Carbocatalysis: N-doped reduced graphene oxide catalyzed esterification of fatty acids with long chain alcohols

Article abstract of DOI:10.1039/c5nj02095f

Nitrogen doped reduced graphene oxide (N-rGO), 5.8% N readily synthesized from the thermal annealing of graphene oxide (GO) in ammonium hydroxide at 453 K, was demonstrated to be a superior metal-free non-acidic carbo-catalyst for the esterification of fatty acids with different alcohols. The effect of various reaction parameters such as reaction temperature, reaction time, catalyst amount etc. has been studied. The developed catalyst was found to be highly stable and exhibited consistent reusability for seven cycles without any significant decrease in the product yields.

Full text of DOI:10.1039/c5nj02095f

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Carbocatalysis: N-doped reduced graphene oxide catalyzed esterification
of fatty acids with long chain alcohols
a
a
a
b
Jyoti Porwal, Neha Karanwal , Savita Kaul and Suman L. Jain *
Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X
First published on the web Xth XXXXXXXXX 200X
DOI: 10.1039/b000000x
5
Nitrogen doped reduced graphene oxide (N-rGO), 5.8% N readily
synthesized from thermal annealing of graphene oxide (GO) in
ammonium hydroxide at 453 K was demonstrated to be a superior
metal-free non-acidic carbo-catalyst for the esterification of fatty
acids with different alcohols. The effect of various reaction
parameters such as reaction temperature, reaction time, catalyst
amount etc. has been studied. The developed catalyst was found to
be highly stable and exhibited consistent reusability for seven cycles
without any significant decrease in the product yields.
have been reported for the esterification of fatty acids. Along
with the recent development of heterogeneous catalysis, the
emerging application of carbon materials such as fullerene,
carbon nanotube, and graphene which are nonꢀpolluting, reusable
and can easily be modified, as metalꢀfree catalyst is receiving
increasingly interest in the area of organic synthesis.
Herein, we describe a first successful application of nitrogen
doped reduced graphene oxide (NꢀrGO; 5.8 wt% N) as a nonꢀ
acidic catalyst for the esterification of fatty acids (Scheme 1).
5
5
1
0
60
1
5
Introduction
1
50 o
C
(
CH
2
)
n
(CH
2
)
n
R2
H O
OH
2 n
(CH )
R1
R2
O
R1
Graphene oxide, an oxidized form of graphene has been
established to be promising candidate for developing reduced
graphene oxide, chemically functionalized graphene and
grapheneꢀbased composites for various applications in the fields
OH
(
2 n
CH )
2
O
O
2
2
3
3
4
4
5
0
5
0
5
0
5
0
1
of electronics, optics and catalysis. Chemical doping is an
effective approach to modulate the electrical and catalytic
properties of graphene and its derivatives. Doping of carbon
network of graphene with heteroatoms such as nitrogen, boron,
phosphorus has gained considerable interest in recent years and
widely been used in electrochemical applications, such as fuel
cells, lithium ion batteries, supercapacitors and for catalytic
65
Scheme 1: Esterification of fatty acids
Results and discussion
2
Synthesis and characterization of the catalyst
applications. Particularly, Nꢀdoped graphene has been reported
to be metal free catalyst for aerobic selective oxidation of
Graphene oxide (GO) sheets were synthesized from graphite
3
benzylic alcohols, and the selective oxidation of ethylbenzene at 70 powder using a modified Hummers method. Nitrogenꢀdoped
4
3
53 K to generate acetophenone ; however, it has never been
graphene oxide was prepared through a simple process by direct
thermal reduction of a GO and ammonium hydroxide at 453 K C
for 5 h by following the literature procedure. The nitrogen
content in the synthesized material was determined by elemental
o
investigated for the esterification of organic acids with alcohols.
