Synthesis and characterization of silica-polymer nanocomposites functionalized with piperazine for the synthesis of β-nitro alcohols

Article abstract of DOI:10.1007/s10562-011-0643-x

In order to compare the activity and selectivity for the synthesis of β-nitro alcohols, piperazine was functionalized directly and after surface modification into the ordered mesoporous SBA-15 framework. The materials were characterized by powder X-ray di

Full text of DOI:10.1007/s10562-011-0643-x

Catal Lett (2011) 141:1548–1556
DOI 10.1007/s10562-011-0643-x
Synthesis and Characterization of Silica–Polymer Nanocomposites
Functionalized with Piperazine for the Synthesis of b-Nitro
Alcohols
•
Divya Sachdev Amit Dubey
Received: 31 March 2010 / Accepted: 3 June 2011 / Published online: 24 June 2011
Ó Springer Science+Business Media, LLC 2011
Abstract In order to compare the activity and selectivity
for the synthesis of b-nitro alcohols, piperazine was func-
tionalized directly and after surface modification into the
ordered mesoporous SBA-15 framework. The materials
were characterized by powder X-ray diffraction,
N2-adsorption–desorption isotherm, FT-IR, SS-NMR and
scanning electron microscopy. The catalyst synthesized via
surface modification under solvent free conditions showed
very high activity and selectivity of b-nitro alcohols com-
pared to the one synthesized by direct functionalization of
SBA-15. Finally the possible reaction pathways were
explained mechanistically.
environmental perspectives [1, 2]. However, due to the
ever growing demand of the day to day products, hazard-
ous homogeneous reagents (H2SO4, HF, NaOH, KOH,
CH3COOH and transition metal containing salts) are still in
use as catalysts for many organic transformations. During
the past few decades, many heterogeneous systems have
been developed for acid catalyzed conversions compared to
solid bases despite of having a decisive role in the synthesis
of fine chemicals [3]. In fact 10–20% of the industrial
processes such as isomerizations, additions, condensation,
alkylations and cyclizations proceed selectively with
higher rates by solid bases [4–7]. Hence, the development
of new one step, green and recyclable solid base catalytic
systems is strongly encouraged [8]. Among various heter-
ogeneous catalysts, ordered mesoporous silica materials are
getting tremendous attention due to their remarkable
properties such as high surface area, tunable pore size
(2–15 nm) and flexibility to incorporate organic and inor-
ganic moieties within highly porous structures with high
dispersion of active species [9]. Particularly mesoporous
SBA-15 functionalized with organic moieties have been
utilized effectively for many acid–base transformations
[10]. Considering the solid base applications, amino-func-
tionalized mesoporous silica materials were effectively
designed either by grafting (post-synthetic) or co-conden-
sation (direct during synthesis) methods to obtain organic–
inorganic hybrid materials for many catalytic conversions
[11–14]. Particularly, the introduction of primary and
secondary aliphatic amino groups on mesoporous silica
materials has also been widely reported for nitroaldol
condensation or Michael addition reactions [13, 15–17].
However, the limited scope and density of the functional
groups achievable and relatively low hydrothermal stability
of the siloxane bond under reactive conditions limit the
practical utilization. Various methods were attempted to
Keywords Mesoporous Á Nitroaldol Á Piperazine Á
Nanocomposites
1 Introduction
Heterogeneous catalysis plays an important role in the
current industrial scenario because of its significant
advantages in terms of easier product recovery, minimizing
disposal problems, regeneration of active sites and for
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-011-0643-x) contains supplementary
material, which is available to authorized users.
D. Sachdev Á A. Dubey (&)
Chemistry Group, Birla Institute of Technology and Science,
Pilani, Rajasthan 333031, India
e-mail: amitdubey75@yahoo.com
Present Address:
A. Dubey
Department of Chemistry, Maulana Azad National Institute of
Technology, Bhopal, India
123

Synthesis and Characterization of Silica–Polymer Nanocomposites
1549
modify the surface properties of the silica framework and
to achieve maximum selectivity of the products, but in
almost all the methods, the resulting materials obtained
were either non porous or disordered in nature [18, 19].
