Synthesis of novel probe 2-chloro-6-methoxy-3-phenyl hydrazone quinoline and its application to detection of persulphate in aqueous ethanol solution by fluorescence turn on

Article abstract of DOI:10.1007/s10847-017-0767-8

Abstract: A highly sensitive and selective fluorimetric detection method has been developed for persulphate anion using fluorescence turn on of 2-chloro-6-methoxy-3-phenyl hydrazone quinoline (Cl-MPHQ) in aqueous ethanol solution. Cl-MPHQ is a weakly fluorescent compound synthesized via a one-step reaction of 2-chloro-6-methoxyquinoline-3-carboxyaldehyde (Cl-MQCA) and phenyl hydrazine. The treatment of Cl-MPHQ with persulphate ion in aqueous ethanol solution (1:1?V/V) generates fluorescent Cl-MQCA, through C=N bond cleavage. The fluorescence intensity increased linearly with the concentration of persulphate ion (0–100?μmol?L^?1). The detection limit of the method is 1?μmol?L^?1determined from the standard deviation of the blank signal (3σ). The relative standard deviation of the method is 3% for 20?μmol?L^?1 of persulphate ion. The proposed method is simple, sensitive and useful for selective detection of persulphate ion in an aqueous ethanol solution. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10847-017-0767-8

Journal of Inclusion Phenomena and Macrocyclic Chemistry (2018) 90:99–104
https://doi.org/10.1007/s10847-017-0767-8
ORIGINAL ARTICLE
Synthesis of novel probe 2-chloro-6-methoxy-3-phenyl hydrazone
quinoline and its application to detection of persulphate in aqueous
ethanol solution by fluorescence turn on
1
2
1
1
1
Dhanshri V. Patil · Vishal S. Patil · Sandeep A. Sankpal · Govind B. Kolekar · Shivajirao R. Patil
Received: 28 February 2017 / Accepted: 21 November 2017 / Published online: 2 December 2017
©
Springer Science+Business Media B.V., part of Springer Nature 2017
Abstract
A highly sensitive and selective fluorimetric detection method has been developed for persulphate anion using fluorescence
turn on of 2-chloro-6-methoxy-3-phenyl hydrazone quinoline (Cl-MPHQ) in aqueous ethanol solution. Cl-MPHQ is a weakly
fluorescent compound synthesized via a one-step reaction of 2-chloro-6-methoxyquinoline-3-carboxyaldehyde (Cl-MQCA)
and phenyl hydrazine. The treatment of Cl-MPHQ with persulphate ion in aqueous ethanol solution (1:1 V/V) generates
fluorescent Cl-MQCA, through C=N bond cleavage. The fluorescence intensity increased linearly with the concentration
−
1
−1
of persulphate ion (0–100 µmol L ). The detection limit of the method is 1 µmol L determined from the standard devia-
−
1
tion of the blank signal (3σ). The relative standard deviation of the method is 3% for 20 µmol L of persulphate ion. The
proposed method is simple, sensitive and useful for selective detection of persulphate ion in an aqueous ethanol solution.
Graphical Abstract
Keywords 2-Chloro-6-methoxy-3-phenyl hydrazone quinoline · Fluorescence turn on · Persulphate ion detection
Introduction
2
−
Persulphate anion (S O ) is a strong, two-electron oxidiz-
2
8
ing agent with a redox potential of 2.01 V [1]. Persulphate
widely used for chemical oxidation of organic contaminants
in polluted soil, ground-water and wastewater [2–11]. Per-
sulphate salts have many uses, such as bleaching of textiles
and natural fibers, removal of thiosulphate anions from
photographic plates, initiators for olefin polymerization and
etching of printed circuit boards and photo resists [12]. The
analytical methods available for the determination of persul-
phate include iodometry and spectrophotometry [5, 13–16].
*
Dhanshri V. Patil
dtp.phy@gmail.com
1
Fluorescence Spectroscopy Research Laboratory,
Department of Chemistry, Shivaji University, Kolhapur,
Maharashtra 416 004, India
2
Department of Chemistry, Sanjeevan Engineering &
Technology Institute, Panhala, Maharashtra 416201, India
Vol.:(0
1
123456789)
3

100
Journal of Inclusion Phenomena and Macrocyclic Chemistry (2018) 90:99–104
Recently, S. Gokulakrishnan et al. proposed a spectropho-
tometric method for determination of persulphates using N,
N-diethyl-p-phenylenediamine as colorimetric reagent [17].
