Synthesis, characterization and use of Schiff bases as fluorimetric analytical reagents (part II)

Article abstract of DOI:10.1155/2011/821616

Many Schiff bases were prepared by condensation reaction of certain aromatic amines with aromatic aldehydes derivatives and then the fluorescence properties of these Schiff bases were examined in acidic and basic media. It is shown that these compounds can be used for fluorimetric monitoring of small pH changes.

Full text of DOI:10.1155/2011/821616

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(1), 180-184
http:www.e-journals.net
Synthesis, Characterization and Use of Schiff Bases
as Fluorimetric Analytical Reagents (Part II)
MOHAMED N. IBRAHIM* and SALAHEDDIN A. I. SHARIF
*Chemistry Department, Faculty of Science, Garyounis University, Benghazi, Libya
Biology Department, Faculty of Education (Qemeenes Branch)
Garyounis University, Benghazi, Benghazi, Libya
mnibrahim46@yahoo.com
Received 11 November 2009; Accepted 29 December 2009
Abstract: Many Schiff bases were prepared by condensation reaction of certain
aromatic amines with aromatic aldehydes derivatives and then the fluorescence
properties of these Schiff bases were examined in acidic and basic media. It is shown
that these compounds can be used for fluorimetric monitoring of small pH changes.
Keywords: Schiff bases, Fluorescent indicators, Anthranilic acid, o-phenylenediamine.
Introduction
Schiff bases derived from aromatic amines and aromatic aldehydes have a wide variety of
applications in many fields, e.g., biological, inorganic and analytical chemistry1-5.
Application of many new analytical devices requires the presence of organic reagents as
essential compounds of the measuring system. They are used, e.g., in optical and
electrochemical sensors, as well as in various chromatographic methods, to enable detection
of enhance selectivity and sensitivity6-8.
Among the organic reagents actually used, Schiff bases possess excellent characteristics,
structural similarities with natural biological substances, relatively simple preparation
procedures and the synthetic flexibility that enables design of suitable structural properities9,10
.
Schiff bases are widely applicable in analytical determination, using reactions of
condensation of primary amines and carbonyl compounds in which the azomethine bond is
formed (determination of compounds with an amino or carbonyl group); using complex
formation reactions (determination of amines, carbonyl compounds and metal ions); or
utilizing the variation in their spectroscopic characteristics following changes in pH and
solvent (pH of solvent polarity indicators)11-13
.
Unfortunately, most Schiff bases are chemically unstable and show a tendency to be
involved in various equilibria, like tautomeric interconversions, hydrolysis, or formation of
ionized species14,15. Therefore, successful application of Schiff bases requires a careful study
of their characteristics.

Synthesis, Characterization and Use of Schiff Bases
181
The Schiff bases prepared are condesation products of aromatic aldehyde derivatives with
aromatic mono- and diamines derivatives and presented in (Scheme 1). In this work the spectroscopic
characteristics and possibilities of analytical applications of these Schiff bases are presented.
I
IV
N
N
NH2
HO
O
OH
OH
N-(4-Hydroxybenzylidene)-benzene-1,2-diamine
p-Hydroxybenzylidene-2-carboxyaniline
II
V
N
N
O
O
NH2
HO
O
N+
O-
N+
O-
p-Nitrobenzylidene-2-carboxyaniline
N-(4-Nitrobenzylidene)-benzene-1,2-diamine
III
VI
N
N
NH
2
N
HO
O
N
N-(4-Dimethylamino-benzylidene)-benzene-1,2-diamine
N-(4-Dimethylaminobenzene)-benzene-1,2-diamine
P-(N,N-Dimethyl)aminobenzylidene-2-carboxyaniline
Scheme 1
Experimental
All chemicals and solvents used for synthesis were of reagent grade. All melting points were
taken on a melting point apparatus and are uncorrected. IR spectra were recorded on a
Shimadzu 5000 instrument. 1H NMR were run on a Jeol 500 MHz instrument using TMS as
internal standard and DMSO as solvent. The spectral analyses were carried out at the NMR
laboratory, Alexandaria University, Alexandaria; the elemental analyses at Microanalytical
center Cairo University, Cairo, Egypt
The Schiff bases (I-VI) were prepared according to the reported methods16,17. The
procedure is as follows: A solution of the amine derivative (0.01 mol) in absolute ethanol (10 mL)
was slowly added to a solution of the aldehyde derivative (0.01 mol) in absolute ethanol (10
o
mL). After stirring the reaction mixture for 2 h (compounds I, II and III), and for 5 h at 60-70 C
and cooling (compounds IV, V and VI), a precipitate was formed which collected by filtration
then washed several times with cold ethanol and recrystallised from ethanol.
p-Hydroxybenzylidene-2-carboxyaniline I was prepared from anthranilic acid and
p-hydroxybenzaldehyde; pale orange; m.p. 229.5-230 oC; 1.6 g (70%) yield. IR (KBr, cm-1)
1
ν = 3500 (OH), 2900 (C-H), 1715 (C=O), 1615 (C=N), 1490 (C=C), 1280,1170(C-O); H
NMR (500 MHz, DMSO); δ (ppm): 6.41-7.66 (8H, m, Ar-H), 8.3 (1H, s, CH=N), 9.70 (1H, s,
Ar-OH), 11.00 (1H, s, COOH); C14H11NO3 (241.2): calcd. C 69.65%, H 4.56%, N 5.80%;
found C 68.92%, H 4.52%, N 5.77%.

