4. Saponification reaction
Dissolve 0.60 g (2.81 mmol) of the hydroxy ester obtained in the previous step in 10 volumes of tetrahydrofuran. 3.4 mL (6.75 mmol) of 2 M sodium hydroxide solution was added slowly. The reaction mixture was heated to 65 °C and kept at this temperature for 3 hours. Upon completion of the reaction, the pH of the reaction mixture was adjusted to 2 by dropwise addition of 3 M hydrochloric acid solution. the mixture was concentrated and dried, followed by extraction of the aqueous phase with ethyl acetate. The organic phase was washed with saturated sodium chloride solution, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to give 0.6 g of crude product. Purification by recrystallization from cold acetonitrile afforded the target product 10-hydroxy-2-decenoic acid as a white solid in 71% yield (0.37 g).
Characterization data:
TLC: Rf = 0.1 (unfolding agent: heptane/ethyl acetate, 6:4, v/v)
1H NMR (300 MHz, CDCl3): δ 1.33-1.37 (m, 6H), 1.45-1.49 (m, 2H), 1.55-1.58 (m, 2H), 2.20-2.25 (q, 2H), 3.62-3.66 (t, 2H), 5.79-5.84 (d, J = 15.6 Hz, 1H), 7.03 -7.10 (dt, J = 15.6 Hz, 1H).
Mass spectrum: [M-Na]+ m/z 209 (calculated value: 186)
Melting point: 62.5 ± 1°C.
