Maleic anhydride, also referred to as cis-butenedioic anhydride, is the acid anhydride of maleic acid. At room temperature, it is a colorless or white solid with an acidic taste, typically forming colorless, orthorhombic crystals in needle-like or plate-like shapes. Its molecular formula is C₄H₂O₃, and its molecular weight is 98.06. Needle-shaped crystals can be obtained by crystallization from chloroform or diethyl ether.

Maleic anhydride has a melting point of 60°C, a boiling point of 82°C at 1.8665 kPa, and a relative density of 1.31460. It is soluble in acetone, chloroform, and diethyl ether, but only slightly soluble in petroleum ether. It reacts with water to produce maleic acid and reacts with alcohols to form esters. Additionally, it can participate in Diels–Alder reactions with compounds containing conjugated double bonds. Maleic anhydride is toxic and can cause severe irritation to mucous membranes.

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Maleic anhydride, also referred to as cis-butenedioic anhydride or toxilic anhydride, is an important unsaturated organic acid anhydride and a fundamental industrial raw material. In pesticide manufacturing, it is used as a precursor for various compounds, including diethyl maleate, an intermediate in the production of the organophosphorus insecticide malathion; 1-phenyl-3,6-dihydroxypyridazine, an intermediate for the insecticide pyridaphenthion; and intermediates used in the production of pyrethroid insecticides such as tetramethrin and fungicides such as captan.

Maleic anhydride is also widely used in the manufacture of unsaturated polyester resins, ink additives, papermaking auxiliaries, and coatings, and has applications in the pharmaceutical and food industries. It is a key raw material for producing unsaturated polyester resins, alkyd resins, the insecticide malathion, the pesticide 4049, which is described as highly effective and low in toxicity, and long-acting sulfonamides. Other applications include the production of coatings, maleated rosin, polymaleic anhydride, and maleic anhydride-styrene copolymers.

Furthermore, maleic anhydride serves as an organic chemical feedstock for synthesizing ink additives, papermaking auxiliaries, plasticizers, tartaric acid, fumaric acid, and tetrahydrofuran.