An aerobic oxidative synthesis of aryl nitriles and primary aryl amides from benzylic alcohols catalyzed by a polymer supported Cu(II) complex

Article abstract of DOI:10.1039/c4nj01457j

A new polymer supported Cu(II) complex has been synthesized and characterized. The catalytic performance of the complex has been tested for the direct conversion of benzylic alcohols to aryl nitriles. In this reaction ammonium formate was used as the nitrogen source and O₂ as the oxidant. Furthermore, the copper-catalyzed one-pot synthesis of primary aryl amides from alcohols was also achieved. The effects of solvents, reaction time and catalyst amount for the aryl nitriles and aryl amides synthesis were reported. This catalyst showed excellent catalytic activity and recyclability. The polymer supported Cu(II) catalyst could be easily recovered by filtration and reused more than five times without appreciable loss of its initial activity.

Full text of DOI:10.1039/c4nj01457j

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Aerobic Oxidative Synthesis of Aryl Nitriles and Primary Aryl Amides
from Benzylic Alcohols Catalyzed by Polymer Supported Cu(II)
Complex
Rostam Ali Molla,a Kajari Ghosh,a K. Tuhina,b* S. M. Islam,a,*
aDepartment of Chemistry,University of Kalyani, Kalyani, Nadia 741235, W.B., India.
bDepartment of Chemistry, B.S. College, Canning, S-24 PGS, 743329, W.B., India.
Abstract
A new polymer supported Cu (II) complex has been synthesized and characterized. The catalytic
performance of the complex has been tested for the direct conversion of benzylic alcohols to aryl
nitriles. In this reaction ammonium formate was used as the nitrogen source and O2 as the
oxidant. Furthermore, copper-catalyzed one-pot synthesis of primary aryl amides from alcohols
was also achieved. The effects of solvents, reaction time and catalyst amount for the aryl nitriles
and aryl amides synthesis were reported. This catalyst showed excellent catalytic activity and
recyclability. The polymer supported Cu (II) catalyst could be easily recovered by filtration and
reused more than five times without appreciable loss of its initial activity.
Key words: Polymer supported catalyst, copper, benzylic alcohols, aryl nitriles, primary aryl
amides.
* Author to whom correspondence should be addressed. Dr. Sk. Manirul Islam, aDepartment of
Chemistry, University of Kalyani ,Kalyani, Nadia, 741235, W.B., India Phone: + 91- 33-2582-
8750, Fax: 91-33-2582-8282, E-mail: manir65@rediffmail.com
b
K. Tuhina, Department of Chemistry, B.S. College, Canning, S-24 PGS, 743329, W.B., India.
Email: tuhina31@yahoo.com
1

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Introduction
Selective oxidation of organic compounds by a catalytic method using O2 or air as an
oxidant has become urgent from the viewpoints of green chemistry.1-5 Aryl nitriles are versatile
building blocks in the synthesis of natural products, pharmaceuticals, agricultural chemicals and
dyes.6-9 Therefore, the development of an efficient catalytic system has recently been
investigated for the synthesis of aryl nitriles. Initially, it was prepared by the nucleophilic
substitution of halides with cyanide ions, However, inorganic cyanide salts, generally toxic, were
used and the reactions produce large amounts of inorganic salts as waste. Environmentally
benign approaches are considerably attractive, and many excellent examples have been reported.
