Heterogeneous viologen catalysts for metal-free and selective oxidations

Article abstract of DOI:10.1039/c8gc03772h

Metal-free oxidation, a green chemistry process, has drawn significant attention from catalysis researchers. However, most oxidation processes are completed by homogeneous metal-free catalysts, whereas heterogeneous metal-free materials have been developed with limited successes. In this study, polymerized ionic networks (PINs) with N,N′-dialkyl-4,4′-bipyridinium units as heterogeneous viologen type of catalysts exhibited high efficiency in the oxidation of aromatic sulfides/alcohols to sulfoxides/aldehydes, respectively (conversion: >90%, selectivity: >95%). The catalytic performance of PINs originates from the electron-accepting ability of the viologen unit, which can reduce H₂O₂ into an active species. Especially, the synthesis of PIN catalysts is a one-step simple polymerization reaction between benzyl bromide and bipyridine in air. The metal-free heterogeneous feature, high selectivity, mild conditions (60 °C, 1 h), and the facile preparation of the catalyst make the current selective oxidation approach attractive.

Full text of DOI:10.1039/c8gc03772h

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: S. Hou, N. Chen,
P. Zhang and S. Dai, Green Chem., 2019, DOI: 10.1039/C8GC03772H.
This is an Accepted Manuscript, which has been through the
Volume 18 Number
7 7 April 2016 Pages 1821–2242
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Accepted Manuscripts are published online shortly after
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Page 1 of 6
PleaseGdroeennoCt haedmjuissttrmy argins
View Article Online
DOI: 10.1039/C8GC03772H
Journal Name
ARTICLE
Heterogenous Viologen Catalysts for Metal-free and Selective
Oxidations
Shengtai Hou,a Nanqing Chen, b Pengfei Zhang a, b,* and Sheng Dai b, c
*
Received 00th January 20xx,
Accepted 00th January 20xx
Metal-free oxidation, a green chemistry process has drawn more attention from catalysis community. However, most
oxidation processes are complete by homogeneous metal-free catalysts, while heterogeneous metal-free materials have
been developed with limited successes. In this work, polymerized ionic networks (PINs) with N, N'-dialkyl-4,4'-bipyridinium
units as heterogeneous viologen type of catalysts exhibit high efficiency in oxidizing aromatic sulfide/alcohol to
sulfoxide/aldehyde, respectively (Conv.: >90%, Sel.: >95%). The catalytic performance of PINs originates from the electron-
accepting ability of viologen unit, which can reduce H2O2 into active species. Especially, the synthesis of PIN catalysts is a
one-step simple polymerization between benzyl bromide and bipyridine in air. The metal-free heterogeneous feature, the
high selectivity, the mild conditions (60 oC, 1 h), and the facile preparation of catalyst make current selective oxidation
attractive.
DOI: 10.1039/x0xx00000x
www.rsc.org/
sulfides (R2S), for example, an electron transfer between R2S
and a metal catalyst can occur and lead to a reactive R2S•+
intermediate that is ready to be oxidized by H2O2. Although
Introduction
16
metal catalyst–H2O2 systems have been thoroughly studied in
past decades, there have been only limited advances in
Selective oxidation of sulfides and alcohols is an
important process in the catalysis community with many
developing heterogeneous metal-free catalysts for selective
applications ranging from organic synthesis to industrial fine-
17-20
oxidation.
From the standpoint of sustainable chemistry
1-5
chemical production.
Traditionally, strong oxidizing agents
and clean catalysis, the design of heterogeneous metal-free
catalysts toward selective oxidation is highly attractive but
difficult.
such as trifluoroperacetic acid, concentrated HNO3–H2SO4, iodic
acid, potassium permanganate, potassium dichromate, and
other hypervalent metal salts, have typically been used for
6-7
those oxidations or oxidative dehydrogenations.
However,
those processes often require excess amounts of oxidants, need
corrosion-resistant instruments, suffer from the production of
poisonous heavy metal ions, and are characterized by over-
oxidation as a result of the uncontrolled activity. In this regard,
hydrogen peroxide (H2O2) is a mild and green source of oxygen,
with water as the only by-product, and various H2O2-based
catalysts have been already developed for selective oxidations.
