Magnetically retrievable magnetite (Fe3O4) immobilized ionic liquid: An efficient catalyst for the preparation of 1-carbamatoalkyl-2-naphthols

Article abstract of DOI:10.1039/c5cy00849b

A magnetite (Fe₃O₄) supported -SO₃H functionalized benzimidazolium based ionic liquid has been synthesized via covalent grafting of benzimidazole on a (3-chloropropyl)triethoxysilane functionalized magnetic nanoparticle followed by quaternization reaction with 1,4-butane sultone. The obtained magnetic nanoparticle supported ionic liquid (IL@MNP) has been characterized by FT-IR, TGA, TEM, XRD, VSM, EDX and elemental analysis. The performance of the prepared catalyst was evaluated in the preparation of 1-carbamatoalkyl-2-naphthols. The magnetite supported catalyst showed excellent catalytic activity and the corresponding products were obtained in high yields in all the tested cases. The heterogeneous nature of the magnetite favoured easy recovery and recyclability of the catalyst through magnetic decantation making the protocol highly advantageous over conventional procedures.

Full text of DOI:10.1039/c5cy00849b

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Magnetically retrievable magnetite (Fe3O4) immobilized ionic
liquid: an efficient catalyst for the preparation of 1-
carbamatoalkyl-2-naphthols
Received 00th January 20xx,
Accepted 00th January 20xx
Harsh N. Dadhania,a Dipak K. Ravala and Abhishek N. Dadhania*b
DOI: 10.1039/x0xx00000x
Magnetite (Fe3O4) supported –SO3H functionalized benzimidazolium based ionic liquid has been synthesized via covalent
www.rsc.org/
grafting of benzimidazole on
a (3-chloropropyl)triethoxysilane functionalized magnetic nanoparticle followed by
quarternization reaction with 1,4-butane sultone. The obtained magnetic nanoparticle supported ionic liquid (IL@MNP)
has been characterized by FT-IR, TGA, TEM, XRD, VSM, EDX and Elemental analysis. The performance of prepared catalyst
was evaluated in the preparation of 1-carbamatoalkyl-2-naphthols. The magnetite supported catalyst showed excellent
catalytic activity and corresponding products were obtained in high yields in all the tested cases. The heterogeneous
nature of the magnetite favoured easy recovery and recyclability of catalyst through magnetic decantation, which makes
the protocol highly advantageous over conventional procedures.
product 1-aminoalkyl-2-naphthols, which possess interesting
1. Introduction
biological activities.18-21 These derivatives have been evaluated
23
for their hypotensive and bradycardic effects.22,
Many
Ionic liquids have attracted increasing interest of chemists, both
in academia and industry due to their unique physical and
chemical properties.1-3 Task-specific ionic liquids have received
much attention as catalyst and alternative reaction media for
various chemical transformations.4, 5 We also reported highly
efficient methodologies for the synthesis of pharmaceutically
important organic moieties using ionic liquid.6-10 In these
methodologies, the ionic liquid not only significantly enhanced
the reaction rate by its inherent Brønsted acidity, but also
provided the homogeneity to the reaction media. However, due
to homogeneous nature of ionic liquid, we encountered a
tedious problem of catalyst separation. To overcome this
problem an ideal approach was thought worth to immobilize the
corresponding ionic liquid on solid support. Such immobilized
ionic liquid facilitates the separation process, easy handling and
storage.11, 12
Magnetically supported catalyst can easily and efficiently be
separated from the reaction mixture by an external magnet. It
facilitates remarkable catalyst recovery without the need for
filtration. Magnetic nanoparticles (MNPs) have emerged as the
support to homogeneous catalyst; due to their insoluble and
paramagnetic nature.13, 14. The ease of separation is one of the
most attractive features of MNPs as compared to its
homogeneous and heterogeneous counterparts.15-17
synthetic strategies for the preparation of 1-carbamatoalkyl-2-
naphthols have been reported by one-pot multi-component
condensation reaction between 2-naphthol, aromatic aldehydes
and alkyl carbamates using various catalysts.24-28 However,
some of these methodologies endure one or more drawbacks
such as longer reaction time, harsh reaction conditions, poor to
moderate yields, large amount of catalyst, use of expensive
metal catalysts and tedious work up. The literature survey
encouraged us to work in this relatively novel but broadly
expanding field.
