Selective aerobic oxidation of alcohols catalyzed by iron chloride hexahydrate/TEMPO in the presence of silica gel

Article abstract of DOI:10.1002/aoc.1862

An environmentally friendly and efficient process whereby FeCl ₃·6H₂O/2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO)-catalyzed oxidation of alcohols to the corresponding aldehydes and ketones is accomplished in the presence of silica gel using molecular oxygen or air as the terminal oxidant. The electron-deficient benzyl alcohol was smoothly oxidized to the corresponding aldehydes with up to 99% isolated yield. It was found that silica gel not only could enhance the catalytic reaction rate but also increase the selectivity for the product. The high performance of FeCl ₃·6H₂O/TEMPO catalyst system in the presence of silica gel might be attributed to the surface silanol groups. UV-visible spectra analysis showed that the Fe (III)-TEMPO complex could serve as the active intermediate species in the present catalytic system. A plausible mechanism of the catalytic system is proposed. Copyright

Full text of DOI:10.1002/aoc.1862

Full Paper
Received: 2 September 2011
Revised: 4 October 2011
Accepted: 10 November 2011
Published online in Wiley Online Library: 5 January 2012
(wileyonlinelibrary.com) DOI 10.1002/aoc.1862
Selective aerobic oxidation of alcohols
catalyzed by iron chloride hexahydrate/TEMPO
in the presence of silica gel
Lianyue Wang,a,b Jun Li,a* Ying Lv,a Gongda Zhaoa and Shuang Gaoa*
An environmentally friendly and efficient process whereby FeCl3•6H2O/2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO)-
catalyzed oxidation of alcohols to the corresponding aldehydes and ketones is accomplished in the presence of silica gel using
molecular oxygen or air as the terminal oxidant. The electron-deficient benzyl alcohol was smoothly oxidized to the
corresponding aldehydes with up to 99% isolated yield. It was found that silica gel not only could enhance the catalytic
reaction rate but also increase the selectivity for the product. The high performance of FeCl3•6H2O/TEMPO catalyst system
in the presence of silica gel might be attributed to the surface silanol groups. UV–visible spectra analysis showed that the
Fe (III)–TEMPO complex could serve as the active intermediate species in the present catalytic system. A plausible mechanism
of the catalytic system is proposed. Copyright © 2012 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: aerobic alcohol oxidation; iron chloride; molecular oxygen; 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO); silica gel
Wang et al.[42] and Yin et al.[43] have made a great breakthrough
in this respect. They developed an efficient three-component
Introduction
The selective oxidation of alcohols to their corresponding carbonyl
compounds is an important functional group transformation in
organic synthesis.[1] Traditionally, the oxidants are required in
stoichiometric quantities.[2] Permanganate, manganese(IV) oxide,
chromium(VI) oxide, dichromate, and ruthenium(VIII) oxide are also
hazardous oxidizing agents. From both an economic and environ-
mental viewpoint, the catalytic oxidation process represents a
promising improvement in this protocol. The use of molecular
oxygen or air as the oxidant is particularly attractive.
