Simple and efficient colourimetric F-sensors and a test paper for fluorine

Article abstract of DOI:10.3184/030823409X12560292679859

A series of colourimetric fluoride ion sensors bearing azo-phenolic hydroxyl and Schiff base groups were synthesised. In CH₃CN solutions, these sensors showed colourimetric single selectivity for F-. An easy-to-prepare test paper based on the s

Full text of DOI:10.3184/030823409X12560292679859

JOURNAL OF CHEMICAL RESEARCH 2009
NOVEMBER, 677–678
RESEARCH PAPER 677
Simple and efficient colourimetric F- sensors and a test paper for fluorine
Tai-Bao Wei, Yan Li, Qi Lin and You-Ming Zhang*
College of Chemistry and Chemical Engineering, Key Laboratory of Polymer Materials of Gansu Province,
Northwest Normal University, Anning East Road No. 967, Lanzhou, Gansu, 730070, P.R. China
A series of colourimetric fluoride ion sensors bearing azo-phenolic hydroxyl and Schiff base groups were
synthesised. In CH3CN solutions, these sensors showed colourimetric single selectivity for F-. An easy-to-prepare
test paper based on the sensor was developed, which could colourimetrically conveniently detect fluoride ion.
Keywords: Schiff base, anion recognition, deprotonation
sensors, we developed a F- detect test paper by absorbing the 3a on
The development of selective optical signalling systems for
treated filter paper, that could colourimetric detect F- conveniently.
anions has received considerable attention in recent decades
Neither did all the anions lead to any significant absorption in the
due to their important roles in biological and environmental
visible region changes, 3a, 3b and 3c showed high sensitivity and
processes.1-3 Fluoride anion recognition is attracting a
selectivity toward F-, competing anions + F- gave absorption changes
mounting interest due to its duplicitous nature. It is a useful
chemical for many industrial applications, and it has been
used in human diet4 and health sciences.5 There are many
receptor species that contain a number of different types of
anion binding group.6,7 For the sensors based on hydrogen
bonds, urea or thiourea units, among others, are usually
used as the binding sites.8 Few receptors bearing a phenolic
O–H have been reported in the literature. With an interest
in developing novel colourimetric anion sensors,9 we have
synthesised a series of anion sensors bearing phenol O–H.
similar to those of single F- experiment (Fig. 2).15 These facts were
indicative of a high selectivity of 3a, 3b and 3c toward F- ion over
other competitive anions.
The interaction properties of receptor 3a and fluoride anion
1
were further investigated by using H NMR titration experiment in
F-
0.4
3a
0.3
Host
0.2
Result and discussion
Cl-
1 was synthesised according to literature methods.10 Sensors 3a–c
were synthesised by the condensation of azo-salicylaldehyde with a
corresponding aminophenol. The results are listed below.
0.1
Br-,I-
2-(2-hydroxyphenylaminomethyl)-4-(4-nitrophenylazo)phenol (3a):
Yield: 74%, m.p. 294–296°C; 1H NMR (DMSO-d6, 400 MHz) d 15.34
(s, 1H, O–H), 10.24 (s, 1H, O–H), 9.27 (s, 1H, N=C–H); IR (cm-1)
v: 3436 (O–H), 1616 (C=N), 1332 (N=N);Anal. Calcd for C19H14N4O4:
C, 62.98; H, 3.89; N, 15.46. Found: C, 63.04; H, 4.01; N, 15.63%.
2-(3-hydroxyphenylaminomethyl)-4-(4-nitrophenylazo)phenol (3b):
Yield: 61%, m.p. 297–299°C; 1H NMR (DMSO-d6, 400 MHz)
d 14.64 (s, 1H, O–H), 9.81 (s, 1H, O–H), 9.14 (s, 1H, N=C–H), IR
(cm-1) v: 3444 (O–H), 1612 (C=N), 1342 (N=N); Anal.Calcd for
C19H14N4O4·1/2H2O: C, 61.45; H, 4.07; N, 15.09. Found: C, 61.54;
H, 3.84; N, 15.22%.
0.0
300
400
500
600
70
Wavelength/nm
3b
F-
0.8
0.6
0.4
0.2
0.0
2-(4-hydroxyphenylaminomethyl)-4-(4-nitrophenylazo)phenol (3c):
Cl-,Br-,I-
1
Yield: 54%, m.p. 300°C; H NMR (DMSO-d6, 400 MHz) d 14.27
(s, 1H, O–H), 9.76 (s, 1H, O–H), 9.14 (s, 1H, N=C–H), IR (cm-1) v:
3445 (O–H), 1615 (C=N), 1332 (N=N); Anal.Calcd for C19H14N4O4:
C, 62.98; H, 3.89; N, 15.46. Found: C, 62.89; H, 3.96; N, 15.67%.
Receptor (3a–c) had a better selectivity for F-. When adding 50
equiv. of F- to the CH3CN solution of (3a–c), visual colour changes
from light yellow to dark purple were observed. In the corresponding
Uv-vis spectrum, a new strong absorption peak appeared at 550 nm
(Fig. 1). Based on the colourimetric recognition abilities of these
Host
0
300
400
500
600
700
Wavelength/nm
OH
F-
OHa
H
C
CHO
+
3c
0.8
0.6
0.4
0.2
0.0
N
NH2
R
-
- -
Host,Cl ,Br ,I
CH3CH2OH
N
N
R
N
N
NO2
NO2
3
1
2
3a 3c
3b
R=o-OHb( ), R=m-OHb( ), R=p-OHb( )
300
400
500
600
700
Wavelength/nm
Scheme 1 Synthesis of receptors.
Fig. 1 The UV-Vis spectra of receptor 3a, 3b, 3c (2 × 10-5 M)
with anions in CH3CN (298K).
* Correspondent. E-mail: zhangnwnu@126.com
PAPER: JC090705