For instance, metal-catalyzed dehydration of aryl oximes or amides, changing the CN source to
DMF via the C-H functionalization of arenes, and especially, oxidative dehydrogenation of
benzylic alcohols, azides or methyl arenes have been extensively investigated.10-27
On the other hand, primary amides are also an important class of compounds that are
used as starting materials for engineering plastics, detergents, and lubricants.28 In organic
synthesis, primary amides are potent substrates for primary amines, nitriles, amino acid
derivates, and heterocycles preparation.29 Biologically, primary amides are present in numerous
biologically active molecules.30 Based on their importance, several methodologies have been
developed for their synthesis.31
With regard to synthesis of primary amides, hydration of nitriles32,33 and rearrangement
of aldoximes34 are attractive procedures. Currently, benzonitrile, its derivatives and acrylonitrile
are being industrially produced by ammoxidation. Thus, for synthesis of benzamide derivatives
and acrylamide, hydration is a reliable procedure from both environmental and economical
viewpoints. In contrast, other nitriles have generally been synthesized by costful non-green
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procedures35 and hydration is not the best choice in these cases. Although the atom efficiency of
rearrangement of aldoximes itself is theoretically 100%, the formation of hydrochloric acid or
sulfuric acid is typically inevitable for preparation of aldoximes.
As alcohols are easily available and inexpensive, it would be advantageous to synthesize
nitriles and primary amides directly from alcohols. Catalytic synthesis of aryl nitrile from alcohol
has been reported36. Amidation of alcohols with ammonium formate as the nitrogen source is an
attractive reaction. Until now, only a few systems for amidation of alcohols or aldehyde have
been reported where ammonia was used as the nitrogen source.37 But these methods suffer from
several drawbacks because most of them are used homogeneous catalytic system. Homogeneous
catalysts have some disadvantages, such as they may easily be destroyed during the course of the
reaction and they cannot be easily recovered after the reaction for reuse. Recently, some
heterogeneously metal catalyzed primary amide synthesis from primary alcohol has been
reported.38 In order to overcome problems related to the homogeneous catalysts, several
supported systems were developed by us39. Aerobic oxidative synthesis of nitriles and primary
amides from alcohol catalysed by heterogeneous copper catalysts are still rare. To get rid from
these serious issues, it is thus desirable to develop an efficient methodology to avoid all these
difficulties.
Thus, we have synthesized polymer supported bis(2-hydroxyanyl)acetylacetonato copper
(II) Schiff base complex (PS-BHA-Cu) as an effective and highly reusable catalyst. Here we
report a green one pot procedure for the synthesis of aryl nitriles and primary aryl amides from
benzylic alcohols catalyzed by PS-BHA-Cu catalyst and O2 as the oxidant.
3

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Experimental Section
Materials
Analytical grade reagents and freshly distilled solvents were used throughout the
experiments. All reagents and substrates were purchased from Merck. Liquid substrates were
predistilled and dried by molecular sieve and solid substrates were recrystallized before use.
Distillation, purification of the solvents and substrate were done by standard procedures. 5.5%
crosslinked chloromethylated polystyrene and copper acetate were purchased from Sigma
Aldrich and used as without further purification.
Physical measurements
The FT-IR spectra of the samples were recorded from 400 to 4000 cm-1 on a
Perkins Elmer FT-IR 783 spectrophotometer using KBr pellets. UV-Vis spectra were taken using
a Shimadzu UV-2401PC doubled beam spectrophotometer having an integrating sphere
attachment for solid samples. Thermogravimetric analysis (TGA) was carried out using a Mettler
Toledo TGA/DTA 851e. Surface morphology of the samples was measured using a scanning
electron microscope (SEM) (ZEISS EVO40, England) equipped with EDX facility. The EPR
(electron paramagnetic resonance) spectra of the fresh and used PS-BHA-Cu catalyst were
recorded for the solid sample at room temperature using a JES-FA200 ESR spectrometer
(JEOL). Copper content in the catalyst was determined using a Varian AA240 atomic absorption
spectrophotometer (AAS). NMR spectra were recorded on a Varian Mercury plus NMR
spectrometer (1H NMR at 300 and 500 MHz) in pure deuterated solvents.
Preparation of polymer supported bis(2- hydroxylanyl)acetylacetone (PS-BHA)
To a 20 mL DMF in a 100 mL round bottom flask 1 gm chloromethylated polystyrene, 2 gm of
bis(2- hydroxylanyl)acetylacetone and 0.03 g NaI were added and heated at 110 °C for 5 days
4

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with stirring. After cooling to roomtemperature the mixture was filtered and washed thoroughly
with methanol and dried in an oven at 80 °C.
