Question

A simple polyamide can be made from ethylenediamine and oxalic acid (Table 17.1 ). Draw the polymer formed when three units of ethylenediamine reacts with three units of oxalic acid.

Short answer

The polymer is a repeating chain of ethylenediamine and oxalic acid units linked by amide bonds.

Step-by-step solution

Understand the Reactants

Identify the chemical structure of ethylenediamine, which is \( \text{NH}_2-\text{CH}_2-\text{CH}_2-\text{NH}_2 \), and oxalic acid, which is \( \text{HOOC-COOH} \). These two molecules will undergo a condensation reaction to form a polyamide.

Determine the Functional Groups

Recognize that the amine group (\( \text{NH}_2 \)) of ethylenediamine will react with the carboxylic acid group (\( \text{COOH} \)) of oxalic acid to form an amide bond (\( \text{CONH} \)).

Plan the Polymer Chain

Since there are three units of each reactant, these units will link in an alternating pattern: oxalic acid, ethylenediamine, oxalic acid, repeating this until all units are consumed.

Form the First Amide Link

For the initial reaction, connect one end of the ethylenediamine to one end of the oxalic acid by removing a molecule of water (\( \text{H}_2\text{O} \)) and forming the first amide bond: \( \text{CONH} \).

Continue the Polymerization

Repeat the condensation process, adding additional units to build up the chain. Connect the second ethylenediamine to the free carboxyl end of the first oxalic acid, then add the second oxalic acid to the free amine end, and continue until all units are linked.

Draw the Polymer

Illustrate the final polymer: \( -\text{NH-CH}_2-\text{CH}_2-\text{NH-CO-CO-NH-CH}_2-\text{CH}_2-\text{NH-CO-CO}- \ldots \), repeating the pattern for the three units.

Key concepts

Ethylenediamine

Ethylenediamine is an organic compound important in the formation of polyamides. It's a simple diamine with the chemical formula \( \text{NH}_2-\text{CH}_2-\text{CH}_2-\text{NH}_2 \). This means it has two amine groups (-NH\(_2\)) attached to an ethylene backbone (a chain of two carbon atoms in this case).

Because of its two amine groups, ethylenediamine is highly reactive and can form elongated chains in reactions with dicarboxylic acids, such as oxalic acid. This ability allows it to act as a monomer in polymer formation.

• Has a simple linear structure
• Acts as a building block in forming polymer chains
• Reacts with carboxylic acids to form amide bonds

Understanding the structure and reactivity of ethylenediamine is crucial in grasping how polyamide chains are synthesized through the repeating process of forming amide bonds.

Oxalic Acid

Oxalic acid is another key player in polyamide synthesis with ethylenediamine. It is a dicarboxylic acid, which means it has two carboxyl groups (-COOH), and its chemical formula is \( \text{HOOC-COOH} \).

These carboxyl groups are highly reactive, especially towards amines, to form amide bonds. In the context of polymer synthesis, oxalic acid acts as a monomer that facilitates the creation of larger, more complex molecules through condensation reactions.

• Contains two carboxyl groups
• Works as a linking agent in polymers
• Reactive in forming amide bonds

Oxalic acid's role in polyamide formation involves bridging ethylenediamine units. It creates long polymer chains that have useful properties in materials and textiles.

Amide Bond

The amide bond is a pivotal chemical link in the formation of polyamides. It is formed when an amine group (-NH\(_2\)) from a molecule like ethylenediamine reacts with a carboxylic acid group (-COOH) from oxalic acid.

The reaction involves the removal of a water molecule in what is called dehydration synthesis, resulting in the linkage \( \text{CONH} \). This bond is extremely strong and stable, giving polyamides their characteristic durability.

• Created through dehydration synthesis
• Forms a \( \text{CONH} \) linkage
• Provides mechanical strength to polymers

Understanding how amide bonds form and their properties is essential for appreciating the strength and resilience of materials made from polyamides, such as nylon.

Condensation Reaction

Condensation reactions are crucial in polymer chemistry, especially for forming polyamides. This type of reaction involves joining two molecules through the formation of a bond while releasing a small molecule, such as water.

In the synthesis of polyamides from ethylenediamine and oxalic acid, each amide bond formed is the result of a condensation reaction. The amine group from ethylenediamine joins with the carboxyl group from oxalic acid, expelling a water molecule and creating the backbone of the polyamide.

• Facilitates the formation of high molecular weight compounds
• Involves the formation of a bond with the release of water
• Central to the production of polymers such as nylons

Condensation reactions are not only essential for making polyamides but also in creating a wide array of materials, making it a fundamental concept in organic and polymer chemistry.