Synthesis and antibacterial activities of some schiff bases

Article abstract of DOI:10.1155/2011/258340

Schiff bases p-hydroxybenzylidene-2-carboxyaniline, p-nitrobenzylidene-2- carboxyaniline, p-(N, N-dimethyl)aminobenzylidene-2-carboxyaniline, N-(4-hydroxybezylidene)-benzene-1,2-diamine, N-(4-nitrobezylidene)benzene-1,2- diamine,N-(4-(N, N-dimethylaminobezylidene)benzene-1,2-diamine, N-(4-(N,Ndimethylamino) benzylidene)naphthalen-1-amine,N-(4-nitrobenzylidene) naphthalen-1-amine,N-(4-chlorobenzylidene)naphthalen-1-amine,sodium-4-(4-(N, N-dimethyl amino)benzylideneamino)naphthalene-1-sulfonate,sodium -4-(4-nitrobenzylideneamino) naphthalene-1-sulfonate and sodium-4-(4- chlorobenzylideneamino) naphthalene-1-sulfonate obtained by condensation of aniline and naphthylamine derivatives with some aromatic aldehydes were characterized by physical and spectral methods. The biological activity of these products were as antibacterial agents against three species of human pathogenic bacteria such as Escherichia coli, Staphylococcus aureus and Klebsiella sp. Nearly 50% of these compounds showed reasonable activity against the bacterial species investigated and we found that the antibacterial activity is dependent on the molecular structure of the compounds.

Full text of DOI:10.1155/2011/258340

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(1), 212-216
http://www.e-journals.net
Synthesis and Antibacterial
Activities of Some Schiff Bases
MOHAMED N. IBRAHIM, SALAHEDDIN A. I. SHARIF§,
AHMAD N. EL-TAJORY* and ASMA A. ELAMARI#
Chemistry Department
Faculty of Science, Garyounis University, Benghazi
§Life Science Department, Faculty of Education (Qemeenes Branch)
Garyounis University, Benghazi, Libya
*Chemistry Department, Faculty of Science (Derna Branch)
Omar El-Mukhtar University, El-Beida, Libya
#Botany Department
Faculty of Science, Garyounis University, Benghazi, Libya
mnibrahim46@yahoo.com
Received 11 November 2010; Accepted 5 January 2011
Abstract Schiff bases p-hydroxybenzylidene-2-carboxyaniline, p-nitrobenz-
ylidene-2-carboxyaniline, p-(N, N-dimethyl)aminobenzylidene-2-carboxyaniline,
N-(4-hydroxybezylidene)-benzene-1,2-diamine, N-(4-nitrobezylidene)benzene-1,2-
diamine,N-(4-(N, N-dimethylaminobezylidene)benzene-1,2-diamine, N-(4-(N,N-
dimethylamino)benzylidene)naphthalen-1-amine,N-(4-nitrobenzylidene)naphthalen-
1-amine,N-(4-chlorobenzylidene)naphthalen-1-amine,sodium-4-(4-(N,N-dimethyl
amino)benzylideneamino)naphthalene-1-sulfonate,sodium -4-(4-nitrobenzylidene-
amino)naphthalene-1-sulfonate and sodium-4-(4-chlorobenzylideneamino)
naphthalene-1-sulfonate obtained by condensation of aniline and naphthyl-
amine derivatives with some aromatic aldehydes were characterized by
physical and spectral methods. The biological activity of these products were as
antibacterial agents against three species of human pathogenic bacteria such as
Escherichia coli, Staphylococcus aureus and Klebsiella sp. Nearly 50% of these
compounds showed reasonable activity against the bacterial species
investigated and we found that the antibacterial activity is dependent on the
molecular structure of the compounds.
Keywords: Schiff bases, Anilines, Naphthylamines, Antibacterial activity.
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 chemistry1-4.

