To easily and efficiently produce a high quality 3,4-dihydro-1,2,3-oxathiazin-4-one-2,2-dioxide compound or a salt thereof.
When a mixture liquid of -ketoamide-N-sulfonic acid represented by formula (1) (wherein R1, R2 and R3 are each H or an organic group inactive to reaction; and X is H) or a salt thereof with an inactive solvent and a mixture liquid of an acid anhydride with an inactive solvent are subjected to cyclization reaction and then subjected to hydrolysis reaction to produce a compound represented by formula (2) or a salt thereof, (A) a step for mixing the reaction product, obtained by cyclizing reaction, with an aqueous solution of sulfuric acid so that the sulfuric acid concentration is 30 wt.% and so as to hydrolyze, and separating the organic layer from the water layer, or (B) a step of washing the organic layer after hydrolysis reaction, with 30 wt.% concentration aqueous solution of sulfuric acid, is at least performed.
ISHIGURO HIRONORI
YAMAMOTO YASUSHI
