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In an open flask, cuprous oxide (0.6 g., 4 mmoles) and 3,5-difluorothiophenol (0.76 g., 4 mmoles) were combined with 25 ml. of dimethylformamide and heated in an oil bath maintained at 150°-160° C. for 2 hours. 5-Bromofuran-3-carboxylic acid was added, the flask was equipped with a reflux condenser, and heating at 150°-155° C. was continued for 16 hours. The reaction mixture was cooled, filtered, the filtrate diluted with 150 ml. of water and product extracted into two 30 ml. portions of ethyl acetate. The combined ethyl acetate extracts were back-washed with water, evaporated to an oil, the oil taken up in ether, product extracted into 12 ml. of 1 N sodium hydroxide, the basic extract acidified with conc. hydrochloric acid and the product extracted back into fresh ether and evaporated to yield crude product as an oil. The oil was chromatographed on approximately 100 ml. of silica gel with hexane/5% acetic acid as eluant, clean fractions (Rf 0.2 on thin layer chromatography with the same eluant) were combined, concentrated to dryness, and crystallized by trituration with hexane to yield purified 5-(3,5-difluorophenylthio)furan-3-carboxylic acid (127 mg., m.p. 128°-130° C., m/e 256).

1. temperaturemaintained at 150°-160° C. for 2 hours
2. customthe flask was equipped with a reflux condenser
3. temperatureheating at 150°-155° C.
4. temperatureThe reaction mixture was cooled
5. filtrationfiltered
6. additionthe filtrate diluted with 150 ml
7. extractionof water and product extracted into two 30 ml
8. washThe combined ethyl acetate extracts were back-washed with water
9. customevaporated to an oil
10. extractionproduct extracted into 12 ml
11. extractionof 1 N sodium hydroxide, the basic extract
12. extractionthe product extracted back into fresh ether
13. customevaporated
14. customto yield crude product as an oil
15. customThe oil was chromatographed on approximately 100 ml
16. concentrationconcentrated to dryness
17. customcrystallized by trituration with hexane
18. customto yield
19. custompurified 5-(3,5-difluorophenylthio)furan-3-carboxylic acid (127 mg., m.p. 128°-130° C., m/e 256)