Patent ID: 7408059

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): wherein R 1 and R 2 are the same as or different from each other and are each a hydrogen atom, alkyl group, alkenyl group, alkynyl group, cycloalicyl group, acyl group, aralkyl group or aryl group; and R 3 is a hydrogen atom, alkyl group, alkenyl group, alkynyl group, cycloalkyl group, acyl group, aralkyl group or aryl group, or a salt thereof, the method comprising the step of subjecting a beta-ketoainide-N-sulfonic acid represented by the following Formula (1): wherein R 1 , R 2 and R 3 are as defined above; and X is a hydrogen atom, or a salt thereof, to cyclization in the presence of an acid anhydride with or without further subjecting the cyclized product to hydrolysis, wherein the cyclization is continuously carried out using a continuous flow reactor selected from a tubular reactor or a motionless mixer having a tube in the tubular reactor or the motionless mixer having an inner diameter of from 0.2 to 30 millimeters, wherein the beta-ketoamide-N-sulfonic acid or the salt thereof and the acid anhydride are cooled to −100° C. to 10° C. before the cyclization, an amount of the acid anhydride for use in the cyclization is 1 to 20 moles per 1 mole of the beta-ketoamide-N-sulfonic acid or the salt thereof, and wherein a premixer selected from the group consisting of a stirred mixer, an ultrasonic mixer, a static mixer and a piping joint is optionally employed with the continuous flow reactor, and when a premixer is employed, a residence time in the premixer ranges from 0.1 to 10 second, and the residence time in the continuous flow reactor ranges from 0.001 to 60 seconds, and when the continuous flow reactor is used without a premixer, the residence time in the continuous flow reactor ranges from 0.1 to 10 seconds.