Ruthenium on chitosan: A recyclable heterogeneous catalyst for aqueous hydration of nitriles to amides

Article abstract of DOI:10.1039/c3gc42004c

Ruthenium has been immobilized over chitosan by simply stirring an aqueous suspension of chitosan in water with ruthenium chloride, and has been utilized for the oxidation of nitriles to amides; the hydration of nitriles occurs in high yield and excellent selectivity, which proceeds exclusively in aqueous medium under neutral conditions. the Partner Organisations 2014.

Full text of DOI:10.1039/c3gc42004c

View Article Online
View Journal
Green Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: N. Baig, M. N.
Nadagouda and R. S. Varma, Green Chem., 2013, DOI: 10.1039/C3GC42004C.
This is an Accepted Manuscript, which has been through the RSC Publishing peer
review process and has been accepted for publication.
Accepted Manuscripts are published online shortly after acceptance, which is prior
to technical editing, formatting and proof reading. This free service from RSC
Publishing allows authors to make their results available to the community, in
citable form, before publication of the edited article. This Accepted Manuscript will
be replaced by the edited and formatted Advance Article as soon as this is available.
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
Volume 12 | Number 9 | September 2010 | Pages 1481–1676
To cite this manuscript please use its permanent Digital Object Identifier (DOI®),
which is identical for all formats of publication.
More information about Accepted Manuscripts can be found in the
Information for Authors.
Please note that technical editing may introduce minor changes to the text and/or
graphics contained in the manuscript submitted by the author(s) which may alter
content, and that the standard Terms & Conditions and the ethical guidelines
that apply to the journal are still applicable. In no event shall the RSC be held
responsible for any errors or omissions in these Accepted Manuscript manuscripts or
any consequences arising from the use of any information contained in them.
ISSN 1463-9262
COMMUNICATION
CRITICAL REVIEW
Luque, Varma and Baruwati
Dumesic et al.
Magnetically seperable organocatalyst Catalytic conversion of biomass
for homocoupling of arylboronic acids to biofuels
1463-9262(2010)12:9;1-U
www.rsc.org/greenchem
Registered Charity Number 207890

Page 1 of 10
Green Chemistry
View Article Online
DOI: 10.1039/C3GC42004C
Ruthenium on chitosan: A recyclable heterogeneous catalyst for aqueous
hydration of nitriles to amides
R. B. Nasir Baig, Mallikarjuna N. Nadagouda and Rajender S. Varma*
Abstract
Ruthenium has been immobilized over chitosan by simply stirring an aqueous suspension
of chitosan in water with ruthenium chloride and has been utilized for the oxidation of
nitriles to amides; the hydration of nitriles occurs in high yield and excellent selectivity,
which proceeds exclusively in aqueous medium under neutral conditions.
In view of the growing consciousness about the environmental issues, tremendous efforts have
been expanded towards the development of new chemical processes that minimize pollution in
the synthesis processes. In the catalysis arena, heterogeneous catalysis addresses these challenges
1
and is a prime choice due to ease of catalyst removal, recovery and recycling. The focus, more
often, has been on the heterogeneous system developed by the immobilization of active metallic
2
species over inorganic material such as silica and alumina. The petrochemical derived polymer
such as polystyrene has also been utilized as a support for the immobilization of transition
3
metals. Thrust for the cleaner and sustainable chemistry has resulted in the shift from
petrochemical-based entities to biorenewable materials. There are several reasons to exploit
abundant natural polymer macrostructures, and in particular those of polysaccharide origin, to
create high-performance and environmentally benign catalysts as they have several functional
groups for metal anchoring. They are chemically stable yet can be degraded biologically; an
attribute that renders their use as polymeric supports for catalysis all the more attractive.
Although there has been a global recognition that natural polysaccharides can be used as
feedstocks for the production of large-scale consumer goods, their use as supports for
4
a
heterogeneous catalysis is also on the rise.
Chitosan is an important amino-polysaccharide
used for the catalytic applications and is usually chemically modified for its role as a catalyst
4
support. Chitosan has been useful for the removal of transition metal from it aqueous mixture
5
without any modification of its back bone. A simple experiment to extract ruthenium nano
particles from aqueous mixture using chitosan was inspiring as ruthenium could be easily
extracted from aqueous solutions with efficiency greater than 99.9%. This prompted us to use the
unmodified chitosan as heterogeneous support for the catalytic application in organic synthesis.
The hydration of nitriles to amides is an important transformation in the pharmaceutical
6
7
industry. It has been conventionally achieved using acids and bases, enzymes, and transition
8
metals. However, under these conditions, various by-products, notably carboxylic acids, are
____________________________________________________________________________
Sustainable Technology Division, National Risk Management Research Laboratory, U. S.
Environmental Protection Agency, MS 443, Cincinnati, Ohio 45268, USA. Fax: 513- 569-7677;
Tel: 513-487-2701. E-mail: varma.rajender@.epa.gov
1

