Substituted Benzoxazole and Catechol Cocrystals as an Adsorbent for CO2 Capture: Synthesis and Mechanistic Studies

Article abstract of DOI:10.1021/acs.cgd.7b00693

We report the synthesis of cocrystals of a substituted benzoxazole and catechol from a primary amine and 3,5-di-tert-butylbenzoquinone. Fourier transform infrared and NMR spectroscopy studies revealed that cocrystals 2 could be synthesized in excellent yield from 1 and 3,5-di-tert-butylbenzoquinone. Introduction of an amine into the cocrystal structure enhanced the CO₂ adsorption capacity of the cocrystals at room temperature from 15.69 to 44.21 mg/g. Our results indicated the ability to use cocrystals for CO₂ capture and to easily modify them to enhance their CO₂ adsorption capacity.

Full text of DOI:10.1021/acs.cgd.7b00693

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Communication
Substituted Benzoxazole and Catechol Cocrystals as an
Adsorbent for CO2 Capture: Synthesis and Mechanistic Studies
Sivanesan Dharmalingam, Min Hye Youn, Ki Tae Park, Hak Joo Kim, and Soon Kwan Jeong
Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b00693 • Publication Date (Web): 02 Aug 2017
Downloaded from http://pubs.acs.org on August 4, 2017
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Substituted Benzoxazole and Catechol
Cocrystals as an Adsorbent for CO2 Capture:
Synthesis and Mechanistic Studies
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Dharmalingam Sivanesan, Min Hye Youn, Ki Tae Park, Hak Joo Kim, Soon Kwan Jeong*
Green Energy Process Laboratory, Korea Institute of Energy Research, 152, Gajeongꢀro,
Yuseongꢀgu, Daejeon 34129, Republic of Korea
KEYWORDS: CO2 adsorption, Cocrystals, Substituted benzoxazole Synthesis, Mechanistic
Studies, CO2 adsorption capacity, Amine effect
ABSTRACT: We report the synthesis of cocrystals of a substituted benzoxazole and catechol
from a primary amine and 3,5ꢀdiꢀtertꢀbutylbenzoquinone. FTꢀIR and NMR spectroscopy studies
revealed that cocrystals 2 could be synthesized in excellent yield from 1 and 3,5ꢀdiꢀtertꢀ
butylbenzoquinone. Introduction of an amine into the cocrystal structure enhanced the CO2
adsorption capacity of the cocrystals at room temperature from 15.69 to 44.21 mg/g. Our results
indicated the ability to use cocrystals for CO2 capture and to easily modify them to enhance their
CO2 adsorption capacity.
Introduction
Globally, the everꢀincreasing concentration of CO2 in the atmosphere due to the industrial
effects of mankind is a widespread concern because of the undesirable effects of the resulting
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climate change that has been observed in recent years1. Various CO2 capture technologies have
been proposed to control the emission of this greenhouse gas in order to reduce the serious threat
that it poses to ecosystems3ꢀ12. The adsorption method is preferred in carbon capture and storage
(CCS)13ꢀ16, and many adsorbents such as zeolites, metal organic frameworks (MOFs), amineꢀ
functionalized materials and activated carbon have been reported to capture CO217ꢀ23. Despite the
many available adsorbents24ꢀ26, it is vital to use the most suitable one to optimize the CO2
separation efficiency in CCS. In this regard, few cocrystals that are able to adsorb CO2 from a
flue gas have been found. Cocrystals are defined as more than two types of molecules that form a
crystalline solid and interact via nonꢀcovalent bonds27,28. Intermolecular interactions within the
cocrystal define the molecular arrangement of the components in the solid state29ꢀ32. Due to their
modularity, cocrystals have been used in solidꢀstate organic synthesis, organic semiconductors
and pharmaceutics33,34. In spite of their many achievements, cocrystals with amine functional
groups have not been used for CO2 adsorption studies in CO2 capture processes. The adsorbents
with amine functional groups have been very effective for CO2 adsorption8.
