Synthesis and extraction abilities of mono-formylated calix[4]-1,3-aza- crown and its hydrazone derivatives

Article abstract of DOI:10.1007/s10847-012-0108-x

By formylation of calix[4]-1,3-aza-crown in hexamethylenetetramine/ trifluoroacetic acid system, the first formylated calix[4]-aza-crown derivative 6 was synthesized in yield of 61%. Reacting compound 6 with salicyloyl hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarbazide afforded four novel calix[4]crown hydrazone derivatives 7a-d in yields of 70-90%. By condensating compound 6 with series of bifunctional reagents, the novel mono-bridged biscalix[4]-aza-crown hydrazone derivatives 8a-c were prepared in high yields. The extraction experiments showed that all new compounds were good receptors for metal cations, especially, for soft metal cations. The extraction results suggested that the hydrazone groups produced favorable influences for binding soft cations. The two calix[4]arene units in compounds 8a-c could bind metal cations concurrently.

Full text of DOI:10.1007/s10847-012-0108-x

J Incl Phenom Macrocycl Chem (2012) 74:257–263
DOI 10.1007/s10847-012-0108-x
ORIGINAL ARTICLE
Synthesis and extraction abilities of mono-formylated
calix[4]-1,3-aza-crown and its hydrazone derivatives
•
Fafu Yang Ziyu Jiao Zhisheng Huang
•
•
•
Jianwei Xie Hongyu Guo
Received: 4 July 2011 / Accepted: 4 January 2012 / Published online: 28 January 2012
Ó Springer Science+Business Media B.V. 2012
Abstract By formylation of calix[4]-1,3-aza-crown in
hexamethylenetetramine/trifluoroacetic acid system, the
first formylated calix[4]-aza-crown derivative 6 was syn-
thesized in yield of 61%. Reacting compound 6 with sali-
cyloyl hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl
hydrazine or phenyl thiosemicarbazide afforded four novel
calix[4]crown hydrazone derivatives 7a–d in yields of
70–90%. By condensating compound 6 with series of
bifunctional reagents, the novel mono-bridged biscalix[4]-
aza-crown hydrazone derivatives 8a–c were prepared in
high yields. The extraction experiments showed that all
new compounds were good receptors for metal cations,
especially, for soft metal cations. The extraction results
suggested that the hydrazone groups produced favorable
influences for binding soft cations. The two calix[4]arene
units in compounds 8a–c could bind metal cations
concurrently.
structural and functional modifications [1]. Calixarenes are
easily modified by all kinds of reaction on their upper rims
or lower rims, such as etherification, esterification,
formylation, sulphonation, nitration, etc. [2–5]. By intro-
ducing the functional groups on upper rim and lower rim
synchronously, the ‘‘so-called’’ polytopic systems com-
bining two or more binding sites were conveniently con-
structed within the same architecture [6, 7]. To attain this
aim, some researches focused on the selective formylation
on upper rims of calixarene derivatives with functional
groups on lower rims. The previous method to prepare this
kind of compounds involved three-step sequences includ-
ing (i) de-tert-butylation, (ii) treatment with alkyl halide to
yield calix[4]arene ethers on lower rim and (iii) formyla-
tion on upper rim to yield formyl calix[4]arenes with
SnCl4 or TiCl4 as catalysts [8–12]. Lately, Chawla’s
et al. [13, 14] reported a simple method to achieve the
direct replacement of p-tert-butyl group of calix[4]are-
nes by formyl group under hexamethylenetetramine/
trifluoroacetic acid system. This method gave different
formylated calixarene derivatives along with the different
groups on lower rims of calixarene, but mono-formylation
calixarene was not obtained in most cases. On the other
hand, survey of literature indicated that bridging calixa-
renes were seldom used as the reacting materials for
formylation and only two normal calix[4]crowns were
formylated on upper rims up to now [15, 16]. In theory,
the formylation of calixcrown would give novel bridging
calixarene derivatives, which might be more favorable for
multiple complexation of guests due to the three-dimen-
sional cavity composed of calixarene and crown ether
units. In this paper, we wish to report the first synthesis of
formylated derivatives of calix[4]-aza-crown and its rela-
ted hydrazone derivatives as well as their extraction abil-
ities for metal cations.
