Maleate

Maleate refers to the dianion of maleic acid or to salts derived from it. Maleic acid is the cis-2-butenedioic acid, with the two carboxyl groups on the same side of the carbon–carbon double bond. The corresponding trans isomer is fumaric acid. In salt form, the two carboxyl groups are deprotonated, giving the maleate dianion (C4H2O4)2−; common salts include disodium maleate (Na2C4H2O4).

Preparation and occurrence: Maleates are typically prepared by neutralizing maleic acid or by reacting maleic anhydride with bases to yield metal or ammonium salts. They occur as reagents and intermediates in organic synthesis, polymer chemistry, and coordination chemistry.

Reactivity and applications: The electron-withdrawing carboxylate groups make the C=C bond of maleate highly activated toward nucleophiles and electron-deficient reactions. Maleate derivatives serve as Michael acceptors and as dienophiles in Diels–Alder reactions. Alkyl or aryl maleates are common monomers or functionalized intermediates in polymer science and can act as crosslinking agents or plasticizers. In coordination chemistry, metal salts of maleate act as bidentate ligands, binding through both carboxylate groups. The related metabolite malate is a different chemical species in biochemistry.

Safety: As with many carboxylate salts, handling should follow general chemical safety practices, including use of appropriate personal protective equipment and awareness of potential irritant properties.