Polymeric PEG35k-Pd nanoparticles: Efficient and recyclable catalyst for reduction of nitro compounds

Article abstract of DOI:10.1080/00397911.2010.523159

The small size polymeric PEG35k-Pd nanoparticles are key attractions for catalysis due to their large surface to volume ratio, non-toxicity, inexpensive, thermal stability, and recoverability. Polymeric PEG35k-Pd nanoparticles in the absence of phosphine ligands are insensitive to the air and moisture and act as an active heterogeneous catalyst for the reduction of nitroarenes. Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications to view the free supplemental file. Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2010.523159

This article was downloaded by: [George Mason University]
On: 17 June 2013, At: 21:04
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Polymeric PEG35k-Pd Nanoparticles:
Efficient and Recyclable Catalyst for
Reduction of Nitro Compounds
Veena Yadav a , Shweta Gupta b , Rupesh Kumar b , Gajendra Singh b
& Rekha Lagarkha a
a Department of Chemistry, Bundelkhand University, Jhansi, India
b Department of Chemistry, University of Delhi, Delhi, India
Accepted author version posted online: 06 Jul 2011.Published
online: 14 Sep 2011.
To cite this article: Veena Yadav , Shweta Gupta , Rupesh Kumar , Gajendra Singh & Rekha Lagarkha
(2012): Polymeric PEG35k-Pd Nanoparticles: Efficient and Recyclable Catalyst for Reduction of
Nitro Compounds, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 42:2, 213-222
To link to this article: http://dx.doi.org/10.1080/00397911.2010.523159
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Synthetic Communications1, 42: 213–222, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.523159
POLYMERIC PEG35k-Pd NANOPARTICLES: EFFICIENT
AND RECYCLABLE CATALYST FOR REDUCTION OF
NITRO COMPOUNDS
Veena Yadav,1 Shweta Gupta,2 Rupesh Kumar,2
Gajendra Singh,2 and Rekha Lagarkha1
1Department of Chemistry, Bundelkhand University, Jhansi, India
2Department of Chemistry, University of Delhi, Delhi, India
GRAPHICAL ABSTRACT
Abstract The small size polymeric PEG35k-Pd nanoparticles are key attractions for cataly-
sis due to their large surface to volume ratio, non-toxicity, inexpensive, thermal stability,
and recoverability. Polymeric PEG35k-Pd nanoparticles in the absence of phosphine
ligands are insensitive to the air and moisture and act as an active heterogeneous catalyst
for the reduction of nitroarenes.
Supplementary materials are available for this article. Go to the publisher’s online
edition of Synthetic Communications1 to view the free supplemental file.
Keywords Catalysis; palladium; PEG35k; recyclable
INTRODUCTION
Functionalized anilines are industrially important intermediates for pharmaceu-
ticals, polymers, herbicides, and other substances and fine chemicals,[1,2] so there is a
strong incentive to develop chemoselective catalysts for the reduction of nitro groups.
Stoichiometric reducing agents such as iron,[2] sodium hydrosulfite,[3] tin,[4] or zinc in
ammonium hydroxide[5] have been successfully used to reduce aromatic nitro com-
pounds. Reduction of aromatic nitro compounds to amines is a very useful synthetic
transformation for which a vast array of reagents has been developed.[6–8] The most
general methodology used for this conversion is catalytic hydrogenation,[9–13] as it is
an economical and effective method, particularly in large-scale reactions. However,
Received August 7, 2010.
