Naked-eye detection of inorganic fluoride in aqueous media using a new azo-azomethine colorimetric receptor enhanced by electron withdrawing groups

Article abstract of DOI:10.1039/c3ra42709a

A new azo-azomethine receptor, containing active phenolic sites, has been designed and synthesized for quantitative detection and colorimetric sensing of inorganic fluoride ion in aqueous media. The introduction of four electron withdrawing groups into th

Full text of DOI:10.1039/c3ra42709a

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PAPER
Naked-eye detection of inorganic fluoride in
aqueous media using a new azo-azomethine
colorimetric receptor enhanced by electron
withdrawing groups†
Cite this: RSC Adv., 2014, 4, 1032
*
Hamid Khanmohammadi and Khatereh Rezaeian
A new azo-azomethine receptor, containing active phenolic sites, has been designed and synthesized for
quantitative detection and colorimetric sensing of inorganic fluoride ion in aqueous media. The
introduction of four electron withdrawing groups into the backbone of the receptor makes the two
phenolic groups efficient hydrogen bonding sites. Hence, the receptor is capable of competing with
water molecules to detect trace amounts of inorganic fluoride ions in aqueous solutions. Accordingly,
the receptor showed a remarkable colour change from light yellow to orange upon the addition of
aqueous solution of NaF, enabling naked-eye Fꢀ sensing without any spectroscopic instrumentation. The
recognition details of Fꢀ sensing were also evaluated using UV-Vis spectroscopy and 1H NMR titration
techniques. The 1H NMR titration revealed that the colorimetric response was considered to be the
direct consequence of hydrogen-bond formation between the phenolic groups of the receptor and
fluoride ions followed by deprotonation. Importantly, the current sensor can detect inorganic fluoride in
water even at 0.058 ppm, which is lower than the World Health Organization (WHO) permissible level.
To the best of our knowledge, there have been very few examples of detection limits lower than the
WHO permissible level for detecting fluoride ion in drinking water (below 1 ppm). The designed sensor
has also shown highly promising results for the qualitative and quantitative detection of fluoride in real
samples like sea water, toothpaste and mouthwash.
Received 2nd June 2013
Accepted 7th October 2013
DOI: 10.1039/c3ra42709a
www.rsc.org/advances
To date a number of colorimetric receptors which are
capable of detecting the uoride ion with high affinity, have
been reported.4 The common recognition moieties of the
Introduction
Anions have been recognized as playing key roles in a wide
range of chemical and biological processes.1 Thus, the design
and also construction of molecular sensors for the recognition
and sensing of physiologically important anions have been in
the forefront of chemistry research.2 In particular, the design of
sensors for the colorimetric detection of anions is increasingly
appreciated since naked eye detection is low cost and does not
require any spectroscopic instrumentation.3a–c Among the bio-
logically important anions, uoride has attracted the interest of
chemists owing to its established role in dental care and the
treatment of osteoporosis.3d–j
reported receptors involve amide, urea and thiourea, ami-
dourea, phenol, pyrrole, imidazolium and indole.5 Generally,
the formation of hydrogen bonds between active sites, N–H and/
or O–H, of these subunits with Fꢀ plays a pivotal role in anion
sensing. However, most receptors are restricted to the detection
of tetrabutylammonium uoride (TBAF) in organic solvents and
there is a paucity of reports regarding the colorimetric detection
of uoride ion in aqueous media.6 This obstacle is attributed to
the fact that water is a highly competitive solvent and partici-
pates in the detection process of Fꢀ by mediating interactions
between the binding partners. In this regard, Fꢀ becomes
solvated strongly even with a trace amount of water.7 The
mentioned blockages limit the discrimination and detection of
inorganic uoride anion in water.
Department of Chemistry, Faculty of Science, Arak University, Arak 38156 8 8349, Iran.
