Solvation of Esters and Ketones in Supercritical CO2 - The Journal of

Article pubs.acs.org/JPCB

Solvation of Esters and Ketones in Supercritical CO2 Daisuke Kajiya,† Masayoshi Imanishi,‡ and Ken-ichi Saitow*,†,‡ †

Natural Science Center for Basic Research and Development (N-BARD) and ‡Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-hiroshima, Hiroshima 739-8526, Japan S Supporting Information *

ABSTRACT: Vibrational Raman spectra for the CO stretching modes of three esters with different functional groups (methyl, a single phenyl, and two phenyl groups) were measured in supercritical carbon dioxide (scCO2). The results were compared with Raman spectra for three ketones involving the same functional groups, measured at the same thermodynamic states in scCO2. The peak frequencies of the Raman spectra of these six solute molecules were analyzed by decomposition into the attractive and repulsive energy components, based on the perturbed hard-sphere theory. For all solute molecules, the attractive energy is greater than the repulsive energy. In particular, a significant difference in the attractive energies of the ester−CO2 and ketone−CO2 systems was observed when the methyl group is attached to the ester or ketone. This difference was significantly reduced in the solute systems with a single phenyl group and was completely absent in those with two phenyl groups. The optimized structures among the solutes and CO2 molecules based on quantum chemical calculations indicate that greater attractive energy is obtained for a system where the oxygen atom of the ester is solvated by CO2 molecules.

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We have investigated supercritical fluid structures with respect to diffusive, rotational, and vibrational motion using dynamic light scattering,40−43 terahertz (THz) absorption,44,45 and Raman spectroscopy,39,46−55 respectively. These studies have been extended to nanomaterial fabrication.56−63 In particular, the local structure around solute molecules has been quantified for various systems using Raman spectroscopy and by theoretical analysis, whereby the attractive and repulsive energies of the solute−solvent interactions are investigated as a function of the fluid density to determine various specific properties and structures.39,51−55 For instance, supercritical Xe, a nonpolar fluid, exhibits the highest attractive energy according to studies on the cis and trans isomers of 1,2-dichloroethylene in Xe compared with other supercritical fluids such as CO2, CHF3, and SF6.51 The attractive energy of a nonpolar trans isomer is higher than that of the polar cis isomer,52 which is attributed to the isotropic and/or anisotropic molecular distribution and orientation.53 We have identified a new driving force to categorize solute−solvent interactions by measurement of the substitution effect on ethylene molecules.55 As the latest work, the introduction of a phenyl group to a ketone was determined to cause a 1.8-fold enhancement of the attractive energy, which is responsible for the increase in the dispersion force.39 In the present study, the vibrational Raman spectra for the CO stretching modes of three prototypical esters (Figure 1) with different functional groups (methyl, a single phenyl, and two phenyl groups) were measured in scCO2. The results were

INTRODUCTION Supercritical fluid (SCF) has attracted considerable attention as a density-tunable medium that enables the control of physicochemical properties such as permittivity, viscosity, and thermal conductivity.1−4 Supercritical carbon dioxide (scCO2) has been most extensively utilized as a solvent for chemical and physical processes because of its low critical point (Tc = 304.1 K, Pc = 7.4 MPa), nontoxicity, and its cost-effectiveness as a fluid.5−21 High solubility of the solute in scCO2 is important for the efficient use of scCO2 in chemical and physical processes.22,23 For example, carbonyl compounds exhibit high solubility in scCO2.23−27 In particular, esters and ketones have served as the most popular carbonyl compounds utilized in scCO2.23−27 To understand the mechanism of both their high solubility and the intermolecular interactions in scCO2, several experimental and theoretical investigations have been reported.27−39 Fink et al. observed a 5-fold increase in solubility by attachment of a carbonyl group onto a solute molecule.27 Kazarian et al. used infrared spectroscopy to observe large interaction between CO2 and the carbonyl group.29 Kilic et al. calculated the stable structure, and the oxygen atom of the carbonyl group is solvated by CO2.33 Recently, Altarsha et al. reported another stable structure where the CO2 molecule lies parallel to the carbonyl group.36 However, the solvation of carbonyl compounds in scCO2 has not been clarified to date because there have been no reports that compare the solvation of esters with that of ketones in scCO2. A detailed understanding of the solvation of carbonyl compounds in scCO2 is also important for the chemical industry to enhance the solubility of solute molecules and achieve higher reactivity and efficiency. © 2016 American Chemical Society

Received: December 1, 2015 Revised: January 7, 2016 Published: January 7, 2016 785