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Herein we report the synthesis of cocrystals from the reaction of a primary amine with
3,5ꢀdiꢀtertꢀbutylbenzoquinone. The cocrystals were characterized by using singleꢀcrystal Xꢀray
analysis, FTꢀIR spectroscopy, NMR spectroscopy, and mass spectrometry. The CO2 adsorption
studies using these cocrystals were carried out at room temperature, and we analyzed the effect
of incorporating an amine group into the cocrystal structure on the CO2 adsorption.
Results and Discussion
Initially, a 1:2 ratio of ethylenediamine and 3,5ꢀdiꢀtertꢀbutylbenzoquinone was stirred at
0 oC for 1 h to obtain 1 as a crystalline solid35. Stirring these reactants under the same conditions,
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except at room temperature for 12 h instead of at 0 C for 1 h, unexpectedly afforded cocrystals
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of substituted benzoxazole and 3,5ꢀdiꢀtertꢀbutylbenzeneꢀ1,2ꢀdiol, 2, in a moderate yield of 12%
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(Scheme 1). 1 and the cocrystals were characterized by using H NMR, C NMR, and FTꢀIR
spectroscopy investigations as well as mass spectrometry. The imine protons of 1 appeared as a
singlet at 8.82 ppm and aromatic protons appeared as a doublet with a JHꢀH coupling constant
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value of 2.2 Hz in the H NMR spectrum; and the 13C spectrum confirmed the presence of
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aromatic and aliphatic carbons (Figure S1). The H and 13C NMR spectra of 2 are shown in
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Figures S1 and S2. The absence of the imine proton peaks at 8.82 ppm in the 1H NMR spectrum
of 2 and the presence of aromatic proton peaks at 7.71 and 7.38 ppm with a JHꢀH coupling
constant value of 1.7 Hz confirmed the presence of the benzoxazole ring in 2 (Figure S2).
The FTꢀIR spectrum of 1 showed a band at 3364 cmꢀ1, corresponding to hydroxyl group
stretching vibrations, and a band at 1482 cmꢀ1 which is corresponding to imine (ꢀC=N) stretching
vibrations. Bands at 3480 cmꢀ1 and 3099 cmꢀ1 were observed for 2, and were attributed to two
different types of hydrogenꢀbonds stretching vibrations, specifically ꢀN…HꢀO and OꢀH…O,
respectively, from 3,5ꢀdiꢀtertꢀbutylcatechol and the substituted benzoxazole. Both 1 and 2 also
yielded a band at 2953 cmꢀ1 (Figure S3), corresponding to –CH stretching vibrations. To
determine how the hydrogen bonding affected the nature of stretching vibrations in the
cocrystals, FTꢀIR spectra were recorded for 3,5ꢀdiꢀtertꢀbutylcatechol and 3,5ꢀdiꢀtertꢀ
butylbenzoquinone and are shown in Figure 4. Bands were observed at 1649 cmꢀ1 and 3448 cmꢀ1,
corresponding to –C=O stretching vibrations of benzoquinone and to the –OH group of 3,5ꢀdiꢀ
tertꢀbutylcatechol, respectively.
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Scheme 1. Syntheses of 1 and 2
Light greenish crystals of 2 were obtained from CH3CN and diethyl ether diffusion
system. The crystal structure of 2 is shown in Figure 1 and the crystal information is given in
Table S1 and S2. 2 crystallized in the triclinic system with space group Pꢀ1 and half a molecule
per asymmetric unit. The distance between the N and C of benzoxazole ring was measured to be
1.2903(15) Å and that between C and O was 1.3588(13), values similar to the previously
reported benzoxazole bond distances36. The bond distance between C and C1A of the
benzoxazole dimer was measured to be 1.450 Å. 2 exhibits two types of intermolecular hydrogen
bonds involving the catechol OH groups and benzoxazole N atoms. The catechol OH groups act
as a donor in N…HꢀO interactions and as an acceptor in OꢀH…O interactions. These
intermolecular hydrogen bonds are stabilizing the crystal structure. The distances between the
acceptor and donor heteroatoms are 2.780 and 2.849 Å, and its respective angles are 141 and
164o (Table S3). These hydrogen bonds distances and angles suggest that in 2 strong hydrogen
bonds are stabilizing the crystal system. Further the intermolecular N…HꢀO and OꢀH…O
hydrogen bonds between benzoxazole and the catechol molecules are generating threeꢀ
dimensional networks in 2 (Figure 2 & S4). Furthermore, to check the purity of cocrystals
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powder XRD data was collected and that was compared with simulated data (Figure S5).
