Oxidative "reverse-esterification" of ethanol with benzyl/alkyl alcohols or aldehydes catalyzed by supported rhodium nanoparticles

Article abstract of DOI:10.1039/c5gc02513c

A very unusual role of polystyrene stabilized rhodium (Rh@PS) nanoparticles as a supported catalyst is described for "reverse-esterification" of ethanol with benzyl/alkyl alcohols or aldehydes. Faster and selective oxidation of ethanol to acetaldehyde and H₂ under Rh@PS catalyzed conditions which restricted further oxidation of benzyl/alkyl alcohols and their in situ reaction gave the corresponding acetate esters following the dehydrogenative-coupling approach. A hitherto redox dehydrogenative-coupling of ethanol and aldehydes has also been explored for the same acetate ester synthesis under Rh@PS catalyzed conditions.

Full text of DOI:10.1039/c5gc02513c

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Oxidative “reverse-esterification” of ethanol with benzyl/alkyl alcohols or aldehydes
catalyzed by supported rhodium nanoparticles
Nitul Ranjan Guha,a,b Saurabh Sharma,a,b Dhananjay Bhattacherjee,a,b Vandna Thakur,a,b Richa
Bharti,a,b C. Bal Reddy,a,b Pralay Das*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A very unusual role of polystyrene stabilized rhodium (Rh@PS) area in the synthetic organic chemistry over the past few
nanoparticles as supported catalyst was described for “reverse- years.6 For primary alcohols, most attention have been
esterifiacation” of ethanol with benzyl/alkyl alcohols or devoted to the direct synthesis of benzoates from the
aldehydes. Faster and selective oxidation of ethanol to oxidative esterification of benzyl alcohols with small aliphatic
acetaldehyde and H2 under Rh@PS catalyzed condition which alcohols such as methanol, ethanol, butanol etc.7 Of all the
restricted further oxidation of benzyl/alkyl alcohols and their in reported esterifications, benzyl alcohols by β-hydride
situ reaction gave corresponding acetate esters following elimination are first oxidized to the respective benzaldehydes
dehydrogenative-coupling
approach.
A
hitherto
redox and are then participated in coupling with alkyl alcohol to
dehydrogenative-coupling of ethanol and aldehydes has also been produce benzoate esters.
explored for the same acetate esters synthesis under Rh@PS
catalyzed conditions.
However, despite the advantage of using ethanol as quasi-
renewable energy source very few work has been carried out
,
on similar oxidative transformations.8 But in all of the
reactions, much more attention has been devoted either to
the direct synthesis of ethyl acetate from the oxidative
dimerisation of ethanol only, in which stoichiometric quantity
of metal oxides as additives at high temperature have to be
used9 or to the synthesis of ethyl benzoates as esterification
products.10 Due to high oxidation potential, higher pKa of the
hydroxyl group and the stronger α-C-H bond, the oxidation of
ethanol is generally hindered relative to benzylic alcohols11
and hence require photocatalytic or electrolytic conditions for
its oxidation.12 The inherent challenge of oxidizing aliphatic
alcohols relative to benzyl alcohols encouraged us to use
ethanol as primary coupling partner in the present catalyst
Introduction
Esters are important precursors and intermediates for fine
chemicals, fragrances, natural products and polymers.1 Among
esters, acetate esters such as hexyl acetate, isoamyl acetate
and 2-phenylethyl acetate act as a solvent in synthesis of
resins, plastic, polishes, and ink; contribute to the aroma of
fruits like those of banana, strawberry, pear and apple and are
thus widely recognized as substantial flavor compounds in
wine and other grape-derived alcoholic beverages.2
Conventional protocols for the synthesis of acetate esters are
Fischer esterification of alcohols, acylation of alcohols with
activated acid derivatives (acyl chlorides and anhydrides), the
acetylation of aromatic alcohols catalyzed by alcohol
acetyltransferase,3 lipase catalyzed enzymatic trans
esterification,4 ketene addition to alcohols and the
condensation of acetaldehyde in the presence of aluminium
ethoxide catalyst.5 Transition metal catalyzed oxidative
esterification/dehydrogenation of alcohols via “hydrogen
auto-transfer process” has emerged as a fundamental research
CHO
R
Previous work
O
Pd, Co, Rh, Au-Pd, Ru, Cu
OH
+
O
CH3
R
R
CH CH OH
3
2
Oxidant, Additive, Base,
Solvent
Beller, Zhu, Molander, Rominger,
Hiroshi, Li, Somyote groups
O
Rh@PS
KOtBu, Solvent
OH
O
CH3
+CH3CH2OH
R
R
a.Natural Product Chemistry & Process Development, CSIR-Institute of Himalayan
Bioresource Technology, Palampur -176061, H.P., India. Fax: (+91)-1894-230-433;
e-mail: pdas@ihbt.res.in; pdas_nbu@yahoo.com
our work
OH
R
CH3CHO
+
b.Academy of Scientific & Innovative Research (AcSIR), New Delhi, India.
