Oxidation of benzyl alcohols to aldehydes and ketones under air in water using a polymer supported palladium catalyst

Article abstract of DOI:10.1016/j.molcata.2014.02.001

This work deals with the catalytic conversion of benzyl alcohols to aldehydes or ketones using a polymer supported palladium catalyst which formed metal nanoparticles under reaction condition. The oxidation reaction was carried out on a series of substituted benzylic alcohols under air in water. The obtained results showed high selectivity also for the oxidation of primary alcohols to aldehydes without over-oxidation products. In addition, the catalyst was recycled several times with negligible metal leaching into solution.

Full text of DOI:10.1016/j.molcata.2014.02.001

Journal of Molecular Catalysis A: Chemical 386 (2014) 114–119
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Oxidation of benzyl alcohols to aldehydes and ketones under air in
water using a polymer supported palladium catalyst
Maria Michela Dell’Annaa,∗, Matilda Malia, Piero Mastrorillia,b
,
Pietro Cotugnoc, Antonio Monopolic
a DICATECh, Politecnico di Bari, via Orabona 4, 70125 Bari, Italy
b Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti Organometallici (CNR-ICCOM), via Orabona 4, 70125 Bari, Italy
c Department of Chemistry, University of Bari “Aldo Moro”, Via Orabona, 4, 70126 Bari, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
This work deals with the catalytic conversion of benzyl alcohols to aldehydes or ketones using a polymer
supported palladium catalyst which formed metal nanoparticles under reaction condition. The oxidation
reaction was carried out on a series of substituted benzylic alcohols under air in water. The obtained
results showed high selectivity also for the oxidation of primary alcohols to aldehydes without over-
oxidation products. In addition, the catalyst was recycled several times with negligible metal leaching
into solution.
Received 8 November 2013
Received in revised form 27 January 2014
Accepted 1 February 2014
Available online 11 February 2014
Keywords:
Polymer-supported palladium
nanoparticles
© 2014 Elsevier B.V. All rights reserved.
Alcohol aerobic oxidation
Green chemistry
Recyclable catalyst
Water solvent.
1. Introduction
high selectivity and turnover numbers [22–24]. The alcohol aerobic
oxidation reaction is also promoted by a variety of recyclable palla-
The oxidation of alcohols to aldehydes and ketones is very
important from the academic and industrial point of view because
compounds containing carbonyl groups are intermediates of
several valuable fine chemicals such as fragrances, perfumes,
flame retardants, pharmaceuticals [1]. Commonly, this reaction is
obtained by adding stoichiometric amounts of inorganic oxidants
(KMnO4 or CrO3) to the alcohol [2]. However, this procedure has the
drawback to give pollutant and toxic by-products. With the aim to
develop greener processes, the use of molecular oxygen as the oxi-
dant has received growing attention in the past years [3,4], being
water the only by-product of the reaction. In this regard, several
methods that use molecular oxygen for the oxidation of alco-
hols under homogeneous and heterogeneous conditions have been
exploited [5], using metal promoters such as: ruthenium [6,7], plat-
inum [8,9], rhodium [10,11], copper [12], chromium [13], bimetallic
gold–palladium [14] and gold [15–18] catalysts. During the past
years there have been significant advances in palladium catalyzed
oxidation reactions [19–21], and when the palladium catalyst was
soluble, the use of particular ligands was crucial because it led to
dium catalysts supported onto insoluble matrices, such as SBA-15
[25], nanocrystalline starch [26], mesocellular foam [27], DNA-
montmorillonite [28], poly(ethylene-glycol) [29], ionic liquid based
organosilica framework [30] and graphene [31]. In these cases, the
active species were found to be mostly palladium nanoparticles
[26–31]. Although noticeable improvements in terms of selec-
tivity and performance have been achieved, there is still need
to develop new recoverable palladium catalysts able to work in
“greener” reaction media, since generally the solvents employed in
the aforementioned heterogeneous catalytic systems are: toluene
[25,26], p-xylene [27], supercritical carbon dioxide [29] and ␣,␣,␣-
trifluorotoluene [30]. Actually, water was used for the recyclable
palladium catalyzed oxidation of several alcohols into carboxylic
acids [28] and really interesting results were obtained in the aerobic
oxidation of alcohols into aldehydes or ketones in water by employ-
ing: an amphiphilic resin dispersion of palladium nanoparticles
[32], an aluminum hydroxide-supported palladium catalyst [33],
hydroxyapatite-supported palladium nanoclusters [34]. However,
in the latter cases, except for the Uozomi amphiphilic resin [32], the
use of water as the solvent was limited to a marginal portion of the
studies, being the activity and recyclability of the catalysts tested
mostly in toluene or trifluorotoluene. The use of water as reaction
media for the aerobic alcohol oxidation would be preferable and it
∗
Corresponding author. Tel.: +39 080 5963695; fax: +39 080 5963611.
