Iron oxalate capped iron-copper nanomaterial for oxidative transformation of aldehydes

Article abstract of DOI:10.1039/c4nj01966k

An efficient, sustainable and green procedure for the synthesis of selective orthorhombic iron(oxalate) capped Fe-Cu bimetallic oxide nanomaterial [Fe(ox)Fe-CuOx] was developed using a sodium borohydride reduction of iron(ii) salt in the presence of oxalic acid at room temperature followed by addition of copper sulfate in water. The reported method is a cost-effective chemical route for producing [Fe(ox)Fe-CuOx] nano material at the gram level with a surface area of 78.4 m² g^-1 and a pore volume of 0.141 cm³ g^-1. The [Fe(ox)Fe-CuOx] nanomaterials were found to be useful as a recoverable catalyst for the oxidative transformation of an aldehyde to its corresponding ester and acid in presence of hydrogen peroxide.

Full text of DOI:10.1039/c4nj01966k

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: R. kashyap, D. J.
Talukdar and S. Pratihar, New J. Chem., 2014, DOI: 10.1039/C4NJ01966K.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
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
Information for Authors.
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 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.
www.rsc.org/njc

Page 1 of 8
New Journal of Chemistry
View Article Online
DOI: 10.1039/C4NJ01966K
Journal Name
RSCPublishing
ARTICLE
Iron Oxalate Capped Iron-copper Nano for
oxidative transformation of aldehydes
Cite this: DOI: 10.1039/x0xx00000x
Rajarshi Kashyap, Dhruba Joyti Talukdar, and Sanjay Pratihar*
Received 00th January 2012,
Accepted 00th January 2012
An efficient, sustainable and green procedure for the synthesis of selective orthorhombic iron(oxalate)
capped Fe-Cu bimetallic oxide nanomaterial [Fe(ox)Fe-CuOx] is developed using sodium borohydride
(NaBH4) reduction of iron(II) salt in presence of oxalic acid at room temperature followed by addition of
CuSO4 in water. The reported method is a cost-effective chemical route for producing [Fe(ox)Fe-CuOx]
nano material in gram level with surface area of 78.4 m2/g and pore volume of 0.141 cc/g. The [Fe(ox)Fe-
CuOx] nanomaterial are found to be useful as a recoverable catalyst for the oxidative transformation of
aldehyde to its corresponding ester and acid in presence of H2O2.
DOI: 10.1039/x0xx00000x
www.rsc.org/
Introduction:
bimetallic Fe-Cu oxide material [Fe(ox)Fe-CuOx] was well
characterized by FT-IR, XRD, SEM, and TEM analysis.
Amongst various nanoparticles, iron oxide nanoparticle has
been of great interest because of their multivalent oxidation
states, abundant polymorphism, and the mutual polymorphous
On the other hand, esters are highly attractive building blocks
as it can readily be interconverted into a number of other
functional groups, and they are frequently employed in industry
as fragrances, medicines, or in polymer construction.5 The
classical route to ester preparation involved the reaction
between carboxylic acids and alcohols or in a stepwise fashion
from carboxylic acid to acid chloride to ester using strong
acids, SOCl2, CDI, DEAD/PPh3, DCC etc.6 However, these
methods have one or more of the following limitations: for
example, lack of broad functional group tolerance, use of toxic
or hazardous reagents, tedious work-up, difficulty in separation
of desired ester from the reaction mixture etc. Towards the
search for new environmentally friendly, atom-efficient
methods which avoid the use of large amounts of condensing
reagents and activators, an attractive approach is the oxidative
esterification of the readily available aldehydes with alcohols.
In the last two decades, various transition-metal catalysts such
as vanadium,7 rhenium,8 silver,9 palladium,10 ruthenium,11
rhodium,12 copper,13 titanium,14 iridium,15 iron,16 nickel,17
Zinc18 calcium and magnesium19 etc. were successfully utilized
for the success of this transformation.
1
changes in nanophase. The easy handling, reasonably low
cost, nontoxicity, and environmentally friendly character of
iron oxide made it enormously popular as a catalyst and are
widely utilized on large scale in laboratory, industrial, and
environmental processes to accelerate various reactions
including oxidation of carbon monoxide, decomposition of soot
and NOx in diesel exhausts, Fischer-Tropsch synthesis of
hydrocarbons, water-gas shift reactions, catalytic oxidations of
other various organic compounds, and catalytic decomposition
of industrial dyes. Most of these applications require the iron
2
oxide nanoparticles to be chemically stable, uniform in size,
and well-dispersed in liquid media. Towards this, various
capping agent, templates was employed to control the size,
morphology and phase of metallic and oxide iron nanoparticle.3
Very recently, we have shown an efficient and green protocol
for the gram level synthesis of orthorhombic iron(oxalate)
capped Fe(0) [Fe(ox)-Fe(0)] nonmaterial using sodium
borohydride (NaBH4) reduction of iron(II) salt in presence of
oxalic acid at room temperature in water.4 During the course of
our study, we have observed the transformation of Fe(0) to
Fe3O4 after keeping the Fe(ox)-Fe(0) at room temperature in
water for a prolonged time (1-2 days) which showed Fe(C2O4)
capped Fe3O4 magnetic nanomaterial [Fe(ox)-Fe3O4]. Now, we
wanted to use the synthesized Fe(ox)-Fe(0) material for the
formation of bimetallic Fe-Cu oxide material. Gratifyingly, we
were able to synthesize orthorhombic iron(oxalate) capped Fe-
Cu oxide material from the reaction between [Fe(ox)-Fe(0)] and
CuSO4 in water. The synthesized iron(oxalate) capped
Scheme 1. Reported oxidative esterification of aldehydes
However, to take the necessary step from academic research to
industrial application for
a
wide range of catalytic
transformations, the catalytic processes have to be sustainable
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 1

New Journal of Chemistry
Page 2 of 8
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C4NJ01966K
with regard to parameters such as solvent, energy source, Fe(C2O4), 2H2O in the brown material [hereafter Fe(ox)Fe-
substrate scope, separation, and the nature of the catalyst.20
A
CuOx].
