Modified Graphene Oxide Based Zinc Composite: an Efficient Catalyst for N-formylation and Carbamate Formation Reactions Through CO2 Fixation

Article abstract of DOI:10.1002/cctc.201801963

Catalytic fixation of CO₂ through chemical reactions is always a challenging task of synthetic chemistry. This paper represents the design and synthesis of an eco-friendly low cost zinc metal containing heterogeneous catalyst of aminically modified Graphene Oxide. Characterization of the catalyst has been carried out by Raman and FTIR spectra, AAS, XRD, TEM, SEM, EDX and N₂ adsorption desorption studies. It was found that the catalyst was very proficient for the CO₂ fixation through N-formylation and carbamate formation reactions of amines. Catalytic N-formylation reaction of both aromatic and aliphatic amines gave high yield of corresponding formylated products in presence of polymethylhydrosiloxane (PMHS) as reducing agent under 1 bar CO₂ pressure and mild temperature. Formation of carbamates from aniline or its derivatives and alkyl/aryl bromide with good product selectivity was also achieved under same CO₂ pressure in presence of our synthesized catalyst at room temperature with solvent-free condition. The catalyst is reusable and e?cient even after six cycles.

Full text of DOI:10.1002/cctc.201801963

Accepted Article
Title: Modified Graphene Oxide based Zinc composite: an efficient
catalyst for N-formylation and carbamate formation reactions
through CO2 fixation
Authors: Resmin Khatun, Surajit Biswas, Md. Sarikul Islam, Imdadul
Haque Biswas, Sk Riyajuddin, Kaushik Ghosh, and Sk.
Manirul Islam
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FULL PAPERS
Modified Graphene Oxide based Zinc composite: an efficient catalyst for N-
formylation and carbamate formation reactions through CO2 fixation
Resmin Khatun,[a] Surajit Biswas,[a] Md Sarikul Islam,[a] Imdadul Haque Biswas,[a] Sk Riyajuddin,[b] Kaushik
Ghosh,[b] Sk Manirul Islam*[a]
Abstract: Catalytic fixation of CO2 through chemical reactions is
always challenging task of synthetic chemistry. This paper
aromatic and aliphatic amines gave high yield of corresponding
formylated products in presence of Polymethylhyrosiloxane as
reducing agent under 1 bar CO2 pressure and mild temperature.
Formation of carbamates from aniline or its derivatives and alkyl/aryl
bromide with good product selectivity was also achieved under same
CO2 pressure in presence of our synthesized catalyst at room
temperature with solvent-free condition. The catalyst is reusable and
efficient even after six cycles.
a
represents the design and synthesis of an eco-friendly low cost zinc
metal containing heterogeneous catalyst of aminically modified
Graphene Oxide. Characterization of the catalyst has been carried
out by Raman and FTIR spectra, AAS, XRD, TEM, SEM, EDX and N2
adsorption desorption studies. It was found that the catalyst was very
proficient for the CO2 fixation through N-formylation and carbamate
formation reactions of amines. Catalytic N-formylation reaction of both
1. Introduction
In the last few years, use of hydrosilanes as a reducing agent of
CO2 has been increased extensively[22]. Cantat and co-workers
have utilized hydrosilane for the formylation of amines through
CO2 fixation[23]. After that couple of other catalysts such as
imidazolium-based ionic liquids[24] and thiazolium carbene[25] were
reported. Although few catalytic systems showed good
recyclability but most of metal based catalysts worked under
homogeneous condition which makes the separation process
difficult and cost-effective. To overcome those difficulties and
CO2 fixation reaction for the formation of value-added products is
the most demanding approach in recent years in order to control
the green house gas[1]. CO2 is anabundant renewable low-cost,
and nontoxic C1 resource which has attracted a great attention in
the field of synthetic chemistry as well as green chemistry[2]. Till
date, different methodologies of CO2 fixation reaction like cyclo
addition of CO2 into aziridines or epoxides[3], formylation and
carboxylation of aliphatic/aromatic halides[4,5], N-formylation[6], N-
methylation[7], carbamates production[8] and oxazolidinones
formation[9] have been developed. Among them N-formylation is
an important class of reaction as through this reaction
formamides are produced which are widely used in the synthesis
of valuable heterocycles and pharmaceutical products as well as
biological intermediates[10-14]. Moreover the formylated products
are also very useful as Lewis base organocatalysts in
hydrosilylation reactions and other organic transformations. In
peptide chemistry formyl group is used for protecting the amine
make the protocol less costly, we have synthesized
a
diethylenetriamine functionalized Graphene Oxide based zinc
metal catalyst, Zn(II)DETA@GO. GO is easily producible,
inexpensive material and synthesized Zn(II)DETA@GO is an
efficient and recylable catalyst for N-formylation reaction under 1
atm CO2 pressure in presence of PMHS reducing agent at
ambident temperature (80°C).
