- In a 500-ml two-necked flask fitted with a mechanical stirrer and calcium chloride guard-tube place 110 ml of dry methanol, 110 ml of pure chloroform, 22 g of anhydrous calcium sulphate, 7.2 g of yellow mercury(n) oxide and 0.55 g of mercury(n) bromide.
- Stir the suspension for 30 minutes and add 16.5 g (0.04 mol) of 2,3,4,6-tetra-O-acetyl-πΌ -D-glucopyranosyl bromide in one portion.
- The temperature of the mixture will rise to about 25-30 °C, the pH of the solution will fall from 7 to 2 and the yellow coloration of the mercury(n) oxide will disappear (1).
- Stir the suspension for a further 90 minutes, filter through a pad of Celite filter-aid and evaporate the filtrate on a rotary evaporator under reduced pressure.
- Dissolve the viscous oil which remains in 10 ml of chloroform, remove the inorganic salts which are precipitated by filtration and wash the residue well with further portions of chloroform.
- Evaporate the chloroform and triturate the resulting viscous oil with methanol until it solidifies.
- Recrystallise from methanol to give pure methyl 2,3,4,6-tetra-O-acetyl-πΌ -D-glucopyranoside, m.p. 104-105 °C, [πΌ]α΄ ²ΒΊ - 18.2° (c 1 in CHC1 3 ). The yield is 13.7g (95%).
Notes to keep in mind:
1. The yellow coloration in the solution disappears
within a few minutes of addition of the glucosyl halide and t.l.c. analysis
(solvent system benzene-methanol, 98:2) reveals virtual completion of
the reaction.
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