Gold nanoparticles immobilized on lipoic acid functionalized SBA-15: Synthesis, characterization and catalytic applications

Article abstract of DOI:10.1016/j.apcata.2013.01.006

Gold nanoparticles immobilized on lipoic acid functionalized SBA-15 (SBA-LAG) catalyst was synthesized via functionalization of SBA-15 with propylamine followed by tethering of lipoic acid and immobilization of gold nanoparticles. The structural and texct

Full text of DOI:10.1016/j.apcata.2013.01.006

Applied Catalysis A: General 454 (2013) 119–126
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Gold nanoparticles immobilized on lipoic acid functionalized SBA-15:
Synthesis, characterization and catalytic applications
Narani Ananda, Pochamoni Ramudua, Kannapu Hari Prasad Reddya, Kamaraju Seetha
Rama Raoa, Bharatam Jagadeeshb, Vemulapalli Sahithya Phani Babub, David Raju Burria,∗
a Catalysis Laboratory, I & PC Division, Indian Institute of Chemical Technology, Hyderabad-500 007, India
b NMR Division, Indian Institute of Chemical Technology, Hyderabad-500 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Gold nanoparticles immobilized on lipoic acid functionalized SBA-15 (SBA-LAG) catalyst was synthesized
via functionalization of SBA-15 with propylamine followed by tethering of lipoic acid and immobilization
of gold nanoparticles. The structural and texctural characteristics of the catalyst have been determined
by N2 adsorption–desorption and low-angle XRD. The successive attachment of spacers has been char-
acterized by 13C CP-MAS NMR, FT-IR and TG-DTA. The size, shape, surface composition and oxidation
state of gold nanoparticles have been determined by XRD, TEM and XPS techniques. SBA-LAG catalyst is
found to be an efficient solid catalyst for producing good to excellent yields of propargylamines by con-
densing three-components such as (i) amine, (ii) aldehyde and (iii) alkyne in one-pot under solvent-free
conditions.
Received 26 September 2012
Received in revised form 5 January 2013
Accepted 7 January 2013
Available online xxx
Keywords:
SBA-15
Lipoic acid
Gold nanoparticles
Propargylamines
Solvent-free system
Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.
1. Introduction
However, lipoic acid capped gold nanoparticles on SBA-15 have not
yet been reported.
Gold, in its bulk form has been regarded to be chemically
inert. Accordingly, bulk gold was considered to be uninteresting
metal from the catalysis point of view. However, recently it is
reported that gold catalysts are extremely active if deposited as
nanoparticles on suitable supports [1–4]. Gold nanoparticles can
be synthesized directly by adsorbing its salts on the supports fol-
lowed by reduction with hydride source. In general, the deposition
of nanoparticles on supports through conventional impregnation,
deposition-precipitation, chemical vapor deposition and sono-
chemical methods are in practice, but the nanoparticles prepared
in these methods are larger in size, easily undergo agglomeration
and leaches under reaction conditions. Hence, in this context, novel
nanoparticles deposition methods are highly desirable. It is real-
ized that the bio-conjugate ligand molecules can significantly limits
the aggregation and improves the stability of the gold nanoparti-
cles [5–12]. Lipoic acid is a natural bio-molecule consisting of five
membered cyclic disulphide and hydrocarbon tail ending with a
carboxylic acid group. Lipoic acid has been the subject of numer-
ous research studies and recently several authors have prepared
lipoic acid capped gold nanoparticles for specific immobilization of
histidine tagged proteins and electroluminescent luminol [13,14].
The advent of mesoporous SBA-15 silica in 1998 [15], has been
emerging as a potential catalyst support, particularly for the stabi-
lization of nanoparticles using a variety of organic spacers such as
NH2, SH, SO3H, CN, COOH [16,17]. The unique features like
high surface area, hexagonal array of pores, large and uniform pore
channels and good thermal stability makes SBA-15 a prominent
support.