Very recently, the surface modified amino-functionalized
ordered mesoporous silica were reported for Knoevenagel
condensation [20].
2 Experimental Methods
2.1 Synthesis of SBA-15
All the chemicals were procured from Sigma-Aldrich and
used without further purification. The synthesis of SBA-15
is carried out using Pluronic (P123) (EO20PO70EO20,
MW = 5800, Aldrich) and TEOS as the surfactant and
silica source, respectively. In a typical synthesis batch with
TEOS, 3 g of P123 was dissolved in 100 g of distilled
water and 5.9 g of conc. HCl (35%). After stirring for 1 h,
7.3 g of TEOS (ACROS, 98%) was added at 35 °C
maintaining the molar ratio of P123: H2O: HCl: TEOS
ratio as 1: 5562.9: 86.29: 42.51 and stirring for 24 h.
Subsequently the mixture was heated for 24 h at 100 °C
under static conditions in a closed polypropylene bottle.
The solid product obtained after the hydrothermal treat-
ment was filtered and dried at 80 °C. The template was
removed by calcinations at 550 °C for 6 h.
Nitroaldol condensation is also a key reaction in the
synthesis of b-nitroalkanols which are extensively
important intermediates in variant organic transformations
[21, 22]. b-nitroalkanols can further be converted to
obtain 2-aminoalcohols for intermediates in chloroam-
phenicol, [23] ephedrine, norephedrine [24, 25], drugs like
S-propanolol [26, 27] and to achieve amino sugars and
ketones [28]. However, selective synthesis of b-nitroal-
cohols via nitroaldol condensation is quite challengeable
because of its predominant dehydration to nitro alkenes
that are susceptible for further polymerization. Moreover,
the aldehydes in presence of strong base results in self
condensation to give aldol product [29]. Therefore in
order to overcome these difficulties, various primary and
secondary amino groups were directly incorporated into
MCM-41 materials [15, 16] yet piperazine as a secondary
cyclic amine has not been functionalized on the surface
modified SBA-15 materials synthesized via radical poly-
merization of monomers into the silica framework for
nitroaldol condensation. In our earlier communication, we
have reported the synthesis of new mesoporous polymer–
silica (KIT-6 with cubic Ia3d symmetry) composite
materials through in situ radical controlled polymerization
of vinylmonomers (styrene and vinyl ferrocene as a
functional monomer) inside the silica mesopores for
hydroxylation of phenol [30]. Therefore in the present
paper, we report the synthesis and characterization of
silica–polymer nanocomposites functionalized with
piperazine for nitroaldol condensation and its comparison
with direct functionalized SBA-15. The method of surface
modification provides a powerful approach via ion-pair
mechanism in controlling b-nitroalcohol selectivity almost
exclusively.
2.2 Synthesis of Direct Functionalized SBA-Piperazine
Catalyst (SBA/PP)
Piperazine was incorporated via post-synthetic grafting
technique. Typically, 10 mL of 3-chloropropyltriethox-
ysilane (CPTS) was mixed with 1 g of SBA-15 under inert
atmosphere in dry toluene (20 mL) under stirring condi-
tions (Fig. 1). The product SBA/CPTS was filtered and
exhaustively washed with ethanol in Soxhlet extractor for
24 h. SBA-15 functionalized with CPTS was dried under
vacuum and used further for functionalization with piper-
azine. Typically, 1 g of SBA/CPTS was mixed with 1 g of
piperazine in 15 mL of triethylamine (acts as a neutralizing
agent for HCl generated during the functionalization) and
refluxed for 24 h under stirring conditions. Finally piper-
azine functionalized SBA-15 was filtrated and washing
thoroughly with dil HCl and water. The functionalization
of SBA-15 with piperazine was further confirmed by nin-
hydrin test that changed the color of solid from white to
pink. The sample was named as SBA/PP.