Esterification of fatty acids with alcohols to give
2
0
corresponding esters is an important reaction and extensively
5
used in the synthesis of biofuels. Esterification reactions are a 75 analysis and was found to be 5.8 wt%. The collected sample was
classic example of reversible reactions and are mostly catalyzed
by homogeneous acid catalysts such as sulphuric acid, which are
corrosive, nonꢀrecyclable and produce undesirable wastes. The
disposal of these undesired materials not only enhance the cost
denoted as NꢀrGO and characterized by FTIR, XRD, SEM, TEM,
XPS and TG analysis.
Fig. 1(A) shows Xꢀray diffraction (XRD) patterns of GO/Nꢀ
o
rGO samples. A sharp peak at 2θ = 10.8 without a graphite peak
o
of the overall process but also leads to an environmental 80 at ca. 2θ = 26.01 confirmed the successful fabrication of GO.
6
o
concern. Thus, the use of solid catalysts in biofuel production
After treating with ammonia, the peak at 2θ = 10.8 disappeared
7
,8
o
has become an area of current research interest.
Biodiesel
and new peaks at 25.3 appeared, indicating that GO was reduced
production using solid catalysts offer several advantages such as
facile recovery of the catalyst, cheaper production costs due to
the reusable nature of the catalyst and also reduce the corrosion
and environmental problems. In this regard, several solid acid
to rGO via the thermal reduction.
9
,10
catalysts such as metal oxides,
sulfonic acid functionalized
1
1,12
13
14
15
mesoporous materials,
polymers, zeolites, clays and
carbon based catalysts have been reported for the esterification
of fatty acids. Recently sulfonic acid functionalized ionic
1
6
1
7
18
19
liquids sulfated zirconia and sulfonated graphene oxide
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Fig. 1: XRD of the GO and NꢀrGO
35
Xꢀray photoelectron spectroscopy (XPS) was performed to
analyze the elemental composition and nitrogen bonding
configurations in NꢀrGO. In addition to carbon and oxygen peaks
in the XPS survey scan spectra of NꢀrGO (Fig. 2a), a nitrogen
peak is clearly exists, confirming the successful formation of Nꢀ
doped rGO. Furthermore, sharp peaks of C1s in NꢀrGO at 284.85
and 284.58 eV in Fig. 2b, corresponding to graphitic or
Fig. 3: FTIR of GO and NꢀrGO
5
0
5
0
The nanostructural features and morphology of the synthesized
material was determined by SEM and HRTEM analysis as shown
in Fig. 4. The Fig. 4a, clearly shows the plenty of wrinkle and
4
0
2
3
1
1
2
sp carbon atoms, suggesting that most of the carbon atoms are
presented in the conjugated forms. Furthermore, small peaks at
folded regions which are mainly attributed to the sp carbons,
linked to the oxygen functionalities in the basal plane and
various structural defects of rGO nanosheets. Furthermore in
elemental mapping, the thorough and uniform distribution of
nitrogen atoms, confirming the successful synthesis of NꢀrGO.
2
86.39 and 289.07 eV which can be attributed to different C–O
bonding configurations, suggesting deoxygenation of the GO
during the Nꢀdoping. Instead, two additional peaks at 285.89 and
45
2
287.48 eV are identified and can be attributed to the Nꢀsp C and
3
Nꢀsp C bonds, respectively. These results demonstrate that
substitution of the Nꢀatoms occurs at the edges or defective sites
of the graphene sheets and nitrogen atoms were successfully
incorporated into the graphene lattice.
Fig. 2: XPS spectra of NꢀrGO
Furthermore, in FTIR of NꢀrGO, the peaks due to oxygen
containing functional groups such as –OH (3432), C=O from
Fig. 4: SEM, HRTEM and elemental mapping of NꢀrGO
ꢀ
1
ꢀ1
2
5
carboxyl/ carbonyl (1736 cm ) and C–O–C (988 and 1227 cm )
were gradually decreased, suggesting the deoxygenation of
graphene oxide at higher temperature. Further, new peaks
50
The Raman spectra of synthesized GO and NꢀrGO as shown in
Fig 6, clearly indicated two bands, a graphite lattice (G band) at
ꢀ
1
ꢀ1
ꢀ
1
ꢀ1
ascribed to C=C (1545 cm ) and C–N (1338 cm ) were appeared
in the spectra of NꢀrGO, confirming the successful doping of
1
569 cm and stronger graphite edges (D band) at 1306.0 cm .
