diacids

Diacids are chemical compounds that contain two acidic functional groups, most commonly carboxyl groups (-CO2H). When a molecule has exactly two carboxyl groups, it is called a dicarboxylic acid. Diacids occur in both aliphatic and aromatic forms and can be naturally occurring or synthetically produced. They are generally diprotic, capable of releasing two protons, with the first dissociation typically stronger than the second depending on the structure.

Common examples include aliphatic diacids such as oxalic acid (ethanedioic), malonic (propanedioic), succinic (butanedioic), glutaric (pentanedioic), and adipic (hexanedioic) acids. Aromatic diacids include the phthalic acids (benzene-1,2-dicarboxylic acid; ortho-), isophthalic acid (benzene-1,3-dicarboxylic acid), and terephthalic acid (benzene-1,4-dicarboxylic acid).

Chemical properties of diacids arise from having two carboxyl groups. They can form diesters and, upon heating, cyclic anhydrides (for example, succinic and phthalic anhydrides). Their acidity is influenced by substitution and ring effects, with the first dissociation usually stronger than the second. Diacids commonly participate in condensation polymerization to form polyesters and polyamides; notable monomers include adipic acid and terephthalic acid used in polymer production.

Occurrence and use: Some diacids occur naturally and serve as metabolic intermediates (for example, succinate in the citric acid cycle; oxalic acid in various plants). Industrially, diacids are produced for polymer synthesis and as monomers in polymers such as polyesters and polyamides (e.g., PET uses terephthalic acid; nylons may use adipic acid).

Safety and handling: Diacids range from relatively benign to hazardous; oxalic acid is notably toxic. Proper chemical hygiene, including protective equipment and awareness of corrosivity, is recommended.