Photocatalytic oxidation of benzyl alcohol by homogeneous CuCl2/solvent: A model system to explore the role of molecular oxygen

Article abstract of DOI:10.1021/acscatal.5b00644

The oxidation of alcohols to the corresponding carbonyl compounds is a pivotal reaction in organic synthesis. Under visible light irradiation, the homogeneous CuCl₂ and cheap solvent oxidized benzyl alcohol into benzaldehyde with a selectivity higher than 95% using molecular oxygen as an oxidant. The formation of a visible light responsive complex between Cu(II) and solvent is responsible for the occurrence of the oxidation of benzyl alcohol. During the photocatalytic process, molecular oxygen was not incorporated into the final benzaldehyde and only involved in the oxidation of Cu(I) into Cu(II) in which it served as a terminal hydrogen acceptor to form H₂O. A similar role of molecular oxygen has also been observed in the heterogeneous TiO₂ photocatalytic system. The understanding of the role of molecular oxygen helps us to further design new classes of synthetic organic reactions by photocatalytic processes.

Full text of DOI:10.1021/acscatal.5b00644

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Article
Photocatalytic oxidation of benzyl alcohol by homogeneous CuCl2/
solvent: a model system to explore the role of molecular oxygen
Chao Meng, Kai Yang, Xianzhi Fu, and Rusheng Yuan
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.5b00644 • Publication Date (Web): 14 May 2015
Downloaded from http://pubs.acs.org on May 19, 2015
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Photocatalytic oxidation of benzyl alcohol by
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homogeneous CuCl /solvent: a model system to
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explore the role of molecular oxygen
Chao Meng, Kai Yang, Xianzhi Fu and Rusheng Yuan*
State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry,
Fuzhou University, Fuzhou 350002, P. R. China
ABSTRACT: The oxidation of alcohols to the corresponding carbonyl compounds is a pivotal
reaction in organic synthesis. Under visible light irradiation, the homogeneous CuCl and cheap
2
solvent oxidized benzyl alcohol into benzaldehyde with a selectivity higher than 95% using
molecular oxygen as oxidant. The formation of a visible light responsive complex between
Cu(II) and solvent is responsible for the occurrence of the oxidation of benzyl alcohol. During
the photocatalytic process, molecular oxygen wasn't incorporated into the final benzaldehyde,
and only involved in the oxidation of Cu(I) into Cu(II) in which it served as a terminal hydrogen
acceptor to form H O. A similar role of molecular oxygen has also been observed in
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heterogeneous TiO photocatalytic system. The understanding of the role of molecular oxygen
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helps us to further design new classes of synthetic organic reactions by photocatalytic process.
KEYWORDS: Photocatalysis; Benzyl alcohol; Copper complex; Selective oxidation;
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Molecular oxygen; Isotopic labelling
1. INTRODUCTION
The selective oxidation of alcohols to carbonyl compounds is one of the fundamental
transformations both in laboratory synthesis and industrial production since aldehydes and
ketones are ubiquitous intermediates in the synthesis of pharmaceuticals and fine chemicals.
Conventional alcohol oxidation not only requires the use of heavyꢀmetal and corrosive
stoichiometric oxidants but also produces large amounts of heavy metal waste. This gives rise to
the development of environmentꢀfriendly catalytic processes utilizing molecular oxygen as
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,2
oxidant that is available at virtually no cost and produces water as only byꢀproduct. The
aerobic oxidation of benzyl alcohol has been performed by using nobleꢀmetal or transitionꢀmetal
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complexes as catalysts in thermal catalysis system. Recently, heterogeneous TiO ꢀbased
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photocatalysis has also emerged as a good candidate for selective oxidation of aromatic alcohols
4ꢀ8
due to the using of sustainable solar energy.
