Manganese incorporated on glucose as an efficient catalyst for the synthesis of adipic acid using molecular O2 in aqueous medium

Article abstract of DOI:10.1016/j.apcata.2017.08.008

A new manganese incorporated on glucose catalyst Mn@CC-SO₃H-NH₂ was synthesized and well characterized using FT-IR, PXRD, EDAX, SEM, TEM, [13] C cross-polarization NMR and BET analysis. The catalyst thus synthesized was studied for its utility in the synthesis of industrially important chemical adipic acid starting from readily available cyclohexanone using molecular O₂ as a source. Adipic acid was obtained in maximum yield of 82% using Mn@CC-SO₃H-NH₂ catalyst in water as a solvent. The catalyst was easily recovered and reused for minimum five runs without any significant loss in the yield of products. Using molecular O₂ as an oxidant and water as a solvent, the reaction is very important from green chemistry perspectives and can also be industrially feasible.

Full text of DOI:10.1016/j.apcata.2017.08.008

Accepted Manuscript
Title: Manganese incorporated on glucose as an efficient
catalyst for the synthesis of adipic acid using molecular O2 in
aqueous medium
Authors: Sagar D. Nale, Pramod V. Rathod, Vrushali H.
Jadhav
PII:
S0926-860X(17)30378-2
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2017.08.008
APCATA 16363
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Applied Catalysis A: General
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Accepted date:
27-4-2017
17-7-2017
5-8-2017
Please cite this article as: Sagar D.Nale, Pramod V.Rathod, Vrushali H.Jadhav,
Manganese incorporated on glucose as an efficient catalyst for the synthesis
of adipic acid using molecular O2 in aqueous medium, Applied Catalysis A,
Generalhttp://dx.doi.org/10.1016/j.apcata.2017.08.008
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Manganese incorporated on glucose as an efficient catalyst for the synthesis
of adipic acid using molecular O2 in aqueous medium
Sagar D. Nale, Pramod V. Rathod and Vrushali H. Jadhav*
Division of Organic Chemistry, CSIR-National Chemical Laboratory, Dr. Homi-Bhabha Road, Pashan, Pune-
411008, India. Email: vh.jadhav@ncl.res.in
Graphical abstract
Highlights
 A new manganese incorporated on glucose catalyst Mn@CC-SO3H-NH2was
synthesized.
 Selective synthesis of adipic acid starting from cyclohexanone using molecular O2 as
a sole oxidant under aqueous condition gave 82% yield with 100% selectivity.
 The Mn@CC-SO3H-NH2 catalyst was found to be highly efficient, highly selective,
easily separable, reusable and environment friendly.
ABSTRACT
A new manganese incorporated on glucose catalyst Mn@CC-SO3H-NH2 was synthesized and
well characterized using FT-IR, PXRD, EDAX, SEM, TEM, 13C cross-polarization NMR and
BET analysis. The catalyst thus synthesized was studied for its utility in the synthesis of
industrially important chemical adipic acid starting from readily available cyclohexanone
using molecular O2 as a source. Adipic acid was obtained in maximum yield of 82% using
Mn@CC-SO3H-NH2 catalyst in water as a solvent. The catalyst was easily recovered and
reused for minimum five runs without any significant loss in the yield of products. Using
molecular O2 as an oxidant and water as a solvent, the reaction is very important from green
chemistry perspectives and can also be industrially feasible.
1

