Improvement in the synthesis of metallophthalocyanines using microwave irradiation

Article abstract of DOI:10.1016/j.tet.2004.10.042

A successful application of microwave irradiation, in which phthalocyanines were synthesized under solventless conditions from 1,2-phthalonitrile or phthalic anhydride and urea in the presence of metal templates is described. It was found that in comparison with conventional heating, the microwave process is a very useful alternative for cyclotetramerization processes because of reduction of the reaction time, better yield, and easy-to-perform procedure. Graphical Abstract.

Full text of DOI:10.1016/j.tet.2004.10.042

Tetrahedron 61 (2005) 179–188
Improvement in the synthesis of metallophthalocyanines using
microwave irradiation
a
Aleksandra Burczyk, Andr e´ Loupy, Dariusz Bogdal and Alain Petit
b
a,*
b
a
Department of Polymer Chemistry and Technology, Politechnika Krakowska, 31-155 Krak o´ w, ul. Warszawska 24, Poland
b
Laboratoire des R e´ actions S e´ lectives Sur Supports, ICMMO, Universit e´ Paris - Sud, bat. 410, 91 405 Orsay, France
Received 24 May 2004; revised 13 October 2004; accepted 14 October 2004
Abstract—A successful application of microwave irradiation, in which phthalocyanines were synthesized under solventless conditions from
,2-phthalonitrile or phthalic anhydride and urea in the presence of metal templates is described. It was found that in comparison with
1
conventional heating, the microwave process is a very useful alternative for cyclotetramerization processes because of reduction of the
reaction time, better yield, and easy-to-perform procedure.
q 2004 Elsevier Ltd. All rights reserved.
1
2,13
1
. Introduction
sensitizers for photodynamic (PDT) cancer therapy,
1
photoconductors in xerography, dyes at recording layers
4
1
for CD-R and DVD-R optical storage discs, as well as
5
Phthalocyanines form nowadays an important group of
organic compounds that belongs to the most studied subjects
1
6,17
diverse catalytic systems.
Recently, the synthesis,
properties and potential application of phthalocyanine
containing polymers were reviewed by McKeowon,
while an example of the preparation of nanoscale organic-
inorganic composites containing rod-like phthalocyanine
19
polymers was published by Kimura et al.
1
of organic functional materials. However, although phtha-
1
8
locyanines have been not identified in the nature yet, they
were one of the first macrocycles that were synthesized and
used as model compounds to mimic the biologically
2
important porphyrines. The most important industrial
application of phthalocyanines is the formation of color
complexes with metal cations that are used as highly stable
Phthalocyanines are usually prepared by the high tempera-
ture cyclotetramerization processes of either phthalonitrile
(1) or phthalic anhydride (2), in which the template effect
afforded by a suitable metal cation is required (Scheme 1).
The reactions can be carried out in a variety of solvents as
3
pigments and dyes. In addition, they can find commercial
4
–6
applications as: photovoltaic materials in solar cells,
systems for fabrication of light emitting diodes (LED),
7
,8
9
liquid crystalline and non-linear optical materials,
10,11
Scheme 1. Synthesis of phthalocyanines from phthalonitrile (1) or phthalic anhydride (2) and urea.
Keywords: Microwave irradiation; Phthalocyanines; Phthalonitrile; Phthalic anhydride; Solventless conditions.
*
Corresponding author. Tel.: C48 12 628 2572; fax: C48 12 628 2038; e-mail: pcbogdal@cyf-kr.edu.pl
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.10.042

180
A. Burczyk et al. / Tetrahedron 61 (2005) 179–188
well as under solvent-free conditions, but both processes
1
require temperature ca. 200 8C and long reaction times. It is
non-classical method of chemical activation might influence
yield, selectivity and time of reaction in comparison with a
conventional thermal treatment under strictly similar sets of
conditions.
