Likely impurities are 2-methylfuran, methyldihydrofurans and hydroquinone (stabiliser, which is removed by distillation under reduced pressures). It is washed with 10% aqueous NaOH, dried, vacuum distilled from CaH2, passed through freshly activated alumina under nitrogen, and refluxed over sodium metal under vacuum. Store it over sodium. [Ling & Kevan J Phys Chem 80 592 1976.] Distil it from sodium under vacuum, and store it with sodium-potassium alloy (this treatment removes water and prevents the formation of peroxides). Alternatively, it can be freed from peroxides by treatment with ferrous sulfate and sodium bisulfate, then solid KOH, followed by drying with, and distilling from, sodium, or type 4A molecular sieves under argon. It may be difficult to remove *benzene if it is present as an impurity (can be readily detected by its ultraviolet absorption in the 249-268nm region). [Ichikawa & Yoshida J Phys Chem 88 3199 1984.] It has also been purifed by percolating through Al2O3 and fractionated collecting fraction b 79.5-80o. After degassing, the material is distilled onto degassed molecular sieves, then distilled onto anthracene and a sodium mirror. The solvent is then distilled from the green solution onto potassium mirror or sodium-potassium alloy, from which it is distilled again. [Mohammad & Kosower J Am Chem Soc 93 2713 1971.] It should be stored in the presence of 0.1% of hydroquinone or 2,6-di-tert-butyl –p-cresol as stabiliser. The R(+)-enantiomer has b 78-80o/atm and D +27.5o (neat), and the S(-)-enantiomer has b 86o/atm and  D -27.0o (neat) [Iffland & Davis J Org Chem 42 4150 1977, Gagnaire & Butt Bull Soc Chim Fr 312 1961, Beilstein 17 III/IV 60, 17/1 V 78.] HARMFUL VAPOURS.