Platinum nanoparticles supported on zirconia mediated synthesis of N-acyl and N-(tert-butoxycarbonyl)amines from nitroarenes and azides

Article abstract of DOI:10.1016/j.molcata.2011.12.002

A convenient and useful protocol has been designed for the synthesis of N-aryl acetamides from the corresponding nitro compounds via a reductive N-acylation process using bi-functional, recyclable heterogeneous platinum nanoparticles supported on zirconia [Pt(0)/ZrO₂] catalyst, employing molecular hydrogen as the environmentally benign reductant and the corresponding anhydrides as acylating agents. N-Boc protected amines were also synthesized in similar lines, from the corresponding azides. The reaction is successfully performed under mild conditions to afford good to excellent yields of the products. The solid bifunctional-catalyst, Pt(0)/ZrO₂ is quantitatively recovered by simple centrifugation and reused for multiple cycles with consistent activity and selectivity.

Full text of DOI:10.1016/j.molcata.2011.12.002

Journal of Molecular Catalysis A: Chemical 355 (2012) 96–101
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Platinum nanoparticles supported on zirconia mediated synthesis of N-acyl and
N-(tert-butoxycarbonyl)amines from nitroarenes and azides
M. Lakshmi Kantama,∗, R. Sudarshan Reddya, K. Srinivasa, R. Chakravartia, B. Sreedhara, F. Figuerasb,
Ch. Venkat Reddyc
a Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500607, India
b Institut de recherche sur la catalyse et l’environnement de Lyon, UMR 5256 Université Lyon 1-CNRS, 2, Avenue Albert Einstein, F-69626, Villeurbanne, France
c 1311 Gilman Hall, Department of Chemistry, Iowa State University, Ames, IA 50011, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A convenient and useful protocol has been designed for the synthesis of N-aryl acetamides from the
corresponding nitro compounds via a reductive N-acylation process using bi-functional, recyclable het-
erogeneous platinum nanoparticles supported on zirconia [Pt(0)/ZrO2] catalyst, employing molecular
hydrogen as the environmentally benign reductant and the corresponding anhydrides as acylating agents.
N-Boc protected amines were also synthesized in similar lines, from the corresponding azides. The reac-
tion is successfully performed under mild conditions to afford good to excellent yields of the products. The
solid bifunctional-catalyst, Pt(0)/ZrO2 is quantitatively recovered by simple centrifugation and reused for
multiple cycles with consistent activity and selectivity.
Received 29 August 2011
Received in revised form
29 November 2011
Accepted 1 December 2011
Available online 11 December 2011
Keywords:
Bi-functional
Heterogeneous
Nanoparticles
Amines
© 2012 Elsevier B.V. All rights reserved.
Azides
1. Introduction
N-arylamide derivatives [9], such as N-aryl chloroacetamides are
useful intermediates for the synthesis of oxyindoles [10].
Organic amines and their derivatives are industrially important
intermediates for several pharmaceuticals, agrochemicals, dyes,
herbicides, pigments, surfactants, pesticides, cosmetics and poly-
mers [1–4]. Reduction of nitro compounds and azides to their
corresponding amines is an important transformation in synthetic
organic chemistry, and protection of primary amines with a suit-
able group plays a major role in multistep synthesis [5]. The
most common technique for the synthesis of anilines involves the
selective hydrogenation of aromatic nitro-compounds [6]. The clas-
sical route practiced in industry for the production of anilines
involves the reduction of nitroarenes employing stoichiometric
amounts of iron powder in the presence of hydrogen source such
as hydrochloric acid or acetic acid [7]. In general, the preparation of
N-arylacetamides involves two steps, i.e. reduction of nitroarenes
to N-arylamines followed by the acylation of N-arylamines to
the corresponding anilides (N-arylacetamides). The conversion of
nitroarenes to their corresponding acetanilides in a one-pot reac-
tion is an important transformation in organic chemistry under
homogeneous conditions [8]. The acetanilides and other type of
In general, direct conversion of nitroarenes to acetanilides are
carried out by iron powder with acetic acid [11], molybdenum
hexacarbonyl/acetic acid [12], Other metal catalysts known to
catalyze this transformation are Au/Al2O3, Au–Pd/Al2O3 [13], plat-
inum oxide [14], rhodium–platinum oxide [14], palladium [15] and
zinc [16]. In addition, the reduction of nitro groups using samar-
ium [17], are also reported. Recently gold catalyzed hydrogenation
of nitro compounds is also reported [18–20]. Some of these pro-
cesses encounter the problem of disposal of a large amount of
metal salts generated during the reaction. Although, homogeneous
iron carbonyls are used extensively in the reductive acylation of
nitroarenes using variety of reducing agents [21], these processes
face the difficulty in product isolation from the iron sludge formed
during the reaction.