Address correspondence to Rupesh Kumar, Department of Chemistry, University of Delhi, Delhi
110007, India. E-mail: chembio005@yahoo.co.in
213

214
V. YADAV ET AL.
these reactions have limited utility in the presence of other reducible functional
groups.[14] Catalytic hydrogenation of nitroarenes over heterogeneous catalysts is a
simple method for the production of aromatic amines. However, the application
of conventional catalytic systems to the reduction of nitroarenes containing other
reducible functional groups (e.g., halogen, carbonyl, cyano, benzyloxy, and alkenic
groups) is problematic because the reaction is often accompanied by the reduction
of these functional groups.[15–17] It is well known that the catalytic properties of het-
erogeneous catalysts are dependent on the particle size of the metal and the surface
structure of the supports.[18–20] Now transition-metal nanoparticles are found to be
effective catalysts for these chemical transformations because of their large surface
area and unique combination of reactivity, stability, and selectivity. In most cases,
the use of different catalysts under a wider range of reaction conditions yields the
corresponding amine quantitatively, without the production of waste products.
Because of the exothermic nature of the reaction and the requirement for a secluded
high-pressure system, numerous safety precautions have to be taken. Palladium
charcoal system is flammable at room temperature, so these systems have handling
problems. Besides this, generally used methods[21–24] require either strong acid
medium, hazardous molecular hydrogen, or high-pressure reactors that corrode the
reaction equipment. Compared to the conventionally used methods, contemporary
catalytic transfer hydrogenation is a safer and greener way that is attracting more
and more attention.[25–29] Hydrazine hydrate is widely employed as hydrogen donor
in catalytic transfer hydrogenation because the hydrazine reduction produces
harmless by-products such as nitrogen gas and water. The reduction of aromatic nitro
compounds using hydrazine or hydrazine hydrate represents a special variation of the
catalytic reduction, where hydrazine is the source of the hydrogen. The hydrogen can
be generated by a variety of H-transfer catalysts.[30–32] Especially with the use of noble
metal catalysts, such as Pd, Pt, or Ru, the catalytic hydrazine reduction gives good
yields comparable to or better than the catalytic hydrogenation. When hydrogenating
halo-nitro aromatics to the corresponding amines, hydrodehalogenation is often an
undesired side reaction. The ease with which the hydrodehalogenation occurs depends
on the ring position of the halogen.[33] Therefore, the search continues for a better
catalyst for the synthesis of aniline derivatives in terms of mild reaction conditions,
operational simplicity, economic viability, and selectivity.[34] Simple and widely avail-
able polymers like such as poly(ethylene glycol) (PEG) as nontoxic, inexpensive,
nonionic, thermally stable, recoverable liquid solvents of low volatility have been used
for various transformations.[35–41] Transition-metal nanoparticles have wide-ranging
applications in catalysis. However, because of their large surface area and surface
energy, they tend to agglomerate during the reactions and therefore need to be stabi-
lized for effective utilization.
RESULTS AND DISCUSSION
Herein, we report for the first time the use of polymeric PEG35k-Pd nano-
particles as catalyst in the reduction of nitroarenes to the corresponding aromatic
amines (Scheme 1).
We expect that the present study could accelerate the investigation of polymeric
PEG35k-Pd nanoparticles as a catalyst in organic synthesis. A common method to

POLYMERIC PEG35k-Pd NANOPARTICLES
215
Scheme 1. Reduction of nitroarenes.
prepare metal nanoparticles involves reduction of metal ions in the presence of
stabilizers such as a surfactant and polymers. We report a novel and facile route
for the preparation of Pd nanoparticles by exploiting PEG, molecular weight 35000
(MW35k), which was found to act as both reducing agent and stabilizer.[42] The
prepared polymeric PEG35k-Pd nanoparticles can be preserved for months without
any change of physical and chemical properties. It was noted that prepared nano-Pd
provides the active and recyclable heterogeneous catalyst for the nitro group
reduction in the absence of phosphine ligands. The reaction was insensitive to the
air and moisture with good yields, and polymeric PEG35k-Pd nanoparticles can be
readily recycled more than 8 times (Fig. 1) without deactivation. Polymeric
PEG35k-Pd nanoparticles were found to act as efficient reduction catalysts for the
conversion of nitroarenes to anilines derivatives in high turn over numbers (TONs)
without affecting the reduction of halogen or other functional groups. Control experi-
ments of nitroarene reduction were performed in the absence of polymeric
PEG35k-Pd nanoparticles according to the general procedure with reagent hydrazine
hydrate at 90–120 ꢀ C for 360 min. The reactions did not produce any desired product.