Previously reported methods are complicated and expen-
sive [5, 13–17] in contrast spectrofluorimetric method using
probe to sense analyte is very simple, sensitive and inexpen-
sive [18, 19]. Thus there is a demand for sensitive and selec-
tive procedures for determination of persulphate in envi-
ronmental samples. The heterocyclic quinoline aldehyde,
Cl-MQCA, undergoes condensation with phenyl hydrazine
to form hydrazone quinoline, Cl-MPHQ, in aqueous solu-
tion which in turn can be separated by cleavage of the C=N
bond into the original components by oxidizing agents like
persulphate. Therefore, weakly fluorescent hydrazone can
regenerate fluorescence by persulphate induced cleavage
of the C=N bond. These synthetic routes prompted us to
prepare 2-chloro-6-methoxy-3-phenyl hydrazone quino-
line (Cl-MPHQ) by condensation of fluorescent 2-chloro-
One‑pot synthesis of 2‑chloro‑6‑methoxy‑3‑phenyl
hydrazone quinoline (Cl‑MPHQ)
The Cl-MPHQ was synthesized according to the procedure
given in Scheme 1. A solution of phenyl hydrazine (0.49 mL,
5 mmol) was added to 2-chloro-6-methoxyquinoline-3-car-
boxyaldehyde (1.105 g, 5 mmol) along with 20 mL distilled
water as a reaction medium. The entire mixture was stirred
at room temperature in round bottom flask for 5–6 h. The
progress of the reaction was monitored by TLC using pet
ether: ethyl acetate mixture in the ratio 7:3. Yellow solid
obtained as a product was separated by filtration at vacuum
and recrystallized from isopropanol solution.
The condensation reaction between 2-chloro-6-meth-
oxyquinoline-3-carboxyaldehyde (Cl-MQCA) and phenyl
hydrazine has given yellow product of Cl-MPHQ having
weight 1.35 gm with yield 85% and mp 187 °C. IR (KBr,
−
1
1
cm ); 3230.87 ʋ(NH), 1604.25 ʋ(HC=N); H NMR
(300 MHz, DMSO d-6): ꢀ10.96 (1H, s), 8.82 (1H, s), 8.21
(1H, s), 7.83–7.80 (1H, d, J = 9 Hz), 7.56–7.55 (1H, d,
J = 3 Hz), 7.51(1H, s), 7.41–7.37 (2H, t), 7.30–7.27 (1H,
d, J = 9 Hz), 7.19–7.16 (1H, d, J= 9 Hz), 6.85–6.81 (1H,
6
-methoxyquinoline-3-carboxyaldehyde (Cl-MQCA) with
phenyl hydrazine and to perform systematic experiments
to follow the decomposition of Cl-MPHQ in presence of
increasing amounts of persulphate solution by measuring
the fluorescence. The present paper explores the suitability
of Cl-MPHQ as sensor for detection of persulphate anion in
aqueous ethanol solution.
1
3
t), 3.91(3H, s); C NMR (75 MHz, DMSO d-6): δ 158.39
(ArC), 145.66 (ArC), 145.07 (CH=N), 142.63 (ArC), 132.40
(ArC), 131.10 (ArCH), 129.68 (ArC), 129.57 (ArCH),
1
29.43 (ArCH), 129.00 (ArCH), 128.09 (ArC), 123.52
(
ArCH), 120.17 (ArCH), 112.85 (ArCH), 107.31 (ArCH),
Experimental
106.49 (ArCH), 56.11 (OCH ); ESI MS: calculated for
3
+
[
M+H] C H N OCl: 312.77; found: 312.10.
1
7
14
3
Reagents and instruments
2
−
General procedure for S O determination
2
8
2
-Chloro-6-methoxyquinoline-3-carboxyaldehyde and
−
3
−1
potassium salts of different anions were purchased from
Alfa Aesar and used without further purification. Ethanol
was of chromatography grade and analytical grade phenyl
hydrazine (Sigma–Aldrich) was used after distillation. Ultra
pure water (Millipore, France) was used to prepare aqueous
ethanol medium.