Organic carbamates are highly important in the field of
pharmaceuticals (as pro-drugs and drugs)[26] and agriculture[27]
.
functional group [15]
.
They grasp
a pivotal role as anti-HIV, anti-diabetic, anti-
inflammatory, anti-progestational, anti-Alzheimer, anti-fungal,
anti-estrogenic, anti-convulsant, anti-bacterial, anti-osteoporosis,
anti-cancer, anti-filarial, anti-helminths, anti-tubercular, anti-
obesity, anti-viral, anti-malarial, drugs and CNS, CVS active
agents[28]. The compounds are very popular for the protection of
Generally two routes are involved in the synthesis of N-
formamides, one is CO2 fixation route and another is non CO2
fixation route where chloral, formaldehyde, paraformaldehyde,
formate, formic acid, methanol etc. are used as CHO sources[16]
and generates copious wastes resulting in poor atom-economy[17]
.
amino group in the peptide chemistry[29]
,
as linker in the
combinatorial chemistry[30] and as intermediate in the organic
synthesis[31]
Carbon dioxide fixation pathway is the cleanest and most
attractive atom-economical green route for the production of N-
formamides. In addition, capturing and utilization of the green
house gas CO2 for manufacturing of fine chemicals is highly
pleasing. Due to the stability of CO2, catalytic N-formylation of
amines using CO2 is a challenging task[18], again, selectivity is a
crucial factor in this protocol as methylated amines may also get
generated as a consequence of over reduction of the formed
.
The traditional methods for the synthesis of organic carbamates
required either cumbersome or toxic reagents, such as carbon
monoxide, phosgene or its derivatives[32]. Replacement of these
reagents by CO2 will be highly appropriate and straightforward. A
numbers of homogeneous and heterogeneous metal catalysts
based on Al, Sn, Ru, and Au etc. have already been developed
for the conversion of amines to carbamates using CO2 as the
carbon source[33]. To improve the reaction conditions potassium
superoxide and macrocyclic polyether were further used for the
preparation of carbamates[34]. Except those catalysts, various
inorganic and organic base-catalyzed or mediated transition
metal-free systems have been introduced recently[35]. But all of
these protocols are involved in either harsh reaction conditions,
such as high pressure and temperature or require additional
reagents and exhibit poor functional group tolerance. Therefore, it
formamides[19]
.
Recently, formamides are synthesized from amines through CO2
fixation reaction using hydrosilanes or molecular hydrogen as the
hydrogen sources.
[a]R. Khatun, Dr. S. Biswas, M. Sengupta, M. S. Islam, I. H. Biswas, Prof. S. M.
Islam
Department of Chemistry, University of Kalyani ,Kalyani, Nadia, 741235, W.B.,
India. E-mail: manir65@rediffmail.com
is highly preferable to build up
a
new cost effective,
[b]S. Riyajuddin, Dr. K. Ghosh
chemoselective and green methodology which would work under
atmospheric CO2 pressure and at room temperature (RT). For
Institute of Nano Science and Technology, Mohali, Punjab-160062, India
these reasons, we have synthesized
a
cheap material,
1
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10.1002/cctc.201801963
ChemCatChem
Zn(II)DETA@GO composite, which can act as an efficient
heterogeneous catalyst in the formation of organic carbamates
through CO2 fixation reaction under 1 bar pressure and at room
temperature.
magnetic stir bar and fitted with condenser was charged with
amine (5 mmol), Polymethylhyrosiloxane (Si-H: 15 mmol),
catalyst (40 mg) and n-Bu2O (10 mL). Then the flask along with
condenser was degassed and sealed with carbon dioxide of
atmospheric pressure using a balloon set up. Then the mixture
was continued to stir for 10 h at 800C. After that the mixture was
cooled and diluted with ethyl acetate. The conversion and
selectivity of the product were checked by Gas Chromatography.
