Preparation of Phthalic Acids - Phthalic, Isophthalic, Terephthalic Acids Preparing

When two carboxylic groups are substituted to benzene ring, phthalic, isophthalic, terephthalic acids are given. According to the substituted location (ortho, para and meta), those acids are names as phthalic, isophthalic, terephthalic.



Phthalic acid preparing

Alkyl benzene compounds heated with strong oxidizing agents. Then alkyl group is oxidized to carboxylic acid group. When two alkyl groups are oxidized, two carboxylic acid groups are given.


Alkyl benzene are oxidized to phthalic acids by following strong oxidizing agents.

  • Acidic potassium permanganate
  • Acidic potassium dichromate
  • Acidic potassium chromate


Phthalic acid preparing

In phthalic acid, one -COOH group is connected relatively to the ortho position of other -COOH group.

phthalic acid preparing

Isophthalic acid Preparing

In isophthalic acid, one -COOH group is connected relatively to the meta position of other -COOH group.

Isophthalic acid preparing

Terephthalic acid Preparing

In terephthalic acid, one -COOH group is connected relatively to the para position of other -COOH group. Terephthalic acid is used to produce teriline, a polymer.

Terephthalic acid preparing

Preparing phthalic acids from benzene

If we need to prepare phthalic acid from benzene, we have to several reactions to prepare alkyl benzene. Here, we are going to discuss how we are prepare alkyl benzene step by step.



Preparing phthalic acid and terephthalic acid from benzene

There are common reactions for preparing phthalic acid and terephthalic acid preparing from benzene.


Friedel craft alkylation - methyl benzene preparing

Benzene is treated with methyl chloride in the presence of anhydrous AlCl3. It gives methylbenzene as the product.


1,2-Dimethylbenzene preration - Methyl benzene and methyl chloride in the presence of anhydrous AlCl3

Again, with excess methyl chloride in the presence of anhydrous AlCl3, methyl benzene give two products. They are 1,2-Dimethylbenzene and 1,4-Dimethylbenzene.


Separating 1,2-Dimethylbenzene and 1,4-Dimethylbenzene

We can use a chemical separation method to separate 1,2-Dimethylbenzene and 1,4-Dimethylbenzene. Distillation can be used as a separation method because boiling points of 1,2-Dimethylbenzene and 1,4-Dimethylbenzene are different.


1,2-Dimethylbenzene oxidation

1,2-Dimethylbenzene is oxidized by acidic potassium permanganate to produce phthalic acid.


1,4-Dimethylbenzene oxidation

1,4-Dimethylbenzene is oxidized by acidic potassium permanganate to produce terephthalic acid.



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Friedel craft alkylation of benzene