Question

What commercial chemical reactions of terephthalic acid would be used to give a common polyester?

Short answer

Terephthalic acid (C8H6O4) reacts with ethylene glycol (C2H6O2) in a condensation polymerization reaction to form polyethylene terephthalate (PET) through the formation of ester linkages (-CO-O-), while releasing water molecules. The chemical equation for this reaction is: \[n \ C_8H_6O_4 + n \ C_2H_6O_2 → [-C_6H_4(COOOC_2H_4OCOC_6H_4)-]_n + (2n-2) \ H_2O\] The physical and mechanical properties of PET are influenced by the degree of polymerization and the presence of ester linkages.

Step-by-step solution

Identify the reactants involved in the reaction

In this case, we will focus on the production of PET. The main reactants involved in the synthesis of PET are terephthalic acid (C8H6O4) from which the polyester's name is derived and ethylene glycol (C2H6O2).

Understand the main reaction mechanism

PET is synthesized using a condensation polymerization reaction, where the carboxylic acid group of terephthalic acid (-COOH) reacts with the alcoholic group of ethylene glycol (-OH), forming an ester linkage (-CO-O-) and releasing a water molecule in the process. This reaction is carried out at high temperatures and under specific catalyst conditions.

Write the chemical equation for the reaction

The balanced overall reaction for the synthesis of PET can be represented as follows: \[n \ C_8H_6O_4 + n \ C_2H_6O_2 → [-C_6H_4(COOOC_2H_4OCOC_6H_4)-]_n + (2n-2) \ H_2O\] Here, the square brackets represent the repeating unit in the PET polymer, and 'n' is the degree of polymerization, indicating the number of monomer units in the polymer chain.

Analyze the polymer properties

The physical and mechanical properties of PET are determined by the length of the polymer chain (degree of polymerization or molecular weight), as well as the presence of the ester linkage. The ester linkage contributes to the polymer's stability, strength, and resistance to heat and certain chemicals, making it suitable for various applications such as in clothing fibers, food packaging, and plastic materials.

Key concepts

Condensation Polymerization

Condensation polymerization is a vital process in polymer chemistry where small molecules like water or methanol are released as by-products. In this process, monomers with two functional groups react to form polymers. In the case of terephthalic acid, it's all about bringing together molecules to create something larger, much like assembling blocks to build a tower.

When terephthalic acid reacts with ethylene glycol, a crucial by-product is water. This makes it different from addition polymerization, which does not produce any by-products. The ester groups formed during condensation polymerization result in the creation of a strong polymer backbone.

• This type of reaction typically requires high temperatures
• Catalysts are often used to speed up the reaction
• The release of water aids in linking the monomer units

By understanding condensation polymerization, one can grasp the foundational techniques to make polymers like Polyethylene Terephthalate (PET).

Polyethylene Terephthalate (PET)

Polyethylene Terephthalate, commonly abbreviated as PET, is a widely used type of polyester. Have you ever used a plastic bottle or worn clothes made of polyester?
That's PET. It is produced by the reaction of terephthalic acid with ethylene glycol.

This polymer is known for its strength, lightweight nature, and clarity. It is highly favored in the consumer goods industry because it's versatile and recyclable.

• PET is utilized in clothing fibers and food packaging
• It has excellent resistance to moisture and many chemicals
• The polymer structure provides substantial durability and strength

The synthesis of PET through condensation polymerization ensures that it has a robust molecular structure, emphasizing its importance in everyday items.

Ester Linkage Formation

Ester linkage formation is a core concept in understanding how PET and similar polymers are made. When terephthalic acid reacts with ethylene glycol, an ester bond is formed. This is an essential step in polymer formation.

Ester linkage is created when the hydroxyl group (-OH) of ethylene glycol reacts with the carboxylic acid group (-COOH) of terephthalic acid. As a result, a water molecule is expelled, leaving behind a bonding link known as an ester group (-CO-O-).

• The ester bond acts as a link between polymer chains
• It is responsible for the strength and elasticity of the polymer
• This bond contributes to the flexibility and resilience of PET

Understanding ester linkages helps one appreciate why polymers like PET have such beneficial properties for both industrial and everyday applications. The ester linkage is not just a chemical bond, but a key aspect of polymer stability and performance.