Numerous reports describe aerobic alcohol oxidation using
transition metals such as Cu,[3–8] Pd,[9–17] Ru,[18–21] Au,[22–24] or
V,[25–29] alone or in conjugation with the nitroxy radical 2,2,6,
6-tetramethylpiperidine N-oxyl (TEMPO)[30–34] as catalysts. In these
studies, noble metals, halogens, extra bases or complicated ligands
are often used. These are typically restricted for use in pharmaceu-
ticals, fragrances and food additives. Therefore the development of
procedures with a green, efficient and inexpensive catalytic system
for aerobic oxidation of alcohols is a worthwhile challenge. Minisci
and co-workers reported an efficient use of Mn(NO3)2 and Co(NO3)2
or Cu(NO3)2 in combination with TEMPO in a CH3COOH catalytic
system for the oxidation of primary, benzylic and secondary
alcohols.[35,36]
catalytic system, consisting of FeCl3•6H2O/TEMPO/NaNO2, in
which NaNO2 as the electron-transfer medium is required for
completing the catalytic cycle. We are particularly interested in
exploring the potential of the iron–TEMPO catalyst system for
aerobic alcohol oxidation without additional co-catalyst. It
was reported that silica gel enhances many reaction rates.[44]
Nishiguchi and Asano[45] reported that metallic nitrates sup-
ported on silica gel were able to efficiently oxidize alcohols
to the corresponding ketones and aldehydes. In this system,
the metallic nitrates were the stoichiometric oxidant. How-
ever, according to our knowledge FeCl3•6H2O/TEMPO-
catalyzed oxidation of alcohols in the presence of silica gel using
O2 as oxidant has never been reported in the literature. We reck-
oned that a simple alcohol oxidation reaction could be performed
using FeCl3•6H2O/TEMPO catalyst system in the presence of silica
gel using O2 as oxidant, in which O2 acts as an ultimate oxidant
and water is the only by-product. A possible reaction mechanism
is also highlighted.
Recently, green, inexpensive and readily available iron salts have
attracted a great deal of attention in modern chemistry.[37–40] In
contrast, iron salts being employed as the catalyst for aerobic
oxidation of alcohols is rarely reported. Martin and Suárez[41] first
reported the Fe(NO3)3/FeBr3 catalytic system for the oxidation of
alcohols, which was effective for chemoselective oxidation of sec-
ondary aliphatic alcohols. It was reported by Dijksman et al.[18] that
Fe(III and II) chlorides in combination with TEMPO showed no cata-
lytic activity for aerobic oxidation of 2-octanol in chlorobenzene.
*
Correspondence to: Shuang Gao, Dalian Institute of Chemical Physics, Chinese
Academy of Sciences, Dalian,116023, People’s Republic of China. E-mail:
sgao@dicp.ac.cn
a Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian,
116023, People’s Republic of China
b Graduate University of the Chinese Academy of Sciences, Beijing, 100049,
People’s Republic of China
Appl. Organometal. Chem. 2012, 26, 37–43
Copyright © 2012 John Wiley & Sons, Ltd.

L. Wang et al.
Table 1. FeCl3•6H2O-catalyzed oxidation of benzyl alcohol to
pressure of oxygen to 0.1 MPa for a slightly longer time (Table 1,
entry 7). The effect of the amount of silica gel was also investi-
gated. As shown in Fig. 1, the amount of silica gel modulated
the oxidation of benzyl alcohol. The conversion increased with in-
creasing amount of silica gel until 0.2 g, and plateaued when over
0.2 g of silica gel was used.
benzaldehydea
Entry
FeCl3•6H2O
TEMPO
Silica gel
Conversion (%)/
selectivity (%)b
1
No
Yes
No
Yes
Yes
Yes
No
Trace
Trace
97/99
35/83
90/88
55/93
95/95
2
Yes
Yes
Yes
Yes
Yes
Yes
3
Yes
Yes
Yes
Yes
Yes
Optimization of the Aerobic Oxidation of Benzyl Alcohol
4
5c
6d
7e
No
The catalytic system was optimized using benzyl alcohol as a test
substrate, and the data are summarized in Table 2. The nature of
the solvent had a crucial impact on the reaction outcome. Thus,
while toluene, PhCF3, dichloromethane or dichloroethane favored
the benzyl alcohol oxidation (Table 2, entries 1–4), n-hexane yielded
only moderate conversion (Table 2, entry 5). The use of polar coordi-
nating solvents such as DMF and CH3CN resulted in low conversions
(Table 2, entries 6 and 7), which might be due to the competitive
coordination of solvent molecules to the metal center and fewer
binding sites for benzyl alcohol and TEMPO.[46] In order to optimize
the environmental properties and to achieve minimal toxicity, tolu-
ene was chosen as a solvent. A variety of iron salts were evaluated
with toluene as a solvent (Table 2, entries 8–13). Fe2(SO4)3 and Fe
(OAc)3 were the least active catalysts, yielding only 8% and 2%
conversion, respectively (Table 2, entries 8 and 9). The conversion
obtained in the presence of FeBr3 was 69% (Table 2, entry 10). It
was observed that when anhydrous FeCl3 was employed as a
catalyst, this resulted in a lower yield than FeCl3•6H2O (Table 2, entry
11). FeCl3•6H2O proved to be an excellent catalyst in terms of
reaction rate and conversion. The reaction could also be accom-
plished using FeCl2•4H2O as a catalyst with a slightly longer reaction
time (Table 2, entries 12 and 13). The results suggested that the iron
counterion had a great effect on the oxidation of benzyl alcohol.
