Improved Synthesis of Soluble Metal-Free/Metal Phthalocyanine Tetracarboxylic Acids and Their Application in the Catalytic Epoxidation of Cyclohexene

Article abstract of DOI:10.1007/s10562-015-1500-0

Soluble metal-free and metal (copper (II), iron (III), and cobalt (II)) phthalocyanine tetracarboxylic acids (5-8) were synthesized using a novel method consisting of improved hydrolysis based on the diazo reaction. The obtained compounds (5-8) were characterized by X-ray diffraction, UV-Vis spectrometry, and FT-IR spectrometry and then utilized as catalysts for the epoxidation of cyclohexene with molecular oxygen as oxidant. Reaction conditions including reaction time, temperature, catalyst amount, and isobutyraldehyde/cyclohexene ratio were optimized to achieve the highest selectivity of cyclohexene oxide. Metal-free phthalocyanine tetracarboxylic acid (5) and metal (copper (II), iron (III), and cobalt (II)) phthalocyanine tetracarboxylic acids (6-8, respectively) were compared. Complexes 6-8 exhibited higher catalytic activity than compound 5 under the optimal conditions. Graphical Abstract: Four soluble metal-free and metal PTCs were synthesized using a novel method, and were utilized as catalysts for the epoxidation of cyclohexene with molecular oxygen as the oxidant. A total of 58.1% selectivity and yield of cyclohexene oxide were achieved under the optimal condition. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-015-1500-0

Catal Lett (2015) 145:1094–1102
DOI 10.1007/s10562-015-1500-0
Improved Synthesis of Soluble Metal-Free/Metal Phthalocyanine
Tetracarboxylic Acids and Their Application in the Catalytic
Epoxidation of Cyclohexene
•
Xiaoling Sun Li Wang Zhi Tan
•
Received: 19 December 2014 / Accepted: 8 February 2015 / Published online: 14 February 2015
Ó Springer Science+Business Media New York 2015
Abstract Soluble metal-free and metal (copper (II), iron
(III), and cobalt (II)) phthalocyanine tetracarboxylic acids
(5–8) were synthesized using a novel method consisting of
improved hydrolysis based on the diazo reaction. The ob-
tained compounds (5–8) were characterized by X-ray
diffraction, UV–Vis spectrometry, and FT-IR spectrometry
and then utilized as catalysts for the epoxidation of cy-
clohexene with molecular oxygen as oxidant. Reaction
conditions including reaction time, temperature, catalyst
amount, and isobutyraldehyde/cyclohexene ratio were op-
timized to achieve the highest selectivity of cyclohexene
oxide. Metal-free phthalocyanine tetracarboxylic acid (5)
and metal (copper (II), iron (III), and cobalt (II)) phthalo-
cyanine tetracarboxylic acids (6–8, respectively) were
compared. Complexes 6–8 exhibited higher catalytic ac-
tivity than compound 5 under the optimal conditions.
Graphical Abstract Four soluble metal-free and metal
PTCs were synthesized using a novel method, and were
utilized as catalysts for the epoxidation of cyclohexene
Keywords Metal-free phthalocyanine Á Metal
with molecular oxygen as the oxidant. A total of 58.1%
selectivity and yield of cyclohexene oxide were achieved
under the optimal condition.
phthalocyanine Á Epoxidation Á Cyclohexene Á
Molecular oxygen
1 Introduction
Phthalocyanine derivatives have been traditionally used as
pigments and dyes [1, 2]. Scholars found that phthalocya-
nines exhibit unique optical, physical, chemical, and cat-
alytic properties because of their extensively delocalized
18p-electron aromatic heterocyclic system [3]. As a result,
phthalocyanines have been utilized as catalysts [4, 5],
chemical sensors [6, 7], solar cells [8–10], and photody-
namic therapy materials [11, 12]. However, phthalocyani-
nes exhibit poor solubility and can only be dissolved in
X. Sun (&) Á L. Wang Á Z. Tan
School of Chemical and Environmental Engineering, Shanghai
Institute of Technology, Shanghai 201418, China
e-mail: xiaolingsun1@msn.com
123

Synthesis of Soluble Metal-Free/Metal Phthalocyanine Tetracarboxylic Acids
1095
concentrated sulfuric acid or strong polar solvents, such as
DMF, DMSO, pyridine, and THF [13]; hence, the use of
phthalocyanines as catalysts in various catalytic reactions
has been significantly limited. Therefore, water-soluble
phthalocyanine derivatives have been synthesized over the
recent years to improve their catalytic properties [14–16].
