Dual channel chromo/fluorogenic chemosensors for cyanide and fluoride ions-an example of in situ acid catalysis of the Strecker reaction for cyanide ion chemodosimetry

Article abstract of DOI:10.1039/c2ob27096j

Two mesitylene based probes, having catechol/phenol units in conjunction to the Schiff base have been synthesized. The probe with a catechol unit can be used to sense and discriminate between F^- and CN^- through different colorimetric and fluorimetric responses using DMSO as solvent. However in DMSO:water (2:1) solution it responds selectively to CN^- ion. The probe with a phenol unit is highly selective and sensitive for CN^- and can be used for naked eye, semiquantitative sensing of CN^- ion in DMSO:water (2:1) solution. The chemodosimetry has been attributed to the acid catalyzed Strecker's reaction of an imine bond and is being reported for the first time in a Schiff's base.

Full text of DOI:10.1039/c2ob27096j

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Dual channel chromo/fluorogenic chemosensors for
cyanide and fluoride ions – an example of in situ acid
catalysis of the Strecker reaction for cyanide ion
chemodosimetry†
Cite this: Org. Biomol. Chem., 2013, 11,
654
Sanyog Sharma, Maninder Singh Hundal* and Geeta Hundal*
Two mesitylene based probes, having catechol/phenol units in conjunction to the Schiff base have been
synthesized. The probe with a catechol unit can be used to sense and discriminate between F− and CN−
through different colorimetric and fluorimetric responses using DMSO as solvent. However in DMSO :
water (2 : 1) solution it responds selectively to CN− ion. The probe with a phenol unit is highly selective
and sensitive for CN− and can be used for naked eye, semiquantitative sensing of CN− ion in DMSO :
water (2 : 1) solution. The chemodosimetry has been attributed to the acid catalyzed Strecker’s reaction
of an imine bond and is being reported for the first time in a Schiff’s base.
Received 30th August 2012,
Accepted 8th November 2012
DOI: 10.1039/c2ob27096j
www.rsc.org/obc
addition of CN− to a Schiff base’s imine bond has scarcely
been studied. The closest examples to this system are the two
Introduction
The importance of anions in biological, environmental and chemodosimeters using salicylaldehyde hydrazone functional-
chemical processes has given impetus to the development of ity10 where addition of cyanide to the imine bond of the hydra-
anion sensing receptors.1,2 Among various anions, fluoride zones has been suggested.
and cyanide have been extensively studied. The fluoride ion is
We have synthesized two mesitylene based dipodal Schiff
undoubtedly important3 in health care but its increasing use base systems incorporating catechol (4) and phenol (5) units as
in the synthesis of materials and biological catalysis4 has led the end groups (Scheme 1) and exploited the anion recogniz-
to its unwanted release, notwithstanding its 0.2 μM limit in ing ability of the –OH group in conjunction with the imine
drinking water. Similarly, the continued use of cyanide ion in group. In DMSO, 4 has been found to act as a naked eye chro-
various industrial processes5 causes its inevitable release in mogenic and ratiometric fluorogenic sensor for F− ion. This
the environment though 2 μM is its maximum allowed concen- compound also behaves as a dual channel chromogenic
tration in drinking water and 20 μM is considered as its lethal
level.6 Consequently there is always a need to develop sensors
to monitor these anions, and even more so for having a multi-
analyte sensing chemosensor catering to more than one ion
with distinctive and selective responses. As most of the chemo-
sensors for CN− ion suffer from unsolicited interference from
other ions, in particular the F− ion, therefore the selectivity is
a paramount issue.7 While there are fewer known chemodosi-
meters8 for F− ions, this sensing approach has been quite suc-
cessfully used in the case of CN− ions owing to its strong
nucleophilicity.9 Despite all these reports the nucleophilic
Department of Chemistry, Guru Nanak Dev University, Amritsar-143005, Punjab,
India. E-mail: geetahundal@yahoo.com, hundal_chem@yahoo.com
†Electronic supplementary information (ESI) available: General experimental
section, characterization of sensors by NMR, IR and mass spectroscopy, changes
in visible color and under UV lamp, absorption spectra, titration study of (4) and
(5) and characterization of chemodosimeter (6). CCDC 898519. For ESI and crys-
tallographic data in CIF or other electronic format see DOI: 10.1039/c2ob27096j
Scheme 1 Synthesis of sensors.