Measured XRD pattern of 2 was closely matched with those in the simulated pattern generated
from singleꢀcrystal diffraction data; it indicates the formation of pure cocrystals.
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Figure 1. Singleꢀcrystal Xꢀray structure of 2
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Figure 2. Crystal packing diagram of 2 showing the N…HꢀO and OꢀH…O hydrogen bonds
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between substituted benzoxazole and catechol. Symmetry codes: [ꢀx, ꢀy, ꢀz+1], [ꢀx+1, ꢀy+1, ꢀ
z+1]
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To understand clearly how the cocrystals were generated from ethylenediamine and 3,5ꢀ
diꢀtertꢀbutylbenzoquinone, equivalent amounts of 1 and 3,5ꢀdiꢀtertꢀbutylbenzoquinone were
suspended with CH3CN in the presence of air. Since 1 was partially soluble in CH3CN, the
mixture of 1 and 3,5ꢀdiꢀtertꢀbutylbenzoquinone was stirred at room temperature. After 12 h of
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stirring, the resulting precipitate was filtered and analyzed using H NMR spectroscopy. The
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resulting H NMR spectrum is shown in Figure 3 and clearly indicated the formation of the
structure in scheme 2 labeled as 3. To further investigate the generation of 3, various FTꢀIR
spectra were recorded, and are shown in Figure 4. Along with bands at 3480 and 3099 cmꢀ1,
which are characteristic FTꢀIR bands for 2, an additional band was observed at 3367 cmꢀ1,
suggesting the presence of a free amine group, and hence the structure of 3 (Scheme 2). We
concluded that an insufficient amount of 3,5ꢀdiꢀtertꢀbutylbenzoquinone led to the formation of 3
(Scheme S1). Hence two equivalents of 3,5ꢀdiꢀtertꢀbutylbenzoquinone were added to the
suspension of 1 in CH3CN. As we expected, this amount led to the formation of 2 as a single
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product with excellent yield (90%) as confirmed with H NMR spectroscopy (Figure 3).
Moreover, in the FTꢀIR spectrum, the absence of –C=O stretching vibrations, shift in –OH group
frequency (3480 cmꢀ1), and change in the hydrogenꢀbonding nature confirmed a complete
conversion of 3,5ꢀdiꢀtertꢀbutylbenzoquinone to 3,5ꢀdiꢀtertꢀbutylcatechol when two equivalents of
3,5ꢀdiꢀtertꢀbutylbenzoquinone were added.
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1
Figure 3. H NMR spectra of A) 1, B) 2, C) the product of reacting 1 and 3,5ꢀdiꢀtertꢀ
butylbenzoquinone at a 1:1 ratio, and D) the product of reacting 1 and 3,5ꢀdiꢀtertꢀ
butylbenzoquinone at a 1:2 ratio
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Figure 4. FTꢀIR spectra of A) 3,5ꢀdiꢀtertꢀbutylcatechol, B) 3,5ꢀdiꢀtertꢀbutylbenzoquinone, C) 2,
i.e., the product of reacting 1 and 3,5ꢀdiꢀtertꢀbutylbenzoquinone at a 1:2 ratio, and D) 3, i.e., the
product of reacting 1 and 3,5ꢀdiꢀtertꢀbutylbenzoquinone at a 1:1 ratio
Scheme 2. Synthesis of 3
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Overall, combining two equivalents of 3,5ꢀdiꢀtertꢀbutylbenzoquinone with one equivalent
of 1 were generated cocrystals 2 as a single product. Here, the reduction of 3,5ꢀdiꢀtertꢀ
butylbenzoquinone to 3,5ꢀdiꢀtertꢀbutylcatechol to generate cocrystals 2 required four protons and
four electrons. When 1 was treated with 3,5ꢀdiꢀtertꢀbutylbenzoquinone in an anhydrous CH3CN
medium under an inert atmosphere, 2 formed with an excellent yield, indicating that the
necessary protons and electrons only came from 1 to form the stable aromatic benzoxazole ring.