Propargylamines and its derivatives are versatile synthetic
intermediates in organic synthesis and important structural skele-
tons of biologically active compounds [18–20]. Traditionally
propargylamines are synthesized by nucleophilic attack of lithium
acetylides or Grignard reagents on imines [21,22]. However, these
reagents must be used in stoichiometric amounts, are highly
moisture sensitive, and require strictly controlled reaction con-
ditions. An alternate green and economic approach to synthesize
propargylamines is accomplished by one-pot three-component
condensation of an amine, an aldehyde and an alkyne via C
H
alkyne-activation on various catalysts [23–25]. Compared to other
transition-metal based catalysts gold complexes exhibited excel-
lent affinity for alkynes. However these homogeneous systems are
economically and environmentally not acceptable because of rapid
reduction of cationic gold complexes into inactive metallic gold
after C H alkyne activation during the reaction [26–37]. In 2007
Kidwai et al. reported the use of unsupported Au(0) nanoparticles
in the preparation of propargylamines[38]. These unsupported Au
∗
Corresponding author. Tel.: +91 4027191712; fax: +91 4027160912.
E-mail addresses: david@iict.res.in, davidrajuburri@yahoo.com (D.R. Burri).
0926-860X/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.01.006

120
N. Anand et al. / Applied Catalysis A: General 454 (2013) 119–126
nanoparticles exhibited excellent catalytic activity similar to those
of homogeneous gold metal complexes. However, this protocol
requires high loading of gold nanoparticles (10%) and the reactions
needs to be conducted under inert conditions. Vinu and co-workers
reported the gold nanoparticles embedded mesoporous carbon
nitride functions as an efficient recyclable heterogeneous catalytic
system for the synthesis of propargylamines [39] but this method
requires carcinogenic organic solvents and limited to very few
substrates. Recently Kantam et al. reported the synthesis of propar-
gylamines using nanocrystalline magnesium oxide stabilized gold
nanoparticles as a catalyst [40], it shows good activity but this pro-
tocol also requires organic solvents, long reaction times and loss of
activity in its repeated use. Very recently Karimi et al. have devel-
oped gold nanoparticles supported periodic mesoporous silica with
ionic liquid frame work catalyst for propargylamines but in this
protocol reaction has conducted in harmful organic solvent [41].
Synthesis of propargylamines using eco-friendly and reusable cat-
alyst under solvent-free conditions is still a thrust area in chemical
field.
designated as SBA-LAG 1, SBA-LAG 1.5, SBA-LAG 2.5, wherein the
suffixed numerical value stands for the loading of Au by weight%.
2.5. Characterization of the catalyst
Solid-state 13C CP-MAS NMR spectra were obtained on a Bruker-
Avance 500 MHz with 10 kHz of spinning rate. Low-angle XRD
patterns were recorded on Ultima IV X-ray diffractometer at 40 kV
and 40 mA using Cu K␣ radiation in the range 0.7–5◦ at room tem-
perature. Wide-angle X-ray diffraction (XRD) patterns of catalysts
was obtained on a Bruker D8 Advance X-ray powder diffractometer
using Ni filtered Cu K␣ radiation at a scan speed of 2◦/min. X-ray
photoelectron spectroscopy (XPS) analysis of the catalyst was car-
ried out by a Kratos analytical spectrophotometer, with Mg K␣
monochromatic excited radiation (1253.6 eV). The residual pres-
sure in the analysis chamber was around 10−9 mbar. The binding
energy (BE) measurements were corrected for charging effects with
reference to the C 1s peak of the adventitious carbon (284.6 eV).
Infrared spectra were recorded on a Bruker Alpha-T, FT-IR sys-
tem, in the scan range of 4000–400 cm−1. A Philips Tecnai F12 FEI
transmission electron microscope (TEM) operating at 80–100 kV
was used to record TEM images. The TGA measurements were car-
ried out using TGA/SDTA 851e thermal system (Mettler Toledo,
Switzerland). The samples were heated in air from 27 to 1000 ◦C
with a heating rate of 10 ◦C/min. During the heating period, the
weight loss and the temperature difference were recorded as a
function of temperature.
Here in, for the first time, using a new and facile strategy,
SBA-LAG catalyst has been synthesized. Synthesis, characterization
and catalytic activity towards the preparation of propargylamines
through three-component one-pot synthesis under solvent-free
conditions have been described.