DOI: 10.1021/acs.jpcb.5b11740 J. Phys. Chem. B 2016, 120, 785−792

The Journal of Physical Chemistry B

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EXPERIMENTAL SECTION

Raman spectra were measured using an in-house built instrument that has been described elsewhere.49−51 The light source was a diode-pumped solid-state (DPSS) laser operated at an excitation wavelength of 532 nm and with a singlefrequency output of 200 mW in front of an optical cell. The laser was incident on the cell, and a camera lens collected the scattered light at an angle of 90°. Raman spectra were recorded by the photon counting method using a monochromator and a photomultiplier tube. The frequency of each Raman spectrum was calibrated to that of the excitation laser. The frequency repeatability of the spectrometer was confirmed to be within ±0.02 cm−1. The high-frequency stability enabled precise measurements of the peak positions in the Raman spectra. Supercritical solutions were prepared by the introduction of accurately weighed solute molecules into a high-pressure vessel. The vessel was filled with a specific quantity of high-pressure CO2 by measuring the weight of the vessel during fluid injection. The solute mole fraction was adjusted to 0.004 ± 0.002. The optical purity of the solution was increased by filtration with a polytetrafluoroethylene membrane filter with a pore size of 0.1 μm. The high-pressure solution generated in the vessel was transferred into a stainless-steel (SUS 316) Raman optical cell.49 The density of the supercritical solutions in the cell was adjusted by releasing high-pressure supercritical solution from the cell. The thermodynamic states for the Raman spectra are plotted on the P−T and P−ρ phase diagrams for CO2, as shown in Figure S1 of the Supporting Information. The temperature of the supercritical solution was maintained at the reduced temperature Tr = T/Tc = 1.02 isotherm, where Tc is the critical temperature. The temperature was adjusted using a setup consisting of a proportional-integral-derivative (PID) controller, heaters, and a thermocouple. The heated sample cell was enclosed in a glass wool insulator to prevent temperature fluctuations and heterogeneity. The pressure was monitored using a pressure transducer that was backed up with an amplifier. Both temperature and pressure fluctuations were within ±0.1% during the measurements. Densities were

Figure 1. Molecular structures of esters and ketones investigated in this work, where R1 and R2 denote functional groups and Me is a methyl group.

then compared with those for three ketones39 with the same functional groups, measured at the same thermodynamic states in scCO2. All of the spectra for the esters and ketones were analyzed using the perturbed hard-sphere theory, and the attractive and repulsive energies were quantified as a function of density. Quantum chemical calculation methods were employed to evaluate the optimized structures between the solute and CO2 molecules for all solute−CO2 systems. As a result, a significant difference in the attractive energy between ester− CO2 and ketone−CO2 systems was observed when the methyl group is attached to the ester or ketone. This difference is produced for a system where an oxygen atom in the ester is solvated by CO2 molecules. In contrast, the difference is significantly reduced in solute systems with a single phenyl group and is completely absent in those with two phenyl groups because solvation at the oxygen atom is disturbed by the phenyl groups. The solvation of esters and ketones in scCO2 is thus investigated by conducting systematic studies on carbonyl compounds.

Figure 2. Typical Raman spectra for the CO stretching modes of esters in scCO2 at Tr = 1.02: (a) methyl acetate, (b) methyl benzoate, and (c) phenyl benzoate. Dotted lines indicate fits using a Lorentzian function. Tr denotes the reduced temperature as Tr = T/Tc, and ρr denotes the reduced density given by ρr = ρ/ρc. 786


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Figure 3. Density dependence of Δνexp for (a) esters and (b) ketones in scCO2 at Tr = 1.02. Solid lines are fits to the experimental data using polynomial functions. Tr denotes the reduced temperature as Tr = T/Tc, and ρr denotes the reduced density given by ρr = ρ/ρc.

calculated from the empirical state equation for CO2 using the P and T values.64 The reduced density ρr varied from 0.08 to 1.6, where ρr is defined by ρr = ρ/ρc and ρc is the critical density. The critical constants for CO2 are Tc = 304.1 K, Pc = 7.4 MPa, and ρc = 0.468 g cm−3.64 The chemical purities of CO2 (Nippon Ekitan), methyl acetate (Nacalai Tesque), methyl benzoate (Tokyo Chemical Industry), and phenyl benzoate (Tokyo Chemical Industry) were commercially guaranteed to be 99.9995, 99, 99.9, and 99.9%, respectively.

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RESULTS AND DISCUSSION Figure 2 shows typical Raman spectra for the three esters as a function of the scCO2 density. The Raman bands at around Table 1. Molecular Parameters Used for Calculation of ΔνR parameters

methyl acetate

methyl benzoate

phenyl benzoate

f (N/cm)a g (N/cm2 × 109)b ν0 (cm−1)c GR/FR = 1/4L (nm−1)d L = 0.0571 × σave(nm)d σave = (σ + σS)/2 (nm)e σ (nm)e σS (nm)e re (nm)f m1d m2d m3d b1d b2d b3d

11.0 −3.07 1770.5 11.3 0.022 0.39 0.38 0.40 0.120 2.67 4.41 4.37 −0.69 −1.75 −2.64

11.5 −2.89 1748.3 10.4 0.024 0.42 0.44 0.40 0.121 2.62 4.41 4.38 −0.45 −1.34 −2.22

12.3 −2.88 1762.6 10.0 0.025 0.44 0.48 0.40 0.121 2.58 4.43 4.38 −0.28 −1.05 −1.95

Reference 65 for methyl acetate, ref 70 for methyl benzoate, and ref 67 for phenyl benzoate. bReference 71. cReference 68. dReference 69. e Reference 72. fReference 73 for methyl acetate, ref 66 for methyl benzoate, and ref 67 for phenyl benzoate.