This clearly showed that the presence of both polymeric PEG35k-Pd nanoparticles
and hydrazine hydrate played important roles in the reduction of nitroarenes in
our reaction system. Preparation of polymeric PEG35k-Pd nanoparticles was
achieved successfully by the reaction of Pd (OAc)2 with PEG35k solution in water
at room temperature under an open atmosphere. Pd(II) ions reduced to Pd(0) because
of the presence of the terminal –OH functional group present in polymer PEG35000
at 90 ꢀC for 2 h (Scheme 2).
Figure 1. Experiments reusing polymeric PEG35-Pd nanoparticles in the reduction of nitroarenes by
hydrazine hydrate.

216
V. YADAV ET AL.
Scheme 2. Synthesis of polymeric PEG35k-Pd nanoparticles.
Polymer PEG35k was used for the immobilization of palladium metal, where
the metal particles could be highly dispersed on the surface of polymer. Polymeric
PEG35k-Pd nanoparticle size was found to be 28 Æ 4 nm [Polymeric PEG35k-Pd
nanoparticles were characterized by quasi elastic light scattering (QELS) and trans-
mission electron microscopy (TEM) (Figs. 2a and 2b. For X-ray diffraction and
ultraviolet, see the Supporting Information, available online).
The polymeric PEG35k-Pd nanoparticles were used in the catalytic reduction
of the nitro group of nitroarenes derivative (Scheme 1). The reaction of nitroarene
derivative was carried out in the presence of the catalyst in N2H2 Á H2O at 90 ꢀC tem-
perature (Table 1). All of the Polymeric PEG35k-Pd nanoparticles exhibited good to
excellent catalytic efficiency in the reduction of the nitro group. Entry 1 (Table 1)
was consumed within 90 min, and high turnover frequencies reached. The selectivity
of the reduction of p-chloroaniline (Entry 8, Table 1) was highly dependent on the
polymeric PEG35k-Pd nanoparticles. The product yield obtained in the reaction
with polymeric PEG35k-Pd nanoparticles was similar to that of commercially avail-
[43]
able Pt=C,
producing large amounts of aniline (entry 1, Table 1). Catalytic
reduction of other nitroarene derivatives (entries 1–14) was also achieved with high
chemoselectivity by using the polymeric PEG35k-Pd nanoparticles. The results
shown in Table 1 suggest that the reduction of nitroarenes over polymeric
PEG35k-Pd nanoparticles is tolerant toward halogens and other functional groups.
Besides the efficiency and selectivity, the reduction over polymeric PEG35k-Pd
nanoparticles has two more advantages: Reusability without leaching of palladium
species and possible application to produce anilines in gram quantities.
Figure 2. (a) QELS data of PEG35k-Pd: plot of population distribution in percentile size distribution
in nanometers. Mean: 36.06, standard deviation: 3.108, polydispersity: 0.007 standard deviation=mean2.
(b) TEM micrographs of polymeric PEG35k-Pd nanoparticles. (Figure is provided in color online.)

POLYMERIC PEG35k-Pd NANOPARTICLES
217
Table 1. Reduction of substituted nitroarenes with hydrazine hydrates in the presence of polymeric
PEG35k-Pd NPs to corresponding anilines
Entry
Substrate
Product
Time (min.)
Yield (%)
100
Reference
[44]
1
2
90
[44]
[44]
100
99
3
4
110
100
97
98
[44]
[44]
[44]
5
6
7
120
110
120
98
98
99
[44]
—
8
9
90
90
99a
99a
—
—
10
11
80
70
99a
100a
—
—
12
60
100a
13
14
90
99a
—
—
100
100a
Note. Reaction conditions: All reactions were carried out with nitroarenes (1 mmol), hydrazine hydrate
(5 eq), and polymeric PEG35k-Pd NPs (1.0 mol%) at 90 ꢀC for 1–2 h in open atmosphere. Products
characterized by 1H and 13C NMR and mass spectroscopic data.
aIsolated yields.

