2-(3,4-Dichlorophenoxy)-5-fluorobenzaldehyde → 2-(3,4-Dichlorophenoxy)-5-fluoro-benzoic acid

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Alternatively, a solution of 4.28 g (15 mmol) of 2-(3,4-dichloro-phenoxy)-5-fluorobenzaldehyde (Preparation no. 5) in 25 mL of acetone was cooled to 5–10° C. and treated via syringe with 5.8 mL (15.6 mmol) of 2.67 M Jones reagent*. After 1 hr at this temperature, the reaction was quenched with 8 mL of isopropanol, allowed to warm to 25° C., and filtered through a pad of d.e. The filtrate was concentrated in vacuo to approximately ¼ volume, diluted with water and extracted several times with CHCl3. The organic layers were washed with water, then with saturated NaCl and finally dried over MgSO4 and concentrated to provide 2-(3,4-dichlorophenoxy)-5-fluoro-benzoic acid as a tan solid, 4.19 g. 1H-nmr (CDCl3, 400 MHz, δ): 7.78 (dd, 1H), 7.38 (d, 1H), 7.27 (m, 1H), 6.98 (m, 2H), 6.81 (dd, 1H). *Jones reagent was prepared from 13.4 g of chromium trioxide and 11.5 mL of concentrated H2SO4, diluted to a final volume of 50 mL with H2O.

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