Maleic Acid is defined as an organic white crystalline solid compound, which contains two carboxylic functional groups (−COOH) molecules. This maleic acid is the cis-isomer of butanediol acid and it is very less stable in nature. This acid is soluble in water and is combustible as well. Maleic Acid can be characterized by a faint odour. Maleic acid IUPAC name is (2Z)-But-2-enedioic acid.
Properties of Maleic Acid
Maleic acid holds a heat of combustion of -1,355 kJ/mol., 22.7 kJ/mol higher compared to fumaric acid. In comparison to fumaric acid, maleic acid is more water-soluble. The melting point of this acid (135 °C) is also very low compared to fumaric acid (287 °C). Both properties of maleic acid may be explained on account of the intramolecular hydrogen bonding that occurs in maleic acid at the intermolecular interactions’ expense, and that is not possible in fumaric acid for some geometric reasons.
Maleic Acid Structural Formula
The structural formula of Maleic Acid (maleic acid structure) is represented in the below figure. Maleic Acid can be used in the production of glyoxylic acid by the ozonolysis process. It's a plant metabolite, a mouse metabolite, and an algal metabolite all rolled into one. Maleic acid molecular formula is C4H4O4.
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Reactions of Maleic Acid
Although commercially it is not practised, maleic acid may be converted into maleic anhydride by dehydration, malic acid by hydration, and succinic acid by hydrogenation (palladium on carbon or ethanol). It reacts either with phosphorus pentachloride or thionyl chloride to produce the maleic acid chloride. Being electrophilic, maleic acid participates as a dienophile in several Diels-Alder reactions.
Use in Pharmaceutical Drugs
Several drugs, which contain amines, are provided as the maleate acid salt, for example, chlorpheniramine, carfenazine, methylergonovine, pyrilamine, and thiethylperazine.
Production and Industrial Applications
In industry, maleic acid can be derived by hydrolysis of maleic anhydride, the latter being produced by the oxidation of either butane or benzene.
Maleic acid is the industrial raw material used in the ozonolysis process to produce glyoxylic acid.
Maleic acid can be used to form the acid addition salts with drugs to make them strongly stable, such as indacaterol maleate.
Also, maleic acid can be used as an adhesion promoter for various substrates, such as zinc and nylon coated metals, for example, galvanized steel, in the adhesives of methyl methacrylate-based.