Undoubtedly, molecular oxygen is indispensable and plays a pivotal role in all these aerobic
transformations of alcohols. Although many researchers have reported the aerobic oxidation of
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benzyl alcohol to benzaldehyde using a variety of catalytic materials, there are only few
investigations about the role of O in the reaction process and most are speculative in nature. In
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,10ꢀ13
the widely used Pd catalysis,
molecular oxygen is not incorporated into the products and
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only involved in the catalyst regeneration. In the P450ꢀcatalyzed oxidation of alcohols,
molecular oxygen is generally incorporated into the oxidized product, but there are also some
exceptions that partial or complete lack of incorporation of molecular oxygen into the carbonyl
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product has been observed. In heterogeneous TiO ꢀbased photocatalysis, Zhang's group found
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that the oxygen atom in the product aldehyde completely came from molecular oxygen by
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isotopic tracer technique. The differences in the role of molecular oxygen in different catalytic
systems prompt us to approach this question by investigating homogeneous and heterogeneous
photocatalytic systems.
15ꢀ24
In addition to palladiumꢀbased catalysts, copperꢀbased catalysts
have also been employed
for the aerobic oxidization of alcohols into aldehydes and ketones under mild conditions, such as
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copperꢀDEAD/DBAD , copperꢀphenanthroline and recently developed copper(Ι)/TEMPO
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catalysts
. Although the copper counterion is critical to the success of the reaction, it is also
necessary to add an additive as the ligand in these reactions. Herein, we found a photocatalytic
system consisting of common copper ions and cheap organic solvent that can be used repeatedly
for the selective oxidation of benzyl alcohol into benzaldehyde without the necessity of other
organic additives. As a model system, detailed isotopic labelling studies were performed to
identify the role of molecular oxygen that is significant for designing various synthetic reactions
by phtotocatalysis.
2. RESULTS AND DISCUSSION
Photocatalytic Oxidation of Alochols. The photocatalytic oxidation of benzyl alcohol by
homogeneous CuCl in different solvents is shown in Table 1. Under visible light irradiation for
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h, the homogeneous CuCl in acetonitrile and acetone afforded 92.5% and 95% conversion of
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a
Table 1．Photocatalytic oxidation of benzyl alcohol by CuCl /solvent
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b
Entry
Solvent
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetone
Time [h]
Conversion [%]
Yield [µmol]
185
Selectivity [%]
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92.5
6.5
95
96
96
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11.8
trace
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trace
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Acetone
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Acetone
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877
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Acetone
trace
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trace
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e
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Acetone
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Acetone
944
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Other
trace
trace
a
General reaction conditions: benzyl alcohol (9.6 mmol), catalyst (0.1 mmol), solution
volume (10 mL), O atmosphere (balloon pressure), light intensity (400 mW•cm , 420~780 nm
wavelength range), room temperature (air cooling, 25 C). Other: solventꢀfree, benzotrifluoride,
dimethyl sulfoxide, N,Nꢀdimethylformamide, ethyl acetate or phenylacetonitrile.
ꢀ
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o
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c
Benzyl
d
o
e
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alcohol (0.2 mmol), solution volume (1 mL). 80 C, no light. Light intensity of 700 mW•cm .
f
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g
o
Light intensity of 1200 mW•cm . 55 C, no light.
benzyl alcohol with a selectivity of 95% for benzaldehyde, respectively (Entries 1 and 7). In the
absence of light irradiation, no conversion of benzyl alcohol was observed even when heating to
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0 °C in acetonitrile and 55 °C in acetone (a temperature close to its boiling point) (Entries 4
and 10). This further confirms why the addition of other organic ligands was required in the
aerobic oxidation of alcohol using copperꢀbased catalysts in thermal catalysis. Similarly, the
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photocatalytic oxidation reaction can't also occur in the absence of one of CuCl and solvent
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(acetonitrile or acetone). When acetonitrile or acetone was replaced by other solvents such as
dimethyl sulfoxide, N,Nꢀdimethylformamide, benzotrifluoride, ethyl acetate or
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phenylacetonitrile, the oxidation of benzyl alcohol can't occur (Entry 13). Upon irradiation with
highꢀintensity visible light, the increased yields of benzaldehyde were observed (Entries
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,6,11,12 and Figure S1), which indicates that the oxidation of benzyl alcohol over CuCl in
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solvent is a typical photocatalytic reaction. The scope of this photocatalytic oxidation of benzyl
alcohol was also extended to a variety of other alcohols (Table 2).
