Tin exchanged zeolite as catalyst for direct synthesis of α-amino nitriles under solvent-free conditions

Article abstract of DOI:10.1016/j.apcata.2012.01.001

Sn exchanged HBeta zeolite was prepared and characterized by PXRD, surface area, TPD and TEM analysis. The Sn exchanged zeolite was found to be highly efficient catalyst for the direct synthesis of α-amino nitrile from various ketones and aldehydes with amine and trimethyl silylcyanide (TMSCN) under solvent-free condition. Excellent yield of α-amino nitrile (up to 96%) was achieved within 10-120 min at room temperature. The Sn exchanged HBeta zeolite was recovered and reused several times without the loss of its catalytic performance.

Full text of DOI:10.1016/j.apcata.2012.01.001

Applied Catalysis A: General 419–420 (2012) 22–30
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Tin exchanged zeolite as catalyst for direct synthesis of ␣-amino nitriles under
solvent-free conditions
Arpan K. Shah, Noor-ul H. Khan∗, Govind Sethia, S. Saravanan, Rukhsana I. Kureshy, Sayed H.R. Abdi,
Hari C. Bajaj
Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research, Institute (CSMCRI), Council of Scientific and Industrial Research (CSIR), G. B. Marg,
Bhavnagar 364021, Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Sn exchanged HBeta zeolite was prepared and characterized by PXRD, surface area, TPD and TEM analysis.
The Sn exchanged zeolite was found to be highly efficient catalyst for the direct synthesis of ␣-amino
nitrile from various ketones and aldehydes with amine and trimethyl silylcyanide (TMSCN) under solvent-
free condition. Excellent yield of ␣-amino nitrile (up to 96%) was achieved within 10–120 min at room
temperature. The Sn exchanged HBeta zeolite was recovered and reused several times without the loss
of its catalytic performance.
Received 18 August 2011
Received in revised form
30 December 2011
Accepted 2 January 2012
Available online 18 January 2012
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Strecker reaction
␣-Amino nitriles
Heterogeneous catalysis
Zeolite
1. Introduction
[11,21,43–53]. Significant among these are Lewis acid/Brønsted
acid catalysts like Fe(cp)2·PF6 [11], PEG [27], sulfamic acid-
There are intentionally different approaches among the
chemists towards the carbon carbon bond forming reactions.
Among these a very elegant and versatile solution is provided
through the addition of cyanide to an imine (Modified Strecker
reaction) which also represents one of the intrigued methods for
preparing ␣-amino acids [1]. ␣-Amino nitrile plays a significant role
in organic chemistry because of its bifunctional nature, an amino
and a nitrile group, thus it offers various synthetic approaches to
different classes of natural and bioactive compounds [2]. ␣-Amino
nitrile is also a valuable prebiotic precursor to porphyrins, corrins,
nicotinic acid, nucleic acids, safromycin A (anti-tumor potency) and
phthalascidin [3]. The versatile synthon ␣-amino nitriles are pre-
pared by the reaction of aldehydes or ketones [4] with amines in
the presence of various cyanide sources such as HCN [3,5], KCN
[6,7], TMSCN [8] and Et2AlCN [9]. Among these TMSCN has emerged
as a promising, effective and relatively safer cyanide source [10]
for the Strecker reaction. These catalytic systems performed well
with aldehydes [11–49] but were not so effective in the case of
ketone in most cases. Nevertheless, there are few catalysts reported
for the Strecker reaction using less reactive electrophilic ketones
functionalized magnetic Fe3O4 nanoparticles [43], sulfonate group
anchored on mesoporous silica [44], tin ion-exchanged montmoril-
lonite [45], nanocrystalline MgO [46], NHC-amidate Pd(II) complex
[47], Li-trifluoroboronate [48], mesoporous aluminosilicate [49],
TMSOTf [50], xanthan sulfuric acid [51], gallium(III)triflate [52],
under ambient or high pressure [21,53] and solvent/solvent-free
conditions. Although some outstanding catalytic systems have
been reported, still there is a plenty of room for improvement,
particularly in terms of catalyst recyclability, high catalyst activ-
ity at lower catalyst loading and conducting the reaction under
solvent-free condition in lesser time. Onaka et al. [45] showed that
individually Na-Mont, Sn(OH)4, SnO2, Sn-MCM-41 and Al-MCM-41
do not catalyze Strecker reaction. However, low to moderate prod-
uct yields were obtained when SnO2/silica (7.2%), SnO2/MCM-41
(22%) and SnO2/SiO2–Al2O3 (37%) were used as catalyst. The best
results were however obtained when Sn-Mont (84% in 3 h) was
used as catalyst. Exploring the utility of Sn exchanged zeolite as
catalyst for this reaction was conspicuously absent despite the fact
that zeolites have been extensively used as solid catalyst in various
organic transformations [54] and is industrially valuable [55,56]
because of its easy synthesis, porous structure with tunable ion
exchange capacity. In view of the above and our ongoing interest in
developing environment friendly and solvent free protocol for var-
ious organic transformations [11,57–59], here we are reporting Sn
∗
Corresponding author. Tel.: +91 0278 2567760; fax: +91 0278 2566970.
