Solubilities of amide compounds in supercritical carbon dioxide

Article abstract of DOI:10.1021/je800434j

2,2′-Oxybis(N,N-diethylacetamide), 2,2′-oxybis(N,N- dibutylacetamide), and 2,2′-oxybis(N,N-dihexylacetamide) were synthesized, and their structures were confirmed by IR, NMR, and elemental analysis. The solubilities of compounds were measured at temperatures ranging from (313 to 333) K and pressures from (8.7 to 16.4) MPa in supercritical carbon dioxide. The measured solubilities were correlated using a semiempirical model. The calculated results showed satisfactory agreement with the experimental data and differed from the measured values by between (4.54 and 30.84) %.

Full text of DOI:10.1021/je800434j

J. Chem. Eng. Data 2008, 53, 2189–2192
2189
Solubilities of Amide Compounds in Supercritical Carbon Dioxide
Jiang-Fan Liu,† Hai-Jian Yang,*,† Wei Wang,† and Zhongxiao Li*,‡
Key Laboratory of Analytical Chemistry of the State Ethnic Affairs Commission, College of Chemistry and Materials Science,
South-Central University for Nationalities, Wuhan, 430074, P. R. China, and Beijing Key Laboratory of Printing & Packaging
Material and Technology, Beijing Institute of Graphic Communication, Beijing 102600, P. R. China
2,2′-Oxybis(N,N-diethylacetamide), 2,2′-oxybis(N,N-dibutylacetamide), and 2,2′-oxybis(N,N-dihexylaceta-
mide) were synthesized, and their structures were confirmed by IR, NMR, and elemental analysis. The
solubilities of compounds were measured at temperatures ranging from (313 to 333) K and pressures from
(8.7 to 16.4) MPa in supercritical carbon dioxide. The measured solubilities were correlated using a
semiempirical model. The calculated results showed satisfactory agreement with the experimental data and
differed from the measured values by between (4.54 and 30.84) %.
determined, and the measured solubilities were also correlated using
a semiempirical model.
Introduction
In recent years, supercritical carbon dioxide (SC-CO2) has
attracted a tremendous amount of attention as a “green” solvent
because it is inexpensive, nontoxic, nonflammable, and recyclable
and has moderate critical constants (T ) 31.06 °C and Pc ) 7.38
MPa).1,2 The properties of SC-CO2 are between liquid and gas
and have much higher diffusivity and lower viscosity than that of
liquid and much stronger solvent power than gas. However, their
practical use has been limited by the need for high CO2 pressure
to dissolve even small amounts of polar, amphiphilic, organome-
tallic, or high-molecular-mass compounds.3,4 So-called “CO2-
philes” can efficiently transport insoluble or poorly soluble materials
into CO2 solvents. As the most of effective CO2-philes are
expensive fluorocarbons, the commercialization of promising CO2-
based processes has only limited success.5
Experimental Section
Chemicals and Apparatus. Diglycolic acid, diethylamine,
dibutylamine, and dihexylamine were purchased from Aldrich
Chem. Co. and used as received without further purification.
Dichlorosulfoxide (SOCl2) was freshly distilled before use. Dichlo-
romethane (CH2Cl2) was distilled over calcium hydride under
argon. 99.99 % purity CO2 was bought from Wuhan Steel Co.
NMR spectra were recorded on a JEOL Al-300 MHz instrument
at ambient temperature using TMS as an internal standard. IR
spectra were measured on a Perkin-Elmer 2000 FT-IR spectrom-
eter. Elemental analysis was performed by using a PE 2400 series
II CHNS/O elemental analyzer. Apparatuses of supercritical carbon
dioxide were bought from JASCO Corporation (Japan): “PU-1580-
CO2”; “CO2 Delivery Pump”; “PU-2080 Plus”; intelligent HPLC
Pump and “BP-1580-81” Back Pressure Regulator.
According to the literature,5-9 hydrocarbons substituted with
carbonyl groups as CO2-philes have appeared economically. In
SC-CO2, the high solubility of these carbonyl systems was
attributed to the electron-donating carbonyl group promoting
Lewis acid-Lewis base interactions with the carbon of CO2
that could promote CO2 solubility.4,5 Ab initio calculations on
simple carbonyl systems revealed that the high degree of
miscibility, melting point depression, and liquid swelling was
attributed to a two-point interaction of the methyl acetate with
CO2, including the Lewis acid-Lewis base interaction and a
weak cooperative hydrogen bond between a proton on the
methyl group and an oxygen of the CO2.5 The high CO2
solubility of hydrocarbons containing acetamide groups was
attributed to the accessibility of the carbonyl functionality to
form a weak complex with CO2.
General Procedure for the Synthesis of Compounds 1 to
3. Three compounds were synthesized according to the methods
shown in Scheme 1.
Diglycolic acid (2.0 g, 0.015 mol) was dissolved in SOCl2
(40 mL, 0.55 mol) and refluxed for 8 h under nitrogen
protection. After being cooled to room temperature, the excess
of SOCl2 was distilled under reduced pressure, and then a
CH2Cl2 solution (20 mL) of dialkyl amine (0.045 mol) was
added dropwise to the reaction system under nitrogen. The
mixture was stirred at room temperature for a whole night. The
reaction mixture was washed with 1 % HCl aq., saturated
NaHCO3 aq., and then twice with water, and the organic phase
was collected and dried over anhydrous Na2SO4. After evapora-
tion under vacuum, the residue was purified by silica gel column
chromatography with petroleum ether/ethyl acetate (1:3 to 1:6)
to get a yellow oil liquid.
Compounds 1: 2,2′-Oxybis(N,N-diethylacetamide). Yield:
82%. IR (KBr) υN-CdO: 1647.4 cm-1. 1H NMR (CDCl3): δ )
4.31 (s, 4H, CH2CdO), 3.28-3.41 (q, 8H, CH2-N), 1.118-1.195
(t, J ) 6.8, 12H, CH3). 13C NMR (CDCl3): δ ) 167.83, 69.21,
40.94, 12.70. Elemental Anal.: C12H20N2O3. Found: C, 59.96;
H, 8.42; N, 11.70; O, 19.96 %. Required: C, 59.98; H, 8.39; N,
11.66; O, 19.97 %.
According to the literature and based on our research results,1,6
the carbonyl group, ether group, and alky group with suitable length
are so-called CO2-philic groups, so in this work, we have designed
and synthesized three new CO2-philic compounds starting from
diglycolic acid, which contains a carbonyl functional group and
ether group, via a simple procedure with high yield. The solubilities
of compounds in SC-CO2 over the pressure range of (8.7 to 16.4)
MPa and at temperatures of (313, 323, and 333) K were
* Corresponding author. Email: yanghaijian@vip.sina.com.
† South-Central University for Nationalities.
‡ Beijing Institute of Graphic Communication.
10.1021/je800434j CCC: $40.75
2008 American Chemical Society
Published on Web 08/21/2008