well known that microwave (MW) irradiation can accelerate
a great number of chemical processes, and, in particular, the
reaction time and energy input are supposed to be mostly
reduced in the reactions that are run for a long time at high
2
0
temperatures under conventional conditions. On the other
hand, the most successful examples of microwave appli-
cations are necessarily found to be related to the use of
solvent-free systems, in which microwaves interact directly
with reagents and, therefore, can more efficiently drive
2
. Results
The synthesis of phthalocyanines under microwave
irradiation has been previously investigated by Shaabani
24
2
5
and Villemin et al. In the former case, the reactions were
carried out applying a domestic oven without any
temperature control, whereas in the latter case the syntheses
were run in a modified domestic oven and microwave
resonance cavity without temperature control as well. It was
found that the results depend upon the quantity of products
and were difficult to reproduce when the reactions were
conducted with small samples less then 5 g. To solve this
problem and control reasonably well temperature during
syntheses under MW conditions so that it was possible to
compare their results with experiments under conventional
2
1,22
chemical reactions.
The possible accelerations of such
reactions are expected to be optimal since they are not
moderate or impeded by solvents. It was assumed and
largely proven that specific (non-purely thermal) MW
effects are related to mechanisms where the polarity is
2
3
increased from the ground state to the transition state. It is
essentially the case of neutral reactants leading to a dipolar
transition state. Thus, we have decided to apply microwave
irradiation for the synthesis of phthalocyanine under
solvent-less conditions in order to check whether such
2
5
Table 1. The synthesis of phthalocyanine–Cu from phthalonitrile (1) and copper (II) chloride dihydrate under microwave and conventional conditions
a
Substrate
Quantity
mmol)
Conditions
Time (min)
Temp. (8C)
Conv. /Yield
(%)/(%)
CHN calc.
CHN found
(
1
2
3
4
5
6
7
1
CuCl
8
2.5
C: 66.74
H: 2.5
N: 19.2
C: 66.74
H: 2.5
N: 19.2
C: 66.74
H: 2.5
N: 19.2
C: 66.74
H: 2.5
N: 19.2
C: 66.74
H: 2.5
N: 19.2
C: 66.74
H: 2.5
N: 19.2
C: 66.74
H: 2.5
C: 66.01
H: 2.59
N: 18.51
C: 62.35
H: 2.42
N: 18.35
C: 17.49
H: 1.85
N: 4.84
C: 66.21
H: 2.83
N: 19.76
C: 66.42
H: 2.38
N: 19.06
C: 46.67
H: 2.91
N: 13.91
C: 66.31
H: 2.58
N: 18.73
2
2
2
2
2
2
2
$2H
$2H
$2H
$2H
$2H
$2H
$2H
2
O
2
O
2
O
2
O
2
O
2
O
2
O
MW
MW
6
10
10
10
10
15
15
6
200–220
180–190
180
86/82
78/70
10/7
1
CuCl
12
2.5
1
CuCl
12
2.5
1
CuCl
12
2.5
MW
MW
6
200–230
190–210
200
90/81
94/88
20/10
76/74
1
CuCl
12
2.5
1
CuCl
12
2.5
1
CuCl
8
2.5
3 drops
MW
230–240
H
2
O
N: 19.2
(
12
2.5
3 drops
(75 mg)
12
75 mg)
8
9
1
1
1
1
CuCl
C: 66.74
H: 2.5
N: 19.2
C: 57.19
H: 2.33
N: 17.28
2
2
2
$2H
$2H
$2H
$2H
$2H
2
O
2
O
2
O
2
O
2
O
MW
MW
MW
MW
MW
6
10
8
200–230
85/76
90/86
86/83
79/72
88/82
H
2
O
1
CuCl
C: 66.74
H: 2.5
N: 19.2
C: 66.81
H: 2.85
N: 19.03
2.5
3 drops
H
2
O
(
75 mg)
0
1
2
1
CuCl
DMF
8
2.5
3 drops
(70 mg)
12
2.5
3 drops
(70 mg)
12
C: 66.74
H: 2.5
N: 19.2
C: 66.83
H: 2.75
N: 18.83
180
1
C: 66.74
H: 2.5
N: 19.2
C: 56.94
H: 2.46
N: 16.91
CuCl
DMF
2
4
150–170
210–220
1
C: 66.74
H: 2.5
N: 19.2
C: 66.40
H: 2.75
N: 18.83
CuCl
DMF
2
2.5
3 drops
10
(
70 mg)
a
Conversion based on the consumption of 1.

