cisbut2enedioic

cisbut2enedioic, also known as maleic acid, is an organic compound with the formula C4H4O4. It is one of two isomers of butenedioic acid, the other being fumaric acid (trans-butenedioic acid). Maleic acid is a dicarboxylic acid, meaning it contains two carboxyl groups. It is a white crystalline solid that is soluble in water.

Maleic acid is primarily produced by the catalytic oxidation of benzene or n-butane. It is an important intermediate in the synthesis of various chemicals, most notably maleic anhydride, which is then used to produce unsaturated polyester resins, coatings, and agricultural chemicals. Maleic acid itself can be used as a food additive (E296), acting as an acidity regulator. It is also employed in the production of pharmaceuticals, copolymers, and as a metal chelator.

The cis configuration of the double bond in maleic acid makes it more reactive than its trans isomer, fumaric acid. This difference in reactivity stems from the proximity of the two carboxyl groups in the cis isomer, which can lead to intramolecular reactions, such as dehydration to form maleic anhydride. Maleic acid is a relatively strong acid, with a pKa1 of 1.9 and a pKa2 of 6.07. It is classified as a weak allergen and is generally recognized as safe (GRAS) by regulatory bodies for specific food applications.