[OH-].[K+].[CH3:3][O:4][C:5]([C:7]1[CH:12]=[CH:11][C:10]([N+:13]([O-:15])=[O:14])=[CH:9][C:8]=1[S:16]([OH:19])(=O)=[O:17])=[O:6].P(Cl)(Cl)([Cl:22])=O>CO>[CH3:3][O:4][C:5]([C:7]1[CH:12]=[CH:11][C:10]([N+:13]([O-:15])=[O:14])=[CH:9][C:8]=1[S:16]([Cl:22])(=[O:19])=[O:17])=[O:6]A solution of 17.3 g (0.27 mol) of potassium hydroxide (88% strength) and 100 ml of methanol is added carefully with vigorous stirring to a solution of 70.9 g (0.27 mol) of 2-methoxycarbonyl-5-nitrobenzenesulfonic acid in 300 ml of methanol. The mixture is cooled to 0° C. and the salt which is precipitated is filtered off, dried and then suspended in 150 ml of sulfolane, 150 ml of acetonitrile and 10 ml of dimethylformamide. After the dropwise addition of 100 ml (1.07 mol) of phosphorus oxychloride, the mixture is heated at boiling for 2.5 h. The reaction mixture is then poured into ice-water. The 2-methoxycarbonyl-5-nitrobenzenesulfonyl chloride (60.1 g, 70% of theory) which has precipitated is filtered off with suction through a Buchner funnel and freed from traces of solvent under reduced pressure. Melting point: 86°-88° C.
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