An efficient and scalable room temperature aerobic alcohol oxidation catalyzed by iron chloride hexahydrate/mesoporous silica supported TEMPO

Article abstract of DOI:10.1016/j.tet.2013.05.076

An efficient room temperature catalytic system FeCl₃· 6H₂O/SBA-15-TEMPO/NaNO₂ for the oxidation of alcohols with dioxygen or air as terminal oxidant has been developed. Various alcohols were oxidized at a low catalyst loading (0.1-1 mol %) to the corresponding carbonyl compounds in good to excellent yields. For the oxidation of benzyl alcohol, the excellent turn-over frequency (TOF) of 81.4 h^-1 was achieved (turn-over number (TON) up to 9770). The catalyst SBA-15-TEMPO can be reused for 10 reaction runs without significant loss of catalytic activity. In addition, the two components FeCl₃·6H₂O and SBA-15-TEMPO can also be reused for at least four reaction runs without appreciable loss of catalytic activity. In the case of large-scale experiment for the oxidation of benzyl alcohol, the desired product benzaldehyde was obtained in 94.5% yield.

Full text of DOI:10.1016/j.tet.2013.05.076

Tetrahedron xxx (2013) 1e5
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An efficient and scalable room temperature aerobic alcohol
oxidation catalyzed by iron chloride hexahydrate/mesoporous silica
supported TEMPO
a
a
b
a
a
a,
*
Lianyue Wang , Jun Li , Xiaoping Zhao , Ying Lv , Hengyun Zhang , Shuang Gao
a
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian National Laboratory for Clean Energy, DNL, Dalian 116023,
People’s Republic of China
b
Shaanxi Yanchang Petroleum (Group) Co., Ltd., Xi’an 716000, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
3 2 2
An efficient room temperature catalytic system FeCl $6H O/SBA-15-TEMPO/NaNO for the oxidation of
alcohols with dioxygen or air as terminal oxidant has been developed. Various alcohols were oxidized at
Received 8 April 2013
Accepted 20 May 2013
Available online xxx
a low catalyst loading (0.1e1 mol %) to the corresponding carbonyl compounds in good to excellent
ꢀ1
yields. For the oxidation of benzyl alcohol, the excellent turn-over frequency (TOF) of 81.4 h was
achieved (turn-over number (TON) up to 9770). The catalyst SBA-15-TEMPO can be reused for 10 reaction
Keywords:
Alcohol oxidation
Iron chloride
runs without significant loss of catalytic activity. In addition, the two components FeCl
3 2
$6H O and SBA-
15-TEMPO can also be reused for at least four reaction runs without appreciable loss of catalytic activity.
In the case of large-scale experiment for the oxidation of benzyl alcohol, the desired product benzal-
dehyde was obtained in 94.5% yield.
Molecular oxygen
2
,2,6,6-Tetramethylpiperidine N-Oxyl
TEMPO)
SBA-15
(
Ó 2013 Elsevier Ltd. All rights reserved.
