Controlled microwave-assisted synthesis of metallophthalocyanines

Article abstract of DOI:10.1142/S1088424612501106

A controlled microwave-assisted strategy has been elaborated for the fast and efficient synthesis of metallophthalocyanines scaffold. Compared to the conventional protocol, reproducibility of products was achieved, accompanied by significantly high purity and excellent yields

Full text of DOI:10.1142/S1088424612501106

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2012; 16: 1110–1113
DOI: 10.1142/S1088424612501106
Published at http://www.worldscinet.com/jpp/
Controlled microwave-assisted synthesis
of metallophthalocyanines
Mozhdeh Seyyedhamzeh, Nasim Ganji and Ahmad Shaabani*
Department of Chemistry, Shahid Beheshti University, G. C., PO Box 19396-4716, Tehran, Iran
Received 22 January 2012
Accepted 23 April 2012
ABSTRACT: A controlled microwave-assisted strategy has been elaborated for the fast and efficient
synthesis of metallophthalocyanines scaffold. Compared to the conventional protocol, reproducibility
of products was achieved, accompanied by significantly high purity and excellent yields.
KEYWORDS: metallophthalocyanine, controlled microwave irradiation, synthesis.
a fraction of the time. In a domestic microwave oven
INTRODUCTION
the irradiation power is generally controlled by on/off
Phthalocyanines (PCs) have been extensively
cycles of the magnetron and it is typically not possible
employed in the oxidation of mercaptans and other
to monitor the reaction temperature in a reliable way.
sulfur compounds in petroleum distillates, oxidation
This disadvantage, combined with the inhomogeneous
of hydrocarbons, regenerative redox fuel cell and
field produced by the low-cost magnetrons and the lack
electrocatalytic oxidation of organic compounds [1–3].
of safety controls, means that the use of such equipment
The metallophthalocyanines (MPCs) are usually
cannot be recommended.
prepared at high temperature and reaction times of
All of today’s commercially available dedicated
several hours are needed [4–8]. Therefore, one of the
microwave reactors for synthesis [14–16] feature
main purposes for the synthesis of metal-free and
built-in magnetic stirrers, direct temperature control
metallophthalocyanines has been to decrease the reaction
of the reaction mixture with the aid of fiber-optic
times as well as the temperature.
probes or IR sensors, and software that enables
In recent years, microwave-assisted organic synthesis
on-line temperature/pressure control by regulation
(MAOS) has emerged as valuable technology among
of microwave power output [17]. These monitoring
synthetic organic chemists. However, replacing the oil
mechanisms in modern microwave reactors allow for
bath with a dedicated microwave reactor provides the
an excellent control of reaction parameters which leads
opportunitytoperformreactionsindramaticallyshortened
to move not only reproducible reaction conditions, but
time as well as increasing yields by using conditions not
enhances product purities by reducing unwanted side
attainable under conventional heating [9–12].
reactions.
For the first time, I have demonstrated that synthesis of
In continuation of our studies to develop
a
MPCs can be speeded up significantly by performing the
reaction in domestic microwave ovens [13]. A reaction
time of several minutes under solvent-free conditions
produced similar yields of the products, however at
fast and effective procedure for the synthesis of
metallophthalocyanines [13, 18, 19], in this work we
wish to report the use of controlled microwave protocol
for optimizing time and temperature in the synthesis of
MPCs from three important raw materials phthalonitrile,
phthalimide and phthalic anhydride upon treatment with
urea and metal salts (Scheme 1).
*Correspondence to: email: a-shaabani@sbu.ac.ir, fax: +98
21-22403041
Copyright © 2012 World Scientific Publishing Company