Yes
Yes
aReaction conditions: 5 mmol benzyl alcohol, 8 mol% FeCl3•6H2O, 2 mol%
TEMPO, 0.2 g silica gel, 5 ml toluene, 0.5 MPa O2, 80ꢀC, 6 h.
bConversion and selectivity are determined by GC analysis using n-nonane
as the internal standard.
cReaction time: 24 h.
dReaction performed at 65ꢀC.
eUnder 0.1 MPa O2.
Results and Discussion
Effect of silica gel on the benzyl alcohol reaction
Initially, we performed benzyl alcohol oxidation (Table 1). There
was very little reaction without FeCl3.6H2O or TEMPO (Table 1,
entries 1 and 2). The results clearly indicated that the presence
of silica gel greatly improved the conversion of benzyl alcohol
as well as the selectivity for benzaldehyde (Table 1, entries 3–6).
The conversion of benzyl alcohol obtained was 97% with the ad-
dition of 0.2 g silica gel for 6 h (Table 1, entry 3), in contrast to
only 35% for 6 h in the absence of silica gel (Table 1, entry 4).
The conversion of benzyl alcohol obtained was 90% by prolong-
ing the reaction time to 24 h without silica gel (Table 1, entry 5).
When the temperature was decreased to 65ꢀC, however, the con-
version of benzyl alcohol obtained was only 55% (Table 1, entry
6). The result suggested that elevated temperature was essential
for high conversion of the substrate. It is noteworthy that a 95%
conversion of benzyl alcohol was also obtained by reducing the
Oxidation of Alcohols Catalyzed by FeCl3•6H2O/TEMPO
The FeCl3•6H2O/TEMPO/silica gel catalytic system exhibits good
catalytic activity for primary and secondary benzylic alcohols. As
shown in Table 3, primary benzylic alcohols were easily oxidized
Table 2. Optimization of the aerobic oxidation of benzyl alcohola
Entry
Fe salt
Solvent
Time Conversionb Yield b
(h)
(%)
(%)
1
FeCl3•6H2O
FeCl3•6H2O
FeCl3•6H2O
FeCl3•6H2O
FeCl3•6H2O
FeCl3•6H2O
FeCl3•6H2O
Fe2(SO4)3
Fe(OAc)3
Toluene
PhCF3
6
6
7
8
6
6
6
6
6
6
6
7
8
97
90
97
93
62
5
96
89
93
86
60
4
2
3
CH2Cl2
4
C2H4Cl2
n-Hexane
DMF
5
6
7
CH3CN
32
8
25
3
8
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
9
2
0.9
10
11
12
13
FeBr3
69
94
72
100
56
85
FeCl3
FeCl2•4H2O
FeCl2•4H2O
70
>99
Figure 1. Dependence of the conversion of benzyl alcohol on the
amount of silica gel. Reaction conditions: 5 mmol benzyl alcohol, 8 mol%
FeCl3•6H2O, 2 mol% TEMPO, silica gel, 5 ml toluene, 0.5 MPa O2, 80ꢀC,
6 h. Conversions are determined by GC analysis using n-nonane as the
internal standard.
aReaction conditions: 5 mmol benzyl alcohol, 8 mol% Fe salt, 2 mol%
TEMPO, 0.2 g silica gel, 5 ml solvent, 0.5 MPa O2, 80ꢀC.
bDetermined by GC.