a
Table 2. Photocatalytic oxidation of different alcohols by CuCl /CH COCH
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Entry
Substrate
Conversion [%]
Product
Selectivity [%]
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29
>95
80
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30
>95
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>95
>95
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25
>95
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a
General reaction conditions: substrate (0.2 mmol), catalyst (CuCl , 0.1 mmol), solvent
acetone, 1 mL) ， light intensity (300 mW•cm , 420~780 nm wavelength range), room
temperature (air cooling, 25 C), irradiation time (1 h), O atmosphere (balloon pressure).
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in Figure 1 and Table S1, the asymmetric unit of CuCl (CH CN) (a) contains one Cu cation,
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Figure 1. Representation of the Xꢀray crystal structure of (a) CuCl (CH CN), (b)
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Cu(H O)Cl (CH COCH ). The influence of incident light wavelength on benzyl alcohol
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conversion in CuCl /CH CN system (c) and CuCl /CH COCH system (d). Reaction conditions:
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Figure 2. GCꢀMS analysis of the products during the photocatalytic oxidation of benzyl alcohol
aꢀe and hꢀp) and cyclohexanol (f,g) by CuCl (aꢀg) and TiO (hꢀp) using isotopic tracer
(
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technique. (a) In acetonitrile. (b,c) Using O in acetone (b) and acetonitrile (c). (d) Using 3A
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molecular sieve and O in acetonitrile. (e) Using Oꢀenriched benzyl alcohol in acetonitrile or
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two Cl anions and one acetonitrile molecule. Compound Cu(H O)Cl (CH COCH ) (b) consists
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of oneꢀhalf Cu cation, one Cl anion, oneꢀhalf water molecule and a quarter of guest acetone
molecule. Both solutions absorb light in the visible regions of the spectrum, and the conversion
of benzyl alcohol is proportional to the strength of the absorption peak of the solution (Figure 1c
and 1d). Similar to the cases of acetonitrile and acetone, the system of CuCl in butanone also
2
has a new absorption band in the visible light region and exhibited a higher reaction efficiency
than that in acetonitrile and acetone (Figure S2 and Table S2). In all cases, only the coexistence
of CuCl and solvent (acetonitrile, acetone or butanone) have absorption band in the visible light
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region, and no obvious changes were observed before and after the addition of benzyl alcohol.
This indicates that a visibleꢀlight responsive complex between CuCl and solvent are responsible
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for the photocatalytic oxidation of benzyl alcohol.
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IsotopeꢀLabeling Studies. When O in the above reaction (Figure 2a) was replaced by O ,
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labeled benzaldehyde (C H CH O) was detected in acetonitrile system after photoirradiation for
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5 h, whereas unlabeled one was obtained in acetone system under the similar conditions (Figure
c and 2b). This result seems to indicate that whether oxygen atom transfer from molecular
oxygen to the product happened or not depends on the solvent used in the photocatalytic
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oxidation of alcohols. Control experiments carried out with Oꢀenriched benzyl alcohol and O
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gave unlabeled benzaldehyde (Figure 2e) in acetonitrile and acetone, which implies that oxygen
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atom in molecular oxygen can easily transfer to the product in both solvents. The above two
completely contradictory results in acetone make us to explore the role of molecular oxygen in
photocatalytic oxidation of benzyl alcohol.
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stirred for 10 min. Labeled benzaldehyde (C H CH O) was detected in CH CN whereas labeled
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acetone (CH C OCH ) was detected in acetone (Figure S3). This indicates that the oxygen atom
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transfer from H O to aldehydes or ketones easily occurred. For comparison, the H NMR spectra
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of pure C H CD OH and D O in CH CN were tested (Figure 3a and 3b). In our experiments,
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Figure 3. H NMR spectra of C H CDO and deuteriumꢀcontaining water in CH CN. (a) Pure
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C H CD OH in CH CN. (b) Pure D O in CH CN. Products in the oxidation of C H CD OH
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using CuCl /CH CN in the presence (d) and absence (c) of molecular sieve 3A. Products in the
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oxidation of C H CD OH using TiO in the presence (f) and absence (e) of molecular sieve 3A.
