What is the Difference Between Phthalic Acid and Terephthalic Acid

The main difference between phthalic acid and terephthalic acid is that phthalic acid is an isomer of the benzene dicarboxylic acid with functional groups in the ortho position, while terephthalic acid is an isomer of benzene dicarboxylic acid with functional groups in the para position.

A benzene dicarboxylic acid is a group of chemical compounds that has two carboxylic acid functional groups attached to the benzene ring. Hence, it is called a dicarboxylic derivative of benzene. Phthalic acid, isophthalic acid, and terephthalic acid are the three isomeric forms of this class.

Key Areas Covered

1. What is Phthalic Acid  
     – Definition, Structure, Uses
2. What is Terephthalic Acid
     – Definition, Structure, Uses
3. Similarities – Phthalic Acid and Terephthalic Acid
     – Outline of Common Features
4. Difference Between Phthalic Acid and Terephthalic Acid
     – Comparison of Key Differences

Key Terms

Phthalic Acid, Terephthalic Acid

What is Phthalic Acid

Phthalic acid is a white crystalline solid with the chemical formula C₈H₆O₄. It is an organic compound that comes from the family of aromatic dicarboxylic acids. There are two carboxylic acid functional groups in a molecule of phthalic acid. They are attached to an aromatic benzene ring. The molecular weight of the compound is 166.13. Its melting point is 410-412 degrees of Fahrenheit, whereas its boiling point is 598.00K. Its density is 1.593 g/cm³. Phthalic acid is soluble in water and in polar solvents but is insoluble in non-polar solvents.

Phthalic acid is produced by the oxidation of naphthalene with potassium permanganate. Moreover, phthalic acid is commonly used as a precursor for the production of plasticizers, dyes, and polyester resins. For example, it helps to produce phthalates, which are a group of chemical compounds manufacturers add to plastic to improve durability and flexibility. Another example of its use in the production of various dyes like phthalocyanine blue and green pigments.

What is Terephthalic Acid

Terephthalic acid is an organic compound with the formula C₆H₄(CO₂H)₂. Another name for it is 1-4-benzene dicarboxylic acid. This is a white solid. Its molar mass is 166.132 g/mol, while its density is 1.519 g/mol. It has a melting point of 300 degrees Celcius, and it is soluble in polar organic solvents.

The production of terephthalic acid involves the catalytic oxidation of p-xylene in the Amoco process. Moreover, P-xylene is present in crude oil.

There are many uses for terephthalic acid. It acts as a carrier in paints. It is also useful as a raw material to make terephthalate plasticizers such as dibutyl terephthalate. In the pharmaceutical industry, it is used as a raw material for certain drugs. Terephthalic acid-based polyesters and polyamides are useful in hot melt adhesives. It is also helpful in the production of polyester fibres, films, and resins.

Terephthalic acid is also used in the production of PET resin, which is a type of thermoplastic polyester used in the production of plastic bottles, containers, and packaging materials due to its high strength and clarity. They are also resistant to chemicals and moisture and help in the production of other types of polymers, such as polybutylene terephthalate and polyethylene naphthalate. In addition, these polymers are useful in the production of electrical components and automotive parts.

However, one adverse effect of using terephthalic acids in production is their negative impact on the environment. A large amount of energy is necessary for the production of this acid. It also emits large amounts of greenhouse gas emissions. Moreover, the disposal of plastic products made from terephthalic acid contributes to environmental pollution and damage to wildlife habitats. Hence, researchers are currently investigating other means of producing terephthalic acid.

Similarities Between Phthalic Acid and Terephthalic Acid

• Phthalic acid and terephthalic acids are white crystalline solids.
• Moreover, both are two organic compounds.

Difference Between Phthalic Acid and Terephthalic Acid

Definition

Phthalic acid is a white crystalline solid with the chemical formula C₈H₆O₄ while terephthalic acid is an organic compound with the formula C₆H₄(CO₂H)₂.

Structure

While phthalic acid is an isomer of the benzene dicarboxylic acid having functional groups in the ortho position, terephthalic acid is an isomer of benzene dicarboxylic acid having functional groups in the para position.

Production

Moreover, the production of phthalic acid involves the catalytic oxidation of naphthalene with potassium permanganate, while the production of terephthalic acid involves the oxidation of p-xylene with oxygen.

Uses

In addition, phthalic acid is used in paint as a carrier, in the production of phthalates, and in drugs. Terephthalic acid is used in the synthesis of polyester, PET, for large-scale manufacturing of synthetic fibres and plastic bottles.

Conclusion

In brief, a benzene dicarboxylic acid is a group of chemical compounds that has two carboxylic acid functional groups attached to the benzene ring. Phthalic acid and terephthalic acid are two isomeric forms of this class. The main difference between phthalic acid and terephthalic acid is that phthalic acid is an isomer of the benzene dicarboxylic acid with functional groups in the ortho position, while terephthalic acid is an isomer of benzene dicarboxylic acid with functional groups in the para position.

Reference:

1. “Phthalic acid.” Pubchem. National Library of Medicine.
2. “Terephthalic Acid – An Overview.” Science Direct.

Image Courtesy:

1. “Phthalic acid 3D ball” By Jynto (talk) – created with Discovery Studio Visualizer. (CC0) via Commons Wikimedia
2. “Terephthalic acid 3D ball” By Jynto (talk) – created with Discovery Studio Visualizer. (CC0) via Commons Wikimedia