E-mail: h-khanmohammadi@araku.ac.ir; Fax: +98-861-4173406; Tel: +98-861-
2777401
On the other hand, highly selective uoride ion receptors are
† Electronic supplementary information (ESI) available: Characterization data of strongly favoured for practical applications. However, it is quite
all compounds, UV-Vis spectrophotometric titarations, stoichiometric
difficult to design colorimetric chemosensors for the recogni-
tion of Fꢀ in water. Indeed, only a few examples of sensors
determination by Benesi–Hildebrand method, Job’s plot, UV-Vis spectral
changes upon addition of protic solvent, gures and photographs showing the
capable of detecting uoride ion in water have been reported.6
sensing behavior, procedure details of interference study and details of
Furthermore, most of the determination processes are limited
to either recognition of TBAF or use of test papers which need
qualitative and quantitative detection of uoride by prepared sensor. See DOI:
10.1039/c3ra42709a
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several minutes to complete detection and are far away from between the OH groups of the sensor and the anionic guest.
real-life applications.8
Therefore, receptor 1 can compete with water for the naked-eye
Therefore, the development of sensors for the direct detec- detection of inorganic uoride in aqueous media.
tion of inorganic uoride in aqueous media accompanied by a
visually striking colour change, naked eye sensing, is an
important target for real-life applications. Kruger et al. devel-
Results and discussion
The synthesis of receptor 1 was achieved by the straightforward
condensation reaction of a,a0-bis(o-aminophenylthio)-1,2-
xylene with 1-(3-formyl-4-hydroxyphenylazo)-2,4-dichloroben-
zene as depicted in Scheme 1. The prepared receptor was
characterized using standard spectroscopic techniques (ESI†).
As an initial test, we checked the colour changes of receptor 1
in DMSO upon the addition of 10 equiv. of tetrabutylammꢀo-
oped a 1,8-naphthalimide-based colorimetric anion sensor
containing the aminothiourea group for the recognition of NaF
in aqueous solutions.9 Subsequently, Das et al. have designed a
receptor for the selective and quantitative extraction of uoride
anions from aqueous solution of sodium uoride.10 Neverthe-
less, the evaluation and discrimination of inorganic uoride in
aqueous media still remains as important a challenge to
chemical analysis.
nium (TBA) salts of Fꢀ, Clꢀ, Brꢀ, Iꢀ, H2PO4ꢀ, ClO4ꢀ, N3ꢀ, NO2
,
NO3ꢀ, AcOꢀ and HSO4ꢀ. As shown in Fig. 1(a), a noticeable
colour change was observed from light yellow to red in the
presence of Fꢀ, AcOꢀ and H2PO4ꢀ. In contrast, other anions
caused no obvious changes in colour. To further study the
colorimetric behaviour of receptor 1, UV-Vis absorption exper-
iments were also performed upon the addition of 10 equiv. of
tetrabutylammonium salts of anions to 1 (2 ꢁ 10ꢀ5mol Lꢀ1 in
DMSO), Fig. 1(b). Free receptor 1 exhibited one absorption band
at 369 nm and a weak tail at ꢂ490 nm. A distinct change was
observed in the spectral pattern in the presence of Fꢀ, AcOꢀ and
H2PO4ꢀ; the extent of the changes was much more for Fꢀ.
Moreover, the addition of anion-based salts to the DMSO
solution of 1 gave a bathochromic shi from 369 nm to ca.
500 nm with Fꢀ, AcOꢀ and H2PO4ꢀ. While other anions induced
negligible spectral responses.
Until now, a number of azo sensors for the detection of
uoride have been reported. However, most of these sensors
have been designed for use in noncompetitive organic sol-
vents.3a,4i–k Recently, Mahapatra and co-workers reported new
chromogenic azo-azomethine receptors for the recognition of
uoride.4i Although the synthesized receptors have been shown
to possess good selectivity and sensitivity for uoride ion in
CH3CN, the sensory system was not able to compete with water.
Thus, Fꢀ sensing in aqueous media was restricted to the use of
test strips which requires several minutes for the detection
process. In pursuit of these, we report here a new member of the
azo-azomethine sensors, receptor 1, (Scheme 1) for the rapid
detection and colorimetric sensing of inorganic uoride ion in
aqueous media. To the best of our knowledge, this is the rst
azo-azomethine receptor used for the qualitative and quantita-
tive detection of uoride in water and real samples. The
prepared molecular sensor, 1, contains azo phenol moieties
serving as sensing units to form hydrogen bonds via the
disposal of OH groups in the presence of anions. In particular,
the presence of four electron withdrawing substituents in the
molecular structure of 1 enhances the acidity of its active sites
and hence allows the formation of stronger hydrogen bonds
In order to further assess the binding characteristics of
receptor 1, we carried out UV-Vis spectrophotometric titrations
by adding a standard solution of TBAF to the dry DMSO solution
of 1 (2 ꢁ 10ꢀ5mol Lꢀ1). As shown in Fig. 2, upon the addition of
Fig. 1 (a) Colour changes of receptor 1 (2 ꢁ 10ꢀ5 mol Lꢀ1 in DMSO)
after addition of 10 equiv. of different anions. From left to right: none,
H2PO4ꢀ, ClO4ꢀ, Brꢀ, Clꢀ, AcOꢀ, Fꢀ, N3ꢀ, HSO4ꢀ, NO2ꢀ, NO3 and Iꢀ
ꢀ
(TBA+ salts). (b) UV-Vis absorption spectra of receptor 1 (2 ꢁ 10ꢀ5mol
Scheme 1 Synthesis of receptor 1.
