Synthesis, characterization and catalytic activities of a reusable polymer-anchored palladium(II) complex: Effective catalytic hydrogenation of various organic substrates

Article abstract of DOI:10.1007/s11243-010-9345-2

A poly(3,6-dibenzaldimino N-vinyl carbazole) Pd(II) complex has been synthesized and characterized by physicochemical and spectroscopic techniques. The complex was found to be highly active toward hydrogenation reactions of various organic substrates under atmospheric pressure at ambient temperature. A tentative reaction mechanism is proposed on the basis of kinetic studies and isolation of reactive intermediates. The catalyst shows good conversion rates, thermal stability and recyclability. Springer Science+Business Media B.V. 2010.

Full text of DOI:10.1007/s11243-010-9345-2

Transition Met Chem (2010) 35:427–435
DOI 10.1007/s11243-010-9345-2
Synthesis, characterization and catalytic activities of a reusable
polymer-anchored palladium(II) complex: effective catalytic
hydrogenation of various organic substrates
Manirul Islam
Anupam Singha Roy
•
Paramita Mondal
Kazi Tuhina
•
•
Received: 2 December 2009 / Accepted: 12 February 2010 / Published online: 27 February 2010
Ó Springer Science+Business Media B.V. 2010
Abstract A poly(3,6-dibenzaldimino N-vinyl carbazole)
Pd(II) complex has been synthesized and characterized by
physicochemical and spectroscopic techniques. The com-
plex was found to be highly active toward hydrogenation
reactions of various organic substrates under atmospheric
pressure at ambient temperature. A tentative reaction
mechanism is proposed on the basis of kinetic studies and
isolation of reactive intermediates. The catalyst shows
good conversion rates, thermal stability and recyclability.
fascinating molecular topologies and potential in the
development of new catalytic materials [8–16]. Among
such species, the complexes of iron(III) [17], palladium(II)
[18, 19], platinum(II) [20, 21], rhodium(I) [22], ruthe-
nium(I) [23, 24] and nickel [25, 26] supported on inorganic
or organic polymers are worthy of mention.
Schiff base complexes of transition metal atoms have
played a significant role in various catalytic reactions to
enhance their yield and product selectivity [27–29]. The
convenient route of synthesis and thermal stability of
Schiff base ligands have contributed to their value in this
context. Transition metals with different ligands immobi-
lized on various supports showed high catalytic activity in
reactions of industrial importance [30].
Introduction
The development of well-defined catalyst systems that
allow rapid and selective chemical transformations and at
the same time can be completely recovered from the
product has received wide prominence [1]. The immobili-
zation of homogeneous transition metal complexes on solid
supports is an object of intense research in order to facil-
itate the recovery and reuse of the catalysts and make the
procedures useful for commercial applications [2–7].
Organic polymer supports can induce specific control over
the catalytic and complexing ability of the ligand. Transi-
tion metals coordinated to polymeric ligands can have
Orthometallated complexes of Pd(II) with various
ligands [31], especially with Schiff bases [32], are efficient
catalysts for the hydrogenation of functional groups like
–NO , –NH OH, [C=C\, [C=N– and [C=O under mild
2
2
reaction conditions in moderately coordinating solvents.
These results encouraged us to investigate the catalytic
activities of polymer-anchored complexes and to under-
stand the effects of such immobilization on their catalytic
activities.
We herein report the synthesis and characterization of a
new poly(3,6-dibenzaldimino N-vinyl carbazole)-anchored
Pd(II) complex catalyst. The paper presents the catalytic
activities of this complex for the liquid phase hydrogenation
of various organic substrates under atmospheric pressure.
The effects of solvent and temperature have been studied.
Since there are only very few reports on mechanistic studies
for the hydrogenations of alkenes using heterogeneous
palladium complexes, we have also done mechanistic
studies for the hydrogenation of styrene. A tentative
mechanism is proposed on the basis of characterization of
the reaction intermediates at various stages of reduction.
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-010-9345-2) contains supplementary
material, which is available to authorized users.