2. Experimental
2.1. Preparation of SBA-15
2.6. Catalytic activity
A
solution of EO20PO70EO20:HCl:TEOS:H2O = 2:60:4.25:15
(mass ratio) was prepared, stirred for 12 h at 40 ◦C and then
hydrothermally treated at 100 ◦C under static condition for 12 h,
subsequently filtered, dried at 100 ◦C and calcined at 500 ◦C for 8 h
to get the parent SBA-15 mesoporous silica support.
A mixture of aldehyde (1 mmol), piperdine (1.1 mmol), pheny-
lacetylene (1.2 mmol) and SBA-LAG (35 mg) was taken in a 25 ml
round bottomed flask, stirred at 100 ◦C for 8 h under solvent-free
condition. After completion of the reaction (monitored by TLC), the
reaction mixture was cooled to room temperature and diluted with
ethyl acetate, the reaction mixture was centrifuged to separate the
catalyst. The crude residue was washed with brine solution, dried
over anhydrous Na2SO4, evaporated to get the crude product and
purified by column chromatography to obtain the desired product.
2.2. Preparation of SBA-NH2
3 g of calcined SBA-15 was pre-treated for 3 h at 150 ◦C in vac-
uum and then refluxed with a solution containing 2.1 ml (9 mmol)
of 3-(aminopropyl) triethoxysilane (APTES) in 50 ml of dry toluene
for 24 h under anhydrous condition. The mixture was filtered,
washed with 150 ml of toluene and dried in oven at 100 ◦C for 12 h,
designated as SBA-NH2.
3. Results and discussions
SBA-LAG was synthesized as shown in Scheme 1. Wherein, the
first step is the functionalization of (3-aminopropyl) triethoxysi-
lane (APTES) on the surface of SBA-15. The second step is the
attachment of lipoic acid to SBA-NH2 by amidation between the
free amine groups and COOH group of lipoic acid. The third step
is the gold nanoparticles immobilization on SBA-LA by reducing
with NaBH4 (Scheme 2).
The loading of propylamine and lipoic acid functionalized on
SBA-NH2 and SBA-LA were determined from C, H, N and S ele-
mental analysis and the loading of gold was determined by ICPMS.
The details of the analysis data are presented in Table 1, which
reveals that the propylamine loading is around 1.55 mmol/g and
2.3. Preparation of SBA-LA
To prepare lipoic acid functionalized SBA-15, lipoic acid
was dissolved in dichloromethane (DCM). Then 1-hydroxy
benzotriazole (HOBT) and 1-ethyl-3-(3-dimethylaminopropyl) car-
bodiimide hydrochloride (EDC) (molar ratio lipoic acid:HOBT:EDC
at 1:1.1:1.5) was added to the above solution under N2 atmosphere.
After stirring for 30 min, the amine functionalized SBA-15 (SBA-
NH2) was added to the mixture and stirred at room temperature for
24 h under inert atmosphere and the material was filtered, washed
with ethanol, dried under vacuum and the material was designated
as SBA-LA.
Table 1
Elemental analysis of SBA-15, SBA-NH2, SBA-LA, SBA-LAG samples.
2.4. Preparation of SBA-LAG
Sample
Analysed by
C (%)
H (%)
N (%)
S (%)
Au (%)
SBA-15
SBA-NH2
SBA-LA
SBA-LAG
SBA-LAG
CHNS
CHNS
CHNS
ICPMS
ICPMS
NF
NF
1.73
2.25
–
NF
2.17
2.21
–
NF
NF
3.75
–
–
–
–
The vacuum dried SBA-LA was added to HAuCl4 in methanol
under stirring and reduced with NaBH4 in inert atmosphere
overnight, and then catalyst was filtered, washed with ethanol and
water, dried under vacuum. Finally the sample was designated as
SBA-LAG, wherein the loading of Au is 2.1 wt%. Following the sim-
ilar method different loadings of Au was immobilized, which are
9.22
14.43
–
2.1
–
–
–
–
2.05a
NF stands for not found.
a
Recycled catalyst.

