SYNTHESIS OF 1,2,3,4,6-PENTA-O-BENZOYL-𝛼-D-GLUCOPYRANOSE (𝛼-D-Glucopyranose pentabenzoate)

• In a 1 -litre flange flask fitted with a multiple socket head carrying a mechanical stirrer, a calcium chloride guard-tube, a 250-ml dropping funnel and a thermometer, place 126 ml of dry pyridine and 105 ml of dry dichloromethane. 

• Cool the flask well in an ice-salt bath and add from the dropping funnel, with stirring, a previously prepared and cooled solution of 127 g (105 ml, 0.9 mol) of benzoyl chloride in 105 ml of dry dichloromethane. 

• Remove the dropping funnel and add 50 g (0.28 mol) of dry powdered 𝛼-D- glucose portionwise to the vigorously stirred benzoylating reagent at a rate which maintains the temperature of the reaction below 10 °C (1). 

• Allow the pink-coloured solution to stand at °C for 24 hours, dilute with 400 ml of dichloromethane and transfer the solution to a 2-litre separatory funnel. 

• Wash the solution successively with several 300 ml portions of dilute aqueous sulphuric acid (2 m), water, saturated aqueous sodium hydrogen carbonate and water. 

• Dry over anhydrous sodium sulphate and remove the dichloromethane on a rotary evaporator to give a yellow solid which is ground up with industrial spirit, filtered and washed well with spirit. ecrystallise the solid from acetone-water to give the pure product, m.p. 184-186 °C, [𝛼]ᴅ²º + 184.4° (c 1.75 in CHC1 3 ). The yield is 149 g (77%).

Notes to keep in mind:

1.  When the experiment is performed without effective cooling, i.e. if the temperature rises to 40-50 °C, a mixture of anomers is obtained which cannot be separated by simple recrystallisation. Frequently in large-scale preparations it is advisable to replace the ice-salt bath with one of acetone-Cardice to ensure good temperature control.