Through column chromatography pure product was separated for
1H NMR.
Herein, we published the synthesis, characterization of an
aminically modified Graphene Oxide based zinc catalyst
(Zn(II)DETA@GO) and its competent catalytic activity towards
CO2 fixation reactions for the preparation of N-formamides and
organic carbamates under mild conditions.
2. Experimental
Preparation of Graphene Oxide (GO):
Synthesis of Graphene oxide was carried out by oxidation of
graphite flakes (Aldrich) using the following reported method[36]. In
this method, a 200 mL mixture of concentrated H3PO4 and H2SO4
(20:180 v/v) was taken in a 500 mL round bottom flask. Then
graphite flakes (1.5 g) were added slowly to the mixture. Next
KMnO4 (9.0 g) was added in portions to the above mixture. After
that, the above solution was continued to stir for 16h at 50°C.
The mixture was then cooled followed by the addition of 3 ml 30%
H2O2. Then it was cooled in ice bath for several hours until the
appearance of brown coloration. The mixture was centrifuged,
decanted and washed properly with hydochloric acid solution
(10%), deionized H2O, EtOH one by one. Finally, the obtained
brown graphene oxide (GO) was dried under vacuum at room
temperature.
Scheme 2. Catalytic N-formylation reaction through CO2 fixation.
General method of the catalytic formation of carbamates
from aniline or its derivatives
Synthesis of carbamates was performed in a 25 mL round bottom
flask, equipped with a magnetic stir bar. Then the flask was
charged with amine (5 mmol), n-butyl or benzyl bromide (5 mmol)
and 40 mg of Zn(II)DETA@GO catalyst and the mixture was
stirred for 3h at room temperature under CO2 atmosphere using
balloon set up. The progress of the reaction was checked by
TLC. After completion of the reaction, mixture was diluted with
EtOAc and worked up with brine solution. Then ethyl acetate part
was collected and dried through sodium sulphate. The conversion
of the product was analyzed by GC. The product was purified by
column chromatography and characterized by 1H NMR.
Synthesis of Zn(II) metal assisted Diethylenetriamine
functionalized Graphene Oxide (Zn(II)DETA@GO):
GO (1g) was suspended in 50 ml toluene in a 100 ml conical flask
and it was sonicated for about 2 hours. Then 0.18 mL (1.68
mmol) of Diethylenetriamine (DETA) was mixed to the solution
which was further sonicated for 1 hour. After that, 27.26 mg (0.2
mmol) of zinc (II) chloride salt was added dropwise and the whole
mixture was continued to stir for 4 hours. In the last step, the
mixture was centrifuged, washed throughly with toluene and
finally dried under vacuum oven at 100°C to get Zn(II)DETA@GO
catalyst.
3. Results and Discussion
3.1. Characterizations
FTIR specta
FTIR spectra of GO and Zn(II)DETA@GO composite is shown in
Figure 1. A broad band in the range 3000-3650 cm-1 centered at
3381 cm-1 in IR spectra of GO is due to the O-H stretching of
adsorbed water molecules, alcohol and carboxylic acid functional
groups. The peak at 1720 cm-1 is attributed to the C=O stretching
associated to carboxyl, ketone and aldehyde groups; 1621 cm-1 to
the sp2 C=C; 1223 cm-1 and 1055 cm-1 to C-O stretching of
phenolic and epoxy groups respectively[37]. In the spectra of
Zn(II)DETA@GO composite the broad bands at 3401 and 3220
cm-1 are due to O-H stretching frequency and -N-H stretching
vibration of amine, respectively. The peak at 1720 cm-1 is
dramatically disappeared in Zn(II)DETA@GO and two new bands
appeared at 1572 cm-1 (-NH bending)[38]
,
1340 cm-1 (-CN
stretching vibration)[39]. These results clearly indicate the effective
grafting of diethylenetriamine on GO surface. The bands at lower
region 616 cm-1 (Zn-O vibration), 578 cm-1 (Zn-N vibration), 472
cm-1 (Zn-O vibration) confirm the complexation of zinc metal to the
amine grafted GO surface[40]
.
Powder XRD analysis
Figure 2 shows the XRD patterns of GO and Zn(II)DETA@GO.
