ARTICLE pubs.acs.org/Organometallics
Efficient Iridium-Catalyzed Decarbonylation Reaction of Aliphatic Carboxylic Acids Leading to Internal or Terminal Alkenes Shinji Maetani,† Takahide Fukuyama,*,† Nobuyoshi Suzuki,‡ Daisuke Ishihara,†,‡ and Ilhyong Ryu*,† † ‡
Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan Kao Corporation, Wakayama, Wakayama 640-8580, Japan
bS Supporting Information ABSTRACT: Vaska’s complex, IrCl(CO)(PPh3)2, when combined with KI as an additive, served as an excellent catalyst for the decarbonylation of long-chain aliphatic carboxylic acids to give internal alkenes with high selectivity. On combination with KI and Ac2O as additives under controlled temperatures, decarbonylation proceeded to give terminal alkenes with high selectivity.
’ INTRODUCTION In conjunction with a rapid consumption of earth’s fossil fuel reservoirs, innovative solutions for future resources are required. Recently the importance of oleochemicals has been recognized for many chemical industries, as they are derived from renewable, environmentally friendly, easily available, low-toxicity raw materials.1 Transition-metal-catalyzed decarbonylation of longchain aliphatic carboxylic acids, which are abundant in vegetable oils and animal fats, is a useful tool for alkene synthesis.2 In this regard, catalytic systems that are based on palladium and rhodium complexes have been developed for this type of degradation reaction. For example, Miller and co-workers previously reported on palladium- and rhodium-catalyzed decarbonylation of aliphatic carboxylic acids, which allowed for selective isolation of the terminal alkenes via continuous distillation in a reactor.2d,e Recently, Goossen and co-workers have developed a catalytic system that uses PdCl2/DPE-phos (DPE-phos = bis(2-diphenylphosphinophenyl) ether) and pivalic anhydride to effectively produce terminal alkenes under mild conditions.2f Although these previous studies focused on the conversion of carboxylic acids to terminal alkenes, the potential of the same system as a means to synthesize internal alkenes is also important from an industrial viewpoint. A mixture of internal alkenes can be used as paper-sizing compositions, lubricant oils, and synthetic intermediates for the surfactant agents, just to name a few.3 Herein, we report that iridium complexes, such as Vaska’s complex4 when combined with KI as an additive, catalyzed both the decarbonylation of aliphatic carboxylic acids to give terminal alkenes and their subsequent isomerization to internal alkenes.5 It was also found that when the iridium catalyst system was combined with KI and Ac2O as additives, the decarbonylation proceeded at lower temperature to give terminal alkenes with high selectivity (Scheme 1).6 r 2011 American Chemical Society
’ RESULTS AND DISCUSSION We surveyed a variety of iridium catalysts and additives for decarbonylation of stearic acid (1a), which is present in palm oil, as a model compound (Table 1). When the reaction was carried out in the presence of a catalytic amount of [IrCl(cod)]2 ([Ir] = 2 mol %, cod = 1,5-cyclooctadiene) and PPh3 (4 mol %) at 250 °C for 3 h under solvent-free conditions, decarbonylation proceeded smoothly to give a mixture of heptadecenes (2a and 3a) in 80% yield (entry 1). The ratio of the internal alkenes 2a and the terminal alkene 3a was 94/6, suggesting that a very rapid isomerization reaction took place in this iridium-catalyzed system. Vaska’s complex, IrCl(CO)(PPh3)2, also afforded a 96/4 mixture of 2a and 3a in 68% yield (entry 2). Interestingly, the use of KI as an additive gave 2a in 91% yield with perfect internal selectivity (>99%) (entry 3). When IrI(CO)(PPh3)2 was used, a similar result was obtained (entry 4),7a which suggested that the addition of KI caused ligand exchange between Cl and I.7 In contrast, the addition of KBr did not improve the reaction (entry 5). The pronounced effect of KI was also observed when IrCl(CO)3/PPh3 and [IrCl(cod)]2/PPh3 were used as the catalyst (entries 6 and 7). The reaction at 200 °C using either KI or Ac2O gave poor results (entries 8 and 9); interestingly, however, addition of both KI and Ac2O improved the product yield to 66% (entry 10). Eventually, by raising the catalyst loading from 2 to 5 mol % and lowering the temperature from 200 to 160 °C, terminal alkene 3a was obtained in 84% yield with high selectivity (entry 11). This result suggests that, in our iridium-catalyzed system, temperature control in the isomerization reaction plays a critical role in distinguishing the products 2a and 3a. The reaction in the absence of phosphine ligands using Received: September 27, 2010 Published: February 22, 2011 1389
dx.doi.org/10.1021/om1009268 | Organometallics 2011, 30, 1389–1394
Organometallics
ARTICLE
Scheme 1. Iridium-Catalyzed Synthesis of Terminal or Internal Alkenes via Decarbonylation of Aliphatic Carboxylic Acids
Table 1. Decarbonylation of Stearic Acid (1a) by Ir Catalysts Combined with Additives under Various Conditionsa
entry
cat.
additive
temp (°C)
yield, %b
Figure 1. GC trace of the reaction mixture following addition of DMDS.
