Acetone → 5-(benzyloxy)-4-oxo-4H-pyran-2-carboxylic acid

232 g (1 mol) of 2-(hydroxymethyl)-5-(phenylmethoxy)-4H-pyran-4-one was put into a 10 l stirring flask containing 6.6 l of acetone and 400 ml of water. The clear solution was cooled to +5° C. by means of an ice bath. While maintaining the temperature at +5° C. to 10° C., 640 ml of Jones reagent (202 g CrO3, 600 ml water, 174 ml H2SO4) was added dropwise over a period of 1 hour. Stirring was continued for 2 hours without cooling. The reaction mixture was filtered through a glass frit and the dark green residue washed with 500 ml of acetone. The filtrate was then evaporated until all of the acetone was removed. To the aqueous, partly crystalline product was added 1.2 l of methanol, and this mixture was then heated to its boiling point. The resulting clear dark green solution was placed in an ice bath and the product allowed to crystallize. The crystalline product was filtered and washed with 500 ml of a cold solvent mixture consisting of 250 ml of methanol +250 ml of water and finally dried. Yield: 195 g. From the mother liquor, a further 5% of the product could be isolated.