A. Burczyk et al. / Tetrahedron 61 (2005) 179–188
181
Table 2. The synthesis of phthalocyanine–Co from phthalonitrile (1) and cobalt (II) chloride hexahydrate under microwave and conventional conditions
a
Substrate
Quantity
mmol)
Conditions
Time (min)
Temp. (8C)
Conv /Yield
(%)/(%)
CHN calc.
CHN found
(
1
2
3
4
5
6
1
12
2.5
C: 67.28
H: 2.80
N: 19.61
C: 67.28
H: 2.80
N: 19.61
C: 67.28
H: 2.80
N: 19.61
C: 67.28
H: 2.80
N: 19.61
C: 67.28
H: 2.80
N: 19.61
C: 67.28
H: 2.80
C: 63.71
H: 2.65
N: 17.89
C: 67.30
H: 2.70
N: 19.50
C: 28.42
H: 2.41
N: 9.42
C: 67.11
H: 2.70
N: 19.40
C: 32.20
H: 2.50
N: 10.45
C: 61.78
H: 2.51
N: 18.20
CoCl
2
2
2
2
2
2
$6H
$6H
$6H
$6H
$6H
$6H
2
2
2
2
2
2
O
O
O
O
O
O
MW
6
6
180
90/86
81/75
10/5
1
12
2.5
CoCl
MW
6
210–220
210
1
12
2.5
CoCl
6
1
12
2.5
CoCl
MW
6
10
10
5
190–200
200
86/80
15/11
88/83
1
12
2.5
CoCl
1
12
2.5
CoCl
H
MW
180–200
2
O
3 drops
75 mg)
12
N: 19.61
(
7
8
9
1
1
1
C: 67.28
H: 2.80
N: 19.61
C: 63.31
H: 2.58
N: 18.73
CoCl
H
2
2
2
$6H
$6H
$6H
$6H
$6H
2
2
2
2
2
O
O
O
O
O
2.5
3 drops
(75 mg)
12
2.5
3 drops
(75 mg)
12
2.5
3 drops
(70 mg)
12
2.5
3 drops
(70 mg)
12
MW
MW
MW
MW
MW
4
10
4
210–220
180–200
160
86/84
90/86
75/67
78/65
84/78
2
O
1
C: 67.28
H: 2.80
N: 19.61
C: 67.20
H: 2.71
N: 19.56
CoCl
H
2
O
1
C: 67.28
H: 2.80
N: 19.61
C: 61.46
H: 2.54
N: 18.02
CoCl
DMF
0
1
1
C: 67.28
H: 2.80
N: 19.61
C: 63.83
H: 2.75
N: 18.83
CoCl
DMF
2
4
180–190
180
1
C: 67.28
H: 2.80
N: 19.61
C: 67.10
H: 2.68
N: 19.34
CoCl
DMF
2
2.5
3 drops
10
(
70 mg)
a
Conversion based on the consumption of 1.
conditions, we have decided to use the dedicated monomode
microwave reactor Synthewave 402 (Prolabo) with accurate
measurement of temperature by an infrared detection
and, in such a case, to initiate a chemical reaction under
microwave conditions at least one of substrates need to be
melting solid that absorbs relatively well microwaves.
2
8
(
calibrated using an optical fiber) during the reaction course.
These features can be ensured by phthalonitrile (1) or
phthalic anhydride (2) that have melting points 139–141 8C
Moreover, such a reactor allows also maintaining of
temperature at a constant value by modulation of emitted
MW power and an efficient mechanical stirring.