E-mail address: mm.dellanna@poliba.it (M.M. Dell’Anna).
1381-1169/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2014.02.001

M.M. Dell’Anna et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 114–119
115
OH
has several benefits, since it is cheap, nontoxic, nonflammable and
allows an easy recovery of the products due to the insolubility in
water of the majority of the organic compounds. Furthermore, the
solubility of molecular oxygen in water is higher than in common
organic solvents. With this scenario in mind, we decided to evaluate
the catalytic activity of a polymer supported palladium catalyst (in
the following Pd-pol) for the aerobic alcohol oxidation in water.
The catalyst was obtained by co-polymerization of the metal-
containing monomer [35] Pd(AAEMA)2 [AAEMA− = deprotonated
form of 2-(acetoacetoxy)ethyl methacrylate] with suitable co-
monomer (ethyl methacrylate) and cross-linker (ethylene glycol
dimethacrylate) [36,37] and it was already found active and recy-
clable in many palladium promoted reactions [38–43], even under
air in water [44]. The reticular and macro porous polymeric support
of Pd-pol is able to immobilize and stabilize palladium nanoparti-
cles (formed under reaction conditions by reduction of the pristine
Pd(II) anchored complex), suitable for the Suzuki cross coupling of
arylhalides with arylboronic acids in water [44] and for the reduc-
tive amination reaction under 1 atm of H2 [42]. Furthermore, the
good swellability in water renders Pd-pol an ideal potential cata-
lyst for reactions carried out in water, since the migration of the
reagents to the active sites would not be hampered by the solid
support.
O
Pd-pol
H2O, K2CO3
O2
or air
Scheme 1. Aerobic oxidation of benzyl alcohol under aerobic conditions in the
presence of Pd-pol.
2.3. Recycling experiments
A
two necked round flask was charged in air with Pd-
pol (0.5 mol% Pd), benzyl alcohol (108.1 mg, 1.0 mmol), K2CO3
(138.2 mg, 1.0 mmol) and water (5 mL) and the whole system was
put in a thermostated bath at 100 ◦C under vigorous magnetic stir-
ring at reflux. After the minimum time needed to reach reaction
completion, the mixture was cooled down to room temperature.
The catalyst was recovered by filtration, washed with water, ace-
tone, and diethyl ether and dried under high vacuum. The recovered
catalyst was weighed and reused employing appropriate amounts
of organic substrate and base, assuming that the palladium content
remained unchanged with the recycles. Iteration of this procedure
was continued for six reuses of the catalyst.
Herein we report on the ability of Pd-pol in efficiently catalyzing
the selective oxidation of a wide variety of alcohols into aldehydes
and ketones under air as the oxidant and water as solvent.
3. Results and discussion
The aerobic oxidation of benzyl alcohol was used as the model
reaction in the presence of Pd-pol as the catalyst (Scheme 1).