4
1. Introduction
reported. Although these systems have been shown high efficiency
for the alcohol oxidation, some limitations still exist with these
The selective oxidation of alcohols into the corresponding car-
bonyl compounds is one of the most important transformations in
organic chemistry, and the carbonyl compounds are used in pro-
duction of bulk and fine chemicals such as perfumes, pharmaceu-
ticals and organic intermediates.1 Traditional methods for this
transformation are the use of stoichiometric oxidants such as
systems. TEMPO is an expensive chemical reagent. Recovery and
recycling of the homogeneous TEMPO is difficulty. The process of its
separation from the product is troublesome. TEMPO residues in the
product will affect the purity of the product. To address some of
these limitations, heterogenization of homogeneous catalysts on
solid supports shows high potential advantages, such as easy sep-
aration, efficient recycling of the supported catalyst.5
2
MnO , chromium salts, and the DesseMartin reagent, which pro-
2
duce large amounts of unwanted toxic waste. From both economic
and environmental viewpoints, molecular oxygen, as a green oxi-
dant, has received intensive attention because dioxygen is in-
expensive and water is produced as the only byproduct. Many
catalytic systems have been shown to be capable of catalyzing al-
cohol oxidation to the corresponding aldehydes and ketones
There have been many reports on the immobilization of TEMPO
6
7
onto either organic or inorganic supports. These supported
TEMPO catalysts were employed in the oxidation of alcohols under
8
Anelli’s and Minisci’s conditions. In Minisci conditions AcOH was
used as a solvent, which was not favourable to the substrates
containing acid-sensitive functional groups. In addition, the
amount of the supported TEMPO was used up to 10 mol %. Quite
recently, Karimi reported a heterogeneous catalytic system con-
3
with molecular oxygen. Of particular interest in this field is the
use of stable nitroxyl radical 2,2,6,6-tetramethylpiperidine-N-oxyl
(
TEMPO) as catalyst. Systems involving TEMPO as catalyst in com-
4 2
sisting of SBA-15-supported TEMPO/Bu NBr/NaNO for the oxida-
tion of alcohols at 50e60 C. While the low loading of supported
TEMPO (1e1.5 mol %) was used, the acidic solvent was used and the
ꢁ
9
bination with metal or metal-free co-catalysts and molecular oxy-
gen as terminal oxidant for the oxidation of alcohols have been
2
toxic and corrosive Br was generated in situ. To our knowledge,
very few catalytic systems have the advantages of using low cata-
lytic amount of recyclable supported TEMPO catalyst for the oxi-
dation of alcohols with dioxygen or air as terminal oxidant at room
*
Corresponding author. Tel./fax: þ86 (0) 411 84379728; e-mail address: sgao@
dicp.ac.cn (S. Gao).
0
040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.05.076
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2
L. Wang et al. / Tetrahedron xxx (2013) 1e5
temperature. Therefore, the development of highly efficient and
reusable catalytic system for the aerobic alcohol oxidation under
mild conditions (room temperature and little catalyst) should at-
tract a great deal of attention from the viewpoint of green and
sustainable chemistry. Liang has reported that FeCl
3 2
/TEMPO/NaNO
catalytic system is capable of selective oxidizing various alcohols
4
f,h
with air as oxidant at room temperature.
While this method
provided a very mild reaction condition and obtained great
achievement in the aerobic alcohol oxidation, the amount of the
homogeneous, non-recyclable TEMPO was needed up to 5 mol %,
which made this route less attractive for practical purposes.
The ordered mesoporous silica based materials as well-defined
catalyst support has aroused great interest for researchers due to
their uniform pore distribution, large void volumes, high surface
10
areas and high hydrothermal stability. Compared with amor-
phous solids and organic polymers, the ordered mesoporous silicas
possibly provide a more comfortable environment for the in-
teraction between catalysts and substrates. We selected a repre-
sentative mesoporous material SBA-15 as support for TEMPO due to
its obvious advantages mentioned above. It has been well docu-
mented that SBA-15 proved to be an excellent support for immo-
11
bilizing organocatalysts or metal nanoparticles. Herein, we
reported an efficient room temperature oxidation of alcohols cat-
alytic system by using a low catalytic amount of SBA-15-supported
TEMPO in conjugation with FeCl
3
$6H
2
O/NaNO
2
co-catalysts with
2
Fig. 1. N sorption isotherms of SBA-15 (a) and SBA-15-TEMPO (b).
dioxygen or air as terminal oxidant.
2
. Results and discussion
The catalyst was prepared from amine-grafted SBA-15 by cou-
pling with 4-oxo-TEMPO through reductive amination. SBA-15 was
obtained using pluronic 123 (EO20PO70EO20, EO¼ethylene oxide,
PO¼propylene oxide, M ¼5800) as the structure-directing tem-
w
plate and tetraethoxysilane (TEOS) as silica precursor under acidic
12
conditions following the well-known procedure. The amine-
functionalized SBA-15 (SBA-15eNH ) was prepared by the post-
2
synthesis grafting process using 3-aminopropyltrimethoxysilane
in refluxing dry toluene.9 The loading of amine was determined
to be 0.30 mmol g-1 by elemental analysis. The resulting SBA-
a
1
2
5eNH was then reacted with methanol solution of 4-oxo-TEMPO
9
a
to afford the grafting of TEMPO catalyst SBA-15-TEMPO. The
unreacted and adsorbed species were removed by thorough wash-
ing with hot methanol using a Soxhlet apparatus. The loading of
TEMPO was determined to be 0.21 mmol g by elemental analysis.