Green Chemistry
Page 2 of 10
View Article Online
DOI: 10.1039/C3GC42004C
generated by the hydrolysis of the starting nitriles and as well as amides. Several protocols,
which predominantly use homogeneous metal complexes, have been reported for the hydration
9
of nitriles. These methods suffer from various drawbacks, especially the difficulty in separation
of product and catalyst from the reaction mixture, as well as the use of an inert atmosphere for
handling air-sensitive metal catalysts. Many sensitive functional groups do not withstand such
harsh conditions, which consequently decrease the selectivity of the reaction protocol.
1
0
11
Heterogeneous catalyst has been utilized, such as alumina, potassium fluoride doped Al O
2
3
1
2
13
14
and phosphates, silica supported manganese oxides, modified hydroxyapatite, and
1
5
ruthenium hydroxide coated on alumina and ferrites. However, turnover numbers of these
protocols are still low and the reusability of the catalyst is difficult. Cadierno and coworkers
developed an excellent hydration protocol in pure water under neutral conditions. Although this
work paved the way for the advancement of the hydration reaction in aqueous medium, the
protocol still needs traditional workup, using organic solvents to isolate the product and exotic
ruthenium complexes as catalysts. The magnetically supported ruthenium catalyst works well for
the aqueous hydration of nitriles. However, they involve tedious synthesis of magnetic support
following by immobilization of ruthenium metal. In our quest for the development of benign and
sustainable pathways for organic synthesis, herein, we report the utility of heterogeneous,
biodegradable, and reusable chitosan-Ru (ChRu) catalyst for the aqueous hydration of nitrile to
amides.
16
1
7
1
8
Result and discussion
The first step in the accomplishment of this goal was the immobilization of ruthenium (Ru) over
chitosan (Scheme 1). The catalyst was prepared by suspending chitosan in the aqueous mixture
of ruthenium chloride overnight at pH, 9 (adjusted using 25% of ammonia). Material with Ru on
o
chitosan was separated using a centrifuge, dried under vacuum at 50 C for 12 hours and the
ensuing catalyst characterized by SEM (Fig.1 a) and using X-ray diffraction (XRD) (Fig 1b); the
signals pertaining to Ru metal were not detected in XRD, possibly due to complexation with
chitosan or its low percentage. However, the presence of Ru-metal has been confirmed by
Energy Dispersive X-ray Spectroscopy (EDS, Figure 2). XPS analysis of ChRu is performed to
analyze the oxidation state of Ru metal.; the binding energy peak for Ru 3d5/2 at 282.5 eV is in
good accordances with Ru(III) ( XPS, Figure 3). The weight percentage of Ru was found to be
6.41 % by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis.
OH
OH
O
O
OH
O
OH
O
O
OH
HO
HO
O
O
HO
O
O
RuCl
3
NH2
O
HO
H N
2
O
O
HO
Ru
NH2
water, NH
3
NH2
NH2
over night
OH
HO
O
O
O
HO
O
O
HO
NH2
NH2
Scheme 1 Synthesis of Chitosan-Ru (ChRu) catalyst
2