Preparation of polymersupported bis (2- hydroxylanyl) acetylacetonato copper Schiff base
catalyst (PS-BHA-Cu): To a 10 mL DMF in a 50 mL round bottom flask was added 500 mg of
polymer-supported bis(2- hydroxylanyl)acetylacetone. After stirring for 1h to swell the polymer,
100 mg of Cu(OAc)2 was added to this mixture and the content was heated for 3 h at 110 °C.
Then the content was filtered and the beads were washed thoroughly with chloroform and dried
in an oven at 80 0C.
CH2Cl
OH
C
C
N
N
OH
OH
C
C
O
O
methanol
reflux
2
+
/NaI
DMF
NH2
C
C
N
N
OH
OH
C
C
N
O
O
Cu(OAc)2
DMF
Cu
N
PS-BHA
PS-BHA-Cu (II)
Scheme 1 Preparation of polymer anchored Cu(II) complex
General procedure of synthesis of aryl nitriles from benzylic alcohols
To a 50 mL round-bottomed flask equipped with a magnetic stirrer, 15 mg of (PS-BHA-
Cu), 0.05 mmol K3PO4, 2.0 mmol HCOONH4, 0.5 mmol of benzylic alcohol and 3 mL of ACN
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were added. The vessel was flushed with O2 (1 atm). The vessel was sealed and the reaction
0
mixture was stirred at 115 C temperature for 16 hours. After cooling to room temperature, the
mixture was partitioned between ethyl acetate and brine. The organic layer was extracted with
ethyl acetate. The combined organic layers were dried over Na2SO4. The residue was purified by
column chromatography (silica gel, EtOAc-PE). All the prepared compounds were confirmed by
1H NMR.
General procedure of synthesis of primary aryl amides from benzylic alcohols
To a 50 mL round-bottomed flask equipped with a magnetic stirrer was charged with
DMF (3 mL), 0.15 mmol of (PS-BHA-Cu), 0.15 mmol of TBHP, 3.0 mmol of benzylic alcohol,
0
25% aq. ammonia 2.6 equiv. with respect to substrate and O2 (1atm) before heating at 80 C for
5h. After cooling the reactor, the O2 was vented from the reactor and the desired compound was
purified by chromatography on silica gel using silica gel, EtOAc-PE. All the prepared
compounds were confirmed by 1H NMR.
Results and Discussion
Characterization of the polymer supported catalyst.
Due to insolubility of the polymer supported copper catalyst in all common organic
solvents, its structural investigation was limited to its physicochemical properties, chemical
analysis, SEM-EDX, TGA, IR and UV-vis spectroscopic data. Table 1 provides the data of
elemental analysis of polymer supported ligand and the polymer supported copper catalyst.
Copper content in the catalyst determined by AAS suggests 4.85 wt% Cu in the catalyst. The
complexation ratio of copper and Schiff base is 1:1.3.
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Table 1: Chemical composition of polymer anchored ligand and polymer supported catalyst
Compound
C%
H%
Cl %
N%
metal%
PS-BHA
85.41
82.30
7.49
7.21
1.22
1.10
3.74
3.68
-
PS-BHA-Cu
4.85
The IR spectra of the synthesized Schiff base PS-BHA showed a broad band between 2855 and
3409 cm-1 due to intermolecular hydrogen bonding v(N-H) and v(OH) enolic vibrations. The
appearance of the absorption band at ≈1700 cm-1 was an indication of the presence of free
carbonyl groups of some unreacted acetylacetone in the prepared Schiff base and complex. A
strong absorption band at 1604 cm-1 was assigned to the (C=N) azomethine group, and the
absorption band between 1061 and 1107 cm-1 was attributed to v(C-O) vibrations. The Schiff
base showed a band at 1574 cm-1 that corresponded to the v(C=C) group. In complex the
intensity of the absorption band corresponding to enolic OH reduced greatly, which was present
in the PS-BHA between 2855 and 3409 cm-1. This reduction in the absorption bands in the IR
spectra of the PS-BHA-Cu provided evidence for its complexation with copper(II) ions. On
complexation, two new bands at 480 and 502 cm-1 appeared that corresponded to vibration
frequencies of bonds formed between copper(II) ions with the enolic oxygen and nitrogen atoms
of the azomethine of the Schiff base.