possible solution for the industrial application of catalyst can be
the increased utilization of heterogeneous catalysts on
biorelevant metals, such as iron, cobalt, and copper, which
would be beneficial with respect to catalyst recycling and
engineering.21 In this regard, Beller et al. successfully reported
reusable Co3O4-based heterogeneous catalysts for the direct
oxidative esterification of alcohols.22 Very recently, Suzuki et
al. reported oxidative esterification of aldehydes with alcohols
proceeds with high efficiency in the presence of molecular
oxygen on supported gold−nickel oxide (AuNiOx) nanoparticle
catalysts.23 Herein, we presented orthorhombic iron(oxalate)
capped Fe-Cu oxide [Fe(ox)Fe-CuOx] material catalyzed
oxidative esterification of various aldehyde in combination with
H2O2 as oxidant in methanol. Upon changing the solvent from
methanol to acetontrile, we could able to do oxidative
transformation of various aldehyde to its corresponding acids in
presence of catalytic amount of [Fe(ox)Fe-CuOx] nanomaterial
in combination with H2O2. The reusability of [Fe(ox)Fe-CuOx]
nanocatalyst was successfully examined seven times with only
Fig. 1 XRD pattern of Fe(ox)Fe-CuOx nanomaterial
a
slight loss of catalytic activity. Both the oxidative
The FTIR spectra of [Fe(ox)Fe-CuOx] nanomaterial was also
recorded and compared with oxalic acid, Fe(C2O4).2H2O, and
[Fe(ox)-Fe(0)] to know the binding behavior of the oxalate with
the brown material (Fig. 2). In case of oxalic acid a peak at
1710 cm-1 has been found, which is characteristic for carbonyl
group. Other two peaks for C-O and C-C bond of oxalic acid
appears at 1260 and 1123 cm-1 (Fig. 2). On the other hand,
Fe(C2O4).2H2O shows characteristic peaks at 1636, 1360, 1315,
819, and 493 cm-1. Particularly, the peak at 1636 and 1360 cm-1
were typical for metal carboxylate, in which oxalic acid is
acting as a bidentate ligand in Fe(C2O4).2H2O. Whereas, the
other peak at 1315, 819 cm-1 occur due to C-O and C-C
stretching vibration.
transformation reaction of aldehyde was successfully scale up
from 1 mmol to 0.3 mol with appreciable turn over frequency
(TOF) and yield.
Results and Discussions
Characterization of Iron-copper Nanoparticle
The synthesized [Fe(ox)Fe-CuOx] nano particle has been
characterized by FTIR, XRD, SEM, and TEM analysis. We
have recently reported the synthesis of single-phase
orthorhombic iron(oxalate) capped Fe(0) [Fe(ox)-Fe(0)]
nanomaterial from the aqueous phase room temperature
reduction of Mohr’s salt, (NH4)2SO4.FeSO4 with sodium
borohydride (NaBH4) in presence of oxalic acid.4 The presence
of Fe(0) in the material was confirmed from the XRD pattern of
the material and the methylene blue reduction by the material.
Now, we wanted to use the reactive Fe(0) for the reduction of
other metal like Cu(II). For this, the reaction between
previously
synthesized
[Fe(ox)-Fe(0)]
material
and
CuSO4.5H2O was done in water at 50 °C for 16h. During the
reaction color of the material turned from blackish to reddish
brown. After the completion of reaction, brown nanomaterial
was separated from the reaction mixture by centrifugation and
washed with water, and dried under vacuum at 100 °C for 36h.
The nanomaterial characterization by X-ray diffraction (XRD)
confirm the presence of orthorhombic Fe(C2O4), 2H2O and
Fe3O4, as the peaks in XRD are in good agreement with
reported XRD pattern of Fe(C2O4), 2H2O and Fe3O4 (Fig. 1).
Some of the XRD peaks are well matched with the standard
XRD pattern of CuO material, which confirms the presence of
CuO in the material. So, we thought that the reactive Fe(0) in
the [Fe(ox)-Fe(0)] material first reduced the Cu(II) to Cu(0),
which is further oxidized into CuO during the course of the
reaction. So, Fe3O4 and CuO has been capped by orthorhombic
Fig. 2 Comparative FT-IR spectrum of Fe(ox)Fe-CuOx with oxalic acid, Fe(ox)-
Fe(0) and Fe(C2O4).2H2O.