L
ꢀ1 in DMSO) in the presence of 10 equiv. of various anions.
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Fig. 3 UV-Vis titration of the receptor (2 ꢁ 10ꢀ5 mol Lꢀ1) in 9 : 1,
DMSO–water with increasing concentrations of NaF (0–10 equiv.) in
water. Inset showing the binding isotherm at selected wavelengths in
9 : 1, DMSO–water.
Fig. 2 UV-Vis absorption spectra of receptor 1 (2 ꢁ 10ꢀ5mol Lꢀ1) in
dry DMSO upon the addition of TBAF (0–10 equiv.). Inset showing the
binding isotherm at selected wavelengths in DMSO.
and Fꢀ ion. These ndings corroborate that the addition of
inorganic uoride to an aqueous solution of 1 produces
absorption spectral changes similar to those seen when TBAF is
added to a receptor solution in dry DMSO. Furthermore, titra-
tion of 10% aqueous solution of 1 with TBAF afforded similar
spectral changes with a binding constant of 2.25 ꢁ 104 Mꢀ1
close to that found in organic solution (Fig. S16, ESI†). In fact,
the presence of four electron withdrawing chlorine substituents
improved the ability of the phenolic OH protons of 1 to form
strong hydrogen bonds7 with Fꢀ, present either as inorganic
uoride or TBAF in competitive aqueous media. The Benesi–
Hildebrand plot11 of 1/[A ꢀ A0] vs. 1/[Fꢀ] for the titration of
receptor 1 with NaF provided a straight line (Fig. 4), corrobo-
rating the formation of a 1 : 1 H-bonded complex with a binding
uoride ion, the band at 369 nm, the p / p* transition of the
chromophores, decreased gradually and simultaneously a new
strong absorption band, attributed to the charge transfer (CT),
formed at 503 nm indicating interaction between uoride ion
and receptor. An analogous investigation was performed for the
addition of the TBA salt of H2PO4ꢀ and AcOꢀ to a solution of 1
in dry DMSO (Fig. S11 and S23, ESI†). The Benesi–Hildebrand
method11 conrmed 1 : 1 stoichiometry with binding constants
of 2.36 ꢁ 104, 1.87 ꢁ 104 and 9.54 ꢁ 103 Mꢀ1for Fꢀ, AcOꢀ and
H2PO4ꢀ, respectively. The 1 : 1 stoichiometry was also deter-
mined by Job’s plot (Fig. S10, S13 and S24, ESI†).
Based on UV-Vis measurements, the detection limits of
receptor 1 towards Fꢀ, AcOꢀ and H2PO4ꢀ in DMSO were found to
be 2.06 ꢁ 10ꢀ6, 3.39 ꢁ 10ꢀ6 and 2.22 ꢁ 10ꢀ6 mol Lꢀ1, respec-
tively. The surprising results of our present study were that upon
the addition of competitive protic solvents such as methanol or
water to the solution of 1 + 10 equiv. Fꢀ in DMSO, the colour and
also absorption spectrum were not reversed12 (Fig. S14, ESI†).
However, progressive addition of a protic solvent to the solution
constant of 1.50 ꢁ 104 Mꢀ1
.
