3542
L. WANG, J. LI, AND X. XUE
and the pure E-enyonic acid (i.e., ximenynic acid), was then separated by repeated
urea fractionation. The route is convenient and economical.
EXPERIMENTAL
Reagents were purchased from commercial sources and used without further
purification unless otherwise indicated. Melting points were determined with an
1
XT-4 melting-point apparatus and are uncorrected. H and 13C NMR spectra were
recorded on Bruker AV-300 (300 MHz) or AV-500 (500 MHz) instruments with
CDCl3 as the solvents, and mass spectra were performed on a Waters Q-TOF Micro.
12-Hydroxyoctadec-9-ynoic Acid (3)
Bromine (11.6 g, 67.5 mmol) was added dropwise to a solution of castor oil (2,
20 g, 67 mmol, containing ꢂ17 g of ricinoleic acid) in ethyl alcohol (12 mL) at ꢀ5 ꢁC
with stirring. When addition was complete, the product was refluxed with potassium
hydroxide (24 g) in water (16 g) for 10 h. The mixture was poured into water (120 mL),
acidified with sulfuric acid (5 M, 60 mL), extracted with diethyl ether (3 ꢃ 100 mL),
and dried over anhydrous sodium sulfate. Removal of ether gave ricinstearolic acid
(20 g). Recrystallization of the crude from petroleum ether gave 12-hydroxyoctadec-
1
9-ynoic acid 3 (12.9 g, 65% yield). Mp 51–53 ꢁC [lit.[4] 52 ꢁC]; H NMR (300 MHz,
CDCl3): d 0.88 (t, 3H, J ¼ 6.6 Hz), 1.29–1.52 (m, 18H), 1.60–1.67 (m, 2H), 2.17 (t,
2H, J ¼ 6.9 Hz), 2.22–2.44 (m, 4H), 3.65–3.73 (m, 1H); 13C NMR (1D þ DEPT,
125 MHz, CDCl3): d 14.0 (CH3), 18.7 (CH2), 22.6 (CH2), 24.6 (CH2), 25.6 (CH2),
27.7 (CH2), 28.6 (CH2), 28.7 (CH2), 28.8 (CH2), 28.9 (CH2), 29.2 (CH2), 31.8
(CH2), 33.9 (CH2), 36.2 (CH2), 70.3 (CH), 76.2 (C), 83.1(C), 179.2 (C); MS (ESI,
negative ion mode): m=z ¼ 295.1 [M ꢀ H]ꢀ; HRMS (ESI, negative ion mode) calcd.
for C18H31O3, m=z: 295.2273 [M-H]ꢀ; found, m=z: 295.2278.
(11E/Z)-Octadecen-9-ynoic Acid (1 and 4)
Thionyl chloride (10 g, 84 mmol) was added to a mixture of ricinstearolic acid
(3) (5.0 g, 16.9 mmol) and pyridine (0.5 mL) with stirring at rt. The mixture was
heated at 60 ꢁC for 3 h, and excess thionyl chloride was removed under reduced
pressure. Water (30 mL) was added to the residue and the mixture was extracted with
diethyl ether (3 ꢃ 30 mL), and the organic extract was washed with water (3 ꢃ 30 mL)
and then dried over anhydrous sodium sulfate. Removal of ether gave the crude
(6.8 g). It was used for next step without further purification.
The crude was refluxed with potassium hydroxide (6.8 g) and water (6.8 mL) in
ethyl alcohol (136 mL) for 24 h, acidified with sulfuric acid (5 M), extracted with
diethyl ether (3 ꢃ 100 mL), and dried over anhydrous sodium sulfate. After the
solvent was evaporated, the residue was purified by column chromatography with
petroleum ether and ethyl acetate (75:25, vol=vol) as eluent to yield a mixture of
(Z)- and (E)-enynoic acids (2.65 g, 57% yield) with 45% (E)-isomer. The ratio of E
1
to Z isomers (1 and 4) was determined by the signals of 12-H at their H NMR
spectrum.