H
N
NH
O
O
O
O
O
Si
N
Si
Cl
O
N
H
Et3N
80 °C
SBA/PP
Fig. 1 Direct functionalization of SBA-15 with piperazine (SBA/PP)
123

1550
D. Sachdev, A. Dubey
2.3 Synthesis of SBA-15/Polymer Nanocomposites
(SBA-PS)
2.4 Functionalization of SBA-PS with Piperazine
(SBA/PS/PP)
The synthesis methodology of SBA/PS (Fig. 2) involves the
incorporation of vinyl monomers (4-chloromethylstyrene
and divinyl benzene), cross linkers and radical initiators into
the SBA-15 mesopore walls via the wet-impregnation
method and equilibrated under reduced pressure to achieve
a uniform distribution similar to our previous report [30].
The monomers adsorbed on the mesopore walls were
subsequently polymerized with controlled temperature
programmed heating.
In a typical synthesis of SBA/PS/piperazine, 1 g of SBA-
xPS was refluxed with 420 mg of piperazine in presence of
10 mL of triethylamine for 24 h. The solid was filtered and
washed well initially with dil HCl and then thoroughly with
water to remove unreacted piperazine. Finally the samples
were named as SBA-xPS/PP where PP stands for piperazine.
2.5 Nitroaldol Reaction
Typically, for 10 wt% polymer loading, 0.0827 g of
4-chloromethylstyrene (CS) (80 mol %), 0.0175 g divi-
nylbenzene (20 mol %), 0.0065 g of AIBN, a, a-9-azoi-
sobutyronitrile (3% relative to the total vinyl group) were
dissolved into 2 mL of solvent (dichloromethane). The
resulting mixture is impregnated uniformly into the
SBA-15 framework. After impregnating the solution,
the sample was heated to 40 °C to remove the dichloro-
methane and subjected to freeze–vacuum–thaw to remove
the residual solvent and air. The sample was sealed in a
Pyrex tube and subjected to controlled temperature pro-
gramming for polymerization. The temperature scheme
follows 45 °C for 24 h, 60 °C for 4 h, 100 °C, 120 °C
and 150 °C for 1 h. Finally the polymer was washed with
ethanol to remove the adsorbed monomers. Similarly 30
and 20 wt% polymer loading over SBA-15 was carried
out. The sample was named as SBA-x PS where x stands
for wt% polymer loading. The role of 4-chloromethyl-
styrene is to make the nature of the surface more hydro-
phobic and functionalize piperazine by replacing chloro
groups in polymer.
The catalytic activity studies were carried out in the liquid
phase. 3 mmol of p-nitrobenzaldehyde and 5 mL of nitro
ethane were mixed at 65 °C (Scheme 1). The desired
amount of the catalyst (10–500 mg) was added to the
reaction mixture under inert atmosphere under stirring
conditions and the reaction was monitored for 24 h. The
products of the reaction were identified by gas chroma-
tography after considering the response factors of the
authentic samples using n-decane as internal standard.
After the completion of reaction, catalyst was filtered and
washed with solvent. Product was isolated using column
chromatography using ethyl acetate: Hexane (2%). The
reaction product was identified and characterized by
1H-NMR and FT-IR (Figure 4S, Supplementary Informa-
tion (SI)). The melting point of the sample was also in
agreement with the literature.