The reaction was significantly affected by different parameters,
such as reaction temperature and presence of the base. After the
explorative experiments summarized in Table 1, the best condi-
tions were found to be those employed in entry 5, that is: benzyl
alcohol (1.0 mmol), Pd-pol (0.5 mol% of Pd), K2CO3 (1.0 mmol), air
(1 atm) in water (5 mL) at 100 ◦C for 6 h.
The reported results revealed that in the absence of base at room
temperature the conversion into benzyl aldehyde was poor both
under air and under 1 atm pressure of O2 (entries 1 and 2), while at
100 ◦C it increased under air up to 57% in 16 h (entry 3) with a 77%
selectivity in benzyl aldehyde, being benzoic acid and its benzyl
ester the over oxidation side-products. The reaction performed at
100 ◦C under dioxygen in the absence of base gave better results
(entry 4) giving a 75% conversion into benzyl aldehyde in 6 h, and
the presence of the base at 100 ◦C (entry 5) increased the catalytic
activity of the system avoiding the use of 1 atm pressure of O2.
The best conditions reported in entry 5 of Table 1 were applied
in the same oxidation reaction carried out in the absence of the
palladium catalyst (entry 6). No oxidation of the model substrate
occurred at all, even after 12 h stirring.
Using the optimized reaction conditions, the activity and the
scope of the catalyst was explored in the aerobic oxidation of a
variety of different primary and secondary alcohols (Table 2).
Table 2 summarizes the most significant results. Both electron
rich (entries 1–3) and electron deficient (entries 4 and 5) deriva-
tives of benzyl alcohol showed excellent reactivity and afforded
the corresponding aldehydes in quantitative yields. As expected,
secondary alcohols were more difficult to oxidize. In fact, 1-
phenylethanol (entry 6) and 1-phenylpropanol (entry 7) furnished
excellent yields of corresponding ketones under optimized reac-
tion conditions, though it was necessary to increase the reaction
times to 16 h to ensure complete conversion. It is also noteworthy
that, under the same conditions, the aerobic oxidation of benzyl
alcohol promoted by a palladium(II) soluble catalyst extensively
used in these kind of reactions,[24] such as palladium acetate (entry
8) gave only 40% conversion of the substrate into benzylaldehyde
2. Experimental
2.1. Materials
Tap water was de-ionized by ionic exchange resins (Millipore)
before use. All other chemicals were purchased from commercial
sources and used as received. Pd-pol was synthesized according to
literature procedure [37]. Palladium content in Pd-pol was assessed
after sample mineralization by atomic absorption spectrometry
using a Perkin–Elmer 3110 instrument. Catalyst mineralization
prior to Pd analyses was carried by microwave irradiation with
an ETHOS E-TOUCH Milestone applicator, after addition of 12 mL
HCl/HNO3 (3:1, v/v) solution to each weighted sample.
GC-MS data (EI, 70 eV) were acquired on
a HP 7890
instrument using a HP-5MS cross-linked 5% PH ME siloxane
(30.0 m × 0.25 mm × 0.25 ␮m) capillary column coupled with a
mass spectrometer HP 5973. The products were identified by com-
parison of their GC-MS features with those of authentic samples.
Reactions were monitored by GLC or by GC-MS analyses. GLC anal-
ysis of the products was performed using a HP 6890 instrument
equipped with a FID detector and a Supelcowax-10 capillary col-
umn (30.0 m × 0.25 mm × 0.25 ␮m). Conversions and yields were
calculated by GLC analysis as moles of oxygenated product per mole
of starting alcohol by using biphenyl as internal standard.
2.2. Typical oxidation of alcohols
Into a reaction vessel with a reflux condenser were placed Pd-pol
(23.1 mg, Pd%w = 2.3), benzyl alcohol (108.1 mg, 1.0 mmol), K2CO3
(138.2 mg, 1.0 mmol) and water (5 mL). The resulting mixture was
stirred at 100 ◦C under 1 atm of air. After 6 h, the mixture was cooled
down to room temperature and the organic product was extracted
with ethyl acetate (3 mL). The water phase was washed with ethyl
acetate (2 × 5 mL) and the organic layers were collected. GLC anal-
ysis of the ethyl acetate solution using biphenyl as an internal
standard gave a 98% yield of benzyl aldehyde with >99% selectivity.

