Oxidation of urazoles to their corresponding triazolinediones under mild and heterogeneous conditions via in situ generation of NO+IOx-

Article abstract of DOI:10.1081/SCC-100104412

A combination of periodic or iodic acids and sodium nitrite in the presence of wet SiO₂ was used as an effective oxidizing agent for the oxidation of urazoles and bis-urazoles to their corresponding triazolinediones under mild and heterogeneous conditions with good yields.

Full text of DOI:10.1081/SCC-100104412

SYNTHETIC COMMUNICATIONS, 31(13), 1965–1970 (2001)
OXIDATION OF URAZOLES TO THEIR
CORRESPONDING TRIAZOLINEDIONES
UNDER MILD AND HETEROGENEOUS
CONDITIONS VIA IN SITU GENERATION
1
2
OF NO IOX
1
,
1
Mohammad Ali Zolfigol, * Gholamabbas Chehardoli,
2
Farhad Shirini, Shadpour E. Mallakpour,
3
3
and Hossein Nasr-Isfahani
1
Chemistry Department, College of Science,
Bu-Ali Sina University, Hamadan 65174, Iran
2
Chemistry Department, College of Science,
Gilan University, Rasht, I.R. Iran
3
Organic Polymer Chemistry Research Laboratory,
College of Chemistry, Isfahan University of Technology,
Isfahan, 84156, I.R., Iran
ABSTRACT
A combination of periodic or iodic acids and sodium nitrite in
the presence of wet SiO was used as an effective oxidizing
2
agent for the oxidation of urazoles and bis-urazoles to their
corresponding triazolinediones under mild and heterogeneous
conditions with good yields.
*
Corresponding author. E-mail: Zolfi@basu.ac.ir
1
965
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

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966
ZOLFIGOL ET AL.
4-Substituted-1,2,4-triazole-3,5-diones (TADs) are notable for their
ability to participate in a wide range of concerted and stepwise condi-
1
tions. Considerable attention has been paid to their additions to activated
–7
1
–4
5
alkenes, electrophilic aromatic substitution, dehydrogenating properties
6
7
and oxidation of alcohols to aldehyde and ketones. The unusual reactivity
which makes 1,2,4-triazoline-3,5-diones (2,4) of interest also makes them
hard to prepare and purify.
Although a wide variety of reagents are capable of effecting these
8
–13
oxidations,
this transformation remains capricious because these com-
pounds are very sensitive to the oxidizing agents and reaction conditions.
However, most of the reported reagents produce by-products which either
destroy, or are difficult to remove from, the sensitive triazolinediones.
Another major drawback to the older procedures is their use of reagents
which are either highly toxic or produce serious disposal problems (or
8
both). Very recently, we among many others have demonstrated that
heterogeneous reagent systems have many advantages such as simple experi-
mental procedures, mild reaction conditions and minimization of chemical
1
4
wastes as compared to the liquid phase counterparts. Therefore, we
decided to apply a completely heterogeneous system and we have investi-
gated a number of different reaction conditions based upon the in situ gene-
þ
À
ration of NO IOx (X ¼ 3 and 4 as an efficient heterogeneous oxidizing
agents) by the strongly acidic solid inorganic acid HIO (its hydrated form
4
e.g. H IO ) and its milder analogue HIO ( K ꢀ 1) and sodium nitrite for
5
6
3
p
a
the oxidation of urazoles. We wish to report a simple, cheap and convenient
method for the effective oxidation of urazoles and bis-urazoles to their
corresponding triazolinediones (2,4) under mild and heterogeneous condi-
tions (Schemes 1 and 2).
Different types of urazoles (1) and bis-urazoles (3) were subjected to
the oxidation reaction in the presence of H IO (I) or HIO (II), NaNO
2
5
6
3
(
III) and wet SiO (50% w/w) in dichloromethane (Schemes 1 and 2).
2
The oxidation reactions were performed under mild and completely hetero-
geneous conditions at room temperature and take place with good yields
(
Table).
This oxidation reaction can be readily carried out only by placing solid
acid (I or II), NaNO (III), urazole (1) or bis-urazole (3), wet SiO (50%
2
2
w/w) and CH Cl as the inert solvent in a reaction vessel and efficiently
2
2
stirring the resulting heterogeneous mixture at room temperature. The tria-
zolinediones (2 and 4) can be obtained simply by filtration and evaporation
of the solvent. The results and reaction conditions are given in the Table.
As mentioned above the oxidation reactions are heterogeneous
because urazoles and bis-urazoles [(1 and 3) white solids] are insoluble in
dichloromethane whereas all of the triazolinediones and bis-triazolinediones

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OXIDATION OF URAZOLES
1967
Scheme 1.
Scheme 2.
[(2 and 4), red and pink respectively] are very soluble in dichloromethane.
Therefore, the oxidation reaction has been performed at the surface of
þ
À
4
wet SiO via in situ generation of NO IO in a small amount. Later on,
2
the oxidation products (2 and 4) migrate to the liquid phase (CH Cl )
2
2
immediately.
The H IO /NaNO system is superior and also more reactive than its
milder analogue e.g. HIO /NaNO and does not affect amide unites in the
5
6
2
3
2
substrate.

