Ionic liquids in green chemistry: catalytic reaction of cyclic ...

L.W. Wijayanti et al. Proceeding of The International Seminar on Chemistry 2008 (pp. 356-362)Jatinangor, 30-31 October 2008ambiguous spectroscopic and elemental analysis dataled us to carry out single crystal X-ray diffractionstudy, which revealed that the white powder was[Dmim] 2 ZnCl 2 Br 2 . The crystals of [Dmim] 2 ZnCl 2 Br 2were grown in a DMSO/toluene solvent mixture atroom temperature. An ORTEP of its molecularstructure is shown in Fig. 1, where selected bonddistances and angles are also provided.The crystal of [Dmim] 2 ZnCl 2 Br 2 contains twoindependent molecules in the asymmetric-crystal unit.Each zinc center is surrounded by four halide ligandsand possesses a distorted tetrahedral ligandenvironment. Unfortunately, the exact position ofbromide and chloride in tetrahedral zinc center couldnot be determined due to a disorder in the crystalsystem. Interestingly, two imidazolium cations werepaired with a tetrahalo zincate dianion ([ZnBr 2 Cl 2 ] 2- )in the solid state.In order to confirm that [Dmim] 2 ZnCl 2 Br 2 is areal-active species for the coupling reactionperformed in the presence of [Dmim]Br and ZnCl 2 ,the activity of [Dmim] 2 ZnCl 2 Br 2 was compared withthat of the catalytic system composed of [Dmim]Brand ZnCl 2 for the coupling reaction of CO 2 andethylene oxide at 100 °C and 500 psig with a molarratio of EO/Zn = 500.As can be seen in Table 1, [Dmim] 2 ZnCl 2 Br 2 wasfound to exhibit the similar activity to the catalyticsystem consisting of [Dmim]Br and ZnCl 2 . The activespecies, [Dmim] 2 ZnCl 2 Br 2 was obtained in high yieldover 90% either by reacting [Dmim]Br with ZnCl 2 orfrom the reaction of [Dmim]Cl and ZnBr 2 , suggestingthat bromide and chloride anions in [Dmim] 2 ZnCl 2 Br 2can be exchanged. Other imidazolium zinc complexeswere similarly prepared.The catalytic activity of [Dmim] 2 ZnCl 2 Br 2 wasevaluated for the coupling reactions of CO 2 andvarious alkylene oxide to produce correspondingalkylene carbonates, and the results are listed in Table2. Most of the alkylene oxides tested were readilyconverted to the corresponding alkylene oxides butthe reactivity of alkylene oxide was greatly affectedby the substituent at the carbon atom of the epoxide.358

L.W. Wijayanti et al. Proceeding of The International Seminar on Chemistry 2008 (pp. 356-362)Jatinangor, 30-31 October 2008Ethylene oxide and alkylene oxides with lessbulkier substituents, produced corresponding alkyleneoxides in high yields. However, alkylene oxides withbulky substituents around epoxide groups gave muchlower yields of alkylene carbonates. This can beclearly seen by comparing the reactivities of 1,2-epoxybutane, glycidylisopropyl ether and t-butylglycidyl ether. The most crowded t-butylglycidylether showed the lowest reactivity while the leastcrowded 1,2-epoxybytane exhibited the highestreactivity. The steric crowdness around epoxide groupis likely to prevent the coordination of alkylene oxideto zinc center. The lower reactivities ofepicholorohydrin and hexafluoropropylene oxide incomparison with propylene oxide can be largelyattributed to the electron-withdrawing effects ofchlorine and fluorine atoms. The presence of highlyelectronegative substituent reduces the electrondensity on the oxygen atom of epoxide, and thereforethe ability of epoxide to coordinate to zinc centerbecome reduced, which is presumed to be the firststep in the coupling reaction. The reason for therelatively lower reactivity of styrene oxide seems tobe a combination of steric and electronic effect ofphenyl group.Various imidazolium zinc tetrahalide complexeswere tested for their activities in the couplingreactions of CO 2 and alkylene oxides (Table 3).The activities of imidazolium zinc tetrahalideswere not significantly affected by the variation ofimidazolium cations. On the other hand, the activitieswere greatly influenced by halide groups bonded tozinc center. From these results, it is likely that theimidazolium cation only plays a role in stabilizing anactive zinc tetrahalide dianion and not in controllingthe activity.The dissociation of a halide ion from the zinctetrahalide dianion and the following attack of thehalide ion on the carbon atom of the epoxide wouldtake place more easily with more nucleophilicbromide ion, giving the following activity order:[ZnBr 4 ] 2- > [ZnBr 2 Cl 2 ] 2- >> [ZnCl4] 2-CO 2 solubility measurementsIn another research work, we also performedsolubility test of CO 2 in ionic liquids. We investigatedthe physical properties of dialkylimidazoliumdialkylphosphates. The products of synthesis 1,3-dimethylimidazoliumdimethylphosphate/[MMIM][Me 2 PO 4 ], 1-ethyl-3-methyl-imidazolium diethylphosphate/[EMIM][Et 2 PO 4 ], and 1-butyl-3-methyl-imidazoliumdibutylphosphate/[BMIM][Bu 2 PO 4 ] estimateddensities at 313.15, 323.15, and at 333.15 K are listedin Table 4. A cation with a long alkyl chain-length359