In this report, we introduce a new magnetic nanoparticle
supported –SO3H functionalized benzimidazolium based acidic
ionic liquid, as a highly efficient catalyst for the preparation of
1-carbamatoalkyl-2-naphthols (Scheme 1) in good yield with
significantly enhanced reaction rate as compared to other
reported methods. IL@MNP was easily separated by magnetic
decantation and was recycled for six times with retention of
activity in the model reaction.
On the other hand, 1-carbamatoalkyl-2-naphthols have emerged
as molecules of great interest mainly due to their hydrolyzed
Scheme 1 Synthesis of 1-carbamatoalkyl-2-naphthols using IL@MNP
aDepartment of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388120,
Gujarat India.
bDepartment of Chemical Sciences, P. D. Patel Institute of Applied Sciences,
Charotar University of Science and Technology, Changa 388421, Gujarat India.
E-mail: abhishekdadhania.bt@charusat.ac.in
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Scheme 2 Synthesis of magnetically supported ionic liquid (IL@MNP)
2. Results and Discussion
2.1 Preparation and characterization of catalyst (IL@MNPs)
The catalyst was prepared according to the procedure shown in
scheme 2. We used Fe3O4 nanoparticles of approximately 8-10
nm for solid support, which were prepared via co precipitation
method29. Subsequently, these particles were functionalized
using (3-chloropropyl)triethoxysilane in ammonia solution by
surface capping method30 to produce (1). Functionalization
provided good stability to nano Fe3O4 against aggregation and
acid corrosion. Furthermore, it also offered suitable binding
sites for further modification. Then, (1) was reacted with
sodium salt of benzimidazole in benzene to yield the precursor
(2). This was further subjected to quarternization reaction with
1,4-butane sultone followed by treatment with one equivalent
H2SO4 to yield the magnetically retrievable acidic ionic liquid
Figure 1 Transmission electron microscope (TEM) images of IL@MNP [fresh (a) & (b),
recycled (c)]
IL@MNP (3)
.
The morphology of IL@MNP was checked by transmission
electron microscopy (TEM) (Figure 1). TEM images displayed
the dark magnetite core surrounded by benzimidazolium linkers
and the core-shell structure of catalyst with an average size of
20-22 nm. In addition, the XRD study of the silane
functionalized magnetic nanoparticle was carried out to confirm
the crystalline nature and surface state. The XRD pattern
(
Figure 2) of the silane functionalized nanoparticles showed
Figure 2 X-Ray diffraction pattern of silane functionalized magnetic nanoparticles
the diffraction peak positions and the relative intensities of the
peaks matched well with the standard Fe3O4 sample (JCPDS
file No. 19-0629).
The detailed investigation about functionalization of magnetic
nanoparticle was done by FT-IR spectroscopy (Figure 3). All
spectra showed characteristic broad band around 3420 cm-1 due
to Si-OH group and adsorbed water. Spectrum (3a) shows the
characteristic band of the Fe–O bond vibration of iron oxide
core at 585 cm−1 31. The strong band observed at around 1095
cm-1 is due to Si–O–Si stretching modes of the silica shell32.
1
Additionally, the band at 2955 cm− , corresponds to the –CH2
group of the chloro-propyl group. Spectrum (3b) shows typical
bands at 1565 and 1635 cm-1 due to C=N and C=C vibration of
benzimidazole ring respectively33. Additionally, the band
observed at 3145 cm-1 is due to sp2 C–H stretching vibrations of
benzimidazole ring revealed the grafting of benzimidazole
moiety. Spectrum (3c) shows the strong bands at 1041 and
1137 cm-1 due to S=O stretching vibration34.
2 | J. Name., 2012, 00, 1-3
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using external magnet. Moreover, no hysteresis was observed
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before and after functionalization whDicOhI: 10d.e1m03o9n/Cs5trCaYt0e0d849itBs
superparamagnetic characteristics35, 36
.
Figure 3 FT-IR spectra of (a) ClPr-Si@Fe3O4, (b) 3-(1-benzimidazole) Pr-Si@Fe3O4 and
(c) IL@MNP
Thermal stability of the catalyst was determined by
thermogravimetric (TG) analysis (Figure 4). The loss of
adsorbed water on the support and silanol groups resulted into
initial weight loss of 3.79% up to 105 ºC. The complete loss of
covalently attached organic moiety was observed in the
temperature range from 200 to 600 ºC. The amount of organic
moiety was found to be about 27% against total solid catalyst.