M. Islam (&) ꢀ P. Mondal ꢀ A. S. Roy
Department of Chemistry, University of Kalyani, Kalyani,
Nadia 741235, WB, India
e-mail: manir65@rediffmail.com
K. Tuhina
Department of Chemistry, B.S. College, S-24 P.G.S.,
Canning 743329, WB, India
123

4
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Transition Met Chem (2010) 35:427–435
Experimental
resulting yellowish brown polymer was filtered off, washed
thoroughly and successively with acetic acid, water, THF
and acetone, and then dried under vacuum.
Analytical grade reagents, freshly distilled solvents, pure
and dry hydrogen gas were used throughout the investi-
gation. The liquid substrates were predistilled and dried by
the appropriate molecular sieve, and the solid substrates
were recrystallized before use. The chloride estimation
was done by Vogel’s silver chloride estimation procedure
Preparation of poly(3,6-diamino N-vinylcarbazole) (3)
A solution of stannous chloride (10 g) in concentrated
hydrochloric acid (HCl) (12 mL) was added to a suspen-
sion of poly(3,6-dinitro-N-vinylcarbazole) (5 g) in 20 mL
of acetic acid [35]. The mixture was stirred at room tem-
perature for 48 h. The resulting yellow polymer was fil-
tered off, washed successively with water, THF, methanol
and acetone. The polymer obtained as the amine hydro-
chloride was dried under vacuum. A sample of the poly(N-
vinylcarbazole-3,6-diamine hydrochloride) (5 g) was then
treated with 5% alcoholic NaOH solution (50 mL) for 6 h
with stirring at 30 °C. The amine thus obtained was filtered
off, washed successively with water and methanol and
finally dried under vacuum.
[
33]. Poly N-vinylcarbazole (Art.No. 368350-5) was sup-
plied by Aldrich. Bis(benzonitrile) palladium(II) chloride
Pd(PhCN) Cl ] was purchased from Arora Matthey and
[
2
2
was used as such without further purification.
A Perkin-Elmer 2400C elemental analyzer was used to
collect microanalytical data (C, H and N). FTIR spectra
-
1
of the samples were recorded from 400–4000 cm on a
Perkin-Elmer FTIR 783 spectrophotometer using KBr
pellets. Thermogravimetric analysis (TGA) was carried out
using a Mettler Toledo TGA/DTA 851e instrument. Sur-
face morphology of the samples was measured using a
Scanning Electron Microscope (ZEISS EVO40, England)
equipped with EDX facility. Diffuse reflectance UV–Vis
spectra were taken using a Shimadzu UV-2401PC double
beam spectrophotometer having an integrating sphere
attachment for solid samples. Palladium content was
determined using a Varian AA240 atomic absorption
spectrophotometer (AAS).
Preparation of poly(3,6-dibenzaldimino
N-vinylcarbazole) (4)
Benzaldehyde (10 mL) was added to a suspension of poly
(3,6-diamino N-vinylcarbazole) (3 g) in dry toluene
(30 mL) and the mixture was refluxed under nitrogen for
72 h using a Dean-Stark apparatus. The suspension of the
Hydrogenation procedure
polymer was filtered off, washed thoroughly with toluene,
tetrahydrofuran and methanol and then dried under
vacuum.
The atmospheric pressure hydrogenation reactions were
carried out in a thermostated glass reactor (100 mL
capacity), equipped with a magnetic stirrer. A solution of
substrate (0.5 mol/L) in DMF (10 mL) containing the
Preparation of Pd(II) poly (3,6-dibenzaldimino
N-vinylcarbazole) complex (5)
0
.010 g (1.20 mmol/L) of the catalyst was stirred under
hydrogen (1.0 Atm). The rate of hydrogen consumption
was measured using a glass manometric apparatus. Ali-
quots of the reaction mixture were withdrawn at various
time intervals, and the products were analyzed using a
Varian 3400 gas chromatograph equipped with a 30 m CP-
SIL8CB capillary column and a flame ionization detector.
After completion of the reaction, the catalyst was filtered
off and the products were identified by using an Agilent
GC–MS (QP-5050).
A suspension of poly(3,6-dibenzaldimino N-vinylcarbazole)
(1 g) in a slightly warm methanolic solution (25 mL) of
Pd(PhCN) Cl (0.7 g) was first stirred for 48 h at room
2
2
temperature and then refluxed in a water bath for 3 h [36].