The ID/IG ratio was found to be increased in NꢀrGO
3
0
nitrogen atoms in the graphene framework. In addition, a peak
corresponding to N–H from NH4 (1458 cmꢀ1) was found, which 55 which is in good agreement with the literature value .
was probably resulting from the reaction of oxygen
(ID/IG=1.34) in comparison to the graphene oxide (ID/IG=0.86),
+
20
functionalities of graphene oxide (carbonyl, carboxyl etc) with
+
ammonia to give NH4 and then deoxygenation of GO (Fig 3).
2
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100
9
8
7
6
5
0
0
0
0
0
370
380
390
400
410
420
430
440
Temperature (K)
30
Fig. 5: Raman spectra of synthesized GO and NꢀrGO
The higher thermal stability of the NꢀrGO was determined by TG
analysis by heating the material under air (Fig. 6). The initial
weight loss about 1ꢀ2 % in NꢀrGO was obtained in the range of
Fig. 7: Effect of temperature on reaction conversion for the esterification of
oleic acid with octanol; catalyst 5 wt %, time 6h
5
To evaluate the effect of catalyst concentration, the esterification
experiments were performed by varying the concentration of the
catalyst from 1.5ꢀ10 wt%. The results of these experiments are
summarized in Fig. 8. It is clearly shown that the reaction was
found to be increased with the catalyst concentration from 1.5 to
5 wt%. However, further increase in catalyst concentration from
3
73ꢀ423 K, which can be attributed to the evaporation of water
physically absorbed between the layers of NꢀrGO. Then the
material was found to be stable upto 623 K and exhibited major
weight loss in the range of 673–1073 K, which can be attributed
to the formation of carbon monoxide (CO) and carbon dioxide
3
4
4
5
5
0
5
0
1
0
2
0
(
CO ) as suggested in the literature.
2
5
to 10 wt % affected the reaction adversely and provided lower
yield of the corresponding ester under identical reaction
conditions. This decrease in the conversion at higher catalyst
concentration is most likely due to the excess availability of
Lewis basic sites with lone pair electrons such as pyridinic which
have a great potential to interact with the acid substrates. The
coordination of the basic Nꢀsites with oleic acid led to proton
transfer from the acidic hydroxyl groups (Brönsted acid sites)
and form quaternary pyridinium species. This kind of acidꢀbase
coordination on the catalyst surface will hamper the reaction of
oleic acid with alcohol and therefore provides loss in activity and
subsequently poor product yield. Based on these studies, we have
considered 5 wt % as the optimum catalyst concentration for
further study.
Fig. 6: TGA of NꢀrGO
1
2
2
5
0
5
Catalysis
Synthesized Nꢀdoped reduced graphene oxide (NꢀrGO; 5.8 wt %
N) sample was initially tested for the esterification of oleic acid
with octanol by varying the reaction parameters such as reaction
temperature, reaction time, catalyst concentration etc. To
evaluate the effect of the reaction temperature, esterification of
oleic acid was performed by varying the temperature from 373 to
4
33 K (Fig 7). As shown, the higher reaction temperature was
found to be favourable for the reaction and at 423 K the
maximum conversion to corresponding ester (98.6%) was
achieved. Further increase in reaction temperature did not affect
the reaction rate and the conversion remained almost same. Thus
we have chosen 423 K as the optimum reaction temperature for
further study.
55
Fig.8: Effect of catalyst concentration on reaction conversion for the
esterification of oleic acid with 1ꢀoctanol at 423 K temperature and 6h
reaction time
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DOI: 10.1039/C5NJ02095F
Kinetic studies
1
00
The kinetic behaviour of the reaction was tested for esterification
of oleic acid with 1ꢀoctanol over NꢀrGO catalyst. Two
parameters have been considered for the kinetic studies i.e effect
of oleic acid concentration and reaction time on the reaction rate.