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Fig. 2 Changes in the UV-vis spectrum of 4 in DMSO (10 μM) on the addition
of various anions (100 μM).
Fig. 1 ORTEP diagram for (5) showing the labeling scheme. Hydrogens and
With F−, the intraligand charge transfer (ICT) band13d,14 at
λmax 355 nm disappears and a new peak appears at λmax
431 nm (εmax 7.3 × 104 M−1 cm−1) with a concomitant color
change from pale yellow to bright yellow. But in case of CN−, a
new absorption peak appears at λmax 445 nm with a lower
absorption (εmax 5.0 × 104 M−1 cm−1) which then shifts to
469 nm (ε = 5.5 × 104 M−1 cm−1) and then tails off up to
600 nm. The bathochromic shift increases with time
(Fig. S14†) and/or with further addition of TBACN. The satur-
ation causes the appearance of a new broad band at 500 nm
(ε = 6.3 × 104 M−1 cm−1). These spectral changes are
accompanied with visual color changes from pale yellow
to bright yellow to reddish orange. There are no visual or
spectroscopic changes with Cl−, Br−, I−, NO3−, ClO4−, AcO−,
HSO4− and H2PO4− ions.
solvent CCl4 have been omitted for clarity.
sensor or a chemodosimeter, depending on the concentration
of CN− ion in DMSO. In water, however it behaves as a highly
selective sensor for CN− ion only. Probe (5) acts as an exclusive,
naked-eye, concentration dependent chromo-fluorogenic
sensor and a chemodosimeter for cyanide ion. Such a chemo-
dosimeter response, to the best of our knowledge is being
studied for the first time in a Schiff base. It is attributed to the
in situ acid catalysis of the Strecker reaction,11 giving addition
of CN− anion to the imine bond.
Results and discussion
As (4) responded to both F− and CN− ions to have a better
insight into the recognition phenomenon UV-vis titrations
were performed. On addition of aliquots of TBAF, to a solution
of (4) in DMSO (Fig. S15†), a significant change was observed
even with 1 μM of anion, so the detection limit15 of fluoride
has to be less than 1.5 μM. The reaction of (4) with TBAF gives
a binding constant, K = 4.68 × 103 M−1 and shows a 1 : 1 stoi-
chiometry (Fig. S16†). This reaction is completely reversible
on addition of water to it suggesting that deprotonation is
involved in the colorimetric response. On the other hand,
gradual addition of CN− anion to (4) leads to a band at 445 nm
at a lower concentration (<37 μM), but at a higher concen-
tration (from 37 to 700 μM) the latter shifts to a longer wave-
length at λmax. 496 nm (Fig. S17†). The stoichiometry of the
reaction is 1 : 2 as found by the Job’s plot and a binding con-
stant K = 7.27 × 103 M−1 (Fig. S18†). The changes are fully
reversible at lower concentrations of the anion but irreversible
at the higher concentrations i.e. the red color once attained
does not disappear not even on addition of water. The detec-
tion limit of cyanide in a solution of (4) in DMSO was found to
be less than 3 μM (Fig. S17†). Addition of TBAOH to (4) causes
changes similar to TBAF (Fig. S19†) and no bands at longer
wavelength were found which means that the sensing involves
deprotonation of the catechol moieties in the presence of
more basic F− ion in DMSO. In the case of CN− ion which is a
weaker base but a stronger nucleophile, it is proposed that
The sensors (4) and (5) were synthesized as shown in
Scheme 1, by a Schiff base condensation reaction of reactant
amine12 1 with 2 or 3, respectively in a chloroform–methanol
mixture in the presence of Zn(ClO4)2 as catalyst. These com-
pounds have been characterized by elemental analyses, IR,
1H, 13C NMR, mass, UV-vis absorption spectroscopy and X-ray
analysis (Fig. S1–S10†).
