Trichloroisocyanuric acid as a novel oxidizing agent for the oxidation of urazoles under both heterogeneous and solvent free conditions

Article abstract of DOI:10.1055/s-2002-34213

Trichloroisocyanuric acid was used as an effective oxidizing agent for the oxidation of urazoles and bis-urazoles to their corresponding triazolinediones under both heterogeneous and also solvent free conditions with excellent yields at room temperature.

Full text of DOI:10.1055/s-2002-34213

LETTER
1633
Trichloroisocyanuric Acid as a Novel Oxidizing Agent for the Oxidation of
Urazoles Under Both Heterogeneous and Solvent Free Conditions
Trichloroisocyanuric
A
o
cid as
a
N
ov
h
el Oxidizing
a
A
gent
f
or
m
the Oxidationof
U
r
m
azoles ad Ali Zolfigol,*a Elaheh Madrakian,a Ezat Ghaemi,a Shadpour Mallakpourb
a
Chemistry Department, College of Science, Bu-Ali Sina University, Hamadan, 65174, Iran.
E-mail: Zolfi@basu.ac.ir
b
Organic Polymer Chemistry Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan, 84156, Iran
Received 1 August 2002
solvent free reactions13 have many advantages such as
simple experimental procedures, mild reaction conditions
and minimization of chemical wastes as compared to the
solution phase counterparts. Therefore, we were interest-
ed to find a heterogeneous system for urazole oxidation
and we have investigated a number of different reac-
tion conditions based upon the in situ generation of
HNO2(NO+)14 or H2O2 (Cl+).15 In continuation of our stud-
ies in this regard,16 we have found that trichloroisocyanu-
ric acid a cheap commercially available reagent used
primarily as a disinfectant and deodorant, has found little
application in organic chemistry.17 Therefore, we wish to
report a simple, cheap and convenient method for the ef-
fective conversion of urazoles and as well as bis-urazoles
to their corresponding triazolinediones (2, 4) by using
trichloroisocyanuric acid both under heterogeneous and
also solvent free conditions (Scheme 1 and Scheme 2).
Abstract: Trichloroisocyanuric acid was used as an effective oxi-
dizing agent for the oxidation of urazoles and bis-urazoles to their
corresponding triazolinediones under both heterogeneous and also
solvent free conditions with excellent yields at room temperature.
Keywords: trichloroisocyanuric, urazoles, bis-urazoles, triazo-
linediones, solvent free conditions
4-Substituted-1,2,4-triazole-3,5-diones (TADs) are nota-
ble for their ability to participate in a wide range of reac-
tivity and reaction types, e.g. [4+2]1,2 and [2+2]3
cycloadditions, ene reactions,4 electrophilic aromatic sub-
stitution,5 dehydrogenating properties6 and oxidation of
alcohols to aldehydes and ketones.7 However, the unusual
reactivity which makes 1,2,4-triazoline-3,5-diones (2, 4)
of interest, to organic chemists makes them difficult to
prepare and purify as well. For example: 4-phenyl-1,2,3-
triazoline-3,5-dione (2e) is an extremely reactive dieno-
phile and enophile which is at least 1000 times more reac-
tive than tetracyanoethylene (TCNE) in the Diels–Alder
reaction with 2-chlorobutadiene and 2000 times more re-
active than maleic anhydride.1 All known methods of syn-
thesis of these compounds require oxidation of the
corresponding 1,2,4-triazolidine-3,5-diones (1, 3), more
commonly known as urazoles.
Different kinds of urazoles and bis-urazoles were subject-
ed to oxidation reaction in the presence of trichloroisocy-
anuric acid in dichloromethane (Scheme 1 and Scheme 2)
or solvent free conditions. The oxidation reactions were
performed under mild conditions at room temperature
with excellent yields. The triazolinedione (2) or bis-tri-
azolinedione (4) can be obtained by simple filtration and
evaporation of the solvent.23–26 The results and reaction
conditions are given in Table 1.
Although a wide variety of reagents are capable of effect-
ing the urazoles oxidation8–11 this transformation remains
capricious because these compounds are very sensitive to
the oxidizing agents and reaction conditions. Moreover,
most of the reported reagents produce some 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
both).8 Recently, we have demonstrated the remarkably
practical use of in situ generated N2O4 gas as a clean and
efficient oxidant for this purpose.1,10,11 It is known that
gaseous N2O4 is corrosive and highly toxic and must be
generated under an effective hood with caution. There-
fore, we decided to develop a new reagent or reagent sys-
tem to overcome the above limitations and provide a clean
and easy work-up. Heterogeneous reagent systems12 or
The synthesis of Diels–Alder adducts of triazolinediones
specially 4-(4 -aminophenyl)triazolinedione are our
main interest for some mechanistic studies of halogena-
tion reactions on its double bond of cyclopentadiene
moieties.1b-c It is interesting to note that, we have had
problems for the oxidation of urazoles containing of func-
tional groups sensetive to the oxidizing agents during our
previous work.14,15,22c For example, we have tried to oxi-
dized the compound 4-(4 -aminophenyl)urazole with dif-
ferent oxidizing agent, but we failed. Here for the first
time we wish to report that, we were able to oxidize this
compound successfully by oxidation with trichloroisocy-
anuric acid. Since the triazolinedione from this compound
is not stable due to the presence of amino group or its salt,
we first generated this triazolinedione in dichloromethane
and then we added cyclopentadiene and sodium carbonate
to the reaction mixture. Thus the Diels–Alder adduct of
the above mentioned compound was prepared in one pot
(Scheme 3). The resulting Diels–Alder adduct was isolat-
ed in high yield. The structure of this adduct was con-
Synlett 2002, No. 10, Print: 01 10 2002.
Art Id.1437-2096,E;2002,0,10,1633,1636,ftx,en;D13502ST.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214