Keywords Calix[4]crown ꢀ Biscalix[4]arene ꢀ
Formylation ꢀ Hydrazone ꢀ Synthesis ꢀ Extraction
Introduction
It is well known that calixarenes are excellent building
blocks to construct molecular receptors with various
F. Yang (&) ꢀ Z. Jiao ꢀ Z. Huang ꢀ J. Xie ꢀ H. Guo
College of Chemistry and Materials, Fujian Normal University,
Fuzhou 350007, People’s Republic of China
e-mail: yangfafu@fjnu.edu.cn
F. Yang
Fujian Key Laboratory of Polymer Materials, Fuzhou 350007,
People’s Republic of China
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J Incl Phenom Macrocycl Chem (2012) 74:257–263
Experimental
the starting materials were disappeared. After distilling off
the solvent by reduced pressure, 10 mL methanol was
added and the precipitate was separated. The crude product
was then recrystallized in CHCl3/MeOH. Compound 7a
was obtained as hazel powder in yield of 87% m.p.
216–218 °C; IR (KBr, cm-1): 3,436 (N–H and O–H),
1,683 (C=O), 1,650 (C=O), 1,602 (C=N); 1HNMR
(400 MHz, CDCl3) d: 1.14 (s, 18H, C(CH3)3), 1.23 (s, 9H,
C(CH3)3), 3.52 (d, 2H, J = 13.6 Hz, ArCH2Ar), 3.64
(d, 2H, J = 13.6 Hz, ArCH2Ar), 3.70 (bs, 4H, NCH2), 4.13
(d, 2H, J = 13.6 Hz, ArCH2Ar), 4.18 (d, 2H, J = 13.6 Hz,
ArCH2Ar), 4.57 (bs, 4H, OCH2), 7.04–7.65 (m, 12 H,
ArH), 8.15 (bs, 2H, OH), 8.44 (bs, 2H, NH), 8.82 (bs, 1H,
OH), 9.21 (s, 1H, CH=N), 11.79 (s, 1H, NH), m/z (%):
895.4 (M?, 100), Anal calcd. for C54H62O8N4, C 72.46, H
6.97, N 6.26; found C 72.38, H 6.98, N 6.20.
1
Melting points were uncorrected. H NMR spectra were
recorded in CDCl3 on a Bruker-ARX 400 instrument, using
TMS as reference. ESI-MS spectra were obtained from
DECAX-30000 LCQ Deca XP mass spectrometer. Ele-
mental analyzes were performed at Vario EL III Elemental
Analyzer. The UV–Vis measurements were performed on
Varian UV–Vis spectrometer. Cation concentrations in
competitive extracting experiments were measured with
Thermo Intrepid XSP Radial ICP-OES. IR spectra were
recorded on a Thermo Nicollet AVATAR 5700 FTIR
spectrometer using KBr pellets in spectral range
4,000–400 cm-1. The picrate salts were prepared accord-
ing to literature [17]. Compound 1–4 and 5 were prepared
according to the references [18] and [19], respectively. The
organic and inorganic reagents were analytical grade or
chemical grade without further purification.
According to the similar procedures as described above,
reacting compound 6 with corresponding reactants (2,4-
dinitrophenyl hydrazine, nicotinyl hydrazine, or phenyl
thiosemicarbazide) gave compounds 7b, 7c, and 7d in
yields of 86, 76, and 71%, respectively. Compound 7b: red
powder, m.p. 216–218 °C; IR (KBr, cm-1): 3,385 (N–H
and O–H), 1,692 (NC=O), 1,616 (C=N); 1HNMR
(400 MHz, CDCl3) d: 1.17 (s, 18H, C(CH3)3), 1.25 (s, 9H,
C(CH3)3), 3.50 (d, 2H, J = 13.2 Hz, ArCH2Ar), 3.58
(d, 2H, J = 13.2 Hz, ArCH2Ar), 3.70 (bs, 4H, NCH2), 4.14
(d, 2H, J = 13.2 Hz, ArCH2Ar), 4.19 (d, 2H, J = 13.2 Hz,
ArCH2Ar), 4.55 (s, 4H, OCH2), 7.07 (s, 4H, ArH), 7.14
(s, 2H, ArH), 7.50 (s, 2H, ArH), 8.0 (s, 1H, ArH), 8.06
(d, 1H, J = 9.6 Hz, ArH), 8.24 (s, 1H, OH), 8.35 (d, 1H,
J = 9.6 Hz, ArH), 8.47 (bs, 2H, NH), 8.97 (bs, 1H, OH),
9.14 (s, 1H, CH=N), 11.25 (s, 1H, NH), m/z (%): 940.1
(M?, 100), Anal calcd. for C53H60O10N6, C 67.63, H 6.42,
N 8.93; found C 67.69, H 6.43, N 8.88.