N. Anand et al. / Applied Catalysis A: General 454 (2013) 119–126
121
Fig. 1. N2 adsorption–desorption isotherms of SBA-15, SBA-NH2, SBA-LA and SBA-
LAG.
The N2 adsorption–desorption isotherms for SBA-15, SBA-NH2,
and SBA-LA and SBA-LAG catalyst are displayed in Fig. 1. It can be
seen that all the four samples displays a type IV isotherm with an
H1 hysteresis loop, characteristic of ordered mesoporous mate-
rials [42]. As shown in PSD curve (inset, Fig. 1), the pores are
distributed in the range of 4.3–6.8 nm. The BET surface area of SBA-
15 and SBA-NH2 are 723 and 492 m2/g, the decrease in surface area
indicates the functionalization of propylamine on the surface of
parent SBA-15. Further decrease in surface area for SBA-LA
(449 m2/g) is noticed. Further decrease in the surface area has been
observed for SBA-LAG. Similar trend has been observed for pore
volume and pore diameter with the introduction of amine, lipoic
acid and Au nanoparticles respectively. This suggests the partial
blockage of pore by the functionalizing agents and Au nanoparti-
cles.
Scheme 1. Schematic representation of SBA-LAG synthesis.
3.2. XRD analysis
Scheme 2. Single-pot synthesis of propargylamines over SBA-LAG catalyst.
The low angle XRD pattern of SBA-15, SBA-NH2, SBA-LA, and
SBA-LAG is shown in Fig. 2. Parent SBA-15 and its functionalized
samples show three well resolved peaks at 0.95–1.1◦, 1.63–1.7◦
and 1.89–1.95◦ respectively on the 2ꢀ scale, which are assigned
the lipoic acid loading is around 1.165 mmol/g. The loading of gold
is approximately 2.1 wt%.
3.1. N2 adsorption–desorption analysis
The textural characteristics of the catalyst right from parent
SBA-15 are determined by N2 adsorption–desorption technique.
The BET surface area, pore volume, pore diameter and pore wall
thickness are depicted in Table 2.
Table 2
Structural and textural characteristics of SBA-15, SBA-NH2, SBA-LA and SBA-LAG.
Characteristics
SBA-15
SBA-NH2
SBA-LA
SBA-LAG
SBET (m2/g)a
Vp (cm3/g)b
Dp (nm)c
723
492
449
0.81
5.90
8.79
9.8
415
0.78
6.10
8.37
9.7
1.05
7.04
9.01
10.4
5.30
0.84
6.89
8.75
10.1
5.00
d(1 0 0) (nm)d
ao (nm)e
t (nm)f
4.70
4.56
a
BET surface area.
Total pore volume.
BJH pore diameter.
d(1 0 0) spacing.
b
c
d
√
e
Unit cell parameter (ao = 2 × d(1 0 0)/ 3).
f
Pore wall thickness (t = ao – pore size).
Fig. 2. Low-angle XRD patterns of SBA-15, SBA-NH2, SBA-LA and SBA-LAG.

122
N. Anand et al. / Applied Catalysis A: General 454 (2013) 119–126
Fig. 3. Wide-angle XRD patterns of SBA-15, SBA-NH2, SBA-LA and SBA-LAG.
Fig. 4. 13C CP-MAS NMR spectra of SBA-NH2 and SBA-LA and 13C NMR spectra of
pure lipoic acid shown in inset.
to (1 0 0), (1 1 0) and (2 0 0) reflections, these results suggest that
the two-dimensional hexagonal mesoporous structure of parent
SBA-15 with space group p6mm remain intact at all the stages of
SBA-LAG catalyst preparation. But after anchoring of propylamine,
lipoic acid followed by immobilization of gold nanoparticles, the
reduction in intensity of (1 0 0) and (1 1 0), (2 0 0) reflections, which
may be due to loss of some regularity in the 2D hexagonal structural
ordering or due to reduction of the scattering contrast between the
SBA-15 silica walls and filled pores with propylamine and lipoic
acid moieties.