Keywords: Manganese, catalyst, adipic acid, water, recyclable.
1. Introduction
Adipic acid is one of the most important industrial chemical required all over the world.1 The
worldwide industrial production of adipic acid is 2.2 million metric tons per year. It is
considered to be the building block for number of different products that are manufactured in
chemical, pharmaceutical and food industries. It is the main precursor to Nylon-6,6 and also
used for the production of polyester, polyresin, polyvinyl chloride.2 Adipic acid is also used
in cosmetics, fertilizers, paper and wax industry. At present adipic acid is produced
industrially by catalytic oxidation of a mixture of cyclohexanol and cyclohexanone using
nitric acid.3 The major drawback for this process is the emission of harmful nitrous oxide
N2O that is commonly thought to cause global warming and ozone depletion as well as acid
rain and smog.4 Adipic acid producers have to face challenge to decompose this N2O safely
without causing any impact on the pollution.
Efforts have been made to develop process for synthesis of adipic acid that can
overcome conventional process. Synthesis starting from cyclohexanone, cyclohexanol,
cyclohexene and cyclohexane have been explored. Bohstrom et al. carried out synthesis of
cyclohexene to adipic acid using tungsten oxide as a catalyst and H2O2 as an oxidant.5
Chavan et al. used Co/Mn catalyst in acetic acid to get 86% selectivity of adipic acid from
cyclohexanone.6 Sato et al. obtained 78 % yield of adipic acid from cyclohexanol using
Na2WO4 catalyst & 30% H2O2.7 Lee et al. used titanium framework substituted
aluminophosphate (TAPO-5) as a catalyst for oxidation of cyclohexene to adipic acid using
2

H2O2 as an oxidant.8 Several other tungstate based catalyst have been reported as well e.g.
H3PW12O40,9 [WO(O2)2.2QOH],10 [BMIm]2WO4 supported on silica sulphamic acid,11
oxotungsten containing SBA-15,12 surfactant peroxotungstates.13 Although reports are
available in literature for synthesis of adipic acid,14-22 the cost of oxidants like H2O2, t-
butylhydroperoxide, drastic reaction conditions, using organic solvents, low yields and
selectivity of adipic acid restricts its use on industrial scale. Thus there still remains a
challenge for researchers to develop an efficient and stable catalyst to develop an industrially
scalable process for the production of adipic acid.
2. Experimental
General Methods. All commercially available reagents were used without further
purification unless otherwise stated. All reactions were carried out using flame-dried
glassware with magnetic stirring. The Mn@CC-SO3H-NH2 catalyst thus obtained was
characterized by known techniques such as FT-IR (Spectrum 400), PXRD (Panalytical X'Pert
Pro), Elemental analysis from EDAX (Nova Nano SEM 450), SEM (Quanta™ Scanning
Electron Microscope), TEM (Tecnai 4220 S-Twin), 13C cross-polarization (CP) magic angle
spining NMR (Jeol ECX 400, at a frequency of 100 MHz with a spinning rate of 8 KHz) and
BET surface area (Micrometrices ASAP 2020). 1H and 13C NMR spectra were recorded on a
Bruker spectrometer using TMS as an internal standard. NMR data are reported as follows:
chemical shift, multiplicity (br = broad singlet, s = singlet, d = doublet, t = triplet, q = quartet,
m = multiplet), coupling constant (Hz) and integration.
Typical procedure for Mn@CC-SO3H-NH2 catalyst preparation
Glucose (2 g) and p-toluene sulfonic acid (0.4 g) were taken in a clean and dry round bottom
flask and stirred at 180 ºC for 24 h under nitrogen. After 24 h, a black solid mass was
obtained which was then washed with millipore water and then with ethanol to obtain a black
3

powder. This black powder was then dried in the oven at 100 ºC for 5 h. After drying to this
black powder was added 10 mL of ethanol and 3-amino propyl triethoxy silane (APTES)
(0.24 mL), sonicated for 30 min and further refluxed at 80 ºC for 8 h. The solid was collected
by filtration and washed with water followed by ethanol and dried in the oven at 100 ºC for 5
h. This black powder was denoted as CC-SO3H-NH2. After drying, to this black powder (1 g)
(CC-SO3H-NH2) was added 10 mL ethanol, MnCl2 (2 g) and further refluxed 80 ºC for 12 h.
The solid was collected by filtration and washed with water followed by ethanol and dried in
oven at 100 ºC for 5-6 h. This black powder was denoted as Mn@CC-SO3H-NH2 catalyst.
General Procedure for synthesis of adipic acid from cyclohexanone by using Mn@CC-
SO3H-NH2 catalysts
A 50 mL two neck round bottom flask was equipped with a reflux condenser. The flask was
charged with 0.1 mL of cyclohexanone, 5 mL of water, 20 wt % of Mn@CC-SO3H-NH2
catalyst. Oxygen was passed through the reaction at a flow of 20 mL/min measured using a
flowmeter. The reaction mixture was then refluxed for required time and the reaction was
monitored using TLC. After completion of the reaction, the reaction mixture was cooled to
room temperature. The reaction mixture was filtered to separate the catalyst. The catalyst was
washed 3-4 times with water followed by methanol. The filtrate was concentrated under
vacuum. The residue left after concentration was washed with ethyl acetate 2-3 times to
remove the unreacted cyclohexanone leaving behind colourless white solid of crude adipic
acid.
3. Results and Discussion
Biomass derived carbonaceous catalyst are promising as biomass is renewable, abundant,
cheap and easy for preparation. Carbonaceous catalyst consists of carbon skeleton that is
stable, insoluble in most acidic/basic conditions as well as organic solvents and easily
separable. Due to our continuous interest in the field of carbonaceous solid acid catalyst,23-25
4

