is a kind of bulk pharmaceutical chemical. There are some basic informations about this crude drug: (1)CAS No.: ; (2)Other Names: Maleic Anhydride; (3)PubChem: 7923; (4)ChemSpider: 7635; (5)UNII: V5877ZJZ25; (6)EC-number: 203-571-6; (7)Molecular formula: C₄H₂O₃; (8)Molar mass: 98.06 g/mol; (9)Appearance: White crystals.

Maleic anhydride is an organic compound. It is the of maleic acid and in its pure state it is a colourless or white solid with an acrid odour. The chemistry of maleic anhydride is very rich, reflecting its ready availability and bifunctional reactivity. It hydrolyzes, producing maleic acid, cis-HOOC–CH=CH–COOH. With alcohols, the half-ester is generated, e.g., cis-HOOC–CH=CH–COOCH₃.

Maleic anhydride is a potent dienophile in Diels-Alder reactions. It is also a ligand for low-valent metal complexes, examples being Pt(PPh₃)₂(MA) and Fe(CO)₄(MA). Maleic anhydride dimerizes in a photochemical reaction to form cyclobutane tetracarboxylic dianhydride (CBTA). This compound is used in the production of polyimides and as an alignment film for liquid crystal displays.