Problem 61 - A Complete Resource Book in Chemistry for JEE Main

Question

Consider the following sequence of reactions. \(\mathrm{HC} \equiv \mathrm{CH} \stackrel{\text { (i) } \mathrm{CuCl}, \mathrm{NH}_{4} \mathrm{Cl}, \text { (ii) } \mathrm{HCl}}{\longrightarrow}(\mathrm{X})\) \(\underline{\text { Polymerization }}{\longrightarrow}(\mathrm{Y})\) The polymer (Y) is (a) PVC (b) Saran (c) Neoprene (d) Chloroprene

Step-by-Step Solution

Answer

The polymer (Y) is (a) PVC.

Step 1: Analyze the Initial Reaction

The initial reaction involves the reaction of acetylene (HC≡CH) with CuCl and NH₄Cl, followed by HCl. This set of reagents is known for converting acetylene into chloroethyne (vinyl chloride), which is the compound (X).

Step 2: Determine the Molecular Formula of (X)

Given the conversion in Step 1, we conclude that compound (X) is vinyl chloride, which has the chemical formula CH₂=CHCl.

Step 3: Analyze the Polymerization Process

The polymerization step involves converting vinyl chloride (X) into a polymer. Vinyl chloride undergoes a chain-growth polymerization reaction to form polyvinyl chloride. Each vinyl chloride monomer adds to the growing chain, with the structure of PVC being represented as [-CH₂-CHCl-]ₙ.

Step 4: Identify the Polymer (Y)

The polymer formed from the polymerization of vinyl chloride is Polyvinyl Chloride (PVC). Thus, the product (Y) is PVC.

Key Concepts

Vinyl Chloride

Vinyl chloride is a chemical compound with the formula \( \text{CH}_2=\text{CHCl} \). It is an important industrial chemical primarily used to make polyvinyl chloride (PVC). This colorless gas has a slightly sweet odor and is highly flammable, making it crucial to handle it with care.
Vinyl chloride is created through the reaction of acetylene with hydrogen chloride, although there are other methods like the thermal cracking of 1,2-dichloroethane. It is one of the fundamental building blocks in the production of various plastic products.

• Used predominantly in creating PVC products.
• Essential in the manufacturing of construction materials, pipes, and medical equipment.
• Plays a role in producing consumer goods due to its versatility.

Understanding the properties and reactions of vinyl chloride is key to mastering concepts in polymer chemistry and industrial applications.

Polyvinyl Chloride (PVC)

Polyvinyl chloride, commonly abbreviated as PVC, is a flexible and durable plastic widely used in various products and industries. PVC is formed through the polymerization of vinyl chloride monomers, resulting in a linear polymer with repeating units of \( [-\text{CH}_2-\text{CHCl}-]_n \).
This versatile material is used in construction, electrical insulation, garments, and manufacturing packaging materials. Its adaptability, resistance to environmental degradation, and low cost make it a preferred choice in industries worldwide.

• Non-toxic in its stable state).
• Can be made rigid or flexible with the addition of plasticizers.
• Weather-resistant, making it ideal for outdoor applications.

Learning about PVC helps understand its impact on daily life. From pipes to vinyl records, PVC's presence is vast and simplifies complex manufacturing processes.

Chain-Growth Polymerization

Chain-growth polymerization is a chemical reaction where the growth of a polymer chain proceeds through successive addition of monomeric units. The process begins with an initiator that reacts with a monomer to form an active site. Vinyl chloride is an example of a monomer that polymerizes via chain-growth to form PVC.
In this type of polymerization, the chain lengthens rapidly. Each step involves adding one monomer molecule at a time. This continues until the monomers are exhausted or the reaction is terminated deliberately.

• Involves three stages: initiation, propagation, and termination.
• Produces polymers with high molecular weight.
• Often facilitated by catalysts to control the process.

Understanding chain-growth polymerization provides insights into the production of crucial polymeric materials like PVC, with applications spanning several industries.