(2s, 3r, 4s, 5r) -2,3,4,5-tetrahydroxyhexanedioic (galactaric) acid: structural features, isomers, complexing properties

A review article describes the features of structure and properties of galactaric acid (H6Gala) as a representative of polyhydroxydicarboxylic acids, which is widely used in analytical chemistry, medicine and agriculture. Galactaric acid (mucic acid) has an unusually low solubility in water for an unsubstituted carbohydrate. This property is accompanied by a relatively high melting-point, 206 C. Crystal-structure analysis was conducted in order to determine the intermolecular forces associated with the low aqueous solubility and high crystal-density of galactaric acid. Its coordination-chemical behavior in reactions with ions of s-, p- and d-metal has been characterized. The FT-IR spectra of compounds of galactaric acid and K+, NH4+, Ca2+, Ba2+, La3+have been interpreted. Spectroscopic evidence shows that the dimeric carboxylic groups of the free acid are dissociated upon formation of the compounds, and the asymmetric and symmetric stretching vibrations of the anionic COO-group in these complexes are observed at about 1600 and 1400 cm-1, respectively. The two carboxylic groups of the galactarate coordinate with Ca2+ions in a monodentate form. One of the carboxylic groups in the Ba2+compounds coordinates in a monodentate state; another group interacts with three cations in a tetradentate form. In the K+, NH4+, and La3+compounds, the COO-groups coordinate in a polydentate manner with the cations. Prospects of research of this acid as a ligand upon complexation with germanium (IV) and tin (IV) has been demonstrated.