Absorption of chlorinated hydrocarbons dissolved in water with pellets made of p-tert-butylcalix[4]arene and silica gel

Article abstract of DOI:10.1246/cl.2012.1412

Powdery crystals of p-tert-butylcalix[4]arene (1) pelletized using silica gel as a binder absorb chlorinated hydrocarbons from saturated aqueous solutions by forming inclusion complexes with compound 1.

Full text of DOI:10.1246/cl.2012.1412

doi:10.1246/cl.2012.1412
1412
Published on the web October 27, 2012
Absorption of Chlorinated Hydrocarbons Dissolved in Water
with Pellets Made of p-tert-Butylcalix[4]arene and Silica Gel
Naoya Morohashi,* Ozora Shibata, and Tetsutaro Hattori*
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University,
6-6-11 Aramaki-Aoba, Aoba-ku, Sendai, Miyagi 980-8579
(Received June 12, 2012; CL-120640; E-mail: morohashi@orgsynth.che.tohoku.ac.jp)
HO
Powdery crystals of p-tert-butylcalix[4]arene (1) pelletized
HO
OH
OH
X
X
using silica gel as a binder absorb chlorinated hydrocarbons
from saturated aqueous solutions by forming inclusion com-
plexes with compound 1.
1: R = t-Bu, X = CH2
2: R = t-Bu, X = S
X
X
3: R = SO3Na, X = S
R
R
R
R
Chlorinated hydrocarbons, such as dichloromethane and
trichloroethene, are good solvents for degreasing and have
been used in the electronic industry, dry cleaning, and so on.
However, many of these substances are harmful to human health
and the environment and, therefore, the removal of chlorinated
hydrocarbons from industrial waste water, as well as drinking
water, is highly desired.1 Calixarenes, e.g., 1 and 2 (Chart 1),
have been widely used as artificial hosts for molecular
recognition.2 Although a considerable number of studies have
been made on the inclusion phenomena of calixarenes,3 few
papers have dealt with the collection of chlorinated hydro-
carbons dissolved in water. Wainwright and co-workers reported
that trihalomethanes (THMs) could be selectively captured from
water containing THMs and other organic compounds by
passing through a column packed with granular activated carbon
which adsorbed p-tert-butylcalix[6]arene on the surface.4 Iki et
al. succeeded in the removal of halogenated hydrocarbons from
water with water-soluble thiacalix[4]arenesulfonic acid 3 via the
formation of inclusion complexes,5 followed by trapping them
with anion-exchange resins.6 However, these methods require
specific materials and/or troublesome manipulations. On the
other hand, Atwood’s group and other laboratories including
ours have recently reported the direct inclusion of guest
molecules from gas phase and liquid phase with crystals of
calixarenes.7 We imagined that as chlorinated hydrocarbons are
hydrophobic, they would be easily absorbed from aqueous
solutions into the crystals of calixarenes. Herein, we wish to
report a simple and facile method for collecting chlorinated
hydrocarbons from water with pellets prepared from powdery
crystals of compound 1 and silica gel. To the best of our
knowledge, this is the first report on the collection of
halogenated hydrocarbons from water with crystals of artificial
host compounds.
Chart 1.
Table 1. Inclusion of chlorinated hydrocarbons with compound 1 by
crystallization from neat guests
Guest
nꢀ
Guest
nꢀ
CH2Cl2
CHCl3
CH2ClCH2Cl
CCl3CH3
CHCl2CH2Cl
1.01
0.86
1.08
0.88
0.98
CHCl2CHCl2
CCl2=CH2
CCl2=CHCl
CCl2=CCl2
0.70
0.83
0.93
0a
aDetermined by 13C NMR analysis.