2.6 Characterization Methods
Powder X-ray diffraction (PXRD) pattern was recorded
on Hecus X-ray systems S3 Model using Cu Ka radiation
Fig. 2 SBA-15 polymer
nanocomposites (SBA-PS)
functionalized with piperazine
insitu polymerization
DVB,CS
H
N
n
n
N
H
Et3N
N
Cl
NH
SBA/PS/PP
123

Synthesis and Characterization of Silica–Polymer Nanocomposites
1551
H3C
NO2
OH
CHO
CH
CH
3
NO2
3
SBA/Pip
+
EtNO
+
2
H3C
+
NO
NO
2
2
O N
2
O N
O N
O2N
2
2
a
b
c
Scheme 1 Nitroaldol condensation
(k = 1.5404 A) from 0–10°. Nitrogen adsorption–desorp-
tion isotherms were measured by using Micromeritics
ASAP 2020 analyzer at -196 °C. The specific surface area
was calculated by the BET method and the pore size
distribution was calculated by Barrett–Joyner–Halenda
(BJH) method from the desorption isotherm of the sam-
ple. SSNMR 13C of samples were recorded on AV500S-
500 MHz high resolution multinuclear FT-NMR spec-
trometer. The IR spectra of samples (as KBr pellets) were
recorded using a Shimadzu FTIR spectrophotometer in
the range of 400–4000 cm-1. SEM images were recorded
on Digital scanning electron microscope-JSM 6100
(JEOL).
6500
6000
5500
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
SBA/PP
SBA/PS/PP
a
b
0
The number of basic sites on the catalyst surface was
determined by Hammett indicators including bromthymol
blue (H = 7.1), phenol red (H = 7.4), cresol purple
(H = 8.3), thymol blue (H = 8.9), phenolphthalein
(H = 9.7), and alizarine yellow (H = 11.0). Soluble
basicity was also determined by stirring 500 mg of SBA/
PP and SBA/PS/PP with 0.02 M HCl solution for 12 h
and finally unadsorbed H? ions were titrated with
Na2CO3.
0.0
0.1
0.2
0.3
0.4
0.5
Scattering Vector (q)
Fig. 3 PXRD pattern of a SBA-(10)PS/PP and b SBA/PP catalysts
3.1.2 N2 Sorption Studies
N2 adsorption isotherms were measured at -196 °C using
a Quantachrome AS-1MP volumetric adsorption analyzer.
Before the adsorption measurements, all samples were out
gassed for 12 h at 80 °C in the degas port of the adsorption
analyzer. The nitrogen adsorption–desorption isotherm
(Fig. 4) of the catalysts showed a type IV adsorption iso-
therm according to the IUPAC classification with H1
hysterisis loop indicative of mesoporous nature of the
samples [9]. The shapes of the isotherms are slightly
deviated from the parallel shape due to the strain generated
in the mesopores of SBA-15 during the incorporation of
piperzine moiety. The surface area, pore volume and pore
diameter decreased with the incorporation of piperazine,
indicating that the piperazine has been incorporated inside
the SBA-framework. All the structural parameters of the
catalysts are included in Table 1.
3 Results and Discussions
3.1 Synthesis and Characterization of Piperazine
Functionalized SBA-15
3.1.1 PXRD
PXRD pattern of the samples at low angles (Fig. 3) shows
the diffraction pattern similar to SBA-15 sample. The
diffraction at (100), (110), and (200) planes can be indexed
to reflections comprising of hexagonal p6 mm space group
indicating that the materials possess the ordered mesopor-
ous structure and piperazine has been uniformly incorpo-
rated into the framework. A careful examination of the
spectrum showed the increase in the intensity of the base
peak in SBA-(10)PS/PP catalyst compared to the SBA/PP
catalyst due to the polymer formation inside the mesopores
of silica materials resulting in an increase in the apparent
density of the mesopore walls [31].