2a/3ac
1
[IrCl(cod)]2/PPh3
250
80
2
IrCl(CO)(PPh3)2
250
68
94/6
3 4
IrCl(CO)(PPh3)2 Irl(CO)(PPh3)2
KI
250 250
(91) 87
>99/1 >99/1
5
IrCl(CO)(PPh3)2
KBr
250
73
90/10
6
[IrCl(cod)]2/PPh3
KI
250
(86)
>99/1
7
IrCl(CO)3/PPh3
KI
250
(87)
8
IrCl(CO)(PPh3)2
KI
200
99/1)
Determination of the Double-Bond Position of Heptadecenes. To a screw capped test tube were added heptadecenes (2a, 60.3 mg, 0.25 mmol), I2 (29.8 mg, 0.12 mmol), and dimethyl disulfide (1 mL) and a magnetic stirring bar. The test tube was flushed with nitrogen and the reaction mixture was stirred for 2 h at room temperature. After the reaction, 30% NaHSO3(aq) was added to reduce I2, and then the mixture was extracted with hexane/Et2O (1/1). The organic phase was subjected to GC (initial temperature 60 °C, initial time 10 min, rate 2 °C/min, final temperature 350 °C, final time 15 min) and GC-MS (initial temperature 60 °C, rate 2 °C/min, final temperature 300 °C, final time 5 min) analysis. Heptadecenes (2a). Obtained as an inseparable mixture (internal/ terminal = >99/1); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.385.47 (m. 2H), 1.95-2.05 (m, 4H), 1.26-1.38 (m, 22H), 0.87-0.98 (m, 6H). Hexadecenes (2b). Obtained as an inseparable mixture (internal/ terminal = >99/1); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.325.47 (m. 2H), 1.95-2.03 (m, 4H), 1.25-1.40 (m, 20H), 0.88-0.97 (m, 6H). Pentadecenes (2c). Obtained as an inseparable mixture (internal/ terminal = 99/1); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.325.47 (m. 2H), 1.95-2.03 (m, 4H), 1.25-1.38 (m, 18H), 0.88-0.98 (m, 6H). Tetradecenes (2d). Obtained as an inseparable mixture (internal/ terminal =99/1); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.325.47 (m. 2H), 1.95-2.05 (m, 4H), 1.26-1.40 (m, 16H), 0.87-0.98 (m, 6H). Tridecenes (2e). Obtained as an inseparable mixture (internal/ terminal = >99/1); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.35-5.45 (m. 2H), 1.96-2.02 (m, 4H), 1.26-1.38 (m, 14H), 0.870.98 (m, 6H). Nonadecenes (2f). Obtained as an inseparable mixture (internal/ terminal = 99/1); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.325.41 (m. 2H), 1.96-2.02 (m, 4H), 1.25-1.36 (m, 26H), 0.86-0.98 (m, 6H). Henicosenes (2g). Obtained as an inseparable mixture (internal/ terminal = >99/1); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.32-5.45 (m. 2H), 1.95-2.03 (m, 4H), 1.25-1.38 (m, 30H), 0.870.98 (m, 6H). Cyclododecene (2j).15. Obtained as an inseparable mixture (E/Z = 69/31); colorless oil. E isomer: 1H NMR (500 MHz, CDCl3) δ 5.37 (m, 2H), 2.05-2.06 (m, 4H), 1.40-1.47 (m, 4H), 1.25-1.36 (m, 12H). Z isomer: 1H NMR (500 MHz, CDCl3) δ 5.37 (m, 2H), 2.05-2.06 (m, 4H), 1.40-1.47 (m, 4H), 1.25-1.36 (m, 12H). 1-Heptadecene (3a).16. Obtained as an inseparable mixture (internal/terminal = 2/98); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.77-5.86 (m, 1H), 4.91-5.01 (m, 2H), 2.01-2.08 (m, 2H), 1.221.39 (m, 26H), 0.88 (t, J = 6.8 Hz, 3H). 1-Hexadecene (3b). Obtained as an inseparable mixture (internal/ terminal = 2/98); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.775.86 (m, 1H), 4.91-5.01 (m, 2H), 1.94-2.06 (m, 2H), 1.26-1.39 (m, 24H), 0.88 (t, J = 6.9 Hz, 3H). The NMR data were identical with those of a commercial sample of 1-hexadecene. 1-Pentadecene (3c).17. Obtained as an inseparable mixture (internal/terminal = 2/98); colorless oil. 1H NMR (500 MHz, CDCl3):