In all the experiments, reaction mixtures were analysed at fixed
interval of times and the residual acid was titrated against an
9
0
5
0
5
0
5
80
70
ꢀ
1
alcoholic solution of KOH (0.01 mol L ) to follow the progress
of the reaction.
1
1
2
2
6
5
0
0
The effect of oleic acid concentration
According to the existing literature reports, esterification
reactions follow first order dependence on the fatty acid
concentration. Thus we assume that equation 1 can be used to
describe the substrate concentration variation with relation to
time:
1
2
3
4
5
6
7
Reaction time (hr)
4
0
Ln[oleic acid] = ꢀkt + In [oleic acid]0……………………………(eq. 1)
t
Fig. 10: Effect of time on reaction conversion for the esterification of oleic
The plot of oleic acid concentration {ln(C /C)} versus time (Fig.
acid with octanol using 5 wt% catalyst and 423 K temperature
0
9) shows a linear relationship of oleic acid conversion with
respect to time. This observation indicates that esterification of
oleic acid follows firstꢀorder dependence with respect to time. It
is important to mention that a high molar excess of octanol in
relation to oleic acid was used to assure that the alcohol
concentration would essentially be remained constant during the
reaction.
In order to extent the scope of the reaction, we further studied
the esterification of fatty acid mixtures obtained by
saponification of various nonꢀedible oils such as Bischofia
javanica and Toona silita seed oils. Fatty acid composition of
these oils has been determined by gas chromatography as given
in Table 1 (entry 5 & 9). For esterification fatty alcohols i.e.
octanol, hexanol, 2ꢀethyl hexanol, decanol were used. All the
substrates were efficiently converted to corresponding esters
with excellent conversion under the optimized experimental
conditions (Table 1). The identity of the products was confirmed
45
50
1
13
by H and C NMR analysis as given in Fig 11.
55
O
1
(
.2ꢀ1.3
CH
22.7
5
.3
2.0
CH
32
4.0
2
64
0.90
CH
14.1
0
.90
CH3
4.1
2
)
6
CH
2
1.6
2
.0
2
5.3
CH
130
1
.2ꢀ1.34 CH
2
2.29
CH
34.3
C
173
CH
3
CH
130
1.2ꢀ1.3
(CH )n
(CH
2
)
4
1
32
2
O
2
2
2.7
22.7
[
1 2 3 4
n= R , R , R , R ]
H
C
2
H
2
C
CH
2
H
2
C
C
C
H
2
H
2
R1= straight chain
60
R
2
= branched chain
Fig. 9: First order plot for esterification of oleic acid with 1ꢀoctanol over Nꢀ
rGO catalyst
H
C
2
H
C
2
3
0
CH
C
H
2
CH
2
Effect of reaction time
3
H C
H
C
2
H
C
2
The effect of reaction time on the esterification reaction was
studied by collecting the samples at regular interval of time and
analyzing by H NMR spectroscopy. From Fig. 10 it is clear that
initially the reaction is very fast with 53.04 % conversion in 1 hr
and as the reaction proceeds, maximum conversion 98.6 % is
observed in 6 h afterwards no significant change is seen.
R
R
3
4
=
H
2
C
C
H
2
65
1
3
5
H
C
2
H
C
2
H
2
CH
2
C
C
H
C
H
2
C
C
H
H
2
2
=
2
1
13
Fig 11: H NMR and C NMR assignment of fatty esters [(E)ꢀoctyl octadecꢀ
9ꢀenoate; (E)ꢀ2ꢀethylhexyl octadecꢀ9ꢀenoate; (E)ꢀhexyl octadecꢀ9ꢀenoate;
70
(E)ꢀdecyl octadecꢀ9ꢀenoate.
