Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-palygorskite

Article abstract of DOI:10.1016/j.tetlet.2005.03.070

Palygorskite-supported Sn complexes were prepared by a simple procedure. Cyclic ketones and acyclic ketones were oxidized by hydrogen peroxide in a reaction catalyzed by palygorskite-supported Sn complexes, affording corresponding lactones or esters with selectivity for the product of 90-100%. The catalysts can be recycled for several times without significant decline in catalytic activity.

Full text of DOI:10.1016/j.tetlet.2005.03.070

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 3505–3508
Baeyer–Villiger oxidation of ketones with hydrogen
peroxide catalyzed by Sn-palygorskite
*
Ziqiang Lei, Qinghua Zhang, Jujie Luo and Xiaoyan He
Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry and Chemical Engineering,
Northwest Normal University, Lanzhou 730070, China
Received 26 October 2004;revised 14 March 2005;accepted 15 March 2005
Available online 8 April 2005
Abstract—Palygorskite-supported Sn complexes were prepared by a simple procedure. Cyclic ketones and acyclic ketones were
oxidized by hydrogen peroxide in a reaction catalyzed by palygorskite-supported Sn complexes, affording corresponding lactones
or esters with selectivity for the product of 90–100%. The catalysts can be recycled for several times without significant decline
in catalytic activity.
ꢀ
2005 Elsevier Ltd. All rights reserved.
The Baeyer–Villiger oxidation was first reported by
Baeyer and Villiger in 1899 when they converted
menthone, camphor, and carvone into the correspond-
They found that Sn-Zeolite beta was a very active and
selective catalyst for the Baeyer–Villiger oxidation of
cycloketones with environmentally benign hydrogen
peroxide as an alternative to organic peroxy acids. The
Sn-zeolite beta was synthesized using dealuminated
nanocrystalline (20 nm) zeolite as seeds and a crystalli-
zation procedure was performed in Teflon-lined stainless
steel autoclaves, which were heated to 140 ꢁC and
rotated over a period of 20 days.
1
ing lactones with Caroꢀs acid as an oxidant. The reac-
tion can be applied in the synthesis of a wide variety of
chemicals, ranging from simple monomers used in the
polyester industry to the more complex molecules that
were applied for the synthesis of pharmaceutical prod-
2
ucts. However, the oxidants used in the traditional
Baeyer–Villiger oxidation are organic peroxy acids
which potentially produce large amounts of harmful
wastes. Much recent effort has been devoted to find
chemically green oxidants along with the recyclable
catalysts.
We report here the catalytic Baeyer–Villiger oxidation of
ketones with a recyclable catalytic system using paly-
gorskite as a catalytic support and 30% hydrogen per-
oxide as oxidant. The catalyst and the catalytic system
we used are similar to those of Cormaꢀs, but the proce-
dure for the preparation of the Sn-palygorskite is much
simpler. Furthermore, palygorskite is a biocompatible
and environmentally friendly natural mineral abundant
in deposits all over the world. The catalyst can be
prepared in large scale and can be recycled.
Supported catalysis, in particular, accord with green
chemistry by allowing easy separation of the products
and permitting the recycling and reuse of the catalyst
with operational and economical advantages. Polymer-
3
–5
6
anchored metal complexes,
7
solid acids, Sn-MCM-
9
8
41, sulfonated resins, titanium silicalites, transition
0
metal-functionalized hydrotalcites, and Sn-synthesized
hydrotalcites are examples of some of the hetero-
geneous catalysts used to perform the Baeyer–Villiger
reaction. The best catalytic system for the Baeyer–
Villiger reaction was reported recently by Corma and
1
Palygorskite is a natural clay mineral characterized by
a porous crystalline structure containing tetrahedral
layers alloyed together by longitudinal sideline chains.
A typical unit cell consists of (Mg,Al) Si O (OH) -
1
1
5
8
20
2
(H O) Æ4H O, with Mg preferentially located in octa-
2
4
2
1
2,13
2+
hedral sites. These mineral clays possess Mg and Al
3+
his colleagues.
1
4
cations that can be easily exchanged. Due to its sorp-
tive and rheological properties, palygorskite is widely
used in different industrial fields. In spite of numerous
studies on the catalytic properties of palygorskite,
organic reactions catalyzed by palygorskite-supported
Keywords: Baeyer–Villiger oxidation;Palygorskite;Ketone oxidation.
*
Corresponding author. Tel.: +86 931 7971687;fax: +86 931
970359;e-mail: leizq@nwnu.edu.cn
7
0
040-4039/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.03.070

