Patent ID: 8263806

Claim:
A process for preparing a sulfonamide of formula I wherein: R 1 , R 2 , R 3 and R 4 are each hydrogen, halogen, cyano, nitro, C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl, C 1 -C 6 -alkoxy or C 1 -C 6 -haloalkoxy; R 5 and R 6 are each C 1 -C 6 -alkyl; by reacting a m-nitrobenzoyl chloride of formula II wherein the variables R 1 , R 2 , R 3 and R 4 are each as defined above: with an amino sulfone of formula III H 2 N—SO 2 NR 5 R 6 III, wherein the variables R 5 and R 6 are each as defined above; under the influence of B equivalents of alkali metal or alkaline earth metal hydroxide as base, wherein, in a first step, the amino sulfone of formula III is reacted with B1 equivalents of alkali metal or alkaline earth metal hydroxide, and, in a second step, the reaction mixture resulting from the first step is reacted with m-nitrobenzoyl chloride of formula II and B2 equivalents of alkali metal or alkaline earth metal hydroxide; wherein B is 1.5-3 equivalents of alkali metal or alkaline earth metal hydroxide with respect to the amino sulfone of formula III; B1 is a subportion of B and is in the range from 0.1-1.3 equivalents of alkali metal or alkaline earth metal hydroxide with respect to the amino sulfone of formula III; and B2 is a subportion of B and is the difference between B and B1.