The reduction of azides to amines is an important and widely
practiced reaction in organic synthesis. It is especially useful
because of the ease of synthesis and high stereoselectivity associ-
ated with the preparation of the precursor azides and the reduction
represents a pivotal step in a stereoselective sequence for the
preparation of amines. Azides can be introduced by displacement
of a suitable nucleofuge or direct conversion of an existing amine
by a diazotransfer reaction. Furthermore, azides are resistant to
many reaction conditions and can be easily reduced to amines
∗
Corresponding author. Tel.: +91 40 27193510; fax: +91 40 2716 0921.
E-mail address: mlakshmi@iict.res.in (M.L. Kantam).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.12.002

M.L. Kantam et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 96–101
97
either generally (hydrogenation, metal hydrides, etc.) or orthog-
NHAc
NO2
onally (Staudinger reaction) [5]. Substitution of a leaving group by
the azide anion, reduction of the azide to an amine, and protec-
tion of the amine as tert-butoxycarbamate (R-NH-Boc) is a standard
process in organic synthesis.
i) Pt/ZrO2, Methanol,
ii) Acetic anhydride, r.t
R
R
Tert-butoxycarbonyl (Boc) is among the most common protect-
ing groups for amines, amino acids, and other nitrogen compounds
due to its chemical stability and ease to deprotection [22]. To
save time and to avoid secondary or parallel reactions or losses of
material during the isolation of certain amines, the reduction and
protection steps are frequently performed in one-pot. However,
there are only few reports in the literature for the direct conversion
of azides to the corresponding N-Boc-amines, such as using phos-
phines [23,24], Pd(OH)2/C in ethanol [25], Fe/NH4Cl in methanol
under sonication [26], and Pd–C [27]. In recent years a number of
heterogeneous catalysts are also reported for the direct conver-
sion of azides to the corresponding N-Boc-amines [28,29]. These
catalysts offer several advantages over their homogeneous coun-
terparts with respect to recovery, recycling as well as minimization
of undesired toxic wastes. Baralt and Holy reported reduction
of nitrobenzene to aniline using polymer anchored anthranilic
acid palladium complexes under high pressures of 500–800 psi at
70–100 ◦C [30]. Hydrogenation of mono and poly-nitro aromat-
ics are realized with high yields by Pd/C catalyst via hydrogen
transfer using cyclohexene in ethanol under reflux conditions [31].
Recently, Shi et al. have reported the reduction of nitroarenes
over nickel–iron mixed oxide catalyst using hydrazine hydrate
under reflux conditions while Huang et al. reported the same
reaction using a platinum nanocatalyst [32,33]. Thus, high tem-
peratures, pressures and longer reaction times accompany these
methods of reduction of nitro compounds. But, there are few
reports on the one-pot conversion of nitroarenes to the correspond-
ing N-arylacetamides [34,35]. Of late, we have reported reductive
acylation of nitroarenes by Fe3+ montmorillonite [36], and other
reports are available in the literature on the reductive acylation of
3-nitro indoles [37], as well as 2- and 3-nitro pyrroles by Pd/C in
methanol [38]. Recyclable heterogeneous catalysis is particularly
attractive due to the ready separation of large quantities of prod-
ucts using small amounts of catalysts and less contamination of
final products [39].
Pt(0),ZrO2, H2 atm
R-N3
R-NH-Boc
(Boc)2O, Methanol, rt
Scheme 1. Reductive acylation of aromatic nitro compounds to amides and azides
to N-Boc protected amines.
observed on a Philips TECNAI F12 FEI transmission electron micro-
scope (TEM). NMR spectra were recorded on a Varian Gemini
(200 MHz), Bruker Avance (300 MHz), Varian Unity (400 MHz)
spectrometer using TMS as an internal standard in CDCl3. Mass
spectra were obtained at an ionization potential of 70 eV [scanned
on VG 70-70H (micro mass)].