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Fig.1. FT-IR Spectra of polymer anchored ligand PS-BHA (a) and PS-BHA-Cu complex (b)
The electronic spectra of the Schiff base PS-BHA showed two absorption bands at 258
and 319 nm for π-π* and n-π* transitions in the Schiff base. The electronic spectra of the ligand
on complexation also showed variations in the absorption bands corresponding to π-π* and n-π*
transitions. Two new absorption bands at 345 nm and 370 nm in the electronic spectrum of the
copper (II) complex were attributed to LMCT. In this complex, the bands around 410-435 nm are
due to d-d transition.40
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1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Catalyst
Ligand
200
300
400
500
600
Wavelength (nm)
Fig.2. DRS-UV-visible absorption spectra of the polymer supported ligand(a) and catalyst(b).
The scanning electron micrographs of PS-BHA (Fig. 3a) and supported PS-BHA-Cu
catalyst (Fig. 3b) clearly show the morphological change which occurred on the surface of
polystyrene after loading of metal on it. An energy dispersive spectroscopy analysis of X-rays
(EDX) data for PS-BHA-Cu catalyst is given in Fig. 4. The EDX data also inform that the
attachment of copper metal on the surface of the polymer matrix.
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Fig.3. FE-SEM images of polymer anchored ligand PS-BHA (A, B) and PS-BHA-Cu (C,D)
complex
Fig.4. EDX image of polymer anchored complex PS-BHA-Cu
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110
100
90
80
70
60
50
40
30
100
200
300
400
500
600
0
Temperature ( C)
Fig. 5. Thermogravimetric weight loss plots for the polymer supported catalyst.
0
Thermal stability of the complex was investigated using TGA-DTA at a heating rate of 10 C /
0
min in air over a temperature range of 30–600 C. TGA-DTA curve of the polymer anchored
catalyst is shown in Fig. 5. The PS-BHA is stable up to 330 0C and thermal decomposition of the
catalyst is start above this temperature. Finally degradation of the PS-BHA-Cu catalyst is
0
occurred above the temperature 380 C. So, we can suggest that the complex is stable up to 360
0C and above this temperature it starts decomposes. Thermo gravimetric study suggests that the
polymer anchored catalyst degrades at considerably higher temperature.
Catalytic activities
Since polymer anchored metal systems exhibit catalytic activity in a wide range of the
industrially important processes and have been extensively studied, we have decided to
investigate the catalytic activity of polymer anchored Schiff base copper complex in the field of
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aerobic oxidative synthesis of aryl nitriles from benzylic alcohols and ammonium formate. Also
we have studied the synthesis of primary aryl amides from benzylic alcohols.
CN
K3PO4 /HCOONH4
ACN / 115 0C
PS-BHA-Cu
OH
R
O2 (1 atm)
CONH2
R
NH (aq)
/ TBHP
3
/ DMF
H2O
80 0C
R
Scheme 2: Aerobic oxidative synthesis of aryl nitrile and aryl amide
Aerobic oxidation of benzylic alcohols into nitriles
To test the catalytic activity of the present catalyst, first aerobic oxidation of benzylic
alcohols into nitriles was tested at 115 0C for 16h. Ammonium formate was used as the nitrogen
source and K3PO4 was used as the base. For optimization of reaction conditions, we choose the
aerobic oxidation of benzyl alcohol as a probe reaction. In this case benzyl alcohol is selectively
converted to benzonitrile (98 %) along with very small amount of benzaldehyde (2%) in the
presence of PS-BHA-Cu and ammonium formate under reaction conditions (Scheme 3).
