Fe3O4 nanoparticles as a new efficient co-catalyst for Pd(ii) in Wacker oxidation of styrene using H2O2 as an oxidant

Article abstract of DOI:10.1039/c5ra08710d

A new highly selective and environment-friendly Wacker oxidation process employing PdCl₂/Fe₃O₄ nanoparticles in H₂O at 100°C using H₂O₂ as an oxidant has been developed. This approach has some advantages such as copper free reaction conditions, green solvent, high yield, excellent selectivity and green oxidant.

Full text of DOI:10.1039/c5ra08710d

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Fe O nanoparticles as a new efficient co-catalyst for Pd(II) in
3
4
Wacker oxidation of styrene using H O as an oxidant
2
2
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Sajjad Keshipour* and Selda Nadervand
A new highly selective and environment-friendly Wacker oxidation the Wacker oxidation has been frequently used in many synthetic
4
process employing PdCl
using H as an oxidant has been developed. This approach has oxidation of a variety of substrates in various reaction conditions.
some advantages such as copper free reaction conditions, green The original conditions required the reaction to be carried out in
2 3 4 2
/Fe O nanoparticles in H O at 100 °C plans. The reaction has been investigated for the efficient
2
O
2
solvent, high yield, excellent selectivity and green oxidant.
water containing HCl, and showed some limitations such as a low
reaction rate and poor selectivity due to formation of unwanted
5
Acetophenone as a simplest aromatic ketone is released from a
number of both human-made as well as natural sources. Recently,
the applications of this compound have been extended into various
research fields, such as: 1) in perfumery to impart an orange-
blossom-like odor; 2) catalyst for the polymerization of olefins; 3) in
organic syntheses especially as a photosensitizer; 4) specialty
solvent for plastics and resins; 5) chemical intermediate for the
odorant, ethyl methyl phenylglycidate, the riot control agent, 2-
chloroacetophenone, 2-bromoacetophenone for dyes, 3-
nitroacetophenone, synthesis of pharmaceuticals; 6) flavoring agent
in non-alcoholic beverages, ice cream, candy, baked goods, gelatins
and puddings, chewing gum, in tobacco; 7) fragrance ingredient in
soaps, detergents, creams, lotions, perfumes; 8) solvent for
synthesis of pharmaceuticals, rubber, chemicals, dyestuffs and
side product(s). Formation of chlorinated compounds due to
rearrangement followed by nucleophilic addition of the chloride
4
anion and corrosion of the reactor are other drawbacks. To
overcome these limitations, many efforts have been focused on
Wacker oxidation to discovery of better catalysts, ligands, co-
6
7
catalyst conditions, new solvents including ionic liquids, new
8
oxidant systems using molecular oxygen, and copper free reaction
9
-11
conditions.
Since Pd(II) was reduced to Pd(0) during the Wacker reaction,
species such as Cu(II) and Fe(III) assisted to the reoxidation of Pd(0)
to Pd(II) to prevent the quenching of the oxidation process. It is
believed that in chloride-free aqueous media, neither Cu(II) nor
1
2
Fe(III) salts are effective in reoxidizing of Pd(0).
In continuation of our efforts to development of new catalytic
1
1
3
corrosion inhibitors. Currently acetophenone mainly comes as a
system, herein a new and efficient strategy was introduced for the
oxidation of styrene to acetophenone by PdCl /Fe
nanoparticles (Fe NPs)/dimethylacetamide (DMA) catalytic
system with H as a green oxidant in H O as a green solvent
Scheme 1). This methodology is extremely simple, and the
oxidation proceeds efficiently without any by-product. Interestingly,
the addition of Fe NPs instead of Cu(II) increases the catalytic
by-product of cumene oxidation to cumene hydroperoxide for the
synthesis of phenol-acetone. The other methods of acetophenone
manufacturing are: oxidation of ethylbenzene, acetylation of
benzene with acetylchloride in presence of aluminum chloride,
catalytically from acetic and benzoic acids, from benzene and acetic
anhydride, by-product in the Hock phenol synthesis and Wacker
a
2
3 4
O
3 4
O
2
O
2
2
(
3
O
4
2
oxidation of styrene.
activity of the palladium and directed the reaction conditions to
green chemistry.