Synthesis of mono-formylated calix[4]-aza-crown 6
A mixture of compound 5 (0.47 g, 0.6 mmol) and hexa-
methylenetetramine (3.4 g, 24 mmol) was stirred in 15 mL
TFA solution for 5 h at room temperature. The detection of
TLC showed the disappearance of materials. Then 40 g ice
was added in the solution. After unfreeze of ice, the solu-
tion was washed by 3 9 10 mL CHCl3 and the CHCl3
solutions were combined together. The combined CHCl3
solution was washed by 10 mL distilled water, dried by
MgSO4, concentrated. The residue was purified by chro-
matographic column (50 cm 9 3 cm, SiO2 100–200 mesh,
acetone/CH2Cl2 (1:20, V/V) as eluant, 400 mL), then
compound 6 was obtained as white powder in yield of 61%.
m.p. 193–195 °C; IR (KBr, cm-1): 1,711 (HC=O), 1,684
(NC=O); 1HNMR (400 MHz, CDCl3) d: 1.15 (s, 18H,
C(CH3)3), 1.25 [s, 9H, C(CH3)3], 3.50 (d, 2H, J = 13.2 Hz,
ArCH2Ar), 3.61 (d, 2H, J = 13.2 Hz, ArCH2Ar), 3.68 (bs,
4H, NCH2), 4.13 (d, 2H, J = 13.2 Hz, ArCH2Ar), 4.18
(d, 2H, J = 13.2 Hz, ArCH2Ar), 4.54 (s, 4H, OCH2), 7.06
(bs, 4H, ArH), 7.13 (s, 2H, ArH), 7.66 (s, 2H, ArH), 8.23
(s, 1H, OH), 8.43 (bs, 2H, NH), 9.26 (s, 1H, OH), 9.79
(s, 1H, CHO), m/z (%): 760.1 (M?, 100), Anal calcd. for
C47H56O7N2, C 74.17, H 7.41, N 3.68; found C 74.10, H
7.49, N 3.59.
Compound 7c: straw yellow powder, m.p. 264–266 °C;
IR (KBr, cm-1): 3,375 (N–H and O–H), 1,677 (C=O),
1,596 (C=N); 1HNMR (400 MHz, CDCl3) d: 1.13 (s, 18H,
C(CH3)3), 1.24 (s, 9H, C(CH3)3), 3.49 (d, 2H, J = 13.2 Hz,
ArCH2Ar), 3.56 (d, 2H, J = 13.2 Hz, ArCH2Ar), 3.68
(s, 4H, NCH2), 4.11 (d, 2H, J = 13.2 Hz, ArCH2Ar), 4.15
(d, 2H, J = 13.2 Hz, ArCH2Ar), 4.53 (s, 4H, OCH2), 7.06
(s, 4H, ArH), 7.10 (s, 2H, ArH), 7.55 (s, 2H, ArH), 7.78
(s, 1H, OH), 8.21 (bs, 2H, ArH), 8.48 (bs, 2H, ArH), 8.72
(s, 1H, OH), 8.90 (s, 2H, NH), 9.25 (s, 1H, CH=N), 9.84 (s,
1H, NH), m/z (%): 902.9 (MNa?, 100), Anal calcd. for
C53H61O7N5, C 72.33, H 6.99, N 7.96; found C 72.24, H
6.94, N 7.89.