Soluble phthalocyanines are usually substituted with ionic-
type or strong polar hydrophilic groups, such as carboxyl,
sulfonic, and ammonium groups [17, 18]. Soluble ph-
thalocyanines are also related to the pH of the solvent [19].
Phthalocyanines have been traditionally prepared
through phthalic anhydride method [20], which can be
divided into two parts: solid state and liquid phase. The
liquid-phase method uses toxic solvents, such as ni-
trobenzene and trichlorobenzene [21]. In this process, the
solvent is recycled, thus causing difficulty in separating the
product. The solid-phase method is a simple process and
does not cause pollution and does not recycle solvents. In
this paper, metal-free and metal phthalocyanine tetracar-
boxylic acid compounds (PTCs) were synthesized using the
solid-phase method. Traditionally, metal-free and metal
phthalocyanine tetraformamido compounds are initially
synthesized [22] and then hydrolyzed to obtain metal-free
and metal PTCs. However, metal-free and metal phthalo-
cyanine tetraformamido compounds exhibit alkali resis-
tance, heat resistance, water resistance, lightfastness, and
insolubility in various polar and non-polar organic sol-
vents. Therefore, strong acids and bases must be used for
the hydrolysis of metal-free and metal phthalocyanine te-
traformamido compounds at a high temperature with a
reaction time of 12 or even 24 h [23]. For this reason, we
improved the hydrolysis process based on the diazo reac-
tion; metal-free and metal phthalocyanine tetraformamido
compounds are dissolved in sulfuric acid solution, reacted
with sodium nitrite solution, and then subjected to acidiz-
ing to obtain purified metal-free and metal PTCs. In this
method, the hydrolysis process changes from a heteroge-
neous to a homogeneous reaction, thus easily reacting at
room temperature and significantly reducing the reaction
time from 12 or 24 h to 0.5–3 h. The improved method
presents high efficiency and low cost and produces prod-
ucts with abundant color and high purity.
has gained significant attention because it is a cheap, envi-
ronmentally clean, and readily available oxidant since
1990s. Mukaiyama first reported epoxidation of olefins cat-
alyzed by nickel (II) complexes with combined use of oxy-
gen and aldehydes [30], then Iqbal explored the epoxidation
with methyl-2-oxocylopentane carboxylate in the presence
of the cobalt (II) catalyst and oxygen [31]. Moreover, Iqbal
et al. [32] reviewed a lot of transition metal complexes as
catalyst for epoxidation of olefins with molecular oxygen.
Thus, in this paper, metal-free and metal PTCs were used as
catalysts for the epoxidation of cyclohexene with molecular
oxygen and isobutyraldehyde at room temperature and at-
mospheric pressure.
In this study, we synthesized metal-free PTC (5) through
the improved method first, which could be regard as a ligand
for its unique central structure. Then we prepared metal PTCs
(6–8) by adding anhydrous metal salts (CoCl2, CuSO4, and
FeCl3) during the preparation of compound 5. All of these
compounds were characterized through IR, UV spectrometry,
and XRD. Catalytic activities of compounds 5–8 were also
screenedusingtheepoxidationofcyclohexenewithmolecular
oxygen as the oxidant under mild conditions. The effects of
different experimental parameters, including reaction time,
temperature, catalyst amount, and isobutyraldehyde/cyclo-
hexene ratio, were further investigated to optimize the reac-
tion conditions.
2 Experimental
2.1 Materials
All solvents and chemicals were of analytical grade, ob-
tained from commercial suppliers, and used without pu-
rification unless otherwise stated.
