Highly selective aqueous heterogeneous oxygenation of hydrocarbons catalyzed by recyclable hydrophobic copper (II) phthalocyanine nanoparticles

Article abstract of DOI:10.1016/j.molcata.2012.02.003

A novel aqueous catalytic method for selective epoxidation of olefins and oxidation of saturated hydrocarbons to ketones using aqueous solution of tetra-n-butylammonium peroxomonosulfate (TBAOX) containing water-insoluble copper (II) phthalocyanine nanoparticles has been developed. No surfactants, additives, toxic reagents or solvents were involved. The impressive turnover numbers obtained for CuPc in this oxidation system displayed the high catalytic activity and relative stability of catalyst. The effective dispersity of CuPc in aqueous solution of TBAOX which yielded particles with average size of 30 nm, was the most important factor to affect the reaction rate. The catalyst could easily be recovered and reused without loss of activity and the reduced form of starting oxidant (n-Bu₄NHSO₄) could also be recycled.

Full text of DOI:10.1016/j.molcata.2012.02.003

Journal of Molecular Catalysis A: Chemical 357 (2012) 141–147
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Highly selective aqueous heterogeneous oxygenation of hydrocarbons catalyzed
by recyclable hydrophobic copper (II) phthalocyanine nanoparticles
Abdolreza Rezaeifarda,∗, Maasoumeh Jafarpoura, Atena Naeimia, Khosro Mohammadib
a Catalysis Research Laboratory, Department of Chemistry, Faculty of Science, University of Birjand, Birjand 97179-414, Iran
b Chemistry Department, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel aqueous catalytic method for selective epoxidation of olefins and oxidation of saturated hydro-
carbons to ketones using aqueous solution of tetra-n-butylammonium peroxomonosulfate (TBAOX)
containing water-insoluble copper (II) phthalocyanine nanoparticles has been developed. No surfactants,
additives, toxic reagents or solvents were involved. The impressive turnover numbers obtained for CuPc
in this oxidation system displayed the high catalytic activity and relative stability of catalyst. The effective
dispersity of CuPc in aqueous solution of TBAOX which yielded particles with average size of 30 nm, was
the most important factor to affect the reaction rate. The catalyst could easily be recovered and reused
without loss of activity and the reduced form of starting oxidant (n-Bu4NHSO4) could also be recycled.
© 2012 Elsevier B.V. All rights reserved.
Received 20 November 2011
Received in revised form 29 January 2012
Accepted 5 February 2012
Available online 14 February 2012
Keywords:
Copper Phthalocyanine
Water
Oxygenation
Peroxomonosulfate
Nanoparticles
Heterogeneous catalyst
1. Introduction
oxidation of organic compounds [5,8–12], led to an innovative het-
erogeneous strategy for clean and selective aqueous oxygenation of
Phthalocyanine transition metal complexes as important indus-
trial pigments have been considered as potential oxidation
catalysts because of their rather cheap and facile preparation in a
large scale and in particularly their chemical and thermal stability.
However, the low solubility of metallophthalocyanines is perhaps
the most significant limitation in their application as catalysts. It
may be overcome by sulfonation and carboxylation at the periph-
ery of the molecule to give rise to water-soluble derivatives [1].
Nevertheless, the separation of water-soluble catalysts from the
aqueous phase is a time consuming process making them out of
recycled materials.
hydrocarbons [13] and alcohols [14] catalyzed by water-insoluble
Fe(III) and Mn (III) porphyrin complexes. Very recently efficient oxi-
dation of alcohols and sulfides in water catalyzed by hydrophobic
copper (II) phthalocyanine (CuPc) as a cheap heterogeneous cata-
lyst has also been developed [15]. Now, we would like to describe
the catalytic potential of CuPc in the epoxidation of olefins and oxy-
genation of saturated C H bonds using TBAOX in an aqueous media
lacking of any organic co-solvents and surfactants (Scheme 1).
