An efficient method for the oxidation of urazoles with [NO+·crown· H(NO3)2-]

Article abstract of DOI:10.1016/S0040-4020(00)01150-9

An ionic complex has been obtained from N₂O₄ in the presence of the macrocyclic polyether 18-crown-6. This crystalline compound was used as an effective oxidizing agent for the oxidation of urazoles to their corresponding triazolinediones at room temperature with excellent yields.

Full text of DOI:10.1016/S0040-4020(00)01150-9

TETRAHEDRON
Pergamon
Tetrahedron 57 (2001) 1627±1629
An ef®cient method for the oxidation of urazoles with
[
1
2
NO ´crown´H(NO ) ]
3 2
a,p
Mohammad Ali Zol®gol, Mohammad Hassan Zebarjadian, Gholamabbas Chehardoli,
a
a
b
Shadpour E. Mallakpour and Mojtaba Shamsipur
c
a
Department of Chemistry, College of Science, Bu-Ali Sina University, P.O. Box 4135, Hamadan 65174, Iran
Organic Polymer Chemistry Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, Iran
b
c
Department of Chemistry, College of Science, Razi University, Kermanshah, Iran
Received 5 September 2000; revised 20 November 2000; accepted 7 December 2000
AbstractÐAn ionic complex has been obtained from N O in the presence of the macrocyclic polyether 18-crown-6. This crystalline
2
4
compound was used as an effective oxidizing agent for the oxidation of urazoles to their corresponding triazolinediones at room temperature
with excellent yields. q 2001 Elsevier Science Ltd. All rights reserved.
1
macrocyclic ethers, we found that 18-crown-6 gives an
ionic complex [NO ´crown´H(NO ) ] in quantitative
3 2
4
4
-Substituted-1,2,4-triazole-3,5-diones (TADs) are notable
1
2
for their ability to participate in a wide range of concerted
and stepwise reactions.1±7 Considerable attention has been
paid to their additions to activated alkenes, electrophilic
aromatic substitution, dehydrogenating properties6 and
oxidation of alcohols to aldehydes and ketones. The
yields with N O gas. By using this new reagent, we report
2
4
1
±4
in this article a simple and convenient method for the effec-
tive conversion of urazoles (1 and 3) to their corresponding
triazolinediones (2 or 4) under mild and heterogeneous
conditions.
5
7
unusual reactivity which makes TADs (2, 4) of interest
also makes them hard to prepare and purify.
Different types of urazoles (1 and 3) were subjected to oxi-
1
2
Although a variety of reagents are capable of effecting these
this transformation is not easy because these
dation reaction in the presence of [NO ´crown´H(NO ) ] in
3 2
8
±11
oxidations,
compounds are very sensitive to the oxidizing agents and
reaction conditions.
dichloromethane (Schemes 1 and 2). The oxidation reac-
tions were performed under mild and completely hetero-
geneous conditions at room temperature with quantitative
yields. As mentioned above, the oxidation reactions are
heterogeneous because urazoles and bis-urazoles [(1, 3)
white solids] are insoluble in dichloromethane whereas,
all the triazolinediones and bis-triazolinediones [(2, 4) red
and pink, respectively] are very soluble in dichloromethane.
As might be expected, the oxidation products (2, 4) migrate
to the liquid phase (CH Cl ) immediately after oxidation.
However, most of the reported reagents produce by-
products which either destroy, or are dif®cult to remove
from, the sensitive triazolinedione. Another major drawback
to the older procedures is their use of reagents which are
either highly toxic or impart serious disposal problems (or
8
both). Very recently we, among many others, have demon-
2
2
strated that heterogeneous reagent systems have many
advantages such as simple experimental procedures, mild
reaction conditions and the minimization of chemical
This oxidation reaction can be readily carried out only by
placing [NO ´crown´H(NO ) ], 1 or 3, SiO (for the
adsorption of HNO and H O) with dichloromethane as
3 2
1
2
3
2
2
1
2
wastes as compared to their liquid phase counterparts.
We were interested in ®nding a new form of heterogeneous
system for urazole oxidation and thus, we have investigated
a number of different reaction conditions based upon the in
solvent in a reaction vessel, and ef®ciently stirring the
resulting heterogeneous mixture at room temperature. The
reactions were completed immediately. The solvent was
evaporated and the extra pure triazolinediones (2 or 4)
were obtained by sublimation of the residue.
1
situ generation of NO . In continuation of our studies on the
application of N O ,
1
,11
metal nitrate dinitrogen tetroxide
complexes and complexation of transition metals with
2
4
1
3
In conclusion, practical and ef®cient oxidation of urazoles
was achieved using the present methodology. The
[NO ´crown´H(NO ) ] complex, with easy preparation
1
Keywords: oxidation; triazolinedione; urazole; [NO ´crown´H(NO
Corresponding author. Tel.: 181-827-1075; fax: 181-827-2404;
e-mail: zol®@basu.ac.ir
2
2
3
)
].
1
2
3 2
p
and handling, can act as a relatively stable and ef®cient
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)01150-9