2.2 Preparation of Metal-Free and Metal PTCs (5–8)
Scheme 1 presents the synthesis pathway of metal-free and
metal PTCs (5–8). Trimellitic anhydride (50 mmol), urea
(0.5 mol), and ammonium molybdate (0.1 mmol) as cata-
lyst were used for preparation. For metal PTCs (6–8),
equivalent amounts (50 mmol) of the corresponding an-
hydrous metal salts (CoCl2, CuSO4, and FeCl3) were
placed into a three-necked flask with a reflux condenser.
After grinding and blending, the reaction mixture was
stirred at 170 °C for 6 h and then cooled to room tem-
perature. The resulting mixture was boiled in 5 mol/L
hydrochloric acid and then filtered. The mixture was si-
multaneously washed with anhydrous ether and absolute
methanol until the filtrate became colorless. Metal-free and
metal phthalocyanine tetraformamido compounds (1–4)
were obtained. Compounds 1–4 were dissolved in 50 %
The epoxidation of cyclohexene to cyclohexene oxide is
an important procedure in chemical and pharmaceutical in-
dustries because the latter is a key intermediate in organic
synthesis of fine chemicals [24, 25]. Many efficient catalysts,
such as nanocrystalline mesoporous TiO2 loaded with RuO2
[26], porous titanosilicate composite [27], and zirconium
phenylphosphonate-anchored methyltrioxorhenium [28],
have been used for the epoxidation of cyclohexene with
H2O2 as the oxidant. Although hydrogen peroxide exhibits
advantages compared with other conventional epoxidants,
such as PhIO, NaClO, and t-BuOOH [29], molecular oxygen
123

1096
X. Sun et al.
Scheme 1 Synthesis of metal-
free and metal phthalocyanine
tetracarboxylic acid complexes
COOH
CONH2
HOOC
H2NOC
N
N
N
N
N
NH
N
N
NH
N
NaNO2
H2SO4
N
N
N
N
HN
HN
COOH
COOH
CONH2
HOOC
H2NOC
5
1
O
O
O
+
COOH
CONH2
O
HOOC
H2NOC
H2N
NH2
N
N
M
N
N
N
N
N
N
N
N
N
NaNO2
H2SO4
M
N
N
N
N
N
COOH
CONH2
HOOC
H2NOC
M: Cu (2), Fe (3), Co (4)
M: Cu (6), Fe (7), Co (8)
H
+
O
sulfuric acid solution (170 mL) and added with 2 mol/L
sodium nitrite solution (14 mL) drop wise while stirring at
5 °C. The reaction mixture was maintained at 30 °C for 1 h
with constant stirring. The solvent was removed through
centrifugal separation and filtration, and the resulting solid
was dissolved in deionized water. The resulting solution
was neutralized with 2 mol/L H2SO4 solution to obtain a
pH of 3. The solution was then filtered after standing for
12 h. The resulting solid was dried in a vacuum oven after
washing. The temperature was maintained at 70 °C and the
vacuum degree at 0.07 MPa for 4 h. Compounds 5–8 were
obtained with a yield of 2.5 (26.9 %), 1.85 (19.8 %), 2.1
(22.5 %), and 2.5 g (26.9 %), respectively.
s
PT
2H
O C 4C 2
,
2
l
C
,
O
+
isobutraldehdeyy
O
Scheme 2 Epoxidation of cyclohexene catalyzed by PTCs
(10 mL), isobutyraldehyde (0.048 mol), cyclohexene
(0.024 mol), and a catalyst (3 % of the mass fraction of
cyclohexene) were placed into a three-necked flask with a
reflux condenser. The resulting mixture was stirred by
bubbling molecular oxygen at 35 °C for 10 h. After cen-
trifugal separation, the resulting solution was analyzed
through GC and GC–MS for qualitative and quantitative
analyses.