Some evidences for formation of CuPc nanoparticles in aqueous
solution of TBAOX which demonstrate the high oxidation activity
of hydrophobic catalyst have also been presented. The catalyst and
the reduced form of oxidant (n-Bu4NHSO4, TBAHSO4) were easily
recovered and reused in the procedure.
Oxone® (2KHSO5•KHSO4•K2SO4) has drawn considerable atten-
tion as
a mild and efficient reagent for various organic
transformations in recent years [2]. Despite, the promising employ-
ment of Oxone® and their organic salts (n-Bu4NHSO5, Ph4PHSO5)
in the oxygenation of hydrocarbons in the presence of metallo-
porphyrins [3–5], attempts at using this versatile oxygen source
in association with phthalocyanine catalysts were virtually unsuc-
cessful [6,7].
2. Experimental
2.1. General remarks
Purity determinations of the products were accomplished by GC
on a Shimadzu GC-16A instrument using a 25 m CBP1-S25 (0.32 mm
ID, 0.5 ␮m coating) capillary column. IR spectra were recorded on
a Perkin Elmer 780 instrument. UV–vis spectra were recorded on
a 160 Shimadzu spectrophotometer. NMR spectra were recorded
in CDCl3 solutions with a Brucker Avance DPX FT-NMR 250 MHz
instrument. The residual CHCl3 in conventional 99.8 atom% CDCl3
Our ongoing research on the development of new application
of tetra-n-butylammonium Oxone® (n-Bu4NHSO5, TBAOX) in the
∗
Corresponding author. Tel.: +98 561 2502516; fax: +98 561 2502515.
E-mail address: rrezaeifard@birjand.ac.ir (A. Rezaeifard).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2012.02.003

142
A. Rezaeifard et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 141–147
100
100
Oxone®
Oxone® + TBAHSO4
N
73
N
N
N
N
80
60
40
20
0
TBAOX
Cu
N
N
O
37
N
21
21
20
19
30 nm
13
8
R
R
n-Bu4NHSO5, Water,
70 oC
30
90
240
Time/min
O
Fig. 1. The comparison of oxidative activity of Oxone®, Oxone®/TBAHSO4 and
TBAOX in the epoxidation of cyclooctene catalyzed by CuPc in water at 25 ◦C.
Scheme 1. Oxygenation of hydrocarbons using TBAOX catalyzed by CuPc nanopar-
ticles in water.
(0.4 mmol) in the presence of a few amount of cheap commercially
available CuPc (0.5 mol%) in bidistilled water at 25 ◦C under air. Only
21% cyclooctene oxide was achieved after 4 h. When an equimolar
amount of TBAHSO4 was accompanied with Oxone®, the oxidation
rate enhanced and 73% epoxide was obtained at the same time. It
should be noted that pure KHSO5·H2O in the absence (20%/90 min)
and in the presence of TBAHSO4 (17%/90 min) did not improve the
olefin conversion. Nevertheless, using TBAOX (0.07 g) the reaction
proceeded smoothly and gave 33 and 100% epoxide yield after 1 and
4 h, respectively (Fig. 1). To increase the conversion rate, different
factors that may affect the cyclooctene oxidation were probed. The
use of different amount of TBAOX in the oxidation of cyclooctene
demonstrated that the reaction required 2 equivalent of oxidant
for full conversion of substrate at 4 h (33 and 51% epoxide yield by
using 0.5 and 1 equivalent of TBAOX, respectively). However, the
reaction rate did not changed by using more amount of oxidant.
Also the same conversions and epoxide yields were observed by
using standard buffered solutions, water-soluble sulfonated cat-
alyst (CuPcS), common nitrogen donors (imidazole and pyridine)
and also sodium dodecyl sulfate at CMC condition (0.008 mol/L).
