Synthesis and extraction studies of 1,2- and 1,3-disubstituted butylcalix[4]arene
amides with oxyions; geometric and conformational effects
Olusegun M. Falana,a H. Fred Koch,a D. Max Roundhill,*a Gregg J. Lumettab and Benjamin P. Hayb
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, USA
Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
26,28-(Dibutylcarbamoyl)methoxy-5,11,17,23-tert-butylca-
lix[4]arene and two geometric isomers of 27,28-(dibu-
RBr
tylcarbamoyl)methoxy-5,11,17,23-tert-butylcalix[4]arene
have been used to extract UVI, MoVI, CrVI and SeVI from
aqueous solution into toluene or isooctane.
K2CO3
OH
OR
OH
OH
HO OR
HO
OH
The selective extraction of metal cations and anions from
aqueous solution into an organic phase is an important goal,
especially if the particular ions are toxic and present in the
environment in significant quantities.1,2 Three such metals are
uranium,3 chromium4–10 and selenium,11 all of which exist
primarily in their hexavalent forms. Although there is con-
siderable diversity between these species there are also some
similarities. The main difference is that whereas SeVI and CrVI
are anions in strongly acidic solution, UVI is a cation. An
important similarity, however, is that these species are high
valent oxophiles, and an amide functionality can potentially act
as a complexant for each of these species. This premise is based
on the logic that such a functionality should not only coordinate
as a hard N,O-donor ligand to such high-valent centers, but
should also function as a neutral host to hydrogen bond with the
protonated form of the oxyanion.
In developing extractants it is important to target specific
solvent systems as well as complexants. Although in earlier
work with calix[4]arenes we have used chloroform as the
organic phase,12–19 we have always been aware that it would be
advantageous to use a less toxic organic such as an alkane. We
have now prepared the geometrically isomeric 1,2- and
1,3-calix[4]arene amides having appended n-butyl substituents
in order that they can be more compatible with such an alkane
phase. In addition to solvent selectivity, the effect of both
geometric and conformational properties of the complexant
needs also to be considered. Since the 1,2 isomer has been
obtained as a separable mixture of geometric isomers, the
availability of such a pair of isomers affords us the opportunity
to compare their relative extraction properties.
1
R = CH2C(O)NBun
2
Scheme 1
due to the NCH2 group at d 3.36, a singlet at d 4.81 due to
OCH2C(O) and an AB pair for the bridging methylenes at d 3.27
and 4.46 [2J(HH) 13 Hz]. The 13C{1H} NMR spectrum shows
the amide carbonyl resonance at d 168.0. Compound 2 (yield
9.0%; mp 130 °C) is characterized as being in the partial cone
conformation with the bis-(dibutylcarbamoyl)methoxy groups
on opposite rims by the presence of a multiplet resonance due to
NCH2 groups at d 3.21–3.42, two inequivalent singlets at d 5.24
and 5.29 due to the pair of OCH2C(O) groups, and two sets of
AB pairs for the inequivalent bridging methylenes at d 4.34 and
4.96 [2J(HH) 13 Hz], and at d 4.68 and 4.70 [2J(HH) 14 Hz].
The 13C{1H} NMR spectrum shows the amide carbonyl
resonance at d 170.0. Compound 3 (yield 9.6%; mp 174–175
°C) is characterized as being in the partial cone conformation
with the bis-(dibutylcarbamoyl)methoxy groups on the same
side of the upper rim by the presence of a multiplet resonance
due to the NCH2 group at d 3.39–3.49, a singlet for OCH2C(O)
at d 4.98, along with two sets of AB pairs for the inequivalent
bridging methylenes at d 3.41 and 4.63 [2J(HH) 13 Hz] and at
d 3.43 and 4.37 [2J(HH) 14 Hz]. The OH resonances are found
at d 9.76 and 10.48. The 13C{1H} NMR spectrum shows the
amide carbonyl resonance at d 169.0. Both the 1H NMR and 13
NMR spectra show additional corresponding resonances for the
other functional groups in these structures of 1–3.
Extraction studies have been carried out with isooctane and
toluene, along with the compounds 1, 2 and 3 (1 mm solutions
of each), and aqueous solutions of the metal salts (1 mm in
C
These three new calix[4]arene amides have been synthesized
using the same general procedures.20 The precursor compound
N,N-dibutyl-2-bromoacetamide has been synthesized in 82%
yield by stirring a mixture of bromoacetic acid and N,N-
dibutylamine in dichloromethane with 1,3-dicyclo-
hexylcarbodiimide for 12 h.
The synthetic route of the calix[4]arene amides involves
reacting 5,11,17,23-tert-butylcalix[4]arene with N,N-dibutyl-
2-bromoacetamide (2.2 equiv.) in the presence of a base. For the
case of 26,28-(dibutylcarbamoyl)methoxy-5,11,17,23-tert-
butylcalix[4]arene 1 the conditions use potassium carbonate in
refluxing acetone for 18 h (Scheme 1), and for the two isomers
OH
OH
HO
OH
RBr
NaH
of
27,28-(dibutylcarbamoyl)methoxy-5,11,17,23-tert-butyl-
OH
OR
calix[4]arene (2, 3), sodium hydride in DMF at 60 °C for 26 h
is used (Scheme 2). Compounds 2 and 3 were obtained in the
same reaction mixture and separated by column chromato-
graphy.
+
OH
OR
OH
OR
OR
OH
These compounds have been structurally characterized by
NMR spectroscopy. Compound 1 (yield 65%; mp 130–132 °C)
is characterized as being in the cone conformation by the
presence of a single triplet resonance in the 1H NMR spectrum
2
3
R = CH2C(O)NBun
2
Scheme 2
Chem. Commun., 1998
503