The FTIR spectra of synthesized Fe(ox)-Fe(0) nanomaterial
well matched with Fe(C2O4).2H2O, which suggest the presence
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 3 of 8
Journal Name
New Journal of Chemistry
View Article Online
ARTICLE
DOI: 10.1039/C4NJ01966K
of iron oxalate in the [Fe(ox)-Fe(0)] material. However, the material is more porous compared to [Fe(ox)Fe(0)] material as
FTIR spectra of [Fe(ox)Fe-CuOx] nanomaterial showed peaks is also evident from SEM and TEM analysis.
at 502, 819, 1319, 1360, and 1691 cm-1. The peak at 1319 and
819 cm-1 occur due to C-O and C-C stretching vibration of
binded oxalate. However, the carbonyl stretching frequency for
metal carboxylate slightly shifted to higher region may be due
to the relatively weak coordination of oxalate with Fe(II) in
[Fe(ox)Fe-CuOx] compared to its parent material. Further, the
shape and morphology of the [Fe(ox)Fe-CuOx] were
investigated with a scanning electron microscope (SEM). The
images of [Fe(ox)Fe-CuOx] material indicate the porous flower
Fig. 4 EDS spectra of the Fe(ox)-Fe-Cu(Ox). The inset shows the position on which
the EDS studies were done.
like morphology of the material (Fig. 3). Energy-dispersive
analysis of X-rays (EDS) spectra of [Fe(ox)Fe-CuOx]
synthesized material. For this, [Fe(ox)Fe-CuOx] promoted
nanomaterial in a single flower shows that the atomic
percentages of Fe and Cu were 43.93% and 12.07%
Now, we were interested to check the catalytic activity of the
oxidative transformation reaction has been done and elaborated
in the next section.
respectively. Whereas, EDS spectrum of a large area consisting
of more than one flower suggest the atomic percentages of Fe
and Cu were 46.96% and 10.96%, respectively (Fig. 4). The
ICP-OES measurements of all the samples were done after
digesting the sample with HCl. The ICP-OES analysis of
[Fe(ox)Fe-CuOx] nanomaterial shows the atomic percentages
of Fe and Cu were 41% and 9%, respectively (Table 4). On the
other hand, oxalate content in the [Fe(ox)Fe-CuOx]
nanomaterial was determined from the KMnO4 titration of
unreacted oxalic acid amount during the synthesis of [Fe(ox)Fe-
CuOx], which suggest the ratio of iron and oxalate is
approximately 3:1.24 So, from above all the analysis the
approximate formula of [Fe(ox)Fe-CuOx] nanomaterial is
Fig. 5 TEM image of Fe(ox)Fe-CuOx
[(C2O4)1.6Fe4.6CuO4].
Fig. 6 Nitrogen adsorption–desorption isotherm of Fe(ox)-Fe(0)
Fig. 3 HR-SEM image of Fe(ox)Fe-CuOx
TEM micrographs of [Fe(ox)Fe-CuOx] nanomaterial showed
ultrafine particles with layered structure (Fig. 5). The N2
adsorption–desorption isotherm and the pore size distribution of
[Fe(ox)Fe(0)] and [Fe(ox)Fe-CuOx] material are shown in
Figure 6 and 7 and confirm the presence of porous structures in
both the material. Upon, the incorporation of CuO in the
[Fe(ox)Fe(0)], surface area and the average pore volume is
increased, which suggest synthesized [Fe(ox)Fe-CuOx]
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 3

New Journal of Chemistry
Page 4 of 8
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C4NJ01966K
reaction condition, the possible Fenton-like reaction in presence
of Iron salt and H2O2 may leads to acid from aldehyde.
Interestingly, we have observed 4-methyl benzoic acid in all the
iron salt or nanomaterial promoted reaction of 4-methyl
benzaldehyde, which further verifies the possibility of Fenton-
like reaction in presence of iron salt and H2O2. Under optimized
reaction condition, both CuO and Cu2O promote the
esterification reaction to its corresponding ester in good yield.
However, in both the cases a little amount of acid was
formed.25 When compared to other nano materials, we found
superiority of [Fe(ox)Fe-CuOx] material towards the oxidative
esterification of of 4-methyl benzaldehyde in methanol at 70 °C
in air (Table 2). So, incorporation of copper in the material
[Fe(ox)Fe-CuOx] increase the surface area as well catalytic
activity of the material as is evident from both the catalyst
screening and BET isotherm.
Fig. 7 Nitrogen adsorption–desorption isotherm of Fe(ox)-Fe-CuOx.
Table
1 Effect of solvent on Fe(Ox)Fe-CuOx promoted oxidative
Fe(ox)Fe-CuOx Promoted oxidative transformation of aldehyde
to methylesters and acids
transformation of aldehyde
Initially,
the
[Fe(ox)Fe-CuOx]
promoted
oxidative
transformation reaction of 4-methyl benzaldehyde was chosen
as a model reaction for the study. Among all the alcoholic
solvents tested, only methanol was effective reaction medium
for the formation of methyl ester (Table 1). However in ethanol,
#
Solvent
Mol( %)a
Time (h)
Acid (1a)
Yield(%)
Ester (2a)
Yield(%)
94
92
91
1
2
3
5
6
7
8
7
MeOH
MeOH
MeOH
MeCN
EtOH
iPrOH
tBuOH
DCE
THF
DMF
DMSO
Water
Toluene
5
2
1
1
1
1
1
1
1
1
1
1
1
10
12
12
12
12
12
12
12
14
16
18
14
14
t
iPrOH, and BuOH we failed to detect any ester or acid, which
92
0
0
indicate that more bulky solvent hindered the esterification
reaction. When we changed the solvent from methanol to
acetonitrile, only acid was detected as the major product. Other
organic solvent like dicholro ethane, tetrahydrofuran (THF),
n,n-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO),
and toluene are also effective for the oxidative acidification of
4-methyl benzaldehyde. But, slightly lower yields were
achieved in DMF solvent. [Fe(ox)Fe-CuOx] promoted both the
oxidative acidification and esterification reaction of 4-methyl
benzaldehyde was tried at room temperature with very low
yield of product. The [Fe(ox)Fe-CuOx] esterification reaction
was tried with varying catalyst loading. No significant
difference was observed when slightly increasing the catalyst
loading from 1 to 5 mol%. Low yield of esterification product
was observed by using only H2O2, which indicate the necessity
of metal ion in the esterification reaction. From screening of
solvent, temperature, and catalyst loading the following
condition has been optimized: catalyst in combination with 6
equivalent of H2O2; methanol as a solvent; temperature 70 ˚C
(Table 1). The esterification reaction was tried with iron and
copper salt at the optimized reaction condition. But, moderate
to poor conversion was achieved with copper and iron salt.