Synthesis of calix[4]-aza-crown hydrazone derivatives
7a, 7b, 7c, and 7d
Compound 7d: straw yellow powder, m.p. 256–257 °C;
IR (KBr, cm-1): 3,380 (N–H and O–H), 1,678 (C=O),
1,599 (C=N); 1HNMR (400 MHz, CDCl3) d: 1.15 (s, 18H,
C(CH3)3), 1.25 (s, 9H, C(CH3)3), 3.49 (d, 2H, J = 13.2 Hz,
ArCH2Ar), 3.54 (d, 2H, J = 13.2 Hz, ArCH2Ar), 3.68
(s, 4H, NCH2), 4.13 (d, 2H, J = 13.2 Hz, ArCH2Ar), 4.17
Under N2 atmosphere, a mixture of compound 6 (0.23 g,
0.3 mmol), salicyloyl hydrazine (0.053 g, 0.35 mmol) and
0.1 mL glacial acetic acid was stirred and refluxed in
25 mL solution of CHCl3 and MeOH (V:V = 3:2) for 10 h
and some precipitate appeared. TLC analysis revealed that
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J Incl Phenom Macrocycl Chem (2012) 74:257–263
259
(d, 2H, J = 13.2 Hz, ArCH2Ar), 4.54 (s, 4H, OCH2),
7.04–7.71 (m, 13H, ArH), 8.19 (s, 1H, OH), 8.27 (s, 1H,
OH), 8.43 (s, 1H, NH), 8.78 (s, 1H, NH), 8.88 (s, 1H,
CH=N), 9.13 (s, 2H, NH), m/z (%): 909.3 (M?, 100), Anal
calcd. for C54H63O6N5S, C 71.25, H 6.97, N 7.69; found C
71.17, H 6.91, N 7.58.
(d, 4H, J = 13.2 Hz, ArCH2Ar), 4.54 (s, 8H, OCH2), 7.07
(s, 8H, ArH), 7.10 (s, 4H, ArH), 7.13 (s, 4H, ArH), 7.65
(s, 4H, ArH), 7.90 (s, 2H, OH), 7.93 (s, 2H, OH), 8.22 (s, 2H,
CH=N), 8.47 (s, 4H, NH), 8.71 (s, 2H, CH=N), m/z (%):
1646.4 (M?, 100), Anal calcd. for C102H118O12N18: C 74.33,
H 7.22, N 6.80; found C 74.39, H 7.26, N 6.69.
Non-competitive extraction experiments of single metal
cation
Synthesis of mono-bridged biscalix[4]-aza-crown
hydrazone derivatives 8a, 8b and 8c
According to the reported method, 3 mL of chloroform
solution containing calixarene derivatives (2.0 9 10-5 M)
and 3 mL of aqueous solution containing a metal picrate
(2.0 9 10-5 M) were placed in a flask [20]. The mixture
was shaken for 5 min and stored for 2 h at 25 °C. The
extraction ability was not affected by further shaking,
indicating that the equilibrium had been attained within
2 h. The aqueous phase was separated and subjected to the
analysis by UV absorption spectrometry in near 357 nm.
The extraction percentage (E%) was determined by the
decrease of the picrate concentration in the aqueous
Under N2 atmosphere, a mixture of compound 5 (0.23 g,
0.3 mmol), 0.1 mL glacial acetic acid and corresponding
difunctional reagent (compounds 2, 3 or 4) was stirred
and refluxed in 25 mL solution of CHCl3 and MeOH
(V:V = 3:2) for 12 h, and some precipitate appeared. TLC
analysis revealed that the starting materials were disap-
peared. After distilling off the solvent by reduced pressure,
10 mL methanol was added and the precipitate was sepa-
rated. The crude product was then recrystallized in CHCl3/
MeOH. Compounds 8a, 8b and 8c were obtained as powders
in yields of 87, 74, and 76%, respectively. Compound 8a:
gray powder, m.p. 264–265 °C; IR (KBr, cm-1): 3,370 (N–H
and O–H), 1,682 (C=O), 1,605 (C=N); 1HNMR (400 MHz,
CDCl3) d: 1.15 [s, 36H, C(CH3)3], 1.25 (s, 18H, C(CH3)3),
1.85 (bs, 4H, CH2CH2CO), 2.83 (bs, 4H, CH2CH2CO), 3.48
(d, 4H, J = 13.2 Hz, ArCH2Ar), 3.55 (d, 4H, J = 13.2 Hz,
ArCH2Ar), 3.67 (s, 8H, NCH2), 4.10 (d, 4H, J = 13.2 Hz,
ArCH2Ar), 4.14 (d, 4H, J = 13.2 Hz, ArCH2Ar), 4.52
(s, 8H, OCH2), 7.06 (s, 8H, ArH), 7.11 (s, 4H, ArH), 7.37
(s, 4H, ArH), 7.50 (s, 2H, OH), 7.60 (s, 2H, OH), 8.46 (s, 2H,
NH), 8.77 (s, 4H, NH), 9.01(s, 2H, CH=N), m/z(%): 1,683.5
(MNa?, 100), Anal calcd. for C100H122O14N8: C 72.35, H
7.41, N 6.75; found C 72.27, H 7.47, N 6.67.