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deuteriumꢀcontaining water was detected by H NMR during the photocatalytic oxidation of
benzylꢀα,αꢀd alcohol (C H CD OH) in acetonitrile (Figure 3c) since molecular oxygen can
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combine with the liberated hydrogen from benzyl alcohol to produce water. Thus, whether O2
participated in the oxidation of benzyl alcohol should exclude the influence of the water
produced during the reaction process. In our system, the formed water was excluded by adding
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molecular sieve 3A with excellent adsorption of water into the reaction solution.
As shown in
Figure 3d, the introduction of molecular sieve 3A removed the produced water in the reaction
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and hardly affected the reaction behavior. The system of benzyl alcohol, O and molecular
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sieve 3A in CH CN gave unlabeled benzaldehyde (Figure 2d), obviously different from the
3
system without molecular sieve. That is to say, molecular oxygen was not really incorporated
into the final product during the photocatalytic oxidation of benzyl alcohol in CH CN. This is
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consistent with the result of using acetone as solvent because a large amount of acetone could
easily exchange its oxygen atom with that of the formed water and greatly decreased the oxygen
exchange between H O and benzaldehyde (Figure S3). In other words, the use of acetone as
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solvent eliminated the influence of the formed water on the isotopic tracer results. When benzyl
alcohol was replaced by cyclohexanol, a same oxygen transfer process was further demonstrated
(Figure 2g and 2f).
The photocatalytic oxidation of benzyl alcohol over typical heterogeneous phototocatalyst
TiO was also tested to further identify the chemical pathway of molecular oxygen. Under UV
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light irradiation, the system of benzyl alcohol and O in CH CN, benzotrifluoride (Btf) or CS
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gave labeled benzaldehyde (C H CH O) (Figure 2i, 2k and 2m). When using Oꢀenriched
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benzyl alcohol and O , unlabeled benzaldehyde was obtained (Figure 2o). These phenomena are
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apparently consistent with Zhang's results that molecular oxygen was incorporated into the
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product. However, the control reactions using dimethyl sulfoxide (DMSO) or acetone as
solvent (Figure 2h) and the cases of adding molecular sieve 3A into the system (Figure 2j, 2l and
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n) indicated that molecular oxygen was not involved into the product during the oxidation
processes, which is good agree with that using homogeneous CuCl catalyst because the solvents
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H O in TiO system (Figure 3e and 3f). When the formed water was eliminated by adding
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stoichiometric reagent of CaH into the reaction system, similar isotopic result was also observed
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(Figure 2p). Therefore, both in homogeneous and heterogeneous photocatalytic systems,
molecular oxygen wasn't incorporated into the final product.
Proposed Catalytic Mechanism and Implications in Synthesis. In the homogeneous
CuCl /solvent system, a simplified mechanism for the oxidation of alcohols is depicted in
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Scheme 1, similar to that using Pd catalysts. When CuCl was dissolved into acetonitrile or
2
Scheme 1. Proposed mechanism for the photocatalytic oxidation of benzyl alcohol by
homogeneous CuCl /solvent.
2
acetone, a complex A with visibleꢀlight absorption was formed. Benzyl alcohol binds to A
through an unshared pair of electrons on hydroxyl oxygen, forming Cuꢀbound alcohol B. Under
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visible light irradiation, intramolecular deprotonation of B forms C followed by subsequent αꢀ
hydride elimination with another A to give benzaldehyde, HCl and CuCl species E. E is oxidized
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to Cu(II) complex (A) by molecular oxygen,
further initiating a second catalytic cycle. In the
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absence of oxygen, the oxidation of benzyl alcohol using CuCl /solvent occurred only in a
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stoichiometric ratio, and ceased when Cu(II) was completely reduced to Cu(I) (Figure 4 and
Figure 4. Periodic oxidation of benzyl alcohol by CuCl (CH CN) with visible light. Reaction
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conditions: catalyst (CuCl , 0.1 mmol), solvent (CH CN, 3 mL), benzyl alcohol (0.96 mmol),
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light intensity (500 mW•cm , 420~780 nm wavelength range).