L.W. Wijayanti et al. Proceeding of The International Seminar on Chemistry 2008 (pp. 356-362)Jatinangor, 30-31 October 2008substituent has low density might be due to entropicreasons, as the density of IL decreases with increasingalkyl chain-length; therefore, there may be more freevolume within the longer alkyl chain IL [33]. Thedensities of all tested RTILs are little influenced bytemperature variations and are decreased astemperature increased.Solubility measurements were performed at closeto and slightly above atmospheric pressure at 313.15,323.15, and 333.15 K and the amount of dissolvedsolute was calculated based on a pressure-decayobservation. The CO 2 solubility on a mole fractionand a volume basis and the CO 2 equilibrium pressuresabove the liquid absorbent are listed in Figure 2, 3,and 4. As can be seen, the CO 2 solubility increaseslinearly with pressure in all of the dialkylimidazoliumdialkylphosphate ionic liquid coefficients of theRTILs show positive deviations from the Raoult’s lawliqin that they are greater than 0.5 f 2or 2.44 MPa [34]Table 4 Room-temperature ionic liquids synthesized in this study, their structures, and experimental densities (ρ)EntryCompoundOO P1 N N OOρ/kg·m -3 (ρ = ± 0.0001)313.15 K 323.15 K 333.15 K1.2510 1.2444 1.2380[MMIM][Me 2 PO 4 ]OOPOC 2 H 52 C 2 H 5 N N OC 2 H 5[EMIM][Et 2 PO 4 ]OC 4 H 9O P O3 C 4 H 9 N N OC 4 H 9[BMIM][Bu 2 PO 4 ]1.1386 1.1321 1.12551.0400 1.0337 1.027110 3 x21816141210864200 50 100 150 200p/kPaFigure 2 Solubility of CO 2 in [MMIM][Me 2 PO 4 ]at (●) 313.15 K, (■) 333.15 K, and (▲)323.15 K at atmospheric pressure10 3 x23025201510500 50 100 150 200 250p/kPaFigure 3 Solubility CO 2 in [EMIM][Et 2 PO 4 ] at (●)313.15 K, (■) 333.15 K, and (▲) 323.15 K atatmospheric pressure360

L.W. Wijayanti et al. Proceeding of The International Seminar on Chemistry 2008 (pp. 356-362)Jatinangor, 30-31 October 2008Table 5 List of variation of Henry’s law coefficient with temperature of 1-3-dialkylimidazolium dialkylphosphate ionic liquidsCompound T/K H 21 /MPa Error a313.15 10.64 0.12[MMIM][Me 2 PO 4 ] 323.15 12.72 0.03333.15 15.22 0.15313.15 6.99 0.03[EMIM][Et 2 PO 4 ] 323.15 8.12 0.04333.15 9.66 0.02313.15 4.98 0.02[BMIM][Bu 2 PO 4 ] 323.15 5.76 0.02333.15 6.85 0.03a Standard errors of the isotherm slopes10 3 x240353025201510500 50 100 150 200p/kPaFigure 4 Solubility CO 2 in [BMIM][Bu 2 PO 4 ] at (●)313.15 K, (■) 333.15 K, and (▲) 323.15 Kat atmospheric pressureIn our experiments, the Henry’s law coefficient at aspecified temperature was estimated from the slope ofa linear fit of the CO 2 solubility in mole fractionversus fugacity. The Henry’s law coefficients atvarious temperatures and the standard error of theisotherm slopes are given in the Table 5. As can beseen, all of the Henry’s law.ConclusionsA series of ionic liquid-based imidazolium zinctetrahalide and (1-R-3-methylimidazolium) 2 ZnX 2 Y 2 ,were prepared by reacting ZnX 2 with (1-R-3-methylimidazolium)Y.The single crystal X-ray structural analysis andelemental analysis of (1,3-dimethylimidazolium) 2ZnBr 2 Cl 2 revealed that two imidazolium cations werepaired with a dibromodichloro zincate dianion.The catalytic activities of imidazolium zinctetrahalide were evaluated for the coupling reactionsof epoxides and CO 2 , and the effects of halide ions,imidazolium cations, temperature and pressure wereinvestigated. The catalytic activity of (1-R-3methylimidazolium) 2 ZnX 2 Y 2 was found to increasewith increasing nucleophilicity of halide ion. But, thesubstitution on the imidazolium cation showed anegligible effect on the catalytic activity. Theformation of cyclic carbonate was strongly dependenton the temperature but independent of the pressure ofCO 2 . The reactivity of alkylene oxide was greatlyaffected by the substituent at the carbon atom of theepoxide. Ethylene oxide and alkylene oxides with lessbulkier substituents produced corresponding alkyleneoxides in high yields. However, alkylene oxides withbulky or electron-withdrawing substituents aroundepoxide groups gave much lower yields of alkylenecarbonates.The CO 2 solubility increases linearly with pressurein all of the dialkylimidazolium dialkylphosphateionic liquids and decreases as temperature increases.It means that dialkylimidazolium dialkylphosphatehave capability to capture CO 2 through physicalinteraction.AcknowledgementsThis work was supported by the Ministry ofEnvironment in Korea and presented by Ms. LuciaWiwid Wijayanti, M.SiReferencesA. Behr, Carbon Dioxide Activation by MetalComplexes, VCH, New York, 1988.D.J. Darensbourg, M.W. Holtcamp, Coord. Chem.Rev. (1996) 153.T. Kim, S. Vijayalakshmi, S. Son, S. Ryu, J. Kim, J.Ind. Eng. Chem. 9 (2003) 481–487.B. Sea, Y. Park, K. Lee, J. Ind. Eng. Chem. 8 (2002)290–296.M. Aresta, E. Quaranta, ChemTech. Mar. (1997) 32–40.A.G. Shaikh, Chem. Rev. 96 (1996) 951–976.D. Lee, J. Hur, B. Kim, S. Park, D. Park, J. Ind. Eng.Chem. 9 (2003) 513–517.J.J. Lagowski, The Chemistry of NonaqueousSolvents, Academic Press, New York, 1976.M. Inaba, Z. Siroma, A. Funabiki, M. Asano,Langmuir 12 (1996) 1535–1540.361