Interestingly, a comparison of the binding constant of 1
towards Fꢀ in aqueous media with that found in organic solu-
tion revealed that the binding affinity remained strong even in
water. It is worth noting that the current system can detect
inorganic uoride even at 0.058 ppm level, which is in accor-
dance with the system reported by Das and co-workers.10
Remarkably, this limit of detection is much lower than the
World Health Organization (WHO) permissible level for the
detection of uoride in drinking water (below 1 ppm).13
ꢀ
of 1 + 10 equiv. H2PO4 in DMSO caused the colour of the
solution to turn from red to yellow. Correspondingly, the
absorption band recovered from 497 nm to 369 nm with a clean
isosbestic point at 407 nm (Fig. S15, ESI†). Similar behaviour was
also observed for AcOꢀ (Fig. S25, ESI†). This phenomenon is
attributed to the fact that protic solvents would compete with
H2PO4ꢀand AcOꢀ anions for the binding sites of the host and
disturb the interaction between the host and guest.4f
From the above ndings we concluded that receptor 1 is
capable of detecting uoride ions in aqueous solution. Hence,
to investigate the applicability of 1, further UV-Vis spectropho-
tometric titrations were performed to detect sodium uoride in
water. Fig. 3 depicts the UV-Vis titration of 1 (2 ꢁ 10ꢀ5mol Lꢀ1
)
in 9 : 1 DMSO–water, with a standard solution of NaF in water.
Upon addition of increasing concentrations of NaF, the colour
changed dramatically from light yellow to orange (Fig. S18,
ESI†), this was associated with a gradual decrease in the char-
acteristic absorption band at 369 nm and the simultaneous
growth of a new intense band at 467 nm. Clearly, the distinct
Fig. 4 Benesi–Hildebrand plot of receptor 1 binding with Fꢀ anion
isosbestic point at 397 nm indicates the interaction between 1 associated with absorbance change at 369 nm in 9 : 1, DMSO–water.
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It has been reported that excess of uoride ions not only in
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potable water but also in toothpaste and osteoporosis drugs is
responsible for causing dental problems and skeletal uo-
rosis.14 Hence, for practical purposes and also to demonstrate
the potential application of the present receptor for the rapid
detection of uoride ion in real samples, we extended our work
to the qualitative detection of uoride in toothpaste. Finally, we
were successful in the naked-eye sensing of uoride ions. The
results were also veried using UV-Vis spectroscopy (Fig. S19,
ESI†).
Recently, we were inspired by Trivedi and co-workers,15 who
reported the quantitative detection of uoride ion in real-life
applications. Therefore, receptor 1 was tested for the detection
of uoride ion in sea water, collected from the Persian Gulf
(latitude 27ꢃ4909400, longitude 52ꢃ6201900) and in commercial
mouthwash. To our surprise, the addition of one drop of sea
water to receptor 1, resulted in a noticeable colour change
from light yellow to orange, suggesting that it is possible to use
1 for the naked-eye detection of uoride ion in sea water.
Moreover, Fꢀ was detected quantitatively by applying a cali-
bration curve obtained from a plot of absorbance vs. various
concentrations of uoride anions (Fig. 5). The value obtained
from the standard plot for sea water, as an unknown sample,
was 0.92 ppm, which is in good accordance with the standard
value.13b Our control studies showed that there was no inter-
ference from phosphate in the colour change resulting from
the reaction of 1 with uoride in sea water (Fig. S21, ESI†).
Additionally, the mentioned sensor system allowed the rapid
recognition and quantitative detection of uoride in mouth-
wash (Fig. S20, ESI†).
Fig. 6 Absorbance changes of receptor 1 corresponding to various
pHs of aqueous solution containing 4 ꢁ 10ꢀ5 mol Lꢀ1NaF.
of 1 are not surprising since similar ndings have been reported
for other colorimetric uoride sensors.8b,9,10
To further study the nature of the interaction between
receptor 1 and uoride, 1H NMR titration experiments were
conducted. Fig. 7 shows the 1H NMR spectra of 1 with different
amounts of TBAF in DMSO-d6. It is clear that the OH protons of
the azo phenol moieties at 13.87 ppm thoroughly disappeared
when only 0.5 equiv. of Fꢀ was added into a solution of 1. This
To investigate the effect of pH on the host–guest binding
affinity, we probed the changes in intensity of the absorption
band at 467 nm attributed to the formation of the receptor 1–Fꢀ
complex , over a broad pH range 2–12. As indicated in Fig. 6,
there is a drastic drop in the intensity of the absorption band in
highly acidic conditions, this is probably due to the protonation
of uoride ion, to form weakly ionized hydrouoric acid,
thereby lowering the affinity of uoride anion to bind to the
receptor active sites.16 As the pH rises, the intensity of the
characteristic band increases, this is probably due to an
increase in the accessibility of the deprotonated uoride to form
strong hydrogen bonds with the receptor. These pH responses
Fig. 5 Calibration curve for the determination of the concentration of Fig. 7 1H NMR spectra of receptor 1 in DMSO-d6 (2 ꢁ 10ꢀ2mol Lꢀ1) in
fluoride anion in sea water.
the absence and in the presence of different amounts of TBAF.
