Saccharic or Aldaric Acids

The term aric is used with the normal configurational prefix the tartaric acids are threaric or erythraric acids, mucic acid is galactaric acid, and -saccharic acid is glucaric acid. The name xylaric acid is much shorter than xylo-trihy-droxyglutaric acid. For an additional discussion see below and Chapter I, particularly p. 28. In the present text both forms are used, but the new usage is preferred. 

Tartronic acid, HOOC—CH(OH)—COOH, or hydroxymalonic acid, may be considered as the simplest of the aldaric acids. It has been obtained by the oxidation of glucose or fructose with hydrogen peroxide and ferrous sulfate 40), It is also formed by the cyanohydrin synthesis from glyoxylic acid (41). The oxidation of glycerol gives only small amounts of this acid. 

Malic acid, HOOC—CH2—CH(OH)—COOH, may be considered as a deoxytetraric (tartaric) acid. It occurs widely in nature in fruits and berries. It is formed by the partial reduction of tartaric acids with HI or by the addition of the elements of water to fumaric or maleic acid. The natural acid is levorotatory in dilute solutions, but the rotation becomes positive with increasing concentration. This effect has also been noticed with L-tar-taric (L-threaric) acid. 

The DL-racemate and the inactive isomer are formed from the L-acid by heating with water at 150 to 170°. Heating with alkali has the same effect, but the yields of the two products vary according to conditions (4 ). Separation is effected on the basis of the much greater solubility of the 

A common form of designation of these acids was to use d and I for the sign of rotation rather than l and d, respectively, for indications of configuration. For further discussion see p. 27. 

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