Table S3). This suggests that Cu(II) complex is responsible for the occurrence of the oxidation of
benzyl alcohol. When O was introduced into this system, Cu(I) complex (E) changed into Cu(II)
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complex which can further transform of benzyl alcohol to benzaldehyde. The involvement of
radical species was ruled out since the introduction of typical radical scavengers such as TEMPO
(2,2,6,6ꢀtetramethylpiperidineꢀNꢀoxyl) and PBN (Nꢀtertꢀbutylꢀαꢀphenylnitrone) can hardly
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inhibit the oxidative reaction (Table S4).
In addition, the oxidation of alcohols is
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benzaldehyde. This led to a false impression that molecular oxygen was incorporated into the
product during the photocatalytic oxidation of benzyl alcohol.
The nature of the oxidation of benzyl alcohol by homogeneous Cuꢀbased complex also
conveys important information for the photocatalytic oxidation of benzyl alcohol by TiO2
photocatalyst. As portrayed in Figure 5, benzyl alcohol was first adsorbed on the surface of TiO2
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Figure 5. Possible processes for TiO catalyzed oxidation of alcohol.
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to form alcoholate species
and then be oxidized by a twoꢀelectron transfer (TET) process in
which O acted as the scavengers of two electrons and protons to produce water (or hydrogen
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peroxide) and didn't participate in the oxidation of benzyl alcohol after excluding the oxygen
exchange between water and benzaldehyde.
In view of the fact that O is only involved in the regeneration of the catalyst, the
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photocatalytic oxidation of benzyl alcohol by CuCl /solvent is a successive dehydrogenation
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reaction in essence. Thus, we propose that if the oxidation potential of the excited catalyst is
large enough to complete the dehydrogenation of various substrates and there is also a reasonable
route for the chemical transformation of the liberated hydrogen, various synthesis reactions can
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be occurred. As expected, the photocatalytic oxidative homocoupling of phenylacetylene was
successfully performed by CuCl /acetonitrile in the presence of molecular oxygen and visible
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light (Figure 6). Under visible light irradiation (300 mW•cm ) for 12 h, phenylacetylene was
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Figure 6. CuCl (CH CN) catalyzed oxidation of phenylacetylene under O atmosphere. Reaction
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conditions: catalyst (CuCl , 0.1 mmol), phenylacetylene (200 µL), solvent (CH CN, 1.8 mL),
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light intensity (300 mW•cm , 420~780 nm wavelength range). Inset: the influence of light
intensity on the product yield (2 h irradiation).
converted into biphenylacetylene in a high yield, about 1209 µmol. When prolonging irradiation
time or changing the light intensity to enhance the number of incident photons, a linear increase
in the yield of 1,4ꢀdiphenylbutadiyne was observed, which confirmed that the reaction proceeded
in a photocatalytic manner (Figure S4).
Similarly, in heterogeneous Pt/TiO photocatalytic systems, the homocoupling or other
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accompanying the continuous evolution of H (Figure 7 and Figure S5). In the absence of O ,
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Figure 7. (A) oxidation profile for dehydrogenation reaction. Reaction conditions: 0.1 mmol of
catalyst, 1.5 mL of solvent (CH CN), 0.5 mL of substrate, irradiation for 12 hours. Timeꢀyield
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curves for the oxidation of benzyl alcohol (B) and benzylamine (C) by Pt/TiO2.
benzyl alcohol can also be converted into benzaldehyde, and the yields of benzaldehyde and H2
increased in a similar trend (B). When using benzylamine as the substrate, both the oxidation
reaction to afford imine and the hydrogenꢀproducing reaction were proceeded simultaneously (C),
and a satisfying yield of 890 µmol for 36 h reaction was obtained. Also, the direct coupling of
toluene containing saturated CꢀH bond occurred to form bibenzyl and hydrogen (Figure 7(c)).
