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Isophthalic acid

IUPAC: benzene-1,3-dicarboxylic acid

C8H6O4 Acids CAS 121-91-5
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Quick Reference
Formula / NotationC8H6O4
CAS Number121-91-5
Molecular Weight166.13
Melting Point653 °F (USCG, 1999)
Boiling PointSublimes
Density1.54 at 77 °F (USCG, 1999) - Denser than water; will sink
SolubilitySoluble in 8000 parts cold water, 460 parts boiling water; freely soluble in alcohol; practically insoluble in petroleum ether
AppearanceIsophthalic acid is a white solid with a slight unpleasant odor. Sinks in water. (USCG, 1999)
Also Known Asbenzene-1,3-dicarboxylic acid; 121-91-5; Benzene-1,3-dicarboxylic acid; 1,3-Benzenedicarboxylic acid; m-Phthalic acid; m-Benzenedicarboxylic acid; Acide isophtalique; Kyselina isoftalova; DTXSID3021485; X35216H9FJ
CategoryAcids

What is Isophthalic acid?

Isophthalic acid is a benzenedicarboxylic acid that is benzene substituted by carboxy groups at position 1 and 3. One of three possible isomers of benzenedicarboxylic acid, the others being phthalic and terephthalic acids. It is a conjugate acid of an isophthalate(1-).

Formula & Notation

C8H6O4

IUPAC Name: benzene-1,3-dicarboxylic acid

Other Names / Synonyms: benzene-1,3-dicarboxylic acid; 121-91-5; Benzene-1,3-dicarboxylic acid; 1,3-Benzenedicarboxylic acid; m-Phthalic acid; m-Benzenedicarboxylic acid; Acide isophtalique; Kyselina isoftalova; DTXSID3021485; X35216H9FJ

Properties & Characteristics

Appearance: Isophthalic acid is a white solid with a slight unpleasant odor. Sinks in water. (USCG, 1999). Molecular formula: C8H6O4. Molecular weight: 166.13 g/mol. Boiling point: Sublimes. Melting point: 653 °F (USCG, 1999). Density: 1.54 at 77 °F (USCG, 1999) - Denser than water; will sink. Solubility: Soluble in 8000 parts cold water, 460 parts boiling water; freely soluble in alcohol; practically insoluble in petroleum ether. Vapor pressure: 0.00000002 [mmHg]. LogP: 1.7.

Physical Data

PropertyValue
Melting Point653 °F (USCG, 1999)
Boiling PointSublimes
Density1.54 at 77 °F (USCG, 1999) - Denser than water; will sink
Molecular Weight166.13
SolubilitySoluble in 8000 parts cold water, 460 parts boiling water; freely soluble in alcohol; practically insoluble in petroleum ether
AppearanceIsophthalic acid is a white solid with a slight unpleasant odor. Sinks in water. (USCG, 1999)

Uses & Applications

Used in industrial chemical synthesis, fertilizer production, battery electrolytes, metal processing, and laboratory acid-base reactions.

Safety Information

Corrosive. Causes severe burns to skin, eyes, and respiratory tract. Wear appropriate PPE including gloves, goggles, and lab coat. Consult SDS before use.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Isophthalic acid
Formula C8H6O4
CAS Number 121-91-5
Molecular Weight 166.13
Category Acids
Synonyms benzene-1,3-dicarboxylic acid; 121-91-5; Benzene-1,3-dicarboxylic acid; 1,3-Benzenedicarboxylic acid; m-Phthalic acid; m-Benzenedicarboxylic acid; Acide isophtalique; Kyselina isoftalova; DTXSID3021485; X35216H9FJ

Frequently Asked Questions

Isophthalic acid is a benzenedicarboxylic acid that is benzene substituted by carboxy groups at position 1 and 3. One of three possible isomers of benzenedicarboxylic acid, the others being phthalic and terephthalic acids. It is a conjugate acid of an isophthalate(1-).

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Editorial standards: Chemical data is sourced from peer-reviewed literature, CAS Registry, NIST WebBook, and PubChem. Safety information reflects guidance from OSHA, ECHA, and IAEA. For educational purposes only — always consult official SDS documentation and qualified professionals before handling chemicals.