The key difference between phthalic acid and terephthalic acid is that phthalic acid is an isomer of benzenedicarboxylic acid having functional groups in the ortho position, whereas terephthalic acid is an isomer of benzenedicarboxylic acid having functional groups in the para position.
Benzenedicarboxylic acid can be described as a group of chemical compounds that has two carboxylic acid functional groups attached to a benzene ring, so we can call them dicarboxylic derivatives of benzene. The three isomeric forms of this class include phthalic acid, isophthalic acid, and terephthalic acid.
CONTENTS
1. Overview and Key Difference
2. What is Phthalic Acid
3. What is Terephthalic Acid
4. Phthalic Acid vs Terephthalic Acid in Tabular Form
5. Summary – Phthalic Acid vs Terephthalic Acid
What is Phthalic Acid?
Phthalic acid can be described as an aromatic dicarboxylic acid having the chemical formula C6H4(COOH)2. The closely related phthalic anhydride is the most common form of phthalic acid, having important uses. It is a commodity chemical that is formed on a large scale. This acidic compound is one of the three isomers of benzenedicarboxylic acid. The other two isomers are isophthalic acid and terephthalic acid.
Figure 01: The Chemical Structure of Phthalic Acid
This substance appears as a white solid, and its density is about 1.59 g/mol. It has a melting point of about 207 degrees Celsius, and its solubility in water is poor. The other chemical names for phthalic acid include 1,2-benzenedioic acid, benzene-1,2-dioic acid, ortho-phthalic acid, etc.
We can produce phthalic acid from the catalytic oxidation of naphthalene or ortho-xylene. This directly forms phthalic anhydride. Its subsequent hydrolysis can also occur in the anhydride.
This chemical compound was first introduced by the French Chemist Auguste Laurent in 1836. This was performed by oxidizing naphthalene tetrachloride. He believed the compound coming from this reaction to be a naphthalene derivative, which led him to name it naphthalic acid. However, the chemical name was corrected later by a Swiss chemist, Jean Charles Galissard de Marignac.
What is Terephthalic Acid?
Terephthalic acid is an aromatic organic compound having the chemical formula C6H4(CO2H)2. It has a para conformation. It occurs as a white crystalline powder. Moreover, it is insoluble in water but soluble in polar organic solvents. The chemical name of this substance is 1,4-benzenedicarboxylic acid.
Figure 02: The Chemical Structure of Terephthalic Acid
When considering the production of terephthalic acid, the major production process is the Amoco process. Here, the acid is produced via oxidation of p-xylene in the presence of oxygen in the air.
There are many uses of terephthalic acid. For example, it is useful as a precursor for PET production (polyethylene terephthalate), used in paints as a carrier compound, as a raw material for certain drugs in pharmaceutical applications, as a filler in certain military smoke grenades, etc.
What is the Difference Between Phthalic Acid and Terephthalic Acid?
Phthalic acid and terephthalic acid are two major isomers of benzenedicarboxylic acid compounds. The key difference between phthalic acid and terephthalic acid is that phthalic acid is an important organic compound and an isomer of benzenedicarboxylic acid having functional groups in the ortho position whereas terephthalic acid is an important organic compound and an isomer of benzenedicarboxylic acid having functional groups in the para position.
The following table summarizes the difference between phthalic acid and terephthalic acid.
Summary – Phthalic Acid vs Terephthalic Acid
Benzenedicarboxylic acid is a group of chemical compounds that has two carboxylic acid functional groups attached to a benzene ring. Phthalic acid and isophthalic acid are two of their isomeric forms. Therefore, the key difference between phthalic acid and terephthalic acid is that phthalic acid has its functional groups in the ortho position, whereas terephthalic acid has its functional groups in the para position.
Reference:
1. “Phthalic Acid.” VEDANTU, 27 Apr. 2022.
Image Courtesy:
1. “Phthalic acid” (Public Domain) via Commons Wikimedia
2. “Terephthalic-acid-2D-skeletal” By Jynto – Own work (Public Domain) via Commons Wikimedia