3.1.3 13C CP-MAS NMR
The incorporation of piperazine into the silica framework
was further confirmed by 13C CPMAS SS NMR. The
spectrum of SBA/PS (Fig. 5) shows peaks at 128, 139 and
120 ppm indicating the presence of aromatic carbons of the
123

1552
D. Sachdev, A. Dubey
240
200
160
120
80
functionalized piperazine [34, 35] compared to the poly-
meric derived SBA-PS/PP catalysts (Fig 1S, SI).
a
3.1.4 FT-IR and Bascity Studies
The FT-IR spectrum (Fig. 6) showed a broad peak
around 3500 cm-1 in all the samples confirming the
presence of N–H stretching of secondary amine (pipera-
zine) incorporated into the mesoporous SBA-15
framework.
b
40
Basicity of the catalyst was calulated by Hamett indi-
cator method and found in range of 8.3 \ H0 \ 11. The
number of basic sites was also determined by the titration
method; 200 mg of the varied catalyst prepared were stir-
red with 10 mL of 0.02 mol/L of HCl for 12 h and the
solution was filtered from the catalyst. The residual H?
ions were titrated with 0.02 mol/L of Na2CO3 to obtain the
amount of HCl adsorbed on the piperazine functionalized
SBA-15. The basicity of SBA-PP catalyst was found to be
lower compared to the SBA-PS/PP catalysts (Fig 2S, (SI)).
This may be due to the better dispersion of the piperazine
moiety after the surface modification in polymeric derived
catalysts.
0.2
0.4
0.6
0.8
Relative Pressure
(P/Po)
Fig. 4 N2-adsorption–desorption isotherm of a SBA-(10)PS/PP and
b SBA/PP
polymer resulted from the monomers chloromethyl styrene
and divinyl benzene [32]. The peak at 25 ppm shows the
presence of the carbon directly linked to mesoporous silica
(–CH2–Si) [33]. Furthermore piperazine linkage to poly-
meric chain was indicated by sharp peak at 48.3 ppm (CH2
piperazine) [34].The intensities of peaks were not recog-
nized fully because of the different concentration of
piperazine in SBA/PP and SBA-(10) PS/PP catalysts.
However, the peaks obtained were sharper in direct
3.1.5 SEM
The SEM images (Fig. 7) of SBA/PS/PP (10%) and after
piperazine incorporation in SBA-(10%) PS/PP showed the
rod shape particles with relatively 1 lm uniform size.
Table 1 Structural parameters of the catalysts
Entry
Materials
Surface area (m2/g)
Pore volume (cm3/g)
Pore size BJHAds (nm)
Piperazinea (%)
1.
2.
3.
a
SBA-15
678
76
1.2
8.2
7.7
5.1
0
SBA/PP
0.16
0.32
7.5
4.2
SBA/(10)PS/PP
294
The amount of piperazine added per gram of the catalyst
Fig. 5 13C CPMAS NMR
spectra of a SBA/PS and
b SBA-(10)PS/PP catalysts
123

Synthesis and Characterization of Silica–Polymer Nanocomposites
1553
PP
3.2 Catalytic Studies
SBA/PP
120
110
100
90
SBA/PS(10)/PP
3.2.1 Effect of the Different Catalysts
Table 2 showed the total conversion and the selectivity of
the desired product (A) for nitroaldol condensation
(Scheme 1). Careful analysis of the results revealed very
high conversion of the products (92%) with 98% selectivity
of the product (A) on SBA-(10) PS/PP catalyst. The cata-
lytic activity decreased with increase in the percentage
loading of the monomers up to 30%. Comparatively lower
activity (70%) and selectivity (85%) of the desired product
(A) was obtained over direct functionalized SBA/PP cata-
lysts. This may be due to the higher surface area and better
dispersion of the active centers inside the surface modified
catalyst compared to the direct grafted catalyst (Fig. 7). It
is to be mentioned here that only 63% conversion of the
products and 72% selectivity of the desired product was
obtained on pure piperazine (homogeneous) indicating the
effect of heterogenization of piperazine on the surface
modified silica framework in controlling the overall
selectivity of the product(s). The higher product selectivity
of the nitroalcohol is in agreement with earlier reports
wherein the secondary amine preferentially gives nitroal-
cohol over nitrioalkene [15, 16]. The best catalyst SBA-
(10) PS/PP was selected for further studies. The variation
of the catalyst weight on the conversion of the products
showed increasing trend with respect to both SBA/PP and
SBA-(10) PS/PP catalyst. Hence catalyst weight of 200 mg
is selected for further catalytic studies.