In this contribution, we introduce
a
class of
heterogeneous viologen catalysts for metal-free and selective
oxidation of sulfides and alcohols with good performance and
activity. Dialkyl viologens (N,N'-dialkyl-4,4'-bipyridinium
dihalides, V2+) as electron acceptors have been widely studied
in electrochemistry because of their inherent redox reactions
(V2+ ↔V+↔ V0). 21-22 Those reversible redox processes can be
promoted chemically, photochemically, or electrochemically
without side reactions. 23-27 The redox and reactive behaviours
of viologens alerted us to their potential as catalysts for
selective oxidations. In an unexpected experiment, we
observed a photoexcited color change of polymerized ionic
networks (PINs) (note: viologen radical cations usually are blue
in color); and a careful investigation of their chemical structure
revealed that PINs are actually highly cross-linked viologens
In general, metal-involved catalysts are used, and they
8-9
function by activating either H2O2 or organic reactants. The
famous Fenton system is such a process, with Fe2+-mediated
H2O2 splitting into •OH radicals active species for the oxidative
10-12
hydroxylation of benzene into phenol.
The formation of
reactive radicals like •OOH is also possible during H2O2
decomposition. On the other hand, metal catalysts may start
with the activation of organic molecules. 13-15 In the oxidation of
with abundant 4,4'-bipyridinium fragments (Figure 1 and
28-29
Scheme 1).
A detailed exploration of PINs-mediated
selective oxidation (control oxidation, reaction optimization,
oxidation kinetics, mechanism study, and substrate scope) was
a.School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University,
Shanghai 200240, China. E-mail: chemistryzpf@sjtu.edu.cn
b.Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996,
USA
C Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
37831, USA. E-mail: dais@ornl.gov
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 6
ARTICLE
Journal Name
View Article Online
DOI: 10.1039/C8GC03772H
Scheme 1. Chemical structures of polymerized ionic networks and model molecules.
then carried out. Finally, an efficient, simple, mild, and catalyst afforded a limited surface area of 2 m2 g-1. It is bulky material
heterogeneous access for metal-free oxidations was without abundant pores. Meanwhile, the SEM image of PIN-1
highlighted.
showed that the catalyst was composed of aggregations of irregular
particles around 1 m, a typical morphology of polymer materials
from solution participation(Figure S3).
Results and Discussion
The selective oxidation of methyl phenyl sulfide (MPS) to
methyl phenyl sulfoxide (MPSO) by 30% H2O2 was selected as a
31-33
model reaction.
No products were observed in an initial blank
run (Table 1, Entry 1). Then, with PIN-1 as a catalyst, a good rate of
conversion (88%) of MPS with a high selectivity for MPSO (98%) was
obtained (Table 1, Entry 2). The H2O2 selectivity is 74% based on
titration. It is clear, and interesting, that PIN-1 as a metal-free
catalyst can promote liquid-phase selective oxidation. To explore
which exact group is responsible for the activity, several model
molecules were prepared. When PIM-1-M1, an ionic model with six
pyridinium cations, was used in the process, the oxidation did not
accelerate (Table 1, Entry 3). This result suggested that the 4,4'-
bipyridinium fragment might contribute to the catalytic activity.
Figure 1. Pictures of PIN-1 in dark or UV conditions.
A series of PINs with six 4,4'-bipyridinium cations per Then, a control oxidation of MPS by PIM-1-M2 (N, N-dibenzyl-4,4'-
repeating unit were prepared by an SN2 nucleophilic bipyridinium dibromide) was carried out, and a moderate conversion
substitution between hexakis(bromomethyl)benzene and 4,4- (27%) of MPS was obtained (Table 1, Entry 4), providing evidence
29
bipyridine.
