Silica supported ferric nitrate nonahydrate: Selective oxidation of benzoins under mild conditions

Article abstract of DOI:10.1081/SCC-120021976

Benzils are selectively obtained in high yields by the oxidation of benzoins under mild reaction conditions using silica supported ferric nitrate nonahydrate.

Full text of DOI:10.1081/SCC-120021976

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Silica Supported Ferric Nitrate Nonahydrate: Selective
Oxidation of Benzoins Under Mild Conditions
Aniruddha M. Paul a , Amit C. Khandekar a & M. A. Shenoy a
a Applied Chemistry Division , Institute of Chemical Technology , University of Mumbai ,
Matunga, Mumbai, India
Published online: 17 Aug 2006.
To cite this article: Aniruddha M. Paul , Amit C. Khandekar & M. A. Shenoy (2003) Silica Supported Ferric Nitrate
Nonahydrate: Selective Oxidation of Benzoins Under Mild Conditions, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 33:15, 2581-2584, DOI: 10.1081/SCC-120021976
To link to this article: http://dx.doi.org/10.1081/SCC-120021976
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 15, pp. 2581–2584, 2003
Silica Supported Ferric Nitrate Nonahydrate:
Selective Oxidation of Benzoins
Under Mild Conditions
*
Aniruddha M. Paul,Amit C. Khandekar,and M. A. Shenoy
Applied Chemistry Division, Institute of Chemical
Technology, University of Mumbai,
Matunga, Mumbai, India
ABSTRACT
Benzils are selectively obtained in high yields by the oxidation of
benzoins under mild reaction conditions using silica supported
ferric nitrate nonahydrate.
Key Words: Benzoins; Silfen; Oxidation; Benzils.
*Correspondence: M. A. Shenoy, Applied Chemistry Division, Institute of
Chemical Technology, University of Mumbai, Nathalal Parikh Marg.,
Matunga, Mumbai 400 019, India; Fax: 91-22-4145619; E-mail: amp_bmk@
yahoo.co.in.
2581
DOI: 10.1081/SCC-120021976
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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2582
Paul,Khandekar,and Shenoy
Table 1. Optimization of molar ratio of ferric nitrate to
benzoin (R1 ¼ C6H5, R2 ¼ C6H5).
Molar ratio
Fe(NO3)3ꢀ9H2O:benzoin
Reaction time
(h)
Yielda
(%)
1:7
1:6
1:5
1:4
1:3
1:2
1:1
5
5
5
5
3
3
3
72
79
83
89
93
95
94
aRefers to pure isolated products.
The synthetic utility of supported reagents for a wide range of
organic reactions has been explored earlier in our laboratory.[1] In con-
tinuation of our progressive investigation on supported reagents, we now
report the selective oxidation of various symmetrical and unsymmetrical
benzoins to the corresponding benzils using silica supported ferric nitrate
nonahydrate (silfen). The reagent, silfen was prepared by simply cogrind-
ing silica gel (230–400 mesh) with ferric nitrate nonahydrate in the ratio
4:1 (w/w) in an agate mortar and used without prior activation.
For the purpose of optimization of molar ratio of ferric nitrate non-
ahydrate to benzoin, we carried out the reaction by varying the molar
ratio from1:1 to 1:7. The optimumratio was found to be 1:3. Even for
the molar ratio of 1:7, a moderate yield of 72% was obtained (Table 1). It
should be noted that the quantity of ferric nitrate nonahydrate required
in this method is much less as compared to the reported methods, e.g., the
ratio is found to be 1:2 in case of clayfen[2] and 2.5:1 in case of ferric
nitrate nonahydrate[3] for the same reaction.
In conclusion, the decrease in the amount of ferric nitrate nonahydrate
results in considerable reduction of NOx evolution along with improved
safety and handling. In addition to this, our reagent is cheap and easy to
prepare, even in large scale using a jar mill or a ball mill. Our method,
therefore, offers a clear advantage over the earlier reported methods.
EXPERIMENTAL
The starting benzoins were prepared as per the reported proce-
dures.[4,5] Melting points are uncorrected and taken in open capillaries

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Ferric Nitrate Nonahydrate
2583
OH
O
Silfen
R
R
2
2
R
R
1
EDC reflux
1
O
O
Scheme 1.
Table 2. Oxidation of benzoins using silica supported ferric nitrate nonahydrate.
M.p.
found
(ꢁC)
M.p.
reported
(ꢁC)
Time Yielda
Entry no.
R1
R2
(h)
(%)
1
2
3
4
5
6
7
8
9
Ph
p-MeC6H4
C6H5
Ph
3
3
3
3
3
3
3
3
4
93
95
93
93
92
92
82
96
92
94–95 93
98–100 102–103
p-MeC6H4
p-ClC6H4
C6H5
76–77
76–77
87–88
86–88
60–61
73
73
p-ClC6H4
p-BrC6H4
C6H5
C6H5
p-BrC6H4
88–89
88–89
61–62
p-MeOC6H4 C6H5
o-ClC6H4 p-MeOC6H4
p-MeOC6H4 p-MeOC6H4
105–106 103–104
128–130 131–132
aRefers to pure isolated products.
The products obtained showed satisfactory physical and spectral data.
on an Oswal precision melting point apparatus. Infrared spectra was
recorded as KBr pellets on a Jasco FTIR 410 E spectrophotometer,
1H NMR spectra was recorded at 500 MHz using CDC13/TMS on a
Bruker X-500 spectrometer.
General Procedure for Oxidation of Benzoins
Benzoin (5 mmo1) and SiO2-Fe(NO3)3ꢀ9H2O (3.4 g, 1.7 mmo1) are
added to ethylene dichloride (20 mL) and the mixture is refluxed for 3
to 4 h (Sch. 1). The completion of reaction was monitored by TLC
(hexane–ethyl acetate, 9:1). The product is isolated by desorption with
hot ethylene dichloride. The excess solvent is removed by distillation. The
product is dissolved in minimum amount of ether and passed through a
short silica column for purification. The products (Table 2) were
1
characterized by their melting points,[4,6] IR and H NMR.

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2584
Paul,Khandekar,and Shenoy
ACKNOWLEDGMENT
The authors are thankful to AICTE, New Delhi and BRNS for
financial assistance. Thanks are also due to Prof. S. D. Samant and
late Dr. B. M. Khadilkar for their valuable suggestions.
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Received in the Netherlands November 11, 2002