The resulting yellowish brown complex was filtered off and
washed successively with THF and methanol, and finally
dried under vacuum.
Preparation of the catalyst
Results and discussion
Preparation of poly (3,6-dinitro-N-vinylcarbazole) (2)
The outline for the preparation of the poly N-vinylcarbaz-
ole–anchored Pd(II) complex, [Pd(C H CH=N–P)(PhCN)
6
4
Poly (N-vinylcarbazole) (5 g) was taken in 1,2-dichloro-
ethane (100 mL). A mixture containing concentrated HNO3
and glacial acetic acid (25 mL ? 50 mL) was added drop-
wise at room temperature to the above suspension with
constant stirring and then refluxed it for 8 h [34]. The
Cl] (P = poly N-vinylcarbazole) is shown in Scheme 1.
Due to the insolubilities of these polymers in all common
solvents, their characterization was limited to their physico-
chemical properties, chemical analysis, SEM, TGA-DTA,
IR and UV–Vis spectroscopic data. The analytical data are
1
23

Transition Met Chem (2010) 35:427–435
429
NO2
N H
2
O N
H N
2
2
HNO3 /
SnCl / HCl
2
N
CH COO H
N
3
N
NaOH
-
CH-CH2-
-CH-CH2-
-CH-CH2-
n
n
n
(
3)
(
1)
(
2)
PhCHO
-CH-CH2-
N
PhCH=N
N=CH Ph
Pd( PhCN) Cl
2
2
N
N
Cl
Cl
N
MeO H
Pd
CH
HC
Pd
NCPh
-CH-CH2-
PhCN
n
(4)
n
(5)
Scheme 1 Synthesis of the polymer-anchored Pd(II) complex
presented in Table 1. Metal content analysis by atomic
absorption spectroscopy suggested 12.8% Pd in the immo-
bilized metal complex. The SEM micrographs of poly (3,6-
dibenzaldimino N-vinylcarbazole) and its palladium com-
plex are presented in (Fig. 1a and b, supplementary) and their
EDX data are given in (Fig 1a and b) respectively. A clear
change in morphology of the polymer after introduction
of the metal was observed by SEM, while EDX analysis
showed a metal content along with C, N and Cl, suggesting
the formation of a metal complex at various sites on the
polymer.
The thermal stability of the complex was investigated
using TGA–DTA at a heating rate of 10 °C/min in air over a
temperature range of 30–600 °C. The TGA–DTA curves
of poly(3,6-dibenzaldimino N-vinylcarbazole) and the
supported Pd(II) complex are shown in (Fig. 2 supple-
mentary). The catalyst decomposes in the temperature range
330–500 °C. The DTA curve reveals that all the decom-
position stages are exothermic in nature. The TG profiles
(Fig. 2 supplementary) suggest that the polymer-anchored
complex degrades at high temperature like the precursor
poly (3,6-dibenzaldimino N-vinylcarbazole) polymers.
Table 1 Analytical and IR spectroscopic data for the functionalized polymer and the Pd(II) complex
-
Other bands (cm ) and assignments
1
Compound
Color
Cl (%) C (%) H (%) N (%) m NO
2
-
cm )
1
(
PNV
Faint yellow
87.1
76.0
5.7
4.5
7.2
PNV–NO
PNV–NH
PNV–NH
2
3
2
Yellowish brown
10.2
1520(s)
340(s)
1520(w) 2550 (mNH
340(w)
1520(w) 3350, 3400 (mNH stretching)
340(w)
1520(w) 1630 (m C=N)
340(w)
1
Cl
Yellow
Yellow
Yellow
7.92
73.9
81.8
84.7
5.2
5.6
5.3
10.0
11.1
8.9
3
Cl)
1
1
[
6 4
(C H CH=N–P)(PhCN)Cl]
1
a
[
6 4
Pd(C H CH=N–P)(PhCN)Cl]
Yellowish
brown
3.09
73.90 4.4
8.2
1520(w) 1620 (m C=N); 2290 (m C:N);
720 (orthometallation); 355 (m Pd–Cl)
1
340(w)
PNV = poly N-vinylcarbazole
P = polymer
a
Pd content; 12.8% for freshly prepared material, 12.8% after fifth reuse
123

4
30
Transition Met Chem (2010) 35:427–435
to the p ? p* and n ? p* transitions of the imine system
in conjugation with the aromatic nuclei (Fig. 3, supple-
mentary). The bands present in the free ligand are not much
shifted in the complex because of the delocalized electron
system. The slight blue shift of the above band is consistent
with coordination to the metal. In the polymer complex,
new bands at 465 nm and 340 nm may be assigned to the
1
1
1
1
A1g ? A and A1g ? B transitions respectively
2g
1g
[
41]. From the microanalytical and spectroscopic data, the
probable structure of the polymer complex may be
described according to Scheme 1.