2
9
and 131–134 8C, respectively, provided that the reaction
mixtures were irradiated strongly enough at the beginning of
experiments. On the other hand, a small amount of a good
microwave absorber added to substrates that do not absorb
microwaves in solid state can initiate an increase of
temperature and, in turn, a chemical reaction. Therefore,
in the further stage of our investigations, we decided to
2
1
First, we decided to use two metal salts as templates for the
formation of phthalocyanines, that is, cobalt (II) chloride
hexahydrate and copper (II) chloride dihydrate, because
these phthalocyanines are usually applied and commercially
available. Moreover, phthalocyanines containing cobalt and
copper templates can be used as effective catalysts in
3
0
check whether a small amount of water or DMF, which are
strong microwave absorbers, can influence reaction by
faster increase of reaction temperature to level so high that
is needed in the synthesis of phthalocyanines. Moreover, a
small amount of solvent can provide better temperature
homogeneity during the syntheses. The results and con-
ditions of all the reactions are presented in Tables 1–3.
1
7
16
oxygenation and oxyhalogenation processes, which are
also of research interest in our labs.
2
6,27
In a typical experiment, the reactions were carried out by
simply mixing and grinding phthalonitrile (1) (1,2-dicya-
nobenzene) with copper or cobalt chloride, and the mixtures
were then irradiated in open vessels in the microwave
reactor. In the case of phthalic anhydride (2), additionally,
an excess of urea was added to the reaction mixture before it
was subjected to microwave irradiation in an open vessel as
well. All the substrates used in the syntheses were solid,
Regarding the reaction of phthalonitrile (1) (Tables 1 and 2),
all the results under different reaction conditions (i.e.,
conventional and microwave) were compared on the basis
of conversion of phthalonitrile (1), yield of the product after
purification with water, acetone, methylene chloride, and

182
A. Burczyk et al. / Tetrahedron 61 (2005) 179–188
Table 3. The synthesis of phthalocyanine–Cu and Co from phthalic anhydride (2) and urea in the presence of ammonium molybdate under microwave and
conventional conditions
a
Substrate
Quantity
(
Conditions
Time (min)
Temp. (8C)
Conv. /Yield
(%)/(%)
CHN calc.
CHN found
mmol)
1
2
3
4
5
2
10
20
2.5
0.1
C: 66.74
H: 2.50
N: 19.2
C: 64.07
H: 2.82
N: 19.04
Urea
CuCl
Ammonium
molybdate
2
Urea
CuCl
Ammonium
molybdate
2
Urea
CuCl
Ammonium
molybdate
2
Urea
CoCl
Ammonium
molybdate
2
2
$2H
2
O
MW
10
200
88/80
82/78
15
15
2.5
2
C: 66.74
H: 2.50
N: 19.2
C: 66.81
H: 2.75
N: 19.21
2
$2H
2
O
MW
6
140–170
15
15
2.5
2
C: 66.74
H: 2.50
N: 19.2
C: 30.81
H: 2.05
N: 10.27
2
$2H
2
O
6
6
5
140–170
180
60/38
60/52
15
15
2.5
2
C: 67.28
H: 2.80
N: 19.61
C: 66.81
H: 2.77
N: 19.48
MW
2
$6H
2
O
15
15
2.5
2
C: 67.28
H: 2.80
N: 19.61
C: 19.68
H: 1.98
N: 5.57
Urea
CoCl
Ammonium
molybdate
6
5
180
18/12
2
(6H
2
O
a
Conversion based on the consumption of 2.
concentrated sulfuric acid and final purity of the product
elemental analysis). For the reaction of phthalonitrile (1)
and copper chloride, it was possible to optimize reaction
conditions under microwave irradiation so that the phthalo-
cyanine–Cu was obtained in a very good yield and high
purity in a relatively short reaction time (Table 1, entries 1,
polarity of a system is enhanced. The rate-determining step
consists of the addition of nitrile via its nitrogen site on the
triple bond on the second nitrile group to form bipolar ions
that in turn can react with water molecules to produce 3-
imino-2,3-dihydro-isoindol-1-one (3). The transition state is
therefore more polar than ground state and consequently
more prone to electrostatic interactions of dipole–dipole
type with the electromagnetic field (Scheme 2). The
stabilization of the transition state is therefore responsible
of reactivity by a decrease of the activation energy.