X-ray crystal structure of (5)
The crystal structure determination of (5) reveals (Fig. 1) that a
solvent molecule of CCl4 gets incorporated during crystalliza-
tion. The structure shows that the dipodal molecule has an
approximate ‘U’ shaped conformation with the central anchor
phenyl ring forming the base. There are strong intramolecular
H-bonding interactions between the OH groups and imine
nitrogens as well as the S atoms which are supporting this con-
formation. The details of the characterization data as well as
the crystal structure are given in the ESI (Fig. S11–S13†).
Colorimetric and chromogenic spectral response of (4)
The anion binding ability of receptor (4) (10 μM) was deter-
mined by the changes in its absorption spectra measured
upon addition of various tetrabutylammonium anions, TBAX
(where X = F−, Cl−, Br−, I−, NO3−, CN−, ClO4−, AcO−, HSO4
−
and H2PO4−) in DMSO (100 μM) (Fig. 2). Upon addition of F−
and CN−, significant changes in the spectra were observed.
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Fig. 3 (a) Full (b) partial 1H NMR of (4) in DMSO-d6 (5 mM) showing changes on addition of F− and CN− anions. (A) Sensor alone (B) with TBAF (50 mM) (C) with
TBACN (50 mM) [labels used in the diagram are shown in ESI, Scheme S1†].
Scheme 2 Proposed reaction mechanism for chemodosimeter formation (6).
deprotonation further leads to nucleophilic attack at the of TBAF and TBACN to a solution of (4) in DMSO-d6. Fig. 3a
–CvN bond. Thus (4) acts as a visual chromogenic chemosen- shows the changes found in the aromatic region in the
sor for F− ion and a unique double channel operating sensor 1H NMR for (4) on their addition. In both cases the –OH
which behaves as a chemosensor for CN− at a concentration signals have disappeared and the spectra show the expected
∼40 μM (4 equivalents) and a ‘naked eye’, concentration or up field in almost all the signals. Most significant, however is
time dependent, chemodosimeter above it. Moreover the the disappearance of the imine signal at δ 8.875 and appear-
visual color changes within 2–3 minutes give different ance of a doublet at δ 5.526 in the case of CN− but not in the
responses to F− and CN− anions and thus may be used for case of F− ion (Fig. 3b). These changes have been attributed
their discrimination.
to the occurrence of a Strecker’s reaction11 by nucleophilic
addition of CN− ion on the imine bond resulting in the for-
mation of a nitrile (6) (Scheme 2). It is well known that
the poor reactivity of the imine bond requires activation for
1H and 13C NMR titration experiments of (4)
The above proposed chemodosimeter is based upon the
1H and 13C NMR changes found on addition of 10 equivalents satisfactory efficiency in the Strecker reaction and hence is
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Fig. 4 Showing the (a) 13C NMR (b) partial DEPT-135 of (4) in DMSO-d6 with TBACN in it, T represents signals due to TBA.
generally activated by a Brønsted or Lewis acid by forming chromogenic sensor only. On the other hand due to the high
iminium ions16 in the case of those imine groups which are basicity of the [HF2]− ion which is produced in the presence
not substituted by an activating group. In the present case, the of F− ion and is recognizable by the tell-tale triplet at
potential H-bonding pocket defined by four catecholic –OH 16.1 (Fig. S21†) it acts as a chromogenic sensor for it.
protons which have the potential to bind anions in a chelate
Fluorogenic spectral response of (4)
tion of the –OH groups results in generation of H+ ions which The fluorescence spectral changes of (4) with various anions
mode, tends to bring the cyanide to their vicinity. Deprotona-
activate the imine group and a nucleophilic addition reaction
of CN− occurs forming a nitrile.
