What is Isophthalic Acid CAS 121-91-5?

It is an aromatic dicarboxylic acid with the formula C8H6O4 and a molecular weight of about 166.13 g/mol. It is also known as 1,3-benzenedicarboxylic acid or m-phthalic acid, and is normally supplied as a white crystalline powder.

How does Isophthalic Acid differ from terephthalic acid?

Isophthalic Acid is the meta-isomer with carboxyl groups in the 1 and 3 positions, while terephthalic acid is the para-isomer with carboxyl groups in the 1 and 4 positions. Isophthalic Acid is often selected for resin formulations requiring improved chemical and hydrolytic resistance, whereas terephthalic acid is more commonly used for high-molecular-weight PET fiber and bottle resin.

What typical properties should buyers check?

Important checks include appearance, purity, acid value, moisture content, and trace impurity levels that can affect polymerization. The material has a high melting point around 345-348 C with sublimation, low water solubility, and a density near 1.5 g/cm3.

How should Isophthalic Acid be stored and handled?

Keep the powder in tightly closed containers in a cool, dry, well-ventilated area, away from moisture, direct sunlight, strong oxidizers, and bases. Dust should be controlled with appropriate ventilation and protective equipment because finely dispersed organic powder can be combustible and may irritate the eyes, skin, or respiratory tract.

Isophthalic Acid CAS 121-91-5

Isophthalic Acid, also called 1,3-benzenedicarboxylic acid or m-phthalic acid, CAS 121-91-5, is an aromatic dicarboxylic acid supplied as a white crystalline powder and positioned for resin and polymer synthesis. Confirm the required grade, then request a quotation with COA/TDS/SDS for bulk supply.

CAS: 121-91-5
Synonyms: 1,3-Benzenedicarboxylic Acid; m-Phthalic Acid
Einecs: 204-506-4
Molecular Formula: C8H6O4
Grade: Industrial / polymer-grade supply
Package: Bags or bulk containers

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Product Description

Isophthalic Acid CAS 121-91-5 is an aromatic dicarboxylic acid with EC 204-506-4 and molecular formula C8H6O4.

Synonyms: 1,3-Benzenedicarboxylic Acid; m-Phthalic Acid.

CAS: 121-91-5.

Molecular formula: C8H6O4.

It is supplied as a white crystalline powder.

It has a molecular weight of about 166.13 g/mol.

It is positioned as an aromatic dicarboxylic acid intermediate for resin and polymer synthesis.

It is used as a monomer in unsaturated polyester resins and alkyd resins.

It is used in powder coatings and specialty polyesters.

Its meta-position carboxyl groups help improve chemical resistance, hydrolytic stability, and mechanical performance.

It is the meta-isomer, differing from terephthalic acid, the para-isomer used for high-molecular-weight PET.

Confirm the required grade, purity, acid value, moisture content, appearance, and related specifications for the chosen grade.

Check compatibility with the target resin, coating, or polymer synthesis process.

Store in tightly closed containers in a cool, dry, well-ventilated area, away from moisture, direct sunlight, strong oxidizers, and bases.

Control dust with appropriate ventilation and protective equipment, since finely dispersed organic powder can be combustible and may irritate eyes, skin, or respiratory tract.

Confirm packaging suitable for the powder form and order quantity, and follow the current SDS.

Confirm grade, packaging, and specification as required.

The page is an RFQ entry point and does not state stock, price, MOQ, or fixed lead time.

For an RFQ, state the intended application, required grade, quantity, packaging, destination, and document needs.

FAQ - Technical & Supply Chain

Q:
What is Isophthalic Acid CAS 121-91-5?

A: It is an aromatic dicarboxylic acid with the formula C8H6O4 and a molecular weight of about 166.13 g/mol. It is also known as 1,3-benzenedicarboxylic acid or m-phthalic acid, and is normally supplied as a white crystalline powder.
Q:
What are the main uses of Isophthalic Acid?

A: It is used mainly as a monomer in unsaturated polyester resins, alkyd resins, powder coatings, and specialty polyesters. Its meta-position carboxyl groups help improve chemical resistance, hydrolytic stability, and mechanical performance in coatings and composites.
Q:
How does Isophthalic Acid differ from terephthalic acid?

A: Isophthalic Acid is the meta-isomer with carboxyl groups in the 1 and 3 positions, while terephthalic acid is the para-isomer with carboxyl groups in the 1 and 4 positions. Isophthalic Acid is often selected for resin formulations requiring improved chemical and hydrolytic resistance, whereas terephthalic acid is more commonly used for high-molecular-weight PET fiber and bottle resin.
Q:
What typical properties should buyers check?

A: Important checks include appearance, purity, acid value, moisture content, and trace impurity levels that can affect polymerization. The material has a high melting point around 345-348 C with sublimation, low water solubility, and a density near 1.5 g/cm3.
Q:
How should Isophthalic Acid be stored and handled?

A: Keep the powder in tightly closed containers in a cool, dry, well-ventilated area, away from moisture, direct sunlight, strong oxidizers, and bases. Dust should be controlled with appropriate ventilation and protective equipment because finely dispersed organic powder can be combustible and may irritate the eyes, skin, or respiratory tract.

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