An investigation of the mechanism of the formation of the cocrystals using FTꢀIR spectroscopy
and 1H NMR spectroscopy suggested that the cocrystals could be obtained in excellent yield and
also showed a new method to synthesize substituted benzoxazole using 3,5ꢀdiꢀtertꢀ
butylbenzoquinone as an oxidizing agent. Based on our spectroscopy studies, an inert
atmosphere reaction, and the singleꢀcrystal Xꢀray structure, we proposed a mechanism which is
shown in Scheme 3.
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Scheme 3. Proposed mechanism for the generation of 2
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Using our cocrystal synthesis method, 4 was synthesized from 3,5ꢀdiꢀtertꢀ
butylbenzoquinone and tri(2ꢀamintheyl)amine to introduce tertiary amine nitrogen in the
cocrystal to enhance the CO2 adsorption capacity (Scheme 4).
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Scheme 4. Synthesis of 4
Thermogravimetric analysis was employed to determine the thermal stability of 1, 2, 3
and 3,5ꢀdiꢀtertꢀbutylcatechol (Figure 5). 1 degraded in two steps, with the first degradation
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beginning at 150 C and ending at 175 C with 6% of the initial weight lost. The second
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degradation step started at 198 C and ended at 198 C with cumulatively 60 % of the initial
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weight lost. Interestingly, 2 degraded in two steps, the first one beginning at 200 C and the
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second one starting at 240 C. To determine the effect of 3,5ꢀdiꢀtertꢀbutylcatechol hydrogen
bonding in 2, 3,5ꢀdiꢀtertꢀbutylcatechol was also analyzed using TGA: it started degrading at 125
oC and was fully degraded by 205 C, i.e., without leaving any residue. These results clearly
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indicated that the presence of hydrogen bonds in cocrystals of substituted benzoxazole and 3,5ꢀ
diꢀtertꢀbutylcatechol increased the thermal stability of 2. For 2 and 3, residue amounting to about
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20% of the initial weight in each case remained at 300 C. These results provided additional
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evidence that hydrogen bonds between the 3,5ꢀdiꢀtertꢀbutylcatechol and substituted benzoxazole
increased the thermal stability of cocrystals 2 and 3.
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Figure 5. TGA analysis curves for 3,5ꢀdiꢀtertꢀbutylcatechol (A), and 1-3
The synthesized cocrystals 2ꢀ4 were tested for CO2 adsorption studies. Important
properties of suitable adsorbents for CO2 removal from flue gas are high CO2 adsorption
capacity, fast kinetics, high CO2 selectivity, mild conditions for regeneration, stability during
extensive adsorption and desorption cycling, tolerance of adsorbents to impurities in the flue gas,
and low cost37. Initially, 2 was tested for CO2 adsorption and desorption at room temperature and
is given in Figure S5. The amount of CO2 adsorbed by 2 was 15.96 mg/g [0.363 mmol/g] at RT
(Figure 6). This result suggests that cocrystals 2 could be used as an adsorbent for CO2 capture.
The adsorption and desorption graph of 2 with CO2 showed that 2 could be easily regenerated for
subsequent cycles (Figure S5). However, the amount of CO2 adsorbed by 2 was not high when
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compare to that of available adsorbents, e.g., 7.56 mmol/g for hyperbranched polyamine26. The
CO2 adsorption and desorption nature of 2 suggested that it could be used in the CO2 capture
process, and further modification in 2 with appropriate functional groups could increase the CO2
adsorption capacity. Secondary amine containing 3 adsorbed CO2 amount was 23.00 mg/g which
is higher than that of 2. The amount of CO2 adsorbed by 4 was measured to be 44.21 mg/g, and
this result clearly indicated that, as we expected, introduction of a tertiary amine into the
cocrystals enhanced the CO2 adsorption capacity. It was reported that tertiaryꢀamineꢀcontaining
adsorbent was more easily regenerate CO2 than the primaryꢀ and secondaryꢀamineꢀcontaining
adsorbents. Although CO2 adsorption capacity was moderate for the synthesized cocrystals 2ꢀ4,
we believe that further modification in the cocrystals could enhance the CO2 adsorption capacity.
