Facile, mild and convenient preparation and characterization of some novel schiff base ligands from synthetic diamines and salicylaldehyde

Article abstract of DOI:10.4314/bcse.v29i1.10

Some novel Schiff base ligands have been prepared through condensation of salicylaldehyde with synthetic various primary diamines under mild reaction conditions. The used aromatic diamines were synthesized in good yields starting from low-cost commercially available materials. In these reactions, the Schiff base products have been afforded with excellent yields and appropriate reaction times. The structure of these ligands has been characterized by IR, ¹H NMR and ¹³C NMR techniques.

Full text of DOI:10.4314/bcse.v29i1.10

Bull. Chem. Soc. Ethiop. 2015, 29(1), 117-122.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v29i1.10
ISSN 1011-3924
 2015 Chemical Society of Ethiopia
FACILE, MILD AND CONVENIENT PREPARATION AND CHARACTERIZATION
OF SOME NOVEL SCHIFF BASE LIGANDS FROM SYNTHETIC DIAMINES AND
SALICYLALDEHYDE
Hossein Naeimi* and Arash Heidarnezhad
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, 87317,
Iran
(Received October 18, 2013; revised October 1, 2014)
ABSTRACT. Some novel Schiff base ligands have been prepared through condensation of salicylaldehyde with
synthetic various primary diamines under mild reaction conditions. The used aromatic diamines were synthesized
in good yields starting from low-cost commercially available materials. In these reactions, the Schiff base products
have been afforded with excellent yields and appropriate reaction times. The structure of these ligands has been
characterized by IR, 1H NMR and 13C NMR techniques.
KEY WORDS: Schiff base, Salicylaldehyde, Preparation, Ligand, Diamine
INTRODUCTION
Synthesis and application of Schiff base compounds have been highly considered in recent
decades. Schiff base compounds especially their complexes have been used in many reactions as
important and significant compounds. Schiff base complexes because of their structures that are
similar to the porphyrin and phthalocyanine rings have been highly considered in inorganic,
organic and biological fields [1]. They are effective at loading oxygen, resisting bacteria and
mimicking enzymes [2]. Much interest have been paid to the ionophore ligand as sensing
materials for neutral carrier type ion-selective electrodes due to the unique properties of the
compounds [3]. The formation of strong complex with good selectivity between some Schiff
bases and different cations has been introduced. These compounds have been used for preparing
ion-selective electrodes for determination of cations in solution with potentiometric methods [4].
Cooperative biometallic catalysis has been documented in several recently reported such as
asymmetric epoxide ring opening reaction [5-9]. In such systems that metal is complexed with
special Schiff bases, one metal is proposed to serve as Lewis acid for epoxide activation and
another as counter ion for the nucleophile [10], reaction of some epoxides with elemental iodine
and bromine in the presence of catalytic amounts of Schiff base complexes of metal(II) for
preparation of haloalcoholes in high yields and regioselectivity [11], mimic peroxidase in the
oxidation of phenol hydrogen peroxides in the presence of Schiff base complexes of Mn(III).
The oxidation of styrene by molecular oxygen with Schiff base compounds as catalyst [12], are
examples from application of Schiff base compounds and their complexes in chemical reactions.
The rapidly emerging field of hetero-binucleating ligands and the coordination chemistry of the
heteronuclear complexes derived from such ligands, have prompted an extension of our work on
the synthesis of these ligands from condensation reactions of salicylaldehyde with the synthetic
diamines [13-17].
In continuation of our research on the synthesis of Schiff bases and their complexes of metal
ions [18-19], we have studied the preparation of several new Schiff bases from the reaction of
salicylaldehyde with synthetic diamines in methanol solution under mild conditions. The
corresponding products were identified and characterized by spectroscopic and physical data.
__________
*Corresponding author. E-mail: naeimi@kashanu.ac.ir