The organic loading in the catalyst was found to be 0.573
mmol·g-1. The loading of IL obtained from TG analysis was
found in good agreement with elemental analysis. Elemental
analysis of catalyst showed 6.75% S, which is equal to IL
loading 0.56 mmol·g-1.
Figure 5 Magnetization curves obtained by VSM at room temperature for (a)
Fe3O4 and (b) IL@MNP
Figure 6 EDX spectrum of IL@MNP
The energy-dispersive X-ray (EDX) spectrum of the IL@MNP
(Figure 6) show the presence of elements C, N, O, Si, S and Fe
in the catalyst, which revealed the grafting of benzimidazolium
ionic liquid on the surface of magnetic nanoparticles.
2.2 Catalytical activity of IL@MNPs for the preparation of 1-
carbamatoalkyl-2-naphthols
The efficacy of the prepared catalyst in preparation of 1-
carbamatoalkyl-2-naphthols was checked. The reaction
condition was optimized on model reaction between 2-
naphthol, benzaldehyde and methyl carbamate under solvent
Figure 4 TG analysis of IL@MNP
The magnetic properties of the IL@MNP and the neat Fe3O4
were checked by vibrating sample magnetometry (VSM). The
field dependent magnetization curves measured at room
temperature with the field sweeping from -10 000 to 10 000 Oe
are depicted in Figure 5. The saturation magnetization of the
sample was found to reduce from 8.95 to 5.88 emu.g-1, due to
the functionalization of Fe3O4. However, it was still sufficient
for magnetic separation of the catalyst from reaction mixture
free condition to yield 4a (Table 1). Initially, the model
reaction without any catalyst or sole Fe3O4 as catalyst showed
no reaction over a period of 60 min (Entry 1). From the results
of subsequent reactions with different amount of catalyst at
various temperatures (Entry 2 to 7), the reaction at 80 ºC with
1.5 mol% of catalyst was found to be the most optimum
reaction condition with 96% yield after 5 min (Entry 5). The
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Table 2 Solvent free synthesis of 1-carbamatoalkyl-2-naphthols using IL@MNPs at 80°C
efficiency of prepared catalyst was also compared with some
other reported catalysts for the synthesis of 4a. Present catalyst
is found better than other reported catalysts in terms of catalyst
recovery, reaction temperature, reaction time and yield. To
check the efficiency and generality of the catalyst, the reaction
of 2-naphthol was carried out with a variety of aryl aldehydes
and alkyl carbamates to yield the corresponding 1-
carbamatoalkyl-2-naphthol derivatives under optimal reaction
condition derived from the model reaction. In all the tested
cases, excellent yields of corresponding 1-carbamatoalkyl-2-
naphthol derivatives were obtained in short reaction time
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DOI: 10.1039/C5CY00849B
M. P. (°C)
Time
(min)
Yield
%
Entry
R
R1
Found
Reported
224 - 226
202 -204
248 - 250
214 - 216
196 – 198
202 – 204
210 – 212
226- 228
218 - 220
208 – 210
182 – 184
206 – 208
166 - 168
194 - 196
186 - 188
222 - 22525
200 - 20225
253 - 25525
172 - 17427
4a
4b
4c
4d
4e
4f
C6H5
CH3
CH3
5
4
96
97
97
94
96
93
92
95
91
93
94
90
90
94
92
4-NO2C6H4
3-NO2C6H4
4-BrC6H4
4-ClC6H4
C6H5
CH3
4
CH3
10
7
198 - 20025
CH3
-
CH3CH2
CH3CH2
CH3CH2
CH3CH2
CH3CH2
PhCH2
PhCH2
PhCH2
PhCH2
PhCH2
5
-
4g
4h
4i
4-FC6H4
6
(
Table 2). The plausible mechanism for the formation of 1-
carbamatoalkyl-2-naphthols catalyzed by IL@MNPs is
proposed in Scheme 3
-
4-NO2C6H4
4-BrC6H4
4-ClC6H4
C6H5
4
.
