Graphene oxide supported dicationic ionic liquid: an efficient catalyst for the synthesis of 1-carbamatoalkyl-2-naphthols

Article abstract of DOI:10.1007/s11164-019-03922-0

This article describes the synthesis, characterization, and catalytic application of graphene oxide (GO) supported imidazolium based dicationic ionic liquid (DIL@GO). The DIL@GO was successfully synthesized through stepwise functionalization of GO. The as prepared DIL@GO was characterized by different microscopic and spectroscopic techniques such as XRD, SEM, TEM, TGA, FT-IR, EDX and CHNS analysis. The catalytic efficiency of the DIL@GO was explored for the synthesis of 1-carbamatoalkyl-2-naphthol derivatives through condensation of aromatic aldehydes, alkyl carbamates and 2-naphthol. The influence of catalyst amount and reaction temperature is examined to optimize the performance of catalytic reactions. It is found that DIL@GO offers a highly efficient solvent-free reaction path for the synthesis of 1-carbamatoalkyl-2-naphthols. Based on this, a plausible mechanism for the conversion is proposed. Additionally, the catalyst showed good stability, facile separation and reusability up to five reaction cycles without significant loss of catalytic activity.

Full text of DOI:10.1007/s11164-019-03922-0

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-03922-0
Graphene oxide supported dicationic ionic
liquid: an efcient catalyst for the synthesis
of 1‑carbamatoalkyl‑2‑naphthols
Nipun Patel1 · Deepak Katheriya1 · Harsh Dadhania2 · Abhishek Dadhania1
Received: 6 January 2019 / Accepted: 28 June 2019
© Springer Nature B.V. 2019
Abstract
This article describes the synthesis, characterization, and catalytic application of
graphene oxide (GO) supported imidazolium based dicationic ionic liquid (DIL@
GO). The DIL@GO was successfully synthesized through stepwise functionaliza-
tion of GO. The as prepared DIL@GO was characterized by diferent microscopic
and spectroscopic techniques such as XRD, SEM, TEM, TGA, FT-IR, EDX and
CHNS analysis. The catalytic efciency of the DIL@GO was explored for the syn-
thesis of 1-carbamatoalkyl-2-naphthol derivatives through condensation of aromatic
aldehydes, alkyl carbamates and 2-naphthol. The infuence of catalyst amount and
reaction temperature is examined to optimize the performance of catalytic reactions.
It is found that DIL@GO ofers a highly efcient solvent-free reaction path for the
synthesis of 1-carbamatoalkyl-2-naphthols. Based on this, a plausible mechanism
for the conversion is proposed. Additionally, the catalyst showed good stability, fac-
ile separation and reusability up to fve reaction cycles without signifcant loss of
catalytic activity.
Keywords Graphene oxide · Dicationic ionic liquid · Heterogeneous catalyst ·
Solvent free
Introduction
Ionic liquids (ILs) have drawn tremendous attention of the scientifc community
due to their potential applications in diferent disciplines such as electrochemistry
[1], organic synthesis [2], chemical separation [3], and material science [4]. ILs are
* Abhishek Dadhania
abhishekdadhania.bt@charusat.ac.in
1
P. D. Patel Institute of Applied Sciences, Charotar University of Science and Technology
(CHARUSAT), Changa 388421, Gujarat, India
2
Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388120, Gujarat, India
Vol.:(0123456789)
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N. Patel et al.
composed of organic cations and inorganic or organic anions. Judicious selection
of cation–anion combination can provide the task specifc physiochemical proper-
ties of ILs. Compared to conventional solvents, ILs have unique properties such
as low vapour pressure, high thermal stability, non-fammability, remarkable solu-
bility, high conductivity, and broad liquid range [5]. Recently, there is an increas-
ing research interest in dicationic ionic liquids (DILs) due to fexibility in tuning
their physiochemical properties as compared to monocationic ionic liquids. Gener-
ally, DILs consist of dications which are linked with either fexible or rigid spacers
(generally an alkyl chain) and two monoanions [6]. There are countless possibilities
to tune the physiochemical properties of DILs through judicious selection of cati-
ons and anions [7]. DILs are extensively studied for their potential applications as
a solvent [8], lubricant [9], nanoparticles coating [10] and catalysis [11]. Despite
many attractive properties, their application in an industrial process is limited due to
their homogeneous nature. To overcome this drawback, its immobilization on solid
support is the best solution. There are many solid supports such as silica, polymer,
metal ions, zeolites, carbon nano tubes (CNTs), etc., have been widely studied for
the heterogenization of ILs [12]. Heterogenization facilitates its easy separation after
completion of the reaction, efortless purifcation, storage and handling as compared
to its homogeneous counterpart.
Nowadays, graphene oxide (GO) emerged as a promising carbon material for the
heterogenization of the homogeneous catalyst due to its unique structural properties
[13]. GO can be obtained through exfoliation of graphite oxide and, hence, possesses
a large surface area for the immobilization of homogeneous moiety [14]. Addi-
tionally, GO possesses good thermal and chemical stability [15]. Besides, GO is a
fexible layered carbon material having diferent functional groups, such as epoxy,
hydroxyl and carboxyl on the basal plane and edges [16–19]. These functional sites
are available for efective anchoring of homogeneous species through covalent func-
tionalization [20]. Further, these hydrophobic groups present on the GO surface may
assist substrate adsorption and, hence, speed up the catalytic reactions [21]. The
immobilization of DILs on the surface of GO can result in an enhanced heterogene-
ous catalytic system with the translation of inherent characteristics of the GO to the
catalyst.