118
Hossein Naeimi and Arash Heidarnezhad
EXPERIMENTAL
Materials
Chemical were purchased from the Merck Chemical Company in high purity. All the materials
were of commercial reagent grade. The synthetic diamines, aldehydes and solvents were
purified by standard procedures.
Apparatus
The FT-IR spectra were obtained with potassium bromide pellets in the range 400-4000 cm-1
1
with a Perkin Elmer 550 spectrometer. H NMR and 13C NMR spectra were obtained at 500
MHz using an Bruker Avance spectrometer in CDCl3 and DMSO-d6 as the solvents and
chemical shifts are expressed in ppm using TMS as internal standard. Mass spectra were
recorded on an Agilent Technology (HP) MS Model: 5973 Network Mass Selective Detector
Instrument by Electron Impact (EI) Ionization mode with an ionization voltage of 70 eV.
Melting points were obtained with a Yanagimoto micro melting point apparatus and are
uncorrected. The purity determination of the substrates and reactions monitoring were
accomplished by TLC on silica gel polygram SILG/UV 254 plates.
Synthesis of diamines
The diamines were synthesized according to the previously reported literatures [20-22].
A typical procedure for preparation of 4,4׳-diamino stilbene (4)
To a solution of p-nitrotoluene (6.8 g, 0.05 mol) in 100 mL of diethylene glycol, a solution of
(11 g, 0.19 mol) potassium hydroxide in 30 mL of water and 10 mL hydrazine hydrate 85% was
added. The resulting mixture was refluxed with stirring for about twenty minutes and then the
condenser was removed to allow the aqueous liquor to evaporate and temperature of the reaction
mixture to rise about 200 ºC, refluxing at this temperature was continued for three hours. Then
the mixture was cooled and diluted with cold water and the separated amino product was filtered
off and recrystallized in acetone-ethanol which gave the pure product as brown crystalline.
A typical procedure for preparation of 4,4׳-diamino stilbene-2,2׳-disulfonic acid (5)
A solution of potassium hydroxide (3 g, 52 mmol) in low amount of water was slowly added
with stirring to a mixture of p-nitrotoluene orthosulfonic acid (2.2 g, 10 mmol), diethylene
glycol (20 mL) and 2.5 mL of hydrazine hydrate 85%. The resulting mixture was refluxed for 30
min, then the condenser was removed and the aqueous liquor was evaporated and refluxing
continued for 2.5 hours. When the reaction was completed, the reaction mixture was cooled and
diluted with water. Then the cooled and diluted reaction mixture was acidified with warm
concentrated hydrochloric acid and the pure product was filtered.
A typical procedure for preparation of 4,4׳-diamino azobenzene (6)
A mixture of glacial acetic acid (100 mL), 5.8 g of p-amino acetanilide, 8 g of sodium perborate
tetrahydrate and 2 g of boric acid were heated with stirring to 50-60 ºC and hold in this
temperature for 6 hours. At the end of reaction, the mixture was cooled and the yellow product
filtered off and washed with water, then the product 4,4׳-bis(acetamido)azobenzene with the
mixture of 30 mL methanol and 30 mL of 6 N hydrochloric acid was hydrolyzed for 1.5 hours.
Bull. Chem. Soc. Ethiop. 2015, 29(1)

Facile and convenient preparation and characterization of some novel Schiff base ligands 119
The reaction mixture was filtered off and the product neutralized by the addition of 2.5 N
sodium hydroxide. Finally, the amino product filtered, washed with water and dried under
reduced pressure.
Synthesis of Schiff base ligands
A typical procedure for preparation of Schiff bases 7 and 9
In a 50 mL round-bottom flask with 10 mL absolute methanol, (0.5 g, 2.3 mmol) of 4,4׳-diamino
azobenzene for preparation of Schiff base (7) and in another round-bottom flask with 10 mL
absolute methanol (0.5 g, 2.25 mmol) of 4,4׳-diamino stilbene for preparation of Schiff base (9)
was added and temperature was raised to 60-70 ºC and stirring was continued until the diamines
was solved. Then, salicylaldehyde (0.56 g, 4.6 mmol) in 5 mL absolute methanol for Schiff base
(7) and (0.55 g, 4.5 mmol) for Schiff base (9) was added and resulting mixtures was refluxed for
about 10-15 min. When the reaction was completed the mixtures was cooled and products was
filtered off, washed with absolute methanol and dried.
Synthesis of Schiff base ligands
A typical procedure for preparation of Schiff base 8
To a stirred solution of 4,4׳-diamino stilbene-2,2׳-disulfonic acid (1 g, 2.6 mmol) in absolute
methanol (20 mL), a solution of (0.1 g, 2.5 mmol) potassium hydroxide in 5 mL of absolute
methanol was added drop wise over a period of 5 min at room temperature. After the addition of
base solution, salicylaldehyde (0.66 g, 5.4 mmol) in absolute methanol (10 mL) was added and
the resulting mixture refluxed for about 30 min. The progressive and completion of the reaction
were monitored by TLC. When the reaction was completed, the brown precipitate was filtered
off and the filtrate was washed with absolute methanol and by evaporating the solvent gave the
desired product as red crystalline.
4,4׳-diaminostilbene. IR/ν (KBr) cm-1: 3350-3370, 2930-3000, 1620-1660, 1510. 1H NMR
(DMSO-d6, 500 MHz) δ (ppm): 8.02 (d, 4H), 7.6 (d, 4H), 7.55 (d, 2H), 3.5 (s, 4H). MS (EI,
m/z): 210 (M+, 85), 184 (59), 118 (37).
4,4׳-Diaminostilbene-2,2׳-disulfonic acid. IR/ν (KBr) cm-1: 3400-3500, 2750-3200, 1490-1610,
1180, 1080. 1H NMR (DMSO-d6, 500 MHz) δ (ppm): 8-11 (s, 2H), 7.71 (d, 2H), 7.6 (d, 2H), 7.2
(s, 2H) 7.20 (d, 2H), 3.52 (s, 4H). MS (EI, m/z): 370 (M+, 10), 208 (30).
1
4,4׳-Diaminoazobenzene. IR/ν (KBr) cm-1: 3350, 3110, 1585, 1400. H NMR (DMSO-d, 500
MHz) δ (ppm): 7.82 (d, 4H), 6.74 (d, 4H), 5.72 (s, 4H). 13C NMR (DMSO-d6) δ (PPM) 149,
145, 125, 114. MS (EI, m/z): 212 (M+, 40), 184 (65).
N,N׳-bis(salicylidine)-4,4׳-diaminostilbene. IR/ν (KBr) cm-1: 3320-3500, 2940-2990, 1605,
1
1150, 1130. H NMR (DMSO-d6, 500 MHz) δ (ppm): 13 (s, 2H), 8.5 (s, 2H), 7-7.9 (m, 16H),
6.8 (d, 2H). MS (EI, m/z): 418 (M+, 7), 392 (11).
N,N׳-bis(salicylidine)-4,4׳-diaminostilbene-2,2׳-disulfonic acid. IR/ν (KBr) cm-1: 3100-3490,
1
3030, 1610, 1470, 1160, 1140. H NMR (DMSO-d, 500 MHz) δ (ppm): 10.8 (s, 2H), 9.80 (s,
2H), 9.76 (s, 4H), 7.84(s, 4H), 7.32 (m, 2H), 6.9 (d, 4H), 6.6 (s, 4H). MS (EI, m/z): 578 (M+, 2),
552 (8).
Bull. Chem. Soc. Ethiop. 2015, 29(1)

