Rapid microwave-assisted solution phase synthesis and spectroscopic characterization of salicylidene-o-aminophenol and its metal(II) complexes

Article abstract of DOI:10.1080/15533170802265749

Salicylidene-o-aminophenol and its Zn(II), Cd(II) complexes are synthesized by rapid microwave-assisted solution phase method and characterized by elemental analysis, IR, ES-MS, and molar conductivity. The structure of salicylidene-o-aminophenol was also

Full text of DOI:10.1080/15533170802265749

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Synthesis and Reactivity in Inorganic, Metal-Organic,
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Rapid Microwave-Assisted Solution Phase Synthesis
and Spectroscopic Characterization of Salicylidene-o-
Aminophenol and Its Metal(II) Complexes
Jian Gao a b & Tong-Tao Xu b
a Jiangsu Key Laboratory of Marine Biotechnology, Huaihai Institute of Technology,
Jiangsu, P.R. China
b Departmemt of Chemical Engineering, Lianyungang Technical College, Jiangsu, P.R.
China
Published online: 04 Sep 2008.
To cite this article: Jian Gao & Tong-Tao Xu (2008) Rapid Microwave-Assisted Solution Phase Synthesis and Spectroscopic
Characterization of Salicylidene-o-Aminophenol and Its Metal(II) Complexes, Synthesis and Reactivity in Inorganic, Metal-
Organic, and Nano-Metal Chemistry, 38:6, 550-552
To link to this article: http://dx.doi.org/10.1080/15533170802265749
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 38:550–552, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533170802265749
Rapid Microwave-Assisted Solution Phase Synthesis
and Spectroscopic Characterization
of Salicylidene-o-Aminophenol and Its Metal(II) Complexes
Jian Gao1,2 and Tong-Tao Xu2
1Jiangsu Key Laboratory of Marine Biotechnology, Huaihai Institute of Technology, Jiangsu, P.R. China
2Departmemt of Chemical Engineering, Lianyungang Technical College, Jiangsu, P.R. China
tion assisted by microwave irradiation in 5 min. They were
characterized by elemental analysis, IR, ES-MS, and molar
conductivity. The formation of salicylidene-o-aminophenol was
also confirmed by X-ray diffraction.
Salicylidene-o-aminophenol and its Zn(II), Cd(II) complexes
are synthesized by rapid microwave-assisted solution phase method
and characterized by elemental analysis, IR, ES-MS, and molar
conductivity. The structure of salicylidene-o-aminophenol was also
confirmed by X-ray diffraction.
EXPERIMENTAL
Keywords salicylidene-o-aminophenol, complex, synthesis, micro-
Materials and Instruments
wave irradiation
All the starting materials and solvents were of analytical
purity. Elemental analysis was determined with a Perkin-Elmer
240C instrument. Solution electrical conductivity was measured
by a BSD-A numerical conductometer (Jiangsu, China) with so-
lution concentration of ∼1.0 × 10−3 mol · dm−3 in methanol
at 279 K. IR spectra were measured as KBr discs using a Nico-
let 5DX FT-IR spectrophotometer. The ES mass spectral mea-
surement of the complexes was carried out on a LCQ System
(Finngann MAT, USA) using methanol as mobile phase.
Microwave irradiation experiments were carried out in HY-
7001 microwave reactor at a frequency of 2.45 GHz with con-
tinuous microwave irradiation power from 0 to 700 W. The
microwave reactor, which was designed by Huaihai Institute of
Technology, was composed of a microwave cavity, electromag-
netic stirrer, water condenser, and microcomputer-based control
system.[11]
INTRODUCTION
Schiff bases and the relevant transition metal complexes
containing nitrogen and oxygen donor atoms play important
role in biologic and inorganic chemistry and have been stud-
ied extensively.[1–4] The traditional synthesis for them is often
carried out by refluxing the mixture of aldehyde (or ketone)
and amine for several hours.[5,6] Its disadvantage of longer re-
action time makes people to seek a more effective method.
Solid-phase reaction at room temperature[7,8] or solvent-free
synthesis assisted by microwave irradiation[9] has been suc-
cessfully employed for Schiff-base formation in the condition
of uniform mixing. However, the remarkable merits of sim-
ple procedure and excellent homodispersity make the solution
synthesis a convenient practicing method, when the reaction
time is highly shortened with the aid of microwave irradiation.
As a heating method, microwave irradiation has been found
to have many uses in chemistry due to its convenient, simple,
rapid, and environmentally friendly characteristics.[10] Herein,
on the basis of previous reports,[6] salicylidene-o-aminophenol
and its metal(II) complexes were synthesized in methanol solu-
Synthesis of Schiff Base and Its Complexes
The mixture of salicylaldehyde (5 mmol) and o-aminophenol
(5 mmol) in 25 cm3 absolute methanol was placed in the mi-
crowave reactor and subjected to microwave irradiation for 5
min. Microcrystals of salicylidene-o-aminophenol (L) were ob-
tained on the removing solvent. Orange-brown single crystals
suitable for X-ray structure determination were obtained by slow
evaporation of its methanol solution for about 4 days at ambient
temperature.
The mixture of salicylaldehyde (5 mmol), M(ClO4)2 · 6H2O
(5 mmol), and o-aminophenol (5 mmol) in 30 cm3 absolute
methanol was placed in the microwave reactor and subjected
to microwave irradiation for 5 min. Microcrystals of complexes
Received 30 November 2007; accepted 12 February 2008.
Address correspondence to Jian Gao, E-mail: gaojian553@163.
com.
The project was supported by Lianyungang Technical College(No.
YKJ200712) and Open-end Funds of Jiangsu Key Laboratory of Marine
Biotechnology, Huaihai Institute of Technology (No. 2006HS007).
550