2.2. Preparation of the catalyst
The Pt(0)/ZrO2 was prepared by the following procedure. Zirco-
nium hydroxide was precipitated from ZrOCl2 (Loba, L.R. grade) at
constant pH 10 with the help of NH4OH. The precipitate was aged at
room temperature for 12 h, filtered and washed several times with
deionized water until free from chloride ions, dried at 120 ◦C for
24 h and calcined at 500 ◦C in a flow of air. The ZrO2 thus obtained
showed a surface area of 105 m2 g−1. To prepare Pt2+/ZrO2, 0.2708 g
of H2PtCl6 was dissolved in 50 mL of distilled water, 5.0 g of cal-
cined ZrO2 added, then the beaker was placed on the hot plate
stirred with a glass rod for several hours. Water was evaporated
while on the hot plate, yielding the Pt2+/ZrO2 as a light yellow
powder (5.2 g). The final catalyst Pt(0)/ZrO2, a grey color solid, was
obtained after hydrogenation at 523 K for 3 h under the hydrogen
flow (30 mL min−1) and used for the reductive acylation of nitro
compounds and for the synthesis of N-Boc protected amines from
azides at room temperature. The elemental analysis the Pt content
in the catalyst was 0.102 mmol/g (Pt content: 2 wt%). TiO2 (surface
area: 200 m2 g−1) was purchased from Fluka and similar procedure
was followed to prepare Pt(0)/TiO2. 1% Pt/C and 1% Pt/Al2O3 were
purchased from Sigma–Aldrich and used for the reductive acylation
of nitro compounds. The catalyst Pt(0)/ZrO2 is well characterized
by XRD, TEM, XPS, TPR, EDX analysis (see Supporting information,
SI).
The solid used as support is zirconia, as evidenced from the XRD
spectrum Fig. S1a, SI. After loading with Pt, an amorphous phase
was observed by XRD (Fig. S1b, SI), after reduction the original pat-
tern of zirconia was restored (Fig. S1c, SI). The XPS analysis of the
unreduced Pt/ZrO2 sample by XPS gave a spectrum containing a
doublet at 73.6 (Pt 4f7/2) and 77 eV (Pt 4f5/2) (Fig. S2a, SI), char-
acteristic of cationic Pt, while after reduction the presence of the
doublet at 71.4 and 74.7 (Fig. S2b, SI) attributed to metallic platinum
[41]. The TPR data shows the cationic platinum species converted
to metallic platinum at 250 ◦C (Fig. S3, SI).
In an endeavor to design newer industrially feasible protocols
for clean, efficient and selective synthesis of various industrially
important organic amines utilizing mild and benign reductants, we
have earlier reported the reduction of nitrobenzene by molecular
hydrogen using heterogeneous nanopalladium and nanoplatinum
catalysts [39,40]. Herein, we report a one-pot synthesis of anilides
and N-Boc protected amines from the reduction of nitro and azido
compounds with molecular hydrogen followed by the reaction with
an acid anhydride to afford the corresponding products at ambi-
ent temperature with good to excellent yields using heterogeneous
platinum(0) supported on zirconia [Pt(0)/ZrO2] as a recyclable cat-
alyst (Scheme 1).
2. Experimental
2.1. General
Nitrobenzene was purchased from S. D. Fine Chemicals Ltd.
Mumbai. ACME silica gel (100–200 mesh) was used for column
chromatography and thin-layer chromatography was performed
on Merck-precoated silica gel 60-F254 plates. All other substituted
nitrobenzenes were purchased from Aldrich or Fluka and used
as received. All the other solvents and chemicals were obtained
from commercial sources and purified using standard methods. The
particle size and external morphology of the samples were
2.3. General procedure for the reductive acylation of nitro
compounds
The catalyst [Pt(0)/ZrO2] (0.015 g, 0.15 mol%) was suspended in
methanol (2.0 mL) and a hydrogen balloon was fitted to the flask
through a rubber septa. The suspended catalyst was stirred under
hydrogen atmosphere for 10 min at room temperature and then
a solution of nitro compound (1.0 mmol) dissolved in methanol

98
M.L. Kantam et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 96–101
Table 2
(2.0 mL) was added to the above stirred solution. The resultant solu-
tion was stirred under hydrogen atmosphere at room temperature
for the specified period. The progress of the reaction was monitored
by thin layer chromatography (TLC). After completion of first step,
the hydrogen balloon was removed and acetic anhydride was added
(0.122 g, 1.2 mmol) using a syringe, to the same flask. The reaction
mixture was stirred further at room temperature and the progress
of the reaction monitored by TLC. After completion of the reaction,
the crude mixture was centrifuged, ethyl acetate (10 mL) was added
to the reaction mixture, then filtered the catalyst, and the remaining
acetic anhydride and acetic acid produced during the reaction was
neutralized with a saturated solution of sodium bicarbonate. The
aqueous and organic layers were separated and the excess solvent
was removed under reduced pressure. The crude reaction mixture
was purified by using short-path column chromatography on sil-
ica gel. The resulting products were analyzed by 1H NMR and mass
spectrometric methods.
