R.L. Magar et al. / Journal of Molecular Catalysis A: Chemical 374–375 (2013) 118–124
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OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
O
O
NH2
Si
OCH3
MeO
MeO
MeO
OH
O
Conc. H2SO4
+ 3
NH2
Si
Si
Tolune, 1100, 10h
NH2
Si
O
OCH3
OH
O
O
O
OH
NH2
Scheme 1. Synthesis of solid supported amino functionalized catalyst GN3.
The recovered solid catalyst was readily regenerated for further
use. These novelties in hand accelerated considerable amount of
research for the use of such catalysts.
2.2. General procedure for the synthesis of catalyst GN3
Functionalized silica was prepared by suspending the silica
gel in 3-aminopropyl-trimethoxysilane (APTMS) solution using
APTMS: silica gel ratios (w/w) 0.3 (1.68 mmol/g) in dry toluene
(solid: liquid) 10:100 w/v). The mixture was refluxed at boiling
temperature for 24 h. After completion of reaction the mixture was
cooled and filtered off. The obtained solid was washed with iso-
propanol thoroughly, and dried at 100 ◦C overnight. The obtained
solid was designated as GN3 and used as the catalyst.
supported heterogeneous catalysts in organic transformations. We
inspired with the findings, when Jasra et al. reported the synthesis
of amino functionalized silica gel (GN3) for the adsorption of Cu (II)
ion [27]. It showed that, polyamine group present in the structure
having strong basic properties selectively adsorption due to Cu (II)
ions. Surprisingly, literature data pointed that, such heterogeneous
polyamine catalyst has not been explored in the organic transfor-
mations. Thus, it is sought to utilize the basic property of amino
functionalized silica gel catalyst (GN3).
2.3. General procedure for the synthesis of
2-amino-4H-chromene derivatives
Owing to the importance of biologically active 2-amino-4H-
chromenes, in the present study it is demonstrated a simple
and highly efficient method for the synthesis of 2-amino-4H-
chromenes by one pot three component reactions of malononitrile,
aldehyde, and activated phenol in water: ethanol solvent system in
the presence of silica gel supported polyamine (GN3) as heteroge-
neous catalyst.
and active methylene compound (1 mmol) was added to
ethanol–water (8:2) solvent system. To this mixture, 10 wt% of sil-
ica gel polyamine catalyst was added. The reaction mixture was
refluxed for appropriate time (as shown in Table 6). The progress of
reaction was monitored on thin layer chromatography. After com-
pletion of reaction as indicated by TLC, reaction mixture was cooled
at room temperature. The solvent was removed under vacuum to
obtain crude product. The obtained crude product was purified by
column chromatography using ethyl acetate/petroleum ether (1:8)
as solvent system to get the desired pure compound.
2. Experimental
All the solvents were used as commercial anhydrous grade
without further purification. Aluminum sheets 20 cm × 20 cm, sil-
ica gel 60 F254, Merck grade TLC plate were used for thin layer
chromatography to determine progress of reaction. The column
chromatography was carried out over silica gel (80–120 mesh).
3. Result and discussion
Silica gel supported polyamine catalyst was prepared by known
literature process [28]. The catalyst was characterized by N2
adsorption-desorption analysis, infrared spectroscopy, thermal
analysis, elemental analysis, powder X-ray diffraction, Si solid
state NMR analysis, scanning and transmission electron microscopy
(Scheme 1).
Melting points were determined in open capillary tube. 1H and 13
C
NMR spectra were recorded on Bruker 300 MHz spectrometer in
CDCl3 solvent. Mass spectra were taken on Polaris-Q Thermoscin-
tific GC-MS.
2.1. General procedure for the synthesis of Silica gel
3.1. Catalyst characterization
Silica gel was synthesized under acidic conditions. A known
amount of sodium silicate solution (23.31 SiO2%; 7.48 Na2O %) was
diluted with deionized water to obtain 12% w/v SiO2 concentra-
tion. The slurry was added to 10.2 N H2SO4 solution under stirring
with peristaltic pump in 12.5 min at room temperature. To adjust
the SiO2 concentration to 8% w/v it is aged for 2 h, and then kept
at 100 ◦C for 112 h in a closed Simax glass bottle. Peristaltic pump
is used to ensure uniform mixing. The silica gel thus obtained was
washed with water till it was sulfate free (confirmed by BaCl2 test).
The sulfate free silica gel was dried at 100 ◦C in oven and further
calcined at 600 ◦C for 6 h. Further it was cooled under vacuum and
stored in a capped bottle over P2O5 in a desiccator.
3.1.1. N2 adsorption-desorption analysis
acterized by N2 adsorption at liquid N2 temperature. Adsorption
isotherms and pore size distribution curves are presented in Fig. 1.
tics of mesoporous silica [29].
Results of surface area calculated by BET (Brunauer–Emmett–
Teller) method, the pore size distributions calculated by BJH
(Barrett–Joyner–Halenda) method, and the total pore volume of
samples are given Table 1. As expected for each functionalized
silica gel, the surface area, total pore volume and pore diame-
ter decreased as the concentration of added organo silane was