Synthesis of novel Hg2+ receptors based on N-benzyloxyamide derivatives and their application to anion-selective electrodes

Article abstract of DOI:10.1039/b008978h

Novel Hg²⁺ receptors having two N-benzyloxyamide groups are synthesized, and their complexation ability toward metal cations is examined. The structure of the formed complexes was elucidated by ESI-MS and ¹H NMR spectroscopy. Deprotonation of the amide groups allows the receptors to form stable complexes with Hg²⁺. As an application of this neutral Hg²⁺ complex, an anion-selective electrode combined with a cationic additive is prepared, and exhibits an anti-Hofmeister selectivity pattern with enhanced selectivity for the iodide anion. The overall selectivity pattern of the electrode is I^- > ClO₄^- > SCN^- ≈ Br^- > salicylate^- > NO₂^- > Cl^- > NO₃^- ? HCO₃^- > SO₄^2- > F^- > H₂PO₄^-.

Full text of DOI:10.1039/b008978h

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Synthesis of novel Hg2؉ receptors based on N-benzyloxyamide
derivatives and their application to anion-selective electrodes†
Shin-ichi Sasaki,a Tsuyoshi Amano,a Satoru Ozawa,a Tomomi Masuyama,a Daniel Citterio,b
Hideaki Hisamoto,‡a Hisao Hori§a and Koji Suzuki*a,b
1
a Department of Applied Chemistry, Keio University, 3-14-1 Hiyoshi, Kohoku-ku,
Yokohama 223-8522, Japan. E-mail: suzuki@applc.keio.ac.jp
b Kanagawa Academy of Science and Technology (KAST), KSP West-614, 3-2-1 Sakato,
Kawasaki 213-0012, Japan
Received (in Cambridge, UK) 8th November 2000, Accepted 10th April 2001
First published as an Advance Article on the web 23rd May 2001
Novel Hg2ϩ receptors having two N-benzyloxyamide groups are synthesized, and their complexation ability
toward metal cations is examined. The structure of the formed complexes was elucidated by ESI-MS and
1H NMR spectroscopy. Deprotonation of the amide groups allows the receptors to form stable complexes
with Hg2ϩ. As an application of this neutral Hg2ϩ complex, an anion-selective electrode combined with a
cationic additive is prepared, and exhibits an anti-Hofmeister selectivity pattern with enhanced selectivity
for the iodide anion. The overall selectivity pattern of the electrode is IϪ > ClO4Ϫ > SCNϪ ≈
BrϪ > salicylateϪ > NO2Ϫ > ClϪ > NO3Ϫ ӷ HCO3Ϫ > SO42Ϫ > FϪ > H2PO4
.
Ϫ
in our complexation study aiming at a new type of halide
ionophore. For example, chloride anion is one of the most
important analytes in biological samples, and the development
of chloride-selective electrodes is of current interest. Because
traditional ISEs based on quaternary ammonium salts follow
the well-known Hofmeister series (the order of the free energy
of hydration of the analyte anions), several ionophores con-
taining metals such as Mn,5 Co,6 Ag,7 In,8 or Hg9,10 have been
examined as halide-selective ionophores. Among them, the
use of the Lewis acidity of the mercury atom is known to be
effective for the detection of chloride anion, and organic
mercury compounds9 as well as inorganic mercury complexes10
have been reported to be excellent halide ionophores. Thus,
we decided to investigate the application of the stable Hg2ϩ–2b
complex to an anion-selective electrode. It turned out that this
electrode is promising as a chloride-selective electrode, because
the response to major interfering anions like SCNϪ, salicylateϪ,
or HCO3Ϫ was limited.
Introduction
The design and synthesis of new receptor molecules for the
selective complexation of ions have attracted much attention
because of their possible application to ion-selective electrodes
(ISEs) or optodes.1 So far, many synthetic receptors, mainly
represented by crown ethers, have been developed for the
purpose of recognizing biologically important cations such as
alkali or alkaline earth metal ions,2 and they have been used as
ionophores for ISEs applied to clinical analysis. Receptors for
transition metal ions, however, are relatively rare in spite of
their importance for environmental monitoring.