we were interested in the synthesis of Mn@CC-SO3H-NH2 catalyst and showed its
remarkable catalytic activity in synthesis of one of the important value added chemical adipic
acid using molecular oxygen as a sole oxidant under mild reaction conditions. For the
preparation of Mn@CC-SO3H-NH2 catalyst, D-glucose was used as a carbon precursor.
Hydrothermal carbonization of glucose and its sulfonation was done in one step by heating
glucose in the presence of p-TSA at 180 ºC. The hydrothermal carbonization promoted the
structure to undergo decomposition, hydrolysis, dehydration, and molecular rearrangement
reaction to produce a polycyclic aromatic structure embedded with active -SO3H, -COOH
and -OH sites.26 In the second step, 3-amino propyl triethoxy silane in ethanol was added to
generate the basic -OSi-CH2CH2CH2NH2 site on the catalyst followed by incorporation of
manganese on the catalyst surface using manganese chloride in ethanol.
The Mn@CC-SO3H-NH2 catalyst thus synthesized was used in the synthesis of adipic acid
from cyclohexanone. The FT-IR spectrum (Figure S1) showed peaks for O=S=O stretching
vibrations in -SO3H groups at 1009 cm-1 and 1031 cm-1 and peak for SO3- stretching at 1154
cm-1, indicating the presence of sulfonic acid groups on the catalyst surface. Peak at 1619 cm-
1 and 1702 cm-1 attributed to the C=C stretching vibrations in aromatic carbons and C=O
stretching vibration of -COOH group. Doublet at 2926 cm-1 attributed for C-H stretching
band and a peak at 1440 cm-1 indicated C-H bending vibration of alkyl groups of amine
terminal silanes. Stretching vibrations for Si-O at 1095 cm-1 and stretching and bending
vibrations of Si-O-C at 1122 cm-1 and 680 cm-1 indicated that silylanization occurred on the
catalyst surface. The peak at 1591 cm-1 due to the N-H bending vibrations confirmed the
presence of amino group on the surface of the catalyst. Bands due to O-H stretching were
observed at 3429 cm-1. The powder X ray diffraction pattern (Figure 2a) of Mn@CC-SO3H-
NH2 showed broad diffraction peak at 2 = 15 to 30º, which can be attributed to amorphous
5