218
V. YADAV ET AL.
Figure 3. Effect of temperature on product yield with temperature variation. (Figure is provided in color
online.)
Temperature Effect
To elucidate the effect of temperature on the reaction conditions, we used
different temperature conditions in our nitro reduction to evaluate the scope
and limitation of the reactions. We found that polymeric PEG35k-Pd nanoparti-
cles catalyzed reduction of aromatic nitro compounds efficiently at 90 ꢀC. Inter-
estingly, the reaction yield decreases at high as well as low temperature
conditions. (Fig. 3).
Optimization of Reaction Conditions
Table 2 shows the optimization of reaction in different conditions. At the high
temperature, the reaction yield goes down. Entries 2, 8, and 9 (Table 2) indicate at
low temperature, low concentration of hydrazine hydrate and low amount of catalyst
loading the reaction yield is poor because of the need for higher activation energy.
Entry 3 (Table 2) shows that the polymeric PEG35k-Pd nanoparticles loading
1 mol% at 90 ꢀC and 5 equivalents hydrazine hydrate have greatest activity for direct
reduction of nitrobenzene to aniline under mild conditions.
Table 2. Results of nitrobenzene reduction to form aniline with supported catalyst 1 mol % polymeric
PEG35k-Pd nanoparticles at different reaction conditions
No.
Catalyst (mol %)
Temp. (ꢀC)
N2H4 Á H2O (eq)
Reaction time (min)
Conversion (%)
1
2
1.0
1.0
1.0
1.0
1.0
0.5
0.5
1.0
1.0
1.0
1.0
90
90
1
4
120
120
90
25
78
100
97
96
85
85
30
85
96
94
3
90
90
5
4
10
5
120
360
120
360
360
360
120
120
5
90
90
6
5
7
90
50
10
5
8
9
80
5
10
11
100
120
5
5

POLYMERIC PEG35k-Pd NANOPARTICLES
219
Recyclability
To check the reusability of the polymeric PEG35k-Pd nanoparticle catalyst,
consecutive cycles were executed, and their results are depicted in Fig. 3. The
polymeric PEG35k-Pd nanoparticles could be recycled by separating them from
the reaction mixture by mild centrifugation and used as a catalyst for the same
reaction again to check for any changes in their catalytic activity. With increasing
number of cycles, the catalytic activity of the polymeric PEG35k-Pd nanoparticles
decreased, and it was lost after eight cycles. The graphical presentation of the
relation between the number of cycles of the reaction and the catalytic activity in
terms of yield is presented in Fig. 1.
CONCLUSION
In conclusion, we have developed an exceedingly efficient and highly chemose-
lective approach to prepare aromatic amines from the corresponding nitroarene
compounds using hydrazine hydrate over polymeric PEG35k-Pd nanoparticles. This
method is simple and environmentally friendly. The present study opens up the
application of polymeric PEG35k-Pd nanoparticles as catalyst in the reduction of
nitroarenes. A detailed mechanistic study is now under investigation. Further studies
to explore the application of PEG35k-Pd nanoparticles as catalyst in other reactions
are under way.
EXPERIMENTAL
Typical Experimental Procedure for Preparation of PEG35k-Pd
Nanoparticles
Palladium acetate Pd(OAc)2 (0.5 mmol) and solid PEG, mol. wt. 35000
(1.0 mmol), were added to water as a solvent. The resulting solution was heated to
90 ꢀC and remained at this temperature for 2 h. The color of the solution turned from
orange to brown and finally turned black, indicating the formation of Pd(0) metal.