Stock solution of Cl-MPHQ (1×10 mol L ) was prepared
−
4
−1
in 1:1 (V/V) ethanol and diluted further to 4×10 mol L
by the same solvent. The anion stock solutions were pre-
pared by dissolving the calculated amounts of the salts in
The Mass spectrum was recorded on LC-MS/MS API-
4
000 ABSCIEX spectrometer. IR spectrum of sample on
KBr disk was recorded on a Shimadzu IR-470 FT-IR spec-
trophotometer. Nuclear Magnetic Resonance spectra were
recorded in DMSO d-6 using a Bruker Avance III-300-MHz
spectrometer with tetra-methyl silane (TMS) as an internal
standard. The fluorescence emission and excitation measure-
ments were carried out on a PC-based spectrofluorimeter
JASCO, Japan (Model FP-750). The absorption spectra were
recorded on a UV-VIS-NIR spectrophotometer [Shimadzu
UV-3600].
Scheme 1 Synthesis of Cl-MPHQ
1
3

Journal of Inclusion Phenomena and Macrocyclic Chemistry (2018) 90:99–104
101
−
3
−1
ultrapure water 1×10 mol L , which were further diluted
The Cl-MQCA is fluorescent while Cl-MPHQ is weakly
fluorescent. Figure 2 shows excitation and fluorescence
spectra of Cl-MQCA in ethanol–water solution. The fluo-
rescence and excitation spectra are mirror images and Stokes
−
4
−1
to 2.5 × 10 mol L by water. The experiments were set
to test behavior of different anions along with anion of cur-
2
−
rent interest i.e. S O . To a 1.0 mL solution of Cl-MPHQ,
2
8
−
−
−
−
2−
2−
−
−1
different anions (Cl , Br , I , F , SO , SO , NO ,
shift is 3255 cm . The small Stokes shift indicates that Cl-
4
3
3
−
−
−
2−
2−
−
−
SCN , HCO , CH COO , C O , CO , IO , BrO and
MQCA exists as an isolated molecule in the aqueous ethanol
medium.
3
3
2
4
3
3
3
2−
−4
−1
S O ) solution with concentration 2.5×10 mol L were
2
8
added and diluted to 5 mL. Only persulphate anion induced
noticeable changes in fluorescence and absorption intensity.
Therefore, a second set in test tubes containing 1 mL of Cl-
MPHQ solution with varying concentrations of persulphate
solution and then diluted to 5 mL. The ratio of ethanol–water
was maintained 1:1 (V/V). Quartz cuvettes were used for
absorption; excitation and emission measurements. Slit
widths were fixed at 5 nm during excitation and emission
measurements.
2
−
Fluorescence titration of Cl‑MPHQ with S O
in solution
2
8
The fluorescence spectra of a mixture of Cl-MPHQ and
persulphate ion were measured in varying concentrations
of persulphate ion, Fig. 3. The fluorescence spectra are
identical with the spectrum of Cl-MQCA and intensity of
emission seen at 374 nm increases with concentration of
2
−
S O ion. This observation demonstrates regeneration of
2
8
Cl-MQCA by oxidation of Cl-MPHQ. Under the reaction
Results and discussion
Photophysical studies of Cl‑MQCA and Cl‑MPHQ
by absorption and fluorescence spectroscopy
The UV–Visible absorption spectra of Cl-MQCA and Cl-
MPHQ recorded in ethanol–water 1:1 (V/V) are shown in
Fig. 1. The spectrum of Cl-MQCA (spectrum-A) shows
bands with maximum at 220, 235 and 337 nm while that of
Cl-MPHQ (spectrum-B) shows bands peaking at 243, 293
and 396 nm. The band at 220 nm in Cl-MQCA is due to
aromaticity and other at 235 and 337 nm are assigned to
ꢀ
→ ꢀ ∗ and n → ꢀ ∗ transitions respectively. The absorp-
tion spectrum of Cl-MPHQ shows two ꢀ → ꢀ ∗ transition
bands at 243 and 293 nm while one more pronounced band
due to n → ꢀ ∗ at 398 nm. Thus, the spectral results indicate
that both Cl-MQCA and Cl-MPHQ are photosensitive and
wavelengths of maximum absorption are well separated.