All these reactions indirectly implied that O just served as a terminal hydrogen acceptor and
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wasn't incorporated into the final product. Therefore, by discerning the role of oxygen in the
photocatalytic oxidation, it is possible to design the reactions to obtain required products.
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. CONCLUSIONS
In conclusion, we have developed a homogeneous visibleꢀlight photocatalytic system consisting
common copper ions and cheap organic solvent for the selective oxidation of benzyl alcohol into
benzaldehyde using molecular oxygen as the oxidant. The results of the isotopic tracer
experiments showed that molecular oxygen didn't transfer to benzaldehyde and only involved in
the catalyst regeneration both in homogeneous and heterogeneous photocatalytic systems. The
understanding of the role of molecular oxygen helps us to further design new classes of synthetic
organic reactions by photocatalytic process.
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4. EXPERIMENTAL DETAILS
Selective oxidation of typical alcohols by copper complexes and TiO ꢀbased photocatalysts.
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All the photocatalytic reactions were performed in a 10 mL quartz glass bottle at ambient
temperature. In a typical sealed reaction system, 0.1 mmol of anhydrous CuCl or TiO was
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thoroughly dispersed in 1 mL solution (0.1 mL benzyl alcohol and 0.9 mL solvent) with a
magnetic stirrer under O (balloon pressure). A 300 W Xenon lamp (PLSꢀSXE300C, Beijing
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Perfect Light Co) equipped with an IRꢀcutoff filter (λ<780 nm) was set on one side of the
reactor, providing the visible light (λ>420 nm) and UV light (λ>320 nm) through the
combination of different filters for copper complexes involved reactions. UV source was also
provided by 4ꢀW UV lamps with certain wavelengths centered at 365 nm (Philips, TUV 4W/G4
T5) for the cases of using TiO or Pt/TiO as typical photocatalysts. After reaction, the reaction
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mixture was filtered through a porous membrane (20 µm in diameter) and then injected into the
GC equipped with FID detector (Agilent Technologies, GC7890A) for analysis. A HPꢀ5 5%
phenyl methyl siloxane column (30 m ×0.32 mm × 0.5 µm) was used. The chemical structures
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of the products were confirmed by comparison with standard chemicals and GCꢀMS (Agilent
Technologies, GC6890N, MS 5973). The conversion for the substrate was described as the ratio
of the moles of the reactant consumed in the reaction to the initial moles of the reactant. The
selectivity was defined as the ratio of the moles of the product to that of the reactant consumed in
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the reaction. O ꢀlabeling experiments proceeded under similar conditions to the photocatalytic
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oxidation of benzyl alcohol except that the normal O atmosphere was replaced by O (97%),
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and the pressure of O was about 0.1 MPa. After reaction, the oxygen isotope abundance of the
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asꢀobtained products was measured by GCꢀMS. Anaerobic oxidation of benzyl alcohols: All
manipulations of airꢀsensitive (or moistureꢀsensitive) materials were carried out with techniques
of using standard Schlenk vessels or in glove box under N atmosphere. Part of the experiments
2
introduced molecular sieve 3A (or CaH ) as the dehydration reagent to remove the moisture in
2
reaction media. All the other oxidative reactions or dehydrogenative reactions employed the
same procedures as mentioned above. The gaseous product such as H was analyzed by a TCD
2
detector on Agilent 7890A equipped with a TDXꢀ01 packed column (3 m × 1.25 mm). Some of
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the deuterated products were detected by H NMR on Bruker AVANCE III 500 operating at 76.8
MHz. D O (20 µL D O dissolved in 1 mL CH CN) and benzyl alcohol (C H ꢀCD OH) (20 µL
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C H ꢀCD OH dissolved in 1 mL CH CN) were selected as reference substances.
