RSC Advances
Paper
light weight, therefore, the disposal of bulky RHA could be a next step, the material was dried to give 2.5 g RHA–[pmim]Cl as
problem. RHA contains considerable amount of amorphous a gray powder.
silica up to 80% and small proportion of impurities such as
21
K O, Na O and Fe O . Therefore, RHA possesses high silica Preparation of 1-methyl-3-(trimethoxysilylpropyl)-
2
2
2 3
content, so it has been employed to produce zeolites and silica imidazolium hydrogen sulfate supported on RHA (RHA–
22,23
powders.
[pmim]HSO4)
Several papers have been published on the application of the
3
g of RHA–[pmim]Cl was suspended in 20 mL of dry CH Cl .
2
2
modied amorphous silica obtained from rice husk ash as the
Under vigorous stirring 2.9 mmol of concentrated H
2
SO
4
24–26
catalyst.
Although useful, the reported method for the
ꢀ
(
97%) was added dropwise in an ice bath (0 C). The mixture
preparation of pure silica from rice husk ash needs various
was then warmed to room temperature and heated under
reux for 30 h. When the formed HCl was completely distilled
22
stages and a long time. On the basis of these points and our
investigations we concluded that, at the same conditions, the
use of RHA as a support for the preparation of the catalysts is
better than the use of silica which is prepared via precipitation
off the solution was cooled and CH
vacuum to afford RHA–[pmim]HSO4 (3.16 g) as the product
Scheme 1).
2 2
Cl was removed under
(
27,28
method during various stages and long time.
General procedure for N-formylation of amines
Experimental section
Reagents and materials
Amine (1 mmol) was added to a mixture of RHA–[pmim]HSO4
(
10 mg, 0.8 mol%) and formic acid (2 mmol) and the resulting
ꢀ
mixture was stirred at 60 C for the appropriate time. Aer
Chemicals were purchased from Fluka, Merck, and Aldrich
chemical companies. All yields refer to the isolated products.
Products were characterized by comparison of their physical
constants and also their IR and NMR spectra with authentic
samples and those reported in the literature. The purity
determination of the substrate and reaction monitoring
were accompanied by TLC on silicagel polygram SILG/UV 254
plates.
completion of the reaction (monitored by TLC), ethylacetate
(
10 mL) was added and the catalyst was separated by ltration.
The organic phase was washed with water (2 ꢂ 10 mL) and dried
over Na SO . The solvent was removed under reduced pressure
2
4
to afford the desired product. The spectral data of new
compounds are as follow:
0
N,N -(1,4-phenylene)-diformamide:
Characterization
The FT-IR spectra were run on a VERTEX 70 Brucker company
(Germany). Thermogravimetric analyses (TGA) were performed
on Polymer Laboratories PL-TGA thermal analysis instrument
ꢀ ꢀ
England). Samples were heated from 25 to 600 C at ramp 10 C
(
ꢁ
1
min under N2 atmosphere. Scanning election microphoto-
graphs (SEM) were obtained on a SEM-Philips XL30. X-ray
diffraction (XRD) measurements were performed at room
temperature on diffractometer Model XRD 6000, PHILIPS Xpert
˚
pro using Co-Ka radiation (K ¼ 1.7890 A) with the beam voltage
1
H NMR (DMSO-d
), 7.52–7.54 (m, 6H, H
.6 (dd, J ¼ 11.2 Hz, J ¼ 2.4 Hz, 1H, H ), 10.07 (d, J ¼ 11.2 Hz,
6
, 400 MHz): 7.13 (s, 1H, H
1
), 7.15 (d, J ¼
and a beam current of 40 kV and 30 mA, respectively.
2
8
1
1
.4 Hz, 1H, H
2
3
), 8.23 (s, J ¼ 2 Hz, 3H, H
4
),
1
2
5
Preparation of 1-methyl-3-(trimethoxysilylpropyl)-
imidazolium chloride ([pmim]Cl)
1
3
H, H ), 10.14 (s, 3H, H ); C NMR (DMSO-d , 100 MHz): 118.7,
6
6
6
19.3, 120.1, 120.6, 134.4, 134.4, 134.8, 159.7, 159.7, 162.9.
A mixture of 10 mmol 1-methylimidazole and 10 mmol (3-
chloropropyl)trimethoxysilane was reuxed at 90 C for 30 h.
Then, the reaction mixture was cooled down. The crude product
ꢀ
Results and discussion
was washed with Et O (2 ꢂ 5 mL) and dried under vacuum. The Catalyst characterization
2
product (slightly yellow viscous oil) was obtained.
4
The infrared spectra of RHA and RHA–[pmim]HSO are shown
in Fig. 1. In the case of RHA, the peaks at 3460 cm is attrib-
ꢁ1
Preparation of 1-methyl-3-(trimethoxysilylpropyl)-
imidazolium chloride supported on RHA (RHA–[pmim]Cl)
uted to the asymmetric stretching mode of –OH group and the
ꢁ1
peaks at 1640 cm is attributed to the bending mode of the
ꢁ1
0.6 g (2 mmol) of [pmim]Cl was dissolved in 25 mL of CH
2
Cl
2
adsorbed water. The strong peak at 1100 cm is assigned to the
27
and treated with 2 g of RHA (used in our previous report ). The asymmetric stretching mode of Si–O–Si and the peaks at 801
reaction mixture was reuxed with stirring for 3 days. Then, the and 468 cm are assigned to the symmetric stretching and
reaction mixture was cooled to room temperature, the solid bending modes of Si–O, respectively.
was isolated by ltration and washed with 20 mL of boiling The RHA–[pmim]Cl and RHA–[pmim]HSO
dichloromethane to remove the unreacted ionic liquid. In the terized on the basis of their FT-IR (Fig. 1). The peaks at 1575 and
ꢁ1
17
4
are also charac-
50632 | RSC Adv., 2014, 4, 50631–50638
This journal is © The Royal Society of Chemistry 2014