- any of three isomeric acids having the formula C8H6O4, especially the ortho isomer (orthophthalic acid ), a colorless, crystalline, slightly water-soluble solid used chiefly in the manufacture of dyes, medicine, and perfume.
- isophthalic acid.
- terephthalic acid.
- a soluble colourless crystalline acid used in the synthesis of dyes and perfumes; 1,2-benzenedicarboxylic acid. Formula: C 6 H 4 (COOH) 2