(Fig. 5) make it a highly selective ratiometric fluorogenic
sensor for F− ion with very small interference only from CN−
A dependence of the change on concentration of the anion ion which vanishes at a higher concentration of analyte. The
suggests that deprotonation is just one step in a multi-step
ligand does not have any fluorescence when excited at 350 nm
process. The doublet at δ 5.526 is assigned to the amine but on the addition of TBAF an emission band appears at
proton and the corresponding signal due to imine proton dis- 560 nm with high intensity. This gives a fluorescent green
appears. The signal due to the proton attached to the chiral C
color under a UV lamp (Fig. S22a†) and the emission has been
is overlapped by the signals due to tetrabutylammonium attributed to the well-known ESIPT phenomenon in such
cation. As the product (6) obtained is a mixture of diastereo- Schiff bases where the steady state emission is dominated
mers with a possible diastereomeric excess of one enantio-
by cis-keto tautomer formed after photoinduced proton
meric pair, each signal in the NMR is accompanied by another transfer.17
signal of much lesser intensity. The formation of (6) is well
supported by the changes in the 13C NMR of the addition
product (Fig. 4a) where the signal at δ 162.9 ppm due to imine
carbon is absent but a signal appears at δ 155 ppm corres-
ponding to the carbon of the added CN group (absent in
DEPT-135) on the positive side (Fig. 4b).
Colorimetric, UV-vis and fluorogenic spectral response of (5)
Among ten anions tested in DMSO, (5) responded only to the
CN− ion as is evident from the absorption (Fig. 6) and emis-
sion bands (Fig. 7) resulting in a color change from almost
colorless to yellow which moves towards reddish with time
(Fig. S23†). From the absorption spectra at 10 equiv. of the
added anion the band at λmax 350 nm has completely vanished
and a new, very broad band starts appearing at 465 nm
(Fig. S24†). The detection limit of cyanide in solution of (5)
was found to be less 3 μM. A comparison with the –OH ion
(Fig. S25†) shows that the channel working for sensing is
similar to (4) i.e. H-bonding at low concentration and due to
deprotonation and chemodosimetry, at a higher concentration
(with a 1 : 2 stoichiometry and binding constant of 3.53 ×
102 M−1 (Fig. S26†). The lesser sensitivity of (5) towards chemo-
dosimetry is expected due to phenol being less acidic
than catechol and has one proton only, deprotonation and
subsequent activation of the imine nitrogen is achieved at a
The signal due to the chiral α-C (Scheme 2) is again over-
lapped by the signals of DMSO in the 13C NMR spectrum
but is clearly visible at δ 39.7 ppm in the DEPT on the positive
side (Fig. 4b). The electrospray ionization mass spectrum
(Fig. S20†) of this solution in DMSO shows a base peak at
786.85 which corresponds to an adduct of DMSO and Na
with [(M + 1)]+ ion (calculated 786.15) which clearly proves the
formation of (6) during the sensing experiment. Based on
the above evidence it may be concluded that (4) behaves as a
chemodosimeter for CN− induced deprotonation. At low con-
centrations of the anion the nitrogen of the imine group is not
protonated and the imine group is not activated for nucleo-
philic attack by the CN− ion therefore (4) behaves as a
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Fig. 5 Showing (a) changes in the fluorescence intensity b) fluorescence ratio [I/Io] of sensor (4) (5 μM) at λmax 560 nm upon addition of various anions (50 μM)
with excitation at 350 nm in DMSO. Io and I are the intensities in the absence and presence of anions respectively.
chromo/fluorogenic responses at low and high concentrations
of the anion.
The fluorescence spectra of (5) exhibited emission bands at
λ(ems) 437 nm and λ(ems) 545 nm. The intensity of the former
band enhances up to ten fold on addition of TBACN
(Fig. S27a†) but not with other anions (Fig. S27b†). This gives a
blue color fluorescence (Fig. S22b†) at very high anion concen-
tration or after 24 hours. This effect may be due to a PET
phenomenon which is reduced when –OH is involved in
H-bonding with the anion resulting in enhancement of signal.
1H NMR titration experiments of (5)
1
The H NMR and mass spectra (Fig. S28†) of the sensor with
Fig. 6 Changes in the UV-vis spectrum of (5) in DMSO (10 μM) on the addition
of various anions (100 μM).