The approach combined the ionization and that the viologen motif indeed promoted the oxidation. To further
polymerization of 4,4'-bipyridine in one process. All PINs are confirm the active site, single-substituted 4,4'-bipyridinium bromide
viologen-based solids that are insoluble in solvents. In contrast, (PIM-1-M3) was designed; but it did not function in this oxidation
viologen molecules are soluble and highly toxic. For example, (Table 1, Entry 5). We attribute its failure to the poor ability of PIM-
paraquat (N, N'-dimethyl-4,4'-bipyridinium dichlorides, a well- M3 to accept electrons, which at the same time revealed the
known viologen) is one of the most widely used herbicides necessity of the double substituted 4,4'-bipyridinium structure for
worldwide. 30 Thus, PINs may serve as safer viologen catalysts.
catalysis.
Then, PIN-2 with a lower-density viologen structure was
evaluated, and the conversion of MPS significantly decreased
(16%), suggesting the vital role of the viologen structure in
X-ray diffraction (XRD) of PIN-1 showed two broad peaks
around 19o and 38o. Therefore, the PIN-1 catalyst is amorphous
material (Figure S1). To study the porous nature of PIN-1 catalyst, N2
sorption measurement at 77K was took out (Figure S2). The PIN-1
oxidation
(Table 1, Entry 6). Moreover, the catalytic
performance somewhat followed the amount of PIN-1 used in
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 6
Green Chemistry
Please do not adjust margins
Journal Name
ARTICLE
the oxidation (1, 2.5, 3.5, 5, 7.5, 10, 15, 20 mg). The decreased
amount of PIN-1 significantly affect the MPS conversion,
View Article Online
DOI: 10.1039/C8GC03772H
To study the effect of solvents, we proceeded to carry out
revealing the key role of PIN-1 in current oxidation (Table S1
,
the catalytic oxidations using water, methanol, ethanol or 1-
butanol as the solvent with other conditions unchanged to
assess the applicability of this methodology. Fortunately,
varying the reaction media did not result in great divergent
outcomes in terms of both activity and selectivity (Table 1,
Entries 11-14). All the reactions process exhibited high
reactivity, and a good conversion (99%) of MPS with a high
selectivity for MPSO (97%) was obtained with methanol as the
solvent, which is better than acetonitrile.
Figure S4). In addition, a control process without 30% H2O2
afforded no products, showing that 30% H2O2 was acting as an
oxidant to incorporate oxygen into the sulfide (Table 1, Entry
7
).
When ethanol (0.5 mL), an
OH radical scavenger, was
added, the oxidation of MPS still occurred, a result that
excluded a pathway via oxidation mediated by

OH radicals
34
(Table 1, Entry 8). To inquire the role of light in catalysis, a
control oxidation was performed in dark. A high conversion of
MPS (93%) with MPSO as primary product was obtained,
indicating that the electron-transfer of PIN-1 was not initiated
by light (Table 1, Entry 9). Then, we carried out the oxidation of
MPS in the presence of NaBr with the aim of clarifying the role
of Br- anions. It is clear that no products were detected (Table
1, Entry 10). When the PIN-1 catalyst was treated with Cl- for
ion-exchange, the MPS conversion decreased from 88% to 11%.
Those data suggested that the oxidation activity originates from
the viologen cation of PIN-1 with Br- as a co-catalyst.
To study the reaction kinetics, the effect of stirring speed on
oxidation was initially tested. When the stirring speed changed from
300 to 1200 rpm, no differences in the catalytic results were
observed. Thus, mass transfer proved not to be rate-limiting in this
process. All the catalytic oxidations were performed at a stirring
speed of 1200 rpm. The evolution of the catalytic performance as a
function of time and reaction temperature was studied over PIN-1 in
detail (Figure 2). As shown in the curves, reaction temperature had a
strong effect on this oxidation: higher temperatures promoted the
reaction rate. The reaction time for 100% conversion of MPS
increased from 70 min to 600 min when the reaction temperature
decreased from 60 C to 30 C. Meanwhile, the reaction rate was
proportional to the primary concentration of the initial substrate
concentration, which suggests that the oxidation proceeds in a first-
order reaction kinetics (Figure S5).
Table 1. Selective oxidation of methyl phenyl sulfide by PINs-based
catalysts. a
Selectivity
Entry
Catalyst
Solvent
Conv.