Wacker oxidation is an efficient strategy for the industrial
production of ketones and aldehydes from ethylenic compounds
which was originally focused on the conversion of ethylene to
O
acetaldehyde in the presence of a catalytic amount of PdCl
2
and
in a mixture of water and an organic solvent. Wacker
oxidation generally proceed using a Pd(II) catalyst, Cu species and
excess O or hydrogen peroxide as an oxidant. Recently the
PdCl , Fe O NPs, DMA
2
3
4
3
CuCl
2
H O , H O
2
2
2
1
2
2
conversion of olefins to corresponding carbonyl products through
Department of Nanochemistry, Nanotechnology Research Centre, Urmia University,
G. C., P. O. Box 165-5715944931, Urmia, Iran.
Email: s.keshipour@urmia.ac.ir.
Scheme 1 Oxidation of styrene to acetophenone
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Table 1. Optimization of the reaction conditions for oxidation of
a
styrene
Entry Catalyst
Solvent Temp. Time Yield
b
(
°C)
(h)
2
(%)
94
26
73
0
1
2
3
4
5
6
7
8
9
1
1
1
1
1
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
2
2
2
2
2
2
2
2
2
2
2
2
H
H
H
H
2
2
2
2
O
O
O
O
100
c
c
d
100
2
100
12
12
4
3 4
Fig. 1 The TEM image of Fe O NPs
100
DMA
DMA
-
100
61
87
28
85
94
86
82
59
37
84
92
e
e
e
e
100
4
100
2
MeCN
EtOH
EtOH
Reflux
Reflux
3
2
c,e
0
1
2
3
4
5
Reflux 12
H
H
H
H
H
2
2
2
2
2
O
O
O
O
O
90
4
80
4
Pd(OAc)
[PdCl (NH
PdCl
2
100
100
100
2
2
3
)
4
]
2
1
a
2
2.5
Reaction conditions: styrene (1 mmol), Fe
3 4
O NPs (10 mol%), DMA (5
Fig. 2 The size distribution diagram of Fe
3
O
4
NPs
b
c
2 2
mol%) H O
(3 mmol), Pd(II) (5 mol%), solvent (5 mL). Isolated yield.
d
e
Without Fe
3
4 2
O . Whitout DMA. H O (3 mmol) was added.
Fe
characterized with TEM (Fig. 1). The TEM image revealed that a
large number of Fe NPs were formed with the particle size
between 10-30 nm (Fig. 2).
new copper free catalytic system was introduced for the
oxidation of styrene to acetophenone using Pd(II)/ Fe NPs/DMA.
3 4
O NPs was prepared from Fe(II) and Fe(III) in basic media and
1
4). The low activity of Pd(OAc) may be attributed to the absence
2
3
O
4
of chloride ion. It should be mentioned that the reaction in the
presence of Fe O with the particle size <5µm was carried out in 4h
3
4
A
with 92% yield (Table 1, entry 15).
3 4
O
While the oxidation reaction in the solvents used in Table 1 gave
acetophenone selectively, the Wacker oxidation of styrene in
toluene and DMSO afforded two products including acetophenone
In this system Pd(II) acted as a main catalyst for the oxidation
reaction and DMA as a ligand activated Pd(II). Reduced Pd(0) atoms
were oxidized into Pd(II) with the reduction of Fe(III) to Fe(II) and
(
(
yields: 57% in toluene, 54% in DMSO) and 2-phenyl acetaldehyde
yields: 11% in toluene, 8% in DMSO).