ÈÀ
Á
É
phase: E% ¼ ½Picꢁblankꢂ½Picꢁwater =½Picꢁblank ꢃ 100 where
[Pic]blank denoted the picrate concentrations in the aqueous
phase after extraction with pure chloroform, and [Pic]water
denoted the picrate concentrations in the aqueous phase
after extraction with chloroform solution containing cal-
ixarene derivatives as extractants. Average of two inde-
pendent experiments was carried out. Control experiments
showed that no picrate extraction occurred in the absence
of the calixarene derivatives. The relative standard devia-
tions from the mean were less than 5%. The test showed
that the pH value in each aqueous phase were neutral
(6.9–7.1) and the values made no change before and after
extraction, which indicated the metal picrates were
extracted successfully.
Compound 8b: brown powder, m.p. 269–271 °C; IR
(KBr, cm-1): 3,440 (N–H and O–H), 1,650 (C=O), 1,601
(C=N); 1HNMR (400 MHz, CDCl3) d: 1.15 (s, 36H,
C(CH3)3), 1.26 (s, 18H, C(CH3)3), 1.42 (bs, 4H,
CH2CH2CH2N), 2.00 (bs, 4H, CH2CH2CH2N), 3.34 (bs,
4H, CH2CH2CH2N), 3.47 (d, 4H, J = 14.0 Hz, ArCH2Ar),
3.52 (d, 4H, J = 14.0 Hz, ArCH2Ar), 3.67 (s, 8H, NCH2),
4.10 (d, 4H, J = 14.0 Hz, ArCH2Ar), 4.16 (d, 4H,
J = 14.0 Hz, ArCH2Ar), 4.53 (s, 8H, OCH2), 7.07 (s, 8H,
ArH), 7.10 (s, 4H, ArH), 7.33 (s, 4H, ArH), 7.60 (s, 2H,
OH), 7.65 (s, 2H, OH), 8.17 (s, 2H, NH), 8.46 (s, 4H, NH),
8.67 (s, 2H, NH), 9.03 (s, 2H, CH=N), m/z (%): 1717.3
(M?, 100), Anal calcd. for C102H128O14N10: C 71.30, H
7.51, N 8.15; found C 71.34, H 7.45, N 8.10.
Competitive extraction experiments of metal cations
Competitive extraction experiments were performed with
equal volumes (10 mL) of an aqueous solution of an
equimolar mixture of picrate salts (Li?, Na?, K?, Cs?,
Cu2?, Ni2?, Co2?, Ag? and Hg2?, 2.0 9 10-5 M each)
and a CHCl3 solution (10 mL) of the hosts (2.0 9 10-5 M)
were mixed in a stopper flask and vigorously shaken for
15 min. The solution was stored for 2 h. This was repeated
three times. Then, the solutions were left standing for 24 h
at 25 °C until phase separation was completed. The relative
concentrations of the cations in the aqueous phase were
determined by ICP-OES. Quantification was made by using
a standard solution containing a mixture of picrate salts
(Li?, Na?, K?, Cs?, Cu2?, Ni2?, Co2?, Ag? and Hg2?).
Blank experiments without adding hosts were carried out
under same experimental conditions.