MPSO
—
MPSO2
—
1
2
—
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
2%
88%
2%
PIN-1
98%
—
2%
—
3
PIN-1-M1
PIN-1-M2
PIN-1-M3
PIN-2
4
27%
2%
97%
—
2%
—
5
6
16%
—
>99%
—
—
7 b
8 c
PIN-1
—
PIN-
1+Ethanol
PIN-1
48%
93%
7%
9 d
CH3CN
93%
98%
—
(In dark)
NaBr
10
11
12
13
14
CH3CN
CH3OH
Ethanol
1-Butanol
H2O
1%
—
—
PIN-1
PIN-1
PIN-1
PIN-1
99%
88%
98%
86%
97%
95%
94%
99%
2%
4%
6%
1%
a
Reaction conditions: methyl phenyl sulfide 1 mmol, catalyst 20
b
mg, CH3CN 4 mL, 30% H2O2 2 mmol, 60 C, 1 h. No H2O2 was
Figure 2. The conversion of MPS and selectivity for MPSO vs. time
plots for the oxidation of MPS by PIN-1/H2O2 at different
temperatures. Reaction conditions: methyl phenyl sulfide 1 mmol,
c
added in the control oxidation. With 0.5 mL ethanol as an
additive. d This run was conducted in the dark.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 6
ARTICLE
Journal Name
PIN-1 20 mg, 30% H2O2 2 mmol, CH3CN 4 mL, 30–60 °C. The final curve attributed to the characteristic peak of dipyridyl C-H stretching band.
View Article Online
DOI: 10.1039/C8GC03772H
shows temperature dependence of the rate parameter in the It might result from the chemical structure change from the 4,4'-
Arrhenius equation for the PIN-1/H2O2 system.
bipyridine to 1,1',4,4'-tetrahydro-4,4'-bipyridine. Those results
reveal that PIN-1 is indeed catalyzing the oxidation process in a
heterogeneous manner.
During the investigation of reaction kinetics, the conversion of
MPS increased almost linearly with reaction time, and the selectivity
for MPSO was kept (>90%). Initial reaction rates under different
It is of great interest that PIN-1 served as a metal-free
reaction temperatures were determined from the kinetic curves at heterogenous catalyst for selective oxidation. A possible reaction
low conversion rates. The k rate constants of MPS oxidation were pathway was then proposed. Previous efforts have already
0.0036 h-1 (30 C), 0.0079 h-1 (40 C), 0.0190 h-1 (50 C), and 0.0381 confirmed the electron-accepting behavior of PIN-1. 36 In the current
h-1 (60 C). The Van’t Hoff approximation rule indicates that the rate case, H2O2 transforms into active species like O2- or OOH by an
constant would increase by 2–3 times if the reaction temperature electron transfer process with formation of viologen radical cations,
increases by 10 K. Thus, this catalyst system roughly followed the and the active species then oxidized sulfide into sulfoxide. At the
Van’t Hoff rule. The activation energy was then calculated using same time, the blue-green radical cations were oxidized back into
35
Arrhenius plots. When the rate constant (ln k) was fitted with PIN-1 by molecular oxygen, a well-known process. 37
reaction temperatures (1/T), a straight-line plot with a correlation
To explore the scope of PIN-1/H2O2, catalytic oxidation of
some other MPS molecules was studied under optimized conditions
(Table 2). Compared with MPS, the oxidation of MPS bearing
electron-withdrawing groups (-F, -Cl, -Br) at the phenyl ring took a
longer time, although all three processes afforded satisfactory
conversion rates and selectivity. The catalyst also worked well in the
oxidation of molecule models with electron-donating groups (-CH3, -
OCH3). For example, 4-(methylphenyl) methyl sulfide was oxidized
smoothly to 4-(methylphenyl) methyl sulfoxide in 1.1 h (Conv.: 99%,
Sel.: >99%). Moreover, alkyl sulfides (e.g., propyl sulfide and dioctyl
sulfide) could be transformed into the corresponding sulfoxides with
good yields (>97%). When the dioctyl sulfide was used as the
substrate, we also separate the sulfoxide product in 92% yield as a
white solid. Therefore, it seems fair to say that PIN-1 is a powerful
metal-free solid catalyst for catalytic oxidation of aromatic sulfide,
which is comparable to the other solid catalysts (Table S2).
coefficient of 0.9985 was obtained. The activation energy (Ea)
calculation for sulfide oxidation by PIN-1 was 66.7 kJ mol-1; this
moderate value suggested that this oxidation method does not
require harsh reaction conditions (Figure 2).