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
Scheme 1. Comparison of oxidative coupling of ethanol with benzyl alcohols
development efforts. Inspired by recent investigations of
oxidative esterification of alcohols10 herein, we demonstrate
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application of Rh@PS catalyst system that promotes selective
oxidative esterification of ethanol and benzyl/alkyl alcohols or
aldehydes following a very unusual and unexplored pathway to
the corresponding acetate esters synthesis.
Results and discussion
In our continuous thirst to develop solid supported transition
metal nanoparticles (NPs) as heterogeneous catalysts14 and
Fig. 2 (a–b) TEM images of Rh nanoparticles supported on polystyrene resin at
different magnifications. (c) HRTEM bright field image of Rh@PS. (d) Particle size
distribution curve based on statistical analysis of TEM images; (e) SAED image of
Rh@PS. (f) HRTEM image indicating lattice fringe spacing corresponding to the
plane [111] and fast Fourier transformation ( FFT) image (right inset).
Fig. 1 Powder X-ray diffraction (XRD) patterns for Rh@PS catalyst
their applications in different area of organic transformations,
Rh@PS was synthesized following our previously reported
procedure15,13 and before application the morphological
feature of the catalytic surface was investigated by XRD (Fig.
1), transmission electron microscopy (TEM) and selected area
inset) give a lattice spacing d = 0.23 nm and d = 0.19 nm, thus,
indicating only (111) and (200) reflections were visible in Fast
Fourier Transformation (FFT) graph (Fig. 2f). The heterogeneity
of the active Rh species in Rh@PS was confirmed by Hg(0)
poisoning test (supporting information) and hot filtration test
(Fig. 3). After addition of mercury to the reaction mixture, no
electron diffraction (SAED) (Fig 2) analysis
.
The presence of metallic Rh particles in power XRD spectra is
indicated by four characteristic reflections originating from the
(111), (200), (220) and (311) crystallographic planes of the fcc
lattice.16 However, during XRD study low intense peaks were
observed due to rigidity of solid support as well as low
concentration of Rh per gram of the support (Fig. 1).
The low field TEM images confirmed the impregnation of
spherical Rh-nanoparticles in the polystyrene matrix (Fig. 2(a-
b)). High resolution TEM (HR-TEM) bright field image of Rh@PS
representing the crystallographic orientation of the Rh NPs
was shown in Fig. 2c. The histogram representing the particle
size distribution was drawn from Fig. 2b by measuring the size
of 493 NPs with the help of Image-J software. The distribution
curve indicated that the average size of Rh NPs was
approximately 1-2 nm (Fig. 2d). SAED pattern was presented in
Fig. 2e contains diffraction rings corresponding to (111), (200),
(220) and (311) crystallographic planes confirming the
existence of crystallites of Rh NPs, which is consistent with the
d-spacing observed in XRD measurements (Fig. 1). HR-TEM
with FEG (field emission gun) source reveals the crystalline
feature of a single Rh NPs having d-spacing 0.23 nm which
corresponds to the (111) reflection plane (Fig. 2f). The electron
diffractogram pattern of the marked region in Fig. 2f (shown in
Fig. 3 Hot filtration test for the Rh@PS catalyzed oxidative reverse esterification
of ethanol with p-OMe benzyl alcohol
conversion of reactant was observed during the Hg(0) test.
Similarly, the hot filtration test showed that no extra yield of
acetate 2a was noticed after the solid catalyst was filtered off
(Fig. 3). These findings revealed that the catalysis of
esterification took place in a true heterogeneous manner as
negligible quantity of rhodium, which is too few to react, was
leached during the esterification reaction.