Next, the effect of catalyst content has been examined. The
system displayed a low catalyst loading of 0.5 mol% for complete
conversion of cyclooctene (38 and 60% epoxide yield by using 0.1
and 0.2 mol% of catalyst, respectively). Nevertheless, an increase in
the catalyst content up to 5 mol% did not enhance noticeably the
reaction rate. In addition, compared with other common Pc com-
plexes, CuPc was proven to have the higher catalytic activity in
the oxidation of olefins. When the catalyst was replaced to FePc
and CoPc with the same catalytic amount, cyclooctene oxide was
achieved in 71 and 86%, respectively within 4 h.
gives a signal at ı = 7.26 ppm, which was used for calibration of
the chemical shift scale. Mass spectra were recorded on a Shi-
madzu GC–MS-QP5050A. MPcs were synthesized according to the
literature [16]. The freshly prepared n-Bu4NHSO5 [5] was a much
stronger oxidant than commercially available samples.
2.2. General procedure for epoxidation of olefin
To a mixture of 110 mg of cyclooctene (1 mmol) and 2.8 mg
of CuPc (0.005 mmol) in 2 ml bidistilled water was added 0.7 g
(2 mmol) of freshly prepared TBAOX. The reaction mixture was
stirred under air at 70 ◦C for 15 min which was monitored by GC
and TLC. After completion of the reaction, the mixture was washed
with ethyl acetate (3 × 2 ml), and the organic phase was separated
and evaporated. If necessary, further purification was performed by
silica chromatography eluted with n-hexane/ethyl acetate (10:1).
2.3. General procedure for oxygenation of saturated
hydrocarbons
To a mixture of 106 mg of ethylbenzene (1 mmol) and 2.8 mg
of CuPc (0.005 mmol) in 2 ml bidistilled water was added 0.7 g
(2 mmol) of freshly prepared TBAOX (1.4 g for others). The reac-
tion mixture was stirred under air at 70 ◦C for 100 min, which
was monitored by GC and TLC. After completion of the reaction,
the mixture was washed with ethyl acetate (3 × 2 ml), and the
organic phase was separated and evaporated. If necessary, further
purification was performed by silica chromatography eluted with
n-hexane/ethyl acetate (10:3).
Finally, our investigation showed that the catalytic activity of
CuPc enhanced significantly with increasing reaction temperature
(Fig. 2). Full conversion of cyclooctene was achieved within 15 min
2.4. Recycling procedure
After completion of the epoxidation of cyclooctene, the product
was isolated by ethyl acetate (3 × 2 ml) and the reaction mixture
was centrifuged and the solid catalyst was separated, washed with
ethyl acetate (3 ml), dried and reused for the similar reaction. The
aqueous phase was lyophilized to obtain TBAHSO4 which can be
reused in the preparation of TBAOX.
100
100
80
60
40
20
0
73
59
53
33
3. Results and discussion
3.1. Preliminary studies
25
40
50
60
70
Temperature/ºC
Knowing that Oxone® has not ability to trigger the epoxidation
reaction in blank condition, preliminary catalytic experiments were
addressed to the oxidation of cyclooctene (0.2 mmol) with Oxone®
Fig. 2. The influence of temperature on the epoxidation of cyclooctene using TBAOX
catalyzed by CuPc in water after 15 min.

A. Rezaeifard et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 141–147
143
Table 1
The effect of different oxidants in the oxidation of cyclooctene catalyzed by CuPc in
water.a
Oxidant
Cyclooctene oxide%b
25 ◦
C
70 ◦
C
H2O2
UHP
TBHP
NaIO4
0
2
1.5
0
0
35
36
0
n-Bu4NIO4
Oxone®
TBAOX
21
11
33
50
13
100
a
The reactions were run under air for 1 h by molar ratio of 200:400:1 for
cyclooctene/oxidant/catalyst.
b
GC yield.
at 70 ◦C. Under these conditions cyclooctene oxide was secured in
95% yield after a simple extraction with ethyl acetate.
The effect of other common oxidants including H2O2, UHP, t-
BuOOH, NaIO4 and n-Bu4NIO4 was examined for epoxidation of
cyclooctene under the catalytic influence of CuPc in water and
found them inactive or less reactive than that of TBAOX at different
temperatures (Table 1).