120
Hossein Naeimi and Arash Heidarnezhad
N,N׳-bis(salicylidine)-4,4׳-diaminoazobenzene. IR/ν (KBr) cm-1: 3310-3450, 3030, 1609, 1170,
1
1150. H NMR (DMSO-d6, 500 MHz), δ (ppm): 13.31 (s, 2H), 8.73 (s, 2H), 8.07 (d, 4H), 7.42
(m, 4H), 7.36 (m, 2H), 7.27 (q, 4H), 6.22 (t, 2H). MS (EI, m/z): 420 (M+, 40), 392 (18).
RESULTS AND DISCUSION
In this research, firstly the aromatic diamines 4, 5 and 6 have been synthesized from compounds
1, 2 and 3 respectively (Scheme 1). These diamines were easily prepared in good yields by
starting from low-cost commercially available materials. The corresponding results of these
reactions are indicated in Table 1. As shown in Table 1, the overall yield of the diamine 1 from
p-nitrotoluene is 32% and the overall yields for 2 and 3 diamines are 73% and 52% respectively.
In IR spectra, the presence of –NH2 group stretching bands in the 3300-3500 cm-1 region for
1
diamines, the lack of HNC=O group stretching band in the 1720 cm-1 region for diamine 3, H
NMR and 13C NMR data are completely consistent with the formulation indicated in Scheme 1.
Scheme 1
Table 1. The results of related to the prepared diamines
Entry Substrate
Reaction time (h) Yielda (%) Product
m.p./oC [Ref.]
226-228 [20]
>400 [20]
1
2
3
p-Nitrotoluene
p-Nitrotoluene orthosulfonic acid
p-Aminoacetanilide
3.2
3
32
73
52
4
5
6
6
238-241 [22]
a Isolated yields based on concern substrates.
In continuation, the reaction of salicylaldehyde with the prepared diamines was carried out
(Scheme 2). The Schiff base ligands 7, 8 and 9 were easily prepared by refluxing and stirring
two equivalents of salicylaldehyde with one equivalent of the diamines 4, 5 and 6 respectively in
anhydrous methanol. The obtained results are summarized in Table 2. As can be seen in Table 2,
these ligands have been afforded in 70-85% yields and reaction times at 10-30 min. The
completion condensation of all primary amino groups was confirmed by the lack of NH2
stretching bands in the 3300-3500 cm-1 regions and the presence of strong stretching bands in
the 1590-1610 cm-1 region in IR spectra. The 1H NMR, 13C NMR and IR data for compounds 7,
8 and 9 are completely consistent with the formulation indicated in Scheme 2.
Bull. Chem. Soc. Ethiop. 2015, 29(1)