Figure 4. Attractive (●), repulsive (△), and experimental net (○) shifts of CO stretching modes for esters (left) and ketones (right) in scCO2 at Tr = 1.02. Tr denotes the reduced temperature as Tr = T/ Tc, and ρr denotes the reduced density expressed as ρr = ρ/ρc. Dotted lines are fits obtained with polynomial functions.

1760, 1740, and 1750 cm−1 are assigned to the CO stretching modes of methyl acetate,65 methyl benzoate,66 and phenyl benzoate,67 respectively. The peak frequency shifts toward the low-energy side as the scCO2 density increases.

Analysis of the peak frequency (ν) using a Lorentzian function indicated that the density dependence of the peak-frequency shift was Δνexp = [(ν − ν0)/ν0] × 100, where ν0 is the peak frequency at zero density.68 Figure 3a shows Δνexp for the three

a

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Figure 5. (a) Attractive shifts for esters (top) and ketones (bottom) in scCO2 at Tr = 1.02. (b) Attractive shifts for esters and ketones with a methyl group (top), a single phenyl group (middle), and two phenyl groups (bottom). The dashed lines act as visual guides to indicate the trend. Tr denotes the reduced temperature as Tr = T/Tc, and ρr denotes the reduced density expressed as ρr = ρ/ρc.

perturbed hard-sphere theory, Δνexp is characterized by the attractive and repulsive components as Δνexp = ΔνA + ΔνR

(1)

where ΔνA and ΔνR are the attractive and repulsive shifts, respectively. The magnitudes of ΔνA and ΔνR represent the energies that the solvent molecules exert on the vibrational coordinates of the solute molecule. ΔνA is derived by subtracting ΔνR from Δνexp, and ΔνR is obtained by calculation using the hard-sphere model:69 ΔνR /ν0 = C1 exp(m1ρ*) + C2 exp(m2ρ*) − C3 exp(m3ρ*) (2)

where Ck = kαRθz(1 − z) exp(bk) and αR = re[−(3g/2f) + (GR/FR)], and mk and bk are empirical parameters related to the size of the solute and solvent molecules. The quantity ρ* is defined as ρ* = ρsσs3, where ρs is the number density and σs is the diameter of the solvent hard sphere. The quantity θ is given by θ = kBT/f re2, where kB is the Boltzmann constant and re is the equilibrium bond length of the CO bond. The value of z is z = re/σ with two hard-sphere cavities, each having a diameter of σ. The terms f and g are the intramolecular quadratic harmonic and cubic anharmonic force constants of the CO bond, and FR and GR are linear and quadratic constants, respectively, which indicate the forces that the solvent molecules exert on the normal coordinates of the solute. Thus, ΔνA and ΔνR for all the solute molecules were obtained k−1

Figure 6. Optimized configurations for methyl acetate and CO2. Red, gray, and white spheres represent oxygen, carbon, and hydrogen atoms, respectively.

esters in scCO2, where that for methyl acetate is the largest. Raman spectra for the three ketones in scCO2 have been previously measured,39 and their Δνexp values are shown in Figure 3b. Note that the magnitudes of Δνexp for the esters are always greater than those for the ketones. To investigate the attractive and repulsive energy components between solute and solvent molecules, Δνexp was analyzed using perturbed hard-sphere theory.69 According to 788


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Figure 9. Optimized structures for an ester (methyl acetate) and ketone (acetone) with 2, 4, 6, or 8 CO2 molecules obtained using the B3LYP/6-311+G(2d,p) level. Black and red dotted lines indicate the type I and II structures, respectively. Red, gray, and white spheres represent oxygen, carbon, and hydrogen atoms, respectively. Blue and green spheres represent oxygen and carbon atoms of CO2, respectively.

from eqs 1 and 2. All parameters used for calculations of the esters and ketones are listed in Table 1 and Table S1, respectively. Figure 4 shows the attractive shift (ΔνA) and repulsive shift (ΔνR) of all the solutes in scCO2, the values of which are listed in Table S2. ΔνR increases with density, and the magnitudes among the three esters are almost the same at the same density. ΔνA also increases with the density and is always higher than ΔνR over the entire range of density; i.e., the magnitude of ΔνA is up to 9 times higher than that of ΔνR. Thus, all of the esters and ketones dissolved in scCO2 are considered to correspond to an attractive mixture within the present experimental range. The magnitudes of ΔνA for all of the solutes are shown in Figure 5a. For the esters, the magnitude of ΔνA increases in the following order: phenyl benzoate ≈ methyl benzoate < methyl acetate. In contrast, the magnitude of ΔνA for the ketones is in the opposite order: acetone < acetophenone < benzophenone. Thus, the magnitude of ΔνA for the methyl groups is significantly different between the ketone and ester, whereas it becomes smaller for a single phenyl group and completely disappears for two phenyl groups, as shown in Figure 5b. To discuss the attractive energy difference for the six carbonyl compounds, the optimized configurations between the solute and solvent molecules were calculated based on density functional theory (B3LYP), using the Gaussian 2009 package.74 The results for methyl acetate and CO2 molecules as representative data are shown in Figure 6. All of the results for the other solutes with CO2 are shown in Figure 7. Two different structures were confirmed, which are expressed as type I and II; i.e., a CO2 molecule is present in the vicinity of a carbonyl oxygen atom (type I) or an ether oxygen atom (type

Figure 7. Optimized configurations between carbonyl compounds and CO2 obtained using the B3LYP/6-311+G(2d,p) level. Red, gray, and white spheres represent oxygen, carbon, and hydrogen atoms, respectively.