Fig. 3. Photographs of 2.8 mg of CuPc in 2 ml bidistilled water at 70 ◦C (A), after
addition of TBAHSO4 and Oxone® (B), after addition of TBAOX (C), sonicated C (D).
amounts of oxidant and gave the related ketones in moderate to
high yields at the same time (48, 79% respectively).
It seems that the attachment of TBAOX to the metal centre
giving a six coordinate adduct [PcCu
O OHSO3] enhances the elec-
3.2. Catalytic oxidation of olefins and saturated hydrocarbons
trophilicity of Cu-coordinated oxygen atom of the oxidant. Easy
oxidation of sulfides to sulfones was achieved by using this species
[12,15]. Nevertheless, oxidation of alcohols [15], olefins and satu-
rated hydrocarbons required higher temperature [17]. Presumably
a high valent [Cu O]+ active species should be involved under this
condition. [17,18] Epoxidation of olefins and oxidation of secondary
To establish the general applicability of the method, various
olefins were subjected to the oxidation protocol using TBAOX under
the catalytic influence of the CuPc at 70 ◦C (Table 2). As summarized
in Table 2, different alkenes are generally excellent substrates for
this catalyst (entries 1–13). It led to complete conversion of cyclo-
hexenes, cyclooctene and norbornene with the formation of the
corresponding epoxides as sole products (entries 1–4). The epoxi-
dation of the least reactive 1-octene as a terminal olefin proceeded
with moderate yield and excellent selectivity (entry 5). However,
the selectivity tends to decrease when the terminal olefin becomes
conjugatedwith phenyl group so that the lower epoxide yields were
obtained for styrenes (entries 6–8). Nevertheless, excellent epoxide
selectivities were observed for ␣-methylstyrne and indene (entries
9 and 10).
C
H bonds accomplished efficiently in the presence of this inter-
mediate. Since ketones were produced as main products in the
oxidation of saturated hydrocarbons, secondary C H bonds are
more sensitive to this oxidation system. Accordingly, secondary
alcohols oxidized selectively in the presence of C C double bond.
Nevertheless, oxidation of primary C H bonds in both benzylic and
aliphatic alcohols proceeded sluggishly under this condition [15].
3.3. Reactivity and stability of catalyst
The chemoselectivity of the procedure was notable. While, the
primary alcohols containing C C double bonds (allylic and homoal-
lylic alcohols) oxidized completely to the corresponding epoxides
under the influence of this catalytic system (entries 11 and 12),
secondary one converted to the related ␣, ␤-unsaturated ketone as
sole product (entry 13).
These results were further supported by performing some com-
petitive reactions between cyclooctene and both benzyl alcohol
as an active primary alcohol, and also less reactive cyclohexanol
(Table 3). Inspection of the results in Table 3 indicates excellent
chemoselectivity for CuPc in the olefin epoxidation rather than
oxidation of primary hydroxyl group (entry 1, >98% cyclooctene
oxide vs. 1.5% benzaldehyde). However, cyclohexanone was formed
as sole product in the oxidation of mixture of cyclohexanol and
cyclooctene (entry 2). It is worthy to mention that lower epox-
idation selectivity was observed for FePc and CoPc than that of
CuPc in the oxidation of cyclooctene in association with benzyl
alcohol (entries 3 and 4; 88 and 80% epoxide selectivity, respec-
tively). These results once again confirm the superiority of CuPc as
oxidation catalyst in the present system.
The high/excellent yields of oxidation products obtained using
this novel oxidation method in desired times display the high cat-
alytic activity and relative stability of CuPc in association with
aqueous solution of TBAOX. It was further supported by the
impressive turnover frequency (TOF) obtained for CuPc in the
oxidation of cyclooctene (8900/h) and tetraline (5100/h) using
10,000:20,000:1 molar ratio for substrate/TBAOX/catalyst indicat-
ing well the high efficiency and stability of the present catalytic
system.