3506
Z. Lei et al. / Tetrahedron Letters 46 (2005) 3505–3508
Figure 2 shows the infrared spectra of natural paly-
gorskite and Sn-palygorskite. The bands at 1026 and
À1
469 cm were attributed to in-layered Si–O–Si bonds.
The band near 800 cm
À1
may correspond to the Al–
O–Si bond. The Lewis and Bronsted acid sites were sit-
uated at 1653 and 1448 cm , respectively, as identified
1
by the adsorption of an n-butylamine probe molecule.
À1
5
There are obvious changes in the IR spectra of Sn-paly-
gorskite compared to that of palygorskite. In the IR
spectra of Sn-palygorskite, the peak near 1448 cm
À1
À1
almost disappears. The strong absorption at 469 cm
is shifted to 539 cm . These may be attributed to the
palygorskite inlaid with tin.
À1
Oxidation of ketones was carried out in a 25 mL glass
reactor. A typical procedure for the Baeyer–Villiger oxi-
dation is as follows: 2-adamantone (15 mg, 0.1 mmol)
and 30% hydrogen peroxide (1.5 equiv) were dissolved
in nitrobenzene or 1,4-dioxane (3 mL). Sn-palygorskite
Figure 1. AFM pattern of palygorskite used for the preparation
of Sn-palygorskite catalyst. The palygorskite particle is about 650 ·
(3 mg) was added, the mixture was heated to 90 ꢁC
350 nm with the thickness of 25–50 nm.
and stirred for 24 h. The products were identified by
GC–MS analysis. Other cyclic ketones and acyclic
ketones were also oxidized in this oxidation system to
give the corresponding lactones or esters. The results
are summarized in Table 1.
catalyst, especially for the oxidation reactions, have
been scarcely reported. We show that upon incorpora-
tion of 2.41 wt% of tin into the framework of palygors-
kite (Fig. 1), Sn-palygorskite was obtained. This
material acts as an efficient and stable heterogeneous
catalyst for the Baeyer–Villiger oxidation of ketones
by 30% hydrogen peroxide.
We confirmed that the oxidation reaction did not occur
in the absence of the catalyst. Moreover, the reaction
did not proceed in the presence of SnCl , or untreated
2
palygorskite was used.
Sn-palygorskite was prepared according to the following
procedure.
Sn-palygorskite possesses high catalytic activity for the
Baeyer–Villiger oxidation of cyclic ketones and acyclic
ketones. In particular, 2-adamantanone, 3-methyl-2-
pentanone and 4-methyl-2-pentanone were converted
into the corresponding lactone or ester almost quantit-
atively. In the case of adamantanone, it is noteworthy
that Sn-palygorskite as heterogeneous catalyst can be
recycled at least four times without significant decline
in catalytic activity.
Palygorskite (1 g) (received from Gansu Kaixi Ecolo-
gical Environment Material Company, powdered to
0
.26–2.93 lm) was leached with 1 N HCl (20 mL) at
room temperature for 1 h. SnCl Æ4H O (2 g) was then
2
2
added to the mixture and the resultant slurry was stirred
at room temperature for 24 h. The products were col-
lected by filtration, washed with copious amounts of
ethanol and water, dried at 333 K under vacuum for
2
2
4 h. The content of Sn in the Sn-palygorskite is
.41 wt% according to chemical analysis.
A possible reaction mechanism using Sn-palygorskite as
catalyst for the Baeyer–Villiger oxidation is shown in
2
2
1
1
5
0
5
0
5
0
1
8
6
4
00
0
1
448
0
2
918
1
653
667
3
622
516
3
555
3
393
4
69
0
5
39
Palygorskite /Sn
........
Palygorskite
.
1
026
20
4000
3500
3000
2500
2000
1500
1000
500
-
1
Wavenumbers(cm )
Figure 2. The IR spectra of palygorskite and Sn-palygorskite.

