Process for preparing 1,2-5,6-diacetone-D-glucose

A process for preparing 1,2-5,6-diacetone-D-glucose which comprises reacting .alpha.-D-glucose in the presence of a Lewis acid selected from the group consisting of boron trifluoride, aluminium (III) halides, copper, iron and tin salts and halides of the rare earths with acetone at a temperature in the range from about 80.degree. to about 120.degree. C., under a pressure of at least about 2.5 bar, distilling off the volatile ingredients, and replacing the quantity of the distillate by acetone until about 12/3 times the original reaction volume has been substituted by acetone, evaporating down the reaction mixture at a temperature in the range from about 30.degree. to about 70.degree. C., mixing with an aqueous solution of a base, evaporating down the reaction mixture at a temperature in the range from about 30.degree. to about 70.degree. C., extracting with an organic extraction agent, evaporating down the extracts, combining the residue remaining after the evaporation with an organic sedimentation agent, heating to a temperature in the range from about 65.degree. to about 80.degree. C., cooling the resulting reaction mixture to a temperature of about 10.degree. C. and isolating the crystals which are produced on cooling.