carbon composed of aromatic carbon sheets oriented in considerably random fashion. The
presence of nitrogen, sulphur, silicon, manganese and chloride was confirmed by Energy
dispersive X-ray analysis (EDAX) (Figure S2), thus confirming the acidic -SO3H, basic OSi-
CH2CH2CH2NH2 and coordination of manganese to the NH groups on the surface of the
Mn@CC-SO3H-NH2 catalyst. SEM analysis (Figure 2b) showed a typical planar structure of
Mn@CC-SO3H-NH2 carbonaceous catalyst maintaining two dimensional structures with
heavy crumpling features. TEM analysis (Figure 2c) showed porous nature of Mn@CC-
SO3H-NH2 carbonaceous catalyst. 13C CP/MAS NMR spectrum (Figure 2d) showed peaks at
128, 154 and 174 ppm indicating presence of polycyclic aromatic carbon atoms, phenolic -
OH and -COOH groups respectively. Broad peak was observed at 140 ppm indicating
aromatic carbons attached to -SO3H. Peaks from 12 ppm to 61 ppm showed the presence of
N-propyl carbons. Using the standard Brunauer-Emmett-Teller (BET) equation BET surface
areas and pore size were found to be 1.93 m2/g and 8.96 Aº.
The performance of Mn@CC-SO3H-NH2 catalyst was studied for the synthesis of adipic acid
starting from readily available cyclohexanone. Initially the formation of adipic acid was
carried out in various solvents using Mn@CC-SO3H-NH2 catalyst at given temperatures
using molecular O2 (20 mL/min) (Table 1). Solvents such as water, DMF, DMSO,
acetonitrile, isopropanol and solvent free conditions were studied for adipic acid formation. It
was observed that in DMF, DMSO and isopropanol the starting remained unconsumed (Table
1, entries 2, 3 & 5) whereas in water, acetonitrile and solvent free conditions a yield of about
81%, 82% and 80 % of adipic acid was obtained respectively.
After completion of the reaction, the solvent was removed under reduced pressure. The
unreacted cyclohexanone was removed by adding ethyl acetate to the remaining crude mass.
The ethyl acetate layer was decanted leaving behind white crystalline solid of adipic acid.
The 1H NMR of this white crystalline solid showed selective formation of adipic acid with
6

100% purity and selectivity (Figure S3). The unreacted cyclohexanone that remained during
the reaction was easily recovered and could be reused in further reactions (Figure S4).
Considering the principles of green chemistry, we optimized the reaction conditions
for synthesis of adipic acid in water as a solvent and also under solvent free conditions. The
reaction was studied at different temperature i.e. 100 ºC, 120 ºC and 140 ºC in water (Table 2,
entries 1-3) and under solvent free conditions (Table 2, entries 4-6). It was observed that in
water and solvent free conditions maximum yield was obtained at 120 ºC with less amount of
cyclohexanone remaining unreacted. As the yields of adipic acid were similar both in case of
water and solvent free conditions, we optimized the further reactions for adipic acid synthesis
in water as a solvent, thus the process can be considered as economic, green and environment
friendly.
Catalyst concentration for Mn@CC-SO3H-NH2 was studied for the synthesis of adipic
acid in water (Table 3). It was observed that as the catalyst concentration increased from 5
wt% to 20 wt% the yield of adipic acid was increased from 62% to 82% respectively. Further
increasing the catalyst concentration did not have any effect on yield of adipic acid.
Comparison of Mn@CC-SO3H-NH2 catalyst vs. literature known catalyst for
synthesis of adipic acid have been shown in Table 4. Catalyst such as hybrid iron
phosphonate,14 Titano silicate molecular sieves,17 hollow structured TS-1,17 Mn modified
hollow structured TS-117 did not give 100% selectivity of adipic acid instead by products like
glutaric acid, succinic acid were formed (Table 4, entries 1-4). Hybrid tin phosphate,20
mesoporous triphosphate20 and H2WO421 gave about 74%, 22% and 91% yield of adipic acid
(Table 4, entries 5-7). In this work, Mn@CC-SO3H-NH2 catalyst (Table 4, entry 8) was found
to give 82 % yield of adipic acid with 100% selectivity which indicating good efficiency of
the catalyst over known literature catalyst for selective synthesis of adipic acid.
7

As the catalyst was easily recoverable at the end of the reaction by simple filtration,
the catalyst was studied for its reusability in the synthesis of adipic acid. As shown in Table
5, Mn@CC-SO3H-NH2 catalyst exhibited consistent yield of the adipic acid even after
subsequent five runs and also the unreacted cyclohexanone which was isolated can be
collected and reused. Synthesis of adipic acid from cyclohexanone was also done on higher
scale. When the reaction was performed on a scale of 10 g of cyclohexanone using 20 wt%
Mn@CC-SO3H-NH2 catalyst and O2 (20 mL/min) in water at 120 ºC after 30 h, it was
observed that 82% yield of adipic acid was obtained and the unreacted cyclohexanone could
be recovered and reused.
4. Conclusion
We have developed an efficient approach for the synthesis of industrially important
chemical adipic acid using the newly synthesized Mn@CC-SO3H-NH2 catalyst using O2 as
an oxidant in water as a solvent. Adipic acid was isolated in good yield and the unreacted
cyclohexanone can be easily separated and reused again for the synthesis of adipic acid. The
catalyst could also be easily recovered and reused without any significant loss in the yield of
8