The diffraction patterns of graphene oxide showed two
characteristic diffraction peaks at 2θ ≈9.9195° and 42.4166° due
to the (002) plane of GO and (100) plane of hexagonal structure
of carbon[41]. After reaction with both diethylenetriamine and Zn
metal on GO surface, the (002) plane of GO slightly moved to a
higher angle of 2θ≈11.3688°. This shifting of the plane is because
of molecular intercalation and sonication[42]. Not only that after
modification with amine and metal a broad peak of centered
nearly at 2θ≈24° appeared which is similar to reduced graphene
confirming the major oxygen containing groups of GO have been
Scheme 1. Schematic presentation of Zn(II)DETA@GO composite
preparation.
Typical procedure for the formation of N-formamide
derivatives using CO2 and PMHS
The general synthesis procedure is described here for the
conversion of amine to corresponding N-formamide using
Zn(II)DETA@GO as catalyst and PMHS as reducing agent
(Scheme 2). In a 25 mL round bottom flask, equipped with a
successfully functionalized[43]
.
2
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10.1002/cctc.201801963
ChemCatChem
Figure 1. FTIR spectra of GO and Zn(II)DETA@GO.
Figure 3. Raman spectra of GO and Zn(II)DETA@GO.
FESEM and HRTEM analysis
Structure and morphology of the catalyst have been predicted
from FESEM and HRTEM analysis. The FESEM images (Figure
4a and 4b) reveal well defined and inter linked 3D graphene
sheets, forming a porous network having appearances of a
sponge like structure. The HRTEM images (Figure 5a and 5b)
expose transparent layers of functionalized graphene oxide.
Figure 4. FESEM images of Zn(II)DETA@GO.
Figure 2. XRD plots of GO and Zn(II)DETA@GO.
Raman spectra
Raman spectra of GO and Zn(II)DETA@GO composite have also
been studied to understand the structural changes that occured
during the chemical reaction from GO to Zn(II)DETA@GO. Pure
graphene oxide displays two characteristic peaks in the Raman
spectrum, one at 1342 cm-1 which is assigned as the D band and
other at 1602 cm-1 which corresponds to the G band (Figure 3).
The D band is associated with the disorders and structural
defects, while G band is usually due to the E2g phonon of sp2
carbon atoms due to the stretching vibrations in graphene
sheets[44]
. In the Raman spectrum of Zn(II)DETA@GO,
appearance of both D and G bands indicate the existence of
graphitic carbon[45]. Based on prevoiuosly reported literatures it
was found that when metal/metal nanoparticles are deposited on
the surface of GO, the intensity ratio of D and G band (ID/IG)
generally increases due to electronic interaction between
metal/metal nanoparticles and GO[46]
.
Here, the intensity ratio (ID/IG) of composite is 0.95 where as that
of graphene oxide is 0.85. Moreover, the peak position of D band
was shifted from 1342 cm-1 to 1351 cm-1 and G band was shifted
from 1602 cm-1 to 1598 cm-1 in Zn(II)DETA@GO. All these results
confirm the electronic interaction between amine-Zn and GO in
Zn(II)DETA@GO, thus indicating the successful incorporation of
Zn metal on DETA@GO.
Figure 5. HRTEM images and elemental mapping of
Zn(II)DETA@GO.
3
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10.1002/cctc.201801963
ChemCatChem
In the HRTEM images, absence of any particles indicates that
active site, Zn is stabilzed through -NH and -NH2 or –OH moieties
of the functionalized graphene oxide. The presence of carbon,
oxygen, nitrogen functionalities and well uniform distribution of
zinc ion in the functionalized graphene oxide have been further
confirmed from elemental mapping (Figure 5c).
Table1.Conditions for optimization of N-formylation reactions of
N-methylaniline using 1 bar CO2 pressurea
Entry
Solvent
Silane
Cat.
Amt.
(mg)
Temp.
