A novel strategy for clean and selective oxygenation of hydrocarbons with n-Bu4NHSO5 in neat water catalyzed by recyclable water-insoluble iron (III) tetraphenylporphyrins

Article abstract of DOI:10.1016/j.catcom.2011.01.013

A novel heterogeneous method for efficient oxygenation of olefins to epoxides and saturated hydrocarbons to the related ketones using tetrabutylammonium peroxomonosulfate (n-Bu₄NHSO₅) in neat water catalyzed by Fe(TPP)Cl and Fe(TDCPP)Cl complexes as water-insoluble catalysts has been developed. The oxidation system proceeds well in the absence of organic co-solvents and surfactants. The electron-deficient Fe(TDCPP)Cl catalyst could easily be recycled and reused without loss of activity and the oxidant's by-product (n-Bu₄NHSO₄) could also be recycled.

Full text of DOI:10.1016/j.catcom.2011.01.013

Catalysis Communications 12 (2011) 761–765
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
A novel strategy for clean and selective oxygenation of hydrocarbons with
n-Bu NHSO in neat water catalyzed by recyclable water-insoluble
4
5
iron (III) tetraphenylporphyrins
Abdolreza Rezaeifard ⁎, Maasoumeh Jafarpour ⁎, Atena Naeimi, Samira Kaafi
Catalysis Research Laboratory, Department of Chemistry, Faculty of Science, University of Birjand, Birjand, 97179-414, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel heterogeneous method for efficient oxygenation of olefins to epoxides and saturated hydrocarbons to
Received 19 September 2010
Received in revised form 10 January 2011
Accepted 13 January 2011
4 5
the related ketones using tetrabutylammonium peroxomonosulfate (n-Bu NHSO ) in neat water catalyzed by
Fe(TPP)Cl and Fe(TDCPP)Cl complexes as water-insoluble catalysts has been developed. The oxidation system
proceeds well in the absence of organic co-solvents and surfactants. The electron-deficient Fe(TDCPP)Cl
catalyst could easily be recycled and reused without loss of activity and the oxidant's by-product
Available online 21 January 2011
4 4
(n-Bu NHSO ) could also be recycled.
Keywords:
©
2011 Elsevier B.V. All rights reserved.
Porphyrin
Peroxomonosulfate
Oxygenation
Hydrocarbons
Water
1
. Introduction
The use of toxic and volatile organic solvents in many catalytic
conditions with tedious work-up procedure. For example, the
synthesis of tetrasodic sulfonated tetraphenylporphyrin (Na TSPP),
4
which is a common and in demand water-soluble porphyrin, required
corrosive sulfuric acid under reflux conditions and many steps for
work-up and purification [15]. Moreover, the separation of water-
soluble catalyst from the aqueous phase is a time consuming process
making it out of recycled materials.
systems mediated by metalloporphyrins mimicking cytochrome
P-450 enzymes [1] has reduced considerably the importance of the
process from both biologically and environmentally points of view.
Moreover, it has been found that reactions in water can facilitate
access to different reactivity and selectivity patterns compared with
those observed in common organic solvents due to its unique physical
and chemical properties [2–6]. In this regard, the use of water as a
reaction solvent has attracted great attention in the recent past and
has become an active area of research in green chemistry [7–10].
Porphyrin complexes are insoluble in water and some requirements
should be provided to surmount this problem. For example, the
surface-active compounds to form micelles or vesicular structures in
aqueous reaction media were used [11]. However, this strategy suffers
from some limitation such as performing the reactions in critical
micellization concentration (CMC) and particularly in the absence of
salts [12]. As a consequence, water-soluble porphyrins as biomimetic
catalysts for oxidation of organic compounds in aqueous media have
been developed [13,14]. Nevertheless, in most cases, to promote the
yield of oxidation products and conversion rates, organic co-solvents
have been used along with a phase transfer agent [13,14]. In addition,
the synthesis of water-soluble porphyrins required harsh reaction
5 4 2 4
The aqueous solution of Oxone® (2KHSO .KHSO .K SO ) as a
cheap and safe oxygen source at neutral pH oxidized olefins to
epoxides but in variable yields. At lower pH, mixtures of epoxides and
diols are obtained [16]. A homogeneous oxidation of water-soluble
organic molecules using Oxone® in aqueous solution in the absence
and in the presence of a water-soluble manganese porphyrin complex
under controlled pH conditions has also been reported [17]. Tetra-
4 5
butylammonium peroxomonosulfate (Bu NHSO , TBAOX), which is
an organic salt of Oxone® has been introduced for using in anhydrous
conditions without recourse to a buffered two-phase system [18]. The
compound is commercially available and also can be prepared easily
by simple mixing of Oxone® and tetrabutylammonium hydrogensul-
4
fate (TBAHSO ) [18–20]. It has been employed in limited oxidation
reactions under non-catalytic conditions in different solvents [21–24].
Very recently, efficient oxidation of alcohols using TBAOX in the
presence of ionic liquid immobilized TEMPO in ionic liquid [bmim]
[PF6] has also been reported [25].
Since the initial promising report on the alkene epoxidation and
alkane hydroxylation with TBAOX catalyzed by manganese
⁎
Corresponding authors. Tel.: +98 561 2502516; fax: +98 561 2502515.
E-mail addresses: rrezaeifard@gmail.com, rrezaeifard@birjand.ac.ir (A. Rezaeifard),
(
III) tetraphenylporphyrin [Mn(TPP)OAc] in dichloromethane [26],
mjafarpour@birjand.ac.ir (M. Jafarpour).
various organic substrates have been successfully subjected to
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.01.013