182
MOHAMED N. IBRAHIM et al.
p-Nitrobenzylidene-2-carboxyaniline (II) was prepared from anthranilic acid and
o
p-nitrobenzaldehyde; yellow-white; m.p. 172-174 C; 1.7 g (62% ) yield. IR (KBr, cm-1)
ν = 3500 (OH), 2900 (C-H), 1720 (C=O), 1610 (C=N), 1480 (C=C), 1495, 1320 (N=O),
1
1285,1170(C-O); HNMR ( 500 MHz, DMSO ); δ (ppm): 6.35-8.28 (8H, m, Ar-H), 8.30
(1H, s, CH=N),10.11 (1H, s, COOH); C14H10N2O4 ( 270.2 ): calcd. C 62.17%, H 3.70%, N
10.36%; found C 61.88%, H 3.65%, N 10.03%.
p-(N,N-Dimethyl)aminobenzylidene-2-carboxyaniline (III) was prepared from
o
anthranilic acid and p-(N,N-dimethylamino)benzaldehyde; pale green; m.p. 198 C; 2.0 g
(75%) yield. IR (KBr, cm-1) ν = 3500 (OH), 2910 (C-H), 1725 (C=O), 1615 (C=N), 1355
(C-N), 1475 (C=C)1280,1170(C-O); 1H NMR (500 MHz, DMSO); δ (ppm): 2.89 (6H, s, N-
(CH3)2), 6.41-7.62 (8H, m, Ar-H), 8.29 (1H, s, CH=N), 9.57 (1H, s, Ar-OH); C16H16N2O2
(268.2): calcd. C 71.58%, H 5.96%, N 10.43%; found C 70.42%, H 5.81%, N 9.33%.
N-(4-Hydroxybezylidene)-benzene-1,2-diamine (IV) was prepared from o-phenylene-
diamine and p-hydroxybenzaldehyde; cotton pale brown; m.p. 148 oC; 1.3 g (64% ) yield. IR
(KBr, cm-1) ν = 3400,3300 (N-H), 3000 (O-H), 3010 (C-H), 1600 (C=N), 1445 (C=C), 1360
1
(C-N); HNMR (500 MHz, DMSO); δ (ppm): 5.00 (2H, s, -NH2), 6.41-7.70 (8H, m, Ar-H),
8.38 (1H, s, CH=N), 10.47 (1H, s, Ar-OH); C13H12N2O ( 212.2 ): calcd. C 73.51%, H 5.65%,
N 13.19%; found C 73.01%, H 5.42%, N 12.87%.
N-(4-Nitrobezylidene)-benzene-1,2-diamine (V) was prepared from o-phenylene-
diamine and p-nitrobenzaldehyde; pale brown; m.p. 317-318 oC; 1.9 g (81%) yield. IR (KBr,
cm-1) ν = 3400,3300 (N-H), 3010 (C-H), 1615 (C=N), 1440 (C=C), 1365 (C-N), 1510, 1330
(N=O); 1H NMR (500 MHz, DMSO); δ (ppm): 5.00 (2H, s, -NH2), 6.40-8.1 (8H, m, Ar-H),
8.38 (1H, s, CH=N); C13H11N3O2 (241.2): calcd. C 64.67%, H 4.56%, N 17.41%; found C
63.28%, H 4.22%, N 15.96%.
N-(4-(N,N-Dimethylaminobezylidene)-benzene-1,2-diamine (VI) was prepared from
o
o-phenylenediamine and p-(N,N-dimethylbenzaldehyde; yellow; m.p. 141-142 C; 0.4 g
(16 %) yield. IR (KBr, cm-1) ν = 3460,3370 (N-H), 2900, 2800 (C-H), 1600 (C=N), 1440
1
(C=C), 1360 (C-N); HNMR ( 500 MHz, DMSO ); δ (ppm): 2.86 (6H, s, -N-(CH3)2), 4.97
(2H, s, -NH2), 6.40-7.66 (8H, m, Ar-H), 8.31 (1H, s, CH=N); C15H17N3 (239.2): calcd.
C75.25%, H 7.10%, N 17.55%; found C 74.90%, H 6.58%, N 17.04%.
Results and Discussion
Fluorescence studies
Fluorescent indicators18,19 have many applications and are generally employed in cases
where colorimetric indicators are difficult to observe or lack sensitivity. Such cases are
found in dark, turbid or coloured solutions or titrations in which a precipitate is formed. A
flash of light from a fluorescent indicator is much easier to see or measure than the
appearance of a weak colour. Fluorescent colours under UV light are often easier to observe
than a weak change in colour in an ordinary colour indicator.
Determination with fluorescent indicators may be carried out in a dark room or the use
of a view box provided with an entry door. UV light (Herolab, 254 nm, NU-4 KL) was used
as a source of radiation. For pH measurements, pH-meter (Mettler-Toledo, MP 220) was
used. The change of fluorescent intensity or colour of a compound caused by a change in pH
may be the results of equilibrium shifts
AH
H+ + A-
AH + hv1
AH*
AH + hν2 fluorescence