Interestingly, Fe(ox)-Fe3O4 or [Fe(ox)-Fe(0)] nanomaterial in
combination with H2O2 are poorly active for the esterification
of 4-methyl benzaldehyde. We have also tried the esterification
reaction with oxalic acid and iron oxalate [Fe(ox)], but in both
the cases low yield of ester was achieved. Whereas, under
optimized reaction condition, Fe3O4 produced only acid in 89%,
which indicate over oxidation or Fenton-like reaction in
presence of Fe3O4 leads to only acid product. Under optimized
0
0
0
0
48
47
10
38
16
56
8
10
11
12
13
Table
2 Effect of catalyst on Fe(Ox)Fe-CuOx promoted oxidative
transformation of aldehyde to ester
#
1
2
3
4
5
6
7
8
9
10
11
12
13
Catalyst
Fe(Ox)Fe-CuOx
Fe3O4
Fe(Ox)-Fe3O4
Fe(Ox)-Fe(0)
FeCl3.6H2O
Fe(Ox)
CuCl2
CuCl
FeCl3 (anhydrous)
-
Mol( %) Time (h) Ester(%)
Acid (%)
1
5
5
5
5
5
5
5
5
12
12
12
12
12
12
12
12
12
12
12
12
12
91
89
16
18
48
8
32
12
36
14
22
11
0
47
0
0
15
25
a
-
9
CuO
Cu2O
Oxalic acid
5
5
5
59
52
10
Reaction condition: 1 mmol aldehyde, 0.5 ml of 30% H2O2, Catalyst (1-5
mol%) was taken in 3 ml methanol and refluxed at 70°C.aReaction was done
with only 0.5 ml of 30% H2O2.
The catalytic acitivity of [Fe(ox)Fe-CuOx] nanomaterial was
compared with other known catalyst. In terms of catalytic
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 5 of 8
Journal Name
New Journal of Chemistry
View Article Online
ARTICLE
DOI: 10.1039/C4NJ01966K
conversion and mol%, superiority of the nanomaterial change was in iron and copper content was observed after 2nd
[Fe(ox)Fe-CuOx] was achieved with other known catalytic cycle. However slight drop down in both the iron and copper
system (Table 3).
content was observed in the [Fe(ox)Fe-CuOx] nanomaterial
after 5th cycle, which suggested suggests slight leaching of both
the metal during oxidation of aldehyde (Table 4).
Table 3 Comparative activity of Fe(Ox)Fe-CuOx catalyst with known
catalyst.
Table 4. Iron and copper content in the sample from ICP measurement.
Material
Fe (wt%)a
Cu (wt%)a
Fe(ox)Fe-CuOx
Fe(ox)Fe-CuOx (after 2 catalytic cycle)
Fe(ox)Fe-CuOx (after 5 catalytic cycle)
41
38
33
9
8
5
#
Catalyst
Mol(
%)
1
Time
(h)
12
Temperature
(°C)
70
Ester
(%)
91
Acid
(%)
1
Fe(ox)Fe-
CuOx
CaCl2
MgCl2
V2O5
aboth the Fe and Cu content was determined from the ICP-OES analysis after
digesting the sample with HCl.
2
3
4
5
10
10
5a
24
24
2
70
70
RT
RT
42
40
94
72
10
6
The substrate scope of the [Fe(ox)Fe-CuOx] promoted
esterification reaction has been tested with various aldehydes
(Table 3). Under optimized reaction condition, 4-methyl
benzaldehyde, benzaldehyde, 4-methoxy benzaldehyde
produced corresponding methyl ester in high yield. The
reaction of 2-bromo benzaldehyde at the optimized condition
gave only 2-bromo benzoic acid as a product in 29% yield. The
sterically bulky bromo group at ortho- position hindered the
ester formation in case of 2-bromo benzaldehyde. Aromatic
aldehydes substituted with electron-withdrawing groups at the
ZnBr2
10
24
3
Reaction condition: 1 mmol aldehyde, 0.5 ml of 30% H2O2, and catalyst (1-
10 mol%) was taken in 3 ml methanol and refluxed at 70°C. The reaction
was done at room temperature after addition of all the reagents under ice
cooled condition.