Screening of various solvents in the reductive acylationa
.
Entry
Solvent
Time [h]
Yield [%]b
1
2
3
4
5
THF
DMF
Ethanol
Toluene
Methanol
3.5
3.5
3.5
3.5
3.5
<5
<5
<5
12
93
a
Reaction conditions: nitrobenzene (1 mmol), Pt(0)/ZrO2 (0.15 mol%), solvent
(3 mL), H2 balloon (1 atm), Ac2O (1.5 mmol), room temperature.
b
Conversion determined by GC.
other hand proved to be ineffective in providing the desired sol-
vent effect in promoting the reaction (Table 2, entry 3), in spite
of being a widely used proton donor solvent [42,43]. The reason
for this cannot be predicted at this point. In THF, the reaction is
very sluggish yielding barely 5% of the product (Table 2, entry
1). In toluene, the yield of the product is poor (Table 2, entry 4).
Strickingly, DMF, which is widely used in high temperature hydro-
genation also resulted in poor yields. The reason cannot be stated
very certainly, but it may be due to the conflict between Lewis
acidic character of the ZrO2 and the Lewis basic character of the
solvent. Thus it can be stated, in accordance to the observations
reported by Li et al., Liu et al. and our group, that the reaction pro-
ceeds well without the addition of any base in the reaction mixture
and utilizes merely the well dispersed Pt nanoparticles to medi-
ate the reaction [40,42,43]. The reaction was found to proceed at
room temperature in methanol in the presence of Pt(0)/ZrO2 cata-
lyst under hydrogen atmosphere followed by the addition of acetic
anhydride in the next step in the same pot for the protection of
the formed amine. This step is also well facilitated by the Lewis
acidic nature of the catalyst and the proton donating solvent e.g.
methanol follows a nucleophilic substitution process in which the
electrophilic carbon centre formation for the subsequent attack of
the amine is facilitated by the Lewis acidic support [44]. There-
fore it can be summarized by stating that the bi-functional catalyst
works successfully in the first step through the metal centre by
binding the molecular hydrogen in the oxidative insertion step and
then finally hydrogenating the nitro compounds and undergoing
the subsequent reductive elimination step [45]. In the second step
of this sequential reaction, the Lewis acidic support facilitates the
reaction majorly by helping in the formation of the carbocation.
2.4. General procedure for synthesis of
N-(tert-butoxycarbonyl)amines
In
a typical experimental procedure, Pt(0)/ZrO2 (20 mg,
0.2 mol%) was added to a mixture of organic azide (1.0 mmol), di-
tert-butyl dicarbonate (436 mg, 2.0 mmol) in methanol (5 mL) at
room temperature. The resultant solution was stirred under hydro-
gen atmosphere at room temperature for specified periods. The
progress of the reaction was monitored by TLC and upon com-
pletion of the reaction, the catalyst was filtered, washed with
ethyl acetate (20 mL) and the excess solvent was removed under
reduced pressure, the crude material was purified by silica gel
chromatography (60–120 mesh) to afford the corresponding tert-
butoxycarbonyl amine.
3. Results and discussion
3.1. Screening of catalysts and solvents
In a quest for the best suited catalyst for the one-pot synthesis
of organic amines, we have investigated the catalytic activities of a
number of solid catalysts. The results are furnished in Table 1.
As can be seen in Table 1, among the different catalysts screened,
Pt(0)/ZrO2 catalyst showed the best result for the reductive acyla-
tion reaction using nitrobenzene as the typical substrate (Table 1,
entry 5) and methanol as the solvent.