E-mail address: khan251293@yahoo.in (N.-u.H. Khan).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2012.01.001

A.K. Shah et al. / Applied Catalysis A: General 419–420 (2012) 22–30
23
exchanged HBeta zeolite catalyzed Strecker reaction under solvent
free condition to get ␣-amino nitriles in excellent yield (up to 96%)
within 10–120 min with an added advantage of recyclability of the
catalyst.
1.4% SnHBeta
2.4% SnHBeta
2. Experimental
2.1. Materials and methods
Nano SnO2
HBeta
X-ray powder diffraction studies at ambient temperature were
carried out using a PHILIPS X’pert MPD system in the 2ꢀ range
10
20
30
2 theta
40
50
60
of 5–65◦ using Cu K␣1 (ꢁ = 1.54056 A). Surface area of the HBeta
˚
zeolite samples were determined by nitrogen adsorption method
at 77.35 K was measured using ASAP 2020 (Micromeritics Inc.,
USA) after activating the sample at 673 K under vacuum. Acidity
of the zeolites was characterized by the TPD of NH3 (Micromerit-
ics, Autochem 2920). The standard procedure for TPD measurement
involved the activation of zeolite in flowing He at 723 K (4 h), cool-
ing to 303 K and adsorbing NH3 from a stream of He–NH3 (10%),
removing the physically adsorbed NH3 by desorbing in He at 373 K
for 1 h and finally carrying out the TPD experiment by raising the
temperature of the catalyst in a programmed manner (10 K/min).
The TPD curves were deconvoluted into peaks and the areas under
the peaks were converted into milliequivalents (mequiv.) of NH3
per gram of catalyst based on injection of known volumes of the
He–NH3 mixture at similar conditions. Elemental analysis was done
on CHNS Analyzer, PerkinElmer model 2400 (USA). FTIR spectra
were recorded by PerkinElmer Spectrum GX spectrophotometer
(USA) in KBr window. An inductively coupled Plasma-Optical emis-
sion spectrophotometer (ICP-OES, Optima 2000 DV, PerkinElmer,
Eden Prarie, MN) was used to determine the weight percentage
of the tin in the SnHBeta zeolites. Transmission electron micro-
scope (TEM) analysis was done using JEOL, JEM-2100 microscope at
200 kV using carbon coated copper grid. HBeta and tin exchanged
HBeta zeolite was dispersed in ethanol and a drop of dispersion
was laid on grid for TEM to determine the surface morphol-
ogy. NMR spectra were recorded on a Bruker F113V spectrometer
(200 MHz and 500 MHz, Switzerland) and were referenced inter-
nally with TMS. For the product purification flash chromatography
was performed using silica gel 60–120 mesh purchased from s.d.
Fine-Chem. Ltd., India.
Fig. 1. XRD pattern of HBeta, nano SnO2 and tin exchanged HBeta zeolites.
solution of SnCl2·2H2O in the solid/liquid ratio 1:100 respectively
at 25 ◦C under stirring for 24 h. The residue was filtered, washed
with hot distilled water, until the washings were free from ions
and dried in air oven at 80 ◦C and calcined at 550 ◦C for 4 h.
An inductively coupled plasma-optical emission spectropho-
tometry showed that the catalysts 2.4% SnHBeta and 1.4% SnHBeta
samples have 2.4 wt% and 1.4 wt% of tin respectively.