762
A. Rezaeifard et al. / Catalysis Communications 12 (2011) 761–765
N
N
N
Fe
O
N
R
R
n-Bu NHSO , Water,
4
5
o
7
0-80 C
O
Scheme 1. Oxygenation of hydrocarbons using TBAOX catalyzed by Fe(TPP)Cl in neat
Fig. 1. The comparison of oxidative activity of Oxone®, Oxone®/TBAHSO
4
and TBAOX in
water.
the epoxidation of cyclooctene catalyzed by Fe(TPP)Cl in water at 25 °C.
oxidation using this organic-soluble oxygen source under catalytic
conditions [27–31]. However, iron-porphyrins virtually showed no
catalytic activity in this oxidation system in organic solvents. Our
attempts to overcome this problem led to an innovative strategy for
efficient and selective oxygenation of olefins to epoxides and
saturated hydrocarbons to the related ketones using aqueous solution
of TBAOX catalyzed by water-insoluble Fe(III) tetraphenylporphyrin
complexes in the absence of any organic co-solvents and surfactants
under heterogeneous conditions (Scheme 1). The catalyst and the
was centrifuged and the solid catalyst was separated, washed with
petroleum ether (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.
3
. Results and Discussions
3.1. Preliminary Studies
reduction product n-Bu
were easily recovered and reused in the procedure.
4 4 4
NHSO (TBAHSO ) from the oxidant TBAOX
The oxidation of cyclooctene using Oxone® in water which did not
proceed in the absence of catalyst was used as a model reaction.
Preliminary catalytic experiments were addressed to the oxidation of
cyclooctene (0.1 mmol) with Oxone® (0.2 mmol) in the presence of
catalytic amount of [Fe(TPP)Cl] (1 mol%) in neat water at 25 °C under
air which led to formation of cyclooctene oxide in 22% yield after 4 h
2
. Experimental
2
.1. General Remarks
(
Fig. 1). When an equimolar amount of TBAHSO4 was accompanied
Purity determinations of the products were accomplished by GC
with Oxone®, the oxidation rate enhanced and 66% epoxide was
obtained after 4 h (Fig. 1). However, the reaction proceeded smoothly
and gave optimal yield using TBAOX as oxidant (0.07 g) in room
temperature at the same time (100% after 4 h, Fig. 1). It was also
observed that complete conversion of cyclooctene required 1 mol% of
the catalyst (Fig. 1). For example, performing the reaction by using
on a Shimadzu GC-16A instrument using a 25-m CBP1-S25 (0.32 mm
ID, 0.5 μm 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 CDCl
solutions with a Brucker Avance DPX FT-NMR 250 MHz instrument.
The residual CHCl in conventional 99.8 at.% CDCl gives a signal at
3
3
3
0
5
.5 mol% of the [Fe(TPP)Cl] catalyst, gave 69% cyclooctene oxide after
h. However, an increase in the catalyst concentration up to 5 mol%
δ=7.26 ppm, which was used for calibration of the chemical shift
scale. Mass spectra were recorded on a Shimadzu GC-MS-QP5050A.
did not affect noticeably the reaction rate. It should be noted that the
addition of imidazole (58%/2 h), pyridine (63%/2 h) and ammonium
acetate (60%/2 h) as common additives, the use of micellar soultions
of sodium dodecyl sulfate (63%/2 h) and Triton X-100 (59%/2 h) at
their CMC conditions and also the sulfonation of porphyrin (68%/2 h),
The free base porphyrins: TPPH
purified by methods reported previously. Iron complexes were
obtained using the FeCl .4H O according to the procedure of Alder
et al. [34]. The freshly prepared Bu NHSO [20] was a much stronger
oxidant than commercially available samples.
2
[32], TDCPP [33] were prepared and
2
2
4
5
[15] did not improve the conversion rate in this oxidation method.
Also, performing the reactions under controlled pH conditions did not
2
.2. General Procedure for Oxygenation of Hydrocarbons using TBAOX
Catalyzed by Fe(TPP)Cl in Water
100
To a mixture of hydrocarbon (1 mmol) and Fe(TPP)Cl (7 mg,
0
.01 mmol) or Fe(TDCPP)Cl (9.8 mg, 0.01 mmol) in neutral water
8
6
4
0
0
0
(
2 ml) was added freshly prepared TBAOX (0.7 g). The reaction
mixture was stirred under air at 70 °C for olefins (15 min) and 80 °C
for saturated hydrocarbons (60 min), which was monitored by GC.
After completion of the reaction, the mixture was washed with
petroleum ether (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).
20
0
25
40
50
60
70
2
.3. Recycling Procedure
Temperature ( C)
After completion of the epoxidation of cyclooctene, the product
Fig. 2. The influence of temperature on the epoxidation of cyclooctene using TBAOX
was isolated by petroleum ether (3×2 ml) and the reaction mixture
catalyzed by Fe(TPP)Cl in water after 15 min.