2 | J. Name., 2012, 00, 1-3
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To begin with, 4-methoxy benzyl alcohol and ethanol were best optimized condition to give highest yield (75%) of the
chosen as benchmark substrates to optimize the condition of acetate ester 2a (Table 1, entry 9). The presence of minute
oxidative coupling under Rh@PS catalyst, and the results are quantity of air in the reaction system was sufficient for the
summarized in Table 1. Different metal loadings such as 0.5
Rh@PS
O
mol%, 1 mol%, 2 mol% and 3 mol% of Rh respectively (Table 1,
OH
C2H5OH
OH
CH3CHO
R
H-Rh@PS
O
Rh@PS
KOtBu
Step I
-H-Rh@PS
Step II
R
+
R
R
+
+
+
CH3CHO
KOtBu
entries 2, 3, 9 and 10) was examined and 2 mol% Rh@PS were
used as optimal catalyst loading. Base and solvent screening
indicated that 4 equiv of KOtBu in 1,4-dioxane or toluene gave
Rh@PS
C2H5O
Step III
Rh@PS
KOtBu
Step IV
Rh@PS
OH
H
CH3
O
O
Table 1. Screen of reaction conditions for acetate esters synthesis from ethanol and p-
H
CH3
O
OMe benzyl alcohola
-H-Rh@PS
β-H- elimination
Rh@PS
Step V
O
CH3
O
R
R
R
Step VI
"hemiacetal"
O
OH
CH3CH2OH
O
CH3
Catalyst
Scheme 2. Possible redox pathway for the oxidative esterification of alcohols
+
Base, Solvent
Temperature
H3CO
Entry
H3CO
1a
2a
Temp. ( oC) Yield (%)b
oxidation reaction and no product was detected under N2
atmosphere (Table 1, entry 16).
Catalyst (2 mol% Rh)
Rh@PS
Base
Solvent
1,4-dioxane
Under this study considering GCMS data for intermediate
KOH
125
60
1
Table 2. Rh@PS catalyzed reaction of substituted benzyl alcohols with ethanol for
acetate esters synthesis.a
KOtBu
KOtBu
KOtBu
2c
3d
4
1,4-dioxane 125
1,4-dioxane 125
Rh@PS
Rh@PS
Rh@PS
27
53
O
C
125
n.d
DMF
OH
CH3CH2OH
O
CH3
Rh@PS
R
R
+
KOtBu, 1,4-dioxane
120-125 oC, 50-55 h
n.r
n.r
5
125
125
125
125
Rh@PS
Rh@PS
Rh@PS
1,4-dioxane
KF
2b-l
Product
1b-l
Substrate
DABCO 1,4-dioxane
6
Temp/Time (oC/hr)
120/53
Yield(%)b
61
Entry
1
n.d
n.d
Na2CO3
1,4-dioxane
1,4-dioxane
7
8
O
K2CO3
KOtBu
KOtBu
KOtBu
KOtBu
Rh@PS
Rh@PS
Rh@PS
OH
O
CH3
CH3
9
1,4-dioxane 125
125
75
75
15
1b
2b
10e
11
1,4-dioxane
O
OH
1c
O
O
Rh@PS
Rh@PS
Rh@PS
Rh@PS
Rh@PS
Acetonitrile 125
65
2
3
120/53
125/55
2c
125
n.d
32
12
PEG-400
O
KOtBu
KOtBu
KOtBu
1,4-dioxane
OH
1d
110
13
14
15
CH3
CH3
57
66
2d
O
Cl
40
70
Cl
1,4-dioxane
Toluene
135
125
125
OH
1e
O
O
4
125/55
Cl
2e
Cl
KOtBu
16f
n.d
n.r
n.r
1,4-dioxane
Rh@PS
Rh/C
OH
CH3
KOtBu
KOtBu
1,4-dioxane
1,4-dioxane
125
125
O
17
18
19
70
120/50
122/55
5
6
1f
2f
RhCl3
KOtBu
1,4-dioxane
n.r
125
[RhCp*Cl2]2
CH3
50
53
S
OH
S
O
O
O
1g
2g
aAll reactions were carried out with p-OMe benzyl alcohol (1 eqv.), ethanol (2
mL), base (4 eqv.), solvent (1.2 mL) and time 55 h. b Isolated yields (2a); n.r = no
reaction; n.d = not detected; traces of p-OMebenzaldehyde were formed. c 0.5
mol% catalyst was taken. d1 mol% catalyst was used. e3 mol% catalyst was
charged. f Reaction conducted at N2 atmosphere.