In this respect, we recently reported that N-benzyloxyamide
derivative 1 selectively forms complexes with Hg2ϩ and that it
is a useful ionophore for ISEs to detect Hg2ϩ with good
reproducibility.3 Most ISEs based on heavy-metal ionophores
developed to date generally demonstrate silver ion selectivity
rather than that for other cations. However, the electrode based
on ionophore 1 having two N-benzyloxyamide groups exhibited
remarkably high selectivity for Hg2ϩ. In order to further investi-
gate the nature of this functional group in detail, we syn-
thesized the new N-benzyloxyamide derivatives 2a and 2b and
examined the structures of their complexes using ESI-MS and
1H NMR spectroscopy. As a result, it was found that 2a and 2b
form stable complexes accompanied by deprotonation of the
amide groups only when Hg2ϩ was added. This is one of the
rare examples of a receptor which can form a neutral complex
with a metal cation.
Transition metals are known to play an important role in the
development of anion receptors;4 therefore, we included anions
† Electronic supplementary information (ESI) available: MS of recep-
tors 1 and 2a with metal cations. See http://www.rsc.org/suppdata/p1/
b0/b008978h/
‡ Present address: Department of Applied Chemistry, Graduate School
of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8566, Japan.
§ Present address: National Institute of Advanced Industrial Science
and Technology, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan.
In this paper, we report that the mercury complexes of
N-benzyloxyamide derivatives are not only interesting from
a structual point of view but also are contributive to the
development of new anion ionophores.
1366
J. Chem. Soc., Perkin Trans. 1, 2001, 1366–1371
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b008978h

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Results and discussion
Synthesis of receptors 2a and 2b
N-Benzyloxyamide derivatives 2a and 2b, which have additional
oxygen atoms and alkyl groups compared with receptor 1, were
prepared from pinacol 3a and hexadecane-1,2-diol 3b, respec-
tively (Scheme 1). The Williamson reaction between 3a and
Fig. 1 MS spectrum of receptor 2a with Agϩ. The sample solution is a
mixture of 2a (2.7 mmol dmϪ3) in PriOH and AgNO3 (2.7 mmol dmϪ3
in MeOH in the volumetric ratio of 1 : 2.
)
Fig. 2 MS spectrum of receptor 2a with Hg2ϩ. The sample solution is
a mixture of 2a (2.7 mmol dmϪ3) in PriOH, NaNO3 (1.1 mmol dmϪ3) in
MeOH, and Hg(AcO)2 (2.7 mmol dmϪ3) in MeOH in the volumetric
proportions of 5 : 5 : 2.
Scheme 1 Reagents and conditions: (a) NaH, allyl bromide, THF,
reflux (4a: 89%; 4b: 82%); (b) (i) NaBH4, BF3ؒEt2O, THF, 0 ЊC; (ii) 3
mol dmϪ3 aq. NaOH, 30% H2O2, rt (5a: 47%; 5b: 24%); (c) (i) NaIO4,
RuCl3ؒH2O, CCl4–CH3CN–water, rt; (ii) TsOH, molecular sieves 3 Å,
benzene–EtOH, reflux (6a: 50%; 6b: 52%); (d) (i) KOH, EtOH–water,
rt; (ii) SOCl2, CH2Cl2, rt; (iii) O-benzylhydroxylamine, pyridine, rt (2a:
24%; 2b: 57%).
the other hand, the spectrum of 2a measured with Hg(AcO)2
exhibited a strong [M Ϫ 2H ϩ Hg ϩ Na]ϩ peak at m/z = 695
as shown in Fig. 2, but the molecular-ion peak of the charged
mercury complex [M ϩ Hg]2ϩ (m/z = 337) was not observed.
These results indicate that the formation of the Hg2ϩ–2a com-
plex is accompanied by deprotonation of the receptor molecule.