(°C)
T
(h)
GC Yield
(%)
1
2
3
4
5
n-Bu2O
n-Bu2O
n-Bu2O
n-Bu2O
PMHS
PMHS
PMHS
PMHS
PMHS
40
40
40
40
40
RT
60
24
24
10
10
10
69
74
N2 adsorption–desorption study
80
92
In order to investigte the surface area and pore size of the
synthesized catalyst, we have done N2 adsorption–desorption
study for Zn(II)DETA@GO. N2 adsorption-desorption isotherm of
catalyst exihibits a typical type IV sorption isotherms with a
hysteresis loop at a relative pressure range of 0.44<p/p0<1.0
(Figure 6)[43]. The pore size distribution curve calculated through
BJH method displayed pores with a typical size of 3.8 nm,
indicating Zn(II)DETA@GO is a kind of mesoporus material. Also,
BET surface area of the catalyst was found 20.697 m²/g.
100
80
80
No
Trace
solvent
6
7
MeCN
PMHS
PMHS
PMHS
PMHS
PMHS
40
40
40
40
00
80
80
80
80
80
10
10
10
10
10
14
12
30
35
dioxane
THF
8
9
Toluene
n-Bu2O
10
No
reaction
75
88
90
92
85
89
82
11
12
13
14
15
16
17
18
n-Bu2O
n-Bu2O
n-Bu2O
n-Bu2O
n-Bu2O
n-Bu2O
n-Bu2O
n-Bu2O
PMHS
PMHS
PMHS
10
20
30
50
40
40
40
40
80
80
80
80
80
80
80
80
10
10
10
10
10
10
10
10
PMHS
PhSiH3
Ph2SiH2
Et3SiH
Ph2MeSiH
89
aReaction conditions: N-methylaniline (5 mmol), silane (15 mmol), solvent (5 ml).
Table 2. Catalytic N-formylation reaction of amines through CO2
fixationa
Entry
Amine
Product
Conv.b
(%)
% of GC
Yield
Time
(h)
TOFc
(h-1)
(isolated
yield)
1
100
92 (88)
10
13.16
1a
1b
2a
2b
Figure 6. Nitrogen adsorption–desorption ishotherm of
Zn(II)DETA@GO
2
3
4
100
100
100
93 (90)
90 (87)
88 (84)
10
8
13.16
16.45
10.96
3.2. Catalysis
Catalytic N-formylation reaction
We examined different reaction paramaters like temperature,
solvent, catalyst amount, reducing agent, etc. taking N-
methylaniline as substrate under 1 atm CO2 pressure. At first
variation of reaction temperature of N-formylation reaction of N-
methylaniline in n-Bu2O medium under 1 bar CO2 pressure in
presence of 40 mg catalyst and PMHS was observed. We got
maximum product yield (92%) at 80°C after 10h (Table 1, entry
3). With increasing temperature at 100°C the yield of product
decreased to 80% due to the formation of methylated product and
polymerization of PMHS (Table 1, entry 4). At room temperature
(RT) and 60°C product yield also decreased to 69% and 74%
respectively may be due to slow reaction rate (Table 1, entry1-2).
Then the above reaction was monitored without solvent under
same reaction condition at 80°C but we got only trace amount of
product for the reaction (Table 1, entry 5). Different solvents were
used for this formylation reaction (Table 1, entry 6-9) but the
maximum yield was obtained using n-Bu2O as solvent. Amount of
catalyst was also monitored for the reaction (Table 1, entry 10-
14), in absence of catalyst no reaction was observed. For further
optimization of the reaction, effect of reducing agent was also
tested (Table 1, entry 15-18).
1c
2c
12
1d
1e
2d
2e
5
6
100
100
85 (80)
82 (80)
12
12
10.96
10.96
1f
2f
7
100
100
91 (88)
80 (77)
8
7
16.45
18.79
1g
2g
8
9
In presence of our synthesized catalyst, we performed N-
formylation reaction with some other amines like substituted
aniline, benzyl amine, cyclohexyl amine, butyl amine etc. under
optimized reaction conditions. Anilines containing both electron-
donating and electron-withdrawing substutients derivatives
produced their corresponding formamide with high selectivity and
yield (Table 2). Besides, other amines (benzyl amine, cyclohexyl
amine, butyl amine) were also very tolerated for producing
formamide with excellent yield (Table 2).
1h
1i
2h
2i
100
92 (87)
5
26.32
aReaction conditions: amine (5 mmol), PMHS (15 mmol based on Si-H), catalyst
(40 mg, 0.038 mmol based on Zn metal), n-Bu2O (10 mL), CO2 (1 atm, balloon),
80°C, bGC conversion, cTOF (turn over frequency) = no. of moles of the
substrate being converted per mole of active site of the catalyst /time (in h).