On the other hand, 1-carbamatoalkyl-2-naphthols are the molecules of huge inter-
est as their hydrolyzed derivatives 1-aminoalkyl-2-naphthols possesses interesting
biological activities as hypotensive and bradycardia agents [22, 23]. These com-
pounds having 1,3-amino-oxygenated functional groups are also present in many
natural products and drugs [24]. There are many reports that have been published for
the synthesis of 1-carbamatoalkyl-2-naphthols by a one-pot multicomponent reac-
tion between aromatic aldehydes, 2-naphthols, and alkyl carbamates using diferent
catalysts [25–29]. Nevertheless, some of the synthesis routes sufer from drawbacks
such as harsh reaction conditions, longer reaction time, lower yield, use of an exces-
sive amount of catalyst, and use of expensive metal catalysts. Therefore, develop-
ment of a highly efcient process for the synthesis of 1-carbamatoalkyl-2-naphthols
is of considerable importance.
In this study, we presented a graphene oxide supported –SO3H functionalized
imidazolium based dicationic ionic liquid (DIL@GO) as an efcient catalyst for
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Graphene oxide supported dicationic ionic liquid: an efcient…
the synthesis of 1-carbamatoalkyl-2-naphthols under solvent free reaction condi-
tions (Scheme 1). After the reaction, DIL@GO can be easily recovered by cen-
trifugation and reused fve times without signifcant loss of its catalytical activity.
Experimental
Materials and methods
All the chemicals were purchased from Sigma-Aldrich (India) and SDFCL. Melt-
ing points were determined by a capillary method using VMP-D melting point
apparatus and were uncorrected. FT-IR spectra were recorded on a Thermo Nico-
let 6700 spectrometer (KBr). X-ray difraction (XRD) patterns were recorded on a
Bruker D-2 Phaser XRD instrument. EDX was done by a scanning electron micro-
scope with EDS (ESEM-EDAX XL-30, Phillips, Netherlands). Thermogravimet-
ric analysis (TGA) was done on a Mettler-Toledo Thermal Analyzer. Scanning
electron microscopy (SEM) images were taken on a JEOL, JSM-6010LA instru-
ment. Transmission electron microscopy (TEM) images were taken on a JEOL,
1
JEM 2100 instrument. H NMR spectra were recorded on a BRUKER 400 MHz.
CHNS analysis was done by an elementar vario MICRO CUBE analyzer.
Synthesis of (3‑chloropropyl)trimethoxysilane functionalized graphene oxide
(ClPr‑Si@GO)
Graphene oxide (GO) was synthesized by Hummers method [30]. Afterwards,
synthesized GO was treated with (3-chloropropyl)trimethoxysilane (CPTMS) to
get functionalized GO [31]. In a typical process, CPTMS (25 mmol) was added to
the GO suspension in toluene (50 mL, 10 mg mL−1), and the mixture was stirred
at refux temperature under nitrogen atmosphere. After 24 h, the reaction mixture
was cooled to room temperature, and solid was separated. The resultant solid was
washed with toluene, ethanol, and water followed by drying at 60 °C to get func-
tionalized ClPr-Si@GO.
Scheme 1 Synthesis of 1-carbamatoalkyl-2-naphthols using DIL@GO
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N. Patel et al.
Synthesis of graphene oxide supported dicationic ionic liquid (DIL@GO)
Dicationic ionic liquid brush was generated through stepwise covalent grafting of
imidazole under refux condition. Initially, sodium imidazole salt was prepared
through treatment of imidazole (12.5 mmol) with sodium hydride (12.5 mmol) in
dry toluene (100 mL) for 2 h. After that, ClPr-Si@GO (500 mg) was added to the
fask and stirred under refux for 24 h. The obtained imidazole functionalized GO
was treated with 1,4-dibromobutane (12.5 mmol) in toluene (100 mL) under refux,
followed by further treatment with sodium imidazole salt for 24 h. The obtained
solid was dispersed in toluene (50 mL) and treated with 1,4-butanesultone (1.70 mL)
at 100 °C for 6 h, followed by treatment with conc. H2SO4 (0.5 mL) at 50 °C for
8 h. The obtained DIL@GO was washed thoroughly with ethanol and dried under
vacuum.
General procedure for the catalytic synthesis of 1‑carbamatoalkyl‑2‑naphthols
In a typical procedure, a mixture of aromatic aldehyde (1 mmol), 2-naphthol
(1 mmol), alkyl carbamate (1.1 mmol), and DIL@GO (0.1 g) was added to the round
bottom fask and stirred at 80 °C. The progress of reaction was monitored through
TLC. After the completion of reaction, crude product was washed thoroughly with
water to remove unreacted starting material. After that, ethanol was added to solid
product and catalyst was separated through centrifugation. After separation, catalyst
was washed with ethanol and dried under vacuum for further use. Pure 1-carbama-
toalkyl-2-naphthols were obtained through solvent evaporation followed by recrys-
tallization. All synthesized compounds were characterized by physical and spectral
methods and found in agreement with reported.
Spectral data for some representative compounds
Methyl ((2-hydroxynaphthalen-1-yl)(3-nitrophenyl)methyl)carbamate (4c) IR (KBr,
cm−1): 3420, 3292, 3088, 2951, 1686, 1629, 1526, 1476, 1364, 1278, 1194, 1043,
970, 827, 752, 679, 517; 1H NMR (400 MHz, DMSO-d6): δ (ppm) 3.60 (s, 3H), 6.94
(d, J=8.8 Hz, 1H), 7.20 (d, J=9.2 Hz, 1H), 7.28 (t, J=7.6 Hz, 1H), 7.40 (s, 1H),
7.54–7.63 (m, 2H), 7.80–7.84 (m, 2H), 7.95 (s, 2H), 8.06 (d, J=8 Hz, 1H), 8.11 (s,
1H), 10.25 (s, 1H).
Methyl ((4-fuorophenyl)(2-hydroxynaphthalen-1-yl)methyl)carbamate (4e) IR
(KBr, cm−1): 3419, 3194, 3074, 2953, 1682, 1629, 1511, 1438, 1335, 1272, 1157,
1068, 1043, 939, 854, 748, 605, 514; 1H NMR (400 MHz, DMSO-d6): δ (ppm) 3.56
(s, 3H), 6.81 (d, J=8.8 Hz, 1H), 7.06–7.11 (m, 2H), 7.19–7.29 (m, 4H), 7.39 (s,
1H), 7.73–7.82 (m, 3H), 7.88 (d, J=7.6 Hz, 1H), 10.15 (s, 1H).
Benzyl ((2-hydroxynaphthalen-1-yl)(2-nitrophenyl)methyl)carbamate (4 g)
IR (KBr, cm−1): 3421, 3246, 3064, 2949, 1699, 1628, 1524, 1437, 1362, 1273,
1
1184, 1062, 961, 940, 832, 778, 697, 608, 557; H NMR (400 MHz, DMSO-d6): δ
(ppm) 5.02 (d, J=12.8 Hz, 1H), 5.08 (d, J=12.8 Hz, 1H), 7.03 (d, J=8.8 Hz, 1H),
1 3