To find out the best catalytic system, along with the chosen cat-
alyst, Pt(0)/ZrO2, a range of solvents having varied physical and
chemical properties and differing immensely in polarities have
been investigated for the reaction among which methanol provided
the best result (Table 2, entry 5; Table 3, entry 5). Ethanol on the
3.2. Scope of the reaction
After optimizing the reaction conditions, the scope of the
reaction was extended to different aromatic nitro compounds
as summarized in Table 4. The halo substituted nitroben-
zenes were converted into the corresponding halo-anilines with
high yields without any concomitant side reaction forming the
Table 1
Screening of various solid catalysts in the reductive acylationa
Table 3
.
Solvent screening for the synthesis of N-Boc amines from organic azides.a
Entry
Catalyst
Time [h]
Yield [%]b
Entry
Solvent
Time [h]
Yield [%]b
1
2
3
4
5
ZrO2
Pt/Al2O3
Pt/C
Pt(0)/TiO2
Pt(0)/ZrO2
3.5
3.5
3.5
3.5
3.5
0
15
70
75
93
1
2
3
4
5
DMF
Ethanol
THF
Toluene
Methanol
8
8
8
8
8
Traces
Traces
<5
18
82
a
a
Reaction conditions: nitrobenzene (1 mmol), catalyst (0.15 mol%), methanol
Reaction conditions: benzyl azide (1 mmol), (Boc)2O (1.0 mmol), Pt(0)/ZrO2 cat-
(3 mL), H2 balloon (1 atm), Ac2O (1.5 mmol), room temperature.
alyst (0.2 mol%), solvent (4.0 mL), H2 balloon (1 atm.), room temperature.
b
b
Conversion determined by GC.
Isolated yields after column chromatography.

M.L. Kantam et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 96–101
99
Table 4
Reductive acylation of various nitroarenes catalyzed by Pt(0)/ZrO2.a
Entry
ArNO2
Amide
Timeb
3
Timec
3.5
4
Yield (%)d
PQ4
PJ Ce
1
2
93,92,91,91e
K
PQ4
K
PJ Ce
3.5
3.5
3.5
3
87
92
91
92
92
88
87
89
93
75
68
En
PJ Ce
En
PQ4
3
4
Dt
PQ4
Dt
PJ Ce
PJ Ce
PJ Ce
4
5
H
H
PQ4
5
3.5
4.5
4.5
4.5
4.5
4
J 5E
PQ4
J 5E
6
4
J 5EQ
QJ E
J QQE
J Q
PQ4
J 5EQ
QJ E
J QQE
J Q
PJ Ce
7
4
PQ4
PJ Ce
8
4
PJ Ce
PQ4
9
4
PJ Ce
PQ4
10
11
3.5
4
J 5EQE
J 5EQQE
PJ Ce
J 5EQE
J 5EQQE
PQ4
5
PQ4
PJ Ce
12
4
5
a
Reaction conditions: nitroarene (1.0 mmol), Pt(0)/ZrO2 catalyst (0.15 mol%), methanol (4.0 mL), H2 balloon (1 atm), Ac2O (1.5 mmol), room temperature.
Time taken for first step (reduction of nitroarene to aminoarene).
Total reaction time.
Isolated yields after column chromatography.
Isolated yield in fourth cycle.
b
c
d
e
dehalogenated product. Even iodo-aniline was obtained with 87%
formation of the product in greater yields. In case of p-nitrophenol,
p-aminophenol formed in the first step is cleanly converted in
the second step to the corresponding N protected amine (Table 4,
entry 10) without any competitive side reaction to form the O pro-
tected product. Thus the catalyst is highly selective in facilitating
N-protection where reactive substituents are present in the initial
nitroarene.We have studied the scope of this reaction with various
aliphatic and aromatic azides using our optimized reaction condi-
yield. The catalyst Pt(0)/ZrO2 is highly chemoselective for this
purpose. Nitroarenes without substituent groups produced higher
yield in shorter reaction time (93%, 3.5 h, Table 4, entry 1).
Nitroarenes containing halo substitution at para position such as
iodo, chloro, bromo and fluoro also smoothly resulted high yields
of the corresponding products (89%, 92%, 91%, 92%, respectively,
Table 4, entries 2–5) in 3–3.5 h. Nitroarenes containing 4-methyl
and 4-methoxy groups afforded corresponding anilides with high
yields (entries 6–7). It is worth mentioning here that the critical and
useful functionalities in organic synthesis such as aldehyde (entry
8), acid (entry 9), phenolic (entry 10), keto (entry 11), and ester
(entry 12) were well tolerated without any side reactions under
the present reaction conditions.