OH
O
CH3
7
125/55
120/50
N
2h
N
1h
O
CH3
CH3
8
9
58
60
1i
OH
O
2i
OH
O
the comparable results, but due to environmental concern
toluene was discarded as reaction media. The quantity of
ethanol was found to be crucial for selective conversion of
acetate esters. While employing variable quantity of ethanol
including 0.5 mL, 1 mL and 1.5 mL separately, a mixture of
acetate ester and aldehyde were detected by GCMS in each
case, although the yield of benzaldehyde is diminished in that
order. However, use of 2 mL of ethanol exclusively formed the
acetate ester, the aldehyde could not be observed.
Subsequently, different Rh-catalyst precursors were
investigated and the results indicated that Rh@PS was found
to be the most active and selective redox reagent for the
synthesis of acetate ester 2a. Finally, Rh@PS (2 mol%), KOtBu
1j
120/50
120/50
O
O
2j
O
CH3
OH
10
60
57
1k
CH3(CH2)10CH2OH
2k
CH3(CH2)10CH2O
O
11
1l
CH3 2l
125/55
aReaction conditions: substituted benzyl alcohols, 1b–l (1 equiv.), KOtBu (4
equiv.), ethanol (2 mL) and Rh@PS (2 mol% Rh) in 1,4-dioxane (1.2 mL). bIsolated
yields
molecules, both benzyl and ethyl alcohols coordinates to the
Rh and through β-hydride elimination generate aldehydes
(step I to II) and formal hydrogen. The liberated formal H2
further reduces benzaldehyde/ benzylalcohol coordinated Rh
to benzyl alcohol (step III) which directly reacts with
o
(4 equiv.), and ethanol (2 mL) at 125 C was found to be the
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acetaldehyde to produce corresponding hemiacetal (Step IV). coupling between their intermediates in a cascade sequence
Finally, acetate ester was formed through Rh-catalyzed β- has been demonstrated.
hydride elimination of the hemiacetal (step VI) (Scheme 2). The newly developed tandem strategy was further applied to a
This indicates that a formal “H2” release takes place (steps I-II number of aromatic and aliphatic aldehydes for “reverse
and V-VI) but the nature of compound (H2 or H2O) released is esterification” reaction (Table 3). Both electron-rich and
still uncertain.
electron-deficient benzaldehydes 1m-p were well tolerated
The Rh@PS catalyst system exhibits a slow and sustainable under the optimized reaction conditions and afforded the
process with broader substrate scope for the oxidative desired acetate esters 2m-p in substantial yields (Table 3,
esterification of various primary alcohols with ethanol. The entries 1-4). Surprisingly, the reaction of aliphatic aldehydes
results provided in Table 2 indicated a high degree of
Table 3 Rh@PS catalyzed reaction of substituted aldehydes with ethanol for acetates
synthesis.a
functional-group tolerance under redox reaction condition.