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indicates the formation of strong hydrogen bonds between heated to reux for 30 min. The mixture was allowed to cool to
uoride anions and active OH groups, as previously reported.17 60 C and a,a0-dibromo-o-xylene (13.20 g, 0.05 mol) was added
ꢃ
With increasing further equiv. of Fꢀ, the signals of Ha and Hb dropwise over a period of 30 min. The mixture was then heated
showed progressive upeld shis, whereas the signal of Hc to reux for 2 h. Aer cooling to room temperature, the reaction
exhibited a progressive reverse shi toward downeld. Simulta- mixture was extracted with chloroform. The organic layer was
neously, an upeld shi of the imine proton (Hd) from 9.00 to dried over anhydrous MgSO4 and then evaporated to dryness.
8.76 ppm was also observed. The evidence above can be attrib- The obtained product was further washed thoroughly with
uted to the two possible effects which are responsible for diethyl ether and dried under vacuum at room temperature.
observed chemical shis upon OH–uoride interaction:4e,18 (1) Yield: 70%,. m. p. 103–106 ꢃC (lit.106 ꢃC).19 1H NMR (DMSO-d6,
through-bond effects, which increase the electron density on the 400 MHz, ppm): d 4.02 (s, 4H), 5.31 (br, 4H), 6.46 (t, 2H, J ¼
phenyl ring and promote an upeld shi of the C–H protons and 7.60 Hz),6.73 (d, 2H, J ¼ 8.00 Hz), 7.05 (m, 8H). IR (KBr, cmꢀ1);
(2) through-space effects, which induce polarization of the C–H 3352 and 3449 (NH), 1607 and 1477 (C]CAr).MS (EI, 70 eV): m/z
bonds, where the partial positive charge creates a downeld shi. (%) ¼ 352 (M+, 63),228 (100), 194 (94), 124 (69), 80 (63).
Interestingly, a typical HF2ꢀ signal was observed in 1H NMR
titration experiments at higher concentration of Fꢀ, indicating
Synthesis of 1-(3-formyl-4-hydroxyphenylazo)-2,4-
dichlorobenzene
that deprotonation of receptor 1 occurred (Fig. S26, ESI†).4i
1
Consequently, the H NMR titration experiments corroborated
A mixture of 2,4-dichloroaniline (1.62 g, 10 mmol) in hydro-
chloric acid (9 mL) and water (4 mL) was heated to 70 C to to
that Fꢀ recognition occurs through initial hydrogen bond
ꢃ
formation between anion and sensor, followed by deprotona-
form a solution. The clear solution was poured into an ice-water
tion. Furthermore, the formation of an initial 1–Fꢀ H-bonding
mixture and was diazotized at 0–5 ꢃC with sodium nitrite (0.7 g,
host–guest complex is supported by the pKa value, determined
10 mmol in water, 10 mL). The cold diazo solution was added to
from spectrophotometric pH titration (Fig. S22, ESI†).
the solution of salicylaldehyde (1.22 g, 10 mmol) in water
(20 mL) containing sodium hydroxide (0.40 g, 10 mmol) and
sodium carbonate (4.24 g, 40 mmol) over a period of 30 min at
Conclusion
ꢃ
ꢃ
0 C. The reaction mixture was stirred for 1 h at 0 C and then
allowed to warm slowly to room temperature. The product was
collected by vacuum ltration and washed with NaCl solution
(100 mL, 10%). The obtained solid was dried under vacuum at
80 ꢃC overnight. Yield: 86%, m. p. 120–123 ꢃC. 1H NMR (DMSO-
d6, 300 MHz, ppm): d 7.29 (d, 1H, J ¼ 8.84 Hz), 8.09 (dd, 1H, J ¼
8.84 Hz, J ¼ 2.16 Hz), 7.55 (d, 1H, J ¼ 8.76 Hz), 7.68 (d, 1H, J ¼
8.76 Hz), 7.89 (s, 1H), 8.19 (d, 1H, J ¼ 2.16 Hz), 10.37 (s, 1H),
11.88 (br, 1H). IR (KBr, cmꢀ1); 1668 (CHO), 1620 (C]C), 1578
(phenol ring), 1485 (N]N), 1287 (C–O), 1246, 1148, 866 and
768. Anal.calcd.forC13H8Cl2N2O2: C, 52.91; N, 9.49; H, 2.73%.
Found: C, 52.62; N, 9.38; H, 2.65%. lmax (nm) (3 (Mꢀ1 cmꢀ1)):
260 (29950), 356 (49260) and 465 (11853) in DMSO.