116
M.M. Dell’Anna et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 114–119
100
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
6
Time( h)
Fig. 1. Recyclability of Pd-pol (0.5 mol% of Pd) in the aerobic oxidation in water of
benzyl alcohol in the presence of K2CO3 (1 eq) at 100 ◦C (t = 6 h).
Fig. 2. Time course for the oxidation of benzyl alcohol catalyzed by Pd-pol. Reaction
conditions: Pd-pol (0.5 mol% of Pd), benzyl alcohol (1.0 mmol), K2CO3 (1.0 mmol),
water (5 mL), 100 ◦C, under air (1 atm).
after 6 h, leading to quantitative conversion only after 16 h reaction,
thus exhibiting a catalytic activity much lower than Pd-pol. On the
other hand, it was reported [34] that the aerobic oxidation of ben-
zyl alcohol with commercially available heterogeneous palladium
catalysts, such as Pd/C, Pd/SiO2 and Pd/Al2O3 gave unsatisfactory
results in terms of both activity and selectivity, because they do not
bear palladium nanoparticles of appropriate size and shape [45,46].
Unfortunately, Pd-pol based catalytic system was inactive with
aliphatic alcohols. In fact, ␤-citronellol and 1-butyl-1-octanol were
reluctant to react, giving the corresponding carbonyl compounds
in 10% and 5% yields for 7 h, respectively, even under 1 atm O2.
The Pd-pol recyclability was explored in the oxidation of benzyl
alcohol. After the first use, the supported catalyst was recovered by
simple filtration and reused in the next run after a washing workup.
The recovered catalyst was successfully employed in the subse-
quent five cycles with a high catalytic activity, giving the product
in excellent yields (93–98%, Fig. 1).
To determine the true nature of the active species in Pd-pol cat-
alytic system, a hot filtration test was performed. To do this, the
solid catalyst was filtered off after the aerobic oxidation of ben-
zyl alcohol had run for 1 h and the conversion reached 40% ca.
The clear filtrate was then stirred under standard reaction condi-
tions at 100 ◦C. After 16 h, the analysis of the catalyst-free reaction
showed that the conversion had stopped at the initial value (40%
ca). In addition, the atomic adsorption analysis carried out on the
digested filtered catalyst revealed a palladium content in the recov-
ered Pd-pol equal to that found in the catalyst before use. Also the
Pd-pol recovered after 6 h reaction had a palladium amount equal
to that found in the pristine catalyst, within the experimental error.
However, it is very important to note that the absence of catalytic
activity in the solid-free filtrate does not always imply no leaching
of Pd species and the amount of leached palladium after each par-
tial or total catalytic run may be below the detection limit. In fact,
atomic adsorption analysis carried out on the catalyst recovered
after six runs revealed a slight decrease of the palladium amount,
being 90% of the initial content.
To gain insight into the kinetics of the reaction, the time course
for the oxidation of benzyl alcohol was monitored periodically, as
shown in Fig. 2, revealing a pseudo-first order reaction with respect
to the benzyl alcohol. Pd-pol seemed to have a negligible induction
period compared to the overall reaction time. However, a fast color
change of the catalyst from yellow to dark gray was observed at
the beginning of the reaction, suggesting that the reaction medium
transforms the pre-catalyst into the active species, i.e. palladium
nanoparticles.