Page 3 of 10
Green Chemistry
View Article Online
DOI: 10.1039/C3GC42004C
3

Green Chemistry
Page 4 of 10
View Article Online
DOI: 10.1039/C3GC42004C
The utility of chitosan supported ruthenium catalyst (ChRu) was then explored in a
heterogeneous catalyzed hydration of nitriles in benign aqueous medium under microwave
(MW) irradiation conditions (Scheme 2). The salient feature of MW-assisted heating is due to
the efficiency of the interaction of polar ChRu-catalysts as well as water molecules with
microwaves; the reaction mixture is rapidly heated under MW irradiation with the precise control
1
9
of the reaction temperature. Initially, experiments were performed to optimize the aqueous
reaction conditions for the hydration of 4-pyridinecarbonitrile as a substrate (Table 1).
O
CN
ChRu/H O
2
NH2
N
o
N
MW, 60 min, 100 C
Scheme 2 ChRu-catalyzed hydration of nitriles
Table 1 Optimization of reaction conditionsa
Yieldb
o
Entry
Catalyst
Time
Temperature ( C)
1
2
3
4
Chitosan
Chitosan
Chitosan
ChRu
30 min
60 min
60 min
25 min
100
100
120
100
-
-
-
<30%
5
6
7
ChRu
ChRu
ChRu
60 min
12 h
120
100
120
>99%
tracec
>
74.4%d
3 h
a) Reactions were carried out with 1 mmol of4-pyridinecarbonitrile, 25 mg ChRu-catalyst, in water
under MW irradiation; b) Reaction was monitored by GCMS; c) Reaction perf ormed under
conventional heating; d) ChRu catalyst with 3.98% Ru loading was used.
First, the reaction was conducted using pure chitosan The hydration reaction did not proceed at
.
o
o
1
00 C or at 120 C even after 60 min of MW exposure (Table 1, entries 1-3). The chitosan was
modified using RuCl , termed chitosan ruthenium-catalyst ChRu (Scheme 1), and tested for the
3
o
hydration of 4-pyridinecarbonitrile with ChRu at 100 C for 25 min under MW irradiation. The
low conversion of nitrile to amide (monitored by GC-MS) was observed (Table 1, entry 4).
o
However, MW exposure for 60 min at 120 C leads to the quantitative conversion to the
corresponding amide (Table 1, entry 5). However, refluxing the reaction mixture for 12 h under
conventional heating resulted in the trace amount of conversion (Table 1 entry 6). Lowering the
catalytic loading of Ru metal reduced its catalytic performance. Oxidation of 4-
pyridinecarbonitrile to corresponding amide, using 3.98% of ChRu catalyst, did not complete
even after 3 h of MW (Table 1, entry 7).
4

Page 5 of 10
Green Chemistry
View Article Online
DOI: 10.1039/C3GC42004C
Table 2 Hydration of nitriles catalyzed by ChRu-catalysta
Conversionb, c
Entry
Substrate
Time
Product
O
CN
1
60 min
>99% (89%)
NH
2
O
O
CN
2
3
4
60 min
60 min
60 min
>99% (91%)
>99% (88%)
>99%( 88%)
NH2
NH2
N
N
CN
N
N
O
CN
N
NH2
NH2
N
O
CN
5
6
75 min
75 min
>99% (85%)
>99% (84%)
N
N
O
O
O
CN
CN
CN
NH
2
MeO
MeO
7
8
60 min
60 min
NH2
NH2
>99% (85%)
>99% (90%)
O N
2
O N
2
OHC
NC
OHC
O
O
CN
CN
NH2
9
60 min
90 min
NH2
+
H N
2
NC
>
93%
O
<7%
NH
2
1
0
>99% (81%)
O
a) Reactions were carried out with 1 mmol of nitrile, 25 mg (0.015 mol %) nanocatalyst,
in water under MW irradiation; b) Reactions were monitored by GCMS; c) Yield in
parentheses represents the isolated yield.
5