This behavior is also coincident with the super-Nernstian
response obtained for the ISE based on ionophore 1,3 which
can be explained by the proton response caused by deproton-
ation of the ionophore upon Hg2ϩ binding. Furthermore, it
was found that the intensity of the Hg2ϩ–2a complex peak
[M Ϫ 2H ϩ Hg ϩ Na]ϩ was much stronger than that of the
Hg2 ϩ –1 complex [M Ϫ 2H ϩ Hg ϩ Na]ϩ measured under the
same conditions, which is probably due to the increased binding
strength caused by the additional two oxygen atoms of receptor
2a.
allyl bromide gave diene 4a, which was converted to diol 5a
by hydroboration in 42% yield. Oxidation of 5a to the corre-
sponding dicarboxylic acid followed by esterification for puri-
fication gave diester 6a in 50% yield. Hydrolysis of 6a and
subsequent treatment with thionyl dichloride gave an acid
chloride, which was treated with O-benzylhydroxylamine to
give receptor 2a in 24% yield. Using essentially the same
procedure, receptor 2b was synthesized from 3b via diene 4b,
diol 5b, and diester 6b in 6% overall yield in seven steps.
Complexation ability of receptor 2a with Hg2؉
In order to confirm the complexation ability of receptor 2a with
metal cations, ESI-MS measurements were undertaken for
a mixture of 2a in PriOH and several cation salts in MeOH.
Fig. 1 shows the spectrum of the mixture of 2a and AgNO3. In
this case, the molecular-ion peak of the complex between 2a
and Agϩ, namely [M ϩ Ag]ϩ, was observed at m/z = 579
together with the sodium complex peak [M ϩ Na]ϩ (m/z = 495).
When the spectra of 2a were measured in the presence of
Ca(NO3)2ؒ4H2O or Ca(AcO)2ؒH2O, both [M ϩ Ca]2ϩ (m/z =
256) and [M ϩ Na]ϩ peaks were observed (data not shown). On
1H NMR measurements were performed in order to obtain
information about the Hg2ϩ–2a complex in solution. Because
of the limited solubility of Hg(AcO)2, a mixed solvent CDCl3–
(CD3)2SO (14 : 1) was used. Fig. 3 shows the 1H NMR spectra
of 2a measured with the sequential addition of Hg(AcO)2. In
the presence of up to 1 eq. of Hg(AcO)2, the spectra exhibited
signals due to both the free receptor and the complex, indi-
cating that the equilibrium of complexation is slow on the
NMR time-scale. For example, the peak of the benzyl protons
at δ 4.87 decreased followed by an increase in a new peak at
J. Chem. Soc., Perkin Trans. 1, 2001, 1366–1371
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δ 4.80. As shown in Fig. 3(e), the signals of 2a have completely
disappeared with the addition of just 1 eq. of Hg(AcO)2. This
result shows that the binding constant of 2a with Hg2ϩ is
considerably large. In addition, it became apparent that a 1 : 1
complex is formed between 2a and Hg2ϩ, because the addition
of more than 1 eq. of Hg(AcO)2 did not cause any change in
the spectrum (not shown). Moreover, with the signal decrease
for the NH proton at δ 9.95, no corresponding new peak of
the complex was found. This observation also suggests that
the complex formation of 2a with Hg2ϩ is accompanied by
elimination of two amide protons from the receptor.
Anion-selective electrode based on the Hg2؉–2b complex
Because the Hg2ϩ–2a complex was found to be stable in solu-
tion, the application of the complex to an ISE as an anion
ionophore was examined. In order to increase the lipophilicity
of the ionophore to prevent leaching from the ISE membrane,
the Hg2ϩ–2b complex having a long alkyl chain was used for the
ISE measurements. The selectivity coefficients of the electrodes
based on the Hg2ϩ–2b complex are shown in Fig. 4. Without
the cationic additive [tridodecyl(methyl)ammonium chloride,
TDDMACl], the electrode based on the complex showed
almost no response to anions except for iodide. This behavior
is similar to that observed for organic mercury compounds9
rather than that for inorganic mercury complexes,10 suggesting
that the deprotonated Hg2ϩ–2b complex is essentially an
electrically neutral species as illustrated in Fig. 5. Therefore, the
amount of the cationic additive was optimized until the best
result was found at 10 mol% of TDDMACl relative to the
ionophore. When more than 10 mol% of the cationic additive
was added, the selectivity of the electrode gradually
approached that of the Hofmeister series (TDDMACl; Fig. 4,
column 1). The electrode based on the Hg2ϩ–2b complex com-
bined with 10 mol% TDDMACl exhibited a strong preference
for the iodide anion, similar to those of organic mercury com-
pounds,9 but with a non-linear response. At the same time,
it should be noted that the selectivity for the biologically
important chloride anion is also excellent, so that this electrode
can be regarded as an example of a chloride-selective electrode.
