S([O-])([O-])=O.[Na+].[Na+].[Br:7][C:8]1[CH:13]=[CH:12][C:11]([CH3:14])=[CH:10][C:9]=1[S:15](Cl)(=[O:17])=[O:16].[OH-].[Na+]>O>[Br:7][C:8]1[CH:13]=[CH:12][C:11]([CH3:14])=[CH:10][C:9]=1[S:15]([OH:17])=[O:16]37.6 g of sodium sulfite are dissolved in 500 ml of water and heated to 70° C. 62 g of 2-bromo-5-methylbenzenesulfonyl chloride are added in portions at this temperature. A 10N aqueous NaOH solution is simultaneously added dropwise here such that the pH of the solution is kept between pH=9 and pH=10. The mixture is stirred at 70° C. for 1.5 hours, and the solution is filtered off and then adjusted to pH=0 in an ice bath using a saturated aqueous HCI solution. It is subsequently stirred for 30 minutes, then the product is filtered off, washed with a little water and dried. 49.6 g of white crystals are obtained,
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