Graphene oxide supported dicationic ionic liquid: an efcient…
7.26–7.34 (m, 8H), 7.39 (t, J=7.6 Hz, 1H), 7.47 (t, J=7.6 Hz, 1H), 7.58–7.66 (m,
2H), 7.72–7.80 (m, 2H), 7.89 (d, J=8.4 Hz, 1H), 8.13 (d, J=8.8 Hz, 1H), 9.81 (s,
1H).
Benzyl ((3-chlorophenyl)(2-hydroxynaphthalen-1-yl)methyl)carbamate (4j) IR
(KBr, cm−1): 3433, 3242, 3069, 2965, 1674, 1628, 1511, 1439, 1326, 1271, 1227,
1182, 1063, 949, 813, 787, 617, 541; 1H NMR (400 MHz, DMSO-d6): δ (ppm) 5.02
(d, J=12.8 Hz, 1H), 5.10 (d, J=12.8 Hz, 1H), 6.88 (d, J=8.4 Hz, 1H), 7.13 (d,
J=7.2 Hz, 1H), 7.20 (d, J=8.8 Hz, 1H), 7.24–7.42 (m, 10H), 7.78 (d, J=9.2 Hz,
1H), 7.81 (d, J=7.6 Hz, 1H), 7.90–7.96 (m, 2H), 10.20 (s, 1H).
Ethyl ((2,4-dichlorophenyl)(2-hydroxynaphthalen-1-yl)methyl)carbamate (4o)
IR (KBr, cm−1): 3408, 3366, 3070, 2981, 1683, 1628, 1517, 1438, 1335, 1269,
1
1242, 1187, 1053, 937, 860, 797, 744, 598; H NMR (400 MHz, DMSO-d6): δ
(ppm) 1.11 (t, J=6.8 Hz, 3H), 3.96–4.00 (m, 2H), 6.79 (d, J=8.4 Hz, 1H), 7.09
(d, J=8.8 Hz, 1H), 7.26 (t, J=7.2 Hz, 1H), 7.37–7.45 (m, 2H), 7.51–7.53 (m, 2H),
7.73 (d, J=9.2 Hz, 1H), 7.79 (d, J=7.2 Hz, 1H), 7.86 (d, J=8.4 Hz, 1H), 7.98 (d,
J=8.8 Hz, 1H), 9.92 (s, 1H).
Results and discussion
Preparation and characterization of the catalyst (DIL@GO)
GO supported dicationic ionic liquid catalyst was prepared according to the pro-
cedure shown in Scheme 2. GO was synthesized by Hummers method [30]. The
as prepared GO possess oxygen-containing functional groups (such as epoxy,
hydroxyl and carboxyl) available for further functionalization. Post-syntyhetic
modifcation of GO was done by immobilization of (3-chloropropyl)trimethoxysi-
lane [31]. Silylation of GO has been researched by several research groups, which
provides a wide range of transformation possibilities for the designing of a novel
catalytic system [32–34]. This silane functionalized GO was then treated with
Scheme 2 Synthesis of graphene oxide supported dicationic ionic liquid (DIL@GO)
1 3

