Diethylene Glycol → 2-Fluorohex-5-ynoic acid

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A mixture of 2-[(methylsulfonyl)oxy]-5-hexynenitrile (7.7 g, 41.1 mmol) and dry potassium fluoride (3.57 g, 61.4 mmol) in 10 ml of dry diethylene glycol was heated with vigorous stirring, at 135° C. under argon for 2 h. The resulting black reaction mixture was taken into 50 ml of water and extracted with ether (3×25 ml). The combined ether extracts were washed with water and then treated with a solution of potassium hydroxide (2.3. g, 61.4 mmol) in 15 ml of water. The resulting mixture was heated with stirring, at 65° C. (bath) for 2.0 h. The ether was distilled off at one atmosphere, and the aqueous solution was cooled to about 25° C., diluted with 50 ml of ice-water, and extracted with ether (3×50 ml). The ether extracts were combined and extracted with 2×50 ml in NaOH solution. The combined NaOH solution was cooled to 0° C. and then acidified to pH 2.5 with cold 3N H2SO4 solution. The resulting acidic aqueous phase was extracted with three times ether. The ether extracts were combined, washed with water, and dried (MgSO4). Concentration of ether at 40° C./~ 35 mm, and evaporative distillation of the resulting crude product at 130°/10 mmHg afforded 1.75 g (33% by weight yield) of 2-fluoro-5-hexynoic acid as a colorless liquid which solidified on cooling to a temperature of -10° C. to -20° C. as a white solid.

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