80
70
N-H
60
Si-O
50
3500
3000
2500
2000
1500
1000
500
wave number (cm-1 )
Fig. 6 FT-IR spectra of piperazine (PP), SBA/PP and SBA-(10) PS/
PP catalysts
Table 2 Effect of different catalyst on the conversion of nitroalco-
hol conversion
Catalyst
Conversiona (%)
Product selectivity (%)
A
B
C
Piperazine
63
52
0
72
70
0
17
15
0
11
15
0
Polystyrene-PP
SBA-15
SBA-NH2
75
70
80
85
92
7
90
12
4
3
SBA/PP
85
96
98
98
2
SBA-(30)PS/PP
SBA-(20)PS/PP
SBA-(10)PS/PP
0
2
0
2
0
Conditions: 3 mmol (p-nitrobenzaldehyde), 5 mL (nitroethane),
temp-65 °C, time (24 h) and catalyst wt (200 mg)
3.2.2 Effect of the Solvent
a
Conversion is based on total products
To further optimize the nitroaldol condensation of p-
nitrobenzaldehyde with nitroethane, different solvents were
chosen to see the influence on total conversion of the
products. A careful examination of solvents under study
(Table 3) indicates that solvent free conditions are the best
conditions to carry out reaction selectively with high con-
versions. Higher conversion in nitro ethane is attributed to
its high dielectric constant 28.06 [36, 37] which helps to
stabilize the transition state as well enhance the solubility
of p-nitrobenzaldehyde (dielectric constant-20). The con-
version and selectivity in other solvents depends on how
reluctantly nitronoate ion is generated and stabilized by
these solvents (Scheme 2).
3.2.3 Effect of the Reaction Temperature
Fig. 7 SEM image of SBA-(10)PS/PP catalyst
Figure 8 showed the effect of temperature on the conver-
sion and selectivity of nitro alcohol. The results concluded
that the conversion of the products and the selectivity of
nitro alcohol product increased with increase in the
These rod shaped structures are uniformly dispersed on
ordered mesoporous silica material resulting in better
activity and selectivity of the b-nitroalcohols.
123

1554
D. Sachdev, A. Dubey
Table 3 Effect of different solvents on the conversion and selectivity of the nitroalcohol (conditions as in Table 2)
Solvents
SBA/PP
SBA/PP
SBA-(10)PS/PP
Conversion (%)
SBA-(10)PS/PP
Conv. (%)
Product sele. (%)
A
Product sele. (%)
A
B
B
Nitroethane
Ethanol
70
60
46
35
25
20
85
80
90
82
84
80
12
14
5
93
68
60
38
26
25
98
96
97
96
98
98
2
3
3
3
2
2
Chloroform
Tetrahydrofuran
Acetonitrile
Methanol
10
7
15
100
90
80
70
60
50
40
30
20
10
0
CH-
O
H3C
H
O
O
slow
H3C
N
O
N
Scheme 2 Stability of nitronoate ion
SBA/Pip
SBA/PS(10)Pip
110
100
90
0
10
20
30
40
time (h)
80
Fig. 9 Variation of conversion and selectivity of b-nitroalcohol with
time (conditions as in Table 2)
70
60
%con SBA-PP
%sel SBA-PP
50
40
30
20
10
modification (Fig. 9). Secondly, the slight color change
(colorless to brown) was observed in SBA/PP catalysts
during the progress of the reaction indicating that the
reactant molecules might be adsorbing on to the surface of
silica and may be blocking the active sites of the catalyst,
resulting in lowering the conversion of the products.
