Tetrasilane
# Tetrasilane

Tetrasilane is a silane with the structure formula $SiH_3–(SiH_2)_2–SiH_3.$ It is the silane analog of butane.

## Preparation

Tetrasilane can be prepared by reacting magnesium silicide $(Mg_2Si)$ with acids like 20% phosphoric acid in 50–60 °C.

    $\mathrm {Mg_{2}Si+\ 4H^{+}\ \longrightarrow \ Si_{n}H_{2n+2}}$

The reaction can produce silanes up to n=15. The reaction of magnesium silicide with 25% hydrochloric acid produces 40% monosilane, 30% disilane, 15% trisilane, 10% tetrasilane and 5% higher silanes. The mixture can be separated by fractional distillation.

In addition, higher silanes can also be obtained by discharges monosilane:

    $\mathrm {SiH_{4}\ \rightarrow \ SiH_{2}\ +\ H_{2}}$
    $\mathrm {SiH_{2}\ +\ SiH_{4}\rightarrow \ H_{3}Si{-}SiH_{3}}$
    $\mathrm {SiH_{2}\ +\ H_{3}Si{-}SiH_{3}\rightarrow \ H_{3}Si{-}SiH_{2}{-}SiH_{3}}$
    $\mathrm {SiH_{2}\ +\ H_{3}Si{-}SiH_{2}{-}SiH_{3}\rightarrow \ H_{3}Si{-}SiH_{2}{-}SiH_{2}{-}SiH_{3}}$

## Properties

Tetrasilane is a colourless, pyrophoric liquid that has a disgusting odour. Even below 54 °C, it will still spontaneous combust. It is even more unstable than trisilane, slowly decomposing at room temperature, releasing hydrogen and forming shorter chain silanes.

## Reactions

Photochemical disproportionation of tetrasilane will produce 3-silylpentasilane and disilane.

    $\mathrm {2\ Si_{4}H_{10}\rightarrow \ Si_{2}H_{6}\ +H_{3}Si{-}SiH(Si_{2}H_{6})_{2}}$

With the presence of aluminium chloride, heating tetrasilane in xylene will allow isomerization to isotetrasilane.

    $\mathrm {2\ H_{3}Si{-}SiH_{2}{-}SiH_{2}{-}SiH_{3}\longrightarrow \ H_{3}Si{-}SiH(SiH_{3})_{2}}$