CONTROLLED MICROWAVE-ASSISTED SYNTHESIS OF METALLOPHTHALOCYANINES 1111
CN
4
CN
O
or
or
N
N
urea
N
(NH4)6Mo7O2
4
M2+
N
NH
M
+
N
controlled MW irradiation
N
N
O
N
O
4
O
M = Co, Ni, Cu, Fe
O
Scheme 1. Synthesis of MPCs
by conventional heating methods from hours to a few
minutes. It is important to note as shown by our own
experience reproducibility of the results had not be
shown, because of the previous works kitchen microwave
ovens were used that is not possible to control conditions.
So, for obtaining reliable results, in this work, we used
a commercially available dedicated microwave reactor
for synthesis MPCs that was equipped with magnetic
stirrers, direct temperature control of the reaction
mixture and software that enables on-line temperature
control by regulation of microwave power output. Time
and temperature are two important parameters that
were selected for our design, and yield was depicted as
response for optimization. For the variation of the factors
we selected 100-120-130 °C steps for the temperature
variation and 5-10-15 min for time. The reagent ratio
and amount of catalyst were kept identical as in previous
design reported work [13].
Figure 1 shows temperature/time profile for the
syntheses of different metallophthalocyanine complexes
of Co, Cu, Ni and Fe from phthalic anhydride. It was
found that the best results were obtained by heating the
mixture of reaction at 130 °C for 5 min.
Encouraged by these results, we carried out the
reactions with phthalimide and phthalonitrile instead
of phthalic anhydride. As can be seen from Fig. 2,
phthalonitrile to produce the best yields with irradiation
EXPERIMENTAL
All microwave irradiation experiments were carried
out in a Microsynth Milestone SRL microwave
apparatus. The reactions were carried out in 100-mL
Teflon vessels, sealed with a Teflon septum and placed
in the microwave cavity. Initially, microwave irradiation
of required watts was used, and the temperature
was ramped from room temperature to the desired
temperature. Once this was reached the reaction mixture
was held at this temperature for the required time. The
reaction mixture was continuously stirred during the
reaction. The temperature was measured with the ATC
(Automatic Temperature Control) system by optical fiber
that enables direct continuous monitoring and control of
a reference vessel. After the irradiation period, gas jet
cooling rapidly cooled the reaction vessel to ambient
temperature. IR and UV-vis spectra were recorded with
a Shimadzu IR-470 spectrometer and UV-vis Shimadzu
2100, respectively.
A typical procedure for preparation of cobalt
phthalocyanine by controlled microwave heating.
The preparation of Co(II) phthalocyanine (Entry 1) is
representative of the general procedure employed for
the Cu, Ni, and Fe complexes. The phthalic anhydride
(0.44 g, 3 mmol), urea (0.78 g, 13 mmol), cobalt(II)
chloride hexaahydrate (0.21 g, 0.9 mmol) and ammonium
heptamolybdate (0.01 g, 0.01 mmol) were ground
together until a homogeneous powder was obtained.
This powder was irradiated at 130 °C for 5 min. For
purification, the crude product was washed with distilled
water (100 mL) to remove excess urea and metal salts.
The separated solid was heated in 0.1 N HCl and 0.1 N
NaOH for 10 min respectively and then filtered and the
pure products were obtained.
RESULTS AND DISCUSSION
As we have previously demonstrated, MPCs can be
easily synthesized by reaction between metal salts, urea
and phthalic anhydride using microwave irradiation [13].
These approaches shorten the reaction time required
Fig. 1. Optimization of reaction conditions for the synthesis of
MPCs from phthalic anhydride
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 1111–1113

1112 M. SEYYEDHAMZEH ET AL.
Fig. 2. Optimization of reaction conditions for the synthesis of MPCs from phthalimide and phthalonitrile
Table 1. Synthesis of MPCs by the reaction of various materials under controlled microwave irradiation
Entry
Product
Phthalonitrile
Phthalimide
Phthalic anhydride
T, °C/t, min
Yield, %
T, °C/t, min
Yield, %
T, °C/t, min
Yield, %
1
2
3
4
[Co(Pc)] from CoCl2.6H2O
[Cu(Pc)] from CuCl2.2H2O
[Ni(Pc)] from NiCl2.6H2O
[Fe(Pc)] from FeCl2.4H2O
110/10
92
91
91
90
120/10
92
91
90
88
130/5
89
91
91
89
Fig. 3. Optimized conditions
at 110 °C for 10 min and in the case of phthalimide
the best result obtained at 120 °C within 10 min using
controlled microwave irradiation. In general, the various
starting materials are converted to MPCs with good
yields. The results for various metallophthalocyanines
are summarized in Table 1. The optimized conditions
for the each of metallophthalocyanines with respect to
phthalic anhydride, phthalimide and phthalonitrile were
shown in Fig. 3.
All of the products are known compounds and their
purities were confirmed by comparison with the literature
[13, 17, 18, 20].
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 1112–1113

CONTROLLED MICROWAVE-ASSISTED SYNTHESIS OF METALLOPHTHALOCYANINES 1113
In conclusion, we have developed an efficient
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method for the generation of a very important class of
metallophthalocyanines, that are commercially used as
dyes and pigments, under controlled microwave heating
in excellent yields. Not only is direct microwave heating
able to reduce chemical reaction times from hours to
minutes, but it is also known to reduce side reactions and
increase the purities and yields of products. Improving
reproducibility of the results and tolerance of various
groups toward the reaction conditions are the merits of
this protocol. It has been demonstrated that the reaction
greatly benefits from the use of microwave irradiation
specially control the temperature during the reaction.
Investigation toward extension of this procedure to other
derivatives is in progress.
Acknowledgements
We gratefully acknowledge the financial support from
the Research Council of Shahid Beheshti University.
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J. Porphyrins Phthalocyanines 2012; 16: 1113–1113