Patent ID: 7662957

Claim:
A method for producing a 3,4-dihydro-1,2,3-oxathiazin-4-one-2,2-dioxide compound represented by the following formula (2) [Formula 2] (wherein R 1 and R 2 are the same as or different from each other and are each hydrogen atom or an organic group inert to a reaction, R 3 is hydrogen atom or an organic group inert to the reaction) or a salt thereof, by mixing a first solution of β-ketoamide-N-sulfonic acid represented by the following formula (1) [Formula 1] (wherein R 1 , R 2 and R 3 are as defined above, and X is hydrogen atom) or a salt thereof dissolved or dispersed in an inert solvent and a second solution of acid anhydride dissolved or dispersed in an inert solvent to be carried out cyclization, and subjecting the cyclized product to hydrolysis to obtain a mixed solution containing a liquid in organic phase and a liquid in aqueous phase, the method comprising at least one step selected from a group consisting of: Step (A) of hydrolyzing the cyclized product by mixing with an aqueous solution of sulfuric acid so that a concentration of the sulfuric acid in the liquid in aqueous phase after the hydrolysis would become 30% by weight or more, and separating the mixed solution to the liquid in organic phase and the liquid in aqueous phase; and Step (B) of washing the liquid in organic phase after the hydrolysis with an aqueous solution of sulfuric acid with a concentration of 30% by weight or more.