Problem 9 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

\((\mathrm{Me})_{2} \mathrm{SiCl}_{2}\) on hydrolysis will produce (a) \((\text { Me })_{2} \mathrm{Si}(\mathrm{OH})_{2}\) (b) \((\mathrm{Me})_{2} \mathrm{Si}=\mathrm{O}\) (c) \(-\left[-\mathrm{O}-(\mathrm{Me})_{2} \mathrm{Si}-\mathrm{O}-\right]_{\mathrm{n}}-\) (d) \(\mathrm{Me}_{2} \mathrm{SiCl}(\mathrm{OH})\)

Step-by-Step Solution

Answer

The product is option (c), the polymeric structure.

Step 1: Understanding the Reaction

In the given problem, we need to determine the product of the hydrolysis of dimethyldichlorosilane, \((\mathrm{Me})_{2} \mathrm{SiCl}_{2}\). Hydrolysis is a chemical reaction that involves the reaction with water (\(\mathrm{H}_2\mathrm{O}\)). In this case, the chlorine atoms are replaced by hydroxyl groups (\(\mathrm{-OH}\)).

Step 2: Initial Hydrolysis

Starting with \((\mathrm{Me})_{2} \mathrm{SiCl}_{2}\), when hydrolyzed, each \(\mathrm{-Cl}\) group can react with water to form \((\mathrm{Me})_{2} \mathrm{Si}(\mathrm{OH})_{2}\). This is initially a possible step where both chlorine atoms are replaced by hydroxyl groups.

Step 3: Polymerization

The product \((\mathrm{Me})_{2} \mathrm{Si}(\mathrm{OH})_{2}\) can further undergo condensation reactions. These reactions involve the elimination of water (\(\mathrm{H}_2\mathrm{O}\)) resulting from the reaction between hydroxyl groups on two molecules. This leads to a polymeric structure \(-\left[-\mathrm{O}-(\mathrm{Me})_{2}\mathrm{Si}-\mathrm{O}-\right]_{\mathrm{n}}-\).

Step 4: Determining the Correct Option

Based on these steps, option \(c\) explores the possibility of creating a polymer, which is the product often formed when compounds like \((\mathrm{Me})_{2} \mathrm{SiCl}_{2}\) undergo hydrolysis followed by condensation. Options (a) and (d) describe intermediate or incomplete hydrolysis steps, and option (b) is incorrect because it would require the elimination of both hydroxyl groups without forming a polymeric oxygen bridge.

Key Concepts

Polymerization

Polymerization is the process of combining many small molecules called monomers into a larger structure known as a polymer. In the hydrolysis of dimethyldichlorosilane (\(( ext{Me})_2 ext{SiCl}_2\)), polymerization involves the formation of siloxane bonds (\(- ext{Si-O-Si}-\)). This occurs after the initial hydrolysis forms a silanol compound (\(( ext{Me})_2 ext{Si(OH)}_2\)).

• Each molecule of dimethyldichlorosilane initially undergoes replacement of chlorine atoms with hydroxyl groups.
• Following this, multiple reactions occur where hydroxyl groups from different molecules result in water elimination.
• The siloxane bonds are formed during this step by condensation reactions.

Polymerization in this context leads to linear or networked siloxane polymers like:\[-ig[- ext{O}-( ext{Me})_2 ext{Si}- ext{O}-ig]_n-\]

Condensation reaction

Condensation reactions are critical chemical processes in the formation of polymers from silanes. During hydrolysis of dimethyldichlorosilane, two \(- ext{OH}\) groups from two different molecules react to form a bond while ejecting a water molecule. This is a classic example of a condensation reaction.

• Water elimination is the key aspect, differentiating condensation from other reactions.
• For every siloxane bond (\(- ext{Si-O-Si}-\)) formed, a molecule of water is removed, allowing for bonding between two monomers.
• These reactions enable the progression from small individual silanol units into more complex chain or network polymers.

Condensation reactions are essential for increasing the molecular weight of compounds and are foundational in synthesizing silicone polymers.

Dimethyldichlorosilane

Dimethyldichlorosilane (\(( ext{Me})_2 ext{SiCl}_2\)) is a versatile organosilicon compound commonly used in the production of silicones. Upon hydrolysis, it readily forms intermediate silanol compounds and further polymerizes into silicone polymers.

• The two chlorine atoms attached to the silicon can be substituted by hydroxyl groups when reacted with water.
• This compound is often utilized as a starting material for creating various types of silicones, ranging from fluids to resins.
• Its properties, like reactivity and functionality, make it indispensable in numerous industrial applications.

Dimethyldichlorosilane's ability to form stable, flexible, and durable polymers expands its usage across many fields, notably in producing waterproofing materials, elastomers, and sealants.