However, no such color change was noted in the polymer
grafted catalyst with the progress of the reaction indicating
that the surface modification helps to avoid the adsorptions
of the reactant molecules and hence enhancing the con-
version of products [16]. The catalyst after the completion
of the reaction was washed thoroughly with nitroethane,
solvents and with water. The catalyst was dried and still the
color change of the catalyst was observed in SBA/PP
catalysts.
%con SBA/PS(10)PP
% sel SBA/PS(10)PP
30
80
130
180
Temp (C)
Fig. 8 Variation of conversion and selectivity of b-nitroalcohol with
temperature (conditions as in Table 2)
temperature up to 65 °C and then decreased with further
increase in temperature. This decrease in the selectivity of
nitro alcohol product (A) may be due to the formation of
nitroalkene via dehydration of nitro alcohol at higher
temperature. Hence the best temperature 65 °C was chosen
for further catalytic activity studies.
3.2.5 Plausible Mechanism
Mechanistically, we believe that piperazine functionalized
SBA-15 both via direct and after surface modification
selectively gives nitro alcohol via ion-pair mechanism [17,
22]. However, in direct functionalized piperazine, the for-
mation of minor product nitroalkene (B, Scheme 3) was
also observed. This selectivity difference resulting in the
3.2.4 Time-on-Stream Studies
Very interesting observations were seen on the conversion
of the products with time. The initial kinetics of the reac-
tion was faster in SBA-(10) PS/PP catalyst compared to
SBA/PP catalysts indicating the influence of the surface
123

Synthesis and Characterization of Silica–Polymer Nanocomposites
1555
H
O
R
OH
OH
OH
OH
NH
O
O
Si
N
Si
NO2
N
R
H
O
O
R
O
N+
O
CH2
CH3
H3C
NO2
nitroalkene
B
CH-
NO2
H3C
Path II
O
Si
PS
Path I
N
O
O
Si
PS
O
N
H
R
O
N
H
O
+
O
NH2
CH2
NO2
CH-
NO2
H3C
H3C
polystyrene framework over SBA-15
PS
HO
O
NO2
Si
PS
N
+
O
R
O
N
H
CH3
nitroalcohol
A
Scheme 3 Plausible mechanism
formation of nitroalkene may be due to the presence of
residual silanol groups that remained after the silylation
with chloropropyltriethoxysilane and hence follows the
reaction pathway II [38]. Comparatively, the surface
modified piperazine, totally cap’s the silanol group and
preferentially favors the reaction by pathway I in generat-
ing selectively nitro alcohol product (A). The melting point
of the product was found to be 90 °C (Literature melting
point 91–93 °C) [26].
catalyst by nitroethane which is highly polar in nature.
Similarly leaching of the active centres, piperazine (SI,
1.2), during the course of reaction (Fig 3S, SI) was also
tested by several blank experiments [39, 40].
4 Conclusions
We have synthesized piperazine functionalized SBA-15
nanocomposites by different routes and compared the
structure- activity relationship for nitroaldol condensation.
The selectivity of the product is fairly controlled by surface
modification process via polymerization of monomers
inside the silica framework. The degree of surface modi-
fication by different methods may pave the role for better
organic transformations.
3.2.6 Reusability
In order to see the reusability of the catalysts SBA-(10) PS/
PP, the catalyst after first cycle was filtered, washed thor-
oughly with chloroform, acetone and finally with water,
dried at 150 °C in the air oven and subjected to fresh
reaction under identical reaction conditions. No difference
in the activity and selectivity was observed up to three
cylcles however, slight decrease in the conversion was
noted afterwards. The decrease in the activity after third
cycle might be due to blockage of the active sites of the
Acknowledgments AD thanks the Institute and Department of
Science and Technology (DST)-New Delhi for financial support (Fast
Track Project). DS thanks CSIR for senior research fellowship. We
thank IISc-Banglore, JNU and IIT-Kanpur for characterizations of the
samples.
123

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D. Sachdev, A. Dubey
21. Akutu K, Kabashima H, Seki T, Hattori H (2003) Appl Catal A
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