-
7
-
4j
7
180 – 18238
202 – 20338
165 – 16738
20038
4k
4l
12
10
12
5
4-FC6H4
4m
4n
4o
4-MeoC6H4
4-NO2C6H4
3-NO2C6H4
196 - 19738
5
2.3 Catalyst recyclability and leaching study
Recyclability and leaching, important factors to judge the
sustainability of any catalyst, were checked on model reaction
between 4-nitrobenzaldehyde, ethyl carbamate and 2-naphthol.
The catalyst was easily recovered by magnetic decantation after
the reaction and was reused in the same model reaction for next
five consecutive cycles with comparable retention in its activity
Scheme 3 Plausible mechanism for the synthesis of 1-carbamatoalkyl-2-naphthols using
IL@MNP
(
Figure 7). The FT-IR spectrum (Figure 8) and TEM image
Table 1 Optimization of reaction condition for the synthesis of 4aa and comparison with (Figure 1) of the recovered catalyst also suggest no significant
the reported catalysts.
change in functionality.
Temperature
Time
(min)
60
15
11
9
5
9
5
Yield
(%)b
NRc
81
89
90
96
85
97
Entry
Catalyst (mol %)
(°C)
80
60
80
100
80
1
2
3
4
5
6
7
None/ Fe3O4 (1.5)
IL@MNP (1.0)
IL@MNP (1.0)
IL@MNP (1.0)
IL@MNP (1.5)
IL@MNP (1.5)
IL@MNP (2.0)
70
80
4-(1-Imidazolium)-
butanesulfonate
Preyssler nanoparticles/SiO2
[Dsim]HSO4
8
80
120
7824
9
90
80
100
60
3
8425
9827
8126
8337
10
11
12
11
3.5
12
NaHSO4/SiO2
SnCl4.5H2O
Figure 7 Recyclability test of catalyst
a Reaction condition: 2-naphthol (2 mmol), benzaldehyde (2 mmol) and methyl
carbamate (2.2 mmol), solvent free. b Isolated yield. c No reaction was observed.
To check leaching of the catalyst, hot EtOH (15 mL) was added
after 2 min of reaction time and the catalyst was easily removed
using external magnet. The same reaction was continued for
another 30 min and was monitored using TLC, Further
conversion was not observed during this period and the overall
yield was found to be 52%. It proved that leaching of the
catalyst was not occurring during the process.
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temperature was maintained for 2 h. After the solution turned
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DOI: 10.1039/C5CY00849B
brown, it was cooled to room temperature and FeSO4·7H2O
(2.8 g) was added. The pH of resultant solution was adjusted to
10 by adding 0.1 M NaOH solution. The obtained precipitates
were subjected to ultrasonic irradiation at 30 to 35 °C for 30
min. Black powder (Fe3O4) was obtained after 5h which was
washed several times with water and dried under vacuum.
Coating
of
Fe3O4
nanoparticles
with
(3-
chloropropyl)triethoxysilane was performed via surface
capping method30. A dispersion of Fe3O4 (6 g) was prepared in
ethanol (200 mL) under sonication for 30 minutes. After that
(3-chloropropyl)triethoxysilane (15 mL) and ammonia solution
(15 mL) were added to the dispersed ethanolic solution of
Fe3O4 and stirred for 24 h at room temperature. The resulting
(3-chloropropyl)triethoxysilane coated Fe3O4 nanoparticles
were washed 4 times with aliquot of 10 mL ethanol each time
Figure 8 FT-IR spectra of fresh and used catalyst.
3. Conclusions
and dried under vacuum
.
We have synthesized and applied a novel magnetic nanoparticle
supported –SO3H functionalized benzimidazolium based ionic
liquid (IL@MNP), as a highly efficient and environmentally
benign catalyst for the synthesis of 1-carbamatoalkyl-2-
naphthols. The notable advantages of this methodology are
magnetic separability and reusability of the catalyst, ease of
reaction, short reaction times, high yields and solvent-free
greener protocol. Thus, it provides an attractive alternative to
the existing methodologies.