H
H
2
2
O
O
2
oxidized Fe(II) to Fe(III). So, the oxidation of styrene (1) with
2
was investigated for optimization of the reaction conditions. It
Also, the reaction was examined under an oxygen atmosphere
created with a balloon instead of H O which the reaction was
was found that 5 mol% PdCl
2 2
in H O with 3 equivalents of H O
2
, 10 mol% Fe
3 4
O NPs and 5 mol% DMA
2
2
2
at 100 °C is the best reaction
performed in long duration (36 h) with 83% yield. Therefore, the
presence of ready oxygen in the reaction media afforded with H O
conditions for the oxidation of styrene. Oxidation of styrene
proceeded to give acetophenone (2) as the sole product in 94%
yield in short reaction duration (2h) without isomerization or
chlorination of styrene (Table 1, entry 1). The reaction needs long
2
2
was accelerated the oxidation process. More importantly, the
oxidation reaction of Fe(II) to Fe(III) needs an oxidant such as H O
2
2
or O which H O due to liquid nature is more effective.
2
2
2
time for high yields in the absence of Fe
and 3). However, performing of the reaction in the absence of Fe
NPs show that oxidation of Pd(0) to Pd(II) can be carried out with
, but in long time and low efficiency. Use of Fe NPs
3 4
O NPs (Table 1, entries 2
Finally, the catalyst amount was evaluated for the oxidation
reaction of styrene. For this propose 5 mL of styrene, 0.05 mmol
PdCl , 0.10 mmol Fe O NPs and 0.05 mmol DMA were added to 15
3
O
4
2
3
4
H
2
O
2
3 4
O
mL H O. The reaction was stirred at 100 °C and 1.5 mL H O added
2
2
2
accelerate the reaction and increases the yield. The ligand is a
necessary component for the oxidation reaction and the reaction
did not perform in the absence of DMA (Table 1, entry 4). After
dropwise to the reaction mixture. After 24h, the GC monitoring
showed that the reaction was stopped. So, the product was isolated
from the reaction mixture with column chromatography in 11%
yield. This result shows that our catalytic system was deactivated
after conversion of 4.7 mmol of styrene to acetophenone.
screening a variety of solvents, H
be the best solvents which H O was selected due to accordance
with the green chemistry principles (Table 1, entries 6-9). It is
important to note, the reaction in organic solvents needs H O (3
mmol) for afford high yield (Table 1, entries 5 and 6). Also, in the
absence of Fe NPs the reaction in EtOH as the solvent gave
higher yields compare to the reaction in H O as the solvent (Table 1,
2
O and EtOH were determined to
2
The results of our catalyst are compared with previously reports
about oxidation of styrene with respect to their catalytic system,
oxidant, solvent, reaction duration, temperature, yield and
2
3
O
4
9
selectivity (Table 2). Pd(0) supported on Fe O (entry 1) has some
3
4
2
advantages such use of O as a cheap oxidant and relatively milder
2
entry 10 compared to entry 3). Temperature is an important factor
for this reaction and the yield was decreased in low temperatures
reaction conditions compared to our report. Therefore, copper free
oxidation reaction, greener solvent and short reaction duration are
advantages of our report.
(Table 1, entries 11 and 12). Among the palladium compounds
tested, PdCl was effective as the catalyst (Table 1, entries 13 and
2
2
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Table 2 Comparasion of the results obtained for oxidation of styrene to acetophenone.
Entry
Catalytic system
Oxidant
Solvent
Time (h) Temp. Isolated yield (%) (I) or GC
Selectivity
yield (%) (G)
(
°C)
75
9
1
2
Pd@Fe O /CuCl
O (balloon) EtOH:H O (4:1)
36
3
94 (I)
100
87
3
4
2
2
1
0
Au-Pd@Al
2
O
3
H
2
O
2
Supercritical
120
68 (G)
CO
2
(9 MPa)
1
1
3
PdCl
2
/NaOAc
O
2
(10 atm)
H O
Ethylene
12
80
61 (I)
100
carbonate
Ionic liquids
Ionic liquids
a
14
4
PdCl2
3
3
2
60
60
100 (G)
80 (G)
94 (I)
62
95
2
2
2
2
2
2
b
14
5
PdCl
2
H
H
O
O
6
PdCl /Fe
2
3
O
4
NPs
H
2
O
100
100
a
b
Best yield for this report. Best selectivity for this report.