Figure 8. Interaction energies for type II structure esters calculated using the counterpoise method with basis set superposition error correction.76 Molecules are expressed by a space-filling model. Red, gray, and white spheres represent oxygen, carbon, and hydrogen atoms, respectively.

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three ketones involving the same functional groups. For all six solute molecules, the peak frequencies of the Raman spectra were commonly shifted to lower energy as the CO2 density increased. The amounts of shift were decomposed into attractive and repulsive energies using the perturbed hardsphere theory. The attractive energy differences among the six carbonyl compounds were discussed with respect to quantumchemical calculations of the optimized configurations between solute and CO2 molecules. From the experimental results, it was determined that (i) attractive energies are always greater than repulsive energies for all the six carbonyl compounds and (ii) esters exhibit greater attractive energy than ketones. The calculated results show that the esters can form type II structures, which are not observed for the ketones. In addition, (iii) the magnitude of the attractive energy for the esters is dependent on the functional group of the ester; i.e., a methyl group results in larger energy, while a phenyl group results in smaller energy. The phenyl group causes steric hindrance, which disturbs the type II structure, on the basis of the calculated results. These findings are expected to be useful for scCO2 utilization with various systems such as polymers, biomolecules, and pharmaceutical agents because carbonyl compounds are found everywhere in nature.

II). The optimized configurations for types I and II are obtained from the initial structures of CO2 located around carbonyl oxygen and ether oxygen atoms, respectively. Figure 7 shows that type I is observed for all the six carbonyl compounds; i.e., type I is characterized by the configuration where the carbon and oxygen atoms of CO2 are in the vicinity of nearest-neighbor carbonyl-oxygen and hydrogen atoms, respectively. On the other hand, the type II structure is only observed in esters; i.e., the type II structure is specific to esters and is characterized by the configuration where the carbon atom of CO2 is present around the ether oxygen. To investigate why the type II emerges only in esters, the interaction energy between ester and CO2 molecules was calculated based on the B3LYP level of theory using Gaussian 09. Here, the interaction energy is defined as the energy difference between the type II structure of an ester and a CO2 molecule and that of the isolated ester and CO2 molecule.75,76 Positive and negative interaction energies indicate unstable and stable type II structures, respectively, for this calculation. Figure 8 shows the calculated interaction energies for methyl acetate, methyl benzoate, and phenyl benzoate. All three esters have negative interaction energies. Accordingly, the type II structure observed with these three esters is established by the formation of stable interaction, i.e., negative energy. Next, the results calculated for the functional-group effect on type II esters are explained. As shown in Figure 8, the magnitude of interaction energy for type II structures is larger for the methyl group and smaller for the phenyl group. Considering the structure, the phenyl group becomes a steric hindrance to CO2 solvation at the ether oxygen, as shown in Figure 8. This steric hindrance causes the longer distance between CO2 and the ether oxygen and results in the smaller interaction energy of type II (Figure S2). Note that the magnitude of the experimentally obtained attractive shift is also smaller with a phenyl group in an ester, as shown in Figure 5. Finally, the optimized structures were examined by increasing the number of CO2 molecules around a solute molecule, based on density functional theory (B3LYP level). Figure 9 shows the structures of the ester or ketone together with 2, 4, 6, or 8 CO2 molecules. These results also indicate that the type II structure is only observed in esters; i.e., several CO2 molecules surround the ether oxygen. With respect to the number density, the Raman spectral measurements were conducted under the condition of 6.4 CO2 molecules nm−3 at ρr = 1.0. In these experiments and analyses, the attractive energy for an ester was greater than that for a ketone, as shown in Figure 5. The number densities of 2, 4, 6, or 8 CO2 molecules for the Raman measurements correspond to ρr = 0.3, 0.6, 0.9, and 1.2, respectively. The number density for the Raman measurements is in good agreement with that based on density functional theory. Therefore, the type II structure corresponds to characteristic structure for an ester that exhibits large attractive energy. It is thus concluded that the introduction of an ether oxygen into a carbonyl compound can produce a solvation site for CO2 molecules and is the reason for the emergence of the large attractive energy in scCO2.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcb.5b11740. Thermodynamic states for Raman spectral measurements, parameters for calculation, and interaction energy (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel & fax +81-82-424-7487; e-mail [email protected] (K.S.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS K.S. acknowledges Professor Yoshio Okamoto of Nagoya University, the research supervisor for the “Structure Control and Function” of PRESTO of the Japan Science and Technology agency (JST) for the construction of the present Raman spectroscopic system. This study was supported by a Grant-in-Aid for Young Scientists (A) (16685001), a Grant-inAid for Scientific Research (B) (21350015) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan, and the Funding Program for Next Generation World-Leading Researchers (GR073) of the Japan Society for the Promotion of Science (JSPS).