20 and 30 equivalents of CN− ion again shows (Fig. 8) the
absence of OH and imine signals, up field shift of aromatic
protons, appearance of the –NH signal at δ 5.69 ppm.
Colorimetric response of sensors in semi-aqueous medium
Since the chemodosimetric detection of CN− ion is irreversible
in water the efficacy of (4) and (5) was checked in water by
using aqueous solutions of (100 μM) TBACN, NaCN and
NaSCN in a DMSO solution of (4) and (5) (10 μM, DMSO : water
2 : 1) which resulted in a similar response as in DMSO in the
form of appearance of red color (Fig. 9) in the solution.
In order to confirm this proposed mechanism (Scheme 2),
the nitrile product from 4 and NaCN was synthesized, separ-
ated, purified and analyzed by 1H NMR, IR and mass
spectrometry (Fig. S29–S31†). Apparently any hydrolysis of the
nitrile into amino acid has not occurred because of the
absence of any acid in the reaction medium at this stage.
Fig. 7 Changes in fluorescence intensity of (5) in DMSO (10 μM) on the
addition of various anions (100 μM).
Conclusions
higher concentration of CN− ion or after a longer reaction time
than (4). Due to this slow chemodosimeter response (5) can be
In summary, we have developed two new –OH containing
Schiff base receptors as F− and CN− ion sensors. Catechol
based sensor (4) works for both F− and CN− ions, albeit
used as a very selective and sensitive chromo/fluorogenic
sensor for CN− ion exclusively, transducing different naked eye
through different channels in DMSO. Its colorimetric response
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Fig. 8 Showing partial 1H NMR of (5 mM) solution of (5) in DMSO-d6 with (A) no TBACN (B) 20 equivalent TBACN (C) 30 equivalent TBACN.
Compounds 2 and 3 were commercially available. The dipodal
amine was prepared as already reported by us.12
X-ray measurement and structure determination
The crystals of compound (5) were grown by slow evaporation
from mixture of CHCl3 and CCl4. X-ray data of the compound
(5) was collected on a Bruker’s Apex-II CCD diffractometer
using Mo Kα (λ = 0.71069) at room temperature. The data were
corrected for Lorentz and polarization effects and empirical
absorption corrections were applied using SADABS from
Bruker. A total of 19 836 reflections were measured out
of which 5877 were independent and 3146 were observed
[I > 2σ(I)] for theta 25°. The structure was solved by direct
Fig. 9 Showing colorimetric response of 4 and 5 with TBACN, NaCN and
NaSCN in DMSO : water 2 : 1 solution.
may be used to discriminate between the two anions within
two minutes whereas its fluorogenic response may do so
instantaneously and with high sensitivity. In DMSO : water (4)
behaves as a colorimetric sensor exclusively for CN− ion. The
phenol based sensor (5) is a highly selective one for CN− ion
and may be used as a semiquantitative chromo/fluorogenic
sensor sensing CN− with colorimetric and fluorogenic
responses for different CN− ion concentrations. The chemo-
dosimeter response of these sensors towards CN− ion is due to
a Strecker’s nucleophilic addition to imine bond of the Schiff
bases.
ˉ
methods in a trigonal R3 space group, using SIR-92 and
refined by full-matrix least squares refinement methods based
on F2, using SHELX-97. The refinement showed a disordered
CCl4 molecule in the structure with C and one Cl atom lying
on the three fold axis with site occupancy of 0.3333. The
disorder in other Cl atom was resolved by splitting it in two
positions and refining anisotropically with restraints on C–Cl
bonding and Cl⋯Cl non-bonding distances. The hydrogens of
the –OH groups were located from the difference Fourier syn-
thesis and were refined isotropically with Uiso values 1.2 times
that of their carrier oxygen atoms, with restraints on the O–H
distance. All non-hydrogen atoms were refined anisotropically.
All hydrogen atoms were fixed geometrically with their Uiso
values 1.2 times of the phenylene and methylene carbons
and 1.5 times of the methyl carbons. All calculations were
performed using Wingx package.