(
3
1
4
, and 5). However, the reaction needed strong heating at the
beginning and the final reaction temperature likely above
00 8C (for example, compare entries 1 and 2 in Table 1). A
2
typical reaction temperature profile in which power of
microwave irradiation and reaction temperature are shown
is presented in Figure 1(a) (Table 1, entry 5). It can be seen
that for the first half of the reaction, maximum MW power
was applied to increase the reaction temperature from 20 to
It was found that molar ratios of the reagents (i.e.,
phthalonitrile (1) to the inorganic salt) influenced the
conversion as well as yields, and the best results were
obtained when 1 was used in an excess in comparison with
copper chloride (Table 1, entries 4 and 5). However, in the
opposite case (Table 1, entry 1), the purity of phthalo-
cyanine–Cu was satisfactory, but it was obtained in lower
yield.
1
00 8C, then when the reaction was initiated a fast
temperature increase was observed together with a sub-
stantial reduction of MW power.
For those reactions under MW irradiation in which the best
results were obtained, the experiments were run under
conventional heating (D—oil bath) (Table 1, entries 2 vs. 3
and 5 vs. 6) with similar sets of conditions (for example,
Fig. 1(a) and (b), respectively). In both cases, the yields
of product under conventional conditions were much lower
As it can be seen in Figure 1(a) and (b), the increase of
temperature at the beginning of phthtalonitrile reaction was
relatively slow (as was mainly concerned with solid material),
and, finally, lengthened the total reaction time under both
microwave and conventional conditions. Therefore, we
decided to add a small amount of a strong microwave absorber
(water or DMF) to the reaction mixture in order to further
reduce reaction time and improve temperature homogeneity
(Table 1, entries 7–12). Applying water as a liquid microwave
absorber, we obtained the best results when the reaction
mixture was maintained for 10 min under microwave
irradiation at 225 8C (Table 1, entry 9). Whereas the product,
phthalocyanine–Cu, was prepared with lower yield when
DMF was added to the reaction mixture under similar
conditions (Table 1, entry 12).
(
7–10% instead of 70–88%), and, which is more important,
purity of the product was unacceptable. Therefore, it was
proven that the solvent-free procedure under microwave
irradiation constitutes here an undeniable improvement for
the reactions that were run with enhanced yields under MW
conditions in comparison with conventional heating
experiments.
The important specific MW effects observed here are
consistent with the consideration of mechanisms and with
the assumption that the MW effects are increased when the

A. Burczyk et al. / Tetrahedron 61 (2005) 179–188
183
2 2
Figure 1. (a) Thermal profile during microwave-assisted solvent-free reaction of 1 with CuCl $2H O (Table 1, entry 5); temperature CNS and power CNS are
programmed temperature and power profiles, respectively. (b) Thermal profile for the solvent-free reaction of 1 with CuCl $2H O (Table 1, entry 6) under
2 2
conventional conditions.
The temperature profiles for the reactions with the addition
of a small amount of water and DMF are presented in
Figures 2 and 3, respectively. In comparison with
Figure 1(a), it can be observed that in both cases further
reduction in reaction times from 15 to 10 min was mainly
due to the reduction of initial time of the reactions from 5 to
possible to obtain the product, phthalocyanine–Co, with a
good yield at temperature lower than 200 8C, but its purity
was still unacceptable, which was proven by elemental
analysis (for example: Table 2, entry 1).