Green Chemistry
Page 6 of 10
View Article Online
DOI: 10.1039/C3GC42004C
Using the above-optimized conditions, the scope of chitosan ruthenium-catalyst ChRu was then
explored for the hydration of a variety of nitriles (Table 2). The catalyst displayed high activity
for hydration of activated, inactivated, aliphatic, and heterocyclic nitriles in pure water including
a variety of benzonitriles derivatives (Table 2, entries 1 & 9) as well as aliphatic nitriles (Table 2,
entries 10) that were smoothly hydrated to the corresponding amides in excellent yield. The rates
were slightly influenced by the electronic effects of the substituent’s on the aromatic ring of the
benzonitriles. Electron donating substituent (Me N-, -OMe, Table 2, entry 5 and 6) required little
2
longer time (75 min) for the completion of reaction whereas in case of electron withdrawing
substituent (-NO , -CN, -CHO, Table 2, entry 7-9) full conversion was observed within 60 min
2
of MW exposure. It was interesting to observe that the selective oxidation of 4-
formylbenzonitrile to corresponding amide could be performed without oxidation of the formyl
group (Table 2, entry 8). The hydration of 1,4 dicyano benzene was time dependent (Table 2
o
entry 9); 60 min exposure to MW at 120 C leads to the selective formation of the monohydrated
derivative (93%, Table 2 entry 9) whereas exposure for longer time (3 h) resulted in the
dihydration of 1,4 dicyano benzene to terephthalamide in quantitative yield.
The separation and recovery of the catalyst is an important step in the synthesis of fine
chemicals, which is generally performed either by centrifuge or by filtration with reduced
efficiency. In this catalytic system, most of the time catalyst was recovered by simply
decantation or centrifuge. Upon completion of the reaction, the mixture turned clear and the
catalyst deposited at the bottom, which can be easily separated from reaction mixture by simple
decantation or using a centrifuge. After the removal of the catalyst, pure crystals of amides
usually appeared in the aqueous layer, which are isolated from the water medium. Thus,
synthesis and purification can be carried out in a benign aqueous medium, without the use of
organic solvents.
The lifetime of the catalyst and its level of reusability are important considerations for practical
application. To clarify this issue, a set of experiments for the hydration of 4-pyridinecarbonitrile
using the ChRu-catalyst were established. After the completion of the first reaction to afford the
o
corresponding amide, the catalyst was recovered, washed with acetone, and dried at 50 C. A
new reaction was then performed with fresh 4-pyridinecarbonitrile under the same conditions.
The chitosan supported ruthenium catalyst ChRu could be used at least three times without any
change in the activity (ESI, Table 1).
Metal leaching was studied by ICP-AES analysis of the catalyst before and after the three
reactions. The Ru concentration was found to be 6.41% before the reaction and 6.36 % after the
reaction. The TEM image of the catalyst taken after the third cycle of the reaction did not show
significant change in the morphology of the catalyst (ESI, Fig. 1 and EDS Fig 2), which indicates
the retention of the catalytic activity after recycling. No Ru metal was detected in the reaction
solvent (water) after completion of the reaction. This confirms the fact the chitosan held the Ru
metal very tightly thus retaining the integrity of the catalyst, minimizing metal leaching, and
facilitating efficient catalyst recycling.
6

Page 7 of 10
Green Chemistry
View Article Online
DOI: 10.1039/C3GC42004C
Conclusion
We have developed a novel biopolymer chitosan supported ruthenium catalyst, which can be
readily prepared in large scale at ambient condition in aqueous media. The chitosan-ruthenium
catalyst catalyzed the hydration of nitriles with high yield and excellent selectivity, which
proceeds exclusively in aqueous medium under neutral conditions. After the completion of the
reaction, the catalyst could be recovered and reused without affecting the reactivity.
Experimental Section:
Experimental procedure for synthesis of chitosan ruthenium catalyst (ChRu):
Chitosan (3 g, medium molecular weight, Aldrich, CSA # 9012-76-4) was suspended in 100 mL
of water. To this suspension, 500 mg of RuCl 3H O was added, pH, 9 was adjusted using 25%
3
.
2
ammonia and stirring was continued overnight. The catalyst was separated using centrifuge
o
(
5000 rpm 5 min), dried under vacuum at 50 C. The catalyst was characterized by SEM (Fig.1 a,
MS) and using X-ray diffraction (XRD) (Fig 1b, MS). The signals pertaining to ruthenium metal
were not detected in XRD; it may be due to complexation with chitosan or low percentage. The
weight percentage of ruthenium was found to be 6.41 % by inductively coupled plasma-atomic
emission spectroscopy (ICP-AES) analysis.
Hydration of nitriles to amides
Nitriles (1.0 mmol), and ChRu (25 mg, 0.015, mol %) were placed in a crimp-sealed thick-
walled glass tube equipped with a pressure sensor and a magnetic stirrer. Water (5 mL) was
added to the reaction mixture. The reaction tube was placed inside the cavity of a CEM Discover
o
focused microwave synthesis system, operated at 120 C (temperature monitored by a built-in
infrared sensor), 100 Watts for 60 min-90 min. After completion of the reaction, the catalyst was
removed from reaction mixture using a centrifuge. Hydration of nitriles has been monitored
using GCMS. The clear liquid was cooled slowly; most of the time analytically pure crystals of
corresponding amide were obtained which can be isolated from water medium by simple
decantation.
References
1
. a) C. J. Li and P. T. Anastas, Chem. Soc. Rev., 2012, 41, 1413; b) R. B. Nasir Baig and
R. S. Varma, Chem. Commun., 2013, 49, 752; c) P. V. D. Voort, D. Esquivel, E. D.
Canck, F. Goethals, I. V. Driessche and F. J. Romero-Salguero, Chem. Soc. Rev.
013, 42, 3913; d) C. Perego and R. Millini, Chem. Soc. Rev., 2013, 42, 3956.
,
2
2
. a) U. Diaz, D. Brunel and A. Corma, Chem. Soc. Rev., 2013, 42, 4083; b) E. L.
Margelefsky, R. K. Zeidan and M. E. Davis, Chem. Soc. Rev., 2008, 37, 1118.
7