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Appl. Organometal. Chem. 2012, 26, 37–43

Selective aerobic oxidation of alcohols promoted by silica gel
Table 3. Oxidation of alcohols catalyzed by FeCl3•6H2O/TEMPOa
Entry
Substrate
Product
Time (h)
O2/Air
Conversionb (%)/Yieldc (%)
O2
Air
97/90
1
7/12
8/18
8/18
100/98(93)
2
3
100/92(90)
100/99(99)
95/80
98/87
4d
24/26
26/42
>99/99(99)
>99/99(99)
26/22
80/79
5d
6d
7d
8
16/24
16/24
6/—
>99/99(98)
100/98
100/98
96/95
—
100/53(50)
98/68
9
9/18
93/66
10
13/—
100/75
—
11
8/—
>99/91(80)
—
12e
13e
14e
15e
24/24
24/—
24/24
24/—
72/67
75/69
92/90
13/8
52/40
—
85/76
—
Appl. Organometal. Chem. 2012, 26, 37–43
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L. Wang et al.
Table 3. (Continued)
Entry
Substrate
Product
Time (h)
O2/Air
24/—
Conversionb (%)/Yieldc (%)
O2
Air
16e
11/4
—
aReaction conditions: 5 mmol alcohol, 8 mol% FeCl3•6H2O, 2 mol% TEMPO, 0.2 g silica gel, 5 ml toluene, 0.5 MPa O2 or air, 80ꢀC.
bConversions are determined by GC.
cYields are determined by GC; values in parentheses are yields of the isolated products.
dConditions: 5 mol% TEMPO.
eConditions: 20 mol% FeCl3•6H2O, 10 mol% TEMPO.
into their corresponding aldehydes with high conversion and yield
(Table 3, entries 1–3). Over-oxidized carboxylic acids were not
observed. As expected, the conversion of electron-deficient
benzylic alcohols took longer compared with electron-rich benzylic
alcohols (Table 3, entries 4–7), whereas a moderate isolated yield
was obtained from a benzylic alcohol containing a p-methoxy
substituent (Table 3, entry 8). Halide-substituted benzyl alcohols
showed good tolerance for the oxidation process (Table 3, entries
6 and 7). Cinnamyl alcohol was also successfully oxidized into
cinnamaldehyde in 80% isolated yield. It was clear that the
conversion of activated secondary benzylic alcohol was high, but
with a moderate yield. Ether was formed as the major by-product,
presumably because of the strong Lewis acidity of FeCl3 (Table 3,
entries 9 and 10). Compared with benzylic alcohols, aliphatic
alcohols were less reactive. Aliphatic secondary alcohols can
also be successfully oxidized into ketones with good yields by
increasing the loading of FeCl3•6H2O and TEMPO (Table 3, entries
12–14). Interestingly, aliphatic secondary alcohols with branched
chains gave excellent results (Table 3, entry 14). In contrast, in the
case of cyclohexanol, the conversion achieved was only 13%
(Table 3, entry 15). Unfortunately, the oxidation of aliphatic primary
alcohols resulted in low conversions. For example, with 1-octanol as
the substrate, the conversion obtained was only 11% (Table 3,
entry 16).
safer.[24] When air was used to replace pure O2, we observed a
slightly lower conversion rate, which can be easily compensated
by prolonging the reaction time (Table 3).
Mechanistic Aspects
Based on the above results, the mechanism of the catalytic
system was investigated. Scheme 1 shows the proposed reaction
process. First, Fe(III) was dispersed on the surface of silica gel.