In fact, the polymeric support of Pd-pol was proven to stabilize
palladium nanoparticles (with diameters ranging from 2 to 10 nm)
formed under air in water at 100 ◦C, as revealed by TEM analysis
[44]. From the above results, it can be concluded that the catalyt-
ically active species are not the original monomeric Pd(II) species,
i.e. [Pd(AAEMA)2], but the in situ generated palladium nanoparticles
formed by thermal decomposition at 100 ◦C, in accordance with the
simulated process proposed by Rozenberg et al. [47]. The lacking
of formation of these Pd nanoparticles may be responsible for the
low activity of Pd-pol in the aerobic alcohol oxidation at room tem-
perature (Table 1, entries 1 and 2). The reaction pathway could be
thus similar to the one proposed by Kaneda and co-workers [34]
starting with an oxidative addition of the alcohol to the coordi-
nately unsaturated palladium(0) at the nanoparticle edge, affording
Pd(II)-alcoholate intermediate, which undergoes a ␤-hydride elim-
ination to produce the corresponding carbonyl compound and a
Pd-hydride species. The reaction of the palladium(II) hydride with
O2 regenerates the initial palladium(0) species (Scheme 2) and
produces H2O2, which fast decomposes into H2O and O2. The base
Table 1
The effect of the oxidant, reaction temperature and base in the aerobic oxidation of benzyl alcohol using Pd-pol catalyst.a
Entry
T (◦C)
Oxidantb
Pd (mol%)
Basec
Time (h)d
Conv. (%)e
Selectivity (%)e
1
2
3
4
5
6
25
25
100
100
100
100
air
O2
air
O2
air
air
0.5
0.5
0.5
0.5
0.5
no
No
No
No
No
K2CO3
K2CO3
7
7
16
6
6
10
13
57
75
>99
0
>99
>99
77
>99
>99
0
16
a
Reaction conditions: benzyl alcohol (1.0 mmol), water (5 mL).
Under 1 atm of O2 or air.
1.0 mmol when present.
Minimum time needed to reach reaction completion.
Assessed by GLC with the internal standard (biphenyl) method.
b
c
d
e

M.M. Dell’Anna et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 114–119
117
Table 2
Aerobic oxidation of alcohols using Pd-pol catalyst in water under air.a
b
Entry
Substrate
Product
Time (h)
Yield (%)
OH
CHO
1
6
98
CHO
OH
2
6
98
OCH3
OCH3
OH
CHO
3
8
95
OCH3
H3CO
H3CO
OCH3
OCH3
OCH3
OH
CHO
4
8
98
NO2
NO2
OH
CHO
5
8
98
F
F
OH
O
6
16
98
OH
O
7
16
98
OH
CHO
c
8
6
16
40
92
a
Conditions: Alcohol (1.0 mmol), Pd-pol (0.5 mol%), K2CO3 (1.0 mmol), water (5 mL), at 100 ◦C.
GLC yields using internal standard (biphenyl) method.
In the presence of Pd(OAc)2 (0.5 mol%).
b
c

118
M.M. Dell’Anna et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 114–119
Ar
O
H
Ar
Pd(0)
Pd(0)
Pd(0)
Pd(0)
Pd(II)
Pd(0)
Pd(0)
Pd(0)
Pd(0)
OH
Pd(0)
Pd(0)
Pd(0)
Pd(0)
Pd(0)
Pd(0)
Pd(0)
Ar
O
C
H
O2
H
H2O2
H
Pd(0)
Pd(0)
Pd(0) Pd(0)
Pd(II)
Pd(0)
Pd(0)
Pd(0)
Scheme 2. Possible reaction mechanism for the oxidation of alcohols promoted by Pd-pol.
may favor the formation of palladium-alkoxide species and/or the
eliminations [48,49].
Several studies already showed that the C H bond cleavage
(␤-hydride elimination) is the rate-determining step of the ben-
zyl alcohol oxidation reaction promoted by noble metal catalysts
[34,48–52]. To get more insights into the mechanism of the present
catalytic reaction, the relative rates of the oxidation of para-
substituted benzyl alcohols (CH3O, CH3, H and NO2 groups) were
examined. The initial rates were measured for the first 15 min
for each reaction [48] and the corresponding kinetic constants (k)
were calculated. A good linearity between the log kX/kH values and
the Hammett constant (ꢀ) parameters for the oxidation of differ-
ent para-substituted benzyl alcohols was obtained (Fig. 3) [53].
