Maleic anhydride

Overview
Maleic anhydride (cis-butenedioic anhydride, toxilic anhydride, dihydro-2,5-dioxofuran) is an organic compound with the formula C4H2O3. In its pure state it is a colourless or white solid with an acrid odour.

Maleic anhydride was traditionally manufactured by the oxidation of benzene or other aromatic compounds. Due to rising benzene prices, most maleic anhydride plants now use n-butane as a feedstock. As of 2006, only few smaller plants continue to use benzene:
 * CH3CH2CH2CH3 + 3.5  O2  →  C2H2(CO)2O  +  4 H2O

Characteristic reactions
The chemistry of maleic anhydride is very rich, reflecting its ready availability and bifunctional reactivity.
 * It hydrolyzes, producing maleic acid, cis-HO2CCH=CHCO2H. With alcohols, the half-ester is generated, e.g., cis-HO2CCH=CHCO2CH3.
 * Maleic anhydride is a potent dienophile in Diels-Alder reactions.
 * Maleic anhydride (MA) is an excellent ligand for low-valent metal complexes, examples being Pt(PPh3)2(MA) and Fe(CO)4(MA).