Figure 3. Selective oxidation of MPS by reused PIN-1 catalyst.
Reaction conditions: methyl phenyl sulfide 1 mmol, catalyst 20 mg
(Recycled), CH3CN 4 mL, 30% H2O2 2 mmol, 60 C, 1 h.
Table 2. Selective oxidation of various sulfides by the PIN-1/H2O2
system.
Conv. Sel.
To study the stability of PIN-1, the reaction mixture was easily
separated by centrifugation, and fresh reactants with H2O2 were
added into the reactor for next run. The PIN-1 catalyst can be used
at least five times without significant loss of activity or selectivity
(Figure 3). After the oxidation of MPS by PIN-1 (Reaction details:
methyl phenyl sulfide 1 mmol, catalyst 20 mg, methanol 4 mL, 30%
H2O2 2 mmol, 60 C, 1 h), the solid catalyst was filtered and the
solution was concentrated for element analysis. Based on the
amount of PIN-1 catalyst, the leaching of nitrogen is negligible (<1%),
while around 1.7% bromide species were detected in the solution.
Moreover, the oxidation was almost stopped if the PIN-1 solid was
removed by a hot filtration (Figure S6).
Entry
1
Substrate
Product
Time(
h)
2.5
(%)
(%)
99%
95%
2
3
4
4
99%
99%
>99%
>99%
4
5
6
1.1
1
99%
88%
97%
>99%
>99%
>99%
Meanwhile, we performed more characterization studies
between the recycled and fresh catalysts. As shown in the SEM
images, both original and reused samples were composed of
irregular particles around 1 m, which were aggerated together, a
typical morphology of polymer catalysts from solution participation
(Figure S3). We also carried out the FTIR spectra. Those characteristic
peaks for fresh and reused PIN-1 were similar (Figure S7). Weaken
zone of the absorption peaks around 3000 cm−1 for the PIN-1 was
1
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 6
Green Chemistry
Please do not adjust margins
Journal Name
ARTICLE
7
1
92%
>99%
View Article Online
S
4
5
86%
DOI: 10.1039/C8>G9C90%3772H
Reaction conditions: methyl phenyl sulfide 1 mmol, PIN-1 20 mg,
CH3CN 4 mL, 30% H2O2 2 mmol, 60 C.
79%
>99%
a
Reaction conditions: alcohol 1 mmol, CH3CN 4 mL, 30% H2O2 2
A gram-scale preparation of MPSO was then investigated. To our
delight, the oxidation of MPS (1.24-gram scale) carried out in the
presence of PIN (100 mg) and H2O2 (20 mmol) in MeOH (30 mL) at 60
oC for 1 h gained MPSO in 90.6% yield. We also make a space-time
yield every 20 minutes and it shown below in Figure 4. An isolated
yield of 95% was obtained in 2 h. This catalyst performed high
efficiency in the reaction. The properties give this methodology great
promise for practical applications.
mmol, PIN-1-Br catalyst 20 mg, 60 oC, 7 h. b The value from a blank
oxidation without PIN-1 catalyst.
Conclusions
In summary, we have introduced a simple, efficient, and stable
catalyst that enables the selective oxidation of aromatic alcohols and
sulfides with good to high activities. Importantly, PIN-1 does not
include metal elements and works in a heterogeneous manner,
which elegantly enriches the limited library of metal-free solid
catalysts available for selective oxidation. The essential point of PIN-
1 lies in the abundant viologen units that were incorporated in the
solid backbone. Compared with highly toxic soluble viologens, the
PIN-1 solid material offers a safer catalyst.