2.3. Experimental procedure for the synthesis of ˛-amino nitrile
using Sn-exchange zeolite
The catalyst Sn-exchange zeolite (10 mg for ketones and 5 mg for
aldehydes) was taken in a 5 ml round bottom vial and sealed with
a rubber septum to which a ketone or an aldehyde (1 mmol) and
aniline (1 mmol) were added at room temperature under stirring.
To the above stirred solution TMSCN (CAUTION: Toxic! 1.3 mmol)
was added in small fractions over a period of 5 min. The progress
of reaction was monitored on TLC. After completion of reaction,
the catalyst was removed by centrifugation and/or filtration. The
solid was washed with methanol. Washings and the filtrate were
combined, concentrated and was subjected to flash column chro-
matography on silica gel (eluted with hexane/ethyl acetate, 90:10)
to get the respective ␣-amino nitriles in good to excellent yield. The
purified products were characterized by melting point, IR, micro-
analysis, 1H and 13C NMR analysis. Characterization data of some
selected products are as follows:
HBeta zeolite having SiO2/Al2O3 ratio of 24 was procured
from Zeochem, Switzerland and SnCl2·2H2O (E. Merck India
Ltd., India). SnCl4, trimethyl silylcyanide (TMSCN), 2-methyl
benzaldehyde, 3-methyl benzaldehyde, 4-methyl benzaldehyde
(all from Merck, Germany), benzaldehyde, 4-methoxy ben-
zaldehyde, 3-methoxy benzaldehyde, 4-fluoro benzaldehyde,
2-fluoro benzaldehyde, 4-chloro benzaldehyde, 1-naphthaldehyde,
2-thiophenecarboxaldehyde, 2-furan-carboxaldehyde, hydrocin-
namaldehyde, hexanal, 3-methyl butyraldehyde, aniline, benzyl
amine (all from Aldrich, USA), acetophenone, propeophenone,
4-chloro acetophenone, 4-bromo acetophenone, 4-methyl ace-
tophenone, 2-methyl cyclohexanone, 4-methyl cyclohexanone,
2ꢀ-acetonaphthone, benzylideneacetone, 2-hexanone (all from
ACROS ORGANICS) and benzophenone (s.d. Fine-Chem. Ltd., India)
were used as received.
2-Phenyl-2-(phenylamino)propanenitrile (Table 5, entry 1):
White solid, m.p., 140–142 ◦C; 1H NMR (CDCl3, 200 MHz) ı = 1.90
(s, 3H), 4.15 (s, 1H), 6.50 (d, J = 8.2 Hz, 2H), 6.77 (t, J = 7.9 Hz, 1H),
7.08 (t, J = 7.9 Hz, 2H), 7.33–7.45 (m, 3H), 7.60 (d, 2H, J = 8.0) ppm;
IR (KBr): 3390, 2929, 2230, 1610, 1522, 1435, 1178, 1090, 756 cm−1
.
2-(N-Anilino)-2-phenylacetonitrile (Table 6, entry 1): White solid;
m.p., 76–78 ◦C; 1H NMR (CDCl3 200 MHz): ı = 4.0 (d, J = 8, 1H), 5.4
(d, J = 8.2, 1H), 6.7 (d, J = 7.6, 2H), 6.9 (t, J = 7.4, 1H), 7.2–7.3 (m, 2H),
7.5–7.5 (m, 3H), 7.5–7.6 (m, 2H) ppm; 13C NMR (50 MHz, CDCl3):
ı = 50.9, 114.8, 118.9, 120.9, 130.0, 130.2, 130.3, 134.5, 145.3 ppm;
IR (KBr) ␯ 3338, 3029, 2940, 2237, 1600, 1515, 1497, 1283, 1243,
1114, 924, 753, 693 cm−1
.