The effective dispersity of CuPc catalyst in aqueous solution of
TBAOX seems to be the most important factor to affect the reac-
tion rate. We studied dispersing extent (D.E. % = (1 − T) × 100) of
title pigment in water medium (Fig. 3). Without TBAOX virtually
CuPc particles were so unstable and hydrophobic, not wetted by
water, that they could not be dispersed at all in water at 70 ◦C even
with extensive sonication (Fig. 3A). The addition of TBAHSO4 in the
absence and in the presence of Oxone® did not improve noticeably
the D. E. (50%; Fig. 3B). Nevertheless, the effect of adding of TBAOX
on the dispersibility was quite strong as demonstrated in Fig. 3C
(68%). As expected, the catalyst agglomerates break-up during the
sonication process improved the D. E. (87%; Fig. 3D).
Then, we applied this oxidation system in the oxygenation of
saturated C H bonds. It was observed that complete conversion of
ethyl benzene took 100 min and gave acetophenone as sole prod-
uct (96% isolated yield) under the same experimental conditions
used for olefin epoxidation (200:400:1, for substrate/TBAOX/CuPc,
70 ◦C). Nevertheless, oxidation of tetralin and indan required higher
Transmission electron microscopy (TEM) analysis confirmed
the strong dispersing effect of TBAOX on CuPc particles. Fig. 4A
shows that CuPc particles are single crystalline with flat edges.
Their shapes are polyhedral and look like elongated cylinders

144
A. Rezaeifard et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 141–147
Table 2
Oxygenation of hydrocarbons using TBAOX catalyzed by CuPc in water.a
Entry
Substrate
Yield%b
Product
1H NMR ı(ppm)
Selectivity %b
O
O
1
2
94
3.1c
2.9c
100
100
91
95
O
3
2.9c
100
O
4
5
96
65
2.9c
100
100
2.5–2.9c
O
O
6
7
63
86
2.7–3.8c
2.7–3.6c
68d
92d
O
Cl
Cl
O
O
2.7–3.7c
81d
Cl
Cl
8
78
9
96
92
2.8–3c
100
100
O
10
4.1–4.3c
OH
OH
2.7c
2.5c
100
100
OH
OH
O
11
12
90
85
O
O
OH
13
94
2–2.4, 6, 7.1
100
O
14
15
96
79
2.6, 7.3–7.6, 7.9
7.4–7.7, 3.1, 2.7
100
100
O

A. Rezaeifard et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 141–147
145
Table 2 (Continued)
Entry
Substrate
Yield%b
Product
1H NMR ı(ppm)
Selectivity %b
O
16
48
8
8, 7.2–7.5 2.6–2.9, 2.1
1.2–1.9, 2.4
100
100
O
17
a
The oxidation of olefins were run under air at 70 ◦C for 15 min (entries 1–13) and saturated hydrocarbons for 100 min (entries 14–17). The molar ratio of sub-
strate:TBAOX:catalyst was 200:400:1 except for entries 15–17 which was 200:800:1.
b
Yields of isolated products. Selectivities were determined by GC and 1H NMR.
ı(ppm) of C H oxiran ring.
The remainders are related benzaldehydes; ıCOH are 10.1, 9.98 and 9.96 ppm for entries 6–8, respectively.
c
d
Table 3
The competitive reactions between olefin and alcohols using TBAOX catalyzed by MPc in water.a
Entry
Catalyst
Substrates
Products (yield%)b
1
2
3
4
CuPc
CuPc
FePc
CoPc
Cyclooctene + benzyl alcohol
Cyclooctene + cyclohexanol
Cyclooctene + benzyl alcohol
Cyclooctene + benzyl alcohol
Cycloocten oxide (>98), benzaldehyde (1.5)
Cycloocten oxide (0), cyclohexanone (100)
Cycloocten oxide (77), benzaldehyde (10)
Cycloocten oxide (80), benzaldehyde (20)
a
The reactions were run under air at 70 ◦C for 15 min and the molar ratio of olefin:alcohol:TBAOX:catalyst was 200:200:400:1.
