Highly efficient oxidation of organic halides to aldehydes and ketones with H5IO6 in ionic liquid [C12mim][FeCl 4]

Article abstract of DOI:10.1016/j.catcom.2010.03.017

A simple, mild, and efficient procedure for the oxidation of organic halides to aldehydes and ketones with H₅IO₆ in ionic liquid [C₁₂mim][FeCl₄] has been developed. The oxidation reactions afford the target products in good to high yields and no overoxidation was observed. The products can be separated by a simple extraction with organic solvent, and the catalytic system can be recycled and reused without loss of catalytic activity.

Full text of DOI:10.1016/j.catcom.2010.03.017

Catalysis Communications 11 (2010) 923–927
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Highly efficient oxidation of organic halides to aldehydes and ketones with H IO in
5
6
ionic liquid [C mim][FeCl ]
12
4
Yu Lin Hu, Qi Fa Liu, Ting Ting Lu, Ming Lu ⁎
Chemical Engineering College, Nanjing University of Science and Technology, Nanjing 210094, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 March 2010
Received in revised form 28 March 2010
Accepted 29 March 2010
Available online 7 April 2010
A simple, mild, and efficient procedure for the oxidation of organic halides to aldehydes and ketones with
IO in ionic liquid [C12mim][FeCl ] has been developed. The oxidation reactions afford the target products
in good to high yields and no overoxidation was observed. The products can be separated by a simple
extraction with organic solvent, and the catalytic system can be recycled and reused without loss of catalytic
activity.
H
5
6
4
©
2010 Elsevier B.V. All rights reserved.
Keywords:
Oxidation
Organic halide
H
5
IO
6
Ionic liquid
1
. Introduction
large liquid range, high thermal stability, wide electrochemical
window, and strong ability to dissolve many chemicals [22].
Therefore, ILs have been widely studied for many applications in
chemical synthesis [23–25], biocatalytic transformations [26,27],
electrochemistry [28], and analytical and separation science [29,30].
In continuation of our interest in exploring green oxidations in
ionic liquids, we report herein a new and efficient method for the
selective oxidation of organic halides to aldehydes or ketones with
Aldehydes and ketones are important classes of chemicals used
extensively for the preparation of a variety of fine or special chemicals
such as drugs, vitamins, fragrances, etc. [1], and versatile methods for
direct conversion of halides to these compounds have been reported [2].
The Hass–Bender [3] and Sommelet reactions [4] are two well-known
methods for such a conversion. While the former method is only
satisfactory for para-substituted benzylic substrates, the latter unfortu-
nately has limited substrate scope. Oxidation with dimethyl sulfoxide
H
IO
5 6
in ionic liquid 1-dodecyl-3-methylimidazolium iron chloride
]) under mild conditions (Scheme 1). Furthermore,
([C12mim][FeCl
4
(
DMSO) [5,6], amine oxides [7], pyridine N-oxides [8], N-alkoxypyr-
idinium salts [9,10], polymer supported reagents [11], pyrazinyl
sulfoxides [12], NaIO -DMF [13], IBX [14], dimethyl selenoxide [15],
[16] and other reagents [17–20] has also been reported. However,
we demonstrate that the catalystic system can be recycled and reused
without any significant loss of catalytic activity.
4
H
O
2 2
2. Experimental
some of the procedures are invariably associated with one or more
disadvantages such as long reaction times, high temperatures, low
yields, difficulties in work up, environmental hazards, etc. Oxidation of
benzyl halides to their corresponding aldehydes and ketones with
potassium nitrate catalyzed by phase transfer catalyst in aqueous media
is another method, which was developed by our group [21], but, the
procedure still suffered from harsh reaction conditions and separation
difficulties. Consequently, there is a great need to develop new and
environmentally-benign procedures that address all the drawbacks.
Ionic liquids (ILs) steadily gain wide recognition as environmen-
tally-benign solvents because of their favourable properties such as
negligible volatility and nonflammability under ambient conditions,
2.1. General
All the chemicals were of analytical grade, purchased from
commercial sources and used without further purification. The ionic
liquids were synthesized according to the literature procedure [31].
Melting points were recorded on a Buchi R-535 apparatus and are
uncorrected. 1H NMR spectra were recorded on a Bruker 400-MHz
spectrometer using CDCl as the solvent with tetramethylsilane (TMS)
3
as an internal standard. Elemental analysis was performed on a Vario
EL III instrument (Elmentar Analysen Systeme GmbH, Germany).
2.2. General procedure for the oxidation of organic halides
To a stirred solution of organic halide (10 mmol) in [C12mim]
⁎
Corresponding author. Tel./fax: +86 025 84315030.
E-mail address: luming1963@163.com (M. Lu).
4 5 6
[FeCl ] (0.4 mmol) was added H IO (11 mmol) and then stirring was
1566-7367/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2010.03.017