678 JOURNAL OF CHEMICAL RESEARCH 2009
0.40
F-
Cl-
other anions+F-
0.35
0.30
Host,Br-,I-
0.25
0.20
0.15
0.10
0.05
0.00
300 350 400 450 500 550 600 650 700
Wavelen th/nm
g
Fig. 3 1H NMR spectra of receptor 3a in DMSO-d6 upon the
addition of various quantities of Bu4NF.
Fig. 2 The UV-Vis spectra of receptor 3a (2 × 10-5 M) in CH3CN
solution in the prensence of various anions.
Received 28 July 2009; accepted 2 October 20009
Paper 09/0705 doi: 10.3184/030823409X12560292679859
Published online: 16 November 2009
DMSO-d6. A partial 1H NMR spectrum of sensor 3a is shown in
1
Fig. 3. Before the addition of anions, the H NMR chemical shifts
of the O–Ha protons on sensor 3a were at d 15.31, 10.31 ppm. After
addition of 0.1 equiv. of tetrabutylammonium fluoride to receptor 3a,
it was found that the O–Ha, O–Hb group proton signal disappeared,
after the addition of 5 equiv. of F-, a new broad signal appeared at
14.88 ppm, with the continuous addition of F-, the signal shifted to
16.03 ppm, which indicated the formation of HF2-.11,12 These results
suggested that the O–H groups possibly underwent a deprotonation
process.13 The deprotonation of O–H groups led to an increase in
electronic density of the phenyl group, which induced the colour
of sensor change and the signal of the –HC=N– proton and phenyl
protons shifted to upfield.
In summary, three novel sensors based on Schiff base and two
phenolic hydroxy groups have been synthesised and characterised.
The Schiff base group and two phenolic hydroxy groups act as the
binding sites for sense anion. These sensors showed high sensitivity
and selectivity toward F- in CH3CN solution. Furthermore, an easy-
to-prepare test paper14 was developed to detect F- in CH3CN solution.
We believe that the anion responsive test paper reported here may
provide the basis for the development of a useful anion detection kit.
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This work was supported by the NSFC (No. 20671077) and
the Natural Science Foundation of Gansu 2008-1-164.
PAPER: JC090705