In order to find out the anchoring of palladium on
polymer support, the polymer catalyst was stirred with an
alcoholic or DMF solution of PPh in the absence or
3
-
2
presence of HCl (10 M) for 12 h at ambient temperature
and then filtered. Atomic absorption spectroscopic studies
detected no palladium in the filtrate. This suggests that the
palladium is complexed within the polymer and could not
be leached out.
Catalytic hydrogenation
The polymer complex proved to be a very effective het-
erogeneous catalyst for the hydrogenation reactions.
Reductions of various organic substrates were carried out
under atmospheric pressure using this catalyst. Aromatic
nitro compounds, alkenes, alkynes, benzaldehyde and
Schiff bases were reduced under atmospheric pressure of
Fig. 1 EDX spectra of poly (3,6-dibenzaldimino N-vinyl carbazole)
(
(
a) and poly (3,6-dibenzaldimino N-vinyl carbazole) Pd(II) complex
b)
H at ambient temperature. The nature and yields of the
2
different products, the initial rate of hydrogenation and the
optimum conditions for the reduction of various substrates
are presented in Table 2.
IR data for the polymer-anchored metal complex and its
precursors are presented in Table 1. Poly (3,6-dibenzaldi-
mino N-vinylcarbazole) shows a characteristic peak at
The reductions were generally possible only in polar
solvents having mild coordinating power. The solvents
may be arranged in the following order of efficiencies:
-
630 cm that may be assigned to the –C=N– stretching
1
1
vibration. This band is shifted toward lower frequency in
the complex consistent with coordination of the nitrogen to
the metal atom. The polymer metal complex exhibited
DMF [ DMSO [ THF [ [ CHCl3; toluene
-
1
important IR peaks at 1620 cm (m (–C=N–) stretching),
The rate of hydrogenation was slow in oxygen donor
solvents like THF and dioxin and was immeasurably slow
in non coordinating solvents like toluene, chloroform,
petroleum ether, benzene, etc.
-
1
-1
1
590 cm
(m (–C=C–) stretching, aromatic), 720 cm
-
1
(
orthometallation) [37], 2290 cm (m (–C:N) of benzo-
nitrile), 455 cm (m (Pd–N) [38] and 355 cm (m (Pd-Cl)
19]. The polymeric complex was found to be diamagnetic,
-
1
-1
[
The influence of temperature on the rate was studied in
DMF keeping other parameter fixed. The reduction of
nitroaromatics increased appreciably with temperature ca.
40 °C. Above this temperature, the rate remained almost
constant. The reduction of various alkenes and Schiff bases
such as maleic acid, fumaric acid and benzylidineaniline
also increased appreciably on increasing the temperature
from 30 to 60 °C.
The polymer complex proved to be an excellent catalyst
for the reduction of various nitroaromatics to the corre-
sponding anilines under atmospheric pressure of hydrogen
at ambient temperature. The yields of amines were almost
8
consistent with a low-spin d square-planar geometry
around Pd(II) [39].