Green Chemistry
Page 8 of 10
View Article Online
DOI: 10.1039/C3GC42004C
3
4
. a) T. V. Khamatnurova and D. E. Bergbreiter, Polym. Chem., 2013, 4, 1617; b) S. Iimura,
D. Nobutou, K. Manabe and S. Kobayashi, Chem. Commun., 2003, 1644.
. a) B. R. Vaddula, A. Saha, R. S. Varma, and John Leazer, Eur. J. Org. Chem. 2012,
6
707; b) M. Chtchigrovsky, A. Primo, P. Gonzalez, K. Molvinger, M. Robitzer, F.
Quignard and F. Taran, Angew. Chem. Int. Ed., 2009, 48, 5916; c) D. J. Macquarrie and
A. Bacheva, Green Chem., 2008, 10, 692; d) M. Bradshaw, J. Zou, L. Byrne, K. S. Iyer,
S. G. Stewartc and C. L. Raston, Chem. Commun., 2011, 47, 12292; e) B. C. E.
Makhubela, A. Jardine and G. S. Smith, Green Chem., 2012, 14, 338; f) D. Kuhbeck, G.
Saidulu, K. R. Reddy and D. Dıaz, Green Chem., 2012, 14, 378.
5
. a) J. Sun, S. Rao, Y. Su, R. Xu and Y. Yang, Colloids. Surf., A, 2011, 389, 97; b) S.
Kadouche, H. Lounici, K. Benaoumeur, N. Drouiche, M. Hadioui and P. Sharrock, J.
Polym. Environ., 2012, 20, 848; b) K. Kondo, Y. Ohigashi and M. Matsumoto, J. Mater.
Sci. Eng. A., 2012, 2, 584; c) A. Moyna, D. Connolly, E. Nesterenko, P. N. Nesterenko
and B. Paull, J. Chromatogr., A, 2012, 1249, 155; d) V. S. Nagpurkar, L. Deshmukh and
L. J. Paliwal, Chem. Sin., 2012, 3, 824; e) B. Zornoza, C. Tellez, J. Coronas, J. Gascon
and F. Kapteijn, Microporous Mesoporous Mater., 2013, 166, 67; f) R. Ramya and P. N.
Sudha, Polym. Compos., 2013, 34, 233; g) S. J. Wu, T. H. Liou, C. H. Yeh, F. L. Mi and
T. K. Lin, J. Appl. Polym. Sci., 2013, 127, 4573.
6
7
. a) C. E. Mabermann, in Encyclopedia of Chemical Technology, Vol. 1 (Ed.: J. I.
Kroschwitz,), Wiley, New York, 1991, p. 251; b) The Chemistry of Amides (Ed.: J.
Zabicky), Wiley-Interscience, New York, 1970.
. R. Opsahl, in Encyclopedia of Chemical Technology, Vol. 2 (Ed.: Kroschwitz, J. I.),
Wiley, New York, 1991, p. 346.
8
9
. P. K. Mascharak, Coord. Chem. Rev., 2002, 225, 201.
. a) J. H. Kim, J. Britten and J. Chin, J. Am. Chem. Soc., 1993, 115, 3618; b) R. Breslow,
R. Fairweather and J. Keana, J. Am. Chem. Soc., 1967, 89, 2135; c) K. L. Breno, M. D.
Pluth and D. R. Tyler, Organometallics., 2003, 22, 1203; d) S. I. Murahashi, S. Sasao, E.
Saito and T. Naota, J. Org. Chem., 1992, 57, 2521; e) M. C. K. B. Dojoman and A. N.
Ajjou, Tetrahedron Lett., 2000, 41, 4845; f) G. Villain, A. Gasket and P. H. Kalck, J.
Mol. Catal., 1981, 12, 103; g) N. V. Kaminskaia and N. M. Kostic, J. Chem. Soc. Dalton
Trans., 1996, 3677; h) T. Ghaffar and A.W. Parkins, Tetrahedron Lett., 1995, 36, 8657; i)
T. Ghaffar and A.W. Parkins, J. Mol. Catal., A 2000, 160, 249. j) N. A. Bokach and V. Y.
Kukushkin, Russ. Chem. Rev., 2005, 74, 153; k) V. Y. Kukushkin and A. J. L. Pombeiro,
Chem. Rev., 2002, 102, 1771.
1
0. C. P. Wilgus, S. Downing, E. Molitor, S. Bains, R. M. Pagni and G. W. Kabalka,
Tetrahedron Lett., 1995, 36, 3469.
1
1
1
1. C. G. Rao, Synth. Commun., 1982, 12, 177.
2. S. Sebti, A. Rhiil, A. Saber and N. Hanafi, Tetrahedron Lett., 1996, 37, 6555.
3. K. T. Li, M. H. Shih, H. W. Huang and C. J. Hu, Synthesis., 1988, 715.
8

