Potassium Carbonate → 2-(4,4-Difluorobut-3-enylthio)benzthiazole

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To the solution of 4-bromo-1,1-difluorobut-1-ene prepared in Example 6 was added potassium carbonate (10.76 g) and 2-mercaptobenzthiazole (9.18 g). The mixture was stirred at 55° C. for 6 hours and then at room temperature overnight. Gas-liquid chromatography of a sample of the reaction mixture showed that a small amount of 4-bromo-1,1-difluorobut-1-ene remained. More potassium carbonate (1.0 g) was added and the mixture heated for another two and a half hours at 55° C., when all of the bromo compound had been consumed. The mixture was cooled to room temperature and filtered. The residue was washed with acetone and the filtrate and washings combined and evaporated under reduced pressure to give the crude product (16.18 g). This was dissolved in dichloromethane. The solution was filtered and washed with dilute sodium hydroxide (2×25 ml) and with brine (2×25 ml), dried over magnesium sulphate, filtered, the filtrate evaporated to give 2-(4,4-difluorobut-3-enyl)thiobenzthiazole, having a gas chromatographic retention time identical with that of an authentic sample. The yield was 63% based on the quantity of 1,4-dibromo-1,1,2-trifluorobutane used in step (b) of Example 1. 2-(4,4-Difluorobut-3-enyl)thiobenzoxazole was prepared in the same way, but using 2-mercapto benzoxazole instead of 2-mercapto benzthiazole.

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