Synthesis and Antibacterial Activities of Some Schiff Bases
213
Application of many new analytical devices requires the presence of organic reagents as
essential compounds of the measuring system. 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 properities5,6. The antibacterial activity is dependent on the
molecular structure of the compound, the solvent used and the bacterial species7-9.
The Schiff bases prepared are condensation products of aromatic aldehyde derivatives with
aromatic amines derivatives and presented below. In this work the spectroscopic characteristics
and antibacterial activity against three species of human pathogenic bacteria such as Escherichia
coli, Staphylococcus aureus and Klebsiella sp of these Schiff bases are presented.
X
X
X = NMe2 , I
N
X = NMe2 , IV
= NO2 , V
= OH , VI
N
= NO2 , II
= OH , III
NH2
COOH
Y
Y
Y = NMe2 , X
Y = NMe2 , VII
= NO2 , VIII
= NO2 , XI
N
NaO3
S
N
= Cl
, XII
= Cl
, IX
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 methods10-12. 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 mL). After stirring the reaction mixture for 2 h (Compounds I, II and III) and for 5 h at
60-70 oC 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)
Compound I was prepared from anthranilic acid and p-hydroxybenzaldehyde; pale orange; m.p.
o
229.5-230 C; 1.6 g (70%) yield. IR (KBr, cm-1) ν = 3500 (OH), 2900 (C-H), 1715 (C=O),
1615 (C=N), 1490 (C=C), 1280,1170(C-O); 1H 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%.
p-Nitrobenzylidene-2-carboxyaniline (II)
Compound II was prepared from anthranilic acid and p-nitrobenzaldehyde; yellow-white; m.p.
o
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), 1285, 1170(C-O); H NMR (500 MHz, DMSO);
1

214
A N. EL-TAJORY et al.
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)
Compound III was prepared from anthranilic acid and p-(N,N-dimethylnamino)benzaldehyde;
pale green; m.p. 198 oC; 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)
It was prepared from o-phenylenediamine 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 (C-N); 1H NMR (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)
o
It was prepared from o-phenylenediamine and p-nitrobenzaldehyde; pale brown; m.p. 317-318 C;
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)
It was prepared from o-phenylenediamine and p-(N,N-dimethylbenzaldehyde; yellow; m.p.
141-142 oC; 0.4 g (16%) yield. IR (KBr, cm-1) ν = 3460,3370 (N-H), 2900,2800 (C-H), 1600
1
(C=N), 1440 (C=C), 1360 (C-N); H NMR (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. C 75.25%, H 7.10%, N 17.55%; found C 74.90%, H 6.58%, N 17.04%.
The Schiff bases (VII-XII) were prepared according to the reported methods10-12. The
procedure is as follows: A solution of the amine derivative (0.01 mol) in absolute ethanol
(10 mL), (with 0.01 mol NaOH for compounds IV-VI), was slowly added to a solution of
the aldehyde derivative (0.01 mol) in absolute ethanol (10 mL). After stirring the reaction
o
mixture for 2 h (Compounds I, II and III) and for 5-10 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.
N-(4-(N,N-Dimethylamino)benzylidene)naphthalene-1-amine (VII)
It was prepared from 1-naphthylamine and p-(N,N-dimethylamino)benzaldehyde; yellow;
o
m.p. 112-114 C; 2.1 g (76%) yield. IR (KBr, cm-1) ν = 3050 (=C-N), 3020 (=C-H), 2900
1
(C-H), 1600 (C=N), 1480 (C=C), 1300 (C-N); H NMR (500 MHz, DMSO); δ (ppm): 2.84
(6H, s, -NMe2), 6.63-7.71 (11H, m, Ar-H), 8.32 (1H, s, CH=N); C19H18N2 (274.3): calcd. C
83%, H 6.5%, N 10.2%; found C 82.8%, H 6.45%, N 10.03%.
N-(4-Nitrobenzylidene)naphthalene-1-amine (VIII)
o
It was prepared from 1-naphthylamine and p-nitrobenzaldehyde; dark yellow; m.p. 164-165 C;
-1
2.3 g (85%) yield. IR (KBr, cm ) ν = 3020 (=C-H), 1600 (C=N), 1480 (C=C), 1510, 1330

