Silane

**Properties**
General
Name	Silane
Chemical formula	Si H₄
Appearance	Colourless gas
Physical
Formula weight	32.1 amu
Melting point	88 K (-185 °C)
Boiling point	161 K (-112 °C)
Density	0.7 ×10³ kg/m³ (liquid)
Solubility	insoluble
Thermochemistry
Δ_fH⁰_gas	? kJ/mol
Δ_fH⁰_liquid	? kJ/mol
Δ_fH⁰_solid	-1615 kJ/mol
S⁰_{gas, 1 bar}	? J/mol·K
S⁰_{liquid, 1 bar}	? J/mol·K
S⁰_solid	283 J/mol·K
Safety
Ingestion	Relatively low toxicity, but avoid exposure where possible.
Inhalation	Relatively low toxicity: may cause coughing, hyperventilation.
Skin	Irritant, may cause redness and swelling.
Eyes	As for skin, may cause irritation.
More info	Hazardous Chemical Database
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

Silane is a chemical compound with chemical formula Si H₄. It is the silicon analog of methane. At room temperature, silane is presumed to be a pyrophoric gas -- it spontaneously undergoes combustion in air without the need for external ignition. However, there is a school of thought which says that silane is stable and that it is the natural formation of larger silanes during production which causes its pyrophoricity. Above 420°C, silane decomposes into silicon and hydrogen; it can therefore be used in the chemical vapor deposition of silicon.

More generally, a silane is any silicon analog of an alkane hydrocarbon. Silanes consist of a chain of silicon atoms covalently bound to hydrogen atoms. The general formula of a silane is Si_nH_2n+2. Silanes tend to be less stable than their carbon analogs because the Si-Si bond has a strength slightly lower than the C-C bond. Oxygen decomposes silanes easily, because the silicon-oxygen bond is quite stable.

There exists a regular nomenclature for silanes. Each silane's name is the word silane preceded by a numerical prefix (di, tri, tetra, etc.) for the number of silicon atoms in the molecule. Thus Si₂H₆ is disilane, Si₃H₈ is trisilane, and so forth. There is no prefix for one; SiH₄ is simply silane. Silanes can also be named like any other inorganic compound; in this naming system, silane is named silicon tetrahydride. However, with longer silanes, this becomes cumbersome.

A cyclosilane is a silane in a ring, just as a cycloalkane is an alkane in a ring.

Branched silanes are possible. The radical SiH₃^- is names silyl, Si₂H₅^- is disilanyl etc. If we have trisilane with a silyl group attached to the middle silicon, we have silyltrisilane. It parallels alkanes.

Silanes can also take the same functional groups as alkanes, OH to make a silanol. There is (at least in principle) a silicon analogue for all carbon alkanes.

Production

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

Si + 3 HCl → HSiCl₃ + H₂

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

4 HSiCl₃ → SiH₄ + 3 SiCl₄

The most commonly used catalysts for this process are metal halides, particularly aluminum chloride.