4
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10.1002/cctc.201801963
ChemCatChem
The comparison between previously reported protocols for the
catalytic N-formylation reaction of N-methylaniline (using silane
as reducing agent) and that of our developed protocol is
summerized in Table 3. Most of the catalytic systems[47a-f] worked
under relatively high CO2 pressure (0.5 MPa-3 MPa) with high
yield (88-96%) of formylated product. There are only few catalytic
protocols[47g-i] reported where the catalysis was performed under
atmospheric CO2 pressure with good product yield (87-94%). But
among them only one catalytic system[47i] was heterogeneous in
nature and the rest were homogeneous in nature where
reusability and recyaclability of the catalyst remained big problem.
Our synthesized catalyst gave high yield (92%) of formyl product
under 1 atm of CO2 pressure after 10h. Moreover, the catalyst
can be recycled and reused; even after six consecutive catalytic
cycles the catalyst conserves its good catalytic efficiency.
Table 3. Comparison table for the catalytic N-formylation reaction of N-methylaniline with other reported systems where silane is used
as reducing agent
Sl.
No.
Catalyst
γ-valerolactone (GVL)
[BMIm]Cl
Reaction conditions
Catalytic nature
Time
(h)
Product
Yield (%)
Ref.
47a
47b
47c
1
2
3
amine (1 mmol), PhSiH3 (2 mmol), Homogeneous
catalyst (1 g), CO2 (3 MPa), 80°C
3
5
96
95
93
amine (1 mmol), PhSiH3 (2 mmol), Heterogeneous
catalyst (1 mmol), CO2 (1.0 Mpa), 30°C.
Pd@HMP-1
amine (1 mmol), Ph2MeSiH (2.5 mmol), Heterogeneous
catalyst (50 mg), dioxane (5 mL), water
(0.3 mL), CO2 (1 Mpa), 60°C
20
4
5
DVB@ISZa
amine (1 mmol), PhSiH3 (1 mmol), Heterogeneous
catalyst (0.25 mol %), CO2 (1.0 Mpa),
40°C
20
4
96
95
47d
47e
Glycine Betaine
amine (0.5 mmol), catalyst (3 mol%), Homogeneous
PhSiH3(1 mmol), CH3CN (1 mL),CO2 (0.5
Mpa), RT
6
7
ILSZ1
amine (1 mmol), PhSiH3 (1 mmol), Heterogeneous
Catalyst (1 mol%), CO2 (0.5 Mpa), 40°C
6
88
87
47f
Cu(OAc)2.H2O
amine (1.4 mmol), PMHS (3.2 mmol Homogeneous
based on Si–H), catalyst (0.001mmol),
Phosphine ligand (P: 0.003 mmol),
dioxane (5 mL), CO2 (1 atm, balloon),
80°C
30
47g
8
9
Cs2CO3
amine (0.5 mmol), PhSiH3 (1 equiv), Homogeneous
catalyst (1 mol %), CO2 (1 atm), CH3CN
(1 mL), RT
12
24
10
90
94
92
47h
47i
[Et4NBr]50%-Py-COF
Zn(II)DETA@GO
amine (1 mmol), catalyst (5 mol%) Heterogeneous
PhSiH3 (2 mmol), CO2 (1 atm), dry DMF
(1 mL), 30°C
10
amine (5 mmol), PMHS (Si–H: 15 mmol), Heterogeneous
catalyst (40 mg, 0.038 mmol based on
Zn metal), n-Bu2O (10 mL), CO2 (1 atm,
balloon), 80°C
This work
aDVB= poly divinylbenzene, SA= ionic liquid-fundtionalized Al(salen)
published[49d] a base (Cs2CO3) catalysed route for the production
of carbamates from amines and alkyl bromide where CO2 is used
as a carbon source (Scheme 3).
