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Article

Metathesis of Fatty Acid Ester Derivatives in 1,1-Dialkyl and 1,2,3-Trialkyl Imidazolium Type Ionic Liquids

1
Department of Chemistry, North-West University (Mafikeng Campus), Private Bag X2046, Mmabatho 2735, South Africa
2
Department of Chemistry, University of Limpopo, PO Box 197, Medunsa 0204, South Africa
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2011, 12(6), 3989-3997; https://doi.org/10.3390/ijms12063989
Submission received: 19 March 2011 / Revised: 18 May 2011 / Accepted: 27 May 2011 / Published: 14 June 2011
(This article belongs to the Section Physical Chemistry, Theoretical and Computational Chemistry)

Abstract

:
The self-metathesis of methyl oleate and methyl ricinoleate was carried out in the presence of ruthenium alkylidene catalysts 14 in [bmim] and [bdmim][X] type ionic liquids (RTILs) (X = PF6, BF4 and NTf2) using the gas chromatographic technique. Best catalytic performance was obtained in [bdmim][X] type ionic liquids when compared with [bmim][X] type ionic liquids. Catalyst recycling studies were also carried out in the room temperature ionic liquids (RTILs) with catalysts 14 in order to explore their possible industrial application.

1. Introduction

Room temperature ionic liquids (RTILs) have been receiving considerable attention as innovative solvents for metal catalyzed organic reactions [16]. Most ionic liquids are based on ammonium, imidazolium, phosphonium, pyridinium, sulphonium, picolinium, pyrrolidinium, thiazolium, oxazolium, and pyrazolium cations. The important properties of ionic liquids, such as affinity to water and miscibility with other solvents, can be adjusted by the proper choice of alkyl substituents and counter anion. The most commonly used ionic liquids in olefin metathesis are 1,3-dialkylimidazolium and 1,2,3-trialkylimidazolium salts. Buijsman and co-workers [3] were the first group that reported the application of ionic liquids as a medium for olefin metathesis. They studied ring closing metathesis (RCM) of several substrates using Grubbs first and second generation catalysts in RTILs, and [bmim][PF6] was found to be the optimal solvent for the reactions. The activity and recyclability of Grubbs second generation catalyst in the self-cross-metathesis of some terminal olefins in RTILs has also been reported by Tang and co-workers [7]. Self-metathesis of 1-octene in 1,3-dialkylimidazolium and 1,2,3-trialkylimidazolium type ionic liquids have been reported by Williams and co-workers [8]. The results from the study showed that ionic liquids with shorter alkyl chain length enhanced the catalytic activity while the longer ones inhibited it. To overcome the problem associated with the leaching of products into the substrate, many charged catalyst systems have been employed [914].
The present work is an extension of our previous one which highlighted the self-metathesis reaction of methyl oleate in [bmim][X] type ionic liquids [15]. In this study, we report the self-metathesis of methyl oleate and methyl ricinoleate using the catalysts [14] in [bmim][X] and [bdmim][X] type ionic liquids (Scheme 1). The study also compares the metathesis activity in [bdmim] and [bmim] type ionic liquids. Catalyst recycling was also carried out in ionic liquids with the catalysts 14.