Then the mixture of PEG35k and palladium nanoparticles was cooled immediately
to ambient temperature to form a solidified mixture. The solids were washed with
doubly distilled water (10 ml) and ether (20 ml) and dried under vacuum at room
temperature for 5 h to afford the corresponding polymeric PEG35k-Pd nanoparti-
cles. Particle sizes were characterized by QELS, TEM, UV spectroscopic techniques.
The average size of polymeric PEG35k-Pd nanoparticles was found to be 28 Æ 4 nm.
Typical Experiment Procedure for the Reduction of Aromatic
Reduction Compounds
Reduction of nitroarenes was performed in a 10 ml, round-bottom flask in the
presence of nitroarenes (entries 1–14) (1.0 mmol), polymeric PEG35k-Pd NPs (1 mol
% polymeric PEG35k-Pd NPs), and hydrazine hydrate (5 equivalents) in an open
atmosphere at 90 ꢀC. After the reaction was completed, polymeric PEG35k-Pd
NPs were removed by centrifugation. The solution was filtered through a pad of
Celite, and then saturated aqueous NaHCO3 (10 ml) was added to the filtrate and

220
V. YADAV ET AL.
extracted with ethyl acetate. The combined organic layers were dried over anhydrous
Na2SO4, concentrated under reduced pressure, and purified by the column chroma-
1
tography to give the aniline derivatives. Products were characterized by H NMR
and 13C NMR and mass spectra. The removed polymeric PEG35k-Pd NPs were
washed with water and diethyl ether, dried under vacuum, and then reused.
ACKNOWLEDGMENT
We are pleased to acknowledge financial support from the Department of
Science and Technology, New Delhi [Grant No. SR=FTP=CS-62=2006], for this
investigation.
REFERENCES
1. Dowing, R. S.; Kunkeler, P. J.; Bekkum, V. H. Catalytic syntheses of aromatic amines.
Catal. Today 1997, 37, 121–136.
2. Winternitz, M. P.; Zeller, M. Preparation of 3-(2,6-dioxo-1-pyrimidinyl)benzoate esters
and herbicidal formulations containing them. World (WO) Patent 91=00278, 1991.
3. Kovar, F.; Armond, F. E. Ethynyl-substituted aromatic ortho diamines and method of
synthesis. U.S. Patent 3 975, 444, 1976.
4. Butera, J.; Bagli, J. Preparation of N-heteroalkyl-substituted 1-aryloxy-2-propanolamines
as antiarrythmics. WO. Patent 91=09023, 1991.
5. Burawoy, A.; Critchley, J. P. Electronic spectra of organic molecules and their interpret-
ation, V: Effect of terminal groups containing multiple bonds on the K-bands of conjugated
systems. Tetrahedron 1959, 5, 340–351.
6. Hudlicky, M. Reductions in Organic Chemistry, 2nd ed.; ACS: Washington, DC, 1996.
7. Kabalka, G. W.; Varma, R. S. Reduction of nitro and nitroso compounds. In Compre-
hensive Organic Synthesis; B. M. Trost, I. Fleming (Eds.); Pergamon: Oxford, 1991; vol.
8, p. 363.
8. Scriven, E. F. V. Azides: Their preparation and synthetic uses. Chem. Rev. 1988, 88,
297–368.
9. Siegrist, U.; Baumeister, P.; Blaser, H. U.; Studer, M. Chem. Ind. 1998, 75, 207.
10. Nishmura, S. Rhodium-platinum oxide as a catalyst for the hydrogenation of organic
compounds. II. Catalyst preparation and effects of platinum in rhodium-platinum oxide.
Bull. Chem. Soc. Jpn. 1961, 34, 1544–1545.
11. Adkins, H.; Cramer, H. I. The use of nickel as a catalyst for hydrogenation. J. Am. Chem.
Soc. 1930, 52, 4349–4358.
12. Adkins, H.; Connor, R. The catalytic hydrogenation of organic compounds over copper
chromite. J. Am. Chem. Soc. 1931, 53, 1091–1095.