Also, the introduced catalytic oxidation reaction is a reoxidant mmol) was added dropwise to the reaction mixture and the
chloride free system which has other advantages including: mixture was stirred at 100 °C for 2h. Upon completion, the
good selectivity (compared to entries 2, 4 and 5), high yield mixtures were cooled to room temperature and the product
(compared to entries 2, 3 and 5) and no need to high pressure extracted with diethyl ether (3 × 5 mL). The combined extracts
(compared to entries 2 and 3).
were then washed with water, dried with MgSO , and analyzed
4
by GC-MS and NMR spectroscopy. For avoiding from organic
solvents, the reaction was repeated with 10.00 mmol styrene,
PdCl (0.09 g, 0.50 mmol), Fe O NPs (0.23 g, 1.00 mmol), DMA
Conclusions
2
3 4
(
0.04 g, 0.50 mmol), H O (30%) (0.30 mL, 30.00 mmol) and
2 2
In conclusion, we have demonstrated the Fe
3
O
4
NPs assisted
H2O (50 mL) and after completion of the reaction during 2h,
reoxidant chloride free Wacker oxidation of styrene into
acetophenone in the presence of PdCl /DMA as a catalyst.
High yield of acetophenone was obtained selectively in the
copper free conditions in short reaction duration. H O as a
green solvent, H as a green oxidant and development an
Fe O was isolated with a magnet and the solvent and DMA
3 4
2
were evaporated with rotary. Then, MgSO was added to the
4
vessel, the solid separated with filtration and pure
acetophenone obtained in 93% yield.
2
2 2
O
organic solvent-free approach are other advantages of this
report.
Acknowledgements
We gratefully acknowledge financial support from the
Research Council of Urmia University.
Experimental
All of the chemical compounds were purchased from
sigmaaldrich.
Notes and references
3 4 3 2
For preparation of Fe O NPs, FeCl .6H O (20 mmol) and
1
HSDB, Acetophenone, 2010, CASRN: 98-86-2. Hazardous
Substances Databank Number: 969. Last Revision Date:
FeCl .4H O (10 mmol) were added to 30 mL distilled water.
2
2
The salt mixture drop wise was added to 120 mL ammonia
solution under nitrogen atmosphere at 70 °C. The solution was
stirred mechanically under vigorous stirring for 30 min. Black
precipitate was decanted by a permanent magnet and washed
by distilled water three times and dried under vacuum at 50 °C
For oxidation of styrene, styrene (0.10 g, 1.00 mmol) was
2
003/10/15.
2
ESIS, European chemical Substances Information System:
European producers of Acetophenone. 2010, Database
hosted
at
the
European
Chemicals
Bureau:
http://ecb.jrc.ec.europa.eu/esis/index.php?GENRE=CASNO&
ENTREE=98-86-2.
G. Dyker, Handbook of C-H Transformations: Applications in
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(a) P. M. Henry, J. Am. Chem. Soc., 1964, 86, 3246. (b) P. M.
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3
4
added to a round bottom flask containing colloidal of PdCl
2
(
0.009 g, 0.05 mmol), Fe
3
O
4
NPs (0.023 g, 0.10 mmol), DMA
O (5 mL). H (30%) (30 µL, 3.00
(0.004 g, 0.05 mmol) and H
2
2 2
O
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DOI: 10.1039/C5RA08710D
Fe O nanoparticles as a new efficient co-catalyst for Pd(II)
3
4
in Wacker oxidation of styrene using H O as an oxidant
2
2
Sajjad Keshipour* and Selda Nadervand
Department of Nanochemistry, Nanotechnology Research Center, Urmia University, G. C., P. O. Box 165-
715944931, Urmia, Iran. Email: s.keshipour@urmia.ac.ir.
5