Problem 26 - A Complete Resource Book in Chemistry for JEE Main

Question

(Me) \(_{2} \mathrm{SiCl}_{2}\) on hydrolysis will produce (a) \((\mathrm{Me})_{2} \mathrm{Si}(\mathrm{OH})_{2}\) (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 correct reaction product is c: - [-O-(Me)_{2}Si-O-]_{n}-.

Step 1: Understand Hydrolysis

Hydrolysis is a chemical reaction where water breaks down a compound. When applied to (Me)_{2}SiCl_{2}, the chlorine atoms are replaced by hydroxyl groups (OH) from water, resulting in the formation of silanols.

Step 2: Initial Reaction with Water

When (Me)_{2}SiCl_{2} undergoes hydrolysis, the Cl atoms are substituted with OH groups. The initial product formed is (Me)_{2}Si(OH)_{2}.

Step 3: Consider Possible Further Reactions

The produced (Me)_{2}Si(OH)_{2} can undergo further reactions. Silanols like (Me)_{2}Si(OH)_{2} are known to condense further, leading to elimination of water and formation of siloxane bonds (Si-O-Si).

Step 4: Observe Potential Polymeric Formation

The continued condensation of silanols can form a polymeric structure where repeated units are linked by siloxane (Si-O-Si) bonds. This process results in the formation of a polymer - [-O-(Me)_{2}Si-O-]_{n}-.

Step 5: Choose the Correct Answer Based on Observations

Since the hydrolysis leads to formation of the initial product (Me)_{2}Si(OH)_{2} and further condensation leads to polymer formation, the correct answer is - [-O-(Me)_{2}Si-O-]_{n}- (Option c).

Key Concepts

Silanol formation

Silanol formation is an essential process in organosilicon chemistry. It begins when water interacts with organosilicon compounds, like \((\text{Me})_2 \text{SiCl}_2\), leading to hydrolysis. In this reaction, water molecules cause chloride ions to be replaced with hydroxyl ions (OH). This substitution results in the creation of silanols, such as \((\text{Me})_2 \text{Si}(\text{OH})_2\).

The ability of silicon to extend its coordination sphere allows these conversions to occur seamlessly. Silanol groups are quite reactive, making them intermediates in further transformations. During the process, the silanol compound retains its original organic skeleton while acquiring new functionalities, such as hydroxyl groups.

• Silanol formation lays the groundwork for further reactions in organosilicon chemistry.
• Hydrolysis is key, facilitated by water reacting with silicon chlorides.
• Organosilicon compounds often undergo rapid conversion to silanols due to the process's simplicity and efficiency.

Siloxane bonds

Siloxane bonds are a hallmark of organosilicon chemistry. These bonds, represented by the Si-O-Si linkage, are formed when silanols undergo condensation reactions. This process involves the elimination of water molecules as hydroxyl groups from adjacent silanols react.

The creation of siloxane bonds serves as a bridge structure, connecting various silicon-based entities. This specific bonding confers stability and contributes to the extensive applications of silicones in industry. Siloxane chains tend to be flexible but resilient, making them perfect for use in materials requiring both strength and elasticity.

• The Si-O-Si bonds in siloxanes offer unique properties such as thermal stability and resistance to many chemical environments.
• Formation is driven by condensation of silanols, highlighting their role as precursors to versatile structures.
• Siloxane linkages are integral in creating durable and reliable polymer architectures.

Polymer formation in organosilicon chemistry

Polymer formation in organosilicon chemistry results from the repetitive joining of monomer units via siloxane bonds. Starting from silanols, through successive condensation steps, a network of siloxane linkages builds up to form extended structures, or polymers.

The essence of these polymers, like the one described by \(-\left[-\text{O}-(\text{Me})_2 \text{SI}-\text{O}-\right]_n-\), lies in the recurring Si-O-Si theme. This motif grants the material unique properties that find use in various fields, including cosmetics, lubricants, and electronics.

These silicone-based polymers often exhibit high flexibility, water repellence, and thermal stability. They are highly valued for their function across diverse environments. By understanding polymer formation, chemists can manipulate molecular architectures for specific applications.

• Siloxane bonds form the backbone of organosilicon polymers.
• The polymers' resilience and adaptability make them indispensable in many technological advancements.
• Mastering polymerization expands the utility of silicones, tailoring them to meet industrial needs.