The resulting Hammett parameter ꢁ was −0.927, suggesting that
the reaction is substituent-sensitive and carbocation species are
involved. The negative ꢁ value indicates a positive charge buildup
in the transition state (Scheme 3), further supporting rate-limiting
␤-hydride elimination. Electron-donating groups can stabilize car-
bocation species which are more easily oxidized.
Scheme 3. Plausible transition state of the ␤ C H bond cleavage step.
the pre-formed resin, followed by metal reduction [54]. It seems
that synthesizing a polymer supported catalyst starting from a
metal containing monomer (as in the case of Pd-pol) allows to
obtain better retained active species compared to the classical way
of synthesis (preparation of the organic support followed by the
anchoring of the metal complex onto it).
It is noteworthy that Pd-pol is superior in terms of palla-
dium leaching and recyclability in the aerobic alcohol oxidation
in water compared with a catalyst similar to it, i.e. palladium
nanoparticles supported onto soluble N,N-dimethylacrylamide
based cross-linked polymers, obtained by grafting Pd(OAc)2 onto
4. Conclusions
In conclusion, we have demonstrated the significant efficiency
of a reticular and porous methacrylic material in the stabilization of
active palladium species (nanoparticles) in the oxidation of alcohols
in water by air. Several types of primary and secondary aromatic
alcohols could be oxidized to their corresponding carbonyl com-
pounds in the presence of a low loading of palladium (0.5 mol%) at
relatively short reaction times (ranging from 6 to 16 h). Moreover,
the catalyst could be easily recovered and reused to give quanti-
tative yield of carbonyl adducts up to six cycles. The hot filtration
test suggested that the catalyst operated through a heterogeneous
pathway, even if atomic spectroscopy analyses revealed a less than
3% palladium leaching after each cycle.
0.4
p-OCH3
p-CH3
0.2
y = -0.9273x + 0.0436
R² = 0.9928
H
0
-0.2
-0.4
-0.6
-0.8
p-NO2
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Acknowledgement
Fig. 3. Hammett plot for the oxidation of benzylic alcohols at 100 ◦C. Conditions:
Pd-pol (0.5 mol% of Pd), benzyl alcohol (1.0 mmol), K2CO3 (1.0 mmol), water (5 mL),
100 ◦C, under air (1 atm).
The authors thank Italian MIUR (project PRIN 2010-2011 n.
2010FPTBSH 001) for financial support.

M.M. Dell’Anna et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 114–119
119
References
[29] Z. Hou, N. Theyssen, A. Brinkmann, W. Leitner, Angew. Chem. Int. Ed. 44 (2005)
1346–1349.
[30] B. Karimi, D. Elhamifar, J.H. Clark, A.J. Hunt, Org. Biomol. Chem. 9 (2011)
7420–7426.
[31] G. Wu, X. Wang, N. Guan, L. Li, Appl. Catal. B: Environ. 136–137 (2013) 177–185.
[32] Y. Uozumi, R. Nakao, Angew. Chem. Int. Ed. 42 (2003) 194–197.
[33] M.S. Kwon, N. Kim, C.M. Park, J.S. Lee, K.Y. Kang, J. Park, Org. Lett. 7 (2005)
1077–1079.
[34] K. Mori, T. Hara, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am. Chem. Soc. 126 (2004)
10657–10666.
[35] M.M. Dell’Anna, G. Romanazzi, P. Mastrorilli, Curr. Org. Chem. 17 (2013)
1236–1273.
[36] M.M. Dell’Anna, P. Mastrorilli, A. Rizzuti, G.P. Suranna, C.F. Nobile, Inorg. Chim.
Acta 304 (2000) 21–25.