Synthesis and Antibacterial Activities of Some Schiff Bases
215
(N=O); 1H NMR (500 MHz, DMSO); δ (ppm): 7.26-8.27 (11H, m, Ar-H), 8.86 (1H, s, CH=N);
C17H12N2O2 (276.3): calcd. C 74%, H 4.3%, N 10.1%; found C 72.9%, H 4.25, N 9.77%.
N-(4-Chlorobenzylidene)naphthalene-1-amine (IX)
It was prepared from 1-naphthylamine and p-chlorobenzaldehyde; pale yellow; m.p. 103-105 oC;
2.08 g (78%) yield. IR (KBr, cm-1) ν = 3020 (=C-H), 1620 (C=N), 1480 (C=C), 1100-1035
1
(C-Cl); H NMR (500 MHz, DMSO); δ (ppm): 7.1-7.9 (11H, m, Ar-H), 8.64 (1H, s, CH=N);
C17H12NCl (265.7): calcd. C 77%, H 4.5%, N 5.3%; found C 76.5%, H 4.49%, N 5.26%.
Sodium-4-(4-(N,N-dimethylamino)benzylideneamino)naphthalene-1-sulfonate (X)
It was prepared from 4-amino-1-naphthalenesulfonic acid and p-(N,N-dimethylamino)benz-
aldehyde; green-yellow; m.p. > 370 oC; 3.6 g (96%) yield. IR (KBr, cm-1) ν = 3600-3100, 1250-
1150 (S=O), 3020 (=C-H), 1600 (C=N), 1480 (C=C), 1310 (C-N), 650 (S-O); H NMR (500
1
MHz, DMSO); δ (ppm): 2.89 (6H, s, -NMe2) 6.68-8.50 (10H, m, Ar-H), 8.37 (1H, s, CH=N).
C19H17N2O3SNa (377.4): calcd. C 60%, H 4.5%, N 7.4%; found C 59.6%, 4.43%, N 7.33%.
Sodium-4-(4-nitrobenzylideneamino)naphthalene-1-sulfonate (XI)
Was prepared from 4-amino-1-naphthalenesulfonic acid and p-nitrobenzaldehyde; dark brown;
o
m.p. > 370 C; 2.3 g (63%) yield. IR (KBr, cm-1) ν = 3600-3100, 1250-1150 (S=O), 3030
(=C-H), 1600 (C=N), 1460 (C=C), 1510, 1350 (N=O), 650 (S-O); H NMR (500 MHz,
1
DMSO); δ (ppm): 7.20-8.61 (10H, m, Ar-H), 8.68 (1H, s, CH=N) C17H11N2O5SNa (379.3):
calcd. C 54%, H 2.9%, N 7.4%; found C 53.5%, H 2.8%, N 7.2%.
Sodium-4-(4-chlorobenzylideneamino)naphthalene-1-sulfonate (XII)
It was prepared from 4-amino-1-naphthalenesulfonic acid and p-chlorobenzaldehyde; grey;
o
m.p. > 370 C; 1.8 g (51%) yield. IR (KBr, cm-1) ν = 3600-3100, 1250-1150 (S=O), 3020
(=C-H), 1620 (C=N), 1470 (C=C), 1100-1035 (C-Cl), 650 (S-O); H NMR (500 MHz,
1
DMSO); δ (ppm): 7.17-8.62 (10H, m, Ar-H), 8.65 (1H, s, CH=N); C17H11NO3ClSNa
(368.8): calcd. C 55%, H 3%, N 3.8%; found C 54.9%, H 2.98%, N 3.7%.
Antibacterial assay
The antibacterial tests were assayed according to the diffusion method. The strains of
bacteria used were Escherichia coli, Staphylococcus aureus and Klebsiella sp. All species
were isolated from patients in Al-Jamahiriya hospital, Benghazi, Libya. The identity of all
the strains was confirmed. A bacterial suspension was prepared and added to the sterilized
nutrient agar (OXID/England) medium before solidification. The medium with bacteria was
poured into sterilized Petri dishes under aseptic condition. Different weights of Schiff bases
o
(5 mg, 10 mg and 20 mg) were placed on the surface of the culture and incubated at 37 C
for 24 h. After incubation, the average of inhibition zones was recorded (mm). Antibacterial
activity was indicated by the presence of clear inhibition zones around the samples.
Results and Discussion
Schiff bases were prepared in this work through condensation of aniline derivatives and
naphthylamine derivatives with some aromatic aldehydes, The IR and NMR spectral data
confirmed their molecular structure. They showed different effects on bacterial species.
Table 1 shows the mean of inhibition zone of some Schiff bases which were tested at
different concentrations of 5, 10 and 20 mg against several species of human pathogenic bacteria.
The results from this study indicated that I, II,III, XI and XII had antibacterial activities against
Escherichia coli and Klebsilla sp which are known as resistant to most commercial antibiotics
used. Also, the compounds I-III and X-XII had effects on Staphylococcus aureus. In contrast, no
effect was observed of IV-IX compounds against all bacterial tested.

216
A N. EL-TAJORY et al.
Table 1. The effect of Schiff bases on bacteria growth
Species of
bacteria
Samples
Mean of inhibition zone, mm
Escherichia coli
Staphlococcus aureus
Klebsilla sp
5 mg 10 mg 20 mg 5 mg 10 mg 20 mg 5 mg 10 mg 20 mg
10
15
20
-
15
25
25
-
22
35
30
-
10
15
12
-
15
20
16
-
18
25
20
-
10
15
15
-
14
24
18
-
18
30
22
-
I
II
III
IV
V
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
VI
VII
VIII
IX
X
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
7
11
28
13
15
35
20
-
-
-
-
-
-
22
9
18
4
22
8
30
16
15
10
20
15
25
25
XI
XII
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