Sodium Hydroxide → 2-(3,5-Dichlorobenzene-1-sulfonyl)-5-(trifluoromethyl)-1,3,4-thiadiazole

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A solution of 75.6 g (0.6 mole) of analytically pure sodium sulfite in 300 ml of water was pre-warmed to 60°-70° C in a beaker. 122.8 g (0.5 mole) of 3,5-dichlorobenzenesulfochloride, and a solution of 40 g (1 mole) of sodium hydroxide in 200 ml of water were synchronously added dropwise from two dropping funnels in such a way that the pH value (measured with an electrode in the reaction solution) was always between 7 and 9; during the addition the mixture was stirred magnetically. The saline solution of the 3,5-dichlorobenzenesulfinate (about 600 ml) was then diluted with 1.8 liters of dimethylformamide and after adding 116.5 g (0.5 mole) of 2-bromo-5-trifluoromethyl-1,3,4-thiadiazole the whole was stirred for 15 hours at 50° C. The sulfone was precipitated completely by adding ice water and was recrystallized from ethanol. 121 g (70% of theory) of 2-(3',5'-dichlorophenylsulfonyl)-5-trifluoromethyl-1,3,4-thiadiazole of melting point 123° C were obtained.

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