To evaluate the effect of amount of nitrogen content in NꢀrGO
catalyst on esterification reaction, we synthesized more amounts
4
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of samples without nitrogen and with different nitrogen content
NꢀrGO (4.2 to 8.2 wt % N). The synthesized catalysts were 45 Table 1: Esterification of different fatty acids and alcohols
a
tested for the esterification of oleic acid with 1ꢀoctanol under
optimized experimental conditions. It was observed that undoped
rGO catalyst did not show any activity even at higher
temperature (450 K) and original substrates were recovered even
after prolonged reaction time (15 h). However, the reaction was
found to be increased with increasing the Nꢀcontent from 4.2 to
Entry
Fatty acids
Fatty alcohol
Conv. Yield
b c
(
%) (%)
5
1
2
.
.
98.6 98
OH
CH -(CH ) CH=CH-(CH ) -COOH
3
2 7
2 7
CH
-(CH
)
CH=CH-(CH
)
-COOH
HO
96.8 96
97.7 97
3
2
7
2
7
5
.8 wt% N in NꢀrGO catalysts with no significant change from
3.
4.
CH3-(CH2)7CH=CH-(CH2)7-COOH
CH -(CH CH=CH-(CH -COOH
OH
OH
1
1
2
2
0
5
0
5
5.8 to 6.2 wt% N. In case of NꢀrGO catalyst having 8.2 wt% N,
the reaction was found to be slow and afforded poor conversion
3
2
)
7
2
)
7
99.2 98.5
4
5
.
Bischofia javanica fatty acids
Major componentꢀ C18:2; other
96.1 98.8
OH
(
62.4 % with respect to oleic acid). These studies suggested that
(
Nꢀdoping in the range of 5.5ꢀ6.2 wt% N) was found to be
optimum and excess doping exhibited adverse effect on the
catalytic activity.
componentꢀC16:0, C18:1, C18:3)
Bischofia javanica fatty acids
6.
HO
95.3 95
97.2 96.8
97.4 97
(Major componentꢀ C18:2; other
componentꢀC16:0, C18:1, C18:3)
Bischofia javanica fatty acids
Reusability of the heterogeneous catalyst is important for the
7
8
9
.
.
.
2
1
OH
OH
large‐scale operation and from an industrial point of view .
After completion of the reaction, the catalyst was separated by
centrifugation, dried and reused for subsequent runs. The
recovered catalyst was used for seven subsequent runs for the
esterification of oleic acid with 1ꢀoctanol by following the
described experimental conditions. The results of these recycling
experiments are shown in Fig 12. As shown, the yield of the
corresponding ester and reaction time remained almost same,
indicating that the catalyst is highly stable and can be reused for
several runs without any significant loss catalytic activity.
(Major componentꢀ C18:2; other
componentꢀC16:0, C18:1, C18:3)
Bischofia javanica fatty acids
4
(Major componentꢀ C18:2; other
componentꢀC16:0, C18:1, C18:3)
Toona cilita fatty acids (Major
componentꢀ C16:0)
Toona cilita fatty acids (Major
componentꢀ C16:0)
OH
89 87
86 84
10.
11.
HO
Toona cilita fatty acids (Major
componentꢀ C16:0)
Toona cilita fatty acids (Major
componentꢀ C16:0)
88 87
89 88
OH
OH
1
2.
4
1
00
a
90
80
70
60
50
40
30
20
10
0
Reaction conditions: catalyst 5 wt%, reaction time 6h, temperature 423 K;
b
conversion of fatty acid to ester was calculated by means of the acid value
AV). The acid value of the reaction mixture was determined by the acid base
titration technique. The conversion of FFA (reduction in acid value) was
(
5
0
calculated using the following equation:
initial acidity and a is the acidity at time t (6 h); Isolated yield
X
FFA = a ꢀ a / a ;where a is the
i t i i
c
t
Experimental Section
55
Techniques used
Ist
Iind
IIIrd
Ivth
Vth
VIth
VIIth
Reaction recycling
The vibrational spectra of samples were recorded on Perkin–
ꢀ
1
Elmer spectrum RXꢀ1 IR spectrophotometer from 450 cm to
ꢀ
1
4
000cm . The micro fine structure of materials was determined
Fig. 12: Results of recycling experiments
by High Resolution Transmission Electron Microscopy using
FEIꢀTecnaiG Twin TEM working at an acceleration voltage of
2
6
6
7
7
0
5
0
5
2
00 kV. For TEM analysis well dispersed aqueous samples were
3
3
4
0
5
0
Although, the exact mechanism of the reaction is not known at
deposited on carbon coated copper grid. Electron diffraction
patterns were evaluated using the ProcessꢀDiffraction software
package. The diffraction pattern and phase structure of materials
2
2
this stage; however based on the literature, we assume that the
NꢀrGO catalyst may provide dual role in activating the acid as
well as alcohol molecule. The basic sites (electron rich) on the
NꢀrGO may abstract proton from alcohol molecule to give
corresponding alkoxide ion. Whereas, the pyrollicꢀN and
gaphitic sp2 N which possesses good electron withdrawing
capability, activate the acid carbonyl group by coordinating with
the oxygen atom of carbonyl group and make the adjacent carbon
atom net positive. The nucleophilic alkoxide ions will attack to
the electrophilic carbon followed by usual esterification reaction
path to give corresponding ester.