a
For practical applications of such heterogeneous nanocatalyst,
lifetime of the catalyst and its reusability are very important
factors. For this, a set of experiments was done for the
esterification of 4-methyl benzaldehyde using
5 mol%
[Fe(ox)Fe-CuOx] nanomaterial in combination with H2O2 in
MeOH at 70 °C. After the completion of the first reaction, the
catalyst was recovered by centrifugation, washed with methanol
for 3-4 times and dried in vacuum and used for next set of
reaction with fresh reactants under the optimized reaction
conditions. Upto 5th catalytic cycle, there is negligible drop
down in the yield of the esterification reaction of 4-methyl
benzaldehyde. However, at the 6th and 7th cycle, slight drop
down in the yield was observed. In terms of TOF, [Fe(ox)Fe-
CuOx] catalyst could be reused at least 5 times without any
change in its activity (Fig. 8).
p
-position
such
as
p
p
-chlorobenzaldehyde,
p-
bromobenzaldehyde, and
-nitrobenzaldehyde react slowly to
form the corresponding methyl esters in good yields. On the
other hand, o-substituted aldehyde such as 2-nitro or 2-fluoro
benzaldehyde reacts very slowly to form the corresponding
methyl 2-nitrobenzoate and methyl 2-fluoro benzoate only in
12% and 12% conversion under optimized reaction condition.
However, at optimized reaction condition 2-choloro
benzaldehyde leads to methyl 2-chlorobenzoate in 74% yield.
So, hydrogen bonding ability of both nitro and fluoro group
with OH may hindered the ester formation and leads to its
corresponding acid or acetal in case of 2-nitro or 2-fluoro
benzaldehyde. The esterification reaction with other
heterocyclic araldehyde like thiophene-2-carbaldehyde went
smoothly to its corresponding ester acid in 53% and 39% yield
respectively. However the esterification reaction does not
proceeds with unsaturated aldehyde like cinamaldehyde even
after longer reaction time, which may be attributed to its low
electrophilicity, hindered the essential hemiacetal formation in
the first step.26 On the other hand, esterification reaction of
terephaldehyde leads to its corresponding dimethyl isphthalate
in 90% and 3-formyl benzoic acid in 8% yield. The
esterification reaction of isophthaldehyde also leads to its
corresponding dimethyl terephthalate in 52% and 4-formyl
benzoic acid in 20% yield. During the [Fe(ox)Fe-CuOx]
promoted esterification reaction, in some cases a minor amount
of acid has been observed due to the over oxidation of
aldehyde, which further does not proceeds to its corresponding
ester.
Fig. 8 catalytic cycle vs turn over frequency (TOF) and yield plot of Fe(ox)Fe-CuOx
catalyzed esterification reaction of 4-methyl benzaldehyde.
The ICP-OES analysis of the used [Fe(ox)Fe-CuOx]
nanomaterial after 2nd and 5th cycle was done. No appreciable
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 5

New Journal of Chemistry
Page 6 of 8
ARTICLE
VJieowuArrtnicalelONnlainme e
DOI: 10.1039/C4NJ01966K
Table
5 Substrate scope for Fe(ox)Fe-Cu(Ox) catalyzed oxidative
transformation of aldehyde to ester
#
Aldehyde
Producta
Time Ester Acid
(h)
12
10
18
20
12
20
12
16
12
14
15
18
14
15
17
20
(%)
91
78
99
81
0
12
68
99
74
48
68
12
53
90
52
0
(%)
1
2
3
4
5
6
7
8
9
4-methylbenzaldehyde
benzaldehyde
1a
1b
1c
1d
1e
1f
1g
1h
1i
12
4-bromobenzaldehyde
4-nitrobenzaldehyde
2-bromobenzaldehyde
2-nitrobenzaldehyde
4-methoxybenzaldehyde
4-chlorobenzaldehyde
2-chlorobenzaldehyde
18
29
41
29
Scheme 3. Mechanism of Fe(ox)Fe-CuOx catalyzed esterification reaction
The [Fe(ox)Fe-CuOx] promoted oxidative transformation of
aldehyde was further extended to acid by changing the solvent
from methanol to acetonitrile. From solvent, temperature, and
catalyst mol% screening the following condition has been
optimized: 1 mol% catalyst in combination with 6 equivalent of
H2O2; acetonitrile as a solvent; temperature 90 ˚C. Under the
16
10 4-(trifluoromethyl)benzaldehyde
11 3-nitrobenzaldehyde
12 2-fluorobenzaldehyde
13 Thiophene-2-carabaldehyde
14 Isophthaldehyde
15 Terephthaldehyde
16 Cinamaldehyde
1j
1k
1l
31
86
39
8
20
0
1l
1mb
1nc
1o
optimized reaction condition,
p-substituted aldehyde like 4-
methoxy bezaldehyde, 4-methyl benzaldehyde, 4-chloro
benzaldehyde, 4-bromo benzaldehyde produced their
corresponding acid in good to moderate yield (Table 4). The o-
substituted aldehyde like 2-chloro benzaldehyde or 2-fluoro
benzaldehyde leads to its corresponding acid in 72% and 88%
yield. Whereas, poor yield was achieved in case of 2-nitro
benzaldehyde. The [Fe(ox)Fe-CuOx] promoted acidification
reaction of isophtahldehyde leads to its corresponding 3-formyl
benzoic acid in 25% yield.