adsorptionedesorption and XRD were used to characterize
the structure of SBA-15 and SBA-15-TEMPO. The N sorption iso-
ꢀ
1
N
2
2
therms of the corresponding SBA-15 and SBA-15-TEMPO are shown
in Fig. 1. Both exhibit typical type-Ⅳ isotherm pattern with a sharp
hysteresis loop, which is characteristic of the ordered mesoporous
materials with narrow pore size distribution. Total pore volume
Fig. 2. XRD patterns of SBA-15 (a) and SBA-15-TEMPO (b).
was obtained from the volume of N
2
adsorbed at P/P
o
¼0.95. Pore
diameter was calculated using the BJH model based on the ad-
sorption branch of the isotherms. SBA-15 has a BET surface area of
well-ordered mesoporous structure. It was also verified that the
porous structure was not changed after the post-grafting synthesis.
We examined the catalytic oxidation of benzyl alcohol with SBA-
15-TEMPO catalyst and the results are shown in Table 1. The re-
2
ꢀ1
, a regular pore diameter of 9.48 nm and a total pore
510 m
g
3
ꢀ1
volume of 0.93 cm g . Compared with the parent material SBA-15,
2
ꢀ1
, a smaller
SBA-15-TEMPO has a lower surface area of 432 m
g
action proceeded using
2
mol mol
%
SBA-15-TEMPO,
8
%
regular pore diameter of 7.68 nm and a total pore volume of
FeCl $6H O, 10 mol % NaNO
3
2
2
in toluene under 1 atm O at room
2
3
ꢀ1
0
.80 cm g . These results may support a fact that organic moieties
temperature for 2 h, and the corresponding benzaldehyde product
was obtained in 99.4% yield. Then we examined the efficiency of the
catalyst SBA-15-TEMPO. When the loading of SBA-15-TEMPO was
reduced from 2 mol % to 0.01 mol %, the product of benzaldehyde
were introduced into the silica channels.
Powder X-ray diffraction patterns of SBA-15 and SBA-15-TEMPO
are shown in Fig. 2. Both consist of three characteristic XRD peaks in
ꢁ
ꢀ1
the range 2
q
<10 . They are typical for SBA-15-type hexagonal
was still obtained in 97.7% yield. The TOF is up to 81.4 h , which is
mesoporous molecular sieves. SBA-15-TEMPO shows slightly lower
diffraction intensity compared to the parent material SBA-15, also
indicating that the organic moieties exist in the mesopores.
TEM images of SBA-15 and SBA-15-TEMPO further confirmed their
an excellent result for a room temperature aerobic alcohol oxida-
tion involving a TEMPO catalyst. These results clearly illuminate
that the supported TEMPO shows high activity for the oxidation of
3 2 2
alcohol in the FeCl $6H O/TEMPO/NaNO catalytic system.
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L. Wang et al. / Tetrahedron xxx (2013) 1e5
3
Table 1
a
The result of the efficiency of the catalyst
SBA-15-TEMPO (x mol%), FeCl
3
.6H
2
O (8 mol%)
, 25 o
OH
O
NaNO
2
(10 mol%), toluene, 1 atm O
2
C
Yieldb (%)
TOF (h
ꢀ1
)
Entry
SBA-15-TEMPO (mol %)
T (h)
1
2
3
2
2
4
3
99.4
96.3
89.8
97.7
24.8
48.1
59.9
81.4
0.5
0.5
0.01
c
4
120
a
Benzyl alcohol 1 mmol.
Determined by GC using internal standard method.