924
Y.L. Hu et al. / Catalysis Communications 11 (2010) 923–927
Table 1
a
Optimization of the reaction conditions for oxidizing benzyl chloride to benzaldehyde.
Entry
Ionic liquid
Ionic liquid/equiv.
Time/h
Yield/%b
1
2
3
4
5
6
7
8
9
[C12mim][FeCl
[C12mim][FeCl
[C12mim][FeCl
[C12mim][FeCl
[C12mim][FeCl
[C12mim][FeCl
[C12mim][FeCl
[C12mim][FeCl
4
4
4
4
4
4
4
]
]
]
]
]
]
]
]
–
4
3
2
2
2
2
2
2
2
2
2
2
42
68
92
94
94
94
93
93
75
78
83
91
0.01
0.03
0.04
0.05
0.04
0.04
0.04
0.04
0.04
0.04
0.04
c
Scheme 1. Oxidation of organic halides to aldehydes and ketones in [C12mim][FeCl
4
].
d
e
4
continued at 30 °C for an appropriate time, the reaction progress was
monitored by TLC. Upon completion, the reaction mixture was
extracted with dichloromethane (3×10 mL). The dichloromethane
[C
[C
[C
4
mim][FeCl
6
mim][FeCl
8
mim][FeCl
4
4
4
]
]
]
1
1
1
0
1
2
[C10mim][FeCl
4
]
3
solution was washed with 5% NaHCO and dried over anhydrous
a
b
c
5 6
Reaction conditions: benzyl chloride (10 mmol), H IO (11 mmol), 30 °C.
Na SO . The product was purified by distillation (liquid product) or
2
4
Isolated yield.
The first run.
The second run.
The third run.
recrystallization from ethyl acetate and hexane (solid product). The
product was characterized by 1H NMR and elemental analysis. The
recovered catalytic system was then recycled under identical reaction
conditions. Spectroscopic data of the selected products are as follows.
d
e
2
.2.1. 4-Tert-butylbenzaldehyde (5)
Colorless oil. H NMR: δ 1.32 (s, CH
.94 (s, CHO, 1H). Anal. Calcd. for C11
4
was performed with [C12mim][FeCl ], the yield increased to 68% in a
shorter time (3 h) when only 0.01 equivalents were used (Table 1,
entry 2). The yield improved with increasing amount of [C12mim]
1
3
, 9H), 7.51–7.77 (m, Ar–H, 4H),
14O: C, 81.44; H, 8.70; O, 9.86.
9
H
Found: C, 81.37; H, 8.70; O, 9.84.
[FeCl
equivalents of [C12mim][FeCl
addition of [C12mim][FeCl ], under the same conditions, did not
enhance significantly the yield (Table 1, entry 5). These experiments
revealed that 2 h and 0.04 equivalents of the promoter were necessary
to complete the reaction. In addition, the IL could be typically
recovered and reused for subsequent reactions with no appreciable
decrease in yields and reaction rates (Table 1, entries 6–8). Besides
4
] (Table 1, entries 2–4), and reached maximum with 0.04
4
] (Table 1, entry 4). However, further
2
.2.2. 2,4,6-Trimethylbenzaldehyde (6)
Colorless oil. H NMR: δ 2.17 (s, CH
4
1
3
, 3H), 2.42 (s, CH
3
, 6H), 7.23
(
s, Ar–H, 2H), 9.91 (s, CHO, 1H). Anal. Calcd. for C10
H
12O: C, 81.04; H,
8
.16; O, 10.80. Found: C, 81.02; H, 8.16; O, 10.78.
2
.2.3. 3,4,5-Trimethoxybenzaldehyde (7)
White solid, mp: 74–76 °C. 1H NMR: δ 3.76 (s, CH
O, 3H), 3.91
O, 6H), 7.12–7.17 (s, Ar–H, 2H), 9.85 (s, CHO, 1H). Anal. Calcd
: C, 61.22; H, 6.16; O, 32.62. Found: C, 61.19; H, 6.17; O,
[C12mim][FeCl
midazolium iron chloride ([C
zolium iron chloride ([C mim][FeCl
iron chloride ([C mim][FeCl ]), and 1-decyl-3-methylimidazolium
iron chloride ([C10mim][FeCl ]) were tested as catalysts in the reaction
(Table 1, entries 9–12). [C12mim][FeCl ] demonstrated the best
performance. The different catalytic effects of ILs may be attributed
to their different abilities of stabilizing and dissolving H IO and the
substrate. Under reaction conditions, H IO may be more soluble in
12mim][FeCl ], leading to higher effective concentration of the
], four other types of ionic liquids, 1-butyl-3-methyli-
mim][FeCl ]), 1-hexyl-3-methylimida-
]), 1-methyl-3-octylimidazolium
3
4
(
s, CH
3
4
4
for C10
H
12
O
4
6
4
3
2.63.
8
4
4
2
.2.4. 3,4-Methylenedioxybenzaldehyde (8)
White solid, mp: 36–38 °C. H NMR: δ 6.05 (s, CH