3. Results and discussion
3.1. Catalyst characterization
2.2. Catalyst synthesis
3.1.1. X-Ray powder diffraction
Sn cations from aqueous solution were introduced into the
highly crystalline HBeta zeolites by the conventional cation
exchange procedure [60]. Zeolite samples having different degree
of tin exchange were prepared by changing the concentration
and solid/liquid ratio during tin exchange. 2.4% SnHBeta and 1.4%
SnHBeta samples were prepared by using 0.01 and 0.005 M aqueous
The diffraction patterns of the HBeta shows the reflections
in the range of 5–35◦ typically of highly crystalline zeolites. It
was observed that on exchange with Sn ion, the intensities of
peaks decreased marginally confirming that the zeolite structure
is retained (Fig. 1). The X-ray diffraction patters of the Sn ion
exchanged zeolite showed the typical peaks of zeolite beta at 2ꢀ

24
A.K. Shah et al. / Applied Catalysis A: General 419–420 (2012) 22–30
300
250
200
150
0.06
0.05
0.04
0.03
0.02
0.01
0.00
1.4% SnHBeta
2.4% SnHBeta
HBeta
1.4% SnHBeta
2.4% SnHBeta
HBeta
20
0
0.0
200
400
600
0.2
0.4
0.6
0.8
1.0
Temperature ( ºC)
Relative Pressure P/PO
Fig. 3. NH3 TPD profiles of the tin exchanged HBeta zeolites.
Fig. 2. N2 adsorption desorption isotherm of HBeta and tin exchanged HBeta zeo-
lites.
(Fig. 2) shows hysteresis loop in the range P/P◦ = 0.5–1, indicating
the presence of non-framework intra-particular porosity [62].
values of 7.25, 7.83, 21.43, 22.42, 25.27, 27.04, 28.79 and 29.55. The
decrease in peak intensity is due to loss in crystallinity caused by the
HCl released during calcination of tin exchanged zeolite samples.
The origin of HCl can be traced to the tin chloride solution used
during the metal exchange step. The tin exchanged zeolite sam-
ples also show three less intensity broad peaks (shown by down
arrow) at 2ꢀ◦ of 26.5, 33.8 and 51.5 in the XRD pattern assigned to
the 1 1 0, 1 0 1 and 2 1 1 plane of poorly crystalline cassiterite phase
(No. 00-041-1445) of SnO2 [60,61]. This shows that in addition to
tin exchange, of some amount of SnO2 crystals are formed during
calcinations. However, no peaks were observed for metallic tin and
SnO and these features are in line with earlier reported [60] tin
exchanged zeolite samples.
3.1.3. Ammonia temperature programmed desorption
The HBeta zeolite contains two types of acidic sites, weak acid
sites at around 180 ◦C and strong acid sites around 326 ◦C (Table 2).
The decrease in desorb ammonia and increase in desorption tem-
perature shows that the amount of these two acidic sites decreases
but their strength increases on tin exchange (Fig. 3). The polarizing
and inductive effects of tin ions weaken the OH bonds of bridg-
ing hydroxyl groups and make them more acidic. The broad peak
centered at around 600 ◦C in all the samples is possibly due to the
dehydroxylation of HBeta zeolite [63] (Table 2).
3.1.4. Transmission electron microscopy (TEM) analysis
Nano-sized SnO2 that we synthesized for the present study in
order to compare its catalytic activity (in Strecker reaction) with
Sn-exchanged zeolite samples showed strong peaks at 2ꢀ◦ of 26.6,
34.0 and 51.8 (Fig. 1).
The photomicrographs obtained by TEM showed well defined
ordered porous structure of HBeta zeolite framework in all the sam-
ples including tin-exchanged zeolite samples indicating that the
zeolite frame work is not destroyed during metal exchange pro-
cess. Besides, some well-formed tin oxide nanoparticles of less than
5 nm are also visible (mostly on the surface) in both 2.4% SnHBeta
(b) and 1.4% SnHBeta (c) which are not found in HBeta zeolite (a)
(Fig. 4). TEM photomicrograph of as synthesized nano-SnO2 (of
∼20 nm size) shows morphology similar to the SnO2 present in
tin-exchanged zeolite samples (Fig. 4).
3.1.2. Surface area and pore size distribution
Micropore and external surface areas of all the zeolite samples
used in the present study were determined from t-plot method.
The surface area and micropore volume were slightly decreased on
tin exchange due to some loss of crystallinity and filling of pores by
large tin cations and some SnO2 nanoparticles formed during cal-
cination in the micropores of zeolite. The observed increase in the
external surface area is a reflection of increased amorphous phase
of zeolite; however contribution from the deposition of some SnO2
nanoparticles on the zeolite surface cannot be ruled out (Table 1).
