicide (), then pouring the mixture into hydrochloric acid. The magnesium silicide reacts with the acid to produce silane gas, which
burns on contact with air and produces tiny explosions. This may be classified as a
heterogeneous acid–base chemical reaction, since the isolated ion in the
antifluorite structure can serve as a
Brønsted–Lowry base capable of accepting four protons. It can be written as : In general, the alkaline-earth metals form silicides with the following
stoichiometries: {{chem2|M^{II}2Si}}, {{chem2|M^{II}Si}}, and {{chem2|M^{II}Si2}}. In all cases, these substances react with Brønsted–Lowry acids to produce some type of hydride of silicon that is dependent on the Si anion connectivity in the silicide. The possible products include and/or higher molecules in the homologous series {{chem2|Si_{
n}H_{2
n+2} }}, a polymeric silicon hydride, or a
silicic acid. Hence, {{chem2|M^{II}Si}} with their zigzag chains of anions (containing two lone pairs of electrons on each Si anion that can accept protons) yield the polymeric hydride {{chem2|(SiH2)_{
x} }}. Yet another small-scale route for the production of silane is from the action of
sodium amalgam on
dichlorosilane, , to yield monosilane along with some yellow
polymerized silicon hydride {{chem2|(SiH)_{
x} }}. ==Properties==