SYNTHESIS OF 1,2-O-CYCLOHEXYLIDENE-𝛼-D-XYLOFURANOSE

Di-(l,2-O-cycIohexyIidene-𝛼-D-xylo-pentodialdofuranose-5-hydrate)-5,5':3',5-dianhydride

• Add a solution of 14.3 g (0.061 mol) of sodium metaperiodate in 220 ml of water dropwise to a well-stirred solution of 1 7.4 g (0.067 mol) of 1 ,2-O-cyclohexylidene-𝛼-D-glucofuranose in 50 ml of water (1). 

• Stir for a further 30 minutes and remove the water at a temperature below 50 °C by evaporation under reduced pressure. 

• Extract the solid residue with three 75 ml portions of dichloromethane and dry the combined extracts over magnesium sulphate. 

• Filter and evaporate to give a residue which crystallises spontaneously. After recrystallisation from acetone the dimer has m.p. 182-183 °C, the yield is 7.9 g (51%).

1,2-O-CycIohexyIidene-𝛼-D-xylofuranose

• In a 250-ml two-necked round-bottomed flask fitted with a mechanical stirrer and dropping funnel, place 2g (0.009 mol) of the dimer dissolved in 50 ml of aqueous ethanol (75% v/v). 

• Add a solution of 1 g (0.053 mol) of sodium borohydride in 50 ml of ethanol from the dropping funnel with stirring. 

• After a further 30 minutes remove the ethanol under reduced pressure (rotary evaporator) and extract the aqueous slurry which remains with three 25 ml portions of dichloromethane. 

• Dry the combined extracts over magnesium sulphate and remove the solvent by evaporation under reduced pressure to give a viscous oil which crystallises on trituration with light petroleum (b.p. 40-60 °C). 

• Recrystallise from benzene-light petroleum (b.p. 40-60 °C) to give the purified product m.p. 84-85 °C, [𝛼]ᴅ²º - 12° (c1 in MeOH). The yield is 1.7 g (82%).

Notes to keep in mind:

1. The progress of the oxidation may be followed by iodimetry. In this method unreacted periodate is reduced by arsenite solution in the presence of iodide at about pH 8. Excess arsenite is then determined by back titration with standard iodine solution.

• For the oxidation described, remove 1 ml of solution, add 10 ml of saturated sodium hydrogen carbonate solution followed immediately by 10ml of 0.05 m sodium arsenite solution and 1 ml of 20 per cent potassium iodide solution. 

• Stand the solution in the dark for 15 minutes and titrate excess arsenite with 0.05 m iodine solution using a starch indicator.

• A spectrophotometric method has been developed which utilises the stronger absorption of periodate ions at 222.5 nm compared to the iodate ion.