[37] M.M. Dell’Anna, P. Mastrorilli, C.F. Nobile, in: P.J.H. Scott (Ed.), Solid-Phase
Organic Syntheses, 2, John Wiley & Sons, Inc., Hoboken, NJ, USA, 2012, pp.
79–86.
[38] M.M. Dell’Anna, M. Gagliardi, P. Mastrorilli, C.F. Nobile, J. Mol. Catal. A: Chem.
158 (2000) 515–520.
[39] M.M. Dell’Anna, P. Mastrorilli, F. Muscio, C.F. Nobile, G.P. Suranna, Eur. J. Inorg.
Chem. 8 (2002) 1094–1099.
[40] M.M. Dell’Anna, P. Mastrorilli, F. Muscio, C.F. Nobile, in: M. Anpo, M. Onaka,
H. Yamashita (Eds.), Science and Technology in Catalysis, Elsevier, Amsterdam,
2002, pp. 133–136.
[41] M.M. Dell’Anna, P. Mastrorilli, C.F. Nobile, G.P. Suranna, J. Mol. Catal. A: Chem.
201 (2003) 131–135.
[42] M.M. Dell’Anna, A. Lofu, P. Mastrorilli, V. Mucciante, C.F. Nobile, J. Organomet.
Chem. 691 (2006) 131–137.
[43] M.M. Dell’Anna, P. Mastrorilli, A. Rizzuti, C. Leonelli, Appl. Catal. A: Gen. 401
(2011) 134–140.
[44] M.M. Dell’Anna, M. Mali, P. Mastrorilli, A. Rizzuti, C. Ponzoni, C. Leonelli, J. Mol.
Catal. A: Chem. 366 (2013) 186–194.
[45] Y. Pereza, M.L. Ruiz–Gonzalez, J.M. Gonzalez–Calbet, P. Concepcion, M. Boronat,
A. Corma, Catal. Today 180 (2012) 59–67.
[46] J. Chen, Q. Zhang, Y. Wang, H. Van, Adv. Synth. Catal. 350 (2008) 453–464.
[47] A.S. Rozenberg, A.A. Rozenberg, G.I. Dzardimalieva, A.D. Pomogailo, Colloid J.
67 (2005) 63–71.
[48] J.A. Mueller, C.P. Goller, M.S. Sigman, J. Am. Chem. Soc. 126 (2004) 9724–
9734.
[1] M.I. Fernandez, G. Tojo, Oxidation of Alcohols to Aldehydes and Ketones: A
Guide to Current Common Practice, Springer, New York, 2006.
[2] J. March, Advanced Organic Chemistry: Reactions Mechanisms, and Structure,
4th ed., John Wiley & Sons, New York, 1992.
[3] T. Mallat, A. Baiker, Chem. Rev. 104 (2004) 3037–3058.
[4] B.-Z. Zhan, A. Thompson, Tetrahedron 60 (2004) 2917–2935.
[5] T. Punniyamurthy, S. Velusamy, J. Iqbal, Chem. Rev. 105 (2005) 2329–2364.
[6] N. Komiya, T. Nakae, H. Sato, T. Naota, Chem. Commun. (2006) 4829–4831.
[7] R.A. Sheldon, I.W.C.E. Arendes, G.–J.T. Brink, A. Dijksman, Acc. Chem. Res. 35
(2002) 774–781.
[8] L. Tonucci, M. Nicastro, N. d’Alessandro, M. Bressan, P. D’Ambrosio, A. Morvillo,
Green Chem. 11 (2009) 816–820.
[9] A. Frassoldati, C. Pinel, M. Besson, Catal. Today 173 (2011) 81–88.
[10] T. Zweifel, J.–V. Naubron, H. Grützmacher, Angew. Chem. Int. Ed. 48 (2009)
559–563.
[11] L. Liu, M. Yu, B.B. Wayland, X. Fu, Chem. Commun. 46 (2010) 6353–6355.