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δ 5.77-5.86 (m, 1H), 4.91-5.01 (m, 2H), 1.94-2.06 (m, 2H), 1.251.39 (m, 22H), 0.88 (t, J = 6.9 Hz, 3H). 1-Tetradecene (3d).17. Obtained as an inseparable mixture (internal/terminal = 4/96); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.78-5.86 (m, 1H), 4.92-5.01 (m, 2H), 1.95-2.06 (m, 2H), 1.261.39 (m, 20H), 0.88 (t, J = 6.9 Hz, 3H). 1-Tridecene (3e).18. Obtained as an inseparable mixture (internal/ terminal = 4/96); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.765.86 (m, 1H), 4.91-5.02 (m, 2H), 2.01-2.09 (m, 2H), 1.26-1.39 (m, 18H), 0.88 (t, J = 6.9 Hz, 3H). 1-Nonadecene (3f).19. Obtained as an inseparable mixture (internal/terminal = 3/97); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.77-5.86 (m, 1H), 4.91-5.01 (m, 2H), 2.02-2.06 (m, 2H), 1.251.39 (m, 30H), 0.88 (t, J = 6.9 Hz, 3H). 1-Henicosene (3g).20. Obtained as an inseparable mixture (internal/ terminal = 2/98); white solid; mp 32.3 °C (lit.21 mp 35.5 °C). 1H NMR (500 MHz, CDCl3): δ 5.77-5.86 (m, 1H), 4.92-5.01 (m, 2H), 2.022.06 (m, 2H), 1.25-1.39 (m, 34H), 0.88 (t, J = 6.9 Hz, 3H). Methyl 8-Nonenate (3p).22. Obtained as an inseparable mixture (internal/terminal = 5/95); colorless oil. 1H NMR (500 MHz, CDCl3): δ 5.76-5.84 (m, 1H), 4.91-5.01 (m, 2H), 3.66 (s, 3H), 2.30 (t, J = 7.6 Hz, 2H), 2.01-2.08 (m, 2H), 1.59-1.65 (m, 2H), 1.31-1.41 (m, 6H). 2-Pentadecanone (5). White solid; mp 39.0 °C (lit.23 mp 38.9 °C). 1 H NMR (500 MHz, CDCl3): δ 2.41 (t, J=7.8 Hz, 2H), 2.13 (s, 3H), 1.55-1.58 (m, 2H), 1.25-1.31 (m, 20H), 0.88 (t, J = 6.9 Hz, 3H). The NMR data were identical with those of a commercial sample of 2-pentadecanone.
’ ASSOCIATED CONTENT
bS
Supporting Information. Text and figures giving experimental procedures and characterization data for the compounds. This material is available free of charge via the Internet at http:// pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*To whom correspondence should be addressed. Tel and fax: þ82 72 254 9695. E-mail:
[email protected] (T.F.);
[email protected] (I.R.).
’ ACKNOWLEDGMENT This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas (No. 2105) and a Grant-in-Aid for Young Scientists from the MEXT. ’ REFERENCES (1) (a) Biermann, U.; Friedt, W.; Lang, S; L€uhs, W.; Machm€uller, G.; Metzger, J. O.; Klaas, M. R.; Sch€afer, H. J.; Schneider, M. P. Angew. Chem., Int. Ed. 2000, 39, 2206. (b) Hill, K. Pure Appl. Chem. 2000, 72, 1255. (c) Demirbas-, A. Energy Convers. Manage. 2003, 44, 2093. (d) Dyer, J. M.; Stymne, S.; Green, A. G.; Carlsson, A. S. Plant J. 2008, 54, 640. (2) (a) Prince, R. H.; Raspin, K. A. Chem. Commun. 1966, 156. (b) Fenton, D. M. U.S. Patent 3,530,198, 1970. (c) Foglia, T. A.; Barr, P. A. J. Am. Oil Chem. Soc. 1976, 53, 737.(d) Miller, J. A.; Nelson, J. A.; Byrne, M. P. U.S. Patent 5,077,447, 1991. (e) Miller, J. A.; Nelson, J. A.; Byrne, M. P. J. Org. Chem. 1993, 58, 18. (f) Goossen, L. J.; Rodríguez, N. Chem. Commun. 2004, 724. (g) N^otre, J. L.; Scott, E. L.; Franssen, M. C. R.; Sanders, J. P. M. Tetrahedron Lett. 2010, 51, 3712. (3) (a) Zhang, J. J.; Lai, S.-M. U.S. Patent 6,348,132, 2002. (b) Brown, D. S.; Doll, M. J. PCT Int. Appl. WO 2005031066, 2005. (c) Baralt, E. J.; 1393
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