2.3 Characterization
3 Results and Discussion
Compounds 5–8 were characterized through X-ray diffrac-
tion, diffuse reflectance UV–Vis, and FT-IR. FT-IR spec-
trumwas performed on a Thermo Nicolet Nexus Magana-
IR500 FT-IR spectrometer with the standard KBr pellet
method. Compounds 5–8 were dissolved in solvents and put
it into quartz cell (10 mm) to detect the UV–Vis spectra by
Shimadzu UV-3600 spectrophotometer. Powder X-ray
diffraction was performed on an X’Pert PRO diffractometer
using Cu Ka (k = 0.0016711 nm) radiation operating at
40 kV and 40 mA with the scanning 2h range from 0° to 90°.
3.1 FT-IR Absorption Spectra
Figure 1 illustrates the comparison of the FT-IR absorption
spectra. The results of the FT-IR spectra of compounds 5–8
are presented in Table 1. Compounds 5–8 featured a car-
boxyl group and showed the characteristic –C=O band at
1711–1717 cm-1 [33] and O–H band at 3425–3450 cm-1
in the IR spectrum. The peaks of compounds 5–8 around
1276–1286 cm-1 were attributed to the C–N= stretching
vibration, whereas the peaks around 1146–1151,
1084–1092, 1055–1065, 938–944, and 735–741 cm-1 were
due to phthalocyanine skeletal vibrations [34]. The peak
around 1420–1421 cm-1 showed that aromatic phenyl ring
existed in the compounds (5–8). The fluctuation range of
2.4 Catalytic Activity Measurement
The general procedure for the epoxidation of cyclohexene
was presented as follows (Scheme 2). 1, 2-Dichloroethane
123

Synthesis of Soluble Metal-Free/Metal Phthalocyanine Tetracarboxylic Acids
1097
also by solvent concentration and types of solvents. Hence,
the UV–Vis spectra of Co-PTC were detected in DMSO at
concentrations of 2 9 10-6, 4 9 10-6, 6 9 10-6, and
8 9 10-6 M. Figure 3 shows that the absorbance of Co-
PTC at B and Q bands increased with increasing DMSO
concentration. Otherwise, the absorbance of Co-PTC in
DMSO and DMF at the same concentration of 2 9 10-6
M
were also detected (Fig. 4). Co-PTC in DMSO showed
stronger absorbance at B and Q bands than that in DMF,
and the maximum absorbance peak demonsted a weak blue
shift.
3.3 X-ray Diffraction
Fig. 1 The FT-IR spectrum of metal-free and metal phthalocyanine
tetracarboxylic acid compounds
The XRD patterns of compounds 5–8 are presented in
Fig. 5; at 2h, two characteristic diffraction peaks, namely, a
broad peak around 5.5° and a sharp peak around 27°, were
observed [39, 40]. The strength of small diffraction peaks
at 5.5° was weak, whereas the large diffraction peaks at 27°
was strong. Table 3 shows the main peaks of PTCs as
follows: metal-free PTCs at 2h of 5.5° and 26.8°, Cu-PTC
at 2h of 5.4° and 27.1°, Fe-PTC at 2h of 5.6° and 26.9°, and
Co-PTC at 2h of 5.7° and 27.0°. The relatively small dif-
ferences in the XRD patterns of compounds 5–8 may be
attributed to the different central atoms; the peak of com-
plex 5 at wide angle was smaller than the peaks of com-
plexes 6–8. Moreover, compounds 5–8 exhibited similar
crystalline structure.
the peaks may be caused by the electron-withdrawing
ability of metal cations. These data showed that compounds
5–8 exhibited the carbon skeleton structure of phthalo-
cyanine and carboxyl groups.