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Synthesis and characterization of CuCl ꢀbased crystal. Typically, anhydrous copper(II)
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chloride (1g, 7.3 mmol) was dissolved into acetonitrile (100 mL) in a glove box under N2
atmosphere to give a yellowꢀgreen solution. The asꢀobtained solution was filtered to remove the
residual solids after stirring for 1 h. The filtrate stayed in glass beaker for an ultraꢀlong period
(
more than 5 days) to ensure a moderate evaporation rate in anhydrous environment. Finally, the
yellowꢀgreen crystals of CuCl (CH CN) were obtained and removed from the filtrate for further
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characterization. This procedure was also applied to the synthesis of Cu(H O)Cl (CH COCH )
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except that acetonitrile was changed to acetone. Variableꢀtemperature Xꢀray singleꢀcrystal
diffraction data of Cu(H O)Cl (CH COCH ) and CuCl (CH CN) were collected on Super Nova
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CCD diffractometer with the graphite monochromated CuꢀKα radiation (λ = 1.54184 Å). The
CrystalClear software package (Rigaku) was used for data collection, cell refinement and data
reduction. Crystal structures were solved by the direct methods and refined by the fullꢀmatrix
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method based on F2 using the SHELXLTL software package . All nonꢀhydrogen atoms were
refined anisotropically and the positions of hydrogen atoms were generated geometrically.
Crystallographic data and details of data collection and refinement for Cu(H O)Cl (CH COCH )
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and CuCl (CH CN) are given in Table S1. The liquid UV–Vis spectra of the solution samples
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were recorded from 200 to 800 nm by using a Cary 5000 UVꢀVisꢀNIR spectrophotometer
Varian, America).
(
Preparation and characterization of Pt/TiO photocatalyst. Pt/TiO photocatalyst was
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prepared by a precipitation deposition method using chloroplatinic acid as the platinum source. 1
g Pꢀ25ꢀTiO was dispersed into 100 mL H O with stirring for 1 h, and 2.8 mL H PtCl (0.1 g/mL)
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solution (1g H PtCl •7H O dissolved in 100 mL H O) was further added into the asꢀobtained
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P25ꢀwater system. Then, the pH of this solution was adjusted by slowly dropwise adding of
NaOH (0.1 mol/L) to reach about 9. The asꢀobtained H PtCl ꢀP25 mixed system was reduced
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with aqueous solution of 0.1 mol/L NaBH containing 0.1 mol NaOH, then it was centrifugated
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+
ꢀ
and washed thoroughly with distilled water (remove the remaining Na and Cl ions). Finally, the
o
solid product was dried at 80 C for 10 h.
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Preparation of O enriched alcohol. The method to synthesize O enriched alcohol is
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similar to the previous report by Zhang . The detailed procedure was described as follows. 0.1 g
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Na was added into 1.5 mL O enriched water (90% H O, J&K Chemical Technology) in a
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flask, 1.0 mL 1ꢀchloromethyl benzene was added into the flask. The mixture was heated to 368
K and refluxed for 48 h with continuous stirring. The product was purified by distillation. The
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O enriched benzyl alcohol was examined by GCꢀMS, and the abundance of C H CH OH was
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about 90%. 20 µL of the mixture product was stirred in 1 mL CH CN to be examined by GC and
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GC/MS. The data show that 20 µL of the mixture product contains 118 µmol of 1ꢀchloromethyl
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benzene and 70 µmol of O benzyl alcohol.
ASSOCIATED CONTENT
Supporting Information.
All extra reaction data, additional crystallographic information, the copies of mass spectra for all
the resulted products in different reactions. This material is available free of charge via the
Internet at http://pubs.acs.org.”
AUTHOR INFORMATION
Corresponding Author
*Eꢀmail: yuanrs@fzu.edu.cn
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
We thank Dr. Yuanyuan Tang, Dr. Zeping Wang, M.S. Kun Huang, and Dr. Liuyi Li for single
crystal Xꢀray diffraction analysis and constructive discussion. This work was financially
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supported by the National Nature Science Foundation of China 21077023, the National Basic
Research Program of China 2014CB239303, the Natural Science Foundation of Fujian Province
of China 2015J01046, and the Independent Research Project of State Key Laboratory of
Photocatalysis on Energy and Environment 2014B01.
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