Purification Methods
Crystallise dehydro-L(+)-ascorbic acid from MeOH. The anhydrous acid is formed by heating it in a vacuum at 100o/1hour to give a crisp glassy product which when shaken with absolute EtOH and then kept at 0o for 2days gives microcrystals of the anhydrous acid. This is then washed with absolute EtOH and dried in a vacuum. It has m 225o(dec) and is stable in acidic solution but decomposes rapidly in alkaline solution. A 1% solution of the anhydrous acid when dissolved in phthalate/HCl buffer pH 3.5 at 60o and cooled to 20o has [] 20D +56o(0minutes), +53.5o(2hours), +19o(3days), -2o(5days) and -6o(6days); then it becomes orange in colour. A freshly prepared 1% solution in H2O has [] D +50o(0minutes), +44o(2hours), +16o(3days) and 0o(5days). [Herbert et al. J Chem Soc 1270 1933, Kenyon et al. J Chem Soc 158 1948, Beilstein 18/5 V 411.]