PS-BHA-Cu
CN
OH
HCOONH4 / K3PO4
O2 (1 atm)
ACN/ 115 0C
Scheme 3 aerobic oxidation of benzylic alcohols into nitriles.
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To find the appropriate reaction conditions various solvents were screened and in order to
identify effective reaction conditions, the reaction was carried out under various catalyst amount
and reaction time (Table 2). We investigated the ability of various solvents like ACN, DMF and
dioxane. The conversion and selectivity of benzonitrile is highest in ACN as compared to the
other solvents like DMF and dioxane. The variation of conversion of the benzyl alcohol at the
given conditions showed that the conversion increased with polymer anchored Cu (II) catalyst. It
has been observed that increase in initial catalyst amount from 5 mg to 20 mg enhance the
conversion from 55% to 94%. Maximum conversion was found at 15 mg catalyst. Also the
reaction was carried out at different time ranging from 10h to 16h and it was found that at 16h
the conversion of benzyl alcohol was 94% at given conditions.
Table 2: Effect of solvent, reaction time and catalyst amount on aryl nitrile synthesis.
Entry
Solvent
Catalyst
amount
(mg)
Time
(h)
Conversion Selectivity
(%)
(%)
1
2
3
4
5
6
ACN
ACN
5
10
13
16
16
16
16
55
73
94
87
79
94
99
98
98
96
96
96
10
15
15
15
20
ACN
DMF
dioxane
ACN
Reaction conditions: alcohol (0.5 mmol), PS-BHA-Cu (15 mg ), HCOONH4 (2.0 mmol), K3PO4
(0.05 mmol), ACN (3 mL), O2 (1 atm.), Temperature (115 0C), 16h.
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Using the optimized conditions, we next explored the scope and generality of the process
(Table 3). It was found that benzylic alcohols carrying electron-donating and electron-
withdrawing groups could be smoothly converted into the desired products with moderate to
excellent yields. Primary benzylic alcohols with a variety of substituents at ortho position afford
the corresponding nitriles in moderate yields. Electron-donating and electron-withdrawing
groups, ranging from −OMe to −CF3 and −NO2 groups, were all well tolerated in the reactions.
Polycyclic or heteroaromatic alcohols, such as naphthalen-1-ylmethanol (Table 3, entry 18) and
furan-2-ylmethanol (entry 16), underwent effective conversion into the nitriles, and oxidation of
1,3-phenylenedimethanol (entry 20) afforded 1,3-dicyanobenzene in high yield. The allylic
alcohol, cinnamyl alcohol (entry 19) afforded α,β-unsaturated nitriles in good yields. It has been
observed in alcohol oxidation reactions, aliphatic substrate was less reactive and corresponding
nitrile was obtained by increasing the PS-BHA-Cu catalyst loading.
Table 3: Polymer supported copper (II) catalyzed aerobic oxidative synthesis of aryl nitriles.
Entry
Substrate
Product
Yield
(%)
CN
OH
1
2
3
4
94
CN
OH
96
90
CN
OH
CN
98
OH
MeO
MeO
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CN
80
83
OH
OH
5
6
OMe
CN
OMe
OMe
OMe
CN
86
80
82
OH
7
8
Cl
Cl
CN
OH
OH
Cl
Cl
CN
9
Cl
Cl
CN
87
OH
10
Br
Br
CN
66
74
79
91
OH
11
12
13
14
NO2
NO2
CN
OH
F3C
F3C
CN
OH
OH
OBn
CN
OBn
N
N
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68
CN
OH
15
S
S
74
93
OH
16
17
CN
O
O
OH
CN
CN
95
88
OH
18
19
CN
OH
CN
CN
CN
8
OH
20
21
6
CN
OH
Reaction conditions: alcohol (0.5 mmol), PS-BHA-Cu (0.05 mmol), K3PO4 (0.05mmol),
HCOONH4 (2.0 mmol) ACN (3 mL), O2 (1 atm.), Temperature (115 0C), 16 h.