Experimental
General information
All the commercially available chemicals were purchased from
Aldrich and used without further purification. All solvents
were dried by standard methods. Unless otherwise specified,
chemicals were purchased from commercial suppliers and
used without further purification. TLC was carried out on
glass sheets pre-coated with silica gel. The 1H and 13C NMR
UV-vis and fluorescence studies
spectra were carried out in DMSO-d6 with TMS as an internal Molecular interaction of 4 and 5 with all anions under study
reference, on a 300 MHz NMR spectrophotometer. The infra- were investigated using UV–vis spectroscopy at 10−5 M and flu-
red spectra (KBr pellet) were recorded using a Varian IR spec- orescence spectroscopy at 5 × 10−6 M for 4 and 10−5 M for 5 in
trophotometer in the range 400–4000 cm−1. The electronic DMSO solution. The changes in the UV-vis spectra of sensors
absorption spectra were recorded on a Shimadzu Phramaspec on the gradual addition of TBAF and TBACN were recorded at
UV-1700 UV-vis spectrophotometer. Mass spectra were a concentration of 10−4 M while for fluorescence the concen-
recorded on a Bruker’s microTOF-QII spectrophotometer. tration of anions used for 4 was 5 × 10−5 M and 10−4 M for 5.
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Job’s plot and stability constant determination
5 h, the color of the solution changed from light yellow to dark
red. Dry chloroform (20 ml) was added to the reaction mixture
and then it was stirred for five minutes. A dark reddish brown
precipitate separated out, was separated by filtration and
washed with chloroform. Then the compound was dried under
vacuum. Yield 40%. mp = above 300 °C; IR (KBr, cm−1) 2246;
1H NMR (300 MHz, DMSO-d6, δ): 2.23 (s, 2H, –NH), 2.32 (s,
6H, –CH3), 2.54 (s, 3H, –CH3), 3.97 (s, 4H, –CH2), 4.04 (s, 2H,
–CH), 6.50–7.88 (m, 15H, –Ar); Elemental analysis calculated
for C39H32N4O4S2: C, 68.40; H, 4.71; N, 8.18; S, 9.36%. Found:
C, 68.48; H, 4.65; N, 8.08; S, 9.25%.
The binding stoichiometry of sensor–anion complexes was
determined by the method of continuous variation (Job’s plot).
Ten solutions were made by varying L : M ratio and keeping
the total concentration of 4 and 5 and anionic guest constant
(5 × 10−5 M) with continuous variation of the mole fraction of
4 and 5. The results indicate the formation of complexes with
stoichiometric ratio of 1 : 1 for TBAF in case of 4 and 1 : 2 for
TBACN in case of 4 and 5. The stability constant of these com-
plexes were determined by a Benesi–Hildebrand plot.
Synthesis of compounds
Compound (4). Compound 1 (0.20 g, 0.510 mmol) was dis-
solved in 10 ml chloroform, to which was added 0.15 g
Acknowledgements
(1.08 mmol) of 2,3-dihydroxybenzaldehyde in 40 ml of metha- MSH and GH are thankful to CSIR (India) for research grant
nol along with 3–4 mg of zinc perchlorate. The color of the No. 01(2406)/10/EMR-II. S. S. is thankful to UGC for senior
solution changed immediately to dark orange from light yellow research fellowship.