Unlike in the synthesis with copper chloride, owing to the
lack initial time in which the reaction temperature slowly
increased from 20 to 100 8C (Fig. 1), the reaction time in the
reaction with cobalt chloride was reduced to 10 min even in
the absence of strong microwave absorbers (i.e., water or
DMF). From the beginning, the reactions of cobalt chloride
were characterized by a strong increase of reaction
1 min, that is, time in which the reaction mixture reached
appropriate reaction temperature ca.200 8C.
Similarly to the reaction with copper chloride, the reaction
of phthalonitrile (1) with cobalt chloride needed to be
carried out at temperature above 200 8C. However, it was

184
A. Burczyk et al. / Tetrahedron 61 (2005) 179–188
Scheme 2. Mechanism of the activation of 1,3-dicyanobenzene during the formation of phthalocyanines.
temperature (Fig. 4; Table 2, entry 4), which was likely due
to higher content of water in hydrated cobalt chloride than
copper chloride. Thus, after addition of small amount of
water or DMF, in comparison with the reactions of copper
chloride (Figs. 1 and 2), a further reduction of reaction
time was not observed and yields were similar (Table 2,
entries 8 and 11). However, in the case of DMF, it was
possible to decrease the reaction temperature to 190 8C
conventional heating (oil bath) (Table 2, entries 3 and 5)
with similar sets of conditions (time, temperature). In both
cases, the yields of product under conventional conditions
were much lower, and, which is more important, purity of
the product was unacceptable. It was again shown that the
solvent-free procedure under microwave irradiation in
comparison with conventional heating experiments gives
better results, which might be explained by a specific
interaction of microwaves with substrates and an influence
(
Table 2, entry 11).
2
3
of non-thermal microwave effect (i.e., increase of reaction
rate that is non adequate to the reaction temperature) during
microwave experiments.
Temperature profiles for the reaction of cobalt chloride with
addition of a small amount of water and DMF (Figs. 5 and 6)
were similar to temperature profiles for the reaction of
copper chloride (Figs. 2 and 3). As soon as microwave
irradiation was applied to the reaction mixtures, the reaction
temperature increased within ca. 60 s from the room
temperature to 200 8C and higher, in which the synthesis
of phthalocyanines can be carried out with good yield and
purity (for example, Table 2, entries 8 and 11). As before,
for those reactions under microwave irradiation in which the
best results were obtained, the experiments were run under
The reactions of phthalic anhydride (2) under microwave
irradiation were compared with those run under conventional
conditions (oil bath) for both copper and cobalt chlorides
(Table3, entry3and5). Similarlytotheexperimentsdescribed
for phthalonitrile (1), the yields of phthalocyanines under
conventional conditions were significantly lower and the
purity was unacceptable. Eventually, it was proven that the
solvent-free procedure under microwave irradiation in
2 2
Figure 2. Thermal profile during microwave-assisted reaction of 1 with CuCl $2H O in the presence of 3 drops (75 mg) of water (Table 1, entry 9);
temperature CNS and power CNS are programmed temperature and power profiles, respectively.

A. Burczyk et al. / Tetrahedron 61 (2005) 179–188
185
2 2
Figure 3. Thermal profile during microwave-assisted reaction of 1 with CuCl $2H O in the presence of 3 drops (70 mg) of DMF (Table 1, entry 12);
temperature CNS and power CNS are programmed temperature and power profiles, respectively.
comparison with conventional heating experiments gave
better results even as the substrate we used less reactive
phthalic anhydride (2) in the presence of urea.
represented by one of the three tautomeric forms
(Scheme 3). The polarized form could exist as transient or
intermediate species in an excited state that decompose into
ammonia and isocyanic acid in the presence of a catalyst
(for example, ammonium molybdate). Ammonia react with
phthalic anhydride to produce phthalimide, which in turn
can react with isocyanic acid to give 3-imino-2,3-dihydro-
isoindol-1-one (3). The reaction can proceed by passing
through a concerted four center mechanism to form carbon
The specific non-thermal MW effects observed in this case
are also clearly consistent with the more polar species
generated during the course of the reaction. The reaction
rate of the formation of phthalocyanine form urea and
phthalic anhydride is proportional to the first power of the
3
2
32
concentration of urea. The urea molecule can be
dioxide.
