Preparation of L-gluconic acid, its conversion to L-glucose via L-gluconolactone and preparation of manno- and mannono-1,4-lactone precursors

摘要

L-Gluconic acid, or salt thereof, is prepared by treating an aqueous solution of 6-bromo-6-deoxy-2,3-anhydro-D-manno-1,4-lactone with a base at a pH of at least 12 and at 45 to 60 {C. In particular, the base is an alkali or alkaline earth metal hydroxide, e.g. potassium, sodium or calcium hydroxide. The L-gluconic acid may be converted to L-glucose, e.g. via L-gluconolactone, 6-Bromo-6-deoxy-2,3-anhydro-D-manno-1,4-lactone may be prepared by reacting 2,6-dibromo-2,6-dideoxy-D-mannono-1,4-lactone with a Lewis base in the presence of a catalytic amount of water. The Lewis base may be an alkali metal fluoride or carbonate, e.g. potassium fluoride, potassium carbonate, caesium carbonate or rubidium fluoride, 2,6-Dibromo-2,6-dideoxy-D-mannono-1,4-lactone may be prepared by reacting D-glucono-1,5-lactone or salt thereof with a hydrogen halide at 40 to 60 {C then adding methanol, maintaining the temperature at 40 to 55 {C and allowing the reaction to proceed to completion. The hydrogen halide may be hydrogen bromide or hydrogen chloride.