The electrode showed a Nernstian response to chloride in
the linear range from 10Ϫ4 to 10Ϫ1 mol dmϪ3 with a slope of
Fig. 3 1H NMR spectra [CDCl3–(CD3)2SO, 14 : 1] of (a) receptor 2a,
(b) 2a with 0.2 eq. Hg(AcO)2, (c) 2a with 0.5 eq. Hg(AcO)2, (d) 2a with
0.75 eq. Hg(AcO)2, and (e) 2a with 1 eq. Hg(AcO)2.
Fig. 4 Potentiometric selectivity coefficients (log KCl pot, j = interfering ion) of the electrodes based on the Hg2ϩ–2b complex with different
Ϫ,j
concentrations of tridodecyl(methyl)ammonium chloride (TDDMACl). The membrane compositions were 3% (by weight) ionophore, 64% mem-
brane solvent o-nitrophenyl octyl ether (o-NPOE), 33% poly(vinyl chloride) (PVC), and 0–100 mol% (relative to the ionophore) TDDMACl. The
measurements were carried out at 25.0 0.5 ЊC.
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J. Chem. Soc., Perkin Trans. 1, 2001, 1366–1371

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5,5,6,6-Tetramethyl-4,7-dioxadecane-1,10-diol 5a. To
a
solution of NaBH4 (6.56 g, 173 mmol) in THF (200 cm3) was
added a solution of diene 4a (38.2 g, 193 mmol) in THF (200
cm3). A solution of boron trifluoride–diethyl ether complex
(32.8 g, 231 mmol) in THF (100 cm3) was then added dropwise
over a period of 1.5 h at 0 ЊC. The reaction mixture was stirred
for 20 h, after which 3 mol dmϪ3 aq. NaOH was added followed
by addition of 30% H2O2. The mixture was stirred for 2 h and
extracted with EtOAc. The extract was dried over Na2SO4 and
evaporated under reduced pressure. The residue was purified by
column chromatography on silica gel (hexane–EtOAc, 1 : 4) to
give the diol 5a (21.3 g, 47%) as a colorless oil, νmax (neat)/cmϪ1
3392, 1363, 1154, 1072; δH (270 MHz) 1.17 (12H, s, Me), 1.76
(4H, quintet, J 5.6, CH2CH2CH2), 3.51 (2H, br s, OH), 3.58
(4H, t, J 5.6, OCH2CH2), 3.74 (4H, br s, HOCH2CH2).
Fig. 5 Proposed structure of the Hg2ϩ–2b complex.
Ϫ55 mV/decade. The detection limit was calculated to be
5.0 × 10Ϫ5 mol dmϪ3. Although the interference of BrϪ is still
high, the response to major interfering anions like SCNϪ,
Ϫ
salicylateϪ, or HCO3 was relatively limited (log KCl ,j: SCNϪ,
Ϫ
5,5,6,6-Tetramethyl-4,7-dioxasebacic acid diethyl ester 6a. To
a solvent mixture (CCl4, 100 cm3; acetonitrile, 100 cm3; water,
150 cm3) were added diol 5a (5.01 g, 24.2 mmol) and sodium
periodate (31.1 g, 145 mmol). The mixture was vigorously
stirred for 20 min, and ruthenium() chloride hydrate (22 mg,
0.10 mmol) was then added in the dark. After being stirred for
1 h, the mixture was extracted with CH2Cl2. The extract was
dried over Na2SO4 and evaporated under reduced pressure to
leave a green solid. Toluene-p-sulfonic acid monohydrate (569
mg, 3.0 mmol) and molecular sieves 3 Å (57 mg) were added
to a solution of the above crude acid in benzene–EtOH (1 : 1;
80 cm3). The mixture was heated under reflux for 24 h. After
cooling of the mixture, water was added and the mixture was
extracted with EtOAc. The extract was dried over Na2SO4 and
evaporated under reduced pressure. The residue was purified by
column chromatography on silica gel (hexane–EtOAc, 4 : 1) to
give the ester 6a (3.88 g, 50% for two steps) as a colorless oil,
νmax (neat)/cmϪ1 1740, 1186, 1151, 1064; δH (270 MHz) 1.12
(12H, s, Me), 1.25 (6H, t, J 7.1, OCH2CH3), 2.47 (4H, t, J 6.2,
COCH2), 3.66 (4H, t, J 6.2, COCH2CH2), 4.13 (4H, q, J 7.1,
OCH2CH3).