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Figure 6. Adsorption of CO2 by 2-4 in mg per adsorbent
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Overall, in a single step substituted benzoxazole and catechol cocrystals were synthesized
from primary amine and 3,5ꢀdiꢀtertꢀbutylbenzoquinone, and it’s a new method to synthesize
substituted benzoxazole using 3,5ꢀdiꢀtertꢀbutylbenzoquinone as an oxidizing agent. Furthermore,
from 1 substituted benzoxazole and benzoxazoline could be easily synthesized by varying the
equivalence of diketones. Currently, we are working on synthesis of various cocrystals from
primary amines and diketones. A study of further roles of various diketones in the formation of
benzoxazole is also underway.
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Conclusions
In summary, we reacted a primary amine and 3,5ꢀdiꢀtertꢀbutylbenzoquinone to form
cocrystals made up of a substituted benzoxazole and a catechol. The formation of benzoxazole in
2 from 1 and benzoquinone suggested that our method should be useful in the synthesis of
substituted benzoxazoles. More importantly, our CO2 adsorption studies revealed that cocrystals
2ꢀ4 could be used for CO2 capture. The higher CO2 adsorption capacity of 4 than that of 2
suggested that the cocrystals could be easily modified to enhance the CO2 adsorption. We expect
our studies to initiate research into the syntheses of many substitutedꢀbenzoxazoleꢀ and catecholꢀ
containing cocrystals and that some of these new products will prove beneficial for CO2 capture.
Experimental Section:
General Consideration: All chemicals purchased were of analytical grade and used without
further purification. FTꢀIR spectra were recorded using the ATR method with a Varian 640ꢀIR
FTꢀIR spectrometer. 1H NMR and 13C NMR were recorded on Varian 300 MHz and Varian 125
MHz instruments, respectively.
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X-ray single crystal structural analysis: A single crystal was mounted at room temperature on
the tips of quartz fibers, coated with ParatoneꢀN oil, and cooled under a stream of cold nitrogen.
Intensity data were collected on a Bruker CCD area diffractometer running the SMART software
package with Mo Kα radiation (λ= 0.71073). The structure was solved by direct methods and
refined on F2 using the SHELXTL software package38. The multiꢀscan absorption correction was
applied with SADABS39, which is part of the SHELXTL program package, and the structure was
checked for higher symmetry by the program PLATON40. All nonꢀhydrogen atoms were refined
anisotropically. In general, hydrogen atoms were assigned idealized positions and given thermal
parameters equivalent to 1.2 times the thermal parameter of the carbon atom to which they were
attached. Data collection and experimental details for the complex 2 (CCDC 1533263) is
summarized in Table S1, and bond angles and distance are summarized in Table S2.
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CO2 adsorption and desorption studies: N2 adsorption−desorption isotherms of cocrystals
were measured on a static volumetric technique instrument (gas sorption analyzer, Micromeritics
ASAP 2020) for determination of the surface area, total pore volume, and the average pore
diameter. Prior to measurement, approximately 100 mg of the coꢀcrystal was degassed at 100 °C
for 8 h under vacuum to eliminate humidity and trapped gases. The N2 adsorption−desorption
data were recorded at liquid nitrogen temperature, 77 K, and applied in a relative pressure (P/Pο)
range from 0 to 1.0. The surface areas (SBET) were calculated using the BET equation by
Brunauer, Emmett, and Teller, which is the most widely used model for determining the specific
surface area. All surface area measurements were calculated from the nitrogen adsorption
isotherms by assuming the area of the nitrogen molecule to be 0.162 nm2. The total pore volume
(Vtot) was assessed by converting the amount of N2 gas adsorbed (expressed in cm3/g at STP) at
relative pressure to the volume of liquid adsorbate. Multilayer CO2 adsorbed by physisorption at
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25 °C and room pressure was measured using the aboveꢀmentioned instrument with a degassing
step prior to analysis. The CO2 analysis was conducted, and a water circulating bath was used to
control the temperature.