product. The reaction conditions are economic and environmentally green compared to the
present industrial procedure available for adipic acid synthesis.
Acknowledgements
V.H.J. thanks DST, INDIA for the INSPIRE Faculty Award (IFA 12, CH-44). V.H.J also
thanks Director, NCL for providing all the infra-structural facilities.
Supplementary data
Supplementary data i.e. spectral data associated with this article can be found, in the online
version.
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10

Fig 1
300
250
200
150
100
50
0
-50
-100
10
20
30
40
50
60
70
80
2 
Fig 2a. XRD spectrum of Mn@CC-SO3H-NH2
Fig 2b. SEM image of Mn@CC-SO3H-NH2
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
280
260
240
220
200
180
160
140
120
Chemical Shift (ppm)
100
80
60
40
20
0
-20
Fig 2c. TEM image of Mn@CC-SO3H-NH2
Fig 2d.13C CP/MAS spectrum of Mn@CC-SO3H-NH2
11

Table 1. Study of adipic acid synthesis in various solvents.a
Entry Solvent
Temp Yieldb
(ºC)
Unreacted
cyclohexanoneb
(%)
1.
water
DMF
100
100
140
81
19
2.
3.
4.
5.
6.
Starting material unconsumed
-
DMSO
Starting material unconsumed
-
acetonitrile 100
isopropanol 80
neat
82
9
-
11
Starting material unconsumed
80
100
Reaction conditions: a) cyclohexanone, 20 wt% Mn@CC-SO3H-NH2 catalyst, O2 (20 mL/min), 30 h, b) Isolated
yield
12

Table 2. Study of synthesis of adipic acid at different temperatures.
Entry
Temp
( ºC)
Yieldc
(%)
Unreacted cyclohexanonec
(%)
1.a
2.a
3.a
4.b
5.b
6.b
100
120
140
100
120
140
81
82
73
80
84
68
19
7
12
11
8
10
Reaction conditions: a) cyclohexanone, 20 wt% Mn@CC-SO3H-NH2 catalyst, O2 (20 mL/min), water, 30 h, b)
cyclohexanone, 20 wt% Mn@CC-SO3H-NH2 catalyst, O2 (20 mL/min), neat, c) Isolated yield.
Table 3. Study of Mn@CC-SO3H-NH2 catalyst concentration for the synthesis of adipic acid.a
Entry
Catalyst conc
(wt%)
Yieldb
(%)
Unreacted cyclohexanoneb
(%)
1.
2.
3.
4.
5
62
70
73
82
21
14
11
7
10
15
20
Reaction conditions: a) cyclohexanone, O2 (20 mL/min), water, 120 ºC, 30 h, b) Isolated yield.
13

Table 4. Comparisons of Mn@CC-SO3H-NH2 catalyst vs. literature known catalyst for synthesis of adipic acid
from cyclohexanone.
Entry Catalyst
Oxidant
O2
Yield (%)
Selectivity (%)
96
1.
2.
Hybrid iron phosphonate
-
-
Titano silicate molecular
sieves
O2
94.6
3.
4.
Hollow structured TS-1
O2
O2
-
-
95.5
85.2
Mn modified Hollow
structured TS-1
5.
6.
7.
8.
Hybrid tin phosphate
Mesoporous triphosphate
H2WO4
None
None
H2O2
O2
74
22
91
82
-
-
-
Mn@CC-SO3H-NH2
100
14

Table 5. Reusability of Mn@CC-SO3H-NH2 catalyst in synthesis of adipic acida
Entry Yieldb
(%)
Unreacted cyclohexanoneb
(%)
11
9
8
9
1.
2.
3.
4.
5.
82
80
81
81
80
8
Reaction conditions: a) cyclohexanone, 20 wt% Mn@CC-SO3H-NH2 catalyst, O2 (20 mL/min), water, 120 ºC,
30 h. b) Isolated yield.
15