Z. Lei et al. / Tetrahedron Letters 46 (2005) 3505–3508
Table 1. Baeyer–Villiger oxidation of several ketones catalyzed by Sn-palygorskite
3507
a
Substrate
Temp (ꢁC)
H
2
O
2
(equiv)
Solvent
Conversion
(%)
Selectivity
(%)
Turnover
number
Product
(
30%)
9
7
0
0
1.5
1.5
Nitrobenzene
100
100
164
O
O
O
O
O
1,4-Dioxane
81
100
132
O
O
O
O
7
7
0
0
1.5
1.5
1,4-Dioxane
1,4-Dioxane
16
37
90
26
61
O
O
C
100
C
CH
3
O
CH3
O
O
O
O
CH
3
90
1.5
1,4-Dioxane
80
100
197
CH3
O
O
9
9
0
0
1.5
1.5
1,4-Dioxane
1,4-Dioxane
44
25
100
100
108
31
CH
O
3
CH
O
3
C(CH
3
)
3
O
3 3
C(CH )
O
C
O
C
CH
CH
3
3
CH
2
CH
CH
CH
CH
3
3
90
90
1.5
1.5
1,4-Dioxane
1,4-Dioxane
100
100
100
100
123
123
CH
3
CH
2
CH
CH
O
CH
3
3
2
3
O
C
O
C
CH CH
CH
CH3 CH CH2
CH3
O
CH3
3
2 2
Reaction condition: substrate 0.1 mmol, 30% H O (1.5 equiv to the ketones), Sn-palygorskite 3 mg, 24 h.
a
Selectivity to the mentioned product listed in the last column.
O
is activated. Hydrogen peroxide subsequently attacks
the electrophilic carbonyl carbon atom. After the
rearrangement, the lactone product is replaced by a
palygorskite
+
2 2
H O
O
Sn2+
H+
£
-
new substrate molecule. This mechanism is analogous
12
O
¦Ä
to that for peracids, which Corma et al.
have
1
8
confirmed by means of an O labeling experiment,
infrared spectroscopy and gas chromatography–mass
spectrometry.
¦Ä
palygorskite
GC MS
-
Established by IR
Sn2+
O
In summary, Sn-palygorskite was prepared by a simple
procedure and shown to act as a highly active catalyst
for the Baeyer–Villiger oxidation of ketones using envi-
ronmentally friendly 30% hydrogen peroxide as oxidant.
The catalyst can also be recycled. Further work explor-
ing the utility of these novel catalysts is on-going in our
laboratory.
O
palygorskite
O
OH
Sn2+
O
O
Criegee adduct
£-
2
H O
H+
+
Figure 3. Catalytic mechanism for the Baeyer–Villiger oxidation
catalyzed by Sn-palygorskite.
Acknowledgements
This work was financially supported by National Natural
Science Foundation of China (No. 20174031 and
20474052). We are especially grateful to Dr. A. J. Sutherland
Figure 3. Firstly, the ketone is coordinated to the
Lewis-acid tin center, and thereby, the carbonyl group

3508
Z. Lei et al. / Tetrahedron Letters 46 (2005) 3505–3508
(Aston University) for critical evaluation of this
manuscript.
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. Hoelderich, W.;Fischer, J.;Schindler, G.;Arntz, P.
German Patent DE 19745442, 1999.
9. Notari, B. Adv. Catal. 1996, 41, 253–334.
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