TON: 9770.
b
c
The recyclability and the stability of the heterogeneous SBA-15-
TEMPO catalyst are significant issues of our concern. There is an
inevitable slight loss of the catalyst during the recovery steps.
While considerable results could also be obtained using a lower
loading of SBA-15-TEMPO, 2 mol % of SBA-15-TEMPO was used to
examine the catalyst recyclability in order to reduce catalyst losses
as much as possible. The reusability of the SBA-15-TEMPO catalyst
Fig. 4. Recyclability of the SBA-15-TEMPO in the oxidation of benzyl alcohol.
Table 2
Oxidation of alcohols catalyzed by FeCl
3
2 2
$6H O/SBA-15-TEMPO/NaNO under di-
a
oxygen atmosphere
was studied using benzyl alcohol as a model substrate. Since FeCl
cannot dissolve in toluene, the SBA-15-TEMPO and FeCl can be
reused together. After fresh reaction, the reaction mixtures were
3
.
OH SBA-15-TEMPO (x mol%), FeCl 6H O (8 mol%)
O
3
2
3
R1
R2
R1
R2
o
2 2
NaNO (10 mol%), toluene, 1 atm O , 25 C
washed with 3ꢂ5 mL toluene. Then, benzyl alcohol and NaNO
2
R1
R2
SBA-15-TEMPO (mol %) T (h) Yieldb (%)
Entry
were added. The recycling results showed that the catalysts can be
1
2
3
CH
CH
3
(CH
(CH
2
)
)
5
2
2
Me
Me
Me
1
1
1
12
12
12
>99
97.3
97.9
reused four times without significant loss of catalytic activity
3
2
(Fig. 3). The fifth reaction can also give good result by prolonging
3 2
(CH ) CH
4
OH
O
1
20
50.9
5
6
7
8
9
C
6
H
5
H
H
H
H
H
H
H
Me
Me
Me
H
H
H
0.1
0.2
0.5
0.3
0.5
0.5
1
0.3
0.5
0.5
1
23
14
12
12
16
16
14
12
12
26
12
7
95
98.4
>99
92.8
p-MeeC
p-CleC
p-BreC
p-NO eC
m-NO eC
o-NO eC
6
H
4
6
H
4
6
H
4
2
6
H
4
92.9
10
11
12
13
14
15
16
17
18
2
6
H
4
93.9 (93)
97.0 (95)
97.6
93.4 (93)
90.7
61.3
95.3
92.8
72.0
2
6
H
4
C
6
H
5
m-CleC
o-CleC H
m-Pyridyl
m-Pyridyl
o-Pyridyl
6
H
4
6 4
c
d
d
1
1
1
6
24
CH
3
(CH
2
)
6
H
a
b
c
Alcohols 1 mmol.
Determined by GC; values parenthesis are the yields of the isolated products.
Reaction performed at 40 C, 0.1 mL AcOH.
Reaction performed at 60 C. 0.1 mL AcOH.
ꢁ
ꢁ
d
Fig. 3. Recyclability of the SBA-15-TEMPOþFeCl
3 2
$6H O in the oxidation of benzyl
alcohol.
containing electron-donating and electron-withdrawing groups
proceeded readily to afford the desired products in excellent yields.
The positions of the substituent on the benzene ring have a certain
effect on the reactivity of benzylic alcohols. The substituent on the
o-position of the benzene ring shows poorer activity than that of
the m- and p-position. A larger amount of SBA-15-TEMPO and
longer reaction time were required for the oxidation of o-
substituted benzylic alcohols. The slow reaction rate of o-
substituted benzylic alcohols can be ascribed to steric hindrance.
Most of transition-metal-based catalytic systems are not capable of
oxidizing the alcohols that contain heteroatoms, because of their
strong coordination to metal centers. This catalytic system showed
good tolerance for the heterocyclic substrates and gave good yields
at an elevated temperature.
the reaction time. The recyclability of the only SBA-15-TEMPO was
also studied. After fresh reaction, the catalyst was filtrated off and
washed with 3ꢂ5 mL CH
2
Cl
2
, 5 mL water and 3ꢂ5 mL acetone. The
recovered catalyst was dried in air. The recycling results were
shown in Fig.4. The catalyst SBA-15-TEMPO can be reused 10 times
with a slight decrease in activity. This also suggests that the SBA-15-
TEMPO catalyst shows high stability for the room temperature
aerobic alcohol oxidation. An important feature is that the selec-
tivity of the product is not affected during the recycling process.
