1800
Leng Y, et al. Sci China Chem September (2012) Vol.55 No.9
works are irreplaceable active centers for this reaction.
In addition to benzyl alcohol, other alcohol substrates
such as cyclohexanol, 1-phenylethyl alcohol, benzhydrol
and 1-octanol were also investigated, as shown in entries
test three times. Figure 4 confirms the very durable catalyst
structure, since the IR spectrum of the recovered catalyst is
very similar to that of the fresh one, which is consistent with
the steady selectivity of the catalyst. The ICP-AES ele-
mental analysis evidenced a slight leaching of [Dmim]1.5PW
(3.0% of W atoms) in the first run, but in subsequent runs,
the leaching amounts were negligible. The decrease of con-
version in the second run therefore seems to be related to
this leaching of the fresh catalyst.
9
–12 of Table 2. It can be seen that good to excellent results
were generally obtained, with 1-octanol as an exceptional
case.Asreportedpreviously,the oxidation of long chain fatty
alcohols is rather difficult over many catalysts, e.g.,
Cu(II)-triethanolamine complexes or supercritical carbon
dioxide-promoted H
5
PV
2
Mo10
O
40 [26, 27].
The hybrid catalyst [Dmim]1.5PW shows comparable ac-
tivity and reusability to supported HPA catalysts [7, 28, 29],
but has the advantage of requiring a simpler preparation.
Additionally, the recovery of the catalyst is much easier
than for homogeneous, phase-transfer, and liquid–liquid
biphasic HPA-based catalysts [9, 30].
3
.4 Catalytic reusability of [Dmim] PW
1
.5
The results of the six-run recycling test for the oxidation of
benzyl alcohol with H over the hybrid catalyst
Dmim]1.5PW are given in Table 3. No significant loss of
2
O
2
[
selectivity was observed; however, the conversion of 92.3%
for the fresh catalyst marginally decreased to 84.7% in the
sixth run. In detail, this decrease of conversion happened
mainly in the second run, and afterwards, further reuse of
the catalyst resulted in rather similar conversions. This
phenomenon was confirmed by conducting the recycling
4 Conclusions
We have prepared a new HPA-based hybrid catalyst
[
Dmim]1.5PW simply by pairing dicationic IL cations with
Keggin phosphotungstate anions. In the heterogeneous oxi-
dation of alcohols with H , the hybrid catalyst offers not
2 2
O
only high conversion and selectivity but also convenient
recovery and quite good reusability. The dicationic structure
is responsible for the hybrid’s solid nature and insolubility,
and thus leads to a heterogeneous catalysis system. The
bulk-type catalysis is suggested to be related to the high
activity of the hybrid catalyst [Dmim]1.5PW.
Table 2 Catalytic performances of various catalysts for the oxidation of
alcohols with H O
2 2
a)
b)
c)
Solubility Con.
in reaction (%)
benzyl alcohol [Dmim]1.5PW insoluble
Sel.
Entry
Substrate
Catalyst
(%)
98.2
84.1
98.8
93.9
95.1
99.4
92.6
85.9
100
1
2
3
4
5
6
7
8
9
92.3
83.5
96.8
95.3
95.7
80.0
43.9
13.5
97.5
benzyl alcohol
benzyl alcohol
benzyl alcohol
benzyl alcohol
H
3
PW12
O
40
soluble
soluble
soluble
soluble
[Bmim]
[Bpy] PW
[CTA] PW
3
PW
3
This work was supported by the National Natural Science Foundation of
China (21136005).
3
benzyl alcohol [Dmim]1.5PMo insoluble
Benzyl alcohol [Dmim]2.5PMoV insoluble
benzyl alcohol
cyclohexanol
[Dmim]
2
SiW
insoluble
1
2
3
Proctor G. 1,9-Oxidation adjacent to oxygen of alcohonls by other
methods. In: Trost BM, Fleming I, Eds. Comprehensive Organic
Synthesis, 1991, 7: 305–327
[Dmim]1.5PW Insoluble
[Dmim]1.5PW insoluble
1
-phenylethyl
alcohol
1
0
98.1
100
Jiang N, Ragauskas AJ. Vanadium-catalyzed selective aerobic
1
1
1
2
benzhydrol
[Dmim]1.5PW insoluble
[Dmim]1.5PW insoluble
87.5
7.4
100
6
alcohol oxidation in ionic liquid [bmim]PF . Tetrahedron Lett, 2007,
4
8: 273–276
1-octanol
85.8
Bagherzadeh M, Amini M, Boghaei DM, Najafpour MM, McKee V.
Synthesis, X-ray structure, characterization and catalytic activity of a
polymeric manganese(II) complex with iminodiacetate. Appl Or-
ganomet Chem, 2011, 25: 559–563
a) Reaction conditions: catalyst 0.1 g, substrate 10 mmol, solvent
CN/H O 10 mL (volume ratio of CH CN to H O 1:1), H (30 wt.%)
mmol, oil bath temperature 90 C, 12 h; b) conversion of alcohols based
on H ; c) selectivity to the corresponding aldehyde or ketone, benzoic
CH
3
2
3
2
2 2
O
6
2
O
2
4
5
6
Liu L, Ma J, Ji L, Wei Y. Molecular sieve promoted copper catalyzed
aerobic oxidation of alcohols to corresponding aldehydes or ketones.
J Mol Catal A, 2008, 291: 1–4
Kozhevnikov IV. Catalysis by heteropoly acids and multicomponent
polyoxometalates in liquid-phase reactions. Chem Rev, 1998, 98:
171–198
acid as the by-product for entries 1–7, and octanoic acid as the by-product
for entry 11.
Table 3 Catalytic reusability of [Dmim]1.5PW for the oxidation of benzyl
a)
alcohol with H
2
O
2
Kasai J, Nakagawa Y, Uchida S, Yamaguchi K, Mizuno N.
[
γ-l,2-H
2
SiV
2
W
10
O
40] immobilized on surface modified SiO
2
as a
Run
1
2
3
4
5
6
heterogeneous catalyst for liquid-phase oxidation with H O . Chem
Eur J, 2006, 12: 4176–4184
Ben-Daniel R, Neumann R. Activation of nitrous oxide and selective
oxidation of alcohols and alkylarenes catalysed by the
[PV Mo O ] polyoxometalate ion. Angew Chem Int Ed, 2003, 42:
2 2
b)
Con. (%)
92.3
98.2
79.8
98.9
84.7
99.1
88.6
99.2
85.0
98.7
84.7
97.8
c)
7
8
Sel. (%)
5
−
a) Reaction conditions: [Dmim]1.5PW 0.1 g, benzyl alcohol 10 mmol,
CN/H O (volume ratio 1:1) 10 mL, H (30 wt.%) 6 mmol, oil bath
2
10 40
CH
3
2
2
O
2
92–95
temperature 90 C, 12 h; b) conversion of benzyl alcohol based on H
selectivity to benzaldehyde.
2
O
2
; c)
Hamamoto H, Suzuki Y, Yamada YMA, Tabata H, Takahashi H,
Ikegami S. A recyclable catalytic system based on a tempera-