3.2 UV–Vis Absorption Spectra
The UV–Vis spectra of phthalocyanines mainly originated
from p ? p* transitions of the strong Q-band
(600–750 nm) and the broad B-band (300–450 nm) with
weak transitions near those bands [35–38]. Compounds 5–8
were dissolved in DMSO before UV–Vis analysis, and
their UV–Vis spectra are shown in Fig. 2. The resulting
absorption wavelength in Table 2 demonstrated that all
compounds (5–8) exhibited a similar specific absorp-
tion peak of the phthalocyanine aromatic ring. The com-
parison of the absorption wavelength showed that the UV–
Vis spectrum of compound 5 exhibited stronger Q-band
absorptions at kmax = 699 nm than the absorptions of
complexes 6–8 at kmax = 686, 664, and 675.2 nm, re-
spectively. This phenomenon could be attributed to the
substitution of the central hydrogen atoms of metal-free
PTC by metal atoms, thus significantly reducing the elec-
tron cloud density of the metal-free PTC ring and in-
creasing the energy level between HUMO and LUMO.
Therefore, the absorptions demonstrated a blue shift.
The UV–Vis spectra of metal PTCs were not only af-
fected by central metal atoms and substituent groups, but
3.4 Catalytic Activity
3.4.1 Effect of Reaction Time on the Epoxidation
of Cyclohexene
The effect of reaction time was initially studied within
2–10 h, and the results are shown in Table 4. The yield and
conversion to cyclohexene oxide drastically increased with
the increasing reaction time from 2 to 8 h. However, the
isomerization of cyclohexene oxide to olefin aldehyde oc-
curred when the reaction time was prolonged to 10 h, thus
decreasing the selectivity. This finding showed that 8 h was
the optimum reaction time to obtain the highest cyclo-
hexene oxide conversion and selectivity.
FT-IR (cm-1
)
Table 1 The FT-IR spectrum
of metal-free and metal
PTCs
phthalocyanine tetracarboxylic
acid compounds
PTC (5)
3425,1685,1 3439, 1717, 1421, 1284, 1151, 1092, 1063, 944, 862, 741
3450, 1715, 1420, 1286, 1148, 1092, 1055, 938, 855, 739
3425, 1711, 1421, 1280, 1146, 1084, 1065, 942,856, 739
3426, 1717, 1420, 1276, 1150, 1091, 1058, 942, 846, 735
Cu-PTC (6)
Fe-PTC (7)
Co-PTC (8)
123

1098
X. Sun et al.
Fig. 2 Absorption spectra of PTCs in DMSO at the concentration of 4 9 10-5 M for a compound 5, b complex 6, c complex 7, and d for
complex 8
Table 2 The UV–Vis spectrum of metal-free and metal phthalo-
cyanine tetracarboxylic acid compounds
PTCs
B-band (nm)
Q-band (nm)
PTC (5)
350.0
353.9
335.0
342.7
636.0, 699.0
637.1, 686.0
636.7, 664.0
605.0, 675.2
Cu-PTC (6)
Fe-PTC (7)
Co-PTC (8)
3.4.2 Effect of Reaction Temperature on the Epoxidation
of Cyclohexene
Fig. 3 Absorption spectra of Co-PTC in DMSO at the concentration
of 2 9 10-6 to 8 9 10-6
The temperature was optimized by maintaining the reaction
time at 8 h, and the effects of reaction temperature are
shown in Table 5. The selectivity and yield of cyclohexene
increased with increasing temperature, peaked at 35 °C,
and then gradually declined. Cyclohexene oxide may be
easily isomerized at a high temperature. Therefore, the
reaction temperature of 35 °C provided the highest cyclo-
hexene conversion and selectivity.