To examine the practicability of the SBA-15-TEMPO catalyst for
the alcohol oxidation, various alcohols including secondary ali-
phatic alcohols, benzylic alcohols, heterocyclic alcohols and also
primary alcohols were oxidized to the corresponding carbonyl
compounds in good to excellent yields and the results were sum-
marized in Table 2. It is clear that the heterogeneous TEMPO cata-
lyst shows excellent activity for the oxidation of alcohols at a low
catalytic amount of SBA-15-TEMPO (0.1e1 mol %). Benzylic alcohols
Using air instead of pure oxygen as oxidant has the obvious
advantage of safety and low cost. We next examined the ability of
the SBA-15-TEMPO catalyst to catalyze the alcohol oxidation using
air instead of pure oxygen as terminal oxidant (Table 3). All alcohols
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4
L. Wang et al. / Tetrahedron xxx (2013) 1e5
Table 3
noted. All products were confirmed by GCeMS with Agilent 6890N
GC/5973 MS detector and the comparison of their GC retention
time with those of authentic samples. GC calculations of conver-
sions and yields were performed on an Agilent 7890A with a flame
Oxidation of alcohols catalyzed by FeCl
3
$6H
2
O/SBA-15-TEMPO/NaNO
2
under air
atmospherea
.
O
OH SBA-15-TEMPO (0.5 mol%), FeCl 6H O (8 mol%)
3
2
R1
R2
R1
R2 NaNO2 (10 mol%), toluene, 1 atm air, 25 C
o
ionization detector. SE-54 capillary column, 30 mꢂ350
m
mꢂ0.5
mm;
ꢁ
ꢁ
FID detector, 300 C; injection: 250 C; carrier gas: nitrogen; carrier
gas rate: 20 mL/min. All substrates and their corresponding prod-
ucts unless otherwise noted were detected under a condition:
Entry
R1
R2
T (h)
Yieldb (%)
1
2
3
4
5
6
7
8
9
CH
(CH
3
(CH
2
)
5
2
Me
Me
H
H
H
24
24
7
81.5
74.4
96.6 (91)
96.6 (94)
96.8
>99
98.5
86.4
94.1
3
)
2
CH
ꢁ
ꢁ
column temperature: 100 C for 7 min, raising to 250 C in a rate of
C
6
H
5
ꢁ
1
5 C/min. 2-Pentanol and its corresponding product were detected
under a condition: column temperature: 30 C for 7 min, raising to
250 C in a rate of 15 C/min. 4-Methyl-2-pentanol and its corre-
sponding product were detected under a condition: column tem-
p-MeeC
p-NO eC
p-BreC
6
H
4
6
ꢁ
2
6
H
4
12
12
6
12
28
ꢁ
ꢁ
6
H
4
H
C
6
H
5
Me
Me
Me
m-CleC
o-CleC
6
H
4
ꢁ
ꢁ
ꢁ
perature: 80 C for 7 min, raising to 250 C in a rate of 15 C/min.
6
H
4
a
Alcohols 1 mmol.
b
4.2. Synthesis of SBA-15
Determined by GC; values parenthesis are the yields of the isolated products.
SBA-15 was synthesized according to the procedure from liter-
ature reported by Stucky and his co-workers. In a typical prepa-
ration procedure, 4.0 g of Pluronic P123 copolymer surfactant
employed were oxidized to the corresponding aldehydes and ke-
tones in good to excellent yields by prolonging the reaction time.