A. Rezaeifard et al. / Catalysis Communications 12 (2011) 761–765
763
affect noticeably on the rate and yield of epoxidation (65%, 62%, 71%,
manganese (II) salts (23% epoxide in the oxidation of cyclooctene
and 10% benzaldehyde in the oxidation of styrene). The effect of other
6
9
2% cyclooctene oxide were obtained after 2 h at 25 °C at pH=2, 4, 7,
, respectively).
2 2 4
common oxidants including H O (and also UHP), t-BuOOH, NaIO
Then, the influence of temperature on the reaction rate was
and n-Bu NIO was examined for epoxidation of cyclooctene under
4
4
examined. It was observed that, an increase in the temperature in this
oxidation system, promoted remarkably the effectiveness of the
catalytic system and full conversion of cyclooctene was achieved
within 15 min at 70 °C (Fig. 2). It should be noted that blank
experiments for oxidation of olefins using TBAOX at 70 °C gave no/
very low yields of the related epoxide (0 and 12% after 60 min for
oxidation of styrene and cyclooctene respectively). Also simple iron
salts virtually showed no catalytic activity in this oxidation system,
nevertheless, a very low oxidation activity was observed for
the catalytic influence of Fe(TPP)Cl in water and found them
completely inactive at different temperatures.
It is noteworthy to mention that this oxidation system proceeds
also well in the presence of Mn(TPP)OAc with no need to any
additives (95% cyclooctene oxide was achieved after 15 min).
Nevertheless, to explore different factors that may affect the reactivity
and selectivity of oxygenation of hydrocarbons in neat water in this
oxidation system, we decided to continue this study by using iron-
porphyrins having no catalytic activity in organic solvents.
Table 1
a
Oxygenation of hydrocarbons using TBAOX catalyzed by Fe(III)-porphyrins in water.
Yield%b
96
Product
1
H NMR δ (ppm)
Selectivity %b
100
Entry
1
Substrate
3.1c
2
3
95
98
2.9c
2.9c
100
100
4
97
2.9c
100
5
6
86 (94)
89 (97)
4.1–4.3c
2.5–2.9c
100(100)
100(100)
d
7
8
95
97
2.7, 3.1, 3.8c
47 (100)
2.8–3c
46 (100)
e
9
24 (39)
1.2–1.9, 2.4
100 (100)
f
1
0
1
81 (97)
69 (81)
2.6, 7.3–7.6, 7.9
7.4–7.7, 3.1, 2.7
N98 (100)
1
100 (100)
f
12
58 (75)
8, 7.2–7.5 2.6–2.9, 2.1
93 (100)
a
The oxidation of olefins were run under air at 70 °C for 15 min (entries 1–8) and for saturated hydrocarbons at 80 °C for 60 min (entries 11–14). The molar ratio of substrate/
TBAOX/catalyst was 100:200:1.
b
Yields of isolated products in the presence of Fe(TPP)Cl. Selectivities were determined by GC and 1H NMR based on the starting substrate. The numbers in parentheses are
isolated yields and selectivities in the presence of Fe(TDCPP)Cl.
c
δ
(ppm) of C―H oxiran ring.
d
e
f
The remainder is benzaldehyde.
The remainder is acetophenone.
The remainder is the corresponding alcohol.