The electronic spectrum of the polymeric complex was
recorded in diffuse reflectance spectrum mode as a BaSO4
disk due to the solubility limitations. A low-spin square-
planar Pd(II) complex may exhibit three spin-allowed d–d
1
1
1
1
transitions designated as A ? A , A ? B and
1
g
2g
1g
1g
1
1
A1g ? E [40]. For the free carbazole ligand, the
g
absorption maximum at 305 nm may be attributed to the
p ? p* transitions of the carbazole and phenyl moieties
and the lower energy peaks at 378 and 439 nm are assigned
1
23

Transition Met Chem (2010) 35:427–435
431
Table 2 Substrates and the
corresponding product(s) for
catalytic reductions
Substrate
Product(s)
Reaction time(h)
% yield
Initial
TOF
-
1
(
min )
Nitrobenzene
Aniline
2.5
4.6
4.9
5.8
5.4
4.2
5.2
4.4
5.6
3.6
5.5
4.9
3.7
3.8
3.4
4.3
4.5
4.6
5.6
5.7
5.2
3.7
5.0
3.8
99
97
96
91
95
98
89
96
94
98
84
94
98
96
97
96
95
95
92
90
95
92
94
94
14.02
9.21
p-Dinitrobenzene
m-Dinitrobenzene
o-Dinitrobenzene
o-Chloronitrobenzene
p-Chloronitrobenzene
o-Nitroaniline
p-Nitroaniline
o-Nitrotoluene
p-Nitrotoluene
p-Nitrophenol
Cyclohexene
p-Phenelenediamine
m-Phenelenediamine
o-Phenelenediamine
o-Chloroaniline
p-Chloroaniline
o-Phenelenediamine
p-Phenelenediamine
o-Toluidine
8.99
7.02
7.62
10.68
9.39
6.77
7.55
p-Toluidine
11.36
7.07
p-Aminophenol
Cyclohexane
8.95
Styrene
Ethylbenzene
11.96
10.89
11.04
10.85
10.72
10.41
8.32
Phenylacetylene
Isoprene
Ethylbenzene
2-Methylbutane
Pentane
1
-Pentene
1-Hexene
-Heptene
Reaction condition:
[
Sub] = 0.5 M;
Hexane
[Cat] = 1.20 mmol/L;
Medium = DMF
1
Heptane
Maleic acid
Succinic acid
Total volume = 10 mL
Fumaric acid
Succinic acid
7.50
Yield refers to GC and GC–MS
analysis (average of two runs)
1
-Nitronaphthalene
1-Aminonaphthalene
1,2-Diphenylethane
Benzylalcohol
N-Phenylbenzylamine
8.06
Diphenylacetylene
Benzaldehyde
10.96
8.25
Turn over frequency
TOF) = moles of substrate
(
converted per mole of Pd per
min
Benzylidineaniline
8.03
quantitative in most cases (Table 2). The rates of reduction
of o-chloronitrobenzene and o-nitrotoluene are lower than
those of non-substituted and p-substituted analogues.
However, the influence of the bulkiness of the substrates on
the rate of hydrogenation is obvious.
hydrogenation of the various substrates may be arranged in
the following order:
Styrene [ Isoprene [ Phenylacetylene [ Pent-1-ene
[
Hex-1-ene [ Hept-1-ene [ cyclohexene
[ Benzaldehyde ꢁ Benzylidineaniline [ Maleic acid
Fumaric acid
The results of preferential hydrogenation of a mixture of
PhNO and o-ClC H NO using the polymer catalyst are
2
6
4
2
[
presented in Fig. 2. Levels of the organic compounds in the
mixture were measured at different intervals by GC anal-
ysis. Reduction of o-chloronitrobenzene started only after
almost complete reduction of nitrobenzene (*95%). It
seems likely that nitrobenzene preferentially coordinates to
the metal rather than sterically hindered o-chloronitroben-
zene and hence the former undergoes preferential
reduction.
Alkenes required an elevated temperature for efficient
hydrogenation. Straight chain alkenes were reduced at faster
rate than branched alkenes. This may be due to steric factors
preventing the approach of the substrate to the metal center
in the polymer matrix. With increasing molecular weight of
alkenes, the rate of hydrogenation decreases, perhaps due to
reduced mobility of higher olefins within the polymer.