The adsorption/desorption isotherm of HBeta and SnHbeta samples
3.2. Catalytic properties of SnHBeta systems
The systematic catalytic study for the synthesis of ␣-amino
nitrile was started using acetophenone and aniline as model sub-
strates (1 mmol scale) with TMSCN as a source of cyanide under
Table 1
Surface area analysis data of Sn-exchange zeolite.
Sample
BET surface area (m2/g)
Micropore surface area (m2/g)
External surface area (m2/g)
Pore volume (cm3/g)
HBeta
2.4% SnHBeta
1.4% SnHBeta
636
576
630
451
363
403
185
213
227
0.209
0.170
0.188
Table 2
Ammonia temperature programmed desorption data of Sn-exchange zeolite.
Sample
Acidity
Temp. (◦C)
mmol/g
Temp. (◦C)
mmol/g
Temp. (◦C)
mmol/g
Total
HBeta
2.4% SnHBeta
1.4% SnHBeta
180
205
199
0.661
0.307
0.379
326
395
363
0.142
0.092
0.043
–
596
625
–
0.803
0.414
0.432
0.015
0.010

A.K. Shah et al. / Applied Catalysis A: General 419–420 (2012) 22–30
25
Fig. 4. TEM images of zeolites (a) HBeta, (b) 2.4% SnHBeta, (c) 1.4% SnHBeta, and (d) nano-SnO2.
Table 3
Optimization of catalyst for the Strecker reaction.a
Entry
Catalyst
Amount of catalyst (mg)
Time (min)
60
Yield (%)b
1
2
No catalyst
No catalyst
–
–
Trace
60
720
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
HBeta zeolite
2.4% SnHBeta
1.4% SnHBeta
SnO2 (commercial)
10
10
10
2.4c
2.4c
10
10
2.4c
10
9.5
5
75
30
48
60
60
75
50
60
30
60
65
75
40
45
60
60
76
93
85
Trace
Trace
78
85
Trace
82
22
82
82
85
d
Nano-SnO2
HBeta zeolite + Nano-SnO2 (2.4%) physical mix
SnO2 (commercial)
SnCl2·2H2O
SnCl2·2H2O
Recycled SnCl2·2H2O
2.4% SnHBeta
2.4% SnHBeta
2.4% SnHBeta
2
20
2.4% SnHBeta
100c
90
SBA-15e
10
20
Trace
1.1% SnSBA-15
8f
a
All reactions were carried out at RT using acetophenone (1 mmol), aniline (1 mmol), TMSCN (1.3 mmol).
Isolated yield.
Reaction was carried at 10 mmol scale.
Nano sized SnO2 was prepared as per the reported procedure [64].
SBA-15 was prepared as per the reported procedure [65].
Calculated by GC.
b
c
d
e
f

26
A.K. Shah et al. / Applied Catalysis A: General 419–420 (2012) 22–30
Table 4
Scope of various solvents for Strecker reaction under optimized catalyst condition.a
Entry
Solvent
Time (min)
Yield (%)b
1
2
3
4
5
6
Solvent free
Methanol
Ethanol
Acetonitrile
Toluene
30
120
120
120
120
120
93
82
83
78
30
45
Chloroform
a
All reactions were carried out at RT using acetophenone (1 mmol), aniline (1 mmol), TMSCN (1 mmol) in 2 mL of solvent.
Isolated yield.
