Transesterification between isoamyl acetate and ethanol in supercritical CO2, ionic liquid, and their mixture
Introduction
Green chemistry has become an identified imaginary trend in this heavily polluted world, which has catalyzed supercritical fluid (SCF) and ionic liquid (IL) to be used as environmental benign substitutes to the toxic and flammable organic solvents [1].
SCFs have received much attention as reaction media [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. SCFs have some unique properties. Their physical properties, such as dielectric constant, density, solubility parameter, and diffusivity, vary significantly with pressure, especially in near-critical region. Therefore, it is possible to optimize chemical reaction rate, conversion, and selectivity by conveniently changing pressure without the need for a harsh chemical change.
Room temperature ILs are organic molten salts at ambient temperature. ILs offer an environmental benign alternative compared to conventional organic solvents as they are nonvolatile and thermally stable. They are excellent solvents for carbonyl compounds, alkyl halides, alcohols and amines, and by changing the ions, they can be miscible with different kinds of substances [12], [13], [14], [15].
Both SC CO2 and ILs are environmentally benign solvents, and each of them has their own unique properties. Combination of the advantages of the two classes of solvents is a new and interesting topic. Very recent work has demonstrated that SC CO2 is highly soluble in some ILs, while the ILs are insoluble in SC CO2 [16], [17]. This feature of CO2/IL systems has been successfully used to separate SC CO2 soluble products from the ILs in some reaction processes [18], [19], [20], [21].
Study on the equilibrium conversion of reversible reactions in CO2/IL mixed solvents is a new and interesting topic. The conversion of some reactions may be tuned effectively by changing operation conditions. In this work, we study the transesterification between isoamyl acetate and ethanol in SC CO2, [bmim][PF6], and SC CO2/[bmim][PF6] mixed solvent, respectively.
Section snippets
Materials
CO2 was supplied by Beijing Analytical Instrument Factory with a purity of 99.995%. Isoamyl acetate, ethanol, ethyl acetate, isoamyl alcohol, and P-TSA were A.R. grade and produced by Beijing Chemical Plant. [bmim][PF6] was prepared using the method reported by other authors [22]. It was dewatered under vacuum at 50 °C for 3 days prior to use.
Apparatus and procedures
The schematic diagram of the apparatus used in this work is shown in Fig. 1. Briefly, it consisted mainly of a high-pressure stainless steel reactor, a
Verification of the extraction procedure
The reaction can be expressed as following.
After the reaction, the reaction mixture contains four components, and all the components should be extracted for analysis. In order to verify that all the reactants and products could be extracted and collected in the extraction process, we did some simulation experiments for the extraction process. In the experiments, 1.250 g amount of the reactant and product mixture (isoamyl acetate+ethyl
Conclusion
The transesterification between isoamyl acetate and ethanol in SC CO2, [bmim][PF6], and in CO2+[bmim][PF6] mixed solvent has been investigated at 65.0 °C and different pressures. It is demonstrated that in compressed CO2 the equilibrium conversion varies significantly as reaction system changes from single phase region to two phase region by tuning pressure. The equilibrium conversion of the reaction in CO2+IL mixture is different from that in CO2 or in the IL. The reason is that the solvent
Acknowledgements
This work was financially supported by National Key Basic Research Project (G2000048010) of China, National Natural Science Foundation of China (20133030).
References (25)
- et al.
Critical points and phase behavior of toluene–CO2 and toluene–H2–CO2 mixture in CO2-rich region
J. Supercrit. Fluids
(2000) - et al.
Measurement of critical points of the methylcyclohexane(MCH)–H2–CO2 system in the CO2-rich region
Fluid Phase Equilib.
(2001) Clean and green … but are they mean?
Nature
(2000)- et al.
A new approach to studying the mechanism of catalytic reactions: an investigation into the photocatalytic hydrogenation of norbornadiene and dimethylfumarate using polyethylene matrices at low temperature and high pressure
J. Am. Chem. Soc.
(2001) - et al.
Supercritical carbon dioxide as solvent and temporary protecting group for rhodium-catalyzed hydroaminomethylation
Chem. Eur. J.
(2001) - et al.
Photochemical carbonylation of ethane under supercritical conditions
Angew. Chem. Int. Ed.
(2001) - et al.
Enhanced regioselectivity of rhodium-catalysed alkene hydroboration in supercritical carbon dioxide
Chem. Commun.
(2000) - et al.
Polymarizations in supercritical carbon dioxide
Chem. Rev.
(1999) - et al.
Homogeneous organic reactions as mechanistic probes in supercritical fluids
Chem. Rev.
(1999) - et al.
Homogeneous catalysis in supercritical fluids
Chem. Rev.
(1999)