Synthesis of Long-Chain Propanoate Ester

In a 300-mL two-necked round-bottomed flask
equipped with a magnetic stirring bar, a rubber septum and an argon
balloon, NaH (60% dispersion in mineral oil, 5.28 g, 132 mmol), and
THF (28 mL) were added, respectively. The reaction mixture was cooled
to 0 °C and 18-crown-6 (7.01 g, 26.6 mmol) in THF (7.0 mL) and
ethyl 2-hydroxypropanoate (14 mL, 120 mmol) in THF (35 mL) were added
to this reaction mixture. The mixture was stirred for 1 h at 0 °C
then hexadecane-1,16-diyl bis(4-methylbenzenesulfonate) 2f (23.9 g, 42.1 mmol) within THF (44 mL) was added to the reaction
mixture. The reaction mixture was warmed to reflux and stirred for
13.5 h. The pH was adjusted to 7 with 5 M H₂SO₄ solution to quench the reaction. The whole mixture was extracted
with diethyl ether (5 × 10 mL). The combined organic phases were
washed with brine (20 mL), dried (with Na₂SO₄), and concentrated in vacuo to give a crude product. The crude product
was purified by flash column chromatography on silica gel (n-hexane/ethyl acetate = 10:1) to give the title compound 3f (7.79 g, 40%). Yellow oil; ¹H NMR (500 MHz,
CDCl₃) δ 4.27–4.15 (m, 4H), 3.93 (q, J = 6.8 Hz, 2H), 3.55 (dt, J = 6.7, 9.0
Hz, 2H), 3.36 (dt, J = 6.7, 9.0 Hz, 2H), 1.63–1.56
(m, 4H), 1.39 (d, J = 6.8 Hz, 6H), 1.33–1.24
(m, 30H); ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 173.6, 75.0, 70.4, 60.7, 29.7, 29.6, 29.6, 29.5, 29.4,
26.0, 18.7, 14.2; IR (neat) 2983, 2925, 2854, 1750, 1460, 1371, 1268,
1194, 1142, 755 cm^–1; HRMS (EI) m/z: [M-C₃H₅O₂]⁺ calcd for C₂₃H₄₅O₄ 385.3318,
found 385.3307.