Synthesis, Characterization and Use of Schiff Bases
183
The use of fluorescent indicators in titration of coloured solutions is probably the most
prominent of the indicator applications. Table 1 below shows the change in colours
according to the pH change:
Table 1. Acid-base fluorescent Schiff bases
Schiff base
pH Range
1.5-2.7
2.7-6.5
6.5-12.5
12.5-14
0.8-1.4
1.5-2.7
2.7-6.0
6.0-12.6
12.6-14
0.95-1.4
1.45-2.0
2.0-6.0
6.0-12.5
12.5-14
1-9.2
Flourescent Colour Change*
non-fl. to pale blue
bright blue
Indicator Solution
0.1 % solution
in 50 % ethanol
I
dark blue
pale blue to blue-green
non-fl.
pale blue
0.1 % solution
in 50 % ethanol
II
bright blue
dark blue
pale blue to blue-green
pale blue
dark blue
bright blue
dark blue
0.1 % solution
in 50 % ethanol
III
pale blue to blue-green
pale blue
bright blue
0.2 % solution
in 70 % ethanol
0.2 % solution
in 70 % ethanol
0.2 % solution
in 70 % ethanol
IV
V
9.2-14
1-14
non-fl.
1.0-6.0
6.0-14
pale blue
dark blue
VI
*Most of the colours are based on visual observations
Whereas, the effect of pH on the statring materials (aromatic amines), listed in the Table 2.
Table 2. Acid-base fluorescent aromatic amine19
Aromatic amine
Anthranilic acid
pH
Colour Change
non-fl. to light blue
light blue to dark blue
dark blue to non-fl.
green to non-fl.
Indicator Solution
0.1 % solution
in 50 % ethanol
1.5-3.0
4.5-6.0
12.5-14
3.1-4.4
o-Phenylenediamine
0.2 % solution
in 70 % ethanol
Conclusion
Most Schiff bases prepared in this work through condensation of anthranilic acid and
o-phenylenediamine with the corresponding aldehyde derivatives show fluorescent
properties, therefore, they can be used as fluorescent indicators.
Compounds I-III showed characteristic colour change on pH range 1-6 (acidic medium)
as well as in basic medium. Compounds IV and VI also showed colour change over a wide
pH range. Compound V prove to be not suitable and showed non-fluorescence property. The
fluorescence of these compounds is pH dependent and can be used for monitoring pH. This
fact opens an attractive possibility of application in optical sensors where pH sensitivity is
required over limited pH range.

184
MOHAMED N. IBRAHIM et al.
Future efforts will be carried out on other types of Schiff bases and study of their
applications as optical sensors.
References
1.
2.
3.
Cimerman Z, Miljanic S and Galic N, Croatica Chemica Acta, 2000, 73(1), 81-95.
Singh P Goel R L and Singh B P, J Indian Chem Soc., 1975, 52, 958-959.
Perry B F Beezer A E Miles R J Smith B W Miller J and Nascimento M G,
Microbois., 1988, 45, 181.
4.
5.
6.
Elmali A Kabak M and Elerman Y, J Mol Struct., 1999, 477, 151.
Patel P R Thaker B T and Zele S, Indian J Chem., 1999, 38A, 563-566.
Valcarcel M and Laque de Castro M D, Flow-Throgh Biochemical Sensors; Elsevier:
Amsterdam, 1994.
7.
8.
9.
Spichiger-Keller U E, Chemical Sensors and Biosensors for Medical and Biological
Applications, Wiley-VCH, Weinheim, 1998.
Lawrence J F and Frei R W, Chemical Derivatization in Liquid Chromatography;
Elsevier: Amsterdam, 1976
Patai S (Ed.), The Chemistry of the Carbon-Nitrogen Double Bond, J Wiley & Sons,
London, 1970.
10. Jungreis E and Thabet S, Analytical Applications of Schiff bases, Marcell Dekker,
New York, 1969.
11. Metzler C M Cahill A and Metzler D E, J Am Chem Soc., 1980, 102, 6075-6082.
12. Dudek G O and Dudek E P, Chem Commun., 1965, 464.
13. Dudek G O and Dudek E P, J Am Chem Soc., 1966, 88, 2407-2412.
14. Cimerman Z and Stefanac Z, Polyhedron, 1985, 4, 1755.
15. Galic N Cimerman Z and Tomisic V, Anal Chim Acta, 1997, 343, 135.
16. Bigelow L A and Eatough H, Org Synth., 1967, 1, 80.
17. Ibrahim M N Hamad K J and Al-Joroshi S H, Asian J Chem., 2006, 18(13), 2404.
18. White C E and Aragauer R J, Fluorescence Analysis, A practical Approach; Marcel
Dekker, Inc.: New York, 1970.
19.
Bishop E, Indicators; Pergamon Press Ltd., Headington Hill Hall:Oxford, 1972.

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