13. Broadbent, H. S.; Slaugh, L. H.; Jarvis, N. L. Rhenium sulfides as liquid-phase hydrogen-
ation catalysts: A comparison with molybdenum sulfide and cobalt polysulfide. J. Am.
Chem. Soc. 1954, 76, 1519–1523.
14. Mosby, W. L. Some 9,10-disubstituted phenanthrenes. J. Org. Chem. 1959, 24, 421–423.
15. Rylander, P. Catalytic Hydrogenation in Organic Synthesis; Academic Press: New York,
1979; p. 112.
16. Baumeister, P.; Studer, M.; Roessler, F. In Handbook of Heterogeneous Catalysis; G. Ertl,
H. Kno¨zinger, J. Weitkamp (Eds.); Wiley-VCH: Weinheim, 1997; p. 2186.
17. Blaser, H. U.; Siegrist, U.; Steiner, H.; Studer, M. Fine Chemicals through Heterogeneous
Catalysis; R. A. Sheldon, H. V. Bekkum (Eds.); Wiley-VCH: Weinheim, 2001; p. 389.

POLYMERIC PEG35k-Pd NANOPARTICLES
221
18. Feldheim, D. L.; Foss, C. A. Jr. Metal Nanoparticles: Synthesis, Characterization, and
Application; Marcel Dekker: New York, 2002.
19. Stiles, A. B. (Ed.) Catalyst Supports and Supported Catalysts; Butterworths: Boston, 1987.
20. Ertl, G.; Kno¨zinger, H.; Weitkamp, J. (Eds.). Handbook of Heterogeneous Catalysis;
VCH: Weinheim, 1997.
21. Doxsee, K. M.; Feigel, M.; Stewart, K. D.; Canary, J. W.; Knobler, C. B.; Cram, D. J. Host–
guest complexation: Preorganization strongly enhances the tendancy of hemispherands to
form hemispheraplexes. J. Am. Chem. Soc. 1987, 109, 3098–3107.
22. Merlic, C. A.; Motamed, S.; Quinn, B. Structure determination and synthesis of fluoro
nissl green: An RNA-Binding fluorochrome. J. Org. Chem. 1995, 60, 3365–3369.
23. Tafesh, A. M.; Weiguny, J. A review of the selective catalytic reduction of aromatic nitro
compounds into aromatic amines, isocyanates, carbamates, and ureas using CO. Chem.
Rev. 1996, 96, 2035–2052.
24. Liu, Y.; Lu, Y.; Prashad, M.; Repic, O.; Blacklock, T. J. A practical and chemoselective
reduction of nitroarenes to anilines using activated iron. Adv. Synth. Catal. 2005, 347,
217–219.
25. Mohapatra, S. K.; Sonavane, S. U.; Jayaram, R. V.; Selvam, P. Reductive cleavage of azo
dyes and reduction of nitroarenes over trivalent iron incorporated hexagonal mesoporous
aluminophosphate molecular sieves. Appl. Catal. B 2003, 46, 155–163.
26. Mohapatra, S. K.; Sonavane, S. U.; Jayaram, R. V.; Selvam, P. Heterogeneous catalytic
transfer hydrogenation of aromatic nitro and carbonyl compounds over cobalt(II) substi-
tuted hexagonal mesoporous aluminophosphate molecular sieves. Tetrahedron Lett. 2002,
43, 8527–8529.
27. Kulkarni, A. S.; Jayaram, R. V. Liquid-phase catalytic transfer hydrogenation of aromatic
nitro compounds on La1ÀxSrxFeO3 perovskites prepared by microwave irradiation. J. Mol.
Catal. A 2004, 223, 107–110.
28. Kulkarni, A. S.; Jayaram, R. V. Liquid-phase catalytic transfer hydrogenation of
aromatic nitro compounds on perovskites prepared by microwave irradiation. Appl.
Catal. A 2003, 252, 225–230.
