Question

Nomex, a condensation copolymer used by firefighters because of its flame- resistant properties, forms from isophthalic acid and \(m\) -aminoaniline. Draw the structure of the dimer. (Hint: Water is eliminated when the bond between the monomers forms.)

Short answer

The structure of the Nomex dimer is formed by connecting two isophthalic acid molecules to two m-aminoaniline molecules through amide bonds, with the elimination of two water molecules.

Step-by-step solution

Understand the Monomers

Identify the two monomers involved in the formation of Nomex. Isophthalic acid has the formula C8H6O4 and consists of a benzene ring with two carboxylic acid groups (COOH) at positions 1 and 3. m-Aminoaniline, also known as 3-aminophenylamine, has the formula C6H8N2 and consists of a benzene ring with an amino group (NH2) and an aniline group (NH2 attached to a benzene ring) at positions 1 and 3 respectively.

Determine the Condensation Reaction

A condensation reaction between an acid and an amine group typically results in an amide bond and the elimination of water. In the case of Nomex, the carboxylic acid group of isophthalic acid will react with the amino group of m-aminoaniline to form an amide linkage (CONH) through a condensation reaction, releasing water in the process.

Draw the Dimer Structure

Draw the structure of Nomex by connecting two monomers together. The amino group of one m-aminoaniline molecule will react with the carboxylic acid group of one isophthalic acid molecule to form an amide bond, and the other amino group of the second m-aminoaniline molecule will react with the remaining carboxylic acid group of the same isophthalic acid molecule, forming another amide bond. Remove two molecules of water (H2O) to show the dimer structure of Nomex.

Key concepts

Condensation Reaction

The condensation reaction is a critical process in polymer chemistry and is fundamental to understanding how various materials, like Nomex, are created. In this reaction, two molecules, or monomers, join together with the elimination of a smaller molecule, often water. This particular kind of chemical reaction forms the backbone of many synthetic polymers used in everyday life.

For Nomex, the reaction involves isophthalic acid and m-aminoaniline. As these monomers react, the water is removed in each step, leading to the formation of new chemical bonds that link the monomers together to form a polymer chain. Condensation reactions are versatile and can be used to create a wide variety of polymers with different properties by varying the monomers.

Amide Bond Formation

Amide bond formation is a specific type of condensation reaction where an amine group from one molecule reacts with a carboxylic acid group from another molecule. The result is an amide bond, denoted as CONH, and the release of water.

Understanding amide bond formation is key to grasping how polymers like Nomex are synthesized. The robustness of amide bonds contributes to the thermal and chemical stability of materials, which is why Nomex is favored for its heat-resistant properties. In the dimer structure of Nomex, two amide bonds form when each amino group from m-aminoaniline reacts with a carboxylic acid from isophthalic acid.

Isophthalic Acid

Isophthalic acid is a benzenedicarboxylic acid with a formula of C8H6O4, and it serves as a key monomer in making certain polyamides and polyesters. The acid groups are located on the first and third (meta) positions of the benzene ring, which explains the 'm' in m-aminoaniline—the other monomer reacting with isophthalic acid.

The structural orientation of the carboxylic acid groups allows for a specific alignment and reaction with amine groups of other monomers, resulting in strong and stable polymeric chains. Isophthalic acid's role in polymer structures contributes significantly to properties such as rigidity, durability, and resistance to solvents and heat.

m-Aminoaniline

m-Aminoaniline, also known as 3-aminophenylamine, is a compound with the formula C6H8N2, featuring an amine group attached to a benzene ring. In the context of Nomex synthesis, m-aminoaniline provides the amine group needed for amide bond formation.

The 'm' indicates that the amino groups are in the meta positions relative to each other on the benzene ring, allowing for the formation of polymer chains with specific structural characteristics. The properties of the resulting material, including its flame resistance, can be attributed to both the structure of the monomers and the nature of the resulting polymer.

Polymer Chemistry

Polymer chemistry is the field of chemistry that studies the synthesis, structure, and properties of polymers. Polymers are long chains of repeating molecular units called monomers, and they make up a wide variety of materials, including plastics, rubbers, and fibers like Nomex.

The dimer of Nomex illustrated in the exercise is a small representative part of the larger macromolecule. The polymerization process involves not just one or two monomer units but usually many thousands, leading to substances with unique physical and chemical properties. Polymer chemistry plays a pivotal role in the development of new materials that can withstand extreme conditions, such as the high temperatures encountered by firefighters, further showcasing the real-world relevance and significance of these chemical reactions.