Oxidative synthesis of primary amides from primary alcohols
In continuation of our interest in oxidative reactions, we were in search of a high-
yielding, catalytic, cheap and environmentally benign system for oxidative synthesis of primary
amides from primary alcohols. When TBHP and NH3 (aq) was added to benzyl alcohol then the
benzamide was the major product instead of benzonitrile under the reaction conditions.
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PS-BHA-Cu
CONH2
TBHP
OH
O2 (1 atm) / NH3 (aq)
DMF /H2O
80 0C
Scheme 4: Aerobic oxidative synthesis of bezamide from benzyl alcohol
We found that PS-BHA-Cu / TBHP system gave the amide as the major product (scheme 4). For
example, when the amidation of benzyl alcohol was carried out using aqueous ammonia (25
0
wt%, 2.6 equiv. with respect to benzyl alcohol) and O2 (1 atm) at 80 C then benzamide was
obtained in 94% yield along with benzonitrile 6%. N,N-dimethylformamide (DMF) was good
solvent likely due to the high solubilities of benzyl alcohol, ammonia, and water (Table 4).
Toluene and dichloromethane gave lower conversion of benzyl alcohol. Thus, we subsequently
carried out the amidation in DMF medium. Next, the amidation of benzyl alcohol was carried out
with various ammonia sources (Table 4). Besides aqueous ammonia, NH4HCO3 and (NH4)2CO3
could act as effective nitrogen sources for the present amidation and gave benzamide in 81% and
73% yields, respectively.
This oxidative amidation was found to be sensitive to the reaction temperature. At lower
0
temperatures (40-60 C) only low to moderate yield was obtained. A reaction temperature of 80
0C was found to be optimal for the model reaction. The amount of pressure of molecular oxygen
0
was varied from 1 atm to 2 atm, 1 atm oxygen pressure resulted in 99% conversion at 80 C
temperature. When oxygen pressure was raised to 2 atm the conversion and selectivity towards
amide remained same. Therefore, 1 atm oxygen pressures were found to be optimum.
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Table 4: Effect of various nitrogen source and temperature
Entry
Nitrogen
source
Temperature
(0C)
Yield
(%)
NH3 (aq)
80
80
80
40
50
60
70
94
81
73
53
61
74
85
1
2
3
4
5
6
7
NH4HCO3
(NH4)2CO3
NH3 (aq)
NH3(aq)
NH3 (aq)
NH3 (aq)
Reaction conditions: alcohol (3 mmol), PS-BHA-Cu (0.05 mmol), TBHP (0.05mmol), 25%
NH3 (aq.) (9 mmol), DMF (3 mL), H2O (1 mL), 5 h.
The scope of the present PS-BHA-Cu catalyzed amidation of primary alcohols was next
examined. Herein, the scope is much extended to various kinds of structurally diverse primary
alcohols. The amidation of benzylic alcohols, which contain electron-donating as well as
electron-withdrawing substituents at different positions, efficiently proceeded to afford the
corresponding substituted benzamide derivatives in excellent yields. The reaction rates for the
amidation of ortho, meta and para-substituted benzyl alcohols were almost the same, and the
corresponding substituted benzamides were obtained. 4-(Methylthio)benzamide was produced in
94% (Table 5, entry 18) yield from the corresponding 4-methylthiobenzyl alcohol without the
oxidation of sulfur. The numbers of electron withdrawing groups at different positions were
tested as well; the benzyl alcohols were converted into primary amides in good yields (Table 5,
entries 7-14). Additionally, various heterocyclic amides were produced to prove the generality of
this methodology (Table 5, entries 15-19). Not only pyridines and thiophene, but also furan can
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be tolerated. In the amidation of aromatic allylic alcohol such as cinnamyl alcohol derivative, the
corresponding aromatic unsaturated amide could be obtained in excellent yields (90% yields).