Compound 8c: yellow powder, m.p. 262–264 °C; IR
(KBr, cm-1): 3,371 (N–H and O–H), 1,692 (C=O), 1,622
(C=N); 1HNMR (400 MHz, CDCl3) d: 1.16 (s, 36H,
C(CH3)3), 1.26 (s, 18H, C(CH3)3), 3.49 (d, 4H, J = 13.2 Hz,
ArCH2Ar), 3.59 (d, 4H, J = 13.2 Hz, ArCH2Ar), 3.69
(s, 8H, NCH2), 4.14 (d, 4H, J = 13.2 Hz, ArCH2Ar), 4.18
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Results and discussion
Synthesis and characterization
formylated calix[4]-aza-crown 6 was prepared in 61% after
chromatographic column. Moreover, it was interesting that
mono-formylated calix[4]-aza-crown 6 was the main
product and no bis-formylated product was separated no
matter how to change the reaction condition, such as pro-
longing the reaction time and raising the reaction temper-
ature. This result was utterly different from the formylated
results of other calix[4]-1,3-substituted esters or ethers,
The synthetic route was shown in Scheme 1. Compounds
1–5 were obtained according to the methods in references
[18, 19]. Then reacting calix[4]-1,3-aza-crown 5 with
hexamethylenetetramine in trifluoroacetic acid, mono-
Scheme 1
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J Incl Phenom Macrocycl Chem (2012) 74:257–263
261
which gave bis-formylation as main products reported by
Chawla’s et al. and our previous experiments [6, 13]. The
different formylated results might be attributed to the
influences of bridging structures of calix[4]-aza-crown. By
condensating compound 6 with salicyloyl hydrazine, 2,4-
dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl
thiosemicarbazide, respectively, a series of novel calix[4]-
aza-crown hydrazone derivatives 7a, 7b, 7c, and 7d were
prepared conveniently in yields of 70–90% after recrys-
tallization. On the other hand, by reacting compound 6 with
bifunctional reagents 2, 3 or 4, novel mono-bridged bi-
scalix[4]-aza-crown hydrazone derivatives 8a, 8b and 8c
were obtained after recrystallization in high yields. It was
worthy of noting that compounds 7a–c and 8a–c were the
first examples of formylated calix[4]-aza-crown derivatives
and biscalix[4]crown derivatives.
fall of complexation abilities in buffered solution. In our
extraction experiment, the pH value in each aqueous phase
were neutral (6.9–7.1) and the values made no change
before and after extraction, which indicated the metal
picrate were extracted successfully. The extraction results
were showed in Figs. 1, 2. It could be seen that new
compounds 6, 7a–7d and 8a–8c showed good extraction
abilities for both hard and soft metal cations. Comparing
with the extraction results of calixarene derivatives with
similar structures in references [6, 14, 21], the good
extraction abilities of new compounds 7a–7d and 8a–8c for
hard and soft metal cations should be attributed to the
favorable influences of oxo-functional groups (including
phenolic hydroxyl group, ether group and carbonyl group)
for binding hard cations and aza(or sulf)-functional groups
The structures of new compounds 7a–d and 8a–c were
confirmed by IR spectra, ESI-MS spectra, elemental ana-
6
7a
7b
7c
7d
8a
8b
8c
90
80
70
60
50
40
30
20
10
0
1
lyzes, H NMR spectra. In the IR spectra, the adsorption
peaks (1,711 cm-1) of formyl groups of compound 6 was
disappeared utterly and new adsorption peaks of C=N
groups were appeared. The ESI-MS spectra of all new
compounds clearly showed corresponding molecular base
peaks (M? or MNa?) respectively, which indicated the
intermolecular Schiff-base condensations were accom-
plished completely. The 1H NMR spectra of all new
compounds exhibited two singlets (2:1) for tert-butyl
groups, two pairs of doublets (1:1:1:1) for the methylene
bridges of the calix[4]arene skeleton, which indicated that
the calix[4]arene units adopt the cone conformation as
showed in Scheme 1. As to the cis/trans conformers about
C(O)–N bond and E/Z geometrical isomers respect to the
C=N double bonds in these new compounds, it could be
deduced that the mixed conformers and isomers were
existed by comparing with the similar structures [21]. But
it was difficult to determine the percentage of different
isomers due to the overlapped signal of NH and OH in IR
spectra and the absence of CH2 groups beside the C(O)–N
bond and C=N double bond, which were crucial factor to
study the percentages of different isomers [21].
Li+
Na+
K+
Cs+
Fig. 1 The extraction percentages of receptors 6, 7a–d and 8a–c for
hard metal cations
6
7a
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
7b
7c
7d
8a
8b
8c
Non-competitive extraction experiments of single metal
cation
The metal cation complexation properties of all new
compounds were preliminarily studied by non-competitive
extraction experiments. There were two methods to study
the extraction abilities. One was that metal picrate was
extracted directly in neutral solution and another was in
buffered solution [20, 22]. Due to the binding abilities of
NH and OH were greatly influenced by pH, the method of
using metal picrates as extract directly in neutral solution
was employed in our extraction experiments to avoid the
0
Cu2+
Ni2+
Co2+
Ag+
Hg2+
Fig. 2 The extraction percentages of receptors 6, 7a–d and 8a–c for
soft metal cations
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Table 1 Competitive extracting percentages (E%) of compounds 7a–d and 8a–c for picrate salts
Cations
Li?