We then tried the absorption of dichloromethane from its
saturated aqueous solution (ca. 0.24 mol L¹1) with powdery
crystals of compound 1. The attempt was attended with
difficulty; the powder added to a stirred aqueous solution of
dichloromethane floated on the liquid surface and formed lumps,
which resulted in diminishing the reproducibility of the
inclusion experiment (vide infra). It occurred to us that this
problem would be solved by using pelletal host materials. After
some trial and error, pellets with suitable mechanical strength
and density could be prepared by grinding a mixture of
compound 1 and silica gel (ca. 1:2 weight ratio) with a mortar
and pestle and compressing the mixture at 4 MPa using a
microtablet maker (5.0 mm i.d. © ca. 0.45 mm thickness).9 Each
pellet prepared in this manner was then sunk into a saturated
aqueous solution of dichloromethane in a screw-cap vial; a large
volume of solution was used to ensure that the guest concen-
tration is quasi-constant throughout the experiment. After the
vial was left at room temperature for a time, the pellet was
picked up from the solution, dried, and analyzed to determine
the host-guest ratio nꢀ. Figure 1 shows the time dependence of
the nꢀ value as compared with that obtained in the absorption
using the powdery absorbent. As mentioned above, the inclusion
with powdery crystals exhibited low reproducibility. In addition,
it was difficult to collect the solvent-absorbed powder from an
aqueous solution by filtration. On the other hand, the pellet
captured dichloromethane in a shorter time with good reprodu-
cibility and was quantitatively collected from the solution. It
should be noted that silica gel did not adsorb dichloromethane,
as evidenced by the experiment using pellets made of only silica
gel. The powder X-ray diffraction (PXRD) pattern of the pelletal
First, the inclusion capability of compound 1 toward
chlorinated hydrocarbons was evaluated by a conventional
crystallization method as follows: A boiling guest solvent was
nearly saturated with compound 1 and the solution was allowed
to cool to room temperature to precipitate inclusion crystals,
which was collected by filtration, dried in vacuo, and analyzed
1
by H NMR spectroscopy. Table 1 lists the average number of
guest molecules included into a host molecule (nꢀ). The obtained
nꢀ values suggest that compound 1 forms 1:1 inclusion
complexes with all the chlorinated hydrocarbons tested except
tetrachloroethene.8
Chem. Lett. 2012, 41, 1412-1413
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1413
Table 2. Inclusion of chlorinated hydrocarbons from saturated aqueous
solutions with pelletal compound 1a
Concentration
/mol L
Guest
nꢀb
¹1
¹1
¹2
¹2
¹3
¹2
¹2
¹3
¹3
CH2Cl2
CHCl3
CH2ClCH2Cl
CCl3CH3
CHCl2CH2Cl
CHCl2CHCl2
CCl2=CH2
2.4 © 10
6.8 © 10
8.8 © 10
8.2 © 10
3.4 © 10
1.7 © 10
2.2 © 10
8.4 © 10
0.92
0.90
0.95
0.65
0.98
0.68
0.19
0.93
c
c
CCl2=CHCl
Figure 1. Inclusion of dichloromethane from its saturated aqueous
solution with powdery crystals of compound 1 ( ) and pelletal compound
1 ( ). The nꢀ values are averages of measurements repeated more than three
times. Error margins are indicated by error bars.
aThe pellet was left in a saturated aqueous solution of chlorinated
b
hydrocarbon for 24 h. Average value of measurements repeated more
c
than three times. The contact time was extended to 168 h.
inclusion capability; the nꢀ value decreased from 0.92 to 0.89,
0.70, 0.86, and 0.72 as the absorption-desorption cycle was
repeated. We also tried the absorption of dichloromethane from
its dilute solutions. However, the pelletal compound 1 did not
absorb dichloromethane from a one-tenth saturated solution
(0.024 mol L¹1).
In conclusion, pellets prepared from a crystalline powder of
p-tert-butylcalix[4]arene (1) and silica gel absorbed various
halogenated hydrocarbons from their saturated aqueous solu-
tions via the formation of inclusion complexes with compound
1. Further efforts to improve the inclusion capability in dilute
solutions are in progress.
Figure 2. PXRD patterns of pelletal compound 1 measured before (a)
and after absorption of CH2Cl2 (b) and after desorption of CH2Cl2 (c).