b
solvent free condition at room temperature (Table 3). In the absence
of a catalyst only traces of product formation was observed (entry
1) in 60 min, however with extended period (720 min) the desired
product was obtained in 60% isolated yield (entry 2). Whereas the
same reaction when conducted in the presence of HBeta zeolite
(10 mg) of high Brønsted acidity, the desired product was obtained
in 76% isolated yield in 75 min (entry 3). Remarkably, the use of Sn2+
exchanged zeolite (2.4% SnHBeta, prepared from the 0.01 mmol
aqueous solution of SnCl2·2H2O) (10 mg) as catalyst gave the prod-
uct in 93% yield within 30 min (entry 4). Interestingly, HBeta zeolite
with lower Sn2+ content (1.4% SnHBeta, prepared from 0.005 mmol
aqueous solution of SnCl2·2H2O) gave relatively lower product
yield (85%) in longer reaction time 48 min (entry 5). At this point it
looked like that Brønsted acid sites (both H and exchanged Sn2+) are
responsible for the increased catalytic activity where contribution
of Sn2+ is relatively more. However, tin exchanged zeolite sam-
ples also showed the presence of well distributed nano-sized SnO2
particles and the possibility of these particles catalyzing (as Lewis
acid sites) the reaction cannot be ruled out entirely. To address this
issue, this reaction was conducted by using commercial grade SnO2
(entry 6) and nano-SnO2 (as synthesized, entry 7) as catalysts and
for the sake of fair comparison the tin content of 2.4% was kept
constant. Noticeably, in both the cases only trace amount of prod-
uct formation took place in 60 min. However, a physical mixture of
nano-SnO2 (2.4%) and HBeta zeolite catalyzed this reaction to give
the product in 78% yield in 75 min (entry 8). This result is at par
with the results obtained with commercial HBeta zeolite sample
(entry 3) implying very little or no contribution of SnO2 in cat-
alyzing this reaction at this Sn loading. However, SnO2 at higher
Sn loadings (10 mg) do catalyze this reaction (entry 9). Further, in
order to rule out the possibility of SnCl2·2H2O (adhered to zeolite)
acting as a catalyst by itself, a catalytic experiment with SnCl2·2H2O
at 2.4% Sn loading was conducted that showed only trace of product
formation in 60 min (entry 10). This experiment rules out the pos-
siblity of contribution SnCl2·2H2O at this Sn loading but at higher
Sn loading SnCl2·2H2O (entry 11) also catalyze the reaction appre-
ciably (82% yield in 30 min). It is to be noted here that the activity
of SnCl2·2H2O comes down drastically (22% yield) during recycle
experiments possibly due to its instability (hydrolysis) under the
reaction condition (entry 12). The results obtained with these sets
of experiments clearly indicate that the catalytic activity of well
distributed Sn2+ ions in exchangeable positions of zeolite cavities
is greater than SnO2 (nano) particles and/or Brønsted acid sites of
zeolite.
2–20 mg/1 mmol of the substrate was used (entries 13–15) under
identical reaction conditions which, revealed that a catalyst load-
ing of 10 mg (entry 4) is optimum to achieve best product yield in
shortest reaction time.
At a relatively higher scale (10× 1 mmol), of the representative
substrate acetophenone with aniline and TMSCN gave the product
in 90% isolated yield in 45 min indicating that the present protocol
is scalable (entry 16, Table 3).
SBA-15 as such does not catalyze the Strecker reaction (entry 17)
however, 8% product formation was observed with 1.1% SnSBA-15
sample (entry 18) (TEM image is given as supporting information)
which is very low as compared with tin exchanged zeolite samples.
Therefore, it can be safely concluded that both bulk and nano-SnO2
poor catalyst for Strecker reaction with ketonic substrate and the
finding is in line with the observations reported in the literature
[45].
The role of solvent was also assessed in Strecker reaction of ace-
tophenone with optimized amount of the catalyst 2.4% SnHBeta
(Table 4). The alcoholic solvents e.g., methanol and ethanol gave
82 and 83% (entries 2 and 3) of corresponding ␣-amino nitrile in
120 min respectively. Whereas, the same reaction when conducted
in acetonitrile, chloroform and toluene afforded the Strecker prod-
uct in 78, 30 and 45% (entries 4, 5 and 6) yield in 120 min. The
results reveal that in the present catalytic protocol some of the sol-
vents e.g., methanol, ethanol and acetonitrile where the mobility of
proton (H+) is more feasible than the solvents like chloroform and
toluene can be effectively used. However, the performance of sol-
vent free condition (entry 1) is better both in terms of product yield
and shorter reaction time than the same reaction when conducted
in the presence of a solvent. This phenomenon is not unusual as sol-
vents are known to compete with reagents on adsorption/catalytic
sites [19].