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REFERENCES

(1) Eckert, C. A.; Knutson, B. L.; Debenedetti, P. G. Supercritical Fluids as Solvents for Chemical and Materials Processing. Nature 1996, 383, 313−318. (2) Special Issue on Supercritical Fluids; Noyori, R., Ed.; Chem. Rev. 1999, 99 (2), 353.10.1021/cr980085a. (3) Supercritical Fluids: Fundamentals and Applications; NATO ASI Series E; Kiran, E., Debenedetti, P. G., Peters, C. J., Eds.; Springer: Netherlands, 2000; Vol. 366.

CONCLUSIONS Vibrational Raman spectra for the CO stretching modes of three esters with different functional groups, i.e., methyl, a single phenyl, and two phenyl groups, were measured in scCO2 along the isotherm Tr = 1.02 within the density range ρr = 0.08−1.6. The results obtained were compared to those for the 790


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The Journal of Physical Chemistry B (4) Supercritical Fluids: Molecular Interactions, Physical Properties, and New Applications; Arai, Y., Sako, T., Takebayashi, Y., Eds.; Springer: Berlin, 2002. (5) Poliakoff, M.; Howdle, S. M.; Kazarian, S. G. Vibrational Spectroscopy in Supercritical Fluids: From Analysis and Hydrogen Bonding to Polymers and Synthesis. Angew. Chem., Int. Ed. Engl. 1995, 34, 1275−1295. (6) Cooper, A. I. Polymer Synthesis and Processing Using Supercritical Carbon Dioxide. J. Mater. Chem. 2000, 10, 207−234. (7) Hasell, T.; Armstrong, J. A.; Jelfs, K. E.; Tay, F. H.; Thomas, K. M.; Kazarian, S. G.; Cooper, A. I. High-pressure Carbon Dioxide Uptake for Porous Organic Cages: Comparison of Spectroscopic and Manometric Measurement Techniques. Chem. Commun. 2013, 49, 9410−9412. (8) Sheldon, R. A. Green Solvents for Sustainable Organic Synthesis: State of the Art. Green Chem. 2005, 7, 267−278. (9) Han, X.; Bourne, R. A.; Poliakoff, M.; George, M. W. Immobilised Photosensitisers for Continuous Flow Reactions of Singlet Oxygen in Supercritical Carbon Dioxide. Chem. Sci. 2011, 2, 1059−1067. (10) Chamberlain, T. W.; Earley, J. H.; Anderson, D. P.; Khlobystov, A. N.; Bourne, R. A. Catalytic Nanoreactors in Continuous Flow: Hydrogenation Inside Single-walled Carbon Nanotubes Using Supercritical CO2. Chem. Commun. 2014, 50, 5200−5202. (11) Earley, J. H.; Bourne, R. A.; Watson, M. J.; Poliakoff, M. Continuous Catalytic Upgrading of Ethanol to n-butanol and > C4 Products over Cu/CeO2 Catalysts in Supercritical CO2. Green Chem. 2015, 17, 3018−3025. (12) Zhang, J.; Han, B. Supercritical or Compressed CO2 as a Stimulus for Tuning Surfactant Aggregations. Acc. Chem. Res. 2013, 46, 425−433. (13) Liu, Z.; Han, B. Synthesis of Carbon-Nanotube Composites Using Supercritical Fluids and Their Potential Applications. Adv. Mater. 2009, 21, 825−829. (14) Caballero, A.; Ayoub, E. D.; Requejo, M. M. D.; Rodríguez, A. D.; Núñez, M. E. G.; Mello, R.; Muñoz, B. K.; Ojo, W. S.; Asensio, G.; Etienne, M.; Pérez, P. J. Silver-Catalyzed C-C Bond Formation Between Methane and Ethyl Diazoacetate in Supercritical CO2. Science 2011, 332, 835−838. (15) Jennings, J.; Beija, M.; Richez, A. P.; Cooper, S. D.; Mignot, P. E.; Thurecht, K. J.; Jack, K. S.; Howdle, S. M. One-Pot Synthesis of Block Copolymers in Supercritical Carbon Dioxide: A Simple Versatile Route to Nanostructured Microparticles. J. Am. Chem. Soc. 2012, 134, 4772−4781. (16) Totten, R. K.; Kim, Y.-S.; Weston, M. H.; Farha, O. K.; Hupp, J. T.; Nguyen, S. T. Enhanced Catalytic Activity through the Tuning of Micropore Environment and Supercritical CO2 Processing: Al(Porphyrin)-Based Porous Organic Polymers for the Degradation of a Nerve Agent Simulant. J. Am. Chem. Soc. 2013, 135, 11720−11723. (17) Totten, R. K.; Olenick, L. L.; Kim, Y.-S.; Chakraborty, S.; Weston, M. H.; Farha, O. K.; Hupp, J. T.; Nguyen, S. T. A Dual Approach to Tuning the Porosity of Porous Organic Polymers: Controlling the Porogen Size and Supercritical CO2 Processing. Chem. Sci. 2014, 5, 782−787. (18) Cormier, P. J.; Clarke, R. M.; McFadden, R. M. L.; Ghandi, K. Selective Free Radical Reactions Using Supercritical Carbon Dioxide. J. Am. Chem. Soc. 2014, 136, 2200−2203. (19) Couto, R.; Chambon, S.; Aymonier, C.; Mignard, E.; Pavageau, B.; Erriguible, A.; Marre, S. Microfluidic Supercritical Antisolvent Continuous Processing and Direct Spray-coating of Poly(3-hexylthiophene) Nanoparticles for OFET Devices. Chem. Commun. 2015, 51, 1008−1011. (20) Grützke, M.; Mönnighoff, X.; Horsthemke, F.; Kraft, V.; Winter, M.; Nowak, S. Extraction of Lithium-ion Battery Electrolytes with Liquid and Supercritical Carbon Dioxide and Additional Solvents. RSC Adv. 2015, 5, 43209−43217. (21) Yan, T.; Xu, J.; Wang, L.; Liu, Y.; Yang, C.; Fang, T. A Review of Upgrading Heavy Oils with Supercritical Fluids. RSC Adv. 2015, 5, 75129−75140.