Wide angle XRD spectrum of SBA-LAG (Fig. 3) shows a broad
peak with less intensity at 38.1◦, which is attributed to (1 1 1) plane
of the Au nanoparticles [43]. However, the diffracted reflections
that are supposed to appear at 44.2◦, 64.7◦ and 77.5◦ associated with
the (2 0 0) (2 2 0) and (3 1 1) planes are not observed, suggesting that
the Au nanoparticles are well dispersed on the surface of SBA-15.
3135 cm−1 in SBA-NH2 is due to NH2 stretching vibration, which is
in hydrogen bonding with OH groups. New bands were observed
in the range of 2932–2864 cm−1 and 1474–1384 cm−1 for SBA-NH2,
SBA-LA and SBA-LAG are corresponding to CH2 stretching and
bending vibrations. A sharp absorption band that appeared for the
SBA-15 at 1629 cm−1 is due to adsorbed water molecule has sub-
stantially reduced in intensity and generated a new infrared band
at 1557 cm−1, which corresponds to N H (primary amine) bending
vibrations [47–50]. After propylamine functionalization, significant
decrease in the intensities of absorption bands that are responsible
for OH groups in the stretching (3437–3369 cm −1) and bending
(967 cm−1) regions, implies the consumption of OH groups due
to anchoring of propylamine onto SBA-15 through chemical bond-
ing. SBA-LA and SBA-LAG has two additional bands at 1651 and
3.3. Solid state 13C CP-MAS NMR analysis
1547 cm−1, which can be assigned to
C O amide (II) stretching
The functionalization of SBA-15 with propylamine followed by
tethering of lipoic acid has been confirmed by solid state 13C NMR
spectra. Fig. 4 shows the solid-state NMR spectra of SBA-NH2 and
SBA-LA. The 13C NMR spectrum of SBA-NH2 shows three signals
at 7.91, 20.42 and 41.3 ppm respectively, representing C1, C2 and
C
3 of the (3-aminopropyl) triethoxysilane (APTES), which confirms
the APTES functionalization on the surface of SBA-15 [44]. The
single peak that appears at 179.4 ppm for the pure lipoic acid
corresponds to
C O of COOH (Fig. 4, Inset). After lipoic acid
treated with SBA-NH2 the peak at 179.4 ppm shifted to 174 ppm,
indicating the formation of amide bond. Additionally, the NMR
spectrum of SBA-LA shows peaks at 174, 56, 40, 39, 36, 34, 29 and
25 ppm, which corresponds to the amidation of lipoic acid with
SBA-NH2 [14].
3.4. FT-IR analysis
FT-IR spectra of (a) SBA-15 (b) SBA-NH2 (c) SBA-LA (d) SBA-
LAG is shown in Fig. 5. A broad band observed in between 3437
and 3369 cm−1 in all the samples, which indicates typically OH
stretching vibration, the band at 1629 cm−1 in SBA-15 and SBA-
NH2 samples due to OH deformation band, the sharp band
around 967 cm−1 is associated with Si OH [45,46] and the band at
Fig. 5. FT-IR spectra of SBA-15, SBA-NH2, SBA-LA and SBA-LAG.

N. Anand et al. / Applied Catalysis A: General 454 (2013) 119–126
123
Fig. 6. Au 4f X-ray photoelectron spectrum and catalyst. Inset shows the survey of
XPS scan of SBA-LAG catalyst.
Fig. 7. Thermograms of SBA-15, SBA-NH2 and SBA-LAG.
3.7. TEM analysis
and NH bending vibrations [13,51]. The results of IR spectra are
in good agreement with the results obtained by NMR technique,
confirming that propylamine and lipoic acid has been successfully
grafted on the surface of SBA-15. 6. In General, the S–S stretching
frequency to be observed in the range of 540–500 cm−1 [52,53],
but it might be masked by the silica SBA-15 peak and also the
The TEM images of SBA-15 and SBA-LAG are shown in Fig. 8.
This reveals that the morphology of the SBA-LAG remains intact
after deposition of Au nanoparticles onto SBA-LA. The TEM image
also reveals the spherical nature of immobilized Au nanoparticles
on SBA-15. The particles size distribution graph is shown in Fig. 8 as
an inset, which shows that the mean diameter of Au nanoparticles
is approximately 8–10 nm.
