SiCl + 2H Properties: Silicon tetrachloride is a colourless fuming liquid and it freezes at - ⁰C In moist air, silicon tetrachloride is hydrolysed with water to give silica and hydrochloric acid. SiCl + 2H O 4HCl + SiO When silicon tetrachloride is hydrolysed with moist ether, linear perchloro siloxanes are formed [Cl-(Si Cl O) n SiCl where n= - . 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. SiCl + 4C H OH Si(OC H ) + 4HCl Tetraethoxy silane Ammonialysis. Similarly silicon tetrachloride undergoes ammonialysis to form chlorosilazanes. 2SiCl + NH Cl Si-NH-SiCl + 2HCl K Ether 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. .
. Silcones: Silicones or poly siloxanes are organo silicon polymers with general empirical formula (R SiO). Since their empirical formula is similar to that of ketone (R CO), they were named “silicones”. These silicones may be linear or cross linked.
Because of their very high thermal stability they are called high –temperature polymers. - - - - Preparation: Generally silicones are prepared by the hydrolysis of dialkyldichlorosilanes (R SiCl ) or diaryldichlorosilanes Ar SiCl , which are prepared by passing vapours of RCl or ArCl over silicon at K with copper as a catalyst. 2RCl+ Si R SiCl Cu / K The hydrolysis of dialkylchloro silanes R SiCl yields to a straight chain polymer which grown from both the sides Si Cl R Cl R Si OH R HO R +2H O -2HCl Si OH R HO R Si OH R HO R -H O Si R HO R Si OH R R Si OH R HO R Si R HO R Si