(22) DeSimone, J. M.; Guan, Z.; Elsbernd, C. S. Synthesis of Fluoropolymers in Supercritical Carbon Dioxide. Science 1992, 257, 945−947. (23) Sarbu, T.; Styranec, T.; Beckman, E. J. Non-fluorous Polymers with Very High Solubility in Supercritical CO2 Down to Low Pressures. Nature 2000, 405, 165−168. (24) Girard, E.; Tassaing, T.; Camy, S.; Condoret, J. S.; Marty, J. D.; Destarac, M. Enhancement of Poly(vinyl ester) Solubility in Supercritical CO2 by Partial Fluorination: The Key Role of Polymer−Polymer Interactions. J. Am. Chem. Soc. 2012, 134, 11920−11923. (25) Hyatt, J. A. Liquid and Supercritical Carbon Dioxide as Organic Solvents. J. Org. Chem. 1984, 49, 5097−5101. (26) Beckman, E. J. A Challenge for Green Chemistry: Designing Molecules That Readily Dissolve in Carbon Dioxide. Chem. Commun. 2004, 1885−1888. (27) Fink, R.; Hancu, D.; Valentine, R.; Beckman, E. J. Toward the Development of “CO2-philic” Hydrocarbons. 1. Use of Side-Chain Functionalization to Lower the Miscibility Pressure of Polydimethylsiloxanes in CO2. J. Phys. Chem. B 1999, 103, 6441−6444. (28) Akimoto, S.; Kajimoto, O. Solvent-induced Shift of the Raman Spectra in Supercritical Fluids. Chem. Phys. Lett. 1993, 209, 263−268. (29) Kazarian, S. G.; Vincent, M. F.; Bright, F. V.; Liotta, C. L.; Eckert, C. A. Specific Intermolecular Interaction of Carbon Dioxide with Polymers. J. Am. Chem. Soc. 1996, 118, 1729−1736. (30) Raveendran, P.; Wallen, S. L. Sugar Acetates as Novel, Renewable CO2-philes. J. Am. Chem. Soc. 2002, 124, 7274−7275. (31) Blatchford, M. A.; Raveendran, P.; Wallen, S. L. Raman Spectroscopic Evidence for Cooperative C−H···O Interactions in the Acetaldehyde−CO2 Complex. J. Am. Chem. Soc. 2002, 124, 14818− 14819. (32) Raveendran, P.; Wallen, S. L. Cooperative C−H···O Hydrogen Bonding in CO2−Lewis Base Complexes: Implications for Solvation in Supercritical CO2. J. Am. Chem. Soc. 2002, 124, 12590−12599. (33) Kilic, S.; Michalik, S.; Wang, Y.; Johnson, J. K.; Enick, R. M.; Beckman, E. J. Effect of Grafted Lewis Base Groups on the Phase Behavior of Model Poly(dimethyl siloxanes) in CO2. Ind. Eng. Chem. Res. 2003, 42, 6415−6424. (34) Danten, Y.; Tassaing, T.; Besnard, M. Vibrational Spectra of CO2-Electron Donor−Acceptor Complexes from Ab Initio. J. Phys. Chem. A 2002, 106, 11831−11840. (35) Cabaco, M. I.; Danten, Y.; Tassaing, T.; Longelin, S.; Besnard, M. Raman Spectroscopy of CO2−acetone and CO2−ethanol Complexes. Chem. Phys. Lett. 2005, 413, 258−262. (36) Altarsha, M.; Ingrosso, F.; Ruiz-Lopez, M. F. A New Glimpse into the CO2-Philicity of Carbonyl Compounds. ChemPhysChem 2012, 13, 3397−3403. (37) Altarsha, M.; Ingrosso, F.; Ruiz-Lopez, M. F. Cavity Closure Dynamics of Peracetylated β-Cyclodextrins in Supercritical Carbon Dioxide. J. Phys. Chem. B 2012, 116, 3982−3990. (38) San-Fabian, E.; Ingrosso, F.; Lambert, A.; Bernal-Uruchurtu, M. I.; Ruiz-Lopez, M. F. Theoretical Insights on Electron Donor− acceptor Interactions Involving Carbon Dioxide. Chem. Phys. Lett. 2014, 601, 98−102. (39) Kajiya, D.; Saitow, K. Investigation of Attractive and Repulsive Interactions Associated with Ketones in Supercritical CO2, Based on Raman Spectroscopy and Theoretical Calculations. J. Chem. Phys. 2013, 139, 054509. (40) Saitow, K.; Ochiai, H.; Kato, T.; Nishikawa, K. Correlation Time of Density Fluctuation for Supercritical Ethylene Studied by Dynamic Light Scattering. J. Chem. Phys. 2002, 116, 4985. (41) Saitow, K.; Kajiya, D.; Nishikawa, K. Dynamics of Density Fluctuation of Supercritical Fluid Mapped on Phase Diagram. J. Am. Chem. Soc. 2004, 126, 422−423. (42) Saitow, K.; Kajiya, D.; Nishikawa, K. Time Evolution of Density Fluctuation in Supercritical Region. I. Non-hydrogen-bonded Fluids Studied by Dynamic Light Scattering. J. Phys. Chem. A 2005, 109, 83− 91. 791