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ZOLFIGOL ET AL.
Table 1. Oxidation of Urazoles (1) and bis-Urazoles (3) to Their Corresponding
Triazolinediones (2, 4) with a Combination of H IO (I) or HIO (II), NaNO (III)
5
6
3
2
and Wet SiO (50% w/w) in Dichloromethane at Room Temperature
2
(
Reagent/Substrate)
c
Urazole
or (bis)
Time
(h)
Yield
(%)
a
Product
I
II
III
8
d
d
d
d
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
3
3
3
3
a
a
b2b
b2b
c
2a
3
–
3
–
4
–
3
–
3
–
3
–
3
–
3
–
6
–
8
–
–
3
–
3
–
4
–
3
–
3
–
3
–
3
–
3
–
6
–
8
3.51 .15 00
3.52
3.51 .15 00
3.52
3.52
3.52
3.51.586
3.52
3.51.590
3.52
3.51
3.51.586
3.51
3.52
3.51.580
3.52
8
2a
100
1
2
2
1
100
80
89
1
1
1
1
2c
2c
2d
2d
c
d
1
1
1
1
d
e
e
82
8
2e
2e
8
80
80
8
8
1
f
f
g
2f
2f
3
3
2g
2g
2h
2h
4a
4a
96
98
1
8
8
5
5
5
5
g
h
h
a
80
7
7
9
9
3
4
4
6
86
83
87
77
a
b4b
b4b
a
All of the isolated products are known and their spectra and physical data have
b
2
been reported in the literature. Wet SiO : substrate (mono) (0.4 g : 1 mmol) and wet
c
SiO : substrate (bis) (1.6 g : 1 mmol). Isolated yields. Conversion.
d
2
In conclusion, practical and efficient oxidation of urazoles and bis-
urazoles have been achieved by the methodology described. The hetero-
geneous nature, cheapness and availability of the reagents, easy procedure
and work-up make this method attractive for large-scale operations. We
believe that the present methodology would be an important addition to
existing methodologies.
EXPERIMENTAL
General: Chemicals were purchased from Fluka, Merck, Riedel-
dehaen AG and Aldrich chemical companies. The oxidation products were
1
characterized by comparison of their spectral (IR, UV, H-NMR, and

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OXIDATION OF URAZOLES
1969
1
3
C-NMR) and physical data with the authentic samples. All urazoles
and bis-urazoles were synthesized according to our previously reported
1
,4,5,10,11
procedures.
Oxidation of 4-Phenyl Urazole (1g) to 4-Phenyl-1,2,4-triazoline-
,5-dione (2g). A Typical Procedure
3
A suspension of compound 1g (0.423 g, 2 mmol), H IO (1.362 g,
5
6
6
mmol), wet SiO2 (50% w/w) (0.8 g) and NaNO2 (0.483 g, 7 mmol) in
dichloromethane (12 ml) was stirred at room temperature for one hour and
then filtered. Anhydrous Na SO (5g) was added to the filtrate. After 20
minutes, the resulting mixture was filtered. Dichloromethane was removed
2
4
ꢁ
15
by water bath (40–50 C) and simple distillation. The yield was 0.400 g
1
0
(
96%) of crystalline red solid (2g), mp 142–145.
0
0
Oxidation of 4,4 -(4,4 -Diphenylmethylene)-bis-urazole (3b) to
Bis(p-3,5-Dioxo-1,2,4-triazoline-4-ylphenyl)methane (4b).
A Typical Procedure
A mixture of 3b (0.366 g, 1 mmol), H IO (1.816 g, 8 mmol), wet
5
6
SiO (50% w/w) (1.6 g) was crushed to a fine powder with a mortar and pestle.
2
The resulting mixture was added to the dichloromethane (60 ml) and the
suspension was vigorously stirred. NaNO (0.621 g, 9 mmol) was also added
2
in four portions (each addition after 30 minutes) to the reaction mixture.
After the final addition the red suspension was allowed to stir for another
120 minutes and was filtered. The filtrate was dried over anhydrous Na SO4
2
(
distillation. The yield was 0.314 g (87%) of crystalline pink solid (4b) mp.
10 g) and was filtered again. Dichloromethane was removed by simple
ꢁ
82–185 C (dec.).
5
1
ACKNOWLEDGMENT
Financial support for this work by the research affair of Bu-Ali Sina
University, Hamadan, Iran, is gratefully acknowledged.
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1
transition metals and any nucleophiles. Also they are very volatile so
ꢁ
that, if temperature rises over than 50 C in the course of removing of
CH Cl , some of TADs are removed with solvent simultaneously.
2
2
Therefore, the temperature must be controlled and dichloromethane
is the best solvent for this purpose.
Received in the UK April 10, 2000

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