M
3.4.3 Effect of Catalyst Amount on the Epoxidation
of Cyclohexene
The catalyst amount was also optimized, and the results are
shown in Table 6. The highest yield of cyclohexene oxide
123

Synthesis of Soluble Metal-Free/Metal Phthalocyanine Tetracarboxylic Acids
1099
Table 3 The X-ray diffraction
PTCs
2h (°)
patterns of metal phthalocya-
nine tetracarboxylic acid
compounds
PTC (5)
5.5
5.4
5.6
5.7
26.8
27.1
26.9
27.0
Cu-PTC (6)
Fe-PTC (7)
Co-PTC (8)
Table 4 Reaction time factor of epoxidation of cyclohexene
Time (h)
Selectivity (%)
Conversion (%)
Yield (%)
2
52.0
49.6
50.0
48.8
23.4
33.30
76.80
95.4
17.3
38.1
47.7
48.8
23.4
4
6
Fig. 4 Absorption spectra of Co-PTC in DMSO and DMF at the
concentration of 2 9 10-6
8
100.0
100.0
M
10
Reaction conditions: 0.02 mol cyclohexene, 0.04 mol isobutyralde-
hyde, 0.06 g Co-PTC, 30 mL/min O2, 10 mL dichloroethane, 35 °C
was 58.1 % with increasing catalyst amount. However, the
yield of cyclohexene oxide declined when the catalyst
amount was further increased. By considering the selec-
tivity of cyclohexene oxide and the conversion of cyclo-
hexene, the catalyst amount of 0.06 g was selected under
identical reaction conditions.
Table 5 Reaction temperature factor of epoxidation of cyclohexene
Temperature (°C) Selectivity (%) Conversion (%) Yield (%)
25
30
35
40
45
41.3
45.7
50.1
44.6
35.9
100.0
100.0
100.0
100.0
100.0
41.3
45.7
50.1
44.6
35.9
3.4.4 Effect of Isobutyraldehyde Amount
on the Epoxidation of Cyclohexene
The amount of isobutyraldehyde was another parameter
that influenced the yield of cyclohexene oxide and thus
should be further optimized. The cyclohexene amount was
set as constant to determine the effect of isobutyraldehyde
amount over a wide range of isobutyraldehyde to cyclo-
hexene molar ratios from 1 to 4. The results are listed in
Table 7. Table 7 illustrates the selectivity and yield of
cyclohexene oxide in relation to the isobutyraldehyde/cy-
clohexene ratio. The selectivity of cyclohexene oxide
Reaction conditions: 0.02 mol cyclohexene, 0.04 mol isobutyralde-
hyde, 0.06 g Co-PTC, 30 mL/min O2, 10 mL dichloroethane, 8 h
easily reached 58.1 % when the isobutyraldehyde/cyclo-
hexene ratio was equal to 2. However, the selectivity of
cyclohexene oxide increased at isobutyraldehyde/cyclo-
hexene ratios higher than 2. Therefore, the isobutyralde-
hyde/cyclohexene ratio of 2 was selected as the optimal
amount for the epoxidation of cyclohexene.
Fig. 5 The X-ray diffraction patterns of PTCs
123

1100
X. Sun et al.
3.4.5 Catalytic Activity of Compounds 5–8
Table 6 The influence of catalyst amount
Catalyst (g)
Selectivity (%)
Conversion (%)
Yield (%)
The results of catalytic activity of compounds 5–8 are
listed in Table 8. Table 8 shows that metal PTCs 6–8 ex-
hibited high catalytic activity with the yield of cyclohexene
oxide ranging from 50.0 to 58.1 %. By using metal-free
PTC 5 as the catalyst for the reaction, only 30.2 % of
cyclohexene oxide yield was obtained. Therefore, the cat-
alytic activity of complexes 6–8 was higher than compound
5.
0.00
0.02
0.04
0.06
0.08
61.2
48.4
55.0
58.1
23.9
21.56
89.20
92.20
100.0
98.0
13.2
43.2
50.7
58.1
23.4
Reaction conditions: 0.02 mol cyclohexene, 0.04 mol isobutyralde-
hyde, 30 mL/min O2, 10 mL dichloroethane, 35 °C, 8 h
All compounds (5–8) are promising catalysts with a high
catalytic activity for the epoxidation of cyclohexene under
the optimal reaction conditions. The recyclability of the
catalyst must be further evaluated.
Table 7 The influence of isobutylaldehyde amount
Isobutyraldehyde/
cyclohexene ratios
Selectivity
(%)
Conversion
(%)
Yield
(%)
3.5 Mechanistic Studies
1
2
3
4
33.2
58.1
56.1
48.7
100.0
100.0
100.0
100.0
33.2
58.1
56.1
48.7
The possible mechanism of hydrolysis is illustrated in
Scheme 3. was obtained through the reaction of HONO
and –NH2ÁN2 was generated through the decomposition of
when heated. The acyl cation was also generated; this ca-
tion immediately combined with the nucleophilic water
molecule. Carboxylic acid was obtained by losing a proton.