N. Patel et al.
sodium salt of imidazole and 1,4-dibromobutane to generate dicationic ionic liq-
uid brush. The obtained product was reacted with 1,4-butane sultone followed by
conc. H2SO4 to get GO immobilized –SO3H functionalized dicationic ionic liquid
catalyst (DIL@GO). The synthesized DIL@GO was then characterized by dif-
ferent spectroscopic and microscopic methods such as Fourier transform infrared
spectroscopy (FT-IR), X-ray Difraction (XRD), Transmission electron micros-
copy (TEM), Scanning electron microscopy (SEM), Thermogravimetric analy-
sis (TGA), Energy dispersive X-ray (EDX) spectroscopy and CHNS elemental
analysis.
FT-IR spectra of GO, ClPr-Si@GO, and DIL@GO are shown in Fig. 1. In the
FT-IR spectrum of GO is shown a broad band at 3429 cm−1 for the –OH stretch-
ing vibrations [35, 36]. The bands at 1713 and 1614 cm−1 correspond to C=O
and C=C vibrations of the aromatic ring, respectively [37, 38]. The band at
1384 cm−1corresponds to skeletal vibrations of C–OH [39, 40]. The band at 1229
and 1048 cm−1 are due to C-O (epoxy) and C-O (alkoxy) stretching vibrations,
respectively [41–43]. The spectrum of ClPr-Si@GO shows two bands around 1098
and 1015 cm−1 due to Si–O–Si stretching vibrations [44, 45]. The bands around
2949 and 2945 cm−1 are due to C–H stretching of the alkyl chain. In the spectrum of
DIL@GO, the band around 1634 cm−1corresponds to the C=C absorption peak. The
bands at 1568 and 1441 cm−1 are due to an imidazole ring’s vibration [46]. The band
at 1055 cm−1is due to –SO3 stretching vibration [47–49]. The band at 1206 cm−1
was attributed to absorbing of S=O stretching vibrations [50].
X-ray difraction (XRD) pattern (Fig. 2) of pure GO shows a sharp peak at
2θ=9.5°, which corresponds to the crystalline nature of the pristine graphene oxide.
The crystallite size of GO was determined using the Scherrer equation and found to
be 10.4 nm. After immobilization of ionic liquid, the crystalline state of graphene
oxide transforms into an amorphous state and thus the sharp peak diminishes, and a
broad difraction peak appears in the XRD pattern of DIL@GO.
Fig. 1 FT-IR spectra of (a) GO, (b) ClPr-Si@GO and (c) DIL@GO
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Graphene oxide supported dicationic ionic liquid: an efcient…
Fig. 2 X-ray difraction patterns of (a) GO and (b) DIL@GO
Fig. 3 SEM images of a, b GO and c, d DIL@GO; TEM images of e GO and f DIL@GO
1 3