ˇ
29. Prasad, K.; Jiang, X.; Slade, J. S.; Clemens, J.; Repic, O.; Blacklock, T. J. New trends in
palladium-catalyzed transfer hydrogenations using formic acid. Adv. Synth. Catal. 2005,
347, 1769–1773.
30. Furst, A.; Berlo, R. C.; Hooton, S. Hydrazine as a reducing agent for organic compounds
(catalytic hydrazine reductions). Chem. Rev. 1965, 65, 51–68.
31. Brieger, G.; Nestrick, T. J. Catalytic transfer hydrogenation. Chem. Rev. 1974, 74,
567–580.
32. Johnstone, R. A. W.; Wilby, A. H.; Entwistle, I. D. Heterogeneous catalytic transfer
hydrogenation and its relation to other methods for reduction of organic compounds.
Chem. Rev. 1985, 85, 129–170.
33. Kosak, J. R.; Jones, W. H. Ed. Catalysis in Organic Synthesis; Academic Press: New
York, 1980; p. 107.
34. Kumar, R.; Chaudhary, P.; Nimesh, S.; Verma, A. K.; Chandra, R. An efficient
synthesis of 1,5-benzadiazepine derivatives catalyzed by silver nitrate. Green Chem. 2006,
8, 519–521.
35. Kumar, R.; Chaudhary, P.; Nimesh, S.; Verma, A. K.; Chandra, R. Polyethylene glycol as
a non-ionic liquid solvent for Michael addition reaction of amines to conjugated alkenes.
Green Chem. 2006, 8, 356–358.
36. Harris, J. M. Poly(ethylene Glycol) Chemistry, Biotechnological and Biomedical Applica-
tions; Plenum Press: New York, 1992, p. 3, Polyethylene Glycol: Chemistry and Biological
Application, ACS Books: Washington, DC, 1997.

222
V. YADAV ET AL.
37. Sauvagnat, B.; Lamaty, F.; Lazaro, R.; Martinez, J.; Poly(ethylene glycol) (PEG) as a new
phase-transfer catalyst in the palladium-catalyzed Heck reaction: Positive effect of the
polymer in the supported synthesis of a-aminoesters. Surf. Chem. Catal. 1998, 777–780.
38. Chandrasekhar, S.; Narsihmulu, C. H.; Sultana, S. S.; Reddy, N. R. Poly(ethylene glycol)
(PEG) as a reusable solvent medium for organic synthesis. Application in the heck
reaction. Org. Lett. 2002, 4, 4399–4401.
39. Jian, S. Z.; Wang, Y. G. Soluble polymer-supported synthesis of trans b-Lactams with
high diastereoselectivity. Chem. Lett. 2004, 33, 866–867.
40. Xia, M.; Wang, Y. G. Soluble polymer-supported synthesis of Biginelli compounds.
Tetrahedron Lett. 2002, 43, 7703–7705.
41. Wang, Y. G.; Zhang, J.; Lin, X. F. Parallel synthesis of pyrazolines on soluble polymer
support. Synlett. 2003, 1467–1468.
42. Ahmadian, P.; Namini, A. A.; Babaluo, B. B. Palladium nanoparticles synthesis using
polymeric matrix: Poly(ethyleneglycol) molecular weight and palladium concentration
effects. IJNN. 2007, 3, 37–43.
43. Takasaki, M.; Motoyama, Y.; Higashi, K.; Yoon, S. H.; Mochida, I.; Nagashima, H.
Chemoselective hydrogenation of nitroarenes with carbon nanofiber-supported platinum
and palladium nanoparticles. Org. Lett. 2008, 10, 1601–1604.
44. Lauwiner, M.; Rys, P.; Wissmann, J. Reduction of aromatic nitro compounds with
hydrazine hydrate in the presence of an iron oxide hydroxide catalyst I. The reduction
of monosubstituted nitrobenzenes with hydrazine hydrate in the presence of ferrihydrite.
Appl. Catal. A: General. 1998, 172, 141–148.