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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. As of 2006, only a few smaller plants continue to use benzene; due to rising benzene prices, most maleic anhydride plants now use n-butane as a feedstock:
- 2 CH3CH2CH2CH3 + 7 O2 → 2 C2H2(CO)2O + 8 H2O
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).