5-hydroxy-2-carboxy-4-pyrone (I) (comenic acid) is prepared by heating an aqueous soln. of 2.5-diketo-gluconic acid. An aqueous soln. contg. 1-30% wt. of the 2,5-diketo-gluconic acid is heated at a temp. of 20-120 degrees C. The metal salts or lower alkyl ester of (I) can also be prepared. The process enables (I) to be prepared economically on a large scale. (I) is an intermediate in the preparation of maltol for use as a food flavouring agent.
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