ϩ1.9; salicylateϪ, ϩ1.2; HCO3Ϫ, Ϫ2.6). The degree of response
to these anions is comparable to that of the ISEs based on a
neutral thiourea derivative, which was recently reported to be a
chloride-selective ionophore.11
Conclusions
We have synthesized two N-benzyloxyamide derivatives and
examined their novel Hg2ϩ complex structures caused by depro-
tonation of the amide groups. Moreover, the stable Hg2ϩ com-
plex was applied to an ISE as an anion-selective ionophore. The
ISE based on this electrically neutral complex combined with a
cationic additive showed a selective response to halide anions,
especially to the iodide anion. As a chloride-selective electrode,
it was found that the effect of lipophilic anions like SCNϪ and
Ϫ
salicylateϪ but also of the more hydrophilic HCO3 could be
considerably reduced compared with the conventional chloride
electrode based on TDDMACl.
Experimental
1H NMR spectra were recorded on a JEOL JNM-GSX270
(1H, 270 MHz) or a JEOL JNM-LA300 (1H, 300 MHz)
spectrometer in CDCl3. Coupling constants J are given in Hz
and all chemical shifts are relative to an internal standard
N,NЈ-Bis(benzyloxy)-5,5,6,6-tetramethyl-4,7-dioxasebacic
acid diamide 2a. To a solution of KOH (2.54 g, 45 mmol)
in EtOH–water (1 : 2, 80 cm3) was added ester 6a (2.00 g,
6.28 mmol), and the mixture was stirred for 12 h at room tem-
perature. The mixture was then concentrated and the resulting
dicarboxylic acid was dried under vacuum and dissolved in
CH2Cl2 (5 cm3) with one drop of DMF. To this solution was
slowly added SOCl2 (1.68 g, 14 mmol). After being stirred for
2 h, the mixture was filtered through a pad of Celite, and the
filtrate was concentrated to leave a yellow oil (1.33 g). To a
solution of O-benzylhydroxylamine hydrochloride (1.49 g, 9.3
mmol) in pyridine (20 cm3) was added the above acid chloride at
0 ЊC, and the mixture was stirred for 2 h at room temperature.
The mixture was acidified with dil. aq. HCl and extracted with
CHCl3. The extract was dried over Na2SO4 and evaporated
under reduced pressure. The residue was purified by column
chromatography on silica gel (CHCl3–EtOAc, 1 : 2) to give the
receptor 2a (714 mg, 24% for three steps) as a white solid,
mp 94–95 ЊC; νmax (KBr)/cmϪ1 3133, 1660, 699; δH (270 MHz)
1.04 (12H, s, Me), 2.30 (4H, br s, COCH2), 3.51 (4H, t, J 5.3,
COCH2CH2), 4.86 (4H, s, PhCH2), 7.32–7.38 (10H, m, Ph),
9.23 (2H, s, NH) (Found: C, 66.03; H, 7.82; N, 5.93. Calc. for
C26H36N2O6: C, 66.08; H, 7.68; N, 5.93%).
of tetramethylsilane. IR spectra were measured with
a
BIO-RAD FTS-60A instrument. Mps were determined on a
BÜCHI B-545 apparatus and are uncorrected. All moisture-
sensitive reactions were carried out under an atmosphere of
nitrogen. All reagents were used as obtained from commercial
suppliers. THF was distilled from benzophenone ketyl under
nitrogen before use. All other solvents were purified according
to standard procedures.