PXRD pattern of 1¢CH2Cl2 prepared by crystallization (d). PXRD pattern
of silica gel is subtracted from patterns a-c.
References and Notes
1
a) P. L. McCarty, Curr. Opin. Biotechnol. 1993, 4, 323. b) S. Yamahara,
S. Nakao, Membrane 1993, 18, 69. c) B. Van der Bruggen, C.
Vandecasteele, Environ. Pollut. 2003, 122, 435. d) M. Peng, L. M. Vane,
S. X. Liu, J. Hazard. Mater. 2003, 98, 69.
2
Reviews: a) C. D. Gutsche, in Calixarenes Revisited in Monographs in
Supramolecular Chemistry, ed. by J. F. Stoddart, The Royal Society of
Chemistry, Cambridge, UK, 1998. b) Calixarenes in Action, ed. by L.
Mandolini, R. Ungaro, Imperial College Press, London, 2000. c)
Calixarenes 2001, ed. by Z. Asfari, V. Böhmer, J. Harrowfield, J. Vicens,
M. Saadioui, Kluwer Academic Publishers, Dordrecht, 2001. d) P. Lhoták,
Eur. J. Org. Chem. 2004, 1675. e) S. Parola, C. Desroches, Collect. Czech.
Chem. Commun. 2004, 69, 966. f) N. Morohashi, F. Narumi, N. Iki, T.
Hattori, S. Miyano, Chem. Rev. 2006, 106, 5291.
a) A. Pochini, A. Arduini, in Calixarenes in Action, ed. by L. Mandolini, R.
Ungaro, Imperial College Press, London, 2000, pp. 37¹61. b) A. Arduini,
A. Pochini, A. Secchi, F. Ugozzoli, in Calixarenes 2001, ed. by Z. Asfari,
V. Böhmer, J. Harrowfield, J. Vicens, M. Saadioui, Kluwer Academic
Publishers, Dordrecht, 2001, pp. 457¹475. doi:10.1007/0-306-47522-
7_25. c) B. Mokhtari, K. Pourabdollah, N. Dalali, J. Coord. Chem. 2011,
64, 743.
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compound 1 measured after the absorption of dichloromethane
(Figure 2b) well agreed with that of inclusion crystals prepared
by the crystallization of compound 1 from dichloromethane
(Figure 2d). In addition, a single-crystal X-ray diffraction
analysis of the inclusion crystal revealed that one dichloro-
methane molecule is included into the cavity of compound 1
(Figure S1).9 These observations clearly indicate that the pellet
absorbs dichloromethane molecules by forming inclusion com-
plexes with compound 1.
The absorption of other chlorinated hydrocarbons was also
tested (Table 2). The pellet was contacted with an aqueous
solution enough time to ensure that the complexation reached
equilibrium. Most of the chlorinated hydrocarbons were cap-
tured in comparable host-guest ratios to those obtained by the
crystallization (Table 1), whereas some guests exhibited lower
host-guest ratios; a similar observation was previously made in
the inclusion of alcohols with thiacalixarene 2.7d Although the
inclusion capability of compound 2 was also examined in both
crystal and pelletal forms (Tables S1 and S2),9 its performance
was inferior to that of compound 1 with regard to the guest
applicability.
3
4
5
6
7
Dichloromethane was desorbed from the pelletal compound
1 by heating it at 140 °C under reduced pressure (0.5-1.0 kPa)
for 72 h, as evidenced by PXRD analysis (Figure 2c as
compared with Figure 2a). Taking advantage of this nature,
the pellet could be recycled at least 5 times with slight loss of the
8
9
Sone et al. reported that the crystallization of compound 1 from CH2Cl2 or
CH2ClCH2Cl gave a 1:1 inclusion complex of compound 1 with the
solvent, see: T. Sone, Y. Ohba, K. Moriya, H. Kumada, K. Ito, Tetrahedron
1997, 53, 10689.
Supporting Information is available electronically on the CSJ-Journal Web
site, http://www.csj.jp/journals/chem-lett/index.html.
Chem. Lett. 2012, 41, 1412-1413
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/