To sum up, we have designed and synthesized a new azo-azo-
methine based anion-receptor for the facile detection of uoride
present in aqueous media without any spectroscopic instru-
mentation. Selective binding of the receptor with uoride ion
through hydrogen-bonding interactions gave rise to a dramatic
colour change from light yellow to orange with a concomitant
bathochromic shi. Our achieved detection limit of Fꢀ ion was
0.058 ppm, which is lower than the WHO recommended level
(below 1 ppm) for safe drinking. Notably, we demonstrated that
the synthesized sensor can also be considered as a tool for the
detection and quantication of uoride ion in real samples.
Experimental
General
Synthesis of 1,2-bis(4-((2,4-dichlorophenyl)diazenyl)-2-((2-
(methylthio)phenylimino)methyl)phenol)methylenbenzene
(1)
All chemicals were purchased from Sigma-Aldrich and used
without further purication. Electronic spectral measurements
were carried out using an Optizen 3220 UV spectrophotometer
in the range of 200–900 nm. FT-IR spectra were recorded with
pressed KBr discs, using an Unicom Galaxy Series FT-IR 5000
spectrophotometer in the region of 400–4000 cmꢀ1. Melting
points were determined with an Electrothermal 9200 apparatus.
NMR spectra were recorded with Bruker AV 300 MHz and
Bruker Avance III 400 MHz spectrometers. C. H. N. analyses
were performed using a Vario EL III elemental analyzer. Mass
spectra were recorded with a FINNIGAN-MATT 8430 mass
spectrometer operating at an ionization potential of 70 eV.
A solution of a,a0-bis(o-aminophenylthio)-1,2-xylene (0.35 g,
1 mmol) in absolute EtOH (10 mL) was added to a stirring
solution of azo-coupled precursor (0.59 g, 2 mmol) in absolute
EtOH (50 mL) during a period of 20 min at 60 ꢃC. The solution
was heated in a water bath overnight at 80 ꢃC with stirring. The
mixture was ltered whilst hot and the obtained precipitate was
washed with hot ethanol (three times) and then with diethyl
ether. The resulting product was dried in air. Yield: 96%, m. p.
172–175 ꢃC. 1H NMR (DMSO-d6, 300 MHz, ppm): d 4.30 (s, 4H),
7.04 (d, 2H, J ¼ 8.80 Hz), 7.20 (m, 2H), 7.30 (m, 6H), 7.46 (m,
6H), 7.60 (d, 2H, J ¼ 8.71 Hz), 7.80 (s, 2H), 7.91 (d, 2H, J ¼
8.80 Hz), 8.15 (s, 2H), 8.99 (s, 2H), 13.86 (br, 2H). IR (KBr, cmꢀ1);
1614 (C]N), 1578 (phenol ring), 1470 (N]N), 1288 (C–O), 1097,
Synthesis of a,a0-bis(o-aminophenylthio)-1,2-xylene
A mixture of 2-aminothiophenol (12.52 g, 0.10 mol) and sodium 831 and 756. Anal. calcd.for C46H32Cl4N6O2S2: C, 60.93; N, 9.27;
hydroxide (4.00 g, 0.10 mol) in deionized water (60 mL) was H, 3.56; S, 7.07%. Found: C, 61.73; N, 9.26; H, 3.16; S,
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7.00%.lmax (nm) (3 (Mꢀ1 cmꢀ1)): 264 (41200) and 369 (50850) in
DMSO.MS (EI, 70 eV): [M]+ ¼ 908 molecular ion peak was not
observed. m/z (%) ¼ 399 (25), 226 (94),198 (44), 161 (61), 145
(100), 124 (89), 80 (69).
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Talanta, 2011, 85, 2673–2680; (j) V. Reena, S. Suganya and
S. Velmathi, J. Fluorine Chem., 2013, 153, 89–95; (k) R. Gu,
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J. F. Biernat and W. Dehaen, Org. Biomol. Chem., 2005, 3,
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Acknowledgements
We are grateful to the Arak University for nancial support of
this work.
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