2. Results and Discussion

2.1. Self-Metathesis of Methyl Oleate

The self-metathesis of methyl oleate was carried out in the presence of ruthenium alkylidene catalysts 14 at 40 °C. The Hoveyda-Grubbs catalysts 3 and 4 were evaluated in 1-butyl 3-methylimidazolium (bmim) and 1-butyl 2,3-dimethylimidazolium (bdmim) based ionic liquids with different anions (PF6, BF4 and NTf2) (Scheme 1). Figure 1 shows the activity of 3 in [bmim] and [bdmim] type ionic liquids. For catalyst 3, similar conversions were observed in [bmim] and [bdmim] type ionic liquids (ILs). As there was not much difference in the catalytic activity, the benefit of selecting a particular IL (among PF6, BF4 and NTf2) was found to be of less importance. For catalyst 4, the highest activity was found in [bdmim][BF4] with a conversion of 85% (Figure 2). Comparing the cations of the ionic liquids, the C2-methylated imidazolium cation [bdmim] led to a slightly better conversion. The benefit of using [bdmim] cation in the ethenolysis of methyl oleate has been previously reported by Thurier et al. [16].
To study the effect of temperature on metathesis activity, the reactions were conducted at temperatures 40 °C and 60 °C. The results are summarized in Table 1. An increase in substrate conversion was observed with increase in temperature. At both the temperatures, the highest substrate conversion was seen with catalyst 4. Generally for all the runs, Hoveyda-Grubbs catalyst 4 exhibited good activity, although isomerization and formation of secondary metathesis products [17] seems to be a drawback. Hoveyda-Grubbs catalyst 3 and 4 showed good solubility in ionic liquid compared to Grubbs catalyst 1 and 2. The reason for the high activity of the Hoveyda-Grubbs second generation catalyst can be attributed to the absence of phosphine ligand. It has been proved that phosphine ligand suppresses the catalyst activity in Ru-catalyzed olefin metathesis [18]. The presence of free phosphine in solution can inhibit coordination of olefins to the transition metal centre by re-association with the active Ru complex. With the non-phosphine Ru complex (catalyst 4), activation occurs through the loss of O→Ru chelation. The styrenyl ether ligand completes less effectively with olefin substrates for Ru chelation [19]. [bdmim] type ILs can prevent the carbene formation of catalyst, which is believed to be formed by the deprotonation of imidazolium cation or from the oxidative addition of imidazolium to Ru centre [20].

2.2. Self-Metathesis of Methyl Ricinoleate

The self-metathesis of methyl ricinoleate was carried out in the presence of catalysts 1 and 2 in [bmim][X] type ILs. Table 2 summarizes the activity of catalysts 14 for the self-metathesis of methyl ricinoleate. For catalyst 1, the highest activity was shown in 5a with a substrate conversion of 45% and the activity was found to be in the order PF6 > BF4 > NTf2 (Figure 3). For catalyst 2, the same trend was followed, with the reaction in 5a yielding the highest conversion of 58% (Figure 4). The primary metathesis products (PMP) obtained from the metathesis of methyl ricinoleate (A) were 9-octadecene- 7,12-diol (B) and dimethyl 9-octadecenedioate (C), as illustrated in Scheme 2 [21].

2.3. Catalyst Recycling in Ionic Liquids

As solvents, ionic liquids are more advantageous than conventional organic solvents, which make them recyclable and environmentally friendly. It has been reported that the ionic liquids could be reused for at least three runs [3,16,22,23]. In a typical experiment, metathesis reaction was carried out in ionic liquids, and, after extraction of reaction products with heptane (2 × 3 mL), the glass reactor was loaded with fresh methyl oleate and was introduced for a new run.
To study the recyclability, Ru catalysts 14, in different ionic liquids, were subjected to consecutive runs (Table 3). Grubbs catalyst 1 proved to be stable in three consecutive runs, with the third run resulting in a decreased conversion. Grubbs catalyst 2 showed an increased conversion in the third cycle when compared with catalyst 1. Comparing the Hoveyda-Grubbs catalysts 3 and 4, the best result was obtained with catalyst 3. The results prove that catalyst 3 can be reused for three runs without loss of activity. In spite of good activity in the first run, the second generation Hoveyda-Grubbs catalyst 4 showed low catalytic activity during the second run.

3. Experimental Section

3.1. Materials and Apparatus

1-Butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide ([bmim][NTf2]), 1-butyl-2,3-dimethylimidazolium hexafluorophosphate ([bdmim][PF6]), 1-butyl-2,3- dimethylimidazolium tetrafluoroborate ([bdmim][BF4]), were all reagent grade chemicals from Sigma-Aldrich. Methyl oleate (≥99%) and methyl ricinoleate (>99%) were obtained from Sigma-Aldrich and were treated with activated alumina and stored under N2 atmosphere at a subzero temperature. Ethyl vinyl ether was purchased from Fluka. Nonadecane purchased from Fluka was used as the internal standard (IS). Ruthenium catalysts 14 were stored under N2 and used as purchased from Sigma-Aldrich. Chromatograms were obtained using Varian Star 3400 CX GC equipped with a DB-624 capillary column (J&W Scientific, 30 m × 0.53 mm) and a flame ionization detector (FID). The oven temperature was held at 200 °C and then increased to 270 °C at a rate of 20 °C min−1. The injector temperature was set at 270 °C and the detector temperature at 300 °C with N2 as carrier gas.