We hold the opinion that the reaction mechanism of
metal PTCs catalyze epoxidation of cyclohexene with
molecular oxygen and isobutyraldehyde is similar to the
published reports [41, 42] which is illustrated in Scheme 4.
First, isobutyraldehyde adsorptions on the central of (Ln)-
Mn? to generate acyl radical with a proton left and the
reduction of Mn? to M(n-1)?, then intermediate complex
species (I) is formed. Second, molecular oxygen adsorp-
tions on intermediate complex species (I) to generate in-
termediate complex species (II) which is unstable for its
structure, then acylperoxy radical released immediately
from intermediate complex species (II) with (Ln)Mn?
Reaction conditions: 0.02 mol cyclohexene, 0.06 g Co-PTC, 30 mL/
min O2, 10 mL dichloroethane, 35 °C, 8 h
Table 8 Epoxidation of cyclohexene by different complexes
Complex
Selectivity (%)
Conversion (%)
Yield (%)
5
6
7
8
43.0
55.6
57.6
58.1
70.3
90.0
30.2
50.0
56.1
58.1
97.4
100.0
Reaction conditions: 0.02 mol cyclohexene, 0.04 mol isobutyralde-
hyde, 0.06 g complex, 30 mL/min O2, 10 mL dichloroethane, 35 °C,
8 h
Scheme 3 Hydrolysis
O
O
N
O
O
HNO2
N2
H2O
mechanism of metal-free and
metal phthalocyanine
tetraformamido complexes
H
+
R
NH2
R
N
N
R
H
2O
R
OH
N
N
M
N
NH
N
N
N
N
N
or
N
R:
N
N
N
HN
N
M: Cu , Fe , Co
123

Synthesis of Soluble Metal-Free/Metal Phthalocyanine Tetracarboxylic Acids
1101
Scheme 4 The reaction
mechanism for the epoxidation
of cyclohexene catalyzed by
PTCs
Program (No. LM201336). The authors thank the Analysis and
Testing Center of Shanghai Institute of Technology for support.
regenerated. Third, acylperoxy radical receives a proton to
form isobutyr-peroxyacid. On one hand, isobutyr-per-
oxyacid reacts with cyclohexene directly to obtain cyclo-
hexene oxide and isobutyric acid as a reaction by-product;
on the other hand, isobutyr-peroxyacid adsorptions on the
central of (Ln)Mn? and transfers an oxygen atom to (Ln)-
Mn?, which may be generate an oxometallic active species
(III) [43] and isobutyric acid as by-product. At last, ox-
ometallic active species (III) reacts with cyclohexene to
generate cyclohexene oxide, and the (Ln)Mn? regenerated
at the same time.
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Four soluble metal-free and metal PTCs (5–8) were syn-
thesized using a novel method. The characterization of the
compounds (5–8) through IR spectra, UV–Vis spectra, and
X-ray diffraction confirmed the existence of the phthalo-
cyanine skeleton and the carboxyl group. Compounds 5–8
were also utilized as catalysts for the epoxidation of cy-
clohexene with molecular oxygen as the oxidant. Reaction
conditions including reaction time, temperature, catalyst
amount, and isobutyraldehyde/cyclohexene ratio were op-
timized to achieve the highest selectivity and yield of cy-
clohexene oxide. A total of 58.1 % selectivity and yield of
cyclohexene oxide were achieved under the optimal con-
dition consisting of a reaction time, temperature, isobu-
tyraldehyde/cyclohexene ratio, and catalyst amount of 8 h,
35 °C, 2 and 0.06 g, respectively.
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Acknowledgments The work was supported by the Shanghai Nat-
ural Science Foundation (No. 4ZR1440900) and Shanghai Alliance
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