100
94.0%
92.7%
90.6%
86.2%
80
60
40
20
0
82.6%
MPS
MPSO
MPSO
2
Conflicts of interest
There are no conflicts to declare.
5.6%
5.0%
4.0%
4.5%
4.6%
0
10 20 30 40 50 60 70 80 90 100110120
Time (min)
Acknowledgements
Figure 4. The yields of MPSO and MPSO2 in the gram-scale oxidation.
Reaction condition: methyl phenyl sulfide 10 mmol, 1.24 g, PIN-1 100
mg, 30% H2O2 20 mmol, MeOH 30 mL, 60 oC.
P. F. Zhang, N. Chen and S. Dai was supported by the Division of
Chemical Sciences, Geosciences, and Biosciences, Office of Basic
Energy Sciences, US Department of Energy. P. F. Zhang and S. T.
H. acknowledge Shanghai Pujiang Program (Grant No.
17PJ1403500), Thousand Talent Program and National Natural
Science Foundation of China (Grant No. 21776174) for the partial
support.
The oxidative dehydrogenation of benzyl alcohols into their
corresponding aldehydes is another profound process in the
synthesis of fine chemicals. Encouraged by the good performance of
PIN-1 in the catalytic oxidation of sulfides, we moved to the oxidation
of benzyl alcohol by PIN–1/H2O2 (Table 3). Compared with sulfide
oxidation, the oxidation of benzyl alcohol required a longer reaction
time. In the presence of PIN–1/H2O2, a high conversion rate (94%) of
benzyl alcohol with a high selectivity for benzaldehyde was obtained
in 7 h; whereas a control run without PIN-1 offered only limited
conversion (5%) of benzyl alcohol. Then, several benzyl alcohols
bearing electron-donating or electron-withdrawing substituents on
the phenyl ring were efficiently oxidized with high selectivity toward
aldehyde products. But, the PIN–1/H2O2 did not work in the oxidation
of an alkyl alcohol. Thus, it is clear that PIN-1 served as an active
metal-free catalyst for selective oxidation of aromatic alcohols.
Notes and references
1
D. Enache, J. K. Edwards, P. Landon, B, Solsona-Espriu, A. F.
Carley, A. A. Herzing, M. Watanabe, C. J. Kiely, D. W. Knight
and G. J. Hutchings, Science 2006, 311, 362–365.
G. J. Brink, I. W. C. E. Arends and R. A. Sheldon, Science 2000,
287, 1636–1639.
2
3
4
5
E. Hiromichi and K. Tsutomu, J. Am. Chem. Soc. 2007, 129
,
8940-8941.
K. Sato, M. Hyodo, M. Aoki, X. Q. Zheng and R. Noyori,
Tetrahedron 2001, 57, 2469-2476.
J. Adamski, M. I. Qadir, J. P. Serna, F. Bernardi, D. L. Baptista,
B. R. Salles, M. A. Novak, G. Machado and J. Dupont, J. Phys.
Chem. C, 2018, 122, 4641–4650
Table 3. Selective oxidation of benzyl alcohols by a PIN-1-Br/H2O2
system. a
6
7
8
9
V. G. Shukla, P. D. Salgaonkar and K. G. Akamanchi, J. Org.
Chem. 2003, 68, 5422-5425.
Metal-Catalyzed Oxidations of Organic Compounds; R. A.
Sheldon and J. K. Kochi, Academic Press: New York, 1981.
A. Prieto, M. Palomino, U. Díaz and A. Corma, Catalysis Today
2014, 227, 87-95.
Entry
1
Substrate
Product
Conv.
Sel.
94%
>99%
(5%)b
2
3
82%
93%
>99%
>99%
A. Mahammed and Z. Gross, J. Am. Chem. Soc. 2005, 127
2883-2887.
,
10 J. H. Yang, G. Sun, Y. Gao, H. Zhao, P. Tang, J. Tan, A. H. Lu and
D. Ma, Energy Environ. Sci. 2013,
6
, 793-798.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 6 of 6
ARTICLE
Journal Name
11 P. F.Zhang, Y. T. Gong, H. R. Li, Z. R. Chen and Y. Wang, RSC
Adv. 2013, , 5121-5126.