Next, alcohol coordinated to the Fe(III) to lead to alkoxy species,
which dissolved in toluene and partially adsorbed on the silica
gel surface. Subsequently, alkoxy species in combination with
TEMPO lead to the formation of the species A (Fe(III)–TEMPO
complex), which was considered to exist in the surface phase
and liquid phase and serve as the active intermediate species
in the present catalytic system. Intramolecular transfer of the
b-hydrogen would lead to obtaining the carbonyl compound,
Fe(II) species, and TEMPOH. The resulting Fe(II) species was
oxidized by TEMPO to Fe(III). TEMPOH was oxidized by molecular
oxygen to TEMPO and water.[47] The following sections are
described to support the proposed reaction process.
Figure 2 shows the evidence for the formation of Fe(III)–TEMPO
complex and the oxidation of Fe(II) to Fe(III) by UV–visible spectros-
copy. It should be noted that the UV–visible measurement was
performed using toluene and the reaction amount of benzyl
alcohol as the solvent. This is due to insolubility of the FeCl3•6H2O
A substantial practical improvement for aerobic oxidation is to
replace pure O2 with air since this reduces cost and is also
Scheme 1. Proposed mechanism for Fe–TEMPO-catalyzed aerobic oxidation of alcohols.
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2012, 26, 37–43

Selective aerobic oxidation of alcohols promoted by silica gel
The role of silica gel in the catalytic system of FeCl3•6H2O/TEMPO
was investigated. Figure 3 shows the catalytic performance of
FeCl3•6H2O/TEMPO in the presence of other solid additives as a
comparison to the silica gel. The acidic molecular sieve of
HZSM-5, the neutral molecular sieve of SBA-15, neutral alumina
and g-alumina could give good conversions of benzyl alcohol,
while the presence of a 3 Å molecular sieve and nano-MgO
decrease the catalytic activity. These results indicate that the pri-
mary role of silica gel is not to remove the water by-product, since
the 3 Å molecular sieve is traditionally used as a dehydrater for
organic solvents and that the main role of the silica gel is not to
widen the surface of iron salts. The surface hydroxyl groups of
the solids appear to be the major contributor in accelerating the
reaction. Therefore we speculate that the silanol groups form a
special reaction field where alcohols and catalysts are accumu-
lated by adsorption. This speculation is supported by the report
that the principal adsorption sites of the silica gel are the surface
Figure 2. UV-visible investigation of Fe(III)–TEMPO complex formation.
and FeCl2•4H2O in pure toluene. As shown in Fig. 2, the UV–visible
spectrum of Fe(III) has the maximum at 341nm; after addition of
TEMPO, the maximum at 341nm disappeared and two new
maxima at 312nm and 351 nm emerged. Actually, the possible
coordination mode of [Fe(dmf)3Cl2]–TEMPO complex has been
studied in detail.[48] The spectrum of [Fe(dmf)3Cl2]–TEMPO
exhibited two maxima at 317 nm and 352 nm. These results
indicate that Fe (III)–TEMPO was formed in the course of alcohol
oxidation. In addition, as the amount of TEMPO is increased, the
wavelength is also shifted. The UV–visible spectrum of Fe(II) (under
N2 condition) has a maximum at 333 nm; after addition of TEMPO,
the maximum at 333 nm disappeared and two new maxima
at 316 nm and 359 nm emerged, which was consistent with the ab-
sorbance of Fe(III):TEMPO (4:2). This demonstrated that Fe(II) was
oxidized to Fe(III) by TEMPO, and formed the Fe (III)–TEMPO
complex with another molecule of TEMPO. The alkoxy-Fe (III)–
TEMPO complex could serve as active intermediate species in the
present catalytic system. It is noteworthy that the same absorption
peak was obtained in the presence of silica gel, indicating that the
addition of silica gel did not change the reaction mechanism.
To the best our knowledge, this is the first report of the
FeCl3•6H2O/TEMPO catalyst system directly activating molecular
oxygen without requiring a co-oxidant for the oxidation of alcohols.