aReaction condition: 1 mmol aldehyde, 0.5 ml of 30% H2O2, 1 mol%
Fe(ox)Fe-Cu(Ox) catalyst (5 mg) was taken in 3 ml methanol and refluxed at
b
70°C. Dimethyl isphthalate in 90% and 3-formyl benzoic acid in 8% yield
c
was observed; Dimethyl terephthalate in 52% and 4-formyl benzoic acid in
20% yield was achieved
Furthermore, under optimized reaction condition benzoic acid
failed to give any desired methyl ester. Whereas, in
esterification of 2-nitrobenzaldehyde, we have observed acetal
in GC-MS analysis, which further suggest that esterification
reaction proceeds via hemiacetal formation mechanism not via
acid (Scheme 2).27
Table
6 Substrate scope for Fe(ox)Fe-Cu(Ox) catalyzed oxidative
transformation of aldehyde to acid
Fe(ox)Fe-Cu(Ox)
O
O
(1 mol%)
H2O2, MeOH
OCH3
OH
0%
#
R
Product
Time
(h)
10
10
14
14
16
14
14
15
14
14
16
Yielda
(%)
68
99
91
32
47
91
95
O
O
H
O
H3CO
O
Fe(ox)Fe-Cu(Ox)
(1 mol%)
H3C
+
CH3
NO2
1
2
3
4
5
6
7
8
9
4-methylbenzaldehyde
benzaldehyde
2a
2b
2c
2d
2e
2f
2g
2h
2i
NO2
NO2
H2O2, MeOH
4-nitrobenzaldehyde
2-nitrobenzaldehyde
4-methoxybenzaldehyde
4-chlorobenzaldehyde
3-nitrobenzaldehyde
2-chlorobenzaldehyde
2-fluorobenzaldehyde
42%
12%
Scheme 2. Fe(ox)Fe-Cu(Ox) promoted reaction of benzoic acid and 2-nitro
benzaldehyde.
72
88
The proposed three step mechanism of the esterification 10 4-(trifluoromethyl)benzaldehyde
43
2j
2k
11
Isophthaldehyde
25b
reaction is as follows; firstly, aldehyde reacts with alcohol in
presence of [Fe(ox)Fe-CuOx] nanomaterial and form
hemiacetal, which further reacts with peroxide complex of
Cu(II) to form ester via the elimination of conjugate base of the
peracid.
aReaction condition: 1 mmol aldehyde, 0.5 ml of 30% H2O2, 1 mol%
Fe(ox)Fe-Cu(Ox) catalyst (5 mg) was taken in 3 ml acetonitrile and refluxed
at 90°C. b3-formyl benzoic acid in 25% yield was observed.
Application of Fe(ox)-Fe-Cu promoted oxidative transformation
in large scale
Now, we were interested to check the activity of [Fe(ox)Fe-
CuOx] nanomaterial for the large scale synthesis of ester and
acid. For that we have stepwise scaled up the esterification
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 7 of 8
Journal Name
New Journal of Chemistry
View Article Online
ARTICLE
DOI: 10.1039/C4NJ01966K
reaction from 1 mmol to 10 mmol to 300 mmol with varying peroxide (H2O2) solution, and required amount of catalyst,
amount of catalyst loading (Table 5). In 10 mmol scale, 10 mg [Fe(ox)Fe-CuOx] was added to it and stirred for 5 min at room
catalyst (0.2 mol%) was sufficient for the conversion of temperature. The reaction mixture was refluxed at a controlled
benzaldehyde to benzoic acid in 85% yield. Further scale up temperature bath for the required time. The progress of the
from 10 mmol to 300 mmol with 100 mg of catalyst for reaction was monitored by TLC at certain intervals. After the
benzaldehyde to benzoic acid conversion ended up with 60% completion, the mixture was centrifuged and the supernatant
yield. We have also tested the esterification reaction of 4- was collected. Finally, the conversion of the aldehyde to the
methyl benzaldehyde with 100 mg of catalyst in 300 mmol respective ester or acid was monitored by GCMS analysis.
scale, which ended up with mixture of methyl 4-methyl
Instruments
benzoate and 4-methyl benzoic acid in 59% and 25 % yield
respectively. On the other hand esterification of benzladehyde All the samples for FTIR study were properly washed with
in 300 mmol scale leads to mixture of methyl benzoate and distilled water at least five times, and then dried under vacuum.
benzoic acid in 39% and 30 % yield respectively.
Finally, samples for the FTIR spectra were recorded using
IMPACT 410 Thermo-Nicolet instrument from thin
a
Table
7 Substrate scope for Fe(ox)Fe-Cu(Ox) catalyzed oxidative
transparent KBr pellet. The XRD patterns of the sample was
recorded on a Philips PW-1710 X-ray diffractrometer (40 kV,
20 mA) using Cu Ka radiation (k = 1.5418 Å) in the 2Ɵ range
of 10–90° at a scanning rate of 0.5 ° min-1. The XRD data were
analyzed using JCPDS software. Surface morphology of all the
samples were recorded by using a scanning electron microscope
(JEOL JSM5800) with an accelerated voltage 5-20 kV. TEM
images were acquired using JEOL JEM-2010 microscopes with
an operating voltage of 200 kV.
transformation of aldehyde to acid in large scale.