1634
M. Ali Zolfigol et al.
LETTER
Scheme 2
We have also used a combination of cyanuric chloride (5,
Figure 1) and NaNO2 in the presence of wet SiO2 for the
oxidation of urazoles. The reaction proceeded via in situ
generation of HNO2 and NO+ respectively.14 Although the
oxidation reaction worked well, but during of work up the
resulting triazolidiones (2 and 4) were contaminated with
some of the cyanuric chloride and it was difficult to isolate
it, even we have tried to purified them with sublimation
technique, but it was unsuccessful.
Scheme 1
firmed by high resolution mass spectroscopy and
elemental analysis.
This new reagent e.g. trichloroisocyanuric acid is an
effective source for the in situ generation Cl+ which be-
haves like HNO2,14 H2O2/MCln and N2O4 (N2O4
15
–
NO+NO3 ).22 Therefore, on the basis of our results and, the
In conclusion, practical and efficient oxidations of ur-
azoles and bis-urazoles have been achieved by the new
methodology described. The chemoselectivity of the
products which were obtained, the following mechanism
may be proposed (Scheme 4).
Table 1 Oxidation of Urazoles (1) and bis-Urazoles (3) to their Corresponding Triazolinediones (2, 4) with Trichloroisocyanuric Acid Both
in Dichloromethane (I) and Solvent Free Conditions (II) at Room Temperature
Urazole or (bis)
Producta
Reagent/Substrateb
Time (h) I (II)
Yieldc (%) I (II)
Mp °C
Found
I
II
1
1
1
1
2
1
1
1
1
2
2
Reportet
98–98.58
5319
1a
1b
1c
1d
1e
1f
2a8
1
1
1
1
4
1
1
1
1
2
2
0.50 (0.50)
0.50 (0.50)
0.50 (0.25)
0.50 (0.25)
0.50 (0.25)
0.50 (0.25)
0.50 (0.25)
0.50 (0.25)
0.50 (0.25)
0.50 (0.25)
0.50 (0.25)
100d (100d)
100d (100d)
98 (94)
97–99
2b19
2c11,19
2d8
54–56
42–44
4411
100 (97)
99 (98)
42–45
44–44.58
95–968
2e8
97–98
2f8,10
2g8
74 (70)
168–175
134–135
125–126
110–113
145–150
182–185 (dec.)
170–17810
130–1328
128–12921
113–11518
146–14921
185 (dec.)21
1g
1h
1i
96 (90)
2h8,21
2i18
63 (63)
98 (98)
3a
3b
4a21
4b21
90 (72)
90 (72)
a All of the isolated products are known compounds and their spectra and physical data have been reported in the literature.
b Molar ratio of trichloroisocyanuric acid in CH2Cl2 (I) mmol and under solvent free conditions (II) mmol.
c Isolated yields.
d Conversion.
Synlett 2002, No. 10, 1633–1636 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Trichloroisocyanuric Acid as a Novel Oxidizing Agent for the Oxidation of Urazoles
1635
References
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Scheme 3
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Scheme 4
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Figure 1
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H. Synlett 2002, 1002.
trichloroisocyanuric acid is very interesting for urazole
compounds containing highly reactive functional group
towards oxidation reaction. Thus this reagent could be
used for the oxidation of a wide variety of urazole deriva-
tives under safe condition.
(17) (a) Firouzabadi, H.; Iranpoor, N.; Hazarkhani, H. Synlett
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Acknowledgement
Financial support for this work by the Research Council of Bu-Ali
Sina University, Hamadan, Iran, and Isfahan University of Techno-
logy, Isfahan, Iran is gratefully acknowledged.
(22) (a) Zolfigol, M. A.; Zebarjadian, M. H.; Chehardoli, G. A.;
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Synlett 2002, No. 10, 1633–1636 ISSN 0936-5214 © Thieme Stuttgart · New York

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M. Ali Zolfigol et al.
LETTER
under simple distillation. The yield was 0.35 g (98%) of
(23) Chemicals were purchased from Fluka, Merck, Riedel-
deHaën AG and Aldrich chemical companies. Yields refer to
isolated pure products. The oxidation products were
crystalline red solid (2e), mp 95–98 °C [Lit8 mp 95–96 °C].
1H NMR (FT-90 MHz, CDCl3/TMS): = 3.90 (quintet, 1 H,
J = 12 Hz), 1.82–1.26 (m, 10 H). 13C NMR (FT-22.5 MHz,
CDCl3/TMS): = 158.77, 53.93, 28.72, 24.96, 24.28.
(25) These compounds are sensitive to the light, heat, alcohols,
ethers, 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 CH2Cl2, some of TADs are
removed with solvent simultaneously. Therefore, the
temperature must be controlled and dichloromethane is the
best solvent for this purpose.
characterized by comparison of their spectral (IR, UV, 1H
NMR, and 13C NMR) and physical data with the authentic
samples. All urazoles and bis-urazoles were synthesized
according to our previously reported procedures.1,4,5,10,11,21
(24) Oxidation of 4-cyclohexyl urazole(1e) to 4-cyclohexyl-
1,2,4-triazoline-3,5-dione(2e) with trichloroisocyanuric
acid, a typical procedure. A mixture of compound 1e
(0.366 g, 2.0 mmol) and trichloroisocyanuric acid (0.232 g,
1.0 mmol) was shaken at r.t. for 0.25 h and dichloromethane
(20 mL) was added to the resulting mixture then filtered.
Dichloromethane was removed by water bath (40–50 °C)25
(26) For running the oxidation reaction under heterogeneous
conditions please see ref. 14.
Synlett 2002, No. 10, 1633–1636 ISSN 0936-5214 © Thieme Stuttgart · New York