Facile and convenient preparation and characterization of some novel Schiff base ligands 121
CHO
OH
CH3OH
KOH
H2N
C
C
NH2
H2N
N N
NH2
H
H
SO3H HO3S
CH3OH
CH3OH
H2N
C
H
C
H
NH2
H
H
H
H
C
C
N
N N
N
C
C
N
C C
N
H
H
HO
HO
OH
OH
9
7
HO S
SO3H
3
H
C
H
C
N
C
H
C
H
N
HO
OH
8
Scheme 2
Table 2. The obtained results for synthesized Schiff bases from salicylaldehyde and synthetic diamines.
Entry Substrate
1
Reaction time (min) Yielda (%) Product
m.p.(oC)
240-244
4,4׳-diaminostilbene (4)
15
85
N,N׳-bis(salicylidine)-4,4׳-
diaminostilbene (7)
2
4,4׳-diaminostilbene
–
35
80
N,N׳-bis(salicylidine)-4,4׳-
diaminostilbene-2,2׳-disulfonic acid
(8)
N,N׳-bis(salicylidine)-4,4׳-diamino
azobenzene (9)
> 400
> 300
2,2׳-disulfonic acid (5)
3
4,4׳-diaminoazobenzene
(6)
15
70
aIsolated yields based on salicylaldehyde.
CONCLUSION
This study describes the synthesis of a new Schiff base ligands derived from salicylaldehyde
with synthetic various primary diamines. In conclusion, we have reported a mild, easy, clean
and a highly efficient method for the synthesis of some novel Schiff bases under mild
conditions. The products have been obtained in high yields and short reaction times. The
structure of products has been assigned by physical and spectroscopic data such as 1H NMR, 13
NMR, infrared (IR), mass spectra and melting points.
C
ACKNOWLEDGEMENT
The authors are grateful to University of Kashan for supporting this work by Grant No.
159148/19.
Bull. Chem. Soc. Ethiop. 2015, 29(1)

122
Hossein Naeimi and Arash Heidarnezhad
REFERENCES
1. Breslow, R.S.; Dong, D. Chem. Rev. 1998, 98, 1997.
2. Doyle, M. P.; Forbes, D. C. Chem. Rev. 1998, 98, 911.
3. Ammann, D.; Morf, W.E.; Anker, P.; Meier, P.C.; Pretsch, E.; Simon, W. Ion Selective
Electrode Rev. 1983, 5, 3.
4. Mazloum Ardakany, M.; Ensafi, A.A.; Naeimi, H.; Dastanpour, A.; Shamelli, A. Russ. J.
Electrochem. 2003, 39, 269.
5. Hansen, K.B.; Leighton, J.L.; Jacobsen, E.N. J. Am. Chem. Soc. 1996, 118, 10924.
6. Tokunaga, M.; Larrow, J.F.; Kakiuchi, F.; Jacobsen, E.N. Science 1997, 277, 936.
7. McCleland, B.W.; Nugent, W.A.; Finn, M.G. J. Org. Chem. 1998, 63, 6656.
8. Matsunaga, S.; Dos, J.; Roles, J.; Vogel, E.M.; Yamamoto, N.; Iida, T.; Yamaguchi, K.;
Shibasaki, M. J. Am. Chem. Soc. 2000, 122, 2252.
9. Schaus, S.E.; Jacobsen, E.N. Org. Lett. 2000, 2, 1001.
10. Joseph, M.; Jacobsen, R.; Eric, N. J. Am. Chem. Soc. 2001, 123, 2687.
11. Sharghi, H.; Naeimi, H. Bull. Chem. Soc. Jpn. 1999, 72, 1525.
12. Khandar, A. A.; Nejati, K.; Rezvani, Z. Molecules 2005, 10, 302.
13. Naeimi, H.; Rabiei Kh.; Salimi, F. Phosphorus, Sulfur, Silicon and Related Elements, 2009,
184, 2351.
14. Van Veggel, F.C. J.; Verboom, M.W.; Reinhoudt, D.N. Chem. Rev. 1994, 94, 279.
15. Beer, P.D. Adv. Inorg. Chem. 1992, 39, 79.
16. Beer, P.D. Endeavour. 1992, 16, 182.
17. Beer, P.D.; Gale, P.A.; Chen, G.Z. Coord. Chem. Rev. 1992, 39, 79.
18. Naeimi, H.; Safari, J.; Heidarnezhad, A. Dyes Pigm. 2007, 73, 251.
19. Sharghi, H.; Khaledi, H.N. Iran J. Chem. Chem. Eng. 1999, 18, 72.
20. Minlon, H. J. Am. Chem. Soc. 1948, 70, 2802.
21. Hein, D.W.; Pierce, S.E. J. Am. Chem. Soc. 1954, 76, 2527.
22. Santurri, P.; Frederick, R.; Stuboings, R. Org. Synth. 1960, 40, 18.
Bull. Chem. Soc. Ethiop. 2015, 29(1)

Copyright of Bulletin of the Chemical Society of Ethiopia is the property of Chemical Society
of Ethiopia and its content may not be copied or emailed to multiple sites or posted to a
listserv without the copyright holder's express written permission. However, users may print,
download, or email articles for individual use.