Next, we extended the solvent-free catalytic protocol to various
aromatic and aliphatic ketones with aniline and TMSCN using 2.4%
SnHBeta as catalyst and the results are summarized in Table 5. It is
understood from the results that the alkyl phenyl ketones in gen-
eral gave very good product yield (entries 1–6; yield, 81–95%) in
short time (15–45 min). The reaction was however relatively slug-
gish (120 min) in the case of benzophenone and ␣,␤-unsaturated
ketone e.g., benzylideneacetone (entries 7 and 8) to give the respec-
tive products in low yields 30 and 25% respectively. Remarkably,
cyclic ketones like 2-Me-/4-Me-cyclohexanone gave good product
yield (∼80%) in 50 min (entries 9 and 10) but linear or branched
aliphatic ketones failed to give any product in 120 min (entries 11
and 12).
In view of the above, 2.4% SnHBeta was used as preferred cat-
alyst in our subsequent studies on Strecker reactions to optimize
reaction parameters and scope of various substrates. Accordingly,
first we varied the catalyst loading in milligrams per 1 mmol of
acetophenone as a model substrate. A catalyst loading ranged over
This protocol at a very low catalyst loading (5 mg of 2.4%
SnHBeta/1 mmol of substrate) worked well for various aldehydes
having variable electronic and steric features to give respec-
tive products in excellent isolated yields (80–96%) in 10–20 min

A.K. Shah et al. / Applied Catalysis A: General 419–420 (2012) 22–30
27
Table 5
Direct Strecker reaction of various ketones in the presence of 2.4% SnHBeta as a catalyst with aniline and TMSCN under solvent free condition.a
Entry
1
Ketone
Time (min)
30
Product
Yield (%)b
93
86
2
3
45
45
81
4
5
6
15
20
35
88
95
89
7c
120
30
8
9
120
50
25
80
10
11
50
82
120
120
00
00
12
a
All reactions were carried out at RT, using 2.4% SnHBeta as catalyst (10 mg), ketone (1 mmol), aniline (1 mmol) and TMSCN (1.3 mmol).
b
c
Isolated yield.
Reaction carried out at 60 ◦C.
(Table 6). Aldehydes as diverse as aromatic with electron with-
This protocol also work well (yield 92% in 20 min) in the Strecker
reaction of benzaldehyde with benzylamine and TMSCN, as demon-
strated at entry 16. Although, catalyst-free sequential addition of
an aromatic aldehyde, amine and TMSCN has been reported ear-
lier to undergo Strecker reaction efficiently, its one-pot version
gave the product in low yields (0–39%) [46]. One-pot Strecker
reaction usually happens efficiently only in the presence of a
catalyst.
drawing and donating substituents at ortho, meta and para
positions (entries 1–10), heterocyclic (entries 11 and 12) and
aliphatic aldehydes (entries 13–15) have undergone Strecker reac-
tion with aniline and TMSCN very efficiently. Distinctly, para
substituted aldehydes have reacted faster than their ortho or meta
counter parts of methyl substituted (entries 2–4), methoxy (entries
5 and 6) and fluoro substituted benzaldehyds (entries 7 and 8).

28
A.K. Shah et al. / Applied Catalysis A: General 419–420 (2012) 22–30
Table 6
Direct Strecker reaction of various aldehydes in the presence of 2.4% SnHBeta as
a
catalyst with aniline and TMSCN under solvent free condition.a
Entry
1
Aldehyde (R)
Time (min)
10
Product
Yield (%)b
96
2
3
4
15
15
10
93
91
96
5
15
91
6
10
10
10
15
94
92
95
93
7c
8
9
10
15
91
11
12
10
10
90
91
13
14
15
20
89
80

A.K. Shah et al. / Applied Catalysis A: General 419–420 (2012) 22–30
29
Table 6 (Continued)
Entry
Aldehyde (R)
Time (min)
20
Product
Yield (%)b
15
88
92
16c
20
a
All reactions were carried out at RT, using 2.4% SnHBeta as catalyst (5 mg), aldehyde (1 mmol), aniline (1 mmol) and TMSCN (1.3 mmol).
Isolated yield.
Reaction carried out using benzyl amine.
b
c
Acknowledgements
Recylcing Graph
100
80
60
40
20
0
N.H. Khan and Arpan K. Shah is thankful to DST and CSIR Network
project on Catalysis for financial assistance, and also the “Analytical
Section” of the Institute for providing instrumentation facilities.
AKS is also thankful to Dr. Santosh Agrawal for useful discussions.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.apcata.2012.01.001.
1
2
3
4
5
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