2190 Journal of Chemical & Engineering Data, Vol. 53, No. 9, 2008
Scheme 1. Synthesis of CO2-Philic Compounds 1 to 3
Anal: C28H56N2O3. Found: C, 71.75; H, 12.03; N, 5.61; O, 10.31
%. Required: C, 71.74; H, 12.04; N, 5.98; O, 10.24 %.
Solubility Test. Solubility measurement was carried out in a
stainless steel view cell (7.11 mL) with two sapphire windows,
which permitted visual observation of the phase behavior.6,7
A
suitable amount of solute was charged into the high-pressure view
cell, and the stainless steel cell was then sealed. The compounds
in the cell were stirred by a magnetic stir bar, and the temperature
was controlled using a temperature controller jacket with a
circulator. A “BP-1580-81” back pressure regulator was used to
keep a stable and accurate pressure. Carbon dioxide was poured
and heated to the experimental temperature. The fluid was stirred
at a fixed pressure to obtain almost an equilibrium state. Stirring
was stopped for observation. The pressure was increased gradually
(2 mL ·min-1) until the compound disappeared and the fluid in
the cell became transparent single phase: this pressure was defined
as dissolution pressure. At each condition, the experiment was
repeated at least three times. The dissolution pressure and tem-
perature were recorded to obtain the density of CO2 in terms of
IUPAC international thermodynamic tables.8-10 The uncertainty
of the dissolution pressure and temperature was ( 0.5 MPa and
( 0.1 °C, respectively.11-13
Results and Discussion
The solubilities of 2,2′-oxybis(N,N-diethylacetamide), 2,2′-
oxybis(N,N-dibutylacetamide), and 2,2′-oxybis(N,N-dihexylac-
etamide) in supercritical CO2 were studied at different conditions
of pressures (8.2 MPa∼16.4 MPa) and temperatures (313 K,
323 K, and 333 K). The resulting solubilities in terms of mole
fraction, x, of the solute were shown in Table 1. Each reported
data point was the average of at least three replicate samples. The
Figure 1. Comparison of solubility experiment and calculated value for
compounds 1 to 3 in supercritical CO2 at: b,O, 313 K; 2,4, 323 K; and
9,0, 333 K. (a) 2,2′-Oxybis(N,N-diethylacetamide) (compound 1). (b) 2,2′-
Oxybis(N,N-dibutylacetamide) (compound 2). (c) 2,2′-Oxybis(N,N-dihexy-
lacetamide) (compound 3). b,2,9, exptl; O,4,0, calcd. Lines represent
correlation by eq 1.
Compounds 2: 2,2′-Oxybis(N,N-dibutylacetamide). Yield:
78%. IR (KBr) υN-CdO: 1648.5 cm-1. 1H NMR (CDCl3): δ )
4.30 (s, 4H, CH2CdO), 3.174-3.331 (t, J ) 8, 8H, CH2-N),
1.26-1.33 (m, 8H, CH2), 1.48-1.55 (m, 8H, CH2), 0.90-0.95
(t, J ) 4.4, 12H, CH3). 13C NMR (CDCl3): δ ) 168.28, 68.94,
46.50, 30.85, 20.01, 13.60. Elemental Anal.: C20H40N2O3.
Found: C, 67.34; H, 11.33; N, 7.90; O, 13.46 %. Required: C,
67.37; H, 11.31; N, 7.86; O, 13.46 %.
Compounds 3: 2,2′-Oxybis(N,N-dihexylacetamide). Yield:
70%. IR (KBr) υN-CdO: 1644.7 cm-1. 1H NMR (CDCl3): 4.30
(s, 4H, CH2CdO), 3.16-3.31 (t, J ) 7.6, 8H, CH2-N),
1.52-1.53 (m, 8H, CH2), 1.29 (m, 24H, CH2), 0.86-0.90 (t, J
) 6.8, 12H, CH3). 13C NMR (CDCl3): δ ) 168.39, 69.04, 46.86,
31.42-31.49, 28.83, 26.50-26.58, 22.46, 13.89. Elemental
Figure 2. Solubility comparison of compounds 1 to 3 in supercritical CO2
at 313 K: b, 2,2′-oxybis(N,N-diethylacetamide) (compound 1); 2, 2,2′-
oxybis(N,N-dibutylacetamide) (compound 2); 9, 2,2′-oxybis(N,N-dihexy-
lacetamide) (compound 3).

