Conversion of maleic acid into fumaric acid:
- Dissolve 10g of maleic acid in 10 ml of warm water, add 20 ml of concentrated hydrochloric acid and boil gently under reflux for 30 minutes.
- Crystals of fumaric acid soon crystallise out from the hot solution.
- Allow to cool, filter off the fumaric acid and recrystallise it from hot 1m hydrochloric acid. The m.p. in a sealed capillary tube is 286-287 °C.
Conversion of maleic acid into maleic anhydride:
CAUTION:All operations must be conducted in an efficient fume cupboard, owing to the highly toxic nature of the solvent.
- Mix l00g of maleic acid with 1,1,2,2-tetrachloroethane (100 ml) in a distillation flask fitted with a Claisen still-head, a thermometer and a condenser set for downward distillation.
- Heat the mixture on an air bath; when the temperature reaches 150°C, 75 ml of 1,1,2,2-tetrachloroethane and between 15 and 15.5 ml of water are present in the receiver.
- Continue the distillation using an air condenser and change the receiver flask when the temperature reaches 190 °C.
- Collect the maleic anhydride at 195-197 °C.
- Recrystallise the crude anhydride from chloroform. The yield of pure maleic anhydride, m.p. 54 °C, is 70g (83%).
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