Hydrochloric Acid → Anhydro-d-mannosan

Participants

Reaction Steps

A mixture of L-gulose (1) (33 g, 0.127 mol) and 0.5 N HCl (330 mL, 0.165 mol) was refluxed for 20 hours. The mixture was cooled and neutralized to pH 6 by a resin (Dowex-2, HCO3-form) with air bubbling. The resin was recycled by washing with 10% HCl, water, methanol, water and saturated NaHCO3 solution. The reaction mixture was filtered and the resin was washed with water (500 mL). The combined filtrate was concentrated to dryness and dried in vacuo overnight. The residue was purified over a column (5 cm depth, silica gel, mesh, CHCl3—CH3OH, 10:1) to give a slightly yellow solid, which was recrystallized from absolute alcohol to give a colorless solid (2) [Rf=0.43 (CHCl3—CH3OH, 5:1), 7.3 g, 35.52%]. The L-gulose Rf=0.07, 11 g) obtained was recycled to give (2) (5 g, total yield 60%): mp 142.5–145° C.; 1H NMR (DMSO-d6) δ 3.22–3.68 (m, 4H, H-2, -3, -4 and -6a), 3.83 (d, J6b,6a=7.25 Hz, 1H, Hb-6), 4.22 (pseudo t, J5,6a=4.61 and 4.18 Hz, H, H-5), 4.46 (d, J2-OH,2=6.59 Hz, 1H, 2-OH, exchangeable with D2O), 4.62 (d, J3-OH,3=5.28 Hz, 1H, 3-OH, exchangeable with D2O), 5.07 (d, J4-OH,4=4.84 Hz, 1H, 4-OH, exchangeable with D2O), 5.20 (d, J1,2=2.19 Hz, 1H, H-1). [α]D25−50.011 (c, 1.61, CH3OH).

Provenance & Evidence