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MALEIC ANHYDRIDE
~ also known as 2,5-Furandione; Maleic acid anhydride; Furan-2,5-dione; 108-31-6; Toxilic anhydride; etc. is the acid anhydride of maleic acid. It is prepared industrially on a large scale for use in coatings and polymers. The maleic anhydride market size is estimated to reach USD 5.08 Billion by the year 2020, at a CAGR of 6.8% between 2015 and 2020.
Chemical structure: It is an organic compound with the chemical formula C2H2(CO)2O or C4H2O3.
Properties: Maleic anhydride is a colorless or white crystal with a pungent smell. It melts at a temperature of 113°F. Its vapors, dusts, and fumes strongly irritate the skin, eyes, and mucous membranes. Flashpoint is 218°F. Auto-ignition temperature is 890°F. It is soluble in water and ether and decomposes in hot solvent.
Production:Â
Maleic anhydride is prepared by oxidation of n-butane or traditionally via the oxidation of benzene.
- N-butane route: The general process converts the methyl groups to carboxylate and removes hydrogen from the backbone. Vanadium phosphate is generally used as the catalyst.
C4H10 + 3.5 O2 → C2H2C2O3 + 4 H2O ∆H = −1236 kJ/mol
The major process entails complete combustion of the butane, a conversion that is two times as exothermic as the partial oxidation.
- Benzene route: Maleic anhydride is traditionally produced by the oxidation of benzene or other aromatic compounds. The catalysts used for the reaction are Molybdenum trioxide and Vanadium pentoxide. Presently, only a small number of plants continue to use benzene.
The traditional method of production using benzene turned out to be too expensive due to the high and still increasing benzene prices. Compliance with the regulations of benzene emissions is another issue.
Chemical reactions and Uses: Upon hydrolysis, Maleic anhydride produces maleic acid, cis-HOOC–CH=CH–COOH. When it is reacted with alcohols, the half-ester is produced, e.g., cis-HOOC–CH=CH–COOCH3.
In the two cases, butane and benzene are passed into a stream of hot air. The mixture is then passed through a catalyst bed at a high temperature. The air to hydrocarbon ratio is regulated to prevent the mixture from igniting.
Maleic anhydride can react with methylene or methine compounds using of sodium acetate as catalyst. These intermediates can consequently be used for generating the Krebs cycle intermediates; aconitic and isocitric acids.
Maleic anhydride is used mainly to make unsaturated polyester resins which can be used in autos, boats, trucks, piping, buildings, and electrical goods. Maleic anhydride can be used to synthesize Lube oil adhesives, which has application in prolonging oil-change intervals and improving engine efficiency.
Maleic anhydride can be used to make pesticides, copolymers, and other organic compounds.
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