Catalytic formation of carbamates throuh CO2 fixation
reaction
Carbamates grasp an inimitable position in the field of agriculture
as well as in medicinal chemistry. These compounds can be
synthesized in a variety of methodologies. Conventionally, the
compounds are produced through the reaction of amines and
alcohols in presence of phosgene (COCl2) which is highly toxic in
nature. To replace the phosgene related pathways and make it
eco-friendly, researchers have developed various protocols
afterward. Use of dialkyl carbonate (such as dimethyl carbonate,
diethyl carbonate etc.) is more eco-friendly and promising reagent
to produce carbamates from respective amines.[48]
Nowadays utilization of CO2 as a C1 feedstock for the synthesis
of carbamates from amines and alcohols or alkyl/aryl halides or
metal alkoxide/alkoxy silanes in presence of catalyst is the most
suitable and desirable route[49]. Previously He et. al. reported the
synthesis of organic carbamates from amines, CO2, and alkyl
halides in presence of K2CO3/PEG400 under homogeneous
Scheme 3. Catalytic synthesis of carbamates from amines,
organohalide and CO2.
To improve that protocol we have designed and developed an
eco-friendly cheap amine functionalized GO based Zn catalyst
catalytic condition[49a]
. Recently Das and his group have
5
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10.1002/cctc.201801963
ChemCatChem
(Zn(II)DETA@GO) which can efficiently produce carbamates from
amines and alky/aryl halide under atmospheric CO2 pressure in
solvent free conditions. Moreover, our catalyst can be recycled
and even after six catalytic cycle, the catalyst maintain its good
catalytic efficacy.
h (Table 4,
entry 1). While the reaction was performed under
same reaction conditions in presence of catalyst (20 mg) we got
58% conversion of the substrates after 5 h (Table 4, entry 2). The
best result was obtained (i.e. 100% conversion of substrates) in
presence of 40 mg of catalyst under same CO2 pressure and
temperature in 3 h (Table 4, entry 4). Different aniline derivatives
and n-butyl bromide or benzyl bromide were used for the
synthesis of carbamates in presence of the catalyst under
optimized reaction conditions. Both electron-donating and
electron-withdrawing substituent of aniline gave very good
conversion as well as selectivity of the desired product (Table 5).
Initially we varied the catalyst amount and reaction time in order
to optimize the reaction conditions through the formation of butyl
phenylcarbamate from aniline and n-butyl bromide as model
reaction and the results are summerised in Table 4. In absence of
catalyst no reaction was occurred between aniline and n-butyl
bromide under 1 atm of CO2 pressure at room temperature in 24
Table 4. Variation of catalyst amount and reaction time for the formation of butyl phenylcarbamate from aniline and n-butyl bromidea
Entry
Catalyst amount (mg)
Time (h)
CO2 pressure (atm)
GC conversion (%)
1
2
3
4
5
0
24
5
5
3
2
1
1
1
1
1
No reaction
20
30
40
40
58
70
100
81
aaniline (5 mmol), n-butyl bromide (5 mmol), room temperature.
Table 5. Substrates scope for the catalytic carbamates formation reaction under 1 atm CO2 pressurea
Entry
Amine
Halide
Product
Conversionb Time
% of GC
yield
(%)
(h)
(isolated
yield)
100
3
98 (95)
1
2
3
4
5
4a
4b
4c
3a
5a
5b
5c
5d
100
100
100
100
3
3
3
3
95 (91)
92 (88)
90 (87)
96 (93)
3b
3c
4d
4e
3d
5e
5f
3e
3f
100
100
3
3
95 (90)
94 (90)
6
7
4f
3g
3h
4g
4h
5g
5h
100
100
3
3
93 (89)
88 (85)
8
9
3i
4i
5i
6
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10.1002/cctc.201801963
ChemCatChem
100
100
3
3
87 (84)
90 (88)
10
11
3j
4j
5j
4k
5k
3k
3l
100
3
92 (89)
12
4l
5l
aReaction conditions: amine (5 mmol), halide (5 mmol), catalyst (40 mg), room temperature, CO2 pressure (1 atm), bGC conversion.
Heterogeneity test of catalyst Zn(II)DETA@GO
Conclusion
To check the heterogeneous nature of our catalyst, we performed
hot filtration test for N-formylation reaction of N-methylaniline. The
N-formylation reaction was carried out under optomized reaction
conditions in presence of the catalyst for 4h. We got 32% yield of
desired product after 4h. Then the catalyst was isolated by
filtration and the filtrate was continued to stir under same reaction
conditions for another 4h. It was observed that the percentage
yield of the desired product remained same after that time.