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Synthesis of 1:To a solution of 3,5ꢀdiꢀtertꢀbutylbenzoquinone (1.46 g, 3.30 mmol) in MeCN (25
mL) was added dropwise a solution of ethylenediamine (0.200 g; 6.65 mmol) in CH3CN (2 mL)
at 0 °C in the presence of air. The resulting mixture was stirred at 0 °C for 1 h and yellow
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precipitate was filtered and dried under high vacuum. Yield: 0.72 g (47%). H NMR (600 MHz,
Chloroformꢀd) δ 8.52 (s, 2H), 7.72 (s, 2H), 7.27 (d, J = 2.2 Hz, 2H), 1.38 (s, 19H), 1.27 (s, 19H).
13C NMR (151 MHz, Chloroformꢀd) δ 154.36, 150.07, 141.69, 136.00, 133.39, 125.91, 109.77,
35.03, 34.62, 31.55, 29.38. Elemental analysis; calculated for 1; C, 77.54; H, 9.54; N, 6.03;
found; C, 77.49; H, 9.45; N, 6.92. LCꢀMass: calculated (M+1) = 466.00, found 466.20.
Synthesis of cocrystals[2]: To a solution of 3,5ꢀdiꢀtertꢀbutylbenzoquinone (1.46 g, 3.30 mmol)
in MeCN (25 mL) was added dropwise a solution of ethylenediamine (0.200 g; 6.65 mmol) in
CH3CN (2 mL) at 0 °C in the presence of air. The resulting mixture temperature was slowly
brought into room temperature and stirred for 12 h. Resulting lightꢀyellow precipitate was
filtered and dried under high vacuum. Yield: 0.72 g (12%). 1H NMR (300 MHz, Chloroformꢀd) δ
7.71 (d, J = 1.7 Hz, 2H), 7.38 (d, J = 1.7 Hz, 2H), 6.81 (d, J = 2.1 Hz, 2H), 6.71 (d, J = 2.1 Hz,
2H), 1.50 (s, 18H), 1.35 (s, 18H), 1.33 (s, 18H), 1.18 (s, 18H). 13C NMR (151 MHz, Chloroformꢀ
d) δ 151.83, 148.93, 147.37, 142.40, 142.10, 141.57, 140.78, 135.66, 134.71, 121.77, 115.93,
115.28, 110.41, 35.22, 34.84, 34.61, 34.32, 31.75, 31.57, 30.02, 29.66, 29.32. Elemental
analysis; calculated for 2; C, 76.95; H, 9.35; N, 3.09; found; C, 76.92; H, 9.29; N, 3.11. LCꢀ
Mass: calculated (M+1) = 461.30, found 461.00.
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Synthesis of 3 from 1 with 1 equivalent of 3,5ꢀdiꢀtertꢀbutylbenzoquinone : To a mixture of imine
(0.100 g, 0.215 mmol) in MeCN (2.5 mL) was added a solution of 3,5ꢀdiꢀtertꢀbutylbenzoquinone
(47.0 mg, 0.215 mmol) in CH3CN (2 mL) at room temperature in the presence of air. The
resulting mixture was stirred at RT for 12 h and yellow precipitate was filtered and dried under
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high vacuum. Yield: 75.82 mg. H NMR (300 MHz, Chloroformꢀd) δ 7.71 (d, J = 1.8 Hz, 1H),
7.37 (d, J = 1.8 Hz, 1H), 6.81 (d, J = 2.3 Hz, 1H), 6.70 (dd, J = 2.2, 1.0 Hz, 2H), 6.50 (d, J = 2.2
Hz, 1H), 5.43 (s, 1H), 5.16 (d, J = 3.7 Hz, 1H), 4.65 (d, J = 3.9 Hz, 1H), 1.50 (s, 9H), 1.35 (s,
13
9H), 1.33 (s, 9H), 1.25 (s, 9H), 1.21 (s, 9H), 1.18 (s, 9H). C NMR (75 MHz, Chloroformꢀd) δ
148.93, 147.38, 144.59, 143.57, 142.40, 137.97, 137.59, 135.66, 134.71, 128.77, 121.77, 117.15,
115.94, 115.29, 114.71, 110.42, 110.03, 76.36, 35.23, 34.86, 34.61, 34.33, 31.76, 31.56, 30.02,
29.86, 29.86. Elemental analysis: calculated for 3; C, 76.82; H, 9.15; N, 5.78; found; C, 75.99;
H, 9.07; N, 5.68. LCꢀMass: calculated (M+1) = 463.30, found 463.90.