After realizing the potential applications of Au nanoparticles,
much effort has been devoted to develop mesoporous mate-
rial supported Au nanoparticles, particularly for preventing the
agglomeration as well as maintaining the high dispersion. It is
evidenced from the literature that the direct synthetic methodolo-
gies prevail over post-synthetic techniques particular to prepare
smaller size and highly dispersed Au nanoparticles [55–61]. The
structural and textural characteristics like BET surface area, pore
diameter, pore volume and particle size of the most relevant publi-
cation are compared in Table 3. The variations in the structural and
textural parameters are mainly depends on the method of prepa-
ration.
S
Au band supposed to be observed in the range of 240–210 cm−1
[52], but the present IR spectrum was recorded in the range of
4000–400 cm−1. So the S S and S Au stretching bands of SBA-LA
and SBA-LAG are not observed.
3.5. XPS analysis
X-ray photoelectron spectra (XPS) analysis is a powerful tech-
nique used to provide information on the chemical oxidation state
of elements present in the synthesized material. The XPS spec-
trum of SBA-LAG displayed in Fig. 6, which depicts the Au4f
core level of the catalyst, showing the binding energies at 84
and 86.7 eV, which are assigned to the spin-orbit splitted com-
ponents of Au (4f7/2) and Au (4f5/2) in the zero oxidation state
of Au, which are in agreement with the reported values [14,51].
The binding energies at 85 and 89 eV are characteristic of cationic
form of Au in +3 oxidation state, which are absent, suggest-
ing the immobilization of Au nanoparticles on the surface of
SBA-15.
3.8. Catalytic activity studies
The catalytic activity of SBA-LAG was investigated for the syn-
thesis of propargylamines by reacting benzaldehyde, piperdine
and phenylacetylene as standard substrates. To optimize the reac-
tion conditions, the reaction was carried out in different solvents
and the results were shown in Table 4, which reveals that under
solvent-free conditions the yields are better. Slightly lower yields
are obtained, when the reaction was performed in CH3CN, Toluene,
and Benzene as solvents (Table 4, Entries 1, 2, 3). DMSO, DMF,
CH3OH and water gave low to moderate yields (Table 4, Entries
4, 5, 6, and 7). The optimized reaction conditions include 1 mmol
of benzaldehyde, 1.1 mmol of piperdine, 1.2 mmol of phenylacety-
lene, 35 mg of catalyst, 100 ◦C temperature, and 8 h reaction time.
In order to elucidate the influence of core size on the activity on
different SBA-LAG catalysts were studied, wherein same amount of
Au is used by taking the different amounts of catalyst, i.e. 31–78 mg
of catalyst (Table 5). It is found that there is a significant decrease
in the conversion with increase core size.
3.6. TGA analysis
To know the amount of functionalized material and its sta-
bility on the surface of SBA-15, thermogravimetric analysis was
made and the resultant thermograms of SBA-15, SBA-NH2 and SBA-
LA were shown in Fig. 7. Thermogram of parent SBA-15 shows a
marginal loss of mass around 2.6%. This mass loss is due to the
loss of adsorbed water on the surface of SBA-15 or the water that
formed from the condensation of hydroxyl groups. The thermo-
grams of all other samples show a significant mass loss between
348 ◦C and 668 ◦C. Beyond this temperature all the thermograms
of samples are constant. The major mass loss is due to the decom-
position of anchored organic moieties [54]. From the TGA results,
it is found that the organic moieties are thermally stable when
they are covalently anchored onto the surface of mesoporous
SBA-15.
To understand the nature of capping agents in the catalytic activ-
ity of Au nanoparticles same amount of Au was also immobilized on

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N. Anand et al. / Applied Catalysis A: General 454 (2013) 119–126
Fig. 8. TEM image of SBA-LAG, inset Au nanoparticle size distribution of SBA-LAG.
Table 3
Comparison of structural and textural characteristics with reported literature.