CO2Me
CO2H
Fe(ox)-Fe-Cu
(mol%)
CHO
H2O2,
R
Solvent, Reflux
R
R
1
2
#
R
solvent
Time
(h)
20
24
24
Scale
(mmol)
10a
Catalyst
(mg)
10
100
100
100
Ester
(%)
Acid
(%)
85
60
25
1
2
3
4
H
H
Me
H
MeCN
MeCN
MeOH
MeOH
300
300b
300
59
39
Conclussion
24
30
aReaction condition: 10 mmol aldehyde, 3 ml of 30% H2O2, 10 mg Fe(ox)Fe-
Cu(Ox) catalyst was taken in 25 ml of acetonitrile and refluxed at 90°C for
required time. bReaction condition: 300 mmol aldehyde, 10 ml of 30% H2O2,
100 mg Fe(ox)Fe-Cu(Ox) catalyst was taken in 150 ml of
acetonitrile/methanol and refluxed for required time.
In summary, iron(oxalate) capped Fe-Cu bimetallic oxide
[Fe(ox)Fe-CuOx] nanoparticle was synthesized using a facile
approach. The porous [Fe(ox)Fe-CuOx] material with good
surface area and surface volume is found to be useful as a
catalyst in presence of H2O2 for the oxidative transformation of
aldehyde to its corresponding ester and acid in moderate to
good yield. In terms of environmental compatibility,
reusability, operational simplicity, [Fe(ox)Fe-CuOx] material
were very simple, effective and economical. The porous nature
of the Fe-Cu bimetallic is also expected to be useful in many
other applications.
Experimental Section
Synthesis of [Fe(ox)Fe-CuOx] Nanomaterial:
In
a
typical procedure, 284 mg of Mohr’s salt,
(NH4)2SO4.FeSO4 was taken in 150 ml of distilled water in a
500 ml conical flask and 126 mg of oxalic acid, H2C2O4 was
added to this and stirred vigorously. In another 500 ml conical
flask, a solution of 1.2 g of sodium borohydride, NaBH4 was
prepared in 100 ml distilled water and was added slowly in an
earlier prepared solution with vigorous stirring. During the
addition, the colour of the solution slowly changed into yellow.
After few minutes, when black Fe nano particle began to
appear, the NaBH4 addition was stopped. To this, earlier
prepared 100 ml 0.01(M) CuSO4 solution was slowly added to
it at 60 °C for 0.5 h. After 5-6 h of addition, the colour of the
solution slowly turned to yellowish brown. After 16 h, the
reaction mixture was centrifuged, washed 3-4 times with water,
collected and dried under vacuum and kept for further
application.
Acknowledgements
Financial support of this work by DST-New Delhi (to SP for
INSPIRE research grant) is gratefully acknowledged. We thank
both the reviewers for their useful suggestion.
Notes and references
Department of chemical sciences, Tezpur University,
Napaam, Asaam-784028, India
Email: spratihar@tezu.ernet.in, spratihar29@gmail.com
Experimental details and GC-MS spectra of all the compounds
are available in Electronic Supporting Information (ESI)]. See
DOI: 10.1039/b000000x
References
General procedure for [Fe(ox)Fe-CuOx] catalyzed oxidative
transformation of aldehyde to its corresponding ester and acid:
For the oxidative esterification of an aldehyde, 1 mmol of the
aldehyde was dissolved in 3 ml methanol or acetonitrile in a 10
ml round bottom flask. After that, 0.5 ml 30% hydrogen
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 7

New Journal of Chemistry
Page 8 of 8
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C4NJ01966K
15
1
(a) V. Polshettiwar, B. Baruwati and R. S. Varma, Green
(a) S. Kiyooka, M. Ueno and E. Ishii, Tetrahedron Lett.
Chem., 2009, 11,127. (b) A. Hu, G. T. Yee and W. Lin, J. Am. 2005, 46, 4639. (b) S.-I. Kiyooka, Y. Wada, M. Ueno, T. Yokoyama
Chem. Soc., 2005, 127, 12486.
and R. Yokoyama, Tetrahedron 2007, 63, 12695.
16
2
(a) S. Wu, Q. He, C. Zhou, X. Qi, X. Huang, Z. Yin, Y.
X.-F. Wu and C. Darcel, Eur. J. Org. Chem. 2009, 1144.
17
Yang and H. Zhang Nanoscale, 2012, 4, 2478. (b) S. Sun and H.
K. Suzuki, T. Yamaguchi, K. Matsushita, C. Iitsuka, J.
Zeng, J. Am. Chem. Soc., 2002, 124, 8204. (c) A. H. Latham and M. Miura, T. Akaogi and H. Ishida, ACS Catal. 2013, 3, 1845.
18
19
E. Williams, Acc. Chem. Res., 2008, 41, 411. (d) S. Laurent, D.
Forge, M. Port, A. Roch, C. Robic, L. V. Elst and R. N. Muller,
Chem. Rev., 2008, 108, 2064.
X. -F. Wu, Tetrahedron Lett. 2012, 53, 3397.
J. -B Feng, J. L. Gong, Q. Li and X. –F. Wu, Tetrahedron
Let. 2014, 55, 1657.
3
20
(a) M. V. Kovalenko, M. I. Bodnarchuk, R. T. Lechner, G.
(a) P. T. Anastas, J. C. Warner, Green Chemistry: Theory
Hesser, F. Schaffler and W. Heiss, J. Am. Chem. Soc., 2007, 129, and Practice, Oxford University, Oxford, 1998. (b) K. Alfonso, J.
