Acidic Dissociation Constants of Alcoholic Hydroxyls of Hydroxycarboxylic Acids: Tartaric Acid

Abstract

THE hydroxycarboxylic acids form very stable complexes with metal ions. In alkaline solution, both the carboxylic and the alcoholic hydroxyl groups take part in complex formation. For the calculation of stability constants of complexes it is necessary to know the acidic dissociation constants of both groups. Since the alcoholic hydroxyls are very weakly acidic and the molecule contains relatively easily dissociable group(s) also, it is not possible to determine the dissociation constants by the usual methods. For mandelic acid the value of the dissociation constant of alcoholic hydroxyl can be calculated from the change of absorbancy at 244 mµ produced by sodium hydroxide¹. However, in general the hydroxycarboxylic acids do not absorb even in far ultra-violet. The acidic dissociation constants of optically active substances may be estimated from the change of rotatory power produced by alkali hydroxide. The present communication deals with tartaric acid.