Problem 152 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

The fibre obtained by the condensation of hexamethylene diamine and adipic acid is (a) nylon-6, 6 (b) dacron (c) rayon (d) teflon

Step-by-Step Solution

Answer

The correct answer is (a) nylon-6, 6.

Step 1: Understanding the Composition

Nylon-6,6 is a polyamide fiber formed by the condensation polymerization of hexamethylene diamine and adipic acid. Identify the components mentioned: hexamethylene diamine is a 6-carbon diamine, and adipic acid is a 6-carbon dicarboxylic acid.

Step 2: Matching Composition with Options

Examine each option: - (a) Nylon-6,6: Composed of hexamethylene diamine and adipic acid. - (b) Dacron: Made from ethylene glycol and terephthalic acid. - (c) Rayon: Not a polyester or polyamide, but a regenerated cellulose fiber. - (d) Teflon: Polytetrafluoroethylene, unrelated to hexamethylene diamine and adipic acid.

Step 3: Selecting the Correct Answer

Based on the matching of nylon-6,6 with hexamethylene diamine and adipic acid, select option (a) as it correctly corresponds to the description.

Key Concepts

Condensation Polymerization

Condensation polymerization is a type of chemical reaction where monomers combine to form a polymer while releasing a small molecule. In the case of Nylon-6,6 synthesis, the monomers involved are hexamethylene diamine and adipic acid. When these two monomers react together, they release water as a by-product.
In terms of chemistry, condensation polymerization typically involves a reaction between a molecule with two functional groups. Here:

• Hexamethylene diamine provides two amine groups (-NH₂).
• Adipic acid provides two carboxylic acid groups (-COOH).

The amine groups react with the acid groups to form an amide linkage, creating long chains of connected monomers - this process forms a polyamide, which in this case, is Nylon-6,6.
This kind of reaction is different from addition polymerization, which doesn't release any by-products. The process is key to creating many synthetic fibers and plastics used widely in everyday materials.

Hexamethylene Diamine

Hexamethylene diamine is a crucial building block of Nylon-6,6. As an organic compound, it has a six-carbon chain backbone. Each end of this chain has an amine group (-NH₂). Its structure makes it suitable for reacting with dicarboxylic acids during condensation polymerization.
In the synthesis of polyamides like Nylon-6,6, hexamethylene diamine acts as a bifunctional monomer. This means that it has two functional sites through which it can link with other molecules. When it reacts with adipic acid, each amine group of hexamethylene diamine bonds with a carboxyl group from the acid, leading to the formation of amide linkages (the backbone of nylon fibers).
Hexamethylene diamine significantly influences the properties of the resulting polymer. Because of its length and the flexibility of its aliphatic backbone, it imparts strength, elasticity, and chemical resistance to the polyamide fibers.

Adipic Acid

Adipic acid is a dicarboxylic acid with six carbon atoms, just like hexamethylene diamine has six carbon atoms but in a different functional group arrangement. Adipic acid is known for its pivotal role in the production of Nylon-6,6 through condensation polymerization.
It contains two carboxyl groups (-COOH) at each end of its carbon chain. These groups are essential for reactive purposes. In the creation of Nylon-6,6, adipic acid reacts with the amine group of hexamethylene diamine. Each reaction between these two groups results in an amide bond, removing a molecule of water in the process.
The presence of adipic acid contributes significantly to the high melting point, durability, and strength of Nylon-6,6 fibers. Its chemical stability and robustness make it a preferred component in the manufacture of performance polyamide fibers for textiles and industrial uses.

Polyamide Fibers

Polyamide fibers, like Nylon-6,6, are a result of the polymerization process where amide linkages are formed along the molecule. These linkages are responsible for the impressive tensile strength and elasticity seen in materials like nylon, making them versatile for various applications.
Characteristics of polyamide fibers, such as resistance to wear and chemicals, as well as moisture-wicking properties, make them ideal for use in clothing, carpets, airbags, and industrial products. The alignment and interaction of the polyamide chains contribute to the softness and durability that these fibers are known for.

• High melting point: Suitable for use in high-temperature environments.
• Durability: Excellent for products that endure significant wear and tear.
• Elasticity: Allows for flexibility and comfort in textile applications.

Nylon-6,6 emerged as one of the first successful synthetic fibers, dramatically changing the textile industry by offering an alternative to natural fibers. Its introduction allowed for the development of a wide range of durable, high-performance products in everyday use.