MICROWAVE-ASSISTED SOLUTION PHASE SYNTHESIS OF METAL(II) COMPLEXES
551
TABLE 1
Analytical data for the compounds
Anal. found (Calcd.) (%)
H
Yield
(%)
ꢀM
(S.cm2.mol−1
Empirical
formula
Compounds
L
)
C
N
96
94
95
—
20
23
C13H11NO2
C13H11NO3Zn
C13H17NO6Cd
73.01
(73.24)
53.20
5.12
(5.16)
3.76
6.61
(6.57)
4.82
(4.78)
3.51
(3.53)
ZnL·H2O
(53.24)
39.34
(3.75)
4.22
CdL·4H2O
(39.29)
(4.28)
were obtained on removing solvent. Table 1 lists analytical data
of the compounds.
Spectroscopic Characterization
Elemental analyses, IR, and ES-MS spectra of the com-
pounds indicated that a Schiff base structure was formed. Con-
densation of all primary amine groups and carbonyl groups is
confirmed by the lack of N-H double stretching bands in the
IR region 3150–3450 cm−1 and the presence of strong C=N
stretching bands at 1623–1630 cm−1. The mass spectra of the
complexes showed that the parent peaks compare well with their
formula weights. The main peak at m/z 276.3 in ZnL·H2O is
assigned to [ZnL+H]+, and the peak at m/z 325.6 in CdL·4H2O
is corresponding to [CdL+H]+. The molar conductivity of the
complexes (ꢀM (CH3OH, 289K) = 20–23 S·cm2·mol−1) is at-
tributable to non-electrolyte and molecular complex. But the
coordination geometry of ZnL·H2O and CdL·4H2O is not very
clear.
Crystallographic Measurements
An orange-brown block single crystal of dimensions
0.14 × 0.30 × 0.38 mm was mounted on a glass fiber. The crys-
tal data were collected at 293(2) K on a Siemens Smart/CCD
area-detector diffractometer with Mo-Kα radiation (λ = 0.71073
◦
˚
A) over the range 2.22≤ θ ≤25.01 with a ω scan mode. Data re-
ductions and cell refinements were performed with Smart-CCD
software. An absorption correction by using SADABS software
was applied. The structures were solved by direct methods and
refined by full-matrix least squares on F2 using SHELXL-97.[12]
The oxygen atoms of hydroxyl groups in one molecular unit L1
were found disordered, and the site occupancy factor of O1,
O2, O1ꢀ, O2ꢀ were fixed at 0.5 and refined isotropically. All H
atoms were placed in calculated position. Table 2 lists relevant
crystallographic data.
TABLE 2
Crystallographic data for salicylidene-o-aminophenol (L)
RESULTS AND DISCUSSION
Empirical formula
Formula weight
Crystal system
Space group
C26H22N2O4
426.46
Monoclinic
C2/c
38.24(3)
9.012(6)
12.295(9)
105.909(12)
4075(5)
Microwave-Assisted Synthesis
Microwave is an electromagnetic wave containing electric
and magnetic field components. Microwave irradiation is known
to induce some specific effects on molecular motion such as
the migration of ions and dipoles, so it can cause molecular-
level heating that leads to homogeneous and quick thermal
reaction.[13] The dependence of the yield of the objective prod-
ucts on the microwave irradiation time, power, and the quantity
of solvent CH3OH was tested in our experiment. The result
shows that the yield increases rapidly with the heating time and
approaches a maximum within ca. 5 min. The quantity of solvent
CH3OH also has inference to the reaction. To a certain range, the
appropriate solvent quantity increase will improve conversion
rate, but the solvent’s continuing rise (more then 30 mL) will
no longer benefit to the reaction. So the solvent volume of 25
to 30 mL is an optimization. In the above optimum condition,
microwave irradiation power was adjusted to 220 W, so that the
reaction system had a moderate reflux.
˚
a/A
˚
b/A
˚
c/A
β/(◦)
3
˚
V /A
Z
8
µ/mm−1
θ range/(◦)
Dcal/(g·cm−3
F(000)
0.095
2.22◦ ≤ θ ≤ 25.01◦
)
1.390
1792
Reflections measured/unique
10,045/3546
[Rint = 0.1547]
1.001
0.0883/0.1656
0.378/−0.625
Goodness of fit on F2
R1/wR2
Largest difference peak and hole/(e·A
−3
˚
)