Article

The Journal of Physical Chemistry B (43) Kajiya, D.; Nishikawa, K.; Saitow, K. Time Evolution of Density Fluctuation in the Supercritical Region. 2. Comparison of Hydrogenand Non-hydrogen-Bonded Fluids. J. Phys. Chem. A 2005, 109, 7365− 7370. (44) Saitow, K.; Nishikawa, K.; Ohtake, H.; Sarukura, N.; Miyagi, H.; Shimokawa, Y.; Matsuo, H.; Tominaga, K. Supercritical-fluid Cell with Device of Variable Optical Path Length Giving Fringe-free Terahertz Spectra. Rev. Sci. Instrum. 2000, 71, 4061−4064. (45) Saitow, K.; Ohtake, H.; Sarukura, N.; Nishikawa, K. Terahertz Absorption Spectra of Supercritical CHF3 to Investigate Local Structure Through Rotational and Hindered Rotational Motions. Chem. Phys. Lett. 2001, 341, 86−92. (46) Nakayama, H.; Saitow, K.; Sakashita, M.; Ishii, K.; Nishikawa, K. Raman Spectral Changes of Neat CO2 Across the Ridge of Density Fluctuation in Supercritical Region. Chem. Phys. Lett. 2000, 320, 323− 327. (47) Saitow, K.; Otake, K.; Nakayama, H.; Ishii, K.; Nishikawa, K. Local Density Enhancement in Neat Supercritical Fluid due to Attractive Intermolecular Interaction. Chem. Phys. Lett. 2003, 368, 209−214. (48) Saitow, K.; Nakayama, H.; Ishii, K.; Nishikawa, K. Attractive and Repulsive Intermolecular Interactions of a Polar Molecule: ShortRange Structure of Neat Supercritical CHF3 Investigated by Raman Spectroscopy. J. Phys. Chem. A 2004, 108, 5770−5784. (49) Otake, K.; Abe, M.; Nishikawa, K.; Saitow, K. Development of a Polarized Raman Spectrometer for Supercritical Fluids Having High Critical Points. Jpn. J. Appl. Phys. 2006, 45, 2801−2806. (50) Saitow, K.; Sasaki, J. Attractive and Repulsive Interactions Among Methanol Molecules in Supercritical State Investigated by Raman Spectroscopy and Perturbed Hard-sphere Theory. J. Chem. Phys. 2005, 122, 104502. (51) Kajiya, D.; Saitow, K. Solute−Solvent Intermolecular Interactions in Supercritical Xe, SF6, CO2, and CHF3 Investigated by Raman Spectroscopy: Greatest Attractive Energy Observed in Supercritical Xe. J. Phys. Chem. B 2010, 114, 8659−8666. (52) Kajiya, D.; Mouri, Y.; Saitow, K. Difference of Solute−Solvent Interactions of cis- and trans-1,2-Dichloroethylene in Supercritical CO2 Investigated by Raman Spectroscopy. J. Phys. Chem. B 2008, 112, 7980−7983. (53) Kajiya, D.; Saitow, K. Solvation Structures of cis- and trans-1,2Dichloroethylene in Supercritical CO2 Investigated by Raman Spectroscopy and Attractive Energy Calculations. J. Phys. Chem. B 2009, 113, 13291−13299. (54) Kajiya, D.; Saitow, K. Site-Selective Solvation in Supercritical CO2 Observed by Raman Spectroscopy: Phenyl Group Leads to Greater Attractive Energy than Chloro Group. J. Phys. Chem. B 2010, 114, 16832−16837. (55) Kajiya, D.; Saitow, K. Significant Substitution Effects in Dipolar and Non-dipolar Supercritical Fluids. J. Chem. Phys. 2011, 134, 234508. (56) Saitow, K. Silicon Nanoclusters Selectively Generated by Laser Ablation in Supercritical Fluid. J. Phys. Chem. B 2005, 109, 3731− 3733. (57) Saitow, K.; Yamamura, T.; Minami, T. Gold Nanospheres and Nanonecklaces Generated by Laser Ablation in Supercritical Fluid. J. Phys. Chem. C 2008, 112, 18340−18349. (58) Saitow, K.; Yamamura, T. Effective Cooling Generates Efficient Emission: Blue, Green, and Red Light-Emitting Si Nanocrystals. J. Phys. Chem. C 2009, 113, 8465−8470. (59) Saitow, K. In Laser Ablation in Liquids: Principles and Applications in the Preparation of Nanomaterials; Yang, G. W., Ed.; Pan Stanford: Singapore, 2012; Vol. 573, Chapter 12. (60) Wei, S.; Yamamura, T.; Kajiya, D.; Saitow, K. White-LightEmitting Silicon Nanocrystal Generated by Pulsed Laser Ablation in Supercritical Fluid: Investigation of Spectral Components As a Function of Excitation Wavelengths and Aging Time. J. Phys. Chem. C 2012, 116, 3928−3934.