4.3 Synthesis of 3-(1-benzimidazole)propyltriethoxysilane@ Fe3O4
(3-(1-benzimidazole)Pr-Si@Fe3O4)
For
covalent
grafting
of
benzimidazole on (3-
chloropropyl)triethoxysilane coated Fe3O4 nanoparticles,
sodium salt of benzimidazole was prepared by reacting
benzimidazole (1.17 g) with 50% sodium hydride in mineral oil
(0.479 g) in dry benzene (25 mL) under inert atmosphere for 3
h. The resultant solution of sodium benzimidazole was mixed
with ClPr-Si@Fe3O4 (5 g) and refluxed for 24 h to get the
precursor 2. It was separated by external magnet, washed
thoroughly with ethanol and dried under vacuum.
4. Experimental
4.1 Materials and methods
Magnetite (Fe3O4) was prepared according to a procedure
reported in literature29 and was used for the support. (3-
4.4 Synthesis of IL@MNP
chloropropyl)triethoxysilane,
benzimidazole,
1,4-butane
3-(1-benzimidazole)Pr-Si@Fe3O4 (3g) and 1,4-butane sultone
(0.34 g) were dispersed in toluene (30 mL) and stirred at 100 ºC
for 6 h. The resultant particles were further treated with conc.
H2SO4 (0.133 mL) at 50 ºC for 8 h and then washed with
toluene. After cooling, the resultant IL@MNP was collected
magnetically, washed thoroughly with ethanol and dried in a
vacuum oven at 100°C.
sultone, were purchased from Sigma–Aldrich, India and were
used without further purification. FT-IR spectra were recorded
on Thermo Nicolet 6700 spectrophotometer using KBr pellets.
Thermal gravimetric analysis (TGA) was performed at a
heating rate of 10°C/min on a Mettler-Toledo TGA. X-ray
diffraction (XRD) study was done on Bruker, D2 Phaser. The
magnetization curves were obtained by a vibrating sample
magnetometer
(VSM-7400,
LAKE
SHORE,
USA).
Transmission electron microscopy (TEM) was done on JEOL,
JEM 2100 model. The EDX was performed using a JOEL JSM-
5610 scanning electron microscope. C, H, N elemental analysis
was carried out on PerkinElmer 2400 series-II elemental
analyzer (PerkinElmer, USA). All the synthesized compounds
were characterized by 1H NMR (400 MHz Bruker Avance,
Switzerland). Melting points were determined on
µThermoCal10 (Analab Scientific Pvt. Ltd) melting points
apparatus and were uncorrected.
4.5 General procedure for the synthesis of 1-carbamatoalkyl-2-
naphthols
A mixture of aldehyde (2 mmol), 2-naphthol (2 mmol), alkyl
carbamate (2.2 mmol) and IL@MNP (1.5 mol %) was stirred
magnetically and after solidification with a small glass rod at 80
ºC in an oil bath. After completion of reaction as indicated by
TLC, the crude reaction mass was washed with hot water to
remove unreacted water soluble starting material. Ethanol was
added to the solid reaction mass and the catalyst was separated
by external magnet from the product solution. Recovered
IL@MNP was washed with ethanol, and used for subsequent
cycles after drying under vacuum. Pure 1-carbamatoalkyl-2-
naphthols were obtained by evaporation of solvent followed by
4.2 Synthesis of (3-chloropropyl)triethoxysilane coated Fe3O4
nanoparticles (ClPr-Si@Fe3O4).
Magnetite (Fe3O4) nanoparticles were synthesized using a
coprecipitation method29. Initially, FeCl3·6H2O (5.4 g) and urea
(3.6 g) were dissolved in water (200 mL) at 90 °C. The
recrystallization.
The
synthesized
1-carbamatoalkyl-2-
naphthols were characterized by the physical and spectral data.
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4.5.1
Methyl(2-hydroxynaphthalen-1-yl)(phenyl)methyl 7.21 (d, J = 8.8 1H), 7.29 (t, J = 7.2, 1H), 7.39-7.47 (m, 3H),
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DOI: 10.1039/C5CY00849B
carbamate (4a) : Yield 96% ; mp 224-226 °C; H NMR (400 7.79-7.91 (m, 3H), 8.14 (d, J = 2.8 Hz, 1H), 8.16 (d, J = 2.8 Hz,
MHz, DMSO-d6): δ (ppm) 3.58 (s, 3H), 6.88 (d, J = 8.8 Hz, 2H) 10.21 (s, 1H) ppm; Anal. Calcd. for C20H18N2O5: C, 65.57 ;
1H), 7.15–7.41 (m, 8H), 7.68 (d, J = 7.4 Hz, 1H, NH), 7.76– H, 4.95 ; N, 7.65%. Found: C, 65.60; H, 4.86; N, 7.62%.