552
GAO AND XU
FIG. 1. Crystal structure of L.
SUPPLEMENTARY MATERIALS
Crystal Structure of Salicylidene-o-Aminophenol (L)
Crystallographic data for the structures in this article have
been deposited with the Cambridge Crystallographic Data Cen-
ter as the supplementary publication nos. CCDC 255222 for
salicylidene-o-aminophenol. Copies of the data can be obtained,
free of charge, on application to CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK.
The structure of salicylidene-o-aminophenol (L) was further
confirmed by single-crystal X-ray diffraction. The crystal struc-
ture of L is shown in Figure 1. It consists of two different
molecular units of L1 and L2, joined together through hydro-
gen bonds and intermolecular van der Waals forces, as shown
in Figure 2. The two units are basically similar but somewhat
different with respect to the bond lengths and bond angles. In
L1, The dihedral angle of the two aromatic rings is 1.4◦ and
almost is coplanar. The centroid–centroid distance of the two
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FIG. 2. The unit cell package of L.
CONCLUSION
Salicylidene-o-aminophenol and its metal(II) complexes
have been synthesized efficiently using microwave irradiation
and characterized by elemental analysis, IR, ES-MS, molar
conductivity, and X-ray diffraction. Compared with the con-
ventional synthesis, microwave synthesis has many advantages
such as higher efficiency, lower solvent consumption, shorter
reaction time, and so on. The result shows that the chemical
reactions in microwave field were influenced by several fac-
tors including microwave irradiation time, power, and solvent.
Microwave-assisted synthesis method provides a simpler route
to obtain Schiff base and its complexes.
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