was determined by XRD using
diffractometer at 40 kV and 40 mA with Cu Kα radiation (λ=
.5418 nm). Thermoꢀgravimetric analysis was carried out for
a Bruker D8 Advance
1
determining the thermal stability of the samples by using a
thermal analyzer TAꢀSDT Qꢀ600 in the temperature range 40 to
900 °C with heating rate of 10 °C/min under nitrogen flow. XPS
measurements were obtained on
a
KRATOSꢀAXIS 165
instrument equipped with dual aluminum–magnesium anodes by
using MgKa radiation (hν =1253.6 eV) operated at 5 kV and 15
mA with pass energy 80 eV and an increment of 0.1 eV.
Synthesis of N-rGO: Graphene oxide (GO) was synthesized
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from graphite flakes using modified Hummers method. The
synthesized graphene oxide was dispersed in water (50 mL, 0.75
mL ) using ultrasonic bath. The resulting suspension was added 60 activity and was found to be robust that could easily be
acids with different fatty alcohols under mild experimental
conditions. The developed catalyst exhibited excellent catalytic
ꢀ
1
with aqueous ammonia (4 mL, 28 wt %) under magnetic stirring
and then the mixture was transferred into Teflonꢀlined autoclave
for heating at 453ꢀ473 K for 6 h. The resulting nitrogen doped
reduced graphene oxide was sonicated for 30 min to remove the
excessive or physisorbed ammonia before dried at 60 °C for 24
h.
Esterification of oleic acid: The esterification experiments were
carried out in a 25 ml round bottomed flask equipped with a
magnetic stirrer and reflux condenser. In a typical experiment,
oleic acid (1 mmol), octanol (1 mmol) and NꢀrGO catalyst (5 wt
recovered and recycled for several runs without any significant
decrease in the catalytic activity. The developed methodology
represents a green and sustainable approach for the esterification
and can further be used for other organic transformations.
5
0
5
0
5
0
5
0
5
0
65
1
1
2
2
3
3
4
4
5
Acknowledgement
We kindly acknowledge Director IIP for his kind permission to
publish these results. We are thankful to the Analytical Science
Division of IIP for providing help in the analyses of the samples.
NK kindly acknowledge CSIR, New Delhi for providing
fellowship under XII five year project.
%
of total weight) was taken and the resulting mixture was
70
stirred and heated at 423K under neat conditions. The progress of
the reaction was monitored by TLC (SiO ). After the reaction,
2
the heterogeneous catalyst was separated by centrifugation, dried
and reused for recycling experiments. Conversion of fatty acid to
the corresponding ester was calculated by means of the acid
value (AV). The acid value of the reaction mixture was
determined by the acid base titration technique. The conversion
of FFA (reduction in acid value) was calculated using the
Notes and references
a
Biofuel Division, CSIR-Indian Institute of Petroleum, Dehradun-248005,
India
b
75
Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Dehradun-
2
48005, India; Tel.: +91-135-2525788; Fax. +91-135-2660202; Email:
suman@iip.res.in
2
3
folowing equation:
XFFA = a ꢀ a / a ; where a is the initial acidity and a is the
i
t
i
i
t
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80
85
2
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under reduced pressure and the product was analyzed by H and
5
1
3
C NMR.