L.W. Wijayanti et al. Proceeding of The International Seminar on Chemistry 2008 (pp. 356-362)Jatinangor, 30-31 October 2008D. Ji, X. Ju, R. He, Appl. Catal. A 203 (2000) 329–333.H. Kawanami, Y. Ikushima, Chem. Commun. (2000)2089–2090.J. Gao, S. Zhong, J. Mol. Catal. A (2001) 168.H. Matzuda, A. Niangawa, R. Nomura, Chem. Lett.(1979) 1261–1262.R. Nomura, A. Ninagawa, H. Matsuda, J. Org. Chem.45 (1980) 3735–3738.H. Kisch, R. Millini, I.J. Wang, Chem. Ber. 119(1986) 1090–1094.W. Du¨mler, H. Kisch, Chem. Ber. 123 (1990) 277–283.M. Ratzenhofer, H. Kisch, Angew. Chem. Int. Ed.Engl. 19 (1980) 317–318.D.J. Darensbourg, M.W. Holtcamp, Macromolecules28 (1995) 7577–7579.M. Cheng, E.B. Lobkovsky, G.W. Coates, J. Am.Chem. Soc. 120 (1998) 11018–11019.M. Cheng, D.R. Moor, J.J. Reczek, B.M.Chamberlain, E.B. Lobkovsky, G.W. Coates, J.Am. Chem. Soc. 123 (2001) 8738-8749.R.L. Paddock, S.T. Nguyen, J. Am. Chem. Soc. 123(2001) 11498–11499.J. Peng, Y. Deng, New J. Chem. 25 (2001) 639–641.H.S. Kim, J.J. Kim, H. Kim, H.G. Jang, J. Catal. 220(2003) 44–46.M. Hasan, I.V. Kozhevnikov, M.R.H. Siddiqui, A.Steiner, N. Winterton, Inorg. Chem. 38 (1999)5637–5641.J.S. Wilkes, J.A. Levisky, R.A. Wilson, C.L. Hussey,Inorg. Chem. 21 (1982) 1263–1264.P.J. Dyson, M.C. Grossel, N. Srinivasan, T. Vine, T.Welton, D.J. Williams, A.J.P.White, T. Zigras, J.Chem. Soc., Dalton Trans. (1997) 3465–3469.L.A. Blanchard, D. Hancu, E.J. Beckman, J.F.Brennecke, Nature 399 (1999) 28-29.J.D. Holbrey, W.M. Reichert, R.P. Swatloski, G.A.Broker, W.R. Pitner, K.R. Seddon, R.D. Rogers,Green Chem. 4 (2002) 407-413.C.J. Bradaric, A. Downard, C. Kennedy, A.J.Robertson, Y. Zhou, Green Chem. 5 (2003) 143-152.E. Kuhlmann, S. Himmler, H. Giebelhaus, P.Wasserscheid, Green Chem. 9 (2007) 233-242.Y. Zhou, A.J. Robertson, J.H. Hillhouse, D.Baumann, Cytec Canada Inc., WO, 2004,2004016631.R.P. Swatloski, J.D. Holbrey, R.D. Rogers, GreenChem. 5 (2003) 361-363.L.A. Blanchard, Z. Gu, J.F. Brennecke, J. Phys.Chem. B. 105 (2001) 2437-2444.P. Scovazzo, D. Camper, J. Kieft, J. Poshusta, C.Koval, R. Noble, Ind. Eng. Chem. Res. 43 (2004)6855-6860.362