LONG-CHAIN DICARBOXYLIC FATTY ACIDS
631
Synthesis of 1,18-octadec-9-enedioic acid (5b). Oleic acid –CO2H), 131.7 (s, –CH=CH–), 35.2 (s), 33.7 (s), 30.9 (s), 30.8
[3b; 89 g (90%), 0.315 mol] was transferred into a 250-mL (s), 30.78 (s), 30.7 (s), 30.6 (s), 30.4 (s), 30.3 (s), 26.3 (s).
three-necked round-bottomed flask via syringe and outgassed
Synthesis of 1,20-eicos-10-enedioic acid (7). Similar to oleic
with nitrogen gas for 0.5 h. 1,3-Bis-(2,4,6-trimethylphenyl)-2- acid, 10-undecenoic acid [6; 10 g (98%), 0.054 mol] underwent
(imidazolidinylidene)(dichlorophenylmethylene)–(tricyclo- self-metathesis in the presence of 46 mg (0.054 mmol) of cata-
hexylphosphine)ruthenium (2; 267 mg, 0.315 mmol), a second- lyst 2. The reaction flask was attached to a mineral oil bubbler,
generation Grubbs catalyst, was then added. The reaction mix- which allowed the gaseous ethylene co-product to escape. The
ture was stirred with a mechanical stirrer and heated at 45°C, mixture was stirred with a mechanical stirrer and heated at
and after ~5 min the diacid began to precipitate from the reac- 45°C, and after ~5 min reaction a white precipitate was ob-
tion mixture. After 24 h reaction, ~10 mg of crude product was served. After 72 h reaction a small amount of the crude prod-
removed from the reaction mixture and transferred to a 2-mL uct was removed from the reaction mixture and methylated as
dram vial. The crude diacid product (5b, Eq. 1) was added to 1 above for GC/MS analysis.
mL of methanol, and two drops of concentrated sulfuric acid
The remainder of the reaction mixture was quenched with
were added. The resulting mixture was heated at 80°C for 0.5 ethyl vinyl ether (~20 mL) and unreacted ether removed under
h (18). The reaction mixture was then quenched with 2 mL of reduced pressure. The residue was recrystallized twice from
1 M Na2CO3 and extracted with diethyl ether (3 × 2 mL); the ~100 mL of acetone to give pure 1,20-eicos-10-enedioic acid
combined ether layers were then washed with water (3 × 2 mL). (7) as a white solid with m.p. = 110–110.5°C [lit. m.p. 108°C
The organic layer was dried with MgSO4, filtered, and solvent (8)]. The isolated yield was 7.5 g (82%). The methyl ester of
was removed under reduced pressure. The methylated diacid diacid 7 was analyzed by GC/MS (retention time t = 23.9 min)
5a was then characterized by GC/MS (retention time = 18 min) and had an [M]+ of m/z 368 (calc. [M]+ m/z for 368.30). 1H
and gave an [M]+ of m/z 340 (calc. [M]+ for 5a is m/z = NMR (CD3OD, 400 MHz): δ 5.39 (m, –CH=CH–, 2H), 2.28
340.26).
(t, J = 7.2 and 7.6 Hz, –CH2CO2H, 4H), 1.97 (m, 4H), 1.58 (m,
The remainder of the crude product was quenched with 4H), 1.31 (m, 20H). 13C NMR (CD3OD, 100 MHz): δ 177.8 (s,
ethyl vinyl ether (20 mL), and excess ether was removed under –CO2H), 131.7 (s, –CH=CH–), 35.1 (s), 33.7 (s), 30.9 (s), 30.6
reduced pressure. The residue was recrystallized twice from a (s), 30.4 (s), 30.2 (s), 26.2 (s).
mixture of hexane (300 mL) and ethyl acetate (50 mL) to give
Synthesis of 7,12-dihydroxyoctadec-9-ene (9). Ricinoleic
pure 1,18-octadec-9-enedioic acid (5b, Eq. 1) as a white solid: acid (8, 400 mg 1.34 mmol) was mixed with 2 (11 mg, 0.013
m.p. 97.5–98.5° °C [lit. m.p. 88°C (8)]. Isolated yield: 35 g mmol) in a 50-mL Schlenk tube under nitrogen gas flow and
(71%). 1H NMR of 1,18-octadec-9-enedioic acid (CD3OD, 400 the mixture was heated at 50°C. After ~0.5 h, a small amount
MHz): δ 5.39 (m, –CH=CH–, 2H), 2.28 (t, J = 7.2 and 7.6 Hz, of white precipitate was observed in the reaction flask. After 3
–CH2CO2H, 4H), 1.98 (m, 4H), 1.60 (m, 4H), 1.32 (m, 16H). d of stirring at 50°C, the reaction mixture was quenched with 2
13C NMR (CD3OD, 100 MHz): δ 177.8 (s, CO2H), 131.6 (s, mL of ethyl vinyl ether, and the volatile components were re-
CH=CH), 35.1 (s), 33.7 (s), 30.8 (s), 30.4 (s), 30.3 (s), 30.2 (s), moved under reduced pressure. The crude product contained
26.2 (s).