Table 5: Polymer supported copper (II) catalyzed aerobic oxidative synthesis of aryl amides.
Entry
Substrate
Product
Yield (%)
O
C
1
OH
OH
94
89
96
NH2
NH2
NH2
O
C
2
3
O
C
OH
O
C
4
5
OH
94
98
NH2
O
OH
OH
C
NH2
MeO
MeS
MeO
O
C
6
95
NH2
MeS
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O
7
8
OH
C
86
NH2
Cl
Cl
Cl
O
C
OH
OH
Cl
95
NH2
O
9
C
97
98
99
NH2
NH2
NH2
Cl
Cl
O
10
11
OH
C
F
F
O
OH
C
F3C
F3C
O
12
OH
C
98
NH2
F3CO
F3CO
O
13
14
OH
C
98
97
NH2
O2N
O2N
O
OH
C
NH2
Br
Br
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O
15
16
OH
OH
C
87
91
N
NH2
N
O
C
NH2
N
N
O
C
17
OH
93
N
NH2
N
S
O
C
18
19
20
S
OH
OH
94
88
90
NH2
NH2
C
O
O
O
O
C
OH
NH2
Reaction conditions: Reaction conditions: alcohol (3 mmol), PS-BHA-Cu (0.05 mmol), TBHP
(0.05 mmol), 25% NH3 (aq.) (9 mmol), DMF (3 mL), H2O (1 mL), O2 (2 atm.), 5 h.
Recycling of catalyst
The catalyst remains insoluble in the present reaction conditions and hence can be easily
separated by simple filtration followed by washing. The catalyst was washed with methanol and
dried at 100 0C. The oxidative synthesis of benzonitrile and benzamide from benzyl alcohol was
carried out with the recycled catalyst under the optimized reaction conditions. The catalyst was
recycled in order to test its activity as well as stability. The obtained results are presented in Fig.
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6. As seen from Fig. 6, the recycled catalyst did not show any appreciable change in the activity
which indicates that the catalyst is stable and can be regenerated for repeated use. Similarly,
recycling of the catalyst was tested for the oxidative amidation of benzyl alcohol. No appreciable
change in conversion as well as selectivity indicates that the catalyst can be reused.
Nitrile synthesis from benzyl alcohol
Amide synthesis from benzyl alcohol
100
95
90
85
1
2
3
4
5
6
Run
Fig.6. Recycling efficiency of PS-BHA-Cu for the benzonitrile and benzamide synthesis from
benzyl alcohol
Conclusion
In the present work, we have developed and characterized an efficient polymer anchored
copper Schiff base complex as the catalyst for the selective aerobic oxidative synthesis of aryl
nitriles and primary aryl amides from benzylic alcohols and molecular oxygen as an oxidant.
This catalyst also shows excellent catalytic activity in oxidative amidation reaction of benzylic
alcohols. The present procedure is simple, efficient and environmentally benign allowing for a
practical route to aryl nitriles and amides. The low cost of the catalytic copper system give this
method potential to production on an industrial scale. Another important factor is the stability
and recyclability of the catalyst under the reaction conditions used. This heterogeneous catalyst
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shows no significant loss of activity in the recycling experiments. The active sites do not leach
out from the support and thus can be reused without appreciable loss of activity, indicating that
the anchoring procedure was effective. The reusability of this catalyst is high and can be reused
six times without significant decrease in its initial activity. We hope that the present catalytic
system has a bright future in industrial application.
Acknowledgments
SMI acknowledges CSIR and DST for financial support. RAM acknowledges UGC,
New Delhi, India for his Maulana Azad National Fellowship (F1-17.1/2012-13/MANF-2012-13-
MUS-WES-9628/SA-III).
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