[12] Z. Hu, F.M. Kerton, Appl. Catal. A: Gen. 413–414 (2012) 332–339.
[13] W. Amer, K. Abdelouahdi, H.R. Ramananarivo, M. Zahouily, E.M. Essassi, A. Fihri,
A. Solhy, Curr. Org. Chem. 17 (2013) 72–78.
[14] P. Miedziaka, M. Sankara, N. Dimitratosa, J.A. Lopez-Sancheza, A.F. Carleya,
D.W. Knighta, S.H. Taylora, C.J. Kielyb, G.J. Hutchingsa, Catal. Today 164 (2011)
315–319.
[15] H. Miyamura, R. Matsubara, Y. Miyazaki, S. Kobayashi, Angew. Chem. Int. Ed.
46 (2007) 4151–4154.
[16] C. Shang, Z.-P. Liu, J. Am. Chem. Soc. 133 (2011) 9938–9947.
[17] N. Asao, N. Hatakeyama, Menggenbateer, T. Minato, E. Ito, M. Hara, Y. Kim,
Y. Yamamoto, M. Chen, W. Zhangi, A. Inouei, Chem. Commun. 48 (2012)
4540–4542.
[18] D. Tsukamoto, Y. Shiraishi, Y. Sugano, S. Ichikawa, S. Tanaka, T. Hirai, J. Am.
Chem. Soc. 134 (2012) 6309–6315.
[19] M.J. Schultz, C.C. Park, M.S. Sigman, Chem. Commun. (2002) 3034–3035.
[20] S.S. Stahl (Ed.), Angew. Chem. Int. 43 (2004) 3400–3420.
[21] L.-Y. Wang, J. Li, Y. Lv, H.-Y. Zhang, S. Gao, J. Organomet. Chem. 696 (2011)
3257–3263.
[22] B.P. Buffin, J.P. Clarkson, N.L. Belitz, A. Kundu, J. Mol. Catal. A: Chem. 225 (2005)
111–116.
[23] I.W.C.E. Arends, G.-J. ten Brink, R.A. Sheldon, J. Mol. Catal. A: Chem. 251 (2006)
246–254.
[24] K.M. Gligorich, M.S. Sigman, Chem. Commun. (2009) 3854–3867.
[25] G. Zhang, Y. Wang, X. Wen, C. Ding, Y. Li, Chem. Commun. 48 (2012)
2979–2981.
[26] S. Verma, D. Tripathi, P. Gupta, R. Singh, G.M. Bahuguna, L.N. Shivakumar, R.K.
Chauhan, K.S. Saranb, S.L. Jain, Dalton Trans. 42 (2013) 11522–11527.
[27] E.V. Johnston, O. Verho, M. Shakeri, C.–W. Tai, P.P. Almgren, K. Eriksson, S.
Oscarsson, J.–E. Bäckvall, Chem. Eur. J. 18 (2012) 12202–12206.
[28] L. Tang, X. Guo, Y. Li, S. Zhang, Z. Zha, Z. Wang, Chem. Commun. 49 (2013)
5213–5215.
[49] L.C. John, A. Gunay, A.J. Wood, M.H. Emmert, Tetrahedron 69 (2013) 5758–
5764.
[50] A. Abad, A. Corma, H. Garcia, Chem. Eur. J. 14 (2008) 212–222.
[51] F. Wang, W. Ueda, J. Xu, Angew. Chem. Int. Ed. 51 (2012) 3883–3887.
[52] M. Wang, F. Wang, J. Ma, M. Li, Z. Zhang, Y. Wang, X. Zhang, J. Xu, Chem.
Commun. 50 (2014) 292–294.
[53] ␴ values were taken from T.H. Lowry, K.S. Richardson, Mechanism and Theory
in Organic Chemistry, 3rd ed., Harper and Row, New York, 1987, pp. 144.
[54] A. Biffis, L. Minati, J. Catal. 236 (2005) 405–409.