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SYNTHESIS, STRUCTURE, AND ALKYLATION OF 4-NITROAMINO-1,2,4-TRIAZOLE
1345
1,2,4-triazole itself: its signals appear separately only
at a very low temperature [8]. It is interesting that
in the H NMR spectrum of isomeric 3-nitroamino-
with hydrochloric acid to obtain free triazolionitro-
imide Ia [2]. Nitronium salts in anhydrous acetonitrile
were used more frequently for the nitration of
N-aminoazoles [2, 5, 14]. Just that procedure was
successful in the preparation of dinitroamino deriva-
tives of both monocyclic 1,2,4-triazole and fused
heterocycles based thereon [5].
1
1,2,4-triazole (Ic), in which the nitroamino group is
attached to C3, the 5-H signal is observed in a weaker
field (
1.15 ppm, Table 1).
The predominance of structure Ia both in the gas
phase and in water was confirmed by the results of
PM3 quantum-chemical calculations. It is known [9]
that the PM3 procedure provides a good agreement
with experimental data for most calculated geometric,
thermodynamic, and other physicochemical param-
eters of azoles. The calculations were performed with
the use of MNDO-90 software package [10]. The gas-
phase enthalpies of formation Hf of isomeric species
Ia and Ib are 88.17 and 93.92 kcal/mol, respectively,
and their dipole moments are 9.32 and 3.93 D. Taking
into account nonspecific solvation (in terms of the
point dipole approximation [11]), it was found that
polar structure Ia in water is even more favorable: the
calculated Hf values are 66.95 and 83.75 kcal/mol
for Ia and Ic, respectively. It should also be noted
that the calculated bond lengths and bond angles in
molecule Ia are very consistent with the X-ray diffrac-
tion data [7]. However, the dihedral angle between the
planes of the nitroimide and heterocyclic fragments
(as might be expected) approaches 90 ; presumably,
the smaller angle in the crystalline state is explained
by the crystal field effect.
Compounds having a nitroamino group at a nitro-
gen atom were reported for the first time in [12, 13],
and the first heterocyclic ylides were pyridine-1-nitro-
imides obtained by treatment of 1-aminopyridine
nitrates [12, 13] or sulfonylimide nitrates [13] with
concentrated nitric acid in the system AcOH Ac2O.
An analogous procedure was succesffully applied to
compounds of the 1,2,4-triazole series. In particular,
1-benzyl-4-phenylsulfonyl-1,2,4-triazolioimides were
thus converted into 1-benzyl-1,2,4-triazol-1-io-4-nitro-
imides [3]. However, the nitration of unsubstituted
4-amino-1,2,4-triazole under the same conditions gave
the initial amine nitrate in a poor yield. Only treat-
ment of 4-amino-1,2,4-triazole with alkyl nitrate in
alcohol in the presence of a base gave the correspond-
ing nitroimide sodium salt which was then neutralized
It is seen that the procedures used previously for
the nitration of 4-amino-1,2,4-triazole and its analogs
require either preliminarily preparation of nitrating
agents or very pure and dry solvents for reactions with
nitronium salts. Therefore, the primary goal of our
study on the properties of 1,2,4-triazol-1-io-4-nitro-
imide was to improve the procedure for its prepara-
tion. For this purpose, it seemed reasonable to apply
direct nitration of 4-amino-1,2,4-triazole under mild
conditions in the system HNO3 Ac2O. Some modi-
fication of the conventional procedure for preparation
of the nitrating mixture was necessary. Our experi-
ments showed that acceptable results are obtained
when initial 4-amino-1,2,4-triazole is preliminarily
acylated by dissolving it in acetic anhydride at
elevated temperature (50 C) and nitric acid is then
added to the cold solution (Scheme 1). In this case,
the target product is formed in a satisfactory yield
and is sufficiently pure.
Up to now, published data on the chemical pro-
perties of nitroimide Ia are limited to methylation
and benzylation of its sodium salt [2]. Therefore, it
was important not to examine the possibility for its
alkylation but to extend a series of alkylating agents
through the use of more complex electrophiles, such
as long-chain alkyl halides and compounds with func-
tional groups capable of undergoing further trans-
formations. Nitroimide Ia may be used as starting
compound for the synthesis of new and practically
important derivatives, e.g., surfactants (which as
a rule have a salt-like structure).
As in our previous study of 3-mercapto-1,2,4-tri-
azole derivatives [15], we examined reactions of nitro-
imide Ia with C10-, C12-, and C16-alkyl halides and
determined the product structure. The alkylation
products described in [2] were characterized only by
the data of elemental analysis. Prolonged heating of
nitroimide Ia with the above halogen derivatives in
Scheme 1.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 9 2002