p-Toluenesulfonic acid → Ethyl cyclohexanoate

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To a solution of cyclohexanecarboxylic acid (23.1 g, 180 mmol) in ethanol (100 mL) was added p-TsOH (1.027 g, 5.4 mmol). The mixture was heated to 78-79° C., and for several hours solvent was slowly distilled off whereas the volume was kept relatively constant by addition of fresh ethanol. Stirring at reflux temperature was continued overnight. An additional portion of p-TsOH (685 mg, 3.6 mmol) was added and the reaction mixture was stirred at 79° C. for an additional 5 h. The cooled reaction mixture was concentrated to nearly ¼ volume, diluted with TBME and extracted with cold aq. NaHCO3. The aqueous phase was extracted with TBME. The organic phases were washed with water until neutral, combined, dried over sodium sulfate and concentrated to give 26.5 g crude product which was distilled at 40° C. (0.25 mbar) to afford 24.5 g (87%) cyclohexanecarboxylic acid ethyl ester, GC purity >99% (area). 1H-NMR (CDCl3, 300 MHz): ppm 1.22 (t, 3H), 1.08-1.80 (m, 8H), 1.85-1.92 (m, 2H), 2.23-2.32 (m, 1H), 4.11 (q, 2H).

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