12benzenedicarboxaldehyde

1,2-Benzenedicarboxylic acid, commonly called phthalic acid, is an organic dicarboxylic acid consisting of a benzene ring substituted with two adjacent carboxyl groups. It is one of three benzenedicarboxylic acid isomers; the others are isophthalic (1,3-) and terephthalic (1,4-) acids. The compound is a colorless or white crystalline solid that can dehydrate to give phthalic anhydride.

Industrial production typically involves oxidation of o-xylene or naphthalene to phthalic anhydride, which is then hydrolyzed to the acid when needed. Laboratory preparations may start from aromatic precursors through controlled oxidation. The molecule’s two acidic carboxyl groups confer typical carboxylic acid reactivity, allowing esterification, formation of anhydrides, and salt formation with bases.

Phthalic acid and its derivatives are important intermediates in chemical manufacturing. Phthalic anhydride is a key precursor to plasticizers (commonly as phthalates), alkyd resins, dyes, pigments, and certain pharmaceuticals. The acid and its salts also find specialized uses in organic synthesis and as reagents in laboratory settings.

Safety considerations include skin and eye irritation on contact and potential environmental concerns associated with some phthalate derivatives. As with many industrial chemicals, handling recommendations call for appropriate personal protective equipment and controls to limit releases to the environment.