Table 5
a
Synthesis of substituted amines from nitrobenzene using Pt(0)/ZrO2
We have studied the applicability of various anhydrides as pro-
tecting agents by in situ generated amine group using nitrobenzene
as the model substrate and the results are presented in Table 5.
As can be seen from this table, all the anhydrides reacted cleanly
and gave amides in good to excellent yields. However, acetic acid
showed poor activity under these reaction conditions (Table 5,
entry 1). The reason for this may be attributed to the formation of a
poor leaving group, OH− during the course of substitution reaction.
The strong leaving groups on the other hand formed in case of Boc,
etc. renders the reaction more facile and therefore facilitates the
.
Entry
Acylating agent
Time [h]
Yield [%]b
1
2
3
4
Acetic acid
Acetic anhydride
(Boc)2O
3.5
3.5
3.5
3.5
40
93
79
82
Propionic anhydride
a
Reaction conditions: nitroarene (1.0 mmol), Pt(0)/ZrO2 catalyst (0.15 mol%),
methanol (4.0 mL), H2 balloon (1 atm), Anhydride (1.5 mmol), room temperature.
b
Isolated yields after column chromatography.

100
M.L. Kantam et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 96–101
Table 6
Synthesis of various N-Boc amines from azides using Pt(0)/ZrO2.a
Entry
Substrate
Prduct
Time [h]
Yield [%]b
N3
NH-Boc
NH-Boc
1
2
7
8
86
82
N3
N3
NH-Boc
OH
OH
3
4
8
81
N3
NH-Boc
OH
N3
OH
10
10
79
82
NH-Boc
5
a
Reaction conditions: organic azide (1 mmol), Boc2O (2 mmol), Pt(0)/ZrO2 (0.2 mol%), methanol (5 mL), H2 atmosphere, room temperature.
Isolated yields.
b
Fig. 1. TEM images of fresh catalyst (a) and used catalyst (b).
tions. As shown in Table 6, all the substrates produced good yields of
surface may be responsible for hindering the active catalytic sites
from coming into contact with the substrate. No quantifiable
amount of leached Pt was detected in the filtrate by AAS analysis.
The effect of the strongly Lewis acidic zirconia as demonstrated
in the formation of the N-acyl and N-Boc-protected amine deriva-
tives, coupled with the absence of any leached metal in the filtrate
suggests that the catalytic process is truly heterogeneous and
occurs on the solid surface [46,47].
the product. Aromatic, benzylic azides, and aliphatic azido alcohols
underwent clean reductions and sequential protection resulting in
good yields of the products under the reaction conditions followed.
3.3. Recycling of the catalyst
After completion of the reaction, the catalyst was separated by
centrifugation and washed with methanol followed by acetone and
then dried in an oven at 120 ◦C. The catalyst was then kept stored
in a vacuum desiccator until the next run. The catalyst was used for
four cycles successively in the reaction of nitrobenzene and acetic
anhydride (model substrate) to yield the product with minimum
loss of activity (Table 4, entry 1). This proves that the catalyst is
efficient and stable for this reaction.
The TEM image of the used catalyst Fig. 1b is similar to the fresh
catalyst Fig. 1a and therefore it could be concluded that the mor-
phology of the catalyst is well maintained after several recycles. A
few agglomerated spots can be noticed in some places which are
responsible for the slight deactivation of the catalyst by the forma-
tion of copious amounts of acids as a byproduct from the protection
of the amines.
4. Conclusion
In summary, we report a convenient, simple, clean and effi-
cient protocol for the reduction of aromatic nitro compounds,
organic azides to amines followed by protection of amines with
acetic anhydride or di-tert-butyl dicarbonate [(Boc)2O] to give
the corresponding N-acyl or N-(tert-butoxycarbonyl)amines using
Pt(0)/ZrO2 catalyst. The catalyst can be conveniently recovered
and reused several times without any practical loss of activity.
This methodology is environment friendly, utilizing only molecu-
lar hydrogen as the reductant. The reaction is smoothly conducted
under mild conditions affording good yields of the products. These
above mentioned advantages make this protocol a cost effective
and therefore, industrially attractive one in the age of stringent
environmental legislations.
Therefore, a minor reduction in the yield of the product is seen
(91% in fourth cycle vs 93% in the first cycle, see Table 4, entry
1) in the subsequent cycles. The presence of acid on the catalyst

M.L. Kantam et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 96–101
101
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