3.2. Metathesis Experiments

All the reactions were performed under a N2 atmosphere in a glass reactor fitted with a thermometer and a rubber septum. For the reaction in RTILs, 0.5 mL of the substrate was added to 1 mL of ionic liquid and stirred for 10 min to attain the reaction temperature. An internal standard (0.05 g) was added followed by the addition of 12.4 mg of catalyst. All the catalysts were soluble in ILs with the substrate forming a biphasic mixture with ILs. Samples were withdrawn by a syringe at regular time intervals for up to 4 hours. The reaction was terminated by immediately quenching with a few drops of ethyl vinyl ether [22]. The quenched sample was diluted with solvent and analyzed by GC.

4. Conclusions

For the self-metathesis of methyl oleate, Hoveyda-Grubbs catalyst 4 provided the best result with enhanced activity. Similar conversions were observed in all the three [bmim][X] type ionic liquids selected. However, when compared with [bdmim][X] type ionic liquids, higher activity was observed, which shows the superiority of [bdmim][X] type ionic liquids as reaction media. Furthermore, it was found that Hoveyda-Grubbs catalyst 3 could be reused for three consecutive runs without loss of activity. Overall, the use of ionic liquids in the metathesis reaction opens a route for the use of vegetable oil as a renewable source of raw materials for the chemical industry.