Considering earlier reports for similar esterification reactions,
it is highly undesired to restrict oxidation of benzyl alcohol but
in this study a reverse order reactivity of electron rich benzyl
alcohols 1b-c was explored to produce corresponding benzyl
acetates 2b-c (61-65%) under optimized condition (Table 2,
entry 1-2). Similarly, benzyl alcohols substituted with electron-
withdrawing Cl atom at –o and –p position of the benzene ring
1d-e produced the desired products 2d-e in 57 and 66% yields
respectively (Table 2, entries 3-4) and no dehalogenation
product was observed by GCMS. Even sterically hindered α-
naphthylmethanol 1f underwent smooth transformation into
the corresponding acetate 2f exclusively in 70% yield (Table 2,
entry 5). Delightly, heterocyclic alcohols 1g-h also reacted with
O
C
Rh@PS
KOtBu, 1,4-dioxane
120-125 oC, 60-65 h
O
CH3
O
R
R
+
CH3CH2OH
1m-s
2m-s
Yield[%]b
55
Entry
1
Substrate
Temp/Time (oC/hr)
Product
O
O
CH3
O
1m
120/60
2m
Me
Me
O
O
2n
CH3
CH3
CH3
51
50
57
O
1n
2
3
120/60
120/62
MeO
MeO
O
O
O
1o
1p
2o
OMe
OMe
O
O
O
125/65
4
5
2p
O
O
OH
CH3CHO
H-Rh@PS
O
Rh@PS
KOtBu
Step I
R
-H-Rh@PS
Step II
R
Cl
Cl
+
R
R
+
C2H5OH
+
+
CH3CHO
KOtBu
Step III
O
Rh@PS
C2H5
O
66
40
Rh@PS
KOtBu
O
1q
O
CH3
O
Step IV
125/65
120/65
2q
Rh@PS
OH
H
CH3
O
O
O
O
CH3
H
CH3
Rh@PS
Step V
O
6
7
-H-Rh@PS
β-H- elimination
O
CH3
1r
1s
O
R
2r
R
R
Step VI
"hemiacetal"
O
45
Scheme 3. Possible redox pathway for the oxidative esterification of aldehydes
120/65
O
O
CH3
2s
with ethanol following reverse order of reactivity
aReaction conditions: substituted benzaldehydes 1m–s (1 equiv.), KOtBu (2.5-3
equiv.), ethanol (2 mL) and Rh@PS (2 mol% Rh) in 1,4-dioxane (1.2 mL). bIsolated
yields
ethanol to afford the corresponding acetate esters 2g-h in 50
and 53% yields respectively (Table 2, entries 6 and 7).
Furthermore, geraniol 1i containing C-C double bond was also
tolerated under the redox conditions and produced the
desired ester 2i in 58% yield (Table 2, entry 8). Moreover,
aliphatic alcohols are known for self oxidative esterification
but interestingly aliphatic primary alcohols 1j-l furnished
anticipated esters 2j-l in 60, 60 and 57% yields, respectively
(Table 2, entries 9-11).
1q and 1r with ethanol also proceeded well to produce alkyl
acetates 2q and 2r respectively in good to moderate yields
(Table 3, entry 5 and 6). Moreover, naturally occurring
citronellal 1s was transformed into the desired acetate 2s with
an equal efficacy (Table 3, entry 7).
To understand the intermediates and reaction mechanism
several cross studies were performed. Without ethanol, benzyl
alcohol 1a becomes oxidized to the respective benzaldehyde
1t in high yield showing that ethanol plays a crucial role to
prevent the oxidation of other alcohols as well to promote
their facile nucleophilic attack in generating hemiacetal
intermediate (Scheme 4a). In scheme 4b, ethanol reduces the
benzaldehyde 1t to the corresponding benzyl alcohol 1a in
good yield. This result clearly indicated that ethanol also serves
as a reducing agent for the synthesis of acetate ester through
cross-dehydrogenative coupling reaction under the present
catalytic conditions. The reduction of p-OMebenzaldehyde 1t
by ethanol is a hydrogen transfer reaction, which follows: i)
the coordination of ethanol onto the metal, ii) the
deprotonation giving rise to a metal-alkoxide species, iii) the
Over the last few years, groups of Molander,17 Rominger,18
20
21
Hiroshi,19 Li and Somyote demonstrated the synthesis of
“ethyl benzoates” through the oxidative esterification of
aldehydes with ethanol using various transition metals as
catalyst. But, in the present study ethanol under Rh@PS
catalyzed conditions acts as a “redox reagent” and becomes
oxidized into acetaldehyde with the formation of H2. The
liberated H2 then in situ reduces aryl/alkyl aldehydes to their
corresponding alcohols and finally coupling of these alcohols
with acetaldehyde through β-H elimination resulted into the
formation of acetate esters (Scheme 3).