Preparation of receptors
5,5,6,6-Tetramethyl-4,7-dioxadeca-1,9-diene 4a. To a stirred
solution of pinacol 3a (10.0 g, 84.6 mmol) in THF (100 cm3)
was added NaH (8.12 g, 338 mmol) in small portions. The
mixture was stirred at room temperature for 1 h, after which a
solution of allyl bromide (41.0 g, 338 mmol) in THF (100 cm3)
was added. The reaction mixture was heated under reflux for
22 h, then MeOH was added to quench the reaction followed by
addition of water. The mixture was extracted with EtOAc and
the extract was dried over Na2SO4. The solvent was evaporated
under reduced pressure, and the residue was purified by column
chromatography on silica gel (hexane–EtOAc, 6 : 1) to give the
diene 4a (12.2 g, 89%) as a yellow oil, νmax (neat)/cmϪ1 1648,
1361, 1157, 917; δH (270 MHz) 1.20 (12H, s, Me), 3.99 (4H, ddd,
J 1.8, 1.8 and 5.0, OCH2), 5.06 (2H, ddt, J 1.8, 1.8 and 10.4,
CH=CH2) and 5.25 (2H, ddt, J 1.8, 1.8 and 17.2, CH=CH2),
5.91 (2H, ddt, J 1.8, 10.4 and 17.2, CH=CH2).
5-Tetradecyl-4,7-dioxadeca-1,9-diene 4b. The reaction of
hexadecane-1,2-diol 3b (10.0 g, 38.7 mmol) with allyl bromide
(18.7 g, 155 mmol) using NaH (6.2 g, 155 mmol) was carried
out as described for the preparation of 4a. The reaction mixture
was worked up as above, and subsequent purification by
chromatography on silica gel (hexane–EtOAc, 24 : 1) gave
J. Chem. Soc., Perkin Trans. 1, 2001, 1366–1371
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diene 4b (10.8 g, 82%) as a colorless oil, δH (270 MHz) 0.88
(3H, t, J 6.6, Me), 1.26–1.54 (26H, m, CH2), 3.41–3.53
in MeOH was added in order to promote ionization of the
neutral species.
(3H, m, OCH CHO), 3.98–4.19 (4H, m, 2 × CH CH᎐CH ),
᎐
2
2
2
5.12–5.31 (4H, m, 2 × CH CH᎐CH ), 5.84–6.00 (2H, m, 2 ×
Electrode preparation and EMF measurements
᎐
2
2
CH CH᎐CH ).
᎐
2
2
PVC matrix-based ion-sensitive membranes were prepared
according to the procedures described previously.12 The poly-
meric membrane composition was 3 wt% ionophore, 64 wt%
membrane solvent o-NPOE, 33 wt% PVC, and 0–100 mol%
(relative to the ionophore) TDDMACl. The membrane
thickness was ≈100 µm. A 6 mm diameter circle was cut
from a prepared membrane and placed on the tip of a PVC ion-
selective electrode body assembly (Liquid Electrode Membrane
Kit, DKK Co., Ltd., Tokyo, Japan). The prepared electrodes
were immersed in 0.1 mol dmϪ3 aq. NaCl for more than 24 h for
preconditioning before use. The external reference electrode
was a double-junction-type Ag–AgCl electrode (HS-305DS,
Toa Electronics, Ltd., Tokyo, Japan). The electrode potential
(EMF) measurements were performed according to the
reported procedure at 25 0.5 ЊC using the electrochemical cell
system, Ag|AgCl| saturated KCl | 0.3 mol dmϪ3 NH4NO3 ||
sample solution|ISE membrane|0.1 mol dmϪ3 NaCl|AgCl|Ag.
All sample solutions were prepared from sodium salts with
0.1 mol dmϪ3 HEPES–NaOH buffer solution at pH 7.0. The
selectivity coefficients Ki,jpot, where i stands for the primary ion
(ClϪ) and j for the interfering ion, were calculated from the
response potentials in the sodium anion salt solution using the
5-Tetradecyl-4,7-dioxadecane-1,10-diol 5b. The hydrobor-
ation of diene 4b (10.8 g, 31.9 mmol) with NaBH4 (1.09 g, 28.7
mmol) and boron trifluoride–diethyl ether complex (5.44 g, 38.3
mmol) was carried out as described for the preparation of 5a.