N. Patel et al.
The structural and morphological analysis of DIL@GO was carried out by
SEM and TEM (Fig. 3). The sheet-like structures can be seen in the SEM images
of pristine GO (Fig. 3a, b). The SEM images of DIL@GO are shown in Fig. 3c,
d, which exhibits less of sheet-like structure and more of a clustered or thicker
structure, which indicates successful grafting of dicationic ionic liquid on the
surface of graphene oxide. The TEM analysis of GO (Fig. 3e) indicates the fat
planer layer of graphene oxide, and in the image of DIL@GO (Fig. 3f), the uni-
formly distributed dicationic ionic liquid can be observed.
The thermogravimetric analysis was done using a nitrogen atmosphere with
a temperature increase rate of 10 °C/min. TGA curves of GO and DIL@GO are
shown in Fig. 4. As shown in the curve of GO, the frst weight loss appears near
100 °C, which can be attributed to the loss of physisorbed water by graphene
oxide. Another weight loss observed between 165 and 245 °C due to the degra-
dation of oxygen-containing functional groups on the surface of GO. The TGA
curve of DIL@GO shows that the functionalized GO is much more thermally sta-
ble than GO. A large weight loss was observed at 550 to 610 °C temperature,
which suggests the thermal decomposition of the immobilized dicationic ionic
liquid on the surface of GO.
Elemental analysis was carried out by using energy dispersive X-ray (EDX)
spectroscopy. The EDX spectrum for DIL@GO is shown in Fig. 5. The spectrum
shows distinct peaks of carbon, nitrogen, oxygen, silicon, and sulfur, which con-
frms the successful grafting of –SO3H functionalized dicationic ionic liquid on
the surface of graphene oxide. Additional confrmation was obtained from CHNS
analysis of the catalyst and found to be 43.37%C, 4.49%H, 2.36%N and 5.68%S.
Fig. 4 TG analysis of (a) DIL@GO and (b) GO
1 3

Graphene oxide supported dicationic ionic liquid: an efcient…
Fig. 5 EDX spectrum of DIL@GO
Catalytic activity of DIL@GO for the synthesis of 1‑carbamatoalkyl‑2‑naphthol
derivatives
The performance of the prepared DIL@GO as a catalyst was explored by the syn-
thesis of 1-carbamatoalkyl-2-naphthols. Diferent parameters were applied for the
optimization of the model reaction between 2-naphthol, benzaldehyde, and methyl
carbamate under solvent-free condition (Table 1). Initially, the reaction was carried
Table 1 Optimization of reaction condition for the model reactiona and comparison with the reported
catalysts
Entry
Catalyst (mg)
Temperature Time (min)
(°C)
Yield (%)
1
2
3
4
5
6
7
8
None
DIL@GO (50)
DIL@GO (50)
DIL@GO (50)
DIL@GO (100)
DIL@GO (150)
[Dsim]HSO4 [51]
Preyssler nanoparticles/SiO2 [52]
4-(1-Imidazolium)-butanesulfonate [53]
SnCl4·5H2O [54]
80
60
80
100
80
80
80
90
80
60
120
10
8
8
3
3
11
3
120
12
3.5
NR
86
89
90
97
97
98
84
78
83
81
9
10
11
NaHSO4/SiO2 [55]
100
a2-Naphthol (1 mmol), benzaldehyde (1 mmol), methyl carbamate (1.1 mmol); solvent free
NR no reaction
1 3