12 E. Brillas, I. Sires and M. A. Oturan, Chem. Rev. 2009, 109
6570–6631.
View Article Online
DOI: 10.1039/C8GC03772H
3
,
13 R. Ricoux, M. Allard, R. Dubuc, C. Dupont, J. D. Mar
′
echal and
J. P. Mahy, Org. Biomol. Chem. 2009, 7, 3208–3211.
14 K. Kaczorowska, Z. Kolarska, K. Mitka, and P. Kowalski,
Tetrahedron 2005, 61, 8315–8327.
15 P. F. Ballistreri,
C. G. Fortuna, A. Pappalardo, G. A.
Tomaselli and R. M. Toscano, Journal of Molecular Catalysis A:
Chemical 2009, 308, 56–60.
16 A. M. Khenkin, G. Leitus and R. J. Neumann, J. Am. Chem. Soc.
2010, 132, 11446–11448.
17 Y. Wang, X. C. Wang and M. Antonietti, Angew. Chem. 2012,
51, 68–89.
18 D. S. Su, S. Perathoner and G. Centi, Chem. Rev. 2013, 113
5782–5816.
,
19 A. Rostami and J. Akradi, Tetrahedron Lett. 2010, 51, 3501–
3503.
20 K. Chen; P. F. Zhang; Y. Wang; H. R. Li, Green Chem. 2014, 16
,
2344-2374.
21 L. A. Vermeulen and M. E. Thompson, Nature 1992, 358, 656-
658.
22 S. S. Anny, M. Ottolenghi and D. Avnir, Nature 1992, 355, 240-
242.
23 D. R. Wheeler, J. Nichols, D. Hansen, M. Andrus, S. Choi and G.
D. Watt, J. Electrochem. Soc. 2009, 156, 1201-1207.
24 W. W. Porter, T. P. Vaid and A. L. Rheingold, J. Am. Chem. Soc.
2005, 127, 16559-16566.
25 D. Melsel, W. A. Mulac and M. S. Matheson, J. Phys. Chem.
1981, 85, 179-187.
26 D. L. Jiang, C. K. Choi, K. Honda, W. S. Li, T. Yuzawa and T. Aida,
J. Am. Chem. Soc. 2004, 126, 12084-12089.
27 Y. Ikeda, M. Ikeda and F. Ito, Solid State Ionics 2004, 169, 35–
40.
28 P. F. Zhang, Z. E. Qiao, X. G. Jiang, G. M. Veith and S.Dai, Nano
Lett. 2015, 15, 823-828.
29 P. F. Zhang, M. Li, B. L. Yang, Y. X. Fang, X. G. Jiang, G. M. Veith,
X. Sun and S. Dai, Adv. Mater. 2015, 27, 8088-8094.
30 H. J. Beckie, Pest Management Science 2011, 67, 1037-1048.
31 T. Iwahama, S. Sakaguchi and Y. Ishii, Tetrahedron Lett. 1998,
39, 9059-9062.
32 G. Abdi, A. Alizadeh, M.M. Khodaei, Mater. Chem. Phy. 2017,
201, 323-330.
33 P. F. Zhang, Y. Wang, H. R. Li and M. Antonietti, Green Chem.
2012, 14, 1904-1908.
34 H. X. Li, J. S. Chen, J. S. Wang, J. H. Sun and M. Antonietti, J.
Am. Chem. Soc. 2011, 133, 8074–8077.
35 Y. Li, X. Xu, P. F. Zhang, Y. T. Gong, H. R. Li, and Y. Wang, RSC
Adv. 2013, 3,10973-10982.
36 J. Lehn, J. Sauvage, and R. Ziessel, Nouveau J. Chem., 1979, 3,
423-427.
37 T. Nakato, K. Kuroda and C. Kato, J. Chem. Soc. Chem.
Commun., 1989, 16, 1144-1145.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins