What Is Isophthalic Acid?
Isophthalic acid is an aromatic dicarboxylic acid, with two carboxyl groups substituted at the meta-position of the benzene ring, also known as benzene-1,3-dicarboxylic acid. It has structural isomers including phthalic acid (ortho-position substitution) and terephthalic acid (para-position substitution).
Isophthalic acid is highly valued as a raw material in the chemical industry, primarily synthesized by oxidizing mixed xylene-containing isomers.
Uses of Isophthalic Acid
Isophthalic acid, with its two functional groups, is a monomer used in polymers, producing resins with excellent heat resistance, electrical properties, and release characteristics. Its applications include functional paints, plasticizers, automotive, marine, and aircraft industry materials. Unsaturated polyester resins made with isophthalic acid have superior properties compared to those made with phthalic acid. Other uses include modifying polyethylene terephthalate (PET) resin for improved transparency, alkyd resins for coatings with good gloss and adhesion, and polyester fibers for enhanced dyeability and texture. Additionally, meta-aramid fibers synthesized from isophthalic acid are used in various industrial materials and protective clothing due to their heat, flame, and corrosion resistance.
Properties of Isophthalic Acid
Isophthalic acid, with the chemical formula C8H6O4 and a molecular weight of 166.14, is a colorless, odorless, needle-like crystal. Its melting point is around 347±2℃. It is slightly soluble in polar solvents like water, acetone, and ethanol at room temperature, but insoluble in non-polar solvents like benzene, toluene, and petroleum ether. Isophthalic acid can form polyester resins through dehydration with polyols and can also react with amines to form amides.
Production Method of Isophthalic Acid
Isophthalic acid is mainly synthesized by oxidizing mixed xylene. Methods include the Amoco method, which air-oxidizes meta-xylene in an acetic acid solvent using organic acid salts of heavy metals and bromine as catalysts, and the sulfur-ammonia oxidation method, which oxidizes methaxylene in an aqueous ammonia solution using sulfur or sulfide as an oxidant.