Page 9 of 10
Green Chemistry
View Article Online
DOI: 10.1039/C3GC42004C
1
1
4. a) F. Bazi, H. El Badaoui, S. Tamani, S. Sokori, A. Solhy, D. J. Macquarrie and S. Sebti,
App. Cat., A 2006, 311, 211; b) K. Mori, K. Yamaguchi, T. Mizugaki, K. Ebitani and K.
Kaneda, Chem. Commun., 2001, 461.
5. a) K. Yamaguchi, M. Matsushita and N. Mizuno, Angew. Chem., 2004, 116, 1602; b) M.
Kotani, T. Koike, K. Yamaguchi and N. Mizuno, Green Chem., 2006, 8, 735.
6. V. Cadierno, J. Francos and J. Gimeno, Chem. Eur. J., 2008, 14, 6601.
7. a) V. Polshettiwar and R. S. Varma, Chem. Eur. J., 2009, 15, 1582; b) R. B. Nasir Baig
and R. S. Varma, Chem. Commun., 2012, 48, 6220.
1
1
1
1
8. a) R. B. Nasir Baig and R. S. Varma, Chem. Commun., 2013, 49, 752; b) R. B. Nasir
Baig and R. S. Varma, Green Chem., 2012, 14, 625; c) R. B. Nasir Baig and R. S.
Varma, Green Chem., 2013, 15, 1839; d) R. B. Nasir Baig and R. S. Varma, Green
Chem., 2013, 15, 398; e) R. B. Nasir Baig and R. S. Varma, Chem. Commun., 2012, 48,
5
4
853; f) A. Saha, R. B. Nasir Baig, J. Leazer and R. S. Varma, Chem. Commun., 2012,
8, 8889.
9. R. B. Nasir Baig and R. S. Varma, Chem. Soc. Rev., 2012, 41, 1559.
9

Green Chemistry
Page 10 of 10
View Article Online
DOI: 10.1039/C3GC42004C
Ruthenium on chitosan: A recyclable heterogeneous catalyst for aqueous
hydration of nitriles to amides
R. B. Nasir Baig, Mallikarjuna N. Nadagouda and Rajender S. Varma*
Sustainable Technology Division, National Risk Management Research Laboratory, U. S.
Environmental Protection Agency, MS 443, Cincinnati, Ohio 45268, USA. Fax: 513- 569-7677;
Tel: 513-487-2701. E-mail: varma.rajender@.epa.gov
Ruthenium has been immobilized over chitosan by simply stirring an aqueous suspension of
chitosan in water with ruthenium chloride and utilized for the oxidation of nitriles to amides; the
hydration of nitriles occurs in high yield and excellent selectivity which proceeds exclusively in
aqueous medium under neutral conditions.
OH
OH
O
O
O
HO
O
O
O
HO
CN
H N
NH2
ChRu
2
NH2
R
R
Ru
o
H O, MW, 120 C
2
OH
HO
O
O
R = H, OMe, NMe , NO , CHO, etc
O
HO
2
2
O
O
HO
NH2
NH2
Chitosan-Ru (ChRu) catalyst