Alkenes with delocalized p-electron systems were reduced
much more quickly, perhaps due to formation of a stronger
metal–alkene complex. The hydrogenation of alkynes
requires even more harsh conditions than those for alkenes
and usually takes place in a stepwise fashion. Thus, phenyl
acetylene forms styrene initially, which is further
hydrogenated to ethylbenzene only after most of the
alkyne has been consumed (Fig. 3). The presence of any
Reduction of dinitroaromatics required higher tempera-
ture. Dinitroaromatics such as m-dinitrobenzene undergo
internal sequential reduction, and the formation of m-
phenylenediamine started only after *85% conversion of
m-dinitrobenzene to m-nitroaniline.
Under atmospheric pressure, the catalyst was highly
effective for the hydrogenation of linear and cyclic olefins,
alkynes, aromatic aldehydes and Schiff bases. The rates of
123

4
32
Transition Met Chem (2010) 35:427–435
1
00
100
80
60
40
20
0
8
0
0
0
0
PhNO2
PhNH2
PhNHOH
PhNO2
PhNH2
6
4
2
PhNHOH
o-ClC H NO
6
4
2
o-ClC H NH
6
4
2
o-ClC H NHOH
6
4
0
0
1
2
3
4
5
6
7
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Time (h)
Time (h)
Fig. 2 Preferential hydrogenation of nitrobenzene in the presence of
o-chloronitrobenzene with the polymer catalyst. [Cat] = 1.20 mmol/
L; PH2 = 1 bar; medium = DMF; total volume = 10 mL; Temp. =
Fig. 4 Effect of acid on the reduction of nitrobenzene with polymer
catalyst. [Cat] = 1.20 mmol/L; PH2 = 1 bar; medium = DMF; total
-
3
volume = 10 mL; Temp. = 25 °C; HCl (10
0.5 M; discontinuous line in the presence of acid, continuous line
2
M); [PhNO ] =
2
5 °C; [PhNO
2
] = 0.5 M; [o-ClC
6 4
H NO
2
] = 0.5 M
in the absence of acid
Phenylacetylene
Styrene
Ethylbenzene
1
00
in the intermediate stage of the reaction, which could not
coordinate with the metal through nitrogen. The reduction
of other substrates was not appreciably affected in the
8
0
0
0
0
-
3
-3
presence of dilute acid (10 M) or alkali (10 M NaOH).
Our polymer complex appears to be superior to Pd/C
6
4
2
(Arora Matthey) in terms of required reaction times,
reaction temperature and yields of products (Table 3).
Reuse of the catalyst
The best advantage of heterogeneous catalysis is often the
possibility of recovering and reusing the catalyst after the
reaction. The capability of reuse of the present polymer
complex was confirmed after five consecutive hydrogena-
tion experiments in DMF medium. After the first run, the
polymer-anchored Pd(II) catalyst was separated by filtra-
tion, washed, dried under vacuum and then subjected to the
second run under the same conditions. This procedure was
repeated with further addition of substrates in appropriate
amounts under optimum reaction conditions, and the nature
and yield of the final products was comparable to the ori-
ginal run. The results summarized in Table 4 demonstrate
that there was almost no change in catalytic activity even
after the fifth reuse. Metal content of the recycled catalyst
remained unaltered, indicating no leaching of the metal
from the polymer support (Table 1).
0
0
1
2
3
4
Time (h)
Fig. 3 Sequential reduction of phenyl acetylene with the polymer
catalyst. [Cat] = 1.20 mmol/L; PH2 = 1 bar; medium = DMF; total
volume = 10 mL; Temp. = 30 °C; [PhC:CH] = 0.5 M
electron-deficient group adjacent to the carbon atom of the
double bond decreases the rate of the reduction. Maleic acid
and fumaric acid were reduced more slowly than styrene,
perhapsdue to decreased electron density ofthe double bond.
Finally, benzaldehyde was reduced to benzylalcohol in good
yield, while benzylidineaniline was reduced to the
corresponding secondary amine with 100% selectivity.
Effect of acid and alkali on the reduction process
The catalytic reduction rates were examined for various
-
Reaction kinetics and mechanism
2
substrates in the presence of acetic acid (10
M) or
-
hydrochloric acid (10 M). The reduction rate of nitro-
3
The kinetic studies were made with the polymer catalyst in
DMF for the hydrogenation of styrene under atmospheric
benzene in the presence of acid decreased rapidly (Fig. 4).
