Compounds of Silicon

Silicones:

•  These are organosilicon polymers containing Si-O-Si linkages.
• These are formed by the hydrolysis of alkyl or aryl substituted chlorosilanes and their subsequent polymerization.
• The alkyl or aryl substituted chlorosilanes are prepared by the reaction of Grignard reagent and silicon tetrachloride.
  
  RMgCl + SiCl₄ → R−SiCl₃ + MgCl₂
  
  2RMgCl + SiCl₄ → R₂SiCl₂ + 2MgCl₂
  
  3RMgCl + SiCl₄ → R₃SiCl + 3MgCl₂
• Hydrolysis of substituted chlorosilanes yields corresponding silanols, which undergo polymerization.
• R₃SiCl on hydrolysis forms only a dimer.
  
  R₃SiOH + HOSiR₃ → R₃Si − O − SiR₃ + H₂O

Silicones are of the following types:

1. Linear silicones
2. Cyclic silicones
3. Cross linked silicones

Properties:

• The lower silicones are oily liquids but higher members containing long chains or ring structures are waxy and rubber-like solids.
• Silicones are stable towards heat.
• Chemical reagents have no action on silicones.
• These are non-toxic.
• Viscosity of silicone oils remains the same at different temperatures.
• Silicones are good electrical insulators.
• Silicones are water repellents.

Uses:

• Used for high temperature oil baths, high vacuum pumps etc as they are highly stable and non-volatile.
• Used for low-temperature lubrication.
• Used in making water-proof cloth and paper as they are water repellent.
• Used in insulating electric motors.