331.
2
3
.
.
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Esterification of fatty acid mixtures of Bischofia javanica and
Toona silita seed oil:
To explore the activity of the synthesized catalyst, fatty acids of
Bischofia javanica and Toona silita oil were obtained by
saponification. Extracted oil (2 g) was saponified with NaOH
(1.1 M) and acidified with HCl with stirring until the pH became
8
288ꢀ8297.
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2
9
9
0
5
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3
2
, followed by extraction with CCl (20 mL x 3), washing with
4
6
.
water (20 mL x 3) and solvent recovery by vacuum distillation to
give white semi solid fatty acids. The fatty acid mixture was
esterified with different fatty alcohols i.e. octanol, 2ꢀethyl
hexanol, hexanol, decanol under optimized conditions i.e. (Nꢀ
rGO catalyst: 5 wt%, reaction time: 6 h and reaction temperature
7. Z. Helwani, M. R. Othman, N. Aziz, J. Kim, W. J. N. Fernando App.
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00 10. V. M. Mello, G.P.A.G. Pousa, M. S.C. Pereira, I. M. Dias, P. A. Z.
4
23 K). Conversion of fatty acid to the corresponding ester was
calculated by acid base titration technique. Further, the
corresponding ester products were purified by passing through
Suarez, Fuel Process. Tech. 2011, 92, 53–57.
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1
13
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9
O); H NMR (CDCl , δppm): 0.90 [t, (ꢀCH )], 1.2ꢀ1.3 [ m, (ꢀ
ꢀ
1
105
205, 19ꢀ30.
8%; IR (neat, cm ): 2933 (CꢀH), 1739 (C=O), 1173 (CꢀC(=O)ꢀ
1
3. M. A. K. Zarchi, F. Mirjalili, N. Ebrahimi, Bull. Korean Chem. Soc.
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1
3
3
CH )], 1.6 [m, (ꢀCOꢀCH ꢀCH )], 2.0 [m, ꢀCH ꢀCH=CHꢀCH ),
14. A. S. Abbas, R. N. Abbas Iraqi J. Chem. Petroleum Eng. 2013, 14 35ꢀ
3.
2
2
2
2
2
1
3
4
2
.29 [t, (ꢀCOꢀCH )], 4.0 [t, (ꢀOꢀCH )], 5.3 [b, (ꢀCH=CHꢀ)];
C
2
2
1
1
1
10 15. D. Konwar, P. K Gogoi, G. Borah, R. Baruah, N. Hazarika, R.
NMR (CDCl , δppm): 14.1 [2x(CH )], 22.7 [2x(CH ꢀCH )], 32
3
3
2
3
Borgohain Ind. J. Chem. Tech. 2008, 15, 75ꢀ78.
[
(CꢀC=CꢀC)], 34.3 [(CꢀCO)], 64 (ꢀOꢀCH ꢀ), 130 [2 (C=C)],
2
1
1
1
6. L. Geng, Y. Wang, G. Yu, Y. Zhu, Catal. Commun , 2011, 13, 26–30.
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1
73[(ꢀCOO)].
15
20
1
2
9. B. Garg, T. Bisht, Y.ꢀC. Ling, RSC Adv., 2014, 4, 57297ꢀ57307.
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Conclusion
2
012, 2, 11249ꢀ11252
5
5
We have demonstrated for the first time the application of
nitrogen doped reduced graphene oxide (NꢀrGO) as an efficient
metal free non acidic carbocatalyst for the esterification of fatty
2
1. K. F. Shelke, S. B. Sapkal, G. K. Kakade, B. B. Shingate, M. S.
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This journal is © The Royal Society of Chemistry [year]
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Table of Content Entry
Nitrogen doped reduced graphene oxide (N-rGO) was found to be an efficient metal free and
heterogeneous catalyst for esterification of different fatty compounds including acid oils with
long chain alcohols.