Figure 4. Time courses for the oxidation of benzyl alcohol over different
activation temperatures of silica gel: (■) 800ꢀC; (●) 650ꢀC; (▲) 300ꢀC; (▼)
off the shelf; (□) without silica gel. Reaction conditions: 5 mmol benzyl
alcohol, 8 mol% FeCl3•6H2O, 2 mol% TEMPO, silica gel 0.2 g, 5 ml toluene,
0.5 MPa O2, 80ꢀC, 6 h. Yields are determined by GC analysis using
n-nonane as the internal standard.
Figure 5. Effect of the different treatment temperatures of silica gel on
oxidation of benzyl alcohol. Reaction conditions: 5 mmol benzyl alcohol,
8 mol% FeCl3•6H2O, 2 mol% TEMPO, 0.2 g silica gel, 5 ml of toluene,
0.5 MPa O2, 80ꢀC, 6 h. Yields are determined by GC analysis using
n-nonane as the internal standard. (□) GC yield.
Figure 3. Effect of solid additives on the oxidation of benzyl alcohol.
Reaction conditions: 5 mmol benzyl alcohol, 8 mol% FeCl3•6H2O, 2 mol% of
TEMPO, 0.2 g of additives, 5 ml toluene, 0.5 MPa O2, 80ꢀC, 6 h. Conversions
are determined by GC analysis using n-nonane as the internal standard.
Appl. Organometal. Chem. 2012, 26, 37–43
Copyright © 2012 John Wiley & Sons, Ltd.
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L. Wang et al.
silanol groups.[49] The effect of silica gel treatment temperature
on the surface concentration of hydroxyl groups has been well
investigated.[50] As the number of hydroxyl groups on the silica
gel surface decreased with increasing temperature, there was a
remarkable difference in the oxidation rate of benzyl alcohol from
the observed kinetic data (Fig. 4).
Figure 5 illustrates the catalytic performance of FeCl3•6H2O/
TEMPO for the oxidation of benzyl alcohol in the presence of
the different treatment temperature of silica gel. In the silica gel
treatment temperature range 100–500ꢀC, benzaldehyde yields
were essentially unchanged. Up to 600ꢀC the yield of benzaldehyde
was obviously reduced. When the treatment temperature of silica
gel was raised to 1100ꢀC, the yield of benzaldehyde decreased
greatly. This might be attributed to the concentration of silanol
groups, which dropped to a certain extent, affecting the reaction
results. Based on the above results, it is most likely that the
enhancement in catalytic performance of FeCl3•6H2O/TEMPO is
due to the surface concentration of the adsorbed reactant.[51,52]
1-octanol and their corresponding products were detected under
the following conditions: column temperature, 100ꢀC for 7 min, rising
to 250ꢀC at a rate of 15ꢀCminÀ1. 2-Pentanol and its corresponding
product were detected under the following conditions: column
temperature, 30ꢀC for 7 min, rising to 250ꢀC at a rate of 15ꢀCminÀ1
.
4-Methyl-2-pentanol and its corresponding product were detected
under the following conditions: column temperature, 80ꢀC for 7min,
rising to 250ꢀC at a rate of 15ꢀCminÀ1
.