Finally, the gram-scale application of this catalytic system is also
demonstrated and benzyl alcohol was taken as a test substrate
12
(
3
EO20PO70EO20 (C
3
H
6
O$C
2
H
4
O)
x
, M
w
¼5800 g/mol) was dissolved in
0 g of water, followed by addition of 120 g of 2 M HCl solution with
(
Scheme 1). A 50 mmol (5.4 g) reaction of benzyl alcohol was
reacted with 0.2 mol % of SBA-15-TEMPO, 5 mol % FeCl $6H O and
mol % NaNO in 20 mL toluene under oxygen atmosphere (bal-
loon) at room temperature. The desired product was obtained in
4.5% yield within 34 h. The result suggests that the heterogeneous
ꢁ
stirring at 35 C. After complete dissolution of P123 in the aqueous
solution, 8.50 g of tetraethoxysilane (TEOS) was added with stirring
3
2
5
2
ꢁ
at 35 C for 20 h. Then, the mixture was transferred into an auto-
ꢁ
clave for condensation overnight at 80 C. The solid obtained was
9
filtered off and dried. The surfactant template was finally removed
catalytic system is a highly practical application for aerobic alcohol
oxidation in the laboratory.
by extraction of the solid with ethanol containing HCl using
ꢁ
a Soxhlet apparatus. SBA-15 was finally dried overnight at 110
C
under vacuum.
SBA-15-TEMPO (0.2 mol%), FeCl
3
.6H
2
O (5 mol%)
OH
O
NaNO
2
(5 mol%), toluene, 1 atm O
2
, 25 o
C
4
.3. Synthesis of aminopropyl functionalized SBA-15 (SBA-
5
0 mmol
94.5% yield
9
a
15eNH
2
)
Scheme 1. Large-scale benzyl alcohol oxidation.
SBA-15eNH
2
was synthesized from the interaction between
SBA-15 with APTES. In a typical preparationprocedure, a suspension
of freshly activated SBA-15 (5 g) with 3-aminopropyltriethoxysilane
3
. Conclusions
(
APTES) (0.4 g) in dry toluene was refluxed overnight. The solid
In conclusion, an efficient room temperature oxidation of alco-
hols catalytic system using the mesoporous silica material SBA-15
functionalized TEMPO in combination with FeCl $6H and
NaNO with oxygen or air as the environmentally benign oxidant
obtained was filtered off and washed with hot toluene using
a Soxhlet apparatus. It was dried overnight at 110 C under vacuum.
ꢁ
3
2
O
2
.4. Synthesis of SBA-15-supported-TEMPO9a
4
has been developed. This heterogeneous catalytic system showed
high activity for various alcohol oxidation to the corresponding
carbonyl compounds in good to excellent yields with low catalytic
amount of supported TEMPO (0.1e1 mol %), especially in the case of
oxidation of secondary aliphatic alcohols to the corresponding
ketones at room temperature. Based on a comparison with the
known protocols for the commonly studied alcohols, this is the
most efficient room temperature aerobic reaction with just
2
A suspension of freshly activated SBA-15-NH (1.5 g) in a dry
CH
3
OH (8 mL), 4-oxo-TEMPO (0.75 mmol, 0.141 g) was added, fol-
CN (0.0625 g, 1 mmol). After stirring at
lowed by an excess of NaBH
3
room temperature for 3 days, the solid obtained was filtered off and
thoroughly washed with hot methanol using a Soxhlet apparatus. It
ꢁ
was dried overnight at 110 C under vacuum.
0
.1e1 mol % of the TEMPO loading so far. Of particular importance,
4
.5. Catalyst characterization
the catalyst could be recycled several times without significant loss
of catalytic activity and the use of a low catalytic amount of SBA-15-
TEMPO (0.2 mol %) on a large-scale experiment can afford the
desired product in excellent yield. The distinctive feature of the
catalysts is easy recovery and recycles, particularly the use of green
and cheap iron salt and commercially available SBA-15, which
makes the catalysts especially useful for practical applications.
Small-angle X-ray powder diffraction was performed on a PAN-
alytical X’PertPro-1 thetaetheta system using Cu Ka radiation in
continuous scan mode ranging from 0.5 e10 operating at 40 mA
and 40 kV. Data were analyzed using the PANalytical X’Pert High-
Score Plus software package. N sorption isotherms were measured
2
at 77 K using a Quantachrome AUTOSORB-1 analyzer. Before the
sorption measurements, samples were out gassed at 423 K for 6 h.