6352. (b) X. W. Teng and H. Yang, J. Mater. Chem., 2004, 14, 774. Colberg, P. J. Dunn, T. Fevig, S. Jenings, T. A. Johnson, H. P. Klein,
(c) J. E. Macdonald, C. J. Brooks and J. G. C. Veinot, C. Knight, M. A. Nagy, D. A. Perry and M. Stefaniak, Green Chem.,
Chem.Commun., 2008, 3777. (d) M. Hermanek, R. Zboril, I. Medrik, 2008, 10, 31. (c) C.-J. Li and P. T. Anastas, Chem. Soc. Rev., 2012,
J. Pechousek, and C. Gregor, J. Am. Chem. Soc. 128, 1675, 2006. (e) 41, 1413. (d) D. Guin, B. Baruwati and S. V.Manorama, Org. Lett.,
E. O. Kajander, N. Ciftcioglu Proc. Natl. Acad. Sci. 1998, 95, 8274. 2007, 9, 1419. (e) B. Kaboudin, R. Mostafalua and T. Yokomatsu,
(f) K. Woo, J. Hong, S. Choi, H.-W. Lee, J. -P. Ahn, C. S. Kim and Green Chem., 2013, 15, 2266. (c) J. H. Clark, Green Chem., 1999, 1,
S. W. Lee Chem. Mater, 2004, 16, 2814. (g) L. M. Bronstein, X. 1.
21
Huang, J. Retrum, A. Schmucker, M. Pink, B. D. Stein and B.
(a) Richardson, H. W. Handbook of Copper Compounds
Dragnea, Chem. Mater., 2007, 19, 3624.
and Applications; Marcel Dekker: New York, 1997. (b) G. Cahiez
4
R. Pegu, K. J. Majumdar, D. J. Talukdar and S. Pratihar, and A. Moyeux, Chem. Rev. 2010, 110, 1435. (c) J. E. Bäckvall,
RSC Adv., 2014, 4, 33446.
Modern Oxidation Methods, Wiley-VCH, Weinheim, 2004. (d) R.
5
J. Otera, Esterification: Methods, Reactions, and A. Sheldon and L. L. Simandi, Dioxygen Activation and
Applications; Wiley-VCH: Weinheim, 2003
Homogeneous Catalytic Oxidation, Elsevier: Amsterdam, 1991. (e)
6
R. C. Larock, Comprehensive Organic Transformations: A S. Stahl, Science 2005, 309, 1824. (f) C. E. Song and S. G. Lee,
Guide to Functional Group Preparation, VCH, New York, 1989, pp. Chem. Rev., 2002, 102, 3495.
22
840–841 and references cited
R. V. Jagadeesh, H.Junge, M..-M. Pohl, J. Radnik, A.
Therein.
Brückner and Matthias Beller, J. Am. Chem. Soc. 2013, 135, 10776
7
23
(a) R. Gopinah and B. K. Patel, Org. Lett., 2000, 2, 577.
K. uzuki, T. Yamaguchi, K. Matsushita, C. Iitsuka, J.
(b) R. Gopinah, B. Barkakaty, B. Talukdar and B. K. Patel, J. Org. Miura, T. Akaogi and H. Ishida, ACS Catal. 2013, 3, 1845.
24
Chem. 2003, 68, 2944. (c)
Please see ESI for the details of KMnO4 titration.
We failed to record C, H, and N data of [Fe(ox)Fe-CuOx]
nanomaterial.
8
J. H. Espenson, Z. Zhu and T. H. Zauche, J. Org. Chem.
1999, 64, 1191.
9
25
S. C. Thomason and D. G. Kubler, J. Chem. Educ. 1968,
Both the CuO and Cu2O were synthesized from the
45, 546
reported procedure; (a) J. Pal, M. Ganguly, C. Mondal, A.
Roy, Y. Negishi and T. Pal, J. Phys. Chem. C 2013, 117,
24640. (b) M. Basu, A. K. Sinha, M. Pradhan, S. Sarkar, Y.
Negishi and T. Pal, J. Phys. Chem. C 2011, 115, 20953.
10
(a) R. Lerebours and C. J. Wolf, J. Am. Chem. Soc. 2006,
128, 13052. (b) C. Liu, J. Wang, L. Meng, Y. Deng, Y. Y. Li and A.
Lei, Angew. Chem. Int. Ed. 2011, 50, 5144. (c) C. Liu, S. Tang, L.
Zheng, D. Liu, H. H. Zhang and A. Lei, Angew. Chem. Int. Ed. 2012,
51, 5662.
26
S. Pratihar, Org. Biomol. Chem., 2014, 12, 5781.
Please see page 14 in ESI.
11
27
(a) S.-I. Murahashi, T. Naota, K. Ito, Y. Maeda and
H.Taki, J. Org. Chem. 1987, 52, 4319. (b) S. Raiendram, D. C.
Trivedi, Synthesis 1995, 153. (c) J. Zhao, C. Mueck-Lichtenfeld and
A. Studer, Adv. Synth. Catal. 2013, 355, 1098.
12
R. Grigg, T. R. B. Mitchell and S. Sutthivaiyakit,
Tetrahedron 1981, 37, 4313.
13
(a) W.-J. Yoo and C.-J. Li, Tetrahedron Lett. 2007, 48,
1033. (b) Y. Zhu and Y. Wei, RSC Adv. 2013, 3, 13668.
14
S. P. Chavan, S. W. Dantale, C. A. Govande, M. S.
Venkatraman and C.Praveen, Synlett 2002, 267.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012