7.82 (m, 2H), 7.93 (d, J = 8.0 Hz, 1H), 10.13 (s, 1H, OH); Anal.
Calcd for: C19H17NO3: C, 74.25; H, 5.58; N, 4.56%. Found: C, 4.5.8
74.25; H, 5.55; N, 4.52%.
Ethyl(4-Chlorophenyl)(2-hydroxynaphthalen-1-yl)
methyl carbamate (4j) : Yield 93% ; mp 208-210 °C; 1H NMR
(400 MHz, DMSO-d6): δ (ppm) 1.17 (t, J = 6.8, 3H), 4.02 (d, J
= 6.8 1H), 4.05 (d, J = 6.8, 1H), 6.83 (d, J = 8.4, 1H), 7.20-7.42
(m, 7H), 7.64-7.83 (m,3H), 7.90 (d, J = 5.6, 1H), 10.14 (s, 1H,
OH) ppm; Anal. Calcd for C20H18ClNO3: C, 67.51; H, 5.10; N,
3.94%. Found: C, 67.50; H, 5.05; N, 3.94%.
4.5.2
Methyl(2-hydroxynaphthalen-1-yl)(4-nitrophenyl)
1
methyl carbamate (4b) : Yield 97% ; mp 202-204 °C; H
NMR (400 MHz, DMSO-d6): δ (ppm) 3.60 (s, 3H), 6.95 (d, J =
7.2 Hz, 1H), 7.22 (d, J = 8.4 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H),
7.40 (d, J = 7.2 Hz, 1H), 7.47 (d, J = 7.2 Hz, 2H), 7.79–7.89
(m, 4H), 8.15 (d, J = 7.6 Hz, 2H), 10.22 (s, 1H, OH); Anal.
Calcd for: C19H16N2O5: C, 64.77; H, 4.58; N, 7.95%. Found: C,
64.70; H, 4.56; N, 7.93%.
4.5.9
Benzyl(2-hydroxynaphthalen-1-yl)(phenyl)methyl
1
carbamate (4k) : Yield 94% ; mp 182-184 °C; H NMR (400
MHz, DMSO-d6): δ (ppm) 5.08 (d, J = 12.8 Hz, 1H), 5.15 (d, i
= 12.8 Hz, 1H), 6.99 (d, J = 8.8 Hz, 1H), 7.07–7.59 (m, 13H),
7.79–7.84 (m, 3H), 7.98 (d, J = 6.4 Hz, 1H, NH), 10.19 (s, 1H,
OH); Anal. Calcd for C25H21NO3: C, 78.31; H, 5.52; N, 3.65%.
Found: C, 78.28; H, 5.57; N, 3.63%.
4.5.3 Methyl(4-Bromophenyl)(2-hydroxynaphthalen-1-yl)
1
methyl carbamate (4d) : Yield 94% ; mp 214-216 °C; H
NMR (400 MHz, DMSO-d6): δ (ppm) : 3.57 (s, 3H), 6.82 (d, J
= 8.8 Hz, 1H), 7.16 (d, J = 8.0 Hz, 2H), 7.21 (d, J = 8.8 Hz,
1H), 7.28 (t, J = 7.2 Hz, 1H), 7.40 (t, J = 7.2 Hz, 1H), 7.44 (d, J
= 6.0 Hz, 2H), 7.73-7.82 (m, 3H), 7.88 (d, J = 6.8 Hz, 1H),
10.15 (s, 1H, OH); Anal. Calcd for C19H16BrNO3: C, 59.08; H,
4.18 ; N, 3.63%. Found: C, 59.05; H, 4.15; N, 3.65%.
4.5.10
Benzyl(4-fluorophenyl)(2-hydroxynaphthalen-1-yl)
methyl carbamate (4l) : Yield 90% ; mp 206-208 °C; 1H NMR
(400 MHz, DMSO-d6): δ (ppm) 5.03 (d, J = 12.8 Hz, 1H), 5.09
(d, J = 12.8 Hz, 1H), 6.88 (d, J = 8.8 Hz, 1H), 7.01–7.16 (m,
2H), 7.21–7.36 (m, 10H), 7.77–7.90 (m, 4H), 10.16 (s, 1H, OH)
ppm; Anal. Calcd for C25H20FNO3: C, 74.80; H, 5.02; N,
3.49%. Found: C, 74.70; H, 5.01; N, 3.47%.