1
628
M. A. Zol®gol et al. / Tetrahedron 57 (2001) 1627±1629
1
. Experimental
1
.1. General
Chemicals were purchased from Fluka, Merck, Riedel-
dehaen AG and Aldrich chemical companies. The oxidation
products were characterized by comparison of their spectral
1
13
(
literature [2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 4a, 4b ].
IR, UV, H NMR, and C NMR) and physical data with
8
15
11
10
8
8
16
8
5
5
All urazoles and bis-urazoles were synthesized according
to our previously reported procedures.
1
,4,5,10,11
The
NO ´crown´H(NO ) ] was synthesized according to the
1
2
[
3
1
2
7
reported procedure, with a slight modi®cation. Here, we
used N O gas instead of liquid N O . Dinitrogen tetroxide
2
4
2
4
(
reported procedure as follows.
N O ) gas was generated in situ according to the previously
2 4
1
,10,11
1
,10,11
1
(
.1.1. Generation of NO ±N O gas
. Lead(II) nitrate
50 g) was crushed into a powder and was dried in an oven
2
2
4
at 1208C for three days. The resulting powder was trans-
ferred into a one-necked round-bottomed ¯ask (250 ml)
which was equipped with an air condenser and a gas trap
containing P O . The ¯ask was heated by a Bunsen burner to
2
5
generate a brownish-red NO ±N O gas, which was used
2
2
4
immediately for the subsequent preparation of
[
1
2
NO ´crown´H(NO ) ].
3 2
1
2
1
.1.2. Preparation of [NO ´crown´H(NO ) ]. A solution
3 2
Scheme 1.
of 18-crown-6 (5.286 g, 0.02 mol) in CH Cl (10 ml) was
2 2
prepared in a three-necked round-bottomed ¯ask (50 ml)
equipped with a magnetic stirrer, a gas inlet tube, a thermo-
meter and a drying tube, and cooled to 2108C with an ice±
reagent as a source for the delivery of nitrosonium ion
(
while, 18-crown-6 can be recycled and reused. The
1
NO ) under mild and homogeneous conditions. Mean-
salt bath while being stirred. Generated NO ±N O gas was
2
2
4
bubbled through this solution for 30 min. The solvent
was evaporated under vacuum at 208C to give the
1
2
[
methane and also more reactive than those reagents
NO ´crown´H(NO ) ] is completely soluble in dichloro-
3 2
1
2
[
NO ´crown´H(NO ) ] complex, as a pale yellow deli-
3 2
1
±9
quescent solid compound I [8.380 g, 0.02 mol (,100%)],
which were reported previously.
We believe that the
1
7
1
mp 50±558C [Lit. mp 53±558C]. H NMR (FT-90 MHz,
CDCl /TMS): 3.536 (s, 24H), 11.464 (s, 1H).
present methodology is an important addition to existing
methodologies.
3
1.1.3. Oxidation of urazole (1c) to substituted triazoline-
dione (2c)Ða typical procedure. A solution of compound
1
2
1
c (0.164 g, 1 mmol), [NO ´crown´H(NO ) , 0.419 g,
3 2
1
mmol] and SiO (0.3 g) in dichloromethane (3 ml) was
2
stirred at room temperature (the reaction was complete
immediately) and then ®ltered. Dichloromethane was
1
8
removed by water bath (40±508C), and simple distillation.
The residue was sublimed at 508C. The yield was 0.135 g
(
4
95%) of crystalline pale red solid (2c), mp 448C [Lit. mp
48C]. H NMR (FT-90 MHz, CDCl /TMS): d 3.63 (t, 2H,
3
1
Jˆ9.02 Hz), 1.68 (sextet, 2H, Jˆ7.55 Hz), 0.94 (t, 3H,
5
13
Jˆ9.02), [Lit. ]. C NMR (FT-90 MHz, CDCl /TMS): d
3
1
59.33, 42.88, 20.59, 10.66.
Acknowledgements
Financial support for this work by the research affair,
Bu-Ali Sina University, Hamadan, Iran, is gratefully
acknowledged.
Scheme 2.

M. A. Zol®gol et al. / Tetrahedron 57 (2001) 1627±1629
1629
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2
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