Racemic malic acid is produced industrially by the double hydration of maleic anhydride. In 2000, American production capacity was 5,000 tons per year. The enantiomers may be separated by chiral resolution of the racemic mixture. S-Malic acid is obtained by fermentation of fumaric acid.
Self-condensation of malic acid in the presence of fuming sulfuric acid gives the pyrone coumalic acid:
Carbon monoxide and water are liberated during this reaction.
Malic acid was important in the discovery of the Walden inversion and the Walden cycle, in which (−)-malic acid first is converted into (+)-chlorosuccinic acid by action of phosphorus pentachloride. Wet silver oxide then converts the chlorine compound to (+)-malic acid, which then reacts with PCl to the (−)-chlorosuccinic acid. The cycle is completed when silver oxide takes this compound back to (−)-malic acid.
-malic acid is used to resolve α-phenylethylamine, a versatile resolving agent in its own right.