Catalyst
Surface area (m2/g)
540
Pore volume (cm3/g)
0.49
Pore diameter (nm)
5.9
Particle size (nm)
3.2–3.7
Ref.
53
Au@MPTS-Al-
SBA-15
0.5% GCM (F)
Au/Ti-G-80
0.16Au11-SBA(20)
Au/10%CeOx/SBA-15
Au@APTS-SBA-15
Au/AF-MSTF
1048
499
866
370
885
–
>1.1
0.87
1.7
0.609
1.27
–
>6.2
6.5
8
6.6
6.79
–
–
1.5
0.8–1.0
4.8
2.1–19.4
1–4
54
55
56
57
58
59
SBA-LAG
415
0.78
6.15
8–10
Present work
Table 4
Influence of solvent in the formation of propargylamines over SBA-LAG catalyst.
the results are summarized in Table 6. Aromatic aldehydes
with electron withdrawing as well as electron donating groups
are investigated. The activity data demonstrate that the functional
groups on the ring did not show any significant effect on the reac-
tion. Both aromatic and aliphatic aldehydes smoothly reacted with
piperdine and phenylacetylene. The yields of desired products are
good to excellent (Table 6, Entries 1–8). Various terminal alkynes
Entry
Solvent
Yield (%)
1
2
3
4
5
6
7
8
CH3CN
Toluene
Benzene
DMSO
DMF
CH3OH
H2O
Neat
75
58
45
20
18
25
28
95
(
CH3, OCH3) with piperdine and benzaldehyde are reacted
smoothly and obtained good yields (Table 6, Entries 9, 10).
3.9. Reusability
Reaction conditions: benzaldehyde (1 mmol), piperdine (1.1 mmol), phenylacety-
lene (1.2 mmol), catalyst (35 mg), 100 ◦C, 8 h.
To evaluate the reusability of the catalyst, the used catalyst was
separated from the reaction mixture, washed with ethyl acetate,
propyl amine functionalized SBA-15, which exhibited lower con-
version (58%) compared to SBA-LAG (95%).
With the optimal reaction conditions in hand, vari-
ous aldehydes and alkynes were used as substrates and
Table 6
SBA-LAG catalysed synthesis of propargylamines.
Entry R1
Amine
R2
Product Yield
(%)
Table 5
1
2
3
4
5
6
7
8
9
Ph (1a)
p-CH3C6H4 (1b)
p-OCH3C6H4 (1c) 2a
Piperdine (2a) -Ph (3a)
4a
4b
4c
4d
4e
4f
4g
4h
4i
95
83
85
90
88
87
95
91
86
90
Influence of Au loading, core size and dispersity on different SBA-LAG catalysts.
2a
3a
3a
3a
3a
3a
3a
3a
S. no.
Catalyst
Core size
(nm)
Poly dispersity
(Pdi)
Conversion
(%)
p-FC6H4 (1d)
p-ClC6H4 (1e)
p-BrC6H4 (1f)
H (1g)
2a
2a
2a
2a
2a
2a
2a
1
2
3
4
SBA-LAG 1 (78)
SBA-LAG 1.5 (52)
SBA-LAG 2.1 (35)
SBA-LAG 2.5 (31)
2–4
5–6
8–10
12–14
0.74
0.91
0.70
1.00
98
96
95
83
C6H11 (1h)
1a
p-CH3C6H4 (3b)
p-OCH3C6H4 (3c) 4j
10
1a
The value shown in parenthesis refers to the amount of catalyst (in mg) used in
the experiment Reaction conditions: benzaldehyde (1 mmol), piperdine (1.1 mmol),
phenylacetylene (1.2 mmol), catalyst (0.04 mol% Au), 100 ◦C, 8 h.
Reaction conditions: Benzaldehyde (1 mmol), piperdine (1.1 mmol), phenylacety-
lene (1.2 mmol), catalyst (35 mg), temperature (100 ◦C) and time (8 h).

N. Anand et al. / Applied Catalysis A: General 454 (2013) 119–126
125
Acknowledgements
Narani Anand and Pochamoni Ramudu are thankful to Council
of scientific and Industrial Research (CSIR) New Delhi, for awarding
research fellowships.
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