The reaction mixture was worked up as above, and purification
by chromatography on silica gel (hexane–EtOAc, 1 : 4) gave
diol 5b (2.90 g, 24%) as a colorless oil, νmax (neat)/cmϪ1 3400,
1120, 1083; δH (300 MHz) 0.88 (3H, t, J 6.6, Me), 1.26 (24H,
br s, CH2), 1.46 (2H, br s, CHCH2), 1.76–1.86 (4H, m,
HOCH2CH2), 3.07 and 3.27 (2H, br, OH), 3.39–3.50 (3H, m,
OCH2CHO), 3.62–3.78 (8H, m, HOCH2CH2CH2).
5-Tetradecyl-4,7-dioxasebacic acid diethyl ester 6b. The oxid-
ation of diol 5b (1.62 g, 4.32 mmol) with sodium periodate
(5.55 g, 25.9 mmol) and ruthenium() chloride hydrate (40 mg,
0.19 mmol) was carried out as described for the preparation of
6a. The crude dicarboxylic acid was converted to the ethyl ester
as above and purified by chromatography on silica gel (hexane–
EtOAc, 4 : 1) to give ester 6b (1.03 g, 52% for two steps) as a
colorless oil, νmax (neat)/cmϪ1 1738, 1186, 1120; δH (300 MHz)
0.88 (3H, t, J 6.8, Me), 1.23–1.49 (32H, m, CH2 and
OCH2CH3), 2.55 and 2.57 (4H, t, J 6.2, 2 × COCH2), 3.38–3.47
(3H, m, OCH2CHO), 3.70–3.89 (4H, m, 2 × COCH2CH2), 4.14
and 4.15 (4H, q, J 7.1, 2 × OCH2CH3).
separate-solution method (SSM; [i] = [j] = 0.1 mol dmϪ3
)
according to the recommendations of IUPAC13 and JIS.14
Acknowledgements
D. C. gratefully acknowledges a post-doctoral fellowship
granted by the Science and Technology Agency of Japan (STA).
N,NЈ-Bis(benzyloxy)-5-tetradecyl-4,7-dioxasebacic
acid
diamide 2b. The hydrolysis of ester 6b (500 mg, 1.09 mmol)
followed by conversion to the acid chloride and subsequent
reaction with O-benzylhydroxylamine hydrochloride were
carried out as described for the preparation of 2a. The crude
product was purified by chromatography on silica gel (CHCl3–
EtOAc, 1 : 2) to give the receptor 2b (379 mg, 57% for three
steps) as a white solid, mp 73–74 ЊC; νmax (KBr)/cmϪ1 3220,
1653, 697; δH (300 MHz) 0.88 (3H, t, J 6.7, Me), 1.25 (26H,
br s, CH2), 2.26–2.35 (4H, m, COCH2), 3.22–3.74 (7H, m,
2 × COCH2CH2 and OCH2CH), 4.83–4.93 (4H, m, PhCH2),
7.30–7.37 (10H, m, 2 × Ph), 9.03 and 9.41 (2H, br s, NH)
(Found: C, 70.58; H, 9.42; N, 4.56. Calc. for C36H56N2O6: C,
70.56; H, 9.72; N, 4.57%).
References
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Hg2؉–2b complex
The Hg2ϩ–2b complex was prepared by shaking a CHCl3 solu-
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was collected, and the solvent was evaporated to dryness.
The formation of the complex was confirmed by 1H NMR
spectroscopy, δH (300 MHz) 0.88 (3H, t, J 6.6, Me), 1.26 (26H,
br s, CH2), 2.30–2.38 (4H, m, COCH2), 3.23–3.74 (7H, m,
2 × COCH2CH2 and OCH2CH), 4.79–4.90 (4H, m, PhCH2),
7.26–7.36 (10H, m, 2 × Ph). The disappearance of the two
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Stock solutions (2.7 mmol dmϪ3) of AgNO3, Hg(AcO)2ؒH2O,
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1370
J. Chem. Soc., Perkin Trans. 1, 2001, 1366–1371

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