Tartaric Acid, DL-Tartaric Acid, d-tartaric Acid, and l-tartaric Acid

Tartaric Acid

Tartaric Acid (2,3-dihydroxybutanedioic Acid) is a naturally occurring dicarboxylic acid containing two stereocenters. It is a molecule capable of existing in at least three different forms: the neutral bi-acid form; the monotartrate form, where one of the carboxylic acid groups has deprotonated to give a carboxylate moiety; and the bitartrate form, in which both acid groups have deprotonated. Furthermore, the molecule chemistry is complicated by the fact that protonated carboxylic acid groups are possibly involved in hydrogen bonds with other acid and alcohol groups, which potentially lead to several intermolecular interactions.

Tartaric Acid is a historical compound, dating back more than 160 years to when Louis Pasteur separated it into two enantiomers with a magnifying lens and a pair of tweezers.

Three stereoisomeric forms

Three stereoisomeric forms of tartaric Acid exist (1) dextrorotatory tartaric Acid (d-tartaric Acid) found in grapes and several other fruits, (2) levorotatory tartaric Acid (l-tartaric Acid) obtained chiefly by resolution of racemic tartaric Acid, and (3) a meso or achiral form. Racemic tartaric Acid (an equal mixture of d- and l-tartaric Acid) is prepared commercially by the molybdenum- or tungsten-catalyzed oxidation of maleic anhydride with hydrogen peroxide. DL-Tartaric Acid is a food additive. It is a white, crystalline powder that is stable in the air and soluble in water, ethanol, and ethyl ether. It is used in the manufacturing of tartrates and in the production of electroplates, chemical fertilizers, glass, foods, pharmaceuticals, etc.

It is manufactured from potassium hydrogen tartrate (wine tartar, cream of tartar – a by-product of the wine-making industry) via calcium salt. (S, S)-Tartaric Acid is also available commercially; it can be obtained from the racemic Acid by several resolution procedures or d-xylose. The highly functionalized and C2-symmetric tartaric acid molecule is perfectly tailored for applications as a resolving agent and chiral ligand. In fact, tartaric Acid is the most frequently used resolving agent for racemic amines.