N. Patel et al.
out without any catalyst (entry 1), and no reaction was observed over a period of
120 min. For the subsequent reactions, diferent amounts of catalyst at various tem-
peratures and times were applied (entry 2–6). The optimal reaction condition was
found at 80 °C with 100 mg of catalyst. The catalytic efciency of DIL@GO was
also compared with some reported catalysts (entry 7–11) and found to be more ef-
cient for the model reaction. The efciency and scope of the catalyst were deter-
mined by synthesizing derivatives of 1-carbamatoalkyl-2-naphthols under optimized
conditions (Table 2). To check the substrate scope, diferently substituted aromatic
aldehydes were treated with methyl-, ethyl- and benzyl-carbamates. The catalyst was
found suitable for all the substrates under this study. All the reactions were com-
pleted very smoothly, with short time and high to excellent isolated yields. Based
on the above results, the plausible mechanism for the synthesis of 1-carbamatoalkyl-
2-naphthols using DIL@GO is shown in Scheme 3. In this reaction, the DIL@GO
activates the carbonyl group of aldehyde through the formation of hydrogen bonds,
which then reacts with 2-naphthol to generate an intermediate. The nucleophilic
addition of alkyl carbamate to this intermediate leads to the targeted 1-carbama-
toalkyl-2-naphthol products.
Recyclability of the catalyst (DIL@GO)
Recyclability is one of the most important aspect of catalysis. Recyclability of DIL@
GO was studied in a model reaction between 2-naphthol, benzaldehyde and methyl
carbamate under optimized conditions for fve cycles. The catalyst shows retention in
Table 2 Synthesis of 1-carbamatoalkyl-2-naphthols using DIL@GO at 80 °C under solvent-free condi-
tions
Entry
R
R1
Time (min)
Yield %
M.P. (°C)
Found
Reported
4a
4b
4c
4d
4e
4f
4 g
4 h
4i
C6H5
CH3
CH3
CH3
CH3
3
3
3
5
6
9
7
7
8
9
5
4
6
5
6
97
96
96
97
95
96
95
94
92
91
94
94
91
93
92
222–224
203–205
244–246
197–199
202–204
180–182
198–200
183–185
205–207
202–204
202–204
223–225
209–211
210–212
207–209
224–226 [56]
202–204 [56]
248–250 [56]
196–198 [56]
203–205 [29]
182–184 [56]
198–200 [57]
186–188 [56]
206–208 [56]
200–202 [29]
202–204 [56]
226–228 [56]
210–212 [56]
208–210 [56]
208–210 [28]
4-NO2 C6H4
3-NO2 C6H4
4-Cl C6H4
4-F C6H4
C6H5
2-NO2 C6H4
3-NO2 C6H4
4-F C6H4
3-Cl C6H4
C6H5
4-NO2 C6H4
4-F C6H4
4-Cl C6H4
2,4-Cl2 C6H3
CH3
C6H5CH2
C6H5CH2
C6H5CH2
C6H5CH2
C6H5CH2
CH3CH2
CH3CH2
CH3CH2
CH3CH2
CH3CH2
4j
4 k
4 l
4 m
4n
4o
1 3

Graphene oxide supported dicationic ionic liquid: an efcient…
Scheme 3 Plausible mechanism for DIL@GO catalyzed synthesis of 1-carbamatoalkyl-2-naphthol
derivatives
Fig. 6 Recyclability test for the DIL@GO
catalytic activity as there was no signifcant drop in the yield of fnal product during
fve cycles (Fig. 6). The comparison of the FT-IR spectra of fresh and used DIL@GO
(Fig. 7) suggest no signifcant change in the functionality.
1 3

N. Patel et al.
Fig. 7 FT-IR spectra of (a) fresh and (b) used DIL@GO
Conclusions
In conclusion, graphene oxide supported –SO3H functionalized dicationic ionic liq-
uid (DIL@GO) was found to be a highly efcient and environment friendly hetero-
geneous catalyst for the synthesis of 1-carbamatoalkyl-2-naphthol derivatives. The
present methodology has some notable advantages such as recyclability, easy cata-
lyst separation and handling, shorter reaction time, a solvent-free approach, and high
yield.
Acknowledgements The authors are grateful to the authorities of Charotar University of Science and
Technology (CHARUSAT), Changa for providing necessary research facilities.
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