2 2
Figure 4. Thermal profile during microwave-assisted solvent-free reaction of 1 with CoCl $6H O (Table 2, entry 4); temperature CNS and power CNS are
programmed temperature and power profiles, respectively.

186
A. Burczyk et al. / Tetrahedron 61 (2005) 179–188
2
Figure 5. Thermal profile during microwave-assisted reaction of 1 with CoCl2$6H O in the presence of 3 drops (75 mg) of water (Table 2, entry 8);
temperature CNS and power CNS are programmed temperature and power profiles, respectively.
Recently, the microwave-assisted procedure for the syn-
thesis of phthalocyanine–Cu from phthalic anhydride (2)
and urea in a solution of alkylbenzene was published by
microwave conditions had smaller average size and
narrower size distribution.
3
3
Park et al. They found that under microwave irradiation
phthalocyanine–Cu could be prepared at lower temperature
and shorter time than those required under conventional
conditions. Moreover, the samples synthesized under
3. Conclusions
In summary, the synthesis of phthtalocyanines under
2 2
Figure 6. Thermal profile during microwave-assisted reaction of 1 with CoCl $6H O in the presence of 3 drops (70 mg) of DMF (Table 2, entry 11);
temperature CNS and power CNS are programmed temperature and power profiles, respectively.

A. Burczyk et al. / Tetrahedron 61 (2005) 179–188
187
4.1.1. Procedure A. Phthalodinitrile (1) (12 mmol, 1.54 g)
and copper chloride dihydrate (2.5 mmol, 0.425 g) were
ground together and placed in a tube. The mixture was
then irradiated in the microwave reactor for time given in
Tables 1 and 2. The crude product was washed successively
with hot water, acetone, dichloromethane and then was
dried. Next the product was twice dissolved in the
concentrated H SO , precipitated from distilled water,
2
4
filtrated off and washed with water to pH neutral. After
drying under reduced pressure, the phthalocyanine–Cu was
analysed.
4.1.2. Procedure B. Phthalic anhydride (2) (10 mmol,
1.49 g), urea (20 mmol, 1.2 g), copper chloride dihydrate
(
(
2.5 mmol, 0.425 g) and ammonium molybdate as a catalyst
2.0 mmol, 0.47 g) were ground together, placed in a tube
and irradiated in the microwave reactor at high power for
time reported in Table 3. After completion of the reaction,
the product was washed hot water, acetone and dichloro-
methane. Finally, the product was twice dissolved in the
concentrated H SO , precipitated from distilled water,
2
4
filtrated off and washed with water to pH neutral. After
drying under reduced pressure, the phthalocyanine–Cu was
analysed.
Scheme 3. Mechanism for condensation of urea with phthalic anhydride.
Acknowledgements
microwave irradiation can be performed easily in a reduced
time scale applying phthalonitrile (1) or phthalic anhydride
This work was undertaken as part of the EC sponsored
programs D32 COST Program (Chemistry in High-Energy
Microenvironments) and Socrates–Erasmus student
exchange program.
(
2) as a substrate. Solvent-free conditions lead by far to the
best results and to easy-to-perform procedures with
considerable improvements over classical methods. More-
over, the application of the dedicated monomode micro-
wave reactor (Prolabo 402) with temperature monitoring
allowed directly comparing two activation modes (i.e., con-
ventional heating and microwave irradiation) and showed
that non-thermal microwave effects might be very favour-
able during microwave experiments. This can be explained
when one considers the enhancement in the polarity of the
system when the reaction is in progress thanks to a well-
fitted mechanism. Eventually, the reactions under conven-
tional conditions that were carried out in the same time scale
gave products in much lower yields of unacceptable purity.
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