However, to the best of our knowledge, no Rh catalyzed
“reverse esterification” protocol involving the oxidation of
ethanol, reduction of aryl/alkyl aldehydes and simultaneous
4 | J. Name., 2012, 00, 1-3
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beta-elimination to form acetaldehyde and a metal hydride, iv) reactivity for esterification reaction. Unusual redox nature of
the coordination of the methoxybenzaldehyde on the metal ethanol in presence of Rh@PS catalyst makes the system an
and it insertion into the metal-hydride bond, v) and finally the unprecedented for acetate ester synthesis comparing the
protonation of the corresponding metal-alkoxide and the existing advanced and traditional methods.
release of the p-OMebenzylalcohol 1a. The coupling reaction
ACKNOWLEDGMENT
proceeds through the in situ formation of acetaldehyde 2t as
an intermediate, which was detected by infrared spectral
analysis (Scheme 4c and supporting information). Finally,
treatment of acetaldehyde 2t with benzyl alcohol 1a leads to
the formation of desired ester 2a confirming the involvement
of hemiacetal generated from acetaldehyde solely (Scheme
4d).
We are grateful to the Director of CSIR-IHBT for providing the
necessary facilities during the course of this work. The authors
thank CSIR, New Delhi for financial support as part of the XIIth
Five Year Plan programme under title ORIGIN (CSC-0108). We
also thank AIRF, JNU-New Delhi, for the TEM and SAED
analysis, SAIF, IIT Bombay for ICP-AES analysis. NRG, SS, DB,
VT, RB and CBR thank UGC and CSIR, New Delhi for awarding
fellowships. CSIR-IHBT communication no. 3886.
The recyclability experiment of Rh@PS was done on p-OMe
benzyl alcohol. After completion, the reaction mixture was
filtered off through a cotton bed, washed with water and
acetone properly, dried over rotary evaporator. Finally, the
Notes and references
Table 4 Recyclability experiment of Rh@PS for oxidative esterification
1
J. Otera, Esterification: methods, reactions, and applications,
Wiley-VCH, Weinheim, 2003.
V. Rojas, Int. J. Food. Microbiol, 2001, 70, 283.
No. of cycles 1st cycle
2nd cycle 3rd cycle
4th cycle
72
6th cycle
71
5th cycle
71
2
3
J. D’Auria, F. Chen and E. Pichersky, Plant Physiol, 2002, 130
466.
,
75
73
73
Yield (%)
4
C. H. Kuo, S. H. Chiang, H. Y. Ju, Y. M. Chen, M. Y. Liao, Y. C.
Liu and C. J. Shieh, Sci Food Agric, 2012, 92, 2141.
Tischtschenko, Chemisches Zentralblatt, 1906, 77, 1309.
G. Guillena, D. J. Ramon and M. Yus, Angew. Chem. 2007,
119, 2410; Angew. Chem. Int. Ed. 2007, 46, 2358.
( a) Q. Xiao, Z. Liu, A. Bo, S. Zavahir, S. Sarina, S. Bottle, J. D.
Riches and H. Zhu, J. Am. Chem. Soc, 2015, 137, 1956; (b) C.
Liu, J. Wang, L. Meng, Y. Deng, Y. Li and A. Lei, Angew. Chem.
Int. Ed, 2011, 50, 5144; (c) N. A. Owston, A. J. Parker, J. M. J.
Williams, Chem.Commun, 2008, 624; (d) X. F. Bai, F. Ye, L. S.
Zheng, G. Q. Lai, C. G. Xia and L. W. Xu, Chem. Comum, 2012,
48, 8592.
recovered dried catalyst was repeatedly used for the same
reaction. The catalyst retained its activity upto six cycles of
reaction with negligible metal leaching.
5
6
7
During the recyclability experiment, Inductively coupled
plasma atomic absorption spectra (ICP-AES) study of the
CHO
Rh@PS, KOtBu
1,4-dioxane, 120 o
5 h
OH
a.
C
H3CO
H3CO
1t: 88%
1a
CHO
CH3CH2OH
8
9
M. Nielsen, H. Junge, A. Kammer and M. Beller, Angew.
Chem. Int. Ed, 2012, 51, 5711.
OH
Rh@PS, KOtBu
1,4-dioxane, 120 o
15h
b.
C
H3CO
H3CO
(a) K. Inui, T. Kurabayashi, S. Sato and N. Ichikawa, J. Mol.
Catal. A: Chem, 2004, 216, 147; (b) P. C. Zonetti, J. Celnik, S.
Letichevsky, A. B. Gaspar and L. G. Appel, J. Mol. Catal. 2011,
334, 29; (c) L. Wang, K. Eguchi, H. Arai and T. Seiyama,
Applied Catalysis, 1987, 33, 107.