Journal of Chemical & Engineering Data, Vol. 53, No. 9, 2008 2191
Table 1. Solubility at Temperature T, Density G, and Mole Fraction
x for Compounds 1 to 3
compound 1
P
F
AAD
%
MPa
kg ·m-3
103x
103xcalcd
T ) 313 K
2.23
3.46
6.13
8.76
11.23
8.7
8.8
9.0
9.1
9.2
407.11
436.05
492.75
517.19
538.22
2.07
2.97
5.99
8.11
10.50
6.98
14.38
2.23
7.47
6.49
T ) 323 K
2.27
3.56
6.39
8.96
11.71
10.1
10.3
10.7
11.0
11.1
398.91
423.74
472.58
505.69
515.81
3.36
4.53
8.15
12.11
13.66
47.90
27.04
27.46
35.16
16.65
T ) 333 K
2.37
3.73
6.69
9.30
11.49
11.3
11.6
12.2
12.7
13.3
381.93
405.21
451.44
487.42
525.64
2.14
2.81
4.83
7.35
11.45
9.84
24.67
27.87
20.94
0.38
compound 2
P
F
AAD
%
MPa
kg ·m-3
103x
103xcalcd
T ) 313 K
1.52
2.37
5.12
6.97
8.8
8.9
9.1
9.2
9.3
436.05
465.37
517.19
538.22
556.08
1.37
2.12
4.52
6.15
7.96
9.52
10.81
11.68
11.85
0.28
7.94
T ) 323 K
1.56
2.40
5.56
6.30
10.3
10.6
11.1
11.2
11.4
423.74
460.74
515.81
525.44
543.31
1.42
2.41
5.29
6.06
7.80
9.20
0.63
4.98
3.85
4.06
8.12
T ) 333 K
1.67
2.58
4.73
6.79
11.5
11.9
12.4
12.7
13.1
397.42
428.55
466.23
487.42
513.54
2.06
3.19
5.40
7.26
10.45
23.73
23.77
14.12
6.94
8.60
21.52
compound 3
P
F
AAD
%
kg ·m-3
103x
103xcalcd
Figure 3. Plots of ln(xP/Pref) vs (F - Fref)/kg·m-3 for compounds at various
temperatures. (a) 2,2′-Oxybis(N,N-diethylacetamide) (compound 1). (b) 2,2′-
Oxybis(N,N-dibutylacetamide) (compound 2). (c) 2,2′-Oxybis(N,N-dihexy-
lacetamide) (compound 3). b, 313 K; 2, 323 K; 9, 333 K.
MPa
T ) 313 K
1.06
1.52
2.79
4.01
9.0
9.4
9.9
10.3
10.5
492.75
571.33
624.05
651.49
662.60
1.24
2.33
3.50
4.26
4.60
16.39
53.06
25.27
6.27
5.26
12.45
mole fractions of the solutes were reproducible within ( 5 %. As
shown in Figure 1 and Figure 2, the solubilities of all three
compounds increased with the increase of pressure at the same
temperature, and at the same pressure, the solubilities decreased
with the increase of temperature and molecular weight.
T ) 323 K
1.17
1.76
2.91
4.22
10.5
10.9
12.2
12.6
13.8
448.59
495.10
599.03
620.03
667.36
0.99
1.43
3.13
3.64
5.00
15.09
18.99
7.66
13.72
4.21
The experimental solubility data for the three compounds
5.22
1 to 3 were correlated using the following equation14-17
T ) 333 K
1.24
1.79
3.12
4.26
11.8
12.7
13.9
15.2
16.4
420.80
487.42
558.17
612.88
650.25
0.98
1.62
2.74
4.02
5.15
20.99
9.17
12.33
5.77
ln(xP ⁄ Pref) ) A + C(F - Fref)
A ) a + b ⁄ T
(1)
(2)
where
5.36
3.96
where x was the mole fraction of the solutes; P was the pressure;
Pref was 0.1 MPa; F was the density of pure CO2 at the
ln(xP/Pref) versus density for compounds (Figure 3) and fitting
the plots to a straight line by least-squares regression to obtain
the A and C parameters. The values of C, obtained from the
experimental temperature and pressure; Fref was 700 kg ·m-3
;
and A, C, a, and b were constants. The first step was plots of

