CHEMSUSCHEM
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ate species in alcohol solvents. In particular, we have shown
that the presence of a carboxylate group on the anion of
TMAAs assists the activation of alcohols to alkylcarbonate
ethylamino)propanoate, 3, were synthesized by using the same
procedure as 1.
1
2
: Melting point, 2108C. H NMR (400 MHz, D O, 298 K): d=2.25 (t,
2
2
H, CH ÀCO ), 2.37 (t, 4H, 2CH ÀN), 2.69 (t, 2H, CH ÀCH ÀCO ),
2
2
2
13
2
2
2
anions during CO absorption in alcoholic solution of TMAAs.
2
+
3
.09 ppm (s, 12H, 4CH ÀN ). C NMR (400 MHz, D O, 298 K):
3
2
d=33.57 (CH ÀCO ), 49.61 (CH ÀN), 52.59 (CH ÀCH ÀCO ), 55.22
2
2
2
2
2
2
+
(
3
2
4CH ÀN ), 181.63 ppm (CO ).
3
2
1
Experimental Section
: Melting point, 1528C. H NMR (400 MHz, D O, 298 K): d=2.26 (t,
2
H, CH ÀCO ), 2.60 (t, 2H, CH ÀCH ÀNH) 2.68 (t, 2H, CH ÀCH ÀCO )
2
2
2
+
2
13
2
2
2
General
3
.08 ppm (s, 12H, 4CH ÀN ). C NMR (400 MHz, D O, 298 K)
3
2
Methyl acrylate, Me NOH solution in water (25 wt%) and amines
d=37.13 (2CH
2
ÀN), 46.68 (CH
2
ÀNH), 50.80 (2CH ÀN), 55.20
2
4
+
were purchased from Aldrich Chemicals Co. and were used as re-
ceived. Methanol was obtained from J. T. Baker. The compositions
of the TMAAs were determined by using a CHNOS elemental ana-
lyzer (Model: Fisons EA 1108) for C, H, and N. NMR spectra were re-
corded on a 400 MHz Bruker NMR spectrometer. FTIR analysis was
conducted by using a Nicolet 380 attenuated total reflectance FTIR
equipped with a Smart MIRacle accessory. The TGA curves were
obtained by using a TA instrument (SDT-2960).
(4CH
3
ÀN ), 181.12 ppm (CO
).
2
Absorption and desorption of CO2
Absorption and desorption experiments were conducted in an
oven at constant temperature by using a similar apparatus de-
[30]
scribed elsewhere. The absorption capacities of the TMAAs were
measured as solutions in water, methanol, or EG. A 30 wt% TMAA
solution (20 g) in water, methanol, or EG was loaded into a 90 mL
high pressure glass vessel equipped with a pressure transducer,
a magnet bar, and gas inlet and outlet valves. The absorption
vessel was degassed under vacuum for 2 min, weighed by using
a balance (OHAUS, EP613C) with an accuracy of 0.001 g, and then
placed in the oven. After the oven reached a specified tempera-
TMAAs were prepared through a multistep process involving the
synthesis of AAE through the Michael addition reaction of an
[28]
amine to methylacrylate and the subsequent hydrolysis followed
[29]
by neutralization with Me NOH.
4
Synthesis of AAEs
ture, with vigorous stirring, 0.1 MPa CO was introduced into the
2
vessel for 60 min from a CO2 cylinder that was equipped with
a pressure transducer and a pressure regulator. After absorption
was complete, the vessel was degassed under vacuum for 2 min,
A typical synthesis of a b-amino acid ester through a Michael addi-
tion reaction was performed as described herein. To a 100 mL two-
necked round-bottom flask containing n-butylamine (14.6 g,
and the weight change upon absorption of CO was measured by
2
0
0
.2 mol) solution in methanol (20 mL), methylacrylate (17.2 g,
.2 mol) solution in methanol (20 mL) was added dropwise at
using the balance. A blank test was conducted with the same
volume of a solvent: water or alcohol. The absorbed CO was des-
2
À208C over a period of 1 h. The resulting solution was then
warmed to ambient temperature and reacted for a further 4 h with
vigorous stirring. Distillation under reduced pressure afforded
orbed in the oven at an elevated temperature of 808C for 1 h by
À1
flowing N into the absorption vessel at a rate of 20 mLmin by
2
using a mass flow controller; the weight change was measured by
using the balance.