Synthesis of 2 from 1 with 2 equivalent of 3,5ꢀdiꢀtertꢀbutylbenzoquinone: To a mixture of imine
(0.100 g, 0.215 mmol) in MeCN (2.5 mL) was added a solution of 3,5ꢀdiꢀtertꢀbutylbenzoquinone
(94.0 mg, 0.430 mmol) in CH3CN (2 mL) at room temperature in the presence of air. The
resulting mixture was stirred at RT for 12 h and yellow precipitate was filtered and dried under
1
high vacuum. Yield: 0.174 g (90%). H NMR (300 MHz, Chloroformꢀd) δ 7.71 (d, J = 1.7 Hz,
2H), 7.38 (d, J = 1.7 Hz, 2H), 6.81 (d, J = 2.1 Hz, 2H), 6.71 (d, J = 2.1 Hz, 2H), 1.50 (s, 18H),
1.35 (s, 18H), 1.33 (s, 18H), 1.18 (s, 18H). 13C NMR (151 MHz, Chloroformꢀd) δ 151.83,
148.93, 147.37, 142.40, 142.10, 141.57, 140.78, 135.66, 134.71, 121.77, 115.93, 115.28, 110.41,
35.22, 34.84, 34.61, 34.32, 31.75, 31.57, 30.02, 29.66, 29.32.
Synthesis of 4: To a solution of 3,5ꢀdiꢀtertꢀbutylbenzoquinone ( 0.225 g, 1.02 mmo) in CH3CN,
tri(2ꢀamintheyl)amine (0.050 g, 0.34 mmol) solution of CH3CN was added at 0oC and stirred for
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1 h. The solution of 3,5ꢀdiꢀtertꢀbutylbenzoquinone(0.225 g, 1.02 mmol) in CH3CN was added in
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RT and stirred for 12 h. Resulting offꢀwhite crystalline solid was filtered and dried. 0.060 g,
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18%. H NMR (300 MHz, Chloroformꢀd) δ 7.78 (d, J = 1.8 Hz, 2H), 7.45 (d, J = 1.8 Hz, 2H),
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6.88 (d, J = 2.2 Hz, 2H), 6.77 (d, J = 2.2 Hz, 2H), 2.17 (d, J = 0.5 Hz, 6H), 1.57 (s, 18H), 1.42 (s,
18H), 1.41 (s, 18H), 1.26 (s, 18H). 13C NMR (75 MHz, Chloroformꢀd) δ 148.90, 148.66, 147.33,
146.62, 144.74, 141.61, 136.33, 134.70, 115.88, 115.30, 110.41, 78.89, 35.22, 34.84, 34.61,
34.62, 31.76, 31.57, 30.94, 30.02, 29.66. Elemental analysis: calculated for 4: C, 76.82; H, 9.15;
N, 5.78; found; C, 76.12; H, 9.05; N, 5.58. LCꢀMass: calculated (M+1) = 747.51, found 747.30.
ASSOCIATED CONTENT
Supporting Information. Xꢀray crystallographic files of 2 in CIF format; 1H and 13C NMR
Spectra, FTꢀIR spectra and Mass data and Xꢀray crystallographic information. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
* jeongsk@kier.re.kr
ACKNOWLEDGMENT
This work was supported by the Korea CCS R&D Center (KCRC) grant funded by the Korea
government (Ministry of Science, ICT & Future Planning; no. 2014M1A8A1049272).
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Crystal Growth & Design - cg-2017-006938.R1
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Substituted Benzoxazole and Catechol Cocrystals as an
Adsorbent for CO2 Capture: Synthesis and Mechanistic
Studies
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Dharmalingam Sivanesan, Min Hye Youn, Ki Tae Park, Hak Joo Kim, Soon Kwan Jeong*
Graphical Abstract:
Synopsis:
The synthesis of cocrystals of a substituted benzoxazole and catechol from a primary amine and
3,5-di-tert-butylbenzoquinone is reported. By varying the equivalence of diketones, from 1
substituted benzoxazole and benzoxazoline were synthesized. Our results indicated the ability to
use cocrystals for CO2 capture and introduction of an amine into the cocrystal structure enhanced
the CO2 adsorption capacity.
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