It is prepared commercially by catalytic oxidation of 2-butene (from petroleum) or benzene.
Properties of Maleic Acid.
Maleic acid crystallises in large monoclinic prisms, mp 130.5°C, having repulsive astringent taste. It is very soluble in water and ethyl alcohol, but moderately soluble in ether. It gives the reaction of a dicarboxylic acid and also of an activated carbon-carbon double bond.
(1) Action of Heat. On heating to 150°C, it dehydrates to form maleic anhydride.
(2) Catalytic Hydrogenation. When hydrogenated in the presence of Raney nickel, it forms succinic acid.
(3) Hydration. It adds molecule of water across the double bond in the presence of a mineral acid, yielding maleic acid.
(4) Reaction with Alkaline KMnO4. When treated with alkaline KMnO4 solution, undergoes hydroxylation to form meso-tartaric acid.
Maleic Acid Uses.
Maleic acid is used.
- For preparing succinic acid, malic acid, tartaric acid, fumaric acid, and several other derivatives.
- As maleic anhydride for polyester resins needed in fibrous glass material, widely used since 1971 for construction of cars, boats, bathroom, gasoline storage tanks, etc.
- As mordant
- As preservative for oils and fats.