(61) Wei, S.; Saitow, K. In Situ Multipurpose Time-resolved Spectrometer for Monitoring Nanoparticle Generation in a Highpressure Fluid. Rev. Sci. Instrum. 2012, 83, 073110. (62) Saitow, K.; Okamoto, Y.; Yano, Y. F. Fractal of Gold Nanoparticles Controlled by Ambient Dielectricity: Synthesis by Laser Ablation as a Function of Permittivity. J. Phys. Chem. C 2012, 116, 17252−17258. (63) Tamamitsu, H.; Saitow, K. Local Enhancement Effect in the Photoluminescence Intensity of Si Quantum Dots: Single Medusatype Particles Investigated by in situ Microscope Spectrometer. Chem. Phys. Lett. 2014, 591, 37−42. (64) Span, R.; Wagner, W. A New Equation of State for Carbon Dioxide Covering the Fluid Region from the Triple-Point Temperature to 1100 K at Pressures up to 800 MPa. J. Phys. Chem. Ref. Data 1996, 25, 1509−1596. (65) Dybal, J.; Krimm, S. Dipole Derivatives and Infrared Intensities of the Ester Group. An Ab Initio and Force Field Study of Methyl Acetate. J. Mol. Struct. 1988, 189, 383−392. (66) Sundaraganesan, N.; Joshua, B. D. Vibrational Spectra and Fundamental Structural Assignments from HF and DFT Calculations of Methyl Benzoate. Spectrochim. Acta, Part A 2007, 68, 771−777. (67) Wrzalik, R.; Merkel, K.; Kocot, A. Ab Initio Study of Phenyl Benzoate: Structure, Conformational Analysis, Dipole Moment, IR and Raman Vibrational Spectra. J. Mol. Model. 2003, 9, 248−258. (68) ν0 is the frequency obtained by extrapolation of the peak frequencies to zero density. (69) Zakin, M. R.; Herschbach, D. R. Vibrational Frequency Shifts Induced by Molecular Compression of Pyridine in Solution. J. Chem. Phys. 1986, 85, 2376−2383. (70) Boerio, F. J.; Bahl, S. K. Vibrational Analysis of Aromatic Esters. Spectrochimica Acta A 1976, 32, 987−1006. (71) Herschbach, D. R.; Laurie, V. W. Anharmonic Potential Constants and Their Dependence upon Bond Length. J. Chem. Phys. 1961, 35, 458−463. (72) Edward, J. T. Molecular volumes and the Stokes-Einstein equation. J. Chem. Educ. 1970, 47, 261−270. (73) Pyckhout, W.; Van Alsenoy, C.; Geise, H. J. Structure of Gaseous Methyl Acetate as Determined by Joint Analysis of Electron Diffraction, Microwave and Infrared Spectroscopy, Supplemented by a Valence Force Field and Constraints from Geometry Relaxed Ab Initio Calculations. J. Mol. Struct. 1986, 144, 265−279. (74) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; et al. GAUSSIAN 09, Revision B.01; Gaussian Inc.: Wallingford, CT, 2010. (75) The calculated energy to obtain the interaction energy is the sum of the electron kinetic energy, the potential energy between electrons and the nucleus, the electron repulsion energy, and the nuclear repulsion energy. (76) Boys, S. F.; Bernardi, F. The Calculation of Small Molecular Interactions by The Differences of Separate Total Energies. Some Procedures with Reduced Errors. Mol. Phys. 1970, 19, 553−566.

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Solvation of Esters and Ketones in Supercritical CO2 - The Journal of

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