Therefore no reaction was performed without catalyst. For furthur
confirmation we have done ICP-AES analysis of the filtrate and
the recovered catalyst. We did not get any metal trace in the
filtrate and in the catalyst got same metal loading as that of fresh
catalyst (6.26%). No leaching of Zn metal from the support was
also confirmed by IR and AAS analysis of fresh and used
catalyst. We got similar IR spectrum of both fresh and used
catalyst (Figure S2) which signified that Zn metal was intact with
the catalyst surface even after the catalytic reaction. Zinc loading
in fresh catalyst and the used catalyst after first cycle was also
found same (6.26 %). AAS analysis was also performed for the
product mixture of N-formylation reaction of N-methylaniline after
isolating the catalyst through filtration but no presence of Zn
metal was found in result. All these experimental data clearly
confirmed the heterogeneous nature of Zn(II)DETA@GO catalyst.
An eco-friendly low cost zinc metal containing heterogeneous
catalyst, (Zn(II)DETA@GO) has been designed and synthesized
and thoroughly characterized with Raman and IR spectroscopy,
XRD, AAS, ICP-AES, SEM, TEM, EDX and N2 adsorption
desorption studies. The catalyst has been found much efficient for
the fixation of CO2 in N-formylation reaction and carbamates
formation reaction of amines. Here, our reported protocol of N-
formylation reaction is cost-effective and environment-friendly
which works at mild temperature under 1 atm of CO2 pressure in
presence of PMHS reducing agent. The production of carbamates
from aniline or its derivatives and organo-halides also executes
under same CO2 pressure at room temperature and solvent-free
condition. Not only that, the catalyst is enough stable and it
preserved its catalytic effectiveness even after six catalytic
cycles.
Acknowledgements
SMI gratefully acknowledges the Department of Science and
Technology,
DST-SERB
(Project
sanction
No.
EMR/2016/004956), New Delhi, India, Board of Research in
Nuclear Science, BRNS (Project sanction No. 37(2)/14/03/2018-
BRNS/37003), Govt. of India and the Council of Scientific and
Industrial
Research,
CSIR
(Project
sanction
No.
02(0284)/16/EMR-II, Dated 06-12-2016), New Delhi, India for
financial support. RK acknowledges for the financial support
provided by University Grants Commission through MANF and
SB acknowledges University Grants Commission for D. S. Kothari
Recyclabity test of the catalyst
The prime characteristics of a heterogeneous catalyst is its easy
separation, recoverability and recyclability. The catalytic
recyclability of our catalyst was checked in both N-formylation
reaction of N-methylaniline and carbamates formation reaction
between aniline and n-butylbromide in use of CO2. The catalyst
was isolated by simple filtration and thoroughly washed with
distilled H2O followed by hot MeOH and Et2O after each catalytic
cycle. Then the catalyst was dried under a vacuum desicator.
Figure 6 established that the catalyst is very efficient even after
use of six cycles.
Post
Doctoral
Fellowship
(Award
letter
no.
F.4-
2/2006(BSR)/CH/16-17/0026). MSI gratefully acknowledges the
Department of Science and Technology; DST-INSPIRE for
financial support (INSPIRE fellow Registration No. IF170931). We
acknowledge Department of Science and Technology (DST) and
University Grant Commission (UGC) New Delhi, India for
providing support to the Department of Chemistry, University of
Kalyani under PURSE, FIST and SAP program. We also
acknowledge Department of Chemistry, Jadavpur University, 188,
Raja S. C. Mallick Rd., Kolkata 700032, West Bengal, India, for
providing PXRD instrument facility.
Keywords: Graphene oxide; Amine functionalized Zn metal; carbon
dioxide fixation; N-Formylation; Organic carbamates.
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10.1002/cctc.201801963
ChemCatChem
Table of Contents
FULL PAPER
Resmin Khatun,Surajit Biswas, Md.
Sarikul Islam, Imdadul Haque Biswas,
Sk Riyajuddin, Kaushik Ghosh, Sk.
Manirul Islam*
Modified Graphene Oxide based Zinc
composite: an efficient catalyst for N-
formylation and carbamate formation
reactions through CO2fixation
CO2 fixation via Formylation and The material is very efficient for the
carbamates formation of amines: Zinc fixation of CO2 through N-formylation
metal ions are attached to theaminically and carbamate formation reactions over
modified
Graphene
Oxideandthe a wide range of amines under very mild
condition.
resulting material is well characterized.
10
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