1t
1a: 79%
Rh@PS, KOtBu
1,4-dioxane, 120 o
c.
CH3CH2OH
CH3CHO
C
2t
1u
55h
O
Rh@PS, KOtBu
1,4-dioxane, 120 o
44h
O
CH3
d.
1a
+
CH3CHO
10 (a) R. Ray, R. D. Jana, M. Bhadra, D. Maiti and G. K. Lahiri,
Chem. Eur. J. 2014, 20, 15618; (b) S. Gowrisankar, H.
Neumann, M. Beller, Angew. Chem. Int. Ed, 2011, 50, 5139;
(c) R. V. Jagadeesh, H. Junge, M. –M. Pohl, J. Radnik, A.
Brückner and M. Beller, J. Am. Chem. Soc. 2013, 135, 10776.
11 J. M. Hoover, B. L. Ryland and S. S. Stahl, J. Am. Chem. Soc.
2013, 135, 2357.
12 (a) D. S. Muggli, J. T. McCue and J. L. Falconer, Journal of
Catalysis, 1998, 173, 470; (b) H. Jin, T. Xiong, Y. Li, X. Xu, M. Li
and Y. Wang, Chem.Commun, 2014, 50, 12637; (c) Z. Huang,
H. Zhou, C. Li, F. Zeng, C. Fua, and Y. Kuang, J. Mater. Chem,
2012, 22, 1781.
C
H3CO
2t
2a: 65%
Scheme 4. Control experiments to prove the redox nature of ethanol and
understanding the reaction mechanism
reaction mixture was analyzed to determine the amount of Rh-
metal leached from the solid surface (Supporting information).
The result of the test showed that only 0.45 ppm of Rh-metal
was leached after six runs of the reaction.
13 N. R. Guha, D. Bhattacherjee and P. Das, Catal. Sci. Technol.
2015,
14 (a) A. K. Shil, S. Kumar, C. Bal Reddy, V. Thakur, S. Dadwal
and P. Das, Org. Lett, 2015, doi:
5, 2575.
Conclusions
In summary,
a
highly efficient nano-impregnated
doi: 10.1021/acs.orglett.5b02701; (b) A. K. Shil and P. Das,
Green Chem, 2013, 15, 3421; (c) A. K. Shil, S. Kumar, S.
Sharma, A. Chaudhary and P. Das, RSC Adv, 2015, 5, 11506.
heterogeneous Rh(0) catalysed cross-dehydrogenating
coupling of ethanol with aryl/ alkyl alcohols or aldehydes
under aerobic conditions has been investigated for the
synthesis of acetate esters in a one pot consecutive approach.
Vast range of aryl/alkyl alcohols or aldehydes has been
targeted to prove in situ redox behaviour of ethanol and its
15 N. R. Guha, C. B. Reddy, N. Aggarwal, D. Sharma, A. K. Shil,
Bandna and P. Das, Adv. Synth. Catal, 2012, 354, 2911.
16 S. Agarwall and J. N. Ganguli, J. Mol. Catal. A: Chem, 2013,
372, 44.
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COMMUNICATION
Journal Name
17 B. A. Tschaen, J. R. Schmink and G. A. Molander, Org. Lett,
2013, 15, 500.
18 A. Stephen, K. Hashmi, C. Lothschtz, M. Ackermann, R.
Doepp, S. Anantharaman, B. Marchetti, H. Bertagnolli, F.
Rominger, Chem. Eur. J, 2010, 16, 8012.
19 M. Shunichi, N. Takeshi, I. Keiichiro, M. Yoshihiro and T.
Hiroshi, J. Org. Chem, 1987, 52, 4319.
20 W. J. Yoo and C. J. Li, Tetrahedron Lett, 2007, 48, 1033.
21 R. Grigg, R. B. M. Thomas and S. Somyote, Tetrahedron,
1981, 37, 4313.
6 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5GC02513C
Graphical abstract:
Oxidative “reverse-esterification” of ethanol with benzyl/alkyl alcohols or aldehydes catalyzed by
supported rhodium nanoparticles
Nitul Ranjan Guha,a,b Saurabh Sharma,a,b Dhananjay Bhattacherjee,a,b Vandna Thakur,a,b Richa Bharti,a,b C. Bal
Reddy,a,b Pralay Das*a,b