Fig. 2 The excitation (a) and emission (b) spectra of Cl-MQCA
[8×10− mol L ] in ethanol-water 1:1 (V/V) medium
5
−1
−
1
Fig. 3 Fluorescence emission spectra of Cl-MPHQ (80 µmol L
)
2
−
−1
Fig. 1 UV–Visible absorption spectra of Cl-MQCA (spectrum-A)
in the absence and presence of S O
(0–100 µmol L ) in etha-
2− −1
2
8
−
5
−1
−5
−1
[
8×10 mol L ] and Cl-MPHQ (spectrum-B) [8×10 mol L ] in
nol–water solution (1:1, V/V). [S O ]=A (0 µmol L ) to K
2 8
1
(100 µmol L−
)
ethanol–water 1:1 (V/V)
1
3

102
Journal of Inclusion Phenomena and Macrocyclic Chemistry (2018) 90:99–104
conditions, the generation of Cl-MQCA by cleavage of C=N
bond is slow, Fig. 4. Seven hours reaction time was selected
as a compromise for analytical determination and accord-
ingly the fluorescence spectra of reaction mixtures were
measured after 7 h.
the plausible fluorescence sensing mechanism for the per-
sulphate ion is given in Scheme 2. The synthesized moiety
Cl-MPHQ is weakly fluorescent because of loss of rigidity
and its parent moiety i.e. aldehyde (Cl-MQCA) is highly
fluorescent.
The inset in Fig. 3 show plot of fluorescence generated
2
−
2−
versus concentration of S O
anion. Under the experi-
Selectivity test of Cl‑MPHQ for S O ion
2
8
2 8
mental conditions, the increase in fluorescence intensity is
directly proportional to the persulphate concentration in the
To evaluate the selectivity of Cl-MPHQ for persul-
phate anion, changes in absorption spectrum caused by
−
1
range of 10–160 µmol L . The detection limit was deter-
mined as three times the standard deviation of the blank
−
1
−
−
−
−
2−
2−
−
100 µmol L of Cl , Br , I , F , SO , SO , NO ,
4
3
3
−
1
−
−
−
2−
2−
−
−
signal (3σ) as 1 µmol L . The relative standard deviation
SCN , HCO , CH COO , C O ,CO , IO , BrO were
3
3
2
4
3
3
3
(
n=7) was 3% for 20 µmol L−1 of persulphate ion.
measured, Fig. 5. The results show that other anions did not
cause any significant absorption changes under the same
experimental conditions.
Time dependent UV–Visible absorption study
The compound Cl-MPHQ on interaction with vari-
ous anions, an appreciable enhancement in fluorescence
intensity is observed only in presence of persulphate ions
(Fig. 6). The detection of persulphate is based on per-
sulphate induced cleavage of C=N bond in Cl-MPHQ.
From Fig. 7, it is observed that the fluorescence emission
The photometry experiment was carried out by adding high
concentration of persulphate to the Cl-MPHQ solution and
regeneration of highly fluorescent aldehyde (Cl-MQCA)
in reaction solution. The UV–Visible absorption spectra
were recorded immediately on addition of persulphate and
after time interval of 2–10 h and finally last spectrum was
recorded after 24 h from the time of mixing. Figure 4 also
includes absorption spectrums of Cl-MPHQ (spectrum-A)
and Cl-MQCA (spectrum-I) for comparison. On addition
of high a concentration of persulphate to Cl-MPHQ solu-
tion, the C=N bond cleavage reaction becomes faster. Thus,
the absorption intensity of bands at 243, 293 and 396 nm
decreases due to oxidation of Cl-MPHQ molecules by per-
sulphate ions. The absorption spectrum (H) of reaction
mixture recorded after 24 h is exactly identical with that
of the Cl-MQCA (spectrum-I). Thus, it is concluded that
the species generated after persulphate induced cleavage is
Cl-MQCA. During the experiment, the initial yellow color
of Cl-MPHQ solution becomes colorless after completion
of the reaction, inset of Fig. 4. Based on these observations,
Scheme 2 Proposed mechanism for “turn on” fluorescence in mix-
ture of Cl-MPHQ and persulphate ion solution
Fig. 5 The absorption spectra of Cl-MPHQ (80 µmol L− ) in ethanol–
1
Fig. 4 The time dependent photometry of reaction between Cl-
−
1
−1
−
MPHQ [60 µmol L ] (spectrum- A) with addition of persulphate
water (1:1, V/V) in the absence and presence of 100 µmol L of Cl ,
−
1
−
−
−
2−
2−
−
−
−
−
2−
[
800 µmol L ] at different time intervals (spectra B to H). Last spec-
Br , I , F , SO , SO , NO , SCN , HCO , CH COO , C O
,
4
3
3
3
3
2
4
−1
2−
−
−
2−
trum at the bottom is of pure Cl-MQCA (spectrum-I) [80 µmol L
]
CO , IO , BrO and S O
3 3 3 2 8
1
3

Journal of Inclusion Phenomena and Macrocyclic Chemistry (2018) 90:99–104
103
Fig. 6 The fluorescence spectra of Cl-MPHQ in ethanol–water
–
1
–