?
The effect is likely to be due to formation of [PhNH OH]
2
pressure of H . The initial rate of hydrogen absorption was
2
1
23

Transition Met Chem (2010) 35:427–435
433
Table 3 Comparison of catalytic activities of the polymer complex with Pd/C
Substrate
Present catalyst
Yield (%)
Pd/C
Products
Aniline
Initial
TON
-
Yield (%)
Initial
TOF
-1
(min )
1
)
(
min
Nitrobenzene
m-Dinitrobenzene
o-Nitro toluene
Phenylacetylene
Styrene
99
96
94
96
98
95
94
14.02
8.99
96
91
87
92
94
94
87
7.89
4.63
4.12
5.84
6.31
5.48
4.39
m-Phenelenediamine
o-Toluidine
7.55
10.89
11.96
10.72
8.25
Ethylbenzene
Ethylbenzene
Hexane
1
-Hexene
Benzaldehyde
Benzylalcohol
Reaction condition: [Sub] = 0.5 M; [Cat] = 1.20 mmol/L; Medium = DMF
Total volume = 10 mL
Yield refers to GC and GC–MS analysis (average of two runs)
Table 4 Recycling of the polymer catalyst for hydrogenation of various organic substrates
Ex No. Substrate
Product(s)
1st recycle
3rd recycle
5th recycle
Initial turnover % yield Initial turnover % yield Initial turnover % yield
-
1
-1
-1
factor (min)
factor (min)
factor (min)
1.
2.
3.
4.
5.
6.
Nitrobenzene
Styrene
Aniline
14.02
11.96
11.36
10.89
8.99
99
98
98
96
96
92
13.96
11.72
11.21
10.62
6.71
96
98
97
92
94
89
13.21
11.63
11.06
10.49
6.39
96
97
95
90
93
88
Ethyl benzene
p-Toluidine
Ethylbenzene
p-Nitrotoluene
Phenylacetylene
m-Dinitrobenzene m-Phenelenediamine
Maleic acid Succinic acid
8.32
8.12
8.01
[sub] = 0.5 M; [Cat] & 1.20 mmol/L (fresh catalyst); medium = DMF; total volume = 10 mL; [Cat] & (1.07–1.19) mmol/L (after 5th
recycle)
Yield refers to GC analysis
determined from graphical extrapolation of the rate curve
to zero time and results were verified by GC analysis of the
product composition at different time intervals.
16
Kinetic studies revealed that the initial rate of hydro-
genation of styrene was first-order dependent on catalyst
12
-
3
concentration in the range of (1.0 - 6.0) 9 10 mol/L at
constant substrate concentration and hydrogen pressure.
The results are given in Fig. 5. The effect of variation of
substrate concentration on the rate was also studied. The
substrate concentration was varied from 0.6–1.6 mol/L.
The initial rate of hydrogenation was independent of sub-
strate concentration in this range, having a constant value
8
4
0
-
1
of 6.7 ± 0.1 mL H min . The initial rate of reduction of
2
styrene was found to be first-order dependent on the
hydrogen pressure in the range of 200–1000 mm of Hg
0
1
2
3
4
5
6
-3
-1
[
Cat] x 10 (mol.lit )
(
Fig. 6). On the basis of kinetic studies, isolation of the
intermediates and based on previous literature [42],
the mechanism shown in Scheme 2 may be suggested for
the reduction of styrene.
Fig. 5 Rate dependence on catalyst concentration for the reduction of
styrene with the polymer catalyst. [styrene] = 0.5 M; medium =
DMF; total volume = 10 mL; Temp. = 30 °C
123

4
34
Transition Met Chem (2010) 35:427–435
synthesis of fine organic chemicals, either in the laboratory
or on an industrial scale.
1
1
2
0
Acknowledgments We thank the Department of Chemistry, Uni-
versity of Calcutta, for providing the instrumental support. One of the
authors, K.T., is thankful to the University Grants Commission
(Eastern Region), India, for financial support. We acknowledge DST,
CSIR and UGC, New Delhi, India, for financial supports.
8
6
4
2
0
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