2-Phenyl-ethyl 1-thio-β-d-galactopyran-oside hemihydrate.

The title compound, C(14)H(20)O(5)S·0.5H(2)O, crystallizes with two organic mol-ecules and a solvent water mol-ecule in the asymmetric unit. In both mol-ecules, the hexa-pyranosyl rings adopt a slightly distorted chair conformation ((5)C(2)) with four substituents in equatorial positions and one substituent in an axial position. The main difference between the organic mol-ecules is the dihedral angle between the phenyl ring and the best plane defined by the O-C(1)-C(2)-C(3) atoms (r.m.s deviations = 0.003 and 0.043 Å) of the hexa-pyranosyl rings [47.4 (4) and 86.5 (4)°]. In the asymmetric unit, mol-ecules are linked by two strong O-H⋯O hydrogen bonds. In the crystal, the components are linked by a total of 10 distinct O-H⋯O hydrogen bonds, resulting in the formation of a two-dimensional network parallel to the ab plane.