–
–
–
2–
(
1:1 V/V) in the presence of 100 µmol L of Cl , Br , I , F , SO
,
4
Fig. 8 Fluorescence quenching/enhancement ratio of Cl-MPHQ
2
–
–
–
–
–
2–
2–
–
–
−1
SO , NO , SCN , HCO , CH COO , C O , CO , IO , BrO
3
3
3
3
2
4
3
3
3
(80 µmol L ) in the absence and presence of various competitive
−1
2–
and S O
2
8
anions (100 µmol L ) in ethanol–water solution (1:1, V/V)
applications it is necessary to detect an analyte in the pres-
ence of competing substrates. Thus, the experiment was
performed for fluorescence detection of persulphate in
the presence of equivalent amount of other competitive
2
−
anions. The set was carried out by adding S O
to the
2
8
−
−
−
−
solution of Cl-MPHQ in the presence of Cl , Br , I , F ,
2
−
2−
−
−
−
−
2−
SO , SO , NO , SCN , HCO , CH COO , C O
,
4
3
3
3
3
2
4
2
−
−
−
CO , IO , BrO anions, Fig. 8. The enhancement in
3
3
3
fluorescence intensity resulting from the addition of per-
sulphate is almost not influenced by subsequent addition
of anions, noticing that even in the presence of some inter-
fering species the Cl-MPHQ can successfully used for the
persulphate detection.
Table 1 compares the analytical performances of the
present method with other reported methods [1, 5, 8, 16,
Fig. 7 Fluorescence quenching/enhancement ratio of Cl-MPHQ
−
1
−1
(
80 µmol L ) to representative anions (100 µmol L ) in ethanol–
1
7]. The methods reported require activator for persul-
water solution (1:1, V/V)
phate determination but in present method activator is not
used. Also, many reported methods are carried out at ele-
vated temperature but present work is carried out at room
temperature. Thus our proposed method is comparatively
superior, simple, sensitive and environmentally benign for
persulphate determination.
of Cl-MPHQ is slightly enhanced with the addition of
−
2−
IO because it is also an oxidizing agent like S O , in
3
2
8
3
−
addition BrO has the same property but did not show any
significant changes in emission intensity. All other anions
give negative response to Cl-MPHQ. Thus, under these
reaction conditions, only persulphate selectively induces
cleavage of C=N bond in Cl-MPHQ. Also, for the practical
Table 1 Comparison of the
Sr. No. Technique
Quenching/enhancement Activator Temperature References
proposed method with other
methods for persulphate
determination
+2
1
2
3
4
5
6
Kinetic
–
Fe
Fe
Fe
Fe
Fe
50 °C
80 °C
Room temp
Room temp. [16]
80 °C [17]
[1]
[5]
[8]
+
+
+
+
2
2
2
2
Spectrophotometric
In situ chemical oxidation
Spectrophotometric
Spectrophotometric
Quenching
–
–
Enhancement
Spectrofluorimetric and
Enhancement in fluores- Not used Room temp. Present work
spectrophotometric
cence intensity
1
3

104
Journal of Inclusion Phenomena and Macrocyclic Chemistry (2018) 90:99–104
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.
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A fluorimetric method was developed using 2-chloro-
5
5–91 (2010)
6
-methoxy-3-phenyl hydrazone quinoline (Cl-MPHQ) for
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sulphate for carbamazepine removal from domestic wastewater.
Water. Res. 48, 229–236 (2013)
detection of persulphate ions based on fluorescence turn
on in aqueous ethanol solution. The method was based
on the selective cleavage of C=N bond in Cl-MPHQ by
persulphate and switching on the fluorescence of Cl-
MQCA by its regeneration. The selectivity of Cl-MPHQ
8
.
Liu, H.Z., Bruton, T.A., Doyle, F.M., Sedlak, D.L.: In situ chemi-
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2
−
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2
8
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2
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2–
–
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2
8
2
2
2
8
5
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A heterogeneous Co O -Bi O composite catalyst for oxidative
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3
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Acknowledgements The authors gratefully acknowledge Department
of Science and Technology (DST) and University Grants Commis-
sion (UGC), New Delhi, for providing Grants to the Department of
Chemistry, Shivaji University, Kolhapur, under FIST and SAP pro-
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