Question

What are silicones? Write its preparation from ${{R}_{2}}SiC{{l}_{2}}$.

Answer 1

Hint: Silicones are the organic silicon polymers which are made by hydrolysis of ${{R}_{2}}SiC{{l}_{2}}$.

Complete step by step solution:
Let us formerly learn about the silicones and about its preparation.
Silicone-
These are the polymers of silicon that are made up of alternate molecules of oxygen and silicon, combined by carbon and hydrogen.
Silicones are used in lubricants, electrical insulation, adhesives, etc. These are rubber like substances and are colourless. Common formula is,
$-{{R}_{2}}Si-O-Si{{R}_{2}}-$ where R = organic group.
Varying the lengths of the repeating chain i.e. -Si-O- chain, a wide variety of compounds with differing properties can be formed.
Properties-
-Thermal conductivity is low.
-Chemical reactivity is low.
-Toxicity is low.
-Is thermally stable.
-Have an ability to repel water.
-Microbiological growth is not supported.
-Have electrical insulation properties.
-Have high gas permeability.
Synthesis of silicone from ${{R}_{2}}SiC{{l}_{2}}$-
Silicones are prepared by the hydrolysis of alkyl substituted silicon halides (here dialkyl dichlorosilane i.e. ${{R}_{2}}SiC{{l}_{2}}$).
Mechanism-
1.${{R}_{2}}SiC{{l}_{2}}$ is prepared by passing vapours of RCl over Si in the presence of copper as a catalyst at 300${}^\circ $C.
2. The hydrolysis of ${{R}_{2}}SiC{{l}_{2}}$ gives dialkyl silanol.
3. Polymerisation of dialkyl silanol will give a linear polymer of silicone.
General reaction,
$RCl\xrightarrow[Si]{Cu-powder}{{R}_{2}}SiC{{l}_{2}}\xrightarrow{{{H}_{2}}O}{{R}_{2}}Si{{\left( OH \right)}_{2}}\xrightarrow{condensation}-O-{{R}_{2}}Si-O-{{R}_{2}}Si-O-$
Thus,
Silicones are the useful polymers in day to day life synthesised from ${{R}_{2}}SiC{{l}_{2}}$.

Note: Silicones are also synthesised from the aryl groups substituted silicon halides.
Silicones texture and properties depends on the extent to which reaction was performed and the polymerisation was done. Hence, a variety of polymers can result according to the reaction conditions.