-Gentiobiose is best purified via the octaacetate which is recrystallised from MeOH, EtOH or better from methyl cellosolve by heating at 80o. The octaacetate (15g) is hydrolysed by suspending it in dry 0.05N NaOMe in MeOH (180mL) for 1hour with occasional shaking at room temperature. Dilute this with H2O to dissolve suspended matter, pass through Amberlite IR-120 and Duolite A-4 columns and the eluate is evaporated under reduced pressure to a syrup. Residual H2O is removed by repeated distillation with absolute EtOH under reduced pressure. The syrup is dissolved in methyl cellosolve (~40mL), filtered, nucleated and placed in an oven at 80o. The crystals are filtered off, washed with absolute EtOH (yield 6.7g, 89%), dried and have m 187-189o. Further recrystallisation from methyl cellosolve gives m 190o, and mutarotates from [] D 28 -1.5o (initial) to +10.6o (final, c 4, H2O). The -octaacetate has m 193o (crystallised from 95% EtOH) and has [] D 20 -5o (c 1.8, CHCl3). [Goldstein & Whelan Methods in Carbohydrate Chemistry I 313 1962, Academic Press, Beilstein 17/7 V 203.]
