SYNTHESIS OF METHYL 𝛽-D-GLUCOPYRANOSIDE

• In a 100-ml conical flask place 5.5 g (0.015 mol) of methyl 2,3,4,6-tetra-O-acetyl- 𝛽 -D-glucopyranoside, 50 ml of dry methanol and 10 ml of a solution of sodium methoxide in methanol previously prepared by the cautious addition of 0.1 g of sodium to 20 ml of methanol. 

• Stopper the flask and allow the solution to stand for 1 hour, then add sufficient ion exchange resin [Zeolite 225 (H🜨)] to render the solution neutral to moist universal indicator paper. 

• Remove the resin by filtration, wash with methanol and evaporate the combined filtrate and washings under reduced pressure (rotary evaporator). Triturate the colourless syrup with absolute ethanol to cause it to solidify and recrystallise from absolute ethanol. The pure methyl 𝛽-d-glucopyranoside has m.p. 108-109 °C, [𝛼]ᴅ²º-30.2° (c2.8 in H 2 0); the yield is 2.4 g (83%).

Cognate preparation: Methyl 𝛽 -D-galactopyranoside

• Use 3.6 g (0.01 mol) of methyl 2,3,4,6-tetra-0-acetyl-𝛽-D-galactopyranoside and proceed as above. After recrystallisation from absolute ethanol, 1.4 g (73%) of the methyl galactopyranoside, m.p. 174-175 °C, [𝛼]ᴅ²º+1.3° (cl in H 2 0), is obtained.