Silicon tetrachloride

Silicon tetrachloride:

Preparation:

Silicon tetrachloride can be prepared by passing dry chlorine over an intimate mixture of silica and carbon by heating to 1675 K in a porcelain tube

SiO₂ + 2C + 2Cl₂ → SiCl₄ + 2CO

On commercial scale, reaction of silicon with hydrogen chloride gas occurs above 600 K

Si + 4HCl  → SiCl₄ + 2H₂

Properties:

Silicon tetrachloride is a colourless fuming liquid and it freezes at -70 ⁰C

In moist air, silicon tetrachloride is hydrolysed with water to give silica and hydrochloric acid.

SiCl₄ + 4H₂O  → 4HCl + Si(OH)₄

When silicon tetrachloride is hydrolysed with moist ether, linear perchloro siloxanes are formed [Cl-(Si Cl₂O)_nSiCl₃ where n=1-6.

Alcoholysis

The chloride ion in silicon tetrachloride can be substituted by nucleophile such as OH, OR, etc.. using suitable reagents. For example, it forms silicic esters with alcohols.

SiCl₄ + C₂H₅OH → 4HCl + Si(OC₂H₅)₄ Tetraethoxy silane

Ammonialysis.

Similarly silicon tetrachloride undergoes ammonialysis to form chlorosilazanes.

Uses:

·           Silicon tetrachloride is used in the production of semiconducting silicon.

·           It is used as a starting material in the synthesis of silica gel, silicic esters, a binder for ceramic materials.