Na?
K?
Cs?
Cu2?
Ni2?
Co2?
Ag?
Hg2?
7a
7b
7c
7d
8a
8b
8c
3.2
3.4
2.6
4.6
7.6
6.2
5.6
8.9
6.8
4.6
5.5
3.5
7.8
8.9
8.4
6.8
5.3
4.9
10.8
8.3
12.5
16.7
18.8
18.2
16.9
20.8
27.7
10.6
9.4
9.4
10.2
12.8
13.5
24.8
27.6
25.3
17.3
13.9
19.5
16.3
19.3
16.8
9.8
4.8
5.2
6.9
10.3
10.9
17.4
17.3
19.4
8.6
8.4
9.2
14.5
13.7
10.7
9.7
10.3
23.6
11.5
10.6
9.9
for binding soft cations according to principle of ‘‘hard and
soft acids and bases’’. On the other hand, the extraction
percentages of compounds 7a–7d, especially for soft metal
cations, were higher than that of precursor 6, which indi-
cated that the hydrazone groups produced advantageous
influences for binding soft metal cations. Moreover, bi-
scalixarene derivatives 8a–8c exhibited far higher extrac-
tion percentage than precursor 6 and compounds 7, which
might suggest the two calix[4]arene units of compounds 8
could bind metal cations synchronously. The extraction
percentages of compound 8a for Ni2? and Ag? were as
high as 85 and 89%, respectively. These non-competitive
extraction experiments suggested that some of novel hosts
were good receptors for test metal cations.
experiments, whereas it were only 2.1 and 1.6 in non-
competitive extraction experiments, respectively. All these
extraction results suggested that new compounds 7a–d and
8a–c were good receptors for metal cations. Especially,
compounds 8a–c with two calixarene units might possess
cooperative complexation capabilities for other compli-
cated guests, such as ion pairs and amino acids, which will
be studied in further work.
Conclusions
The first formylated calix[4]-aza-crown 6 was synthesized
by reacting calix[4]-1,3-aza-crown with hexamethylene-
tetramine in TFA in high yield. Reacting compound 6 with
salicyloyl hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl
hydrazine or phenyl thiosemicarbazide afforded four novel
calix[4]arene hydrazone-based receptors 7a–d in yields of
70–90%. On the other hand, by reacting compound 6 with
series of bifunctional reagents, novel mono-bridged bi-
scalix[4]-aza-crown hydrazone derivatives 8a–c were pre-
pared in high yields. The non-competitive and competitive
extraction experiments showed that all new compounds
were good receptors for hard and soft metal cations. The
extraction results suggested that the hydrazone groups are
favorable for binding soft metal cations and the two
calix[4]arene units in compounds 8a–c could bind metal
cations concurrently.
Competitive extraction experiments of metal cations
Based on the non-competitive extraction experiments, the
competitive extraction experiments were carried out to
investigate the complexation selectivity for metal cations.
The competitive extraction percentages were summarized
in Table 1. It can be seen that compounds 7a–d and 8a–c
showed good extraction abilities towards both hard and soft
metal cations, the extraction percentages for soft metal
cations were higher than that for hard metal cations. Also,
the extraction percentages of biscalix[4]arenes 8a–c were
higher than that of compounds 7a–d. These results were in
accordance with non-competitive extraction experiments.
Moreover, it was worthy of noting that the total extraction
percentages (the addition of each extraction percentage) of
compounds 8a–c for metal cations exceeded 100%. The
biggest total extraction percentage of compound 8b was as
high as 145%. These results could be explained that the
two calix[4]arene units of compounds 8a–c could bind
metal cations concurrently. On the other hand, comparing
with the extraction selectivity in non-competitive extrac-
tion experiments, the extraction selectivity was improved
in competitive extraction experiments. For examples, the
extraction ratios Ni2?/Li? and Ag?/Hg2? of compound 8c
were up to 4.9 and 2.6 in competitive extraction
Acknowledgments The financial support from the National Natural
Science Foundation of China (No: 20402002), Fujian Natural Science
Foundation of China (No. 2011J01031), Project of Fujian provincial
department of education (JA11044), Program for excellent young
researchers in university of Fujian Province (JA10056) were greatly
acknowledged.
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