A What are silicones? State the uses of silicones.

B What are boranes? Give a chemical equation for the preparation of diborane.

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Solution

$Silicones$

Silicones are organosilicon polymers, which have $(- R_{2} S i O -)$ as a repeating unit. Silicones being surrounded by non-polar alkyl groups are water repelling in nature

$Uses of Silicones$

Silicones have wide applications as follows:

They are used as sealant, greases, electrical insulators and for waterproofing of fabrics.

Being biocompatible they are also used in surgical and cosmetic plants.

$Boranes$

Boron forms a number of hydrides. These are called boranes. The simplest boron hydride $(B H_{3})$ is unknown. Since $B H_{3}$ is an electron deficient molecule, it dimerises to achieve stability and exists as $B_{2} H_{6}$ known as diborane. The most important hydride is diborane (i.e. $B_{2} H_{6}$ ).

$Preparation of Diborane$

1. It is prepared by treating lithium aluminium hydride with boron trifluoride in diethyl ether.

$4 {B F}_{3} + 3 L i A l H_{4} \to 2 B_{2} H_{6} + 3 L i F + 3 A l F_{3}$

2. A convenient laboratory method for the preparation of diborane involves the oxidation of sodium borohydride with iodine.

$2 N a B H_{4} + I_{2} \to 2 B_{2} H_{6} + 2 N a I + H_{2}$

3. Diborane is produced on an industrial scale by the reaction of $B F_{3}$ with sodium hydride.

$2 B F_{3} + 6 N a H 450 K - -- \to B_{2} H_{6} + 6 N a F$

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