and a precipitate separated out within half an hour. The pre-
cipitate was filtered, washed with methanol and dried. Yield
76%. Orange solid; mp = 165–167 °C; IR (KBr, cm−1) 1612,
3382 (br); H NMR (300 MHz, DMSO-d6, δ): 2.23 (s, 6H, –CH3),
References
1
2.38 (s, 3H, –CH3), 4.12 (s, 4H, –CH2), 6.79 (t, 2H, –Ar, J = 7.8),
6.88 (s, 1H, –Ar), 6.92 (d, 2H, –Ar, J = 9.0), 7.07 (d, 2H, –Ar, J =
7.95), 7.28–7.39 (m, 4H, –Ar), 7.48 (d, 2H, J = 7.65), 7.56 (d, 2H,
J = 7.5), 8.87 (s, 2H, –CHvN), 9.08 (s, 2H, –OH), 13.05 (s, 2H,
–OH); 13C NMR (75 MHz, DMSO-d6, δ): 14.9 (–CH3), 19.2
(–CH3), 31.6 (–CH2), 117.8 (–Ar), 118.9 (–Ar), 119.2 (–Ar), 122.9
(–Ar), 126.1(–Ar), 127.1(–Ar), 127.8 (–Ar), 130.3 (–Ar), 133.5
(–Ar), 136.4 (–Ar), 144.9 (–Ar), 145.5 (–Ar), 148.9 (–Ar), 162.9
(CHvN); Elemental analysis calculated for C37H34N2O4S2:
C, 70.00; H, 5.40; N, 4.41; S, 10.10%. Found: C, 69.99; H, 5.31;
N, 4.30; S, 10.08%; HRMS m/z 657.21 [M + Na] ion.
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Compound (5). Compound 1 (0.20 g, 0.331 mmol) was dis-
solved in 10 ml chloroform, to which was added 0.0810 g
(0.663 mmol) of 2-hydroxybenzaldehyde in 40 ml of methanol
along with 3–4 mg of zinc perchlorate. The reaction mixture
was stirred for 2 h, after the completion of the reaction the
solvent was evaporated and the product was recrystallized from
methanol as a yellow solid. Yield 60%. mp = 110–112 °C; IR
1
(KBr, cm−1) 1608, 3411; H NMR (300 MHz, DMSO-d6, δ): 2.23
(s, 6H, –CH3), 2.30 (s, 3H, –CH3), 4.09 (s, 4H, –CH2), 6.82 (s,
1H, –Ar), 6.88 (d, 2H, –Ar, J = 8.1), 6.95 (t, 2H, –Ar, J = 7.5), 7.32
(t, 4H, –Ar, J = 6.3), 7.40 (t, 4H, –Ar, J = 8.1), 7.54 (d, 2H, J =
6.3), 7.60 (d, 2H, J = 6.9), 8.84 (s, 2H, –CHvN), 12.92
(s, 2H, –OH); 13C NMR (75 MHz, DMSO-d6, δ): 14.8 (–CH3),
19.2 (–CH3), 31.7 (–CH2), 116.6 (–Ar), 118.0 (–Ar), 126.4 (–Ar),
127.6 (–Ar), 129.9 (–Ar), 130.3 (–Ar), 132.7 (–Ar), 133.1 (–Ar),
133.4 (–Ar), 136.3 (–Ar), 136.7 (–Ar), 145.7 (–Ar), 160.2 (–Ar),
3 (a) K. L. Krik, Biochemistry of Halogens and Inorganic
Halides, Plenum Press, New York, 1991, 591;
(b) M. Kleerekoper, Endocrinol. Metab. Clin. North Am.,
1998, 27, 441; (c) S. Matsuo, K. Kiyomiya and M. Kurebe,
Arch. Toxicol., 1998, 72, 798; (d) D. Briancon, Rev. Rhum.
Engl. Ed., 1997, 64, 78; (e) K. J. Wallace, R. I. Fagmemi,
F. J. Folmer-Anderson, J. Morey, V. M. Lynth and E.
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162.7
(CHvN);
Elemental
analysis
calculated
for
C37H34N2O2S2: C, 73.72; H, 5.69; N, 4.65; S, 10.64%. Found:
C, 73.73; H, 5.54; N, 4.62; S, 10.59%; HRMS m/z 603.21
[M + 1]+ ion.
Compound (6). Compound 4 (0.20 g, 0.292 mmol) was dis-
solved in
5
ml DMSO, to which was added 0.143
g
4 (a) K. Barthelet, J. Marrot, D. Riou and G. Férey, Angew.
Chem., Int. Ed., 2002, 41, 281; (b) C. Serre, F. Millange,
(2.918 mmol) of NaCN. The reaction mixture was stirred for
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