References

  1. Olivier-Bourbigou, H; Magna, L. Ionic liquids: Perspectives for organic and catalytic reactions. J. Mol. Catal. A: Chem 2002, 182, 419–437. [Google Scholar]
  2. Sledz, P; Mauduit, M; Grela, K. Olefin metathesis in ionic liquids. Chem. Soc. Rev 2008, 37, 2433–2442. [Google Scholar]
  3. Buijsman, RC; van Vuuren, E; Sterrenburg, JG. Ruthenium-catalyzed olefin metathesis in ionic liquids. Org. Lett 2001, 3, 3785–3787. [Google Scholar]
  4. Csihony, S; Fischmeister, C; Bruneau, C; Horvath, IT; Dixneuf, PH. First ring-opening metathesis polymerization in an ionic liquid. Efficient recycling of a catalyst generated from a cationic ruthenium allenylidene complex. New J. Chem 2002, 26, 1667–1670. [Google Scholar]
  5. Semeril, D; Olivier-Bourbigou, H; Bruneau, C; Dixneuf, PH. Alkene metathesis catalysis in ionic liquids with ruthenium allenylidene salts. Chem. Commun 146–147.
  6. Mayo, KG; Nearhoof, EH; Kiddle, JJ. Microwave accelerated ruthenium catalyzed olefin metathesis. Org. Lett 2002, 4, 1567–1570. [Google Scholar]
  7. Ding, X; Lu, X; Hui, B; Chen, Z; Xiao, M; Guo, B; Tang, W. Olefin self-cross-metathesis catalyzed by the second generation Grubbs carbene complex in room temperature ionic liquids. Tetrahedron Lett 2006, 47, 2921–2924. [Google Scholar]
  8. Williams, DBG; Ajam, M; Ranwell, A. Highly selective metathesis of 1-octene in ionic liquids. Organometallics 2006, 25, 3088–3090. [Google Scholar]
  9. Audic, N; Clavier, H; Mauduit, M; Guillemin, JC. An ionic liquid-supported ruthenium carbene complexe: A robust and recyclable catalyst for ring-closing olefin metathesis in ionic liquids. J. Am. Chem. Soc 2003, 125, 9248–9249. [Google Scholar]
  10. Clavier, H; Audic, N; Mauduit, M; Guillemin, JC. Ring-closing metathesis in biphasic BMI.PF6 ionic liquid/toluene medium: A powerful recyclable and environmentally friendly process. Chem. Commun 2282–2283.
  11. Yao, Q; Sheets, M. An ionic-liquid tagged second generation Hoveyda-Grubbs ruthenium carbene complex as highly reactive and recyclable catalyst for ring-closing metathesis of di-, triand tetrasubstituted dienes. Cheminform 2005, 36. [Google Scholar] [CrossRef]
  12. Liu, G; Zhang, J; Wu, B; Wang, J. Carborane as a tunable tag for Ru catalysts: Generating an anion appended recyclable and robust catalyst suitable for the non-covalent binding concept. Org. Lett 2007, 9, 4263–4266. [Google Scholar]
  13. Thurier, C; Fischmeister, C; Bruneau, C; Olivier-Bourbigou, H; Dixneuf, PH. Ionic imidazolium containing ruthenium complexes and olefin metathesis in ionic liquids. J. Mol. Catal. A Chem 2007, 268, 127–133. [Google Scholar]
  14. Rix, D; Clavier, H; Coutard, Y; Gulajski, L; Grela, K; Mauduit, M. Activated pyridiniumtagged ruthenium complexes as efficient catalysts for ring-closing metathesis. J. Organomet. Chem 2006, 691, 5397–5405. [Google Scholar]
  15. Thomas, PA; Marvey, BB. C18:1 methyl ester metathesis in [bmim][X] type ionic liquids. Int. J. Mol. Sci 2009, 10, 5020–5030. [Google Scholar]
  16. Thurier, C; Fischmeister, C; Bruneau, C; Olivier-Bourbigou, H; Dixneuf, PH. Ethenolysis of methyl oleate in room temperature ionic liquids. ChemSusChem 2008, 1, 118–122. [Google Scholar]
  17. Marvey, BB; Segakweng, CK; Vosloo, HCM. Ruthenium carbene mediated metathesis of oleate-type fatty compounds. Int. J. Mol. Sci 2008, 9, 615–625. [Google Scholar]
  18. Sanford, MS; Love, JA; Grubbs, RH. Mechanism and activity of ruthenium olefin metathesis catalysts. J. Am. Chem. Soc 2001, 123, 6543–6554. [Google Scholar]
  19. Hoveyda, AH; Gillingham, DG; Van Veldhuizen, JJ; Kataoka, O; Garber, SB; Kingsbury, JS; Harrity, JPA. Ru complexes bearing bidentate carbenes: From innocent curiosity to uniquely effective catalysts for olefin metathesis. Org. Biomol. Chem 2004, 2, 8–23. [Google Scholar]
  20. Thurier, C; Fischmeister, C; Bruneau, C; Olivier-Bourbigou, H; Dixneuf, PH. Ethenolysis of methyl oleate in room-temperature ionic liquids. ChemSusChem 2008, 1, 118–122. [Google Scholar]
