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According to our previous findings [5, 6], a complex mixture is formed in the reaction of
N-unsubstituted 3-nitro- (9) and 5-methyl-3-nitro-1,2,4-triazoles (10) with excess dialkyl sulfate (DAS)
including products of N-monoalkylation and 1,4-dialkylation of the 3-nitro-5-R-1,2,4-triazoles and
1,4-dialkyl-5-R-1,2,4-triazol-5-ones. The major products of the alkylation of nitrotriazoles 9 and 10 by dimethyl
sulfate (DMS) are N-monomethyl-3-nitro-5-R-1,2,4-triazoles (the overall yield of the isomer mixture is 53-73%
and the ratio of the products, N(1)-, N(2)-, and N(4)-methyl-3-nitro-5-R-1,2,4-triazoles is, on the average,
0.035:1.0:7.75). The fraction of 1,4-dimethyl- and 1,3,4-trimethyl-1,2,4-triazol-5-ones in the product mixture is
3-6%, while the yield of 1,4-dimethyl- and 1,4,5-trimethyl-3-nitro-1,2,4-triazolium salts is only 8-12% [5].
Increasing the excess of DMS to two- or three-fold reduces the yield of the products of the
N-monomethylation of the nitrotriazoles to 15-24% and enhances the yield of the 1,4-dimethyl- and
1,4,5-trimethyl-3-nitro-1,2,4-triazolium methyl sulfate salts 11 and 12 or perchlorate salts 13 and 14 to 45-60%.
When diethyl sulfate (DES) was used [6], the N-monosubstituted 3-nitro-5-R-1,2,4-triazoles gave only
N(2)-isomers, namely, 1-ethyl-5-nitro- and 1-ethyl-3-methyl-5-nitro-1,2,4-triazoles, and N(4)-isomers 6 and 8 (the
overall yield of the mixture was 26.3 and 45.3% and the ratio of the N(2)- and N(4)-isomers was 1.0:2.7 and
1.0:2.3, respectively). The yield of the ethylated triazolones, 1,4-diethyl- (36.7%) and 1,4-diethyl-
3-methyl-1,2,4-triazol-5-ones (29.4%) was much greater when compared to the methyl analogs. The yield of the
1,4-diethyl- (15) and 1,4-diethyl-5-methyl-3-nitro-1,2,4-triazolium ethyl sulfate salts (16) and the corresponding
perchlorate salts (17 and 18) was low, as in the case of using DMS as the quaternizing agent (9.7 and 5.5%).
The use of mild alkylating agents such as methyl iodide and ethyl bromide for quaternization of the
alkylnitrotriaozoles was unsuccessful. Thus, in light of the rather high activity of dialkyl sulfates in the
formation of quaternary salts from N-unsubstituted nitrotriazoles [5, 6], it appeared desirable to employ these
alkylating agents for the further study of the quaternization of the indicated N-alkylnitrotriazoles.
The question of selectivity arises in the study of the quaternization of N-monosubstituted
alkylnitrotriazoles. The position of the alkyl substituent at the ring nitrogen atoms of N(1)- and
N(4)-monosubstituted 5-nitro-5-R-1,2,4-triazoles has a significant effect on the reaction conditions required and
the yield, structure, and properties of the products obtained (Table 1). Two nonequivalent atoms are available for
attack by the electrophilic agent in derivatives of 1-alkyl- (N(2) and N(4)) and 4-alkyl- 3-nitro-5-R-1,2,4-triazoles
(N(1) and N(2)). Nitrotriazoles with substituted nitrogen atoms, in particular, N(1)-substituted derivatives, probably
cannot be quaternized in the α-position to the substituent due to reduced nucleophilicity and steric hindrance.
Thus, quaternization of 1-alkylnitrotriazoles 1-4 by dialkyl sulfates proceeds selectively at the most basic N(4) atom
and leads to 1,4-dimethyl-, 1,4,5-trimethyl- (11-14) and 1,4-diethyl-, 1,4-diethyl-5-methyl-3-nitro-1,2,4-triazolium
methyl sulfates and perchlorates 15-18:
R1
R1
O2N
O2N
O2N
N
N
N
R1 SO4
–
R1SO4
NH4ClO4
2
ClO4
–
+
+
N
N
N
R
R
N
R
N
N
R1
11,12,15,16
R1
13,14,17,18
R1
1–4
1, 11, 13 R = H, R1 = Me; 2, 15, 17 R = H, R1 = Et;
3, 12, 14 R = R1 = Me; 4, 16, 18 R = Me, R1 = Et
The formation nitrotriazolium salts 11, 12, 15, and 16 from 1-substituted nitrotriazoles 1-4 proceeds
through the following scheme. The electrophilic reagent attacks the nitrotriazoles at the unshared electron pair of
N(4), which is available for coordination, or at the π-bond of this atom with localization of the substituent at
787