1911 Encyclopædia Britannica/Malic Acid
MALIC ACID (Hydroxyethylene Succinic Acid, C4H6O5, an organic acid found abundantly in the juice of many plants, particularly in mountain-ash berries, in unripe apples and in grapes. The acid potassium salt is also found in the leaves and stalks of rhubarb. Since the acid contains an asymmetric carbon atom, it can exist in three forms, a dextro-rotatory, a laevo-rotatory and an inactive form; the acid obtained in the various synthetic processes is the inactive form. It may be prepared by heating racemic acid (see TARTARIC ACID) with fuming hydriodic acid; by heating fumaric acid (q.v.) with water at 150-200º C.; by the action of nitrous acid on inactive aspartic acid; and by the action of moist silver oxide monobrom-succinic acid. It forms deliquescent crystals, which are readily soluble in alcohol and melt at 100º C. When heated for some time at 130º C. it yields fumaric acid (q.v.), and on rapid heating at 180º C. gives maleic anhydride and fumaric acid. It yields coumarins when warmed with sulphuric acid and phenols (H. v. Pechmann, Ber., 1884, 17, 929, 1649 et seq.). Potassium bichromate oxidizes it to malonic acid; nitric acid oxidizes it to oxalic acid; and hydriodic acid reduces it to succinic acid. The inactive variety may be split into the component active forms by means of its cinchonine salt (G. J. W. Bremer, Ber., 1880, 13, 352).