1
methyl-3-(butylamino)propanoate with a yield of 94%. H NMR
spectroscopy (400 MHz, DMSO, 298 K): d=2.42 (t, 2H, CH ÀCO ),
2
2
2
.47 (t, 2H, CH ÀNH), 2.72 (t, 2H, CH -CH ÀCO ), 3.59 ppm (s, 3H,
2
2
2
2
13
CH ÀO). C NMR (400 MHz, DMSO, 298 K): d=31.70 (CH ÀCO ),
Theoretical investigation
3
2
2
3
4.33 (CH ÀCH -NH), 44.91 (CH ÀCH ÀCO ), 48.74 (CH ÀNH), 50.97
2
2
2
2
2
2
The interactions of TMAAs with CO were theoretically investigated
2
[
(
CH ÀO), 172.53 ppm (CO ). Elemental analysis calcd (%) for
3
2
31]
by using the Gaussian 09 program. The geometry optimizations
and thermodynamic corrections were performed with a hybrid
Becke 3-Lee–Yang–Parr (B3LYP) exchange–correlation function with
the 6-31+G* basic sets for C, H, N, and O. All stationary points
were verified as minima by using full calculation of Hessian and
harmonic frequency analysis. The effect of bulk solvent was taken
into account in the single point calculations through the self-con-
sistent reaction field theory (SCRF), based on the polarizable con-
tinuum model (IEFPCM-UFF) and implemented in the Gaussian
C H NO : C 60.38; H 10.69; N 8.80. Found (%): C 59.99; H 10.74; N
8
17
2
8
.68.
Synthesis of TMAAs
A typical synthesis of a TMAA though the hydrolysis of AAE fol-
lowed by neutralization with Me NOH was performed as described
4
herein. In a 100 mL round-bottom flask, methyl-3-(butylamino)-
propanoate (15.90 g, 0.10 mol) was reacted with an aqueous solu-
[32,33]
program.
tion of Me NOH (25 wt%, 22.75 g, 0.10 mmol) at 808C for 2 h. After
4
completion of the reaction, volatiles were removed under reduced
pressure to yield the desired TMAA; tetramethylammonium 3-(bu-
tylamino)propanoate, 1, with a yield of 98%. Melting point, 1408C.
1
Acknowledgements
H NMR (400 MHz, D O, 298 K): d=0.75 (d, 3H, CH ÀCH ), 1.16 (m,
2
3
2
2
2
4
4
1
H, CH ÀCH ), 1.29 (m, 2H, CH ÀCH ÀCH ), 2.17 (t, 2H, CH ÀCO ),
3
2
3
2
2
2
2
.39 (t, 2H, CH ÀNH), 2.58 (t, 2H, CH ÀCH ÀCO ), 3.04 ppm (s, 12H,
We acknowledge financial support grants from Korea CCS R&D
Center, funded by the Ministry of Education, Science, and Tech-
nology of the Korean government.
2
2
2
2
+
13
CH ÀN ). C NMR (400 MHz, D O, 298 K): d=37.29 (CH ÀCO ),
3
2
2
2
+
5.69 (CH ÀCH -CO ), 48.26 (CH ÀNH), 55.21 (4CH ÀN ),
2
2
2
2
3
80.36 ppm (CO ). Elemental analysis calcd (%) for C H N O :
2
11 26
2
2
C 60.55; H 11.92; N 12.96. Found (%): C 60.38; H 12.01; N 13.00.
Other TMAAs including tetramethylammonium 3-(dibutylamino)-
propanoate, 2, and tetramethylammonium 3-(2-(diethylamino)-
Keywords: amino acids · carbon dioxide capture · hydrogen
bonds · michael addition. · molecular modeling
ꢀ
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2013, 6, 890 – 897 896