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.

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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).