7
64
A. Rezaeifard et al. / Catalysis Communications 12 (2011) 761–765
Fe(TDCPP)Cl
Fe(TPP)Cl
3
.2. Catalytic Oxygenation of Unsaturated and Saturated Hydrocarbons
in Neat Water
98
98
98
97
96
100
92
88
84
85
To establish the general applicability of the method, various olefins
were subjected to the oxidation protocol using TBAOX under the
catalytic influence of the Fe(TPP)Cl at 70 °C (Table 1). As summarized
in Table 1, different alkenes are generally excellent substrates for this
catalyst (entries 1–8). It led to complete conversion of cyclohexenes,
cyclooctene and norbornene with the formation of the corresponding
epoxides as sole products (entries 1–4). The conversion and
selectivity of indene were 86 and 100%, respectively (entry 5). The
epoxidation of the least reactive 1-octene as a terminal olefin proceed
with excellent yield and selectivity (entry 6). However, the lower
epoxide selectivities were obtained for electron-poor styrene and α-
methylstyrne with benzaldehyde and acetophenone formed as the
side products (entries 7, 8). Then, we performed this oxidation system
under the catalytic influence of hindered and electron-deficient Fe
80
60
40
20
0
1
2
3
4
5
Reaction Cycles
Fig. 3. Recycling of the catalytic system for the epoxidation of cyclooctene in water.
4. Conclusion
(
TDCPP)Cl (TDCPP=meso-tetradichlorophenylporphyrin), and found
it completely selective to the epoxide formation for all substrates. It
should be noted that, despite the decreasing in the pH during the
reaction (~2), no trace of diol was observed in the reaction mixture.
Then, we applied this oxidation system in the oxygenation of
saturated C-H bonds. Oxygenation of ethyl benzene under the same
experimental conditions used for olefin epoxidation in the presence of
Fe(TPP)Cl at 70 °C gave acetophenone as main product in low yield
In conclusion, water-insoluble Fe (III) and Mn(III) tetraphenylpor-
phyrin complexes are excellent catalysts for effective activation of
TBAOX in water in the epoxidation of olefins and oxygenation of
saturated hydrocarbons to ketones in good/excellent yields and
selectivities with no need to organic co-solvents, surfactants and
nitrogenous bases. The employment of neat water as a standard
‘green’ solvent in this high yielding oxidation method as well as easy
and safe work-up procedure and reusability of catalyst and by-
product providing ready scalability, makes it more attractive for
practical goal. Further works using other complexes and in the
oxidation of different substrates are currently under investigation.
(
20%) after 1 h. The increasing the catalyst and oxidant concentrations
did not noticeably affect the yield of oxidation product (b40%).
However, an increase in the temperature up to 80 °C enhanced
remarkably the yield of acetophenone (81%) at the same conditions
(
1 mol% catalyst, 0.07 g TBAOX) with excellent selectivity (N98%).
Under these conditions, different saturated hydrocarbons oxidized with
low/high yields (24–81%) with the formation of the corresponding
ketones as main products (N93%). However, higher yields (39–97%) and
excellent selectivity (100%) of carbonyl compounds were achieved in
the presence of Fe(TDCPP)Cl in the oxidation of saturated hydrocarbons.
The high/excellent yields of oxidation products in particularly in
the oxidation of the less reactive substrates such as 1-octene (Table 1,
entry 6) and saturated hydrocarbons (Table 1, entries 9–12) obtained
using this novel oxidation method in desired times displays the high
catalytic activity and relative stability of Fe-porphyrin complexes in
association with aqueous solution of TBAOX. It was further supported
by the impressive turnover numbers obtained for simple Fe(TPP)Cl in
the oxidation of cyclooctene (9600/24 h) and tetraline (5400/24 h)
using 10000:20000:1 molar ratio for substrate/TBAOX/catalyst
indicating well the high efficiency of the present catalytic system.
We have also studied the recycling of the catalyst. For this purpose,
cyclooctene as a model compound was oxidized with TBAOX in the
presence of 1 mol% of Fe-porphyrin catalyst in 70 °C in water (Fig. 3).
After completion of the reaction, the solid catalyst was separated by
centrifuging and was reused for the subsequent reaction under the
similar reaction conditions. It was found that if electron-deficient Fe
Acknowledgements
Support for this work by Research Council of University of Birjand
is highly appreciated.
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