General Experimental Procedure
The oxidation of all alcohols was carried out in a Teflon-lined 316 L
stainless steel autoclave. The initial air in the autoclave was ex-
changed three times with oxygen. Typically, FeCl3•6H2O (0.4mmol)
and silica gel (0.2 g) were added to the autoclave, followed by 5 ml
toluene. After stirring for 2 min, benzyl alcohol (5 mmol) was added
and stirred for 5 min, then TEMPO (0.1 mmol) was added. After the
autoclave was closed, oxygen was charged to 0.5 MPa. The auto-
clave was placed in an oil bath which was pre-heated to 80ꢀC. The
reaction mixture was monitored by GC. When the reaction was
finished, the autoclave was cooled to room temperature and
carefully depressurized. The reaction mixture was loaded directly
on a small pad of silica flushing with hexane to remove the toluene
and the product was eluted with dichloromethane. The solvent was
concentrated in vacuo and the product was further purified by
column chromatography over silica gel (n-hexane:ethylacetate,
Conclusions
We have developed an environmentally friendly and efficient
FeCl3•6H2O/TEMPO/ silica gel-catalyzed method for the oxidation
of alcohols to their corresponding aldehydes and ketones with
moderate to excellent yields. In this catalytic system, silica gel, as
the additive, plays an important role. Its presence speeds up the
oxidation rate to a remarkable degree. A plausible mechanism of
the catalytic system is proposed, in which the Fe(III)–TEMPO
complex might serve as the active intermediate species. Simple
and green catalysts will be very practical and useful in the prepara-
tion of fine chemicals.
1
10:1) to afford benzaldehyde (502 mg, yield 93%). H and 13C NMR
spectra data of all isolated products were in accord with the literature.
Sample preparation for UV–visible investigation of Fe(III)–
TEMPO complex formation
The UV–visible measurement was performed using toluene and the
reaction amount of benzyl alcohol as the solvent. This is due to the
insolubility of FeCl3•6H2O and FeCl2•4H2O in pure toluene. Into a
10 ml A-grade volumetric flask was added precisely 0.108 g
FeCl3•6H2O. 0.5407 g benzyl alcohol was added, followed by 2 ml
toluene. The mixture was swirled vigorously for approximately
2 min, and then 0.0156 g TEMPO was added. The reaction was
swirled vigorously for approximately 2 min to allow for complex
formation to occur, and then was diluted to volume. 0.1ml of this
solution was transferred to a fresh 10 ml A-grade volumetric flask
and diluted to volume. This final solution was then immediately an-
alyzed (See Supporting Information for details).
Experimental
General Chemical Reagents
All chemicals used in this study were analytical grade, commercially
available and used without further purification unless otherwise
noted. Silica gel was 200–300 mesh, with a surface area of
172.1 m2 gÀ1 and average pore diameter 2.182 nm.
General Measurement
1H NMR and 13C NMR spectra were recorded on a Bruker 400 MHz
NMR spectrometer using CDCl3 as the solvent with tetramethylsilane
SUPPORTING INFORMATION
as an internal reference. H and 13C positive chemical shifts (d) in
1
ppm are downfield from tetramethylsilane (CDCl3: dC =77.0 ppm;
residual CHCl3 in CDCl3: dH = 7.26 ppm). Determination of conver-
sions and yields by gas chromatography (GC) was performed on
an Agilent 7890A with a flame ionization detector (FID). All products
were confirmed by gas chromatography–mass spectrometry (GC-
MS) with an Agilent 6890N GC/5973 MS detector and comparison
of their GC retention time with those of authentic samples. The
UV–visible spectra were recorded on a Shimadzu-2550 spectrometer
with 10 mm path length of quartz sample cells at 298 K. Wavelength
range, 240–900 nm; SE-54 capillary column, 30 m  250 mm 1mm;
FID, 300ꢀC; injection, 250ꢀC; carrier gas, nitrogen; carrier gas rate, 2 ml
minÀ1. Benzyl alcohol, 3-methyl-benzyl alcohol, 4-methyl-benzyl
alcohol, 4-nitrobenzyl alcohol, 3-nitrobenzyl alcohol, 4-methoxybenzyl
alcohol, 4-bromobenzyl alcohol, 4-chlorobenzyl alcohol, cinnamyl
alcohol, 1-(4-chlorophenyl)ethanol, DL-1-phenylethanol, 2-octanol,
Supporting information may be found in the online version of
this article.
Acknowledgments
We gratefully acknowledge financial support from the National
Natural Science Foundation of China (No. 20643006), the Scientific
Research Foundation for the Returned Overseas Chinese Scholars,
State Education Ministry and the National Basic Research Program
of China (2009CB623505).
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