Crystal and molecular structure of the dihydrate of the artificial sweetener lactitol: 4-O-β-d-galactopyranosyl-d-glucitol.2H2O

Abstract Crystallization of lactitol from aqueous ethanol readily yields crystals of the monohydrate, the structure of which has recently been reported. Slow evaporation of very concentrated aqueous syrups results in the crystalline dihydrate. The space group is P 4 3 2 1 2 with a = 8.762(2), c = 45.508(8) A, V = 3493.8(13) A 3 , Z = 8, D c = 1.446 g cm −3 , R = 0.037 for 2017 unique observed reflections and 310 variables. The galactopyranosyl ring has the 4 C 1 chair conformation and the carbon chain of the glucitol fragment has a non-planar, bent MAA conformation. The conformations about the glycosidic C(1)O(1) and O(1)C(14) bonds are different from those observed in the monohydrate: the torsion angles O(5)C(1)O(1)C(14) and C(1)O(1)C(14)C(13) differ by 29.6° and 15.0°, respectively. The orientations of the terminal C(11)O(11) bonds with respect to the carbon-atom chain of the glucitol fragment also differ appreciably: in the dihydrate the pertinent torsion angle is −47.3(3)° and in the monohydrate 75.5(2)°. All hydroxyl groups are involved in a complex three-dimensional system of hydrogen bonds, in which the two water molecules constitute an important cohesive element