4.5.4
Methyl(4-chlorophenyl)(2-hydroxynaphthalen-1-yl)
methyl carbamate (4e) : Yield 96% ; mp 196-198 °C; 1H
NMR (400 MHz, DMSO-d6): δ (ppm) 3.57 (s, 3H), 6.85 (d, J =
8.4 Hz, 1H), 7.21–7.42 (m, 7H), 7.77–7.82 (m, 3H), 7.89 (d, J =
7.2 Hz, 1H), 10.17 (s, 1H, OH) ppm; Anal. Calcd for
C19H16ClNO3: C, 66.77; H, 4.72; N, 4.10%. Found: C, 66.75;
H, 4.69; N, 4.07%.
4.5.11
Benzyl(2-hydroxynaphthalen-1-yl)(3-Nitrophenyl)
methyl carbamate (4o) : Yield 92% ; mp 186-188 °C; 1H
NMR (400 MHz, DMSO-d6): δ (ppm) 5.05 (d, J = 12.0 Hz,
1H), 5.13 (d, J = 12.0 Hz, 1H), 6.98 (d, J = 8.8 Hz,1H), 7.21 (d,
J = 8.8 Hz, 1H), 7.25-7.43 (m, 7H), 7.56 (t, J = 8.0 Hz, 1H),
7.67 (d, J = 8.0 Hz, 1H), 7.80-7.84 (m,2H), 7.94 (d, J = 7.6 Hz,
1H), 8.06-8.17 (m, 3H), 10.22 (s, 1H, OH) ppm; anal. calcd for
C25H20N2O5: C, 70.08; H, 4.71; N, 6.54%. Found: C, 70.05; H,
4.72; N, 6.55%.
4.5.5
Ethyl(2-hydroxynaphthalen-1-yl)(phenyl)methyl
1
carbamate (4f) : Yield 93% ; mp 202-204 °C; H NMR (400
MHz, DMSO-d6): δ (ppm) 1.17 ( t, J = 6.8, 3H), 4.01 (d, J =
7.2, 1H), 4,04 (d, J = 7.2, 1H), 6.88 (d, J = 8.8, 1H), 7.17-7.30
(m, 7H), 7.40 (t, J = 7.2, 1H), 7.59 ( S, 1H), 7.76-7.82 (m, 2H),
7.93 (d, J = 7.2 Hz, 1H, NH), 10.13 (s, 1H, OH) ppm ; Anal.
Calcd for C20H19NO3: C, 74.75; H, 5.96; N, 4.36%. Found: C,
74.66; H, 5.92; N, 4.34%.
Acknowledgements
We gratefully acknowledge the research facilities provided by
Department of Chemistry, Sardar Patel University and P. D.
Patel Institute of Applied Sciences, CHARUSAT. Authors also
thankful to CSMCRI, Bhavnagar and SICART, Vallabh
Vidyanagar for providing analysis facilities at concessional
rates. H.N.D. thanks the University Grant Commission, New
Delhi for research fellowship under UGC BSR Scheme 2013 -
2015.
4.5.6
Ethyl(4-Fluorophenyl)(2-hydroxynaphthalen-1-yl)
methyl carbamate (4g) : Yield 92% ; mp 210-212 °C; 1H
NMR (400 MHz, DMSO-d6): δ (ppm) 1.16 (t, J = 6.8, 3H), 3.99
(d, J = 6.8, 1H), 4.03 (d, J = 6.8, 1H), 6.82 (d, J = 8.4, 1H),
7.08 (t, J = 8.8, 2H), 7.19-7.30 (m, 4H), 7.40 (t, J = 6.8, 1H),
7.70 (d, J = 8.8, 1H), 7.80-7.89 (m, 2H), 7.92 (d, J = 8.0, 1H),
10.15 (s, 1H, OH)ppm; Anal. Calcd for C20H18FNO3: C, 70.78
; H, 5.35 ; N, 4.13%. Found: C, 70.75; H, 5.34; N, 4.13%.
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6 | J. Name., 2012, 00, 1-3
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