  21. Segakweng, CK. Olefin metathesis in oleochemistry-application of ruthenium catalysts to vegetable oil-derived olefins. MS Thesis, July 2007; pp. 66–67. [Google Scholar]
  22. Buchowicz, W; Mol, J. Catalytic activity and selectivity of Ru(=CHPh)Cl2(PCy3)2 in the metathesis of linear olefins. J. Mol. Catal. A Chem 1999, 148, 97–103. [Google Scholar]
  23. Hsu, J; Yen, Y; Chu, Y. Baylis-Hillman reaction in [bdmim][PF6] ionic liquid. Tetrahedron Lett 2004, 45, 4673–4676. [Google Scholar]
Figure 1. Activity of 3 for the self-metathesis of methyl oleate in different ILs.
Figure 1. Activity of 3 for the self-metathesis of methyl oleate in different ILs.
Ijms 12 03989f1
Figure 2. Activity of 4 for the self-metathesis of methyl oleate in different ILs.
Figure 2. Activity of 4 for the self-metathesis of methyl oleate in different ILs.
Ijms 12 03989f2
Figure 3. Activity of 1 for the self-metathesis of methyl ricinoleate in different ionic liquids.
Figure 3. Activity of 1 for the self-metathesis of methyl ricinoleate in different ionic liquids.
Ijms 12 03989f3
Figure 4. Activity of 2 for the self-metathesis of methyl ricinoleate in different ionic liquids.
Figure 4. Activity of 2 for the self-metathesis of methyl ricinoleate in different ionic liquids.
Ijms 12 03989f4
Scheme 1. Ruthenium catalysts and imidazolium ionic salts.
Scheme 1. Ruthenium catalysts and imidazolium ionic salts.
Ijms 12 03989f5
Scheme 2. Primary metathesis products from self-metathesis of methyl ricinoleate.
Scheme 2. Primary metathesis products from self-metathesis of methyl ricinoleate.
Ijms 12 03989f6
Table 1. Activity of 3 and 4 for the self-metathesis of methyl oleate in [bmim] and [bdmim][X] type ionic liquids.
Table 1. Activity of 3 and 4 for the self-metathesis of methyl oleate in [bmim] and [bdmim][X] type ionic liquids.
RTILCatalystTemperature (°C)Conversion (%)Selectivity a (%)
5a1405799
26597
35599
47896
1605999
27594
35798
48793
5b1405899
26796
35699
47996
1606199
27894
35997
48795
5c1405799
26496
35499
47497
1606099
27396
35999
48595
6a3405799
48198
3606097
49095
6b3405899
48599
3606097
4409295
0.5 mL of MO (MO/Ru ratio = 100), 1 mL of IL, reaction time = 4 h;
aselectivity towards PMPs.
Table 2. Activity of 1 and 2 for the self-metathesis of methyl ricinoleate.
Table 2. Activity of 1 and 2 for the self-metathesis of methyl ricinoleate.
RTILCatalystTemperature (°C)Conversion (%)Selectivity a (%)
5a1604599
25899
5b1604199
25699
5c1603899
2605599
0.2 mL of MR (MR/Ru ratio = 100), 0.5 mL of IL, reaction time = 4 h;
aselectivity towards PMPs.
Table 3. Recycling of catalysts in [bmim][BF4] a and [bdmim][BF4] a,b.
Table 3. Recycling of catalysts in [bmim][BF4] a and [bdmim][BF4] a,b.
CatalystConversion (%)Selectivity (%)
11st run: 57 (58)99
2nd run: 56 (56)99
3rd run: 42 (45)98
21st run: 67 (72)99
2nd run:50 (60)97
3rd run:45 (57)97
31st run: 56 (58)99
2nd run: 56 (58)99
3rd run: 49 (53)99
4th run: 22 (30)99
41st run: 74 (85)99
2nd run: 40 (54)95
3rd run: 15 (23)95
aAll reactions were performed at 40 °C for 4 hours, substrate/Ru = 100;
bvalues in bracket are for [bdmim][BF4].

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MDPI and ACS Style

Thomas, P.A.; Marvey, B.B.; Ebenso, E.E. Metathesis of Fatty Acid Ester Derivatives in 1,1-Dialkyl and 1,2,3-Trialkyl Imidazolium Type Ionic Liquids. Int. J. Mol. Sci. 2011, 12, 3989-3997. https://doi.org/10.3390/ijms12063989

AMA Style

Thomas PA, Marvey BB, Ebenso EE. Metathesis of Fatty Acid Ester Derivatives in 1,1-Dialkyl and 1,2,3-Trialkyl Imidazolium Type Ionic Liquids. International Journal of Molecular Sciences. 2011; 12(6):3989-3997. https://doi.org/10.3390/ijms12063989

Chicago/Turabian Style

Thomas, Priya A., Bassie B. Marvey, and Eno E. Ebenso. 2011. "Metathesis of Fatty Acid Ester Derivatives in 1,1-Dialkyl and 1,2,3-Trialkyl Imidazolium Type Ionic Liquids" International Journal of Molecular Sciences 12, no. 6: 3989-3997. https://doi.org/10.3390/ijms12063989

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