GC yields.
b
Fig. 4. Plausible mechanism for formation of CuPc nanoparticles in aqueous solution of TBAOX. TEM images represent: pencil-like morphology of CuPc in water (A), and
spherical nanoparticles after addition of TBAOX (B) and (C).

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A. Rezaeifard et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 141–147
Fig. 5. Recycling of the catalytic system for the epoxidation of cyclooctene in water.
Fig. 7. The IR spectrum of the fresh CuPc complex (A) and after 7 times reuses in
aqueous oxidation of cyclooctene (B).
(pencil-like morphology) with diameters of about 50–70 nm and
lengths of 80–250 nm. By addition of TBAOX this morphology col-
lapsed and spherical particles were obtained with size ranging
between 20 and 50 nm (Fig. 4B and C). The good dipersibility of
catalyst treated with TBAOX is due largely to the fact that TBAOX
as a quaternary salt acts as a stabilizer [19,20] as well as oxidant,
so that n-Bu4N chains adhering to the pigment surface, prevent
catalyst particles from agglomerating (Fig. 4) [21].
To examine the effect of D.E. on the catalytic activity of CuPc,
oxidation of norbornene under different conditions was evaluated
using aqueous solution of TBAOX at 60 ◦C. With magnetic stirring,
a moderate yield of norbornene oxide (59%) was observed within
15 min. In second experiment aqueous mixture of CuPc was ini-
tially sonicated for 15 min. After that TBAOX was added and then
the reaction mixture was stirred magnetically, which led to 68%
yield of epoxide at the same time. When ultrasound was used as
the stirring method, a significant increase in the epoxide yield was
observed (92%). However, thorough mixing of the reactants and
the production of hot spots should also be taken into account for
enhancing reaction rate by ultrasonic irradiation [22].
These promising results encouraged us to evaluate the reusabil-
ity of the catalyst. After isolation of water-insoluble products by
using ethyl acetate as an environmentally benign solvent, the solid
catalyst was separated from the aqueous solution by centrifuging
and was reused for the subsequent reaction under the similar reac-
tion conditions. The averaged isolated yield of cyclooctene oxide
for seven runs was 93.8%, demonstrating well the high reusabil-
ity of the catalyst in this oxidation system (Fig. 5). The stability of
CuPc in this oxidation system was also established by spectropho-
tometry. It was found that the mediation of CuPc in the oxidation
of cyclooctene with aqueous solution of TBAOX does not change
noticeably the electronic absorption spectra of catalyst after seven
runs (Fig. 6). In addition, the IR spectra were identical for the fresh
and reused catalysts demonstrating the stability of the Pc structure
under the real catalytic conditions (Fig. 7). Moreover, the reduced
form of oxidant’s (TBAHSO4) was separated by lyophilizing of
aqueous phase and reused in the preparation of TBAOX. Therefore,
from the stand point of greener chemical processes, the use of CuPc
as catalyst in combination with aqueous solution of TBAOX do not
lead to three major sources of waste: organic solvents, catalysts and
harmful by-products. These advantages for this high yielding oxida-
tion method along with the low cost for preparation of CuPc offered
ready scalability. For example, the use of a semi scale-up procedure
(25 mmol) for epoxidation of cyclooctene and norbornene in the
presence of CuPc led to isolation of the related epoxides in 92 and
95% yields, respectively.
4. Conclusion
In conclusion, hydrophobic CuPc complex dispersed in aque-
ous solution of TBAOX which yielded particles with average size of
30 nm, catalyzed efficiently epoxidation of olefins and oxygenation
of saturated hydrocarbons to ketones in good/excellent yields and
selectivities. No surfactants, additives, toxic reagents or solvents
and by-product were involved and no laborious purifications were
necessary. These conditions along with the use of water as a stan-
dard “green” solvent as well as easy and safe work-up procedure
and reusability of catalyst and by-product are cost effective, envi-
ronmentally benign and posses high generality which makes title
methodology suitable for industrial goal.
Acknowledgements
Support for this work by Research Council of University of Bir-
jand is highly appreciated and we also thank the referees for their
valuable comments.
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