2192 Journal of Chemical & Engineering Data, Vol. 53, No. 9, 2008
Table 2. Solubility Constants a, b, and C Obtained from the Data
Correlation Procedure
semiempirical model, and good agreement was obtained between
the correlated results and the experimental data. This work might
provide basic information for designing and synthesizing new
low-cost, nonfluorous CO2-philic compounds.
compounds
a
b/K
C/m3 ·kg-1
2,2′-oxybis(N,N-diethylacetamide) 12.58336 -3258.49 0.012807
2,2′-oxybis(N,N-dibutylacetamide) 22.61084 -6518.76 0.015079
2,2′-oxybis(N,N-dihexylacetamide) 10.63849 -3458.75 0.008657
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calculated data and the experimental data were compared
(Figure 1). Finally, the average absolute relative deviation
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(3)
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Received for review June 17, 2008. Accepted July 20, 2008. We are
grateful to the National Natural Science Fundation of China (No.
20607031) and “Youth Chen-Guang Project” of Wuhan Bureau of
Science and Technology (20065004116-34) for financial support. The
project was also sponsored by SRF for ROCS, SEM (2006-331), and
Beijing Key Laboratory of Printing
Technology (KF060102).
& Packaging Material and
Figure 4. Plots of A vs 1/T for compounds 1 to 3: b, 2,2′-oxybis(N,N-
diethylacetamide) (compound 1); 2, 2,2′-oxybis(N,N-dibutylacetamide)
(compound 2); 9, 2,2′-oxybis(N,N-dihexylacetamide) (compound 3).
JE800434J