the diol 9, ricinoleic acid, and diacid 5b was methylated using
Synthesis of 1,22-docos-11-enedioic acid (5c). 1,22-Docos- the procedure described above. The methylated product (116
11-enedioic acid (5c) was synthesized from 3c as described mg) was reacted with 400 µL of N,O-bis(trimethylsilyl)trifluo-
above in the self-metathesis of oleic acid (3b). Pure 5c was ob- roacetamide and 120 µL of pyridine at room temperature for 1
tained by recrystallization from a mixture of hexane (100 mL) h (18). The silylated product was purified by passage through a
and ethyl acetate (10 mL) to give 5c in 74% yield (m.p. = silica gel column [~20 g; i.d. × length 1.2 × 25 cm (0.5 ×
104–106.5°C). The methyl ester of diacid 5c was analyzed by 10in.)] using hexane/ethyl acetate (9:1 vol/vol) as eluant to give
GC/MS: (retention time t = 24 min) and had an [M]+ of m/z 396 34.5 mg of 7,12-bis(trimethylsiloxy)octadec-9-ene (9a) as a
1
(calc. [M]+ for 5c is m/z = 396.60). H NMR (CD3OD, 400 yellow oil, 28.9 mg of the silylated methyl ester of 8, and 35.3
MHz): δ 5.4 (m, –CH=CH–, 2H), 2.28 (t, J = 7.6 and 7.2 Hz, mg of the methyl ester of 5b. Both steps gave quantitative re-
–CH2CO2H, 4H), 1.99 (m, 4H), 1.58 (m, 4H), 1.31 (m, 24H). action yields. GC/MS of 9a (retention time t = 15.8 min) gave
13C NMR (CD3OD, 100 MHz): δ 177.9 (s, CO2H), 131.7 (s, an [M]+ at m/z = 427 (calc. [M]+ for 9a is m/z = 428.84). 1H
CH=CH), 35.2 (s, CH2CO2H), 33.7 (s), 30.9 (s), 30.7 (s), 30.6 NMR of 9a (CDCl3, 200 MHz): δ 5.43 (m, –CH2CH=CH, 2H),
(s), 30.5 (s), 30.4 (s), 30.3 (s), 26.2 (s).
3.6 (m, –CHOSi(CH3)3, 2H), 2.14 (m, –CH2CH=CH, 4H), 1.26
Synthesis of 1,26-hexacos-13-enedioic acid (5d). Diacid 5d (m, 20H), 0.878 (m, 6H), 0.085 (s, –OSi(CH3)3, 18H). 13C
was synthesized from 3d as above. The pure diacid was ob- NMR of 9a (CDCl3, 50 MHz): δ 129.1 (s, –CH=CH–), 72.7 (s,
tained by recrystallization from acetone in a yield of 70%, m.p. –CHOSi(CH3)3), 41.2 (s), 37.1 (s), 31.9 (s), 29.4 (s), 25.7 (s),
o
= 105–107.5 C [lit. m.p. = 96 °C (8)]. The methyl ester of 22.6 (s), 14.1 (s, –CH3), 0.414 (s, –OSi(CH3)3).
diacid 5d was analyzed by GC/MS (retention time t = 28.2
min) and had an [M]+ of m/z 452 (calc. [M]+ m/z 452.38). 1H
RESULTS AND DISCUSSION
NMR (CD3OD, 200 MHz): δ 5.4 (m, CH=CH, 2H), 2.28 (t, J
= 7.4 Hz, CH2CO2H, 4H), 1.97 (m, CH2CH=CH, 4H), 1.6 (m, The solvent-free self-metathesis of oleic acid was carried out
4H), 1.30 (m, 32H). 13C NMR (CD3OD, 50 MHz): δ 177.9 (s, under a nitrogen atmosphere with 0.1 mol% of Grubbs catalyst
JAOCS, Vol. 83, no. 7 (2006)