4
1
2
, 2H), 6.85–7.54
: C, 64.00; H,
(
m, Ar–H, 3H), 9.87 (s, CHO, 1H). Anal. Calcd for C
8
H
6
O
3
5
6
4
.03; O, 31.97. Found: C, 63.99; H, 4.01; O, 31.98.
5
6
[C
4
2
.2.5. 3,7-Dimethyl-2,6-octadienal (12)
Colorless liquid. H NMR: δ 1.57 (s, CH
oxidant. The reaction procedure apparently did not result in the
oxidation of benzaldehyde since no benzoic acid was detected.
With these results in hand, we subjected other organic halides to
the oxidation reactions, and the results are listed in Table 2. It is clear
that various types of benzylic, allylic, and aliphatic halides, both
primary and secondary, can be successfully oxidized to the
corresponding aldehydes and ketones in good to high yields
(Table 2). Various functionalities such as alkyl, alkoxy, alkene double
bonds, fluoro, chloro and nitro groups can tolerate the reaction.
However, aliphatic halides were less reactive, and longer reaction time
was needed to reach good yields (Table 2, entries 17 and 18). It was
also observed that the electronic nature of the substituents on the
aromatic ring has some impact on the reaction rate. Substrates with
electron-withdrawing groups (Table 2, entries 9, 10, and 15) are less
reactive than the ones with electron-donating groups (Table 2, entries
2–8).
1
3
, 3H), 1.91 (s, CH
, 4H), 5.10 (s, CH, 1H), 5.85 (d, J=7.0 Hz,
CH, 1H), 9.80 (d, J=7.0 Hz, CHO, 1H). Anal. Calcd for C10 16O: C,
3
, 3H), 2.23
(
3 2 2
s, CH , 3H), 2.61 (m, CH CH
H
7
8.90; H, 10.59; O, 10.51. Found: C, 78.88; H, 10.59; O, 10.50.
2
.2.6. 4-Nitrobenzaldehyde (15)
Light yellow solid, mp: 104–106 °C. H NMR: δ 8.12–8.34 (m, Ar–H,
H), 10.24 (s, CHO, 1H). Anal. Calcd for C NO : C, 55.63; H, 3.33; N,
1
4
9
7
H
5
3
.27; O, 31.76. Found: C, 55.60; H, 3.34; N, 9.26; O, 31.78.
2
.2.7. Cinnamaldehyde (16)
1
Colorless oil. H NMR: δ 6.64 (d, J=16.7 Hz, CH, 1H), 6.71 (dd,
J=6.5, 16.7 Hz, CH, 1H), 7.36–7.51 (m, Ar–H, 5H), 9.65 (d, J=6.5 Hz,
CHO, 1H). Anal. Calcd for C O: C, 81.79; H, 6.10; O, 12.11. Found: C,
8
9 8
H
1.75; H, 6.11; O, 12.13.
3
. Results and discussion
4. Conclusions
The initial study was carried out using benzyl chloride as the
substrate to optimize the reaction conditions, and the results are
summarized in Table 1. At first, the oxidation was tested with H IO as
the oxidant in the presence and absence of [C12mim][FeCl ]. In the
absence of [C12mim][FeCl ], the reaction proceeded very slowly, and
the yield was only 42% after 4 h (Table 1, entry 1). When the reaction
In conclusion, we have developed a simple and efficient procedure
for the oxidation of organic halides to aldehydes and ketones with H
5 6
IO
5
6
in ionic liquid [C12mim][FeCl ]. Most importantly, the catalytic system is
4
4
very easy to handle and can be recycled and reused without loss of
catalytic activity. The scope, the definition of mechanism, and synthetic
applications of the oxidation are currently under investigation.
4

Y.L. Hu et al. / Catalysis Communications 11 (2010) 923–927
925
Table 2
a
Oxidation of organic halides to aldehydes and ketones.
Entry
Substrate
Product
Time/h
Yield/%b
1
2
94
93
1
2
3
4
5
6
2
3
4
5
6
1.5
1.5
1.5
1.5
1.5
93
95
96
98
7
8
9
1.5
1.5
2
98
95
92
7
8
9
(continued on next page)

926
Y.L. Hu et al. / Catalysis Communications 11 (2010) 923–927
Table 2 (continued)
Entry
Substrate
Product
Time/h
2.5
Yield/%b
91
10
10
1
1
2
1.5
97
96
11
1
2
12
1
1
3
4
2
93
95
13
2.5
14
1
5
6
2.5
90
94
1
1
1
5
6
7
1
2
1
1
7
8
3
3
88
90
18
a
Reaction conditions: organic halide (10 mmol), H
Isolated yield.
5
IO
6
(11 mmol), [C12mim][FeCl
4
] (0.4 mmol), 30 °C.
b
Acknowledgements
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