ꢁ
ꢁ
4
4
. Experimental section
Total pore volume was obtained from the volume of N
2
adsorbed at
P/P
o
¼0.95. Pore diameter was calculated using the BJH model based
.1. General information
on the adsorption branch of the isotherms. Specific surface areas
were calculated using the BET model. Transmission electron mi-
crographs (TEM) were acquired on a FEI Tecnai G2 Spirit at an ac-
celeration voltage of 120 kV. The elemental analyses of catalysts
All chemical reagents were purchased from commercial sup-
pliers and used without further purification unless otherwise
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L. Wang et al. / Tetrahedron xxx (2013) 1e5
5
(
C/H/N) were analyzed on a PerkineElmer 2400 CHN Elemental
Ragauskas, A. J. J. Org. Chem. 2006, 71, 7087; (h) Yin, W. L.; Chu, C. H.; Lu, Q. Q.;
Tao, J. W.; Liang, X. M.; Liu, R. H. Adv. Synth. Catal. 2010, 352, 113; (i) Jessica, M.
H.; Stahl, S. S. J. Am. Chem. Soc. 2011, 133, 16901 For representative examples of
metal-free assisted TEMPO-catalyzed aerobic alcohols oxidations, see: (j) Liu,
R. H.; Liang, X. M.; Dong, C. Y.; Hu, X. Q. J. Am. Chem. Soc. 2004, 126, 4112; (k) Liu,
R. H.; Dong, C. Y.; Liang, X. M.; Hu, X. Q. J. Org. Chem. 2005, 70, 729; (l) Xie, Y.;
Mo, W. M.; Xu, D.; Shen, Z. L.; Sun, N.; Hu, B. X.; Hu, X. Q. J. Org. Chem. 2007, 72,
Analyzer.
4
.6. Typical procedure for the oxidation of benzyl alcohol
A mixture of FeCl
2 mol %, 95.2 mg) in toluene (2 mL) was stirred for 1 min at
room temperature in a 25 mL flask. Benzyl alcohol (1 mmol,
08 mg) was then added to the mixture. After stirring for 2 min,
NaNO (10 mol %, 6.9 mg) was added to the mixture. The resulting
3 2
$6H O (8 mol %, 21.6 mg), SBA-15-TEMPO
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1
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2
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mixture was transferred to an autoclave. After the autoclave was
closed, dioxygen was charged to 0.1 MPa. The progress of the re-
action was monitored by GC using n-nonane as an internal
standard.
5. Lu, Z. L.; Lindner, E.; Mayer, H. A. Chem. Rev. 2002, 102, 3543.
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6
(
b) Dijksman, A.; Arends, I. W. C. E.; Sheldon, R. A. Synlett 2001, 102; (c) Tanyeli,
4
.7. General procedure for obtained isolated yield
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After completion of the reaction, the reaction mixture was fil-
tered off and washed with dichloromethane. The solvent was
concentrated in vacuo and the product was further purified by
column chromatography over silica gel with a mixture of ethyl
acetate/hexane as eluent. H and C NMR spectra data of all iso-
lated products were in accord with the literature.
1
13
7
. (a) Bolm, C.; Fey, T. Chem. Commun. 1999, 1795; (b) Ciriminna, R.; Bolm, C.;
Avnir, D.; Pagliaro, M. Chem. Commun. 2000, 1441; (c) Fey, T.; Fischer, H.;
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4
.8. The recovery of the SBA-15-TEMPO catalyst
After completion of the reaction, the reaction mixture was fil-
tered off and catalyst was washed with 3ꢂ5 mL CH
2
Cl
2
, 5 mL water
8. (a) Anelli, P. L.; Biffi, C.; Montanari, F.; Quici, S. J. Org. Chem. 1987, 52, 2559; (b)
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Please cite this article in press as: Wang, L.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.05.076