Purification Methods
D-Galactose (40g) is dissolved in hot H2O to establish the equilibrium of and anomers; then the solution is cooled to 0o and poured into absolute EtOH (500mL). Stir vigorously and crystallisation occurs within a few minutes, and more rapidly if seeded, filter the crystals immediately (7g, [] D 20 +65o (initial, c 4 in H2O). This mixture of and anomers is further separated by dissolving in an equal weight of cold H2O, filtering and adding to ice cold absolute EtOH (250mL) and stirring for 1minute when crystals separate, then filter them off. After two such crystallisations, the initial [] D 20 is +53o. This can be further purified by shaking with 80% EtOH for 2minutes, filtering, washing with EtOH and Et2O, and drying in a vacuum desiccator to give -Dgalactose (15g) with m 167o, [ ] D 20 +52o (initial, c 4 in H2O) mutarotating to +80.4o. Acetylation of Dgalactose with hot NaOAc/Ac2O gives -D-galactopyranoside pentaacetate m 1 4 2o, [ ] D 25 +25 (c 4 in CHCl3). [Wolfrom & Thompson Methods in Carbohydrate Chemistry I 120 1962, Academic Press, Beilstein 1 IV 4336.]
