Oxidative N—N coupling of N-alkyl-3-aminopyrazoles to azopyrazoles in aqueous solutions of NaOCl and NaOBr

Article abstract of DOI:10.1007/s11172-021-3072-z

The influence of the structures of N-alkyl-3-aminopyrazoles on their transformation into azopyrazoles on treatment with sodium hypohalogenites was studied. The reaction of 3-aminopyrazoles unsubstituted at position 4 containing donor substituents with neu

Full text of DOI:10.1007/s11172-021-3072-z

Russian Chemical Bulletin, International Edition, Vol. 70, No. 1, pp. 164—170, January, 2021
164
Oxidative N—N coupling of N-alkyl-3-aminopyrazoles to azopyrazoles
in aqueous solutions of NaOCl and NaOBr
B. V. Lyalin, V. L. Sigacheva, B. I. Ugrak, and V. A. Petrosyan
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. E-mail: lyalin@ioc.ac.ru
The influence of the structures of N-alkyl-3-aminopyrazoles on their transformation into
azopyrazoles on treatment with sodium hypohalogenites was studied. The reaction of 3-amino-
pyrazoles unsubstituted at position 4 containing donor substituents with neutral solutions of
sodium hypohalogenites leads to mixtures of 3,3´-azopyrazoles (yields 1—40%) and 4,4´-dihalo-
3,3´-azopyrazoles (yields 20—79%). In this case, generation of 3,3´-azopyrazoles is favored by
the addition of NaOH to the reaction mixture. The N—N coupling of aminopyrazoles with
acceptor substituents in the aromatic ring results in the selective formation of 3,3´-azopyrazoles
even in neutral media. The reactions of 4-substituted 3-aminopyrazoles with NaOBr afford only
3,3´-azopyrazoles. The regularities of occurrence of all the above processes are discussed.
Key words: N-alkyl-3-aminopyrazoles, 3,3´-azopyrazoles, 4,4´-dihalo-3,3´-azopyrazoles,
oxidative N—N coupling, sodium hypochlorite (hypobromite).
Oxidation of aromatic amines is one of the demanded
preparation of an aqueous solution of NaOCl under the
conditions of galvanostatic undivided electrolysis of NaCl,
and the second step was the reaction of obtained NaOCl
with aminopyrazoles (Scheme 1).
methods for synthesis of aromatic azo compounds. At the
same time, the use of heavy metal salts as oxidants in these
reaction is not environmentally friendly.1—3 The use of
metal hypohalogenites for these purposes seems more at-
tractive. For example, we showed the principal possibility
of transformation of 3-aminopyrazoles
As earlier described2 aminopyrazole 1a, aminopyr-
azoles 1b,c with the donor substituents in the cycle on
treatment with NaOCl give (see Table 1, entries 1 and 3)
the corresponding azopyrazoles 2, 4-chloro-3-aminopyr-
azoles 3, and products of oxidative N—N coupling of the
latter: 4,4´-dichloroazopyrazoles 4. According to the
earlier proposed2 interpretation of the occurrence of par-
ticular steps of the process, hydrolysis of NaOCl affords
hypochlorous acid HOCl, which is a very weak acid
(рKa 7.30)4 but a strong electrophile. For these reasons,
HOCl can attack a molecule of aminopyrazole 1a—с at
both the NH2 group to generate N-chloroaminopyrazoles
5a—с and the N atom of the pyrazole cycle to form
4-chloroaminopyrazoles 3a—c (see Scheme 1). Chloro-
aminopyrazoles 5a—с give azopyrazoles 5 due to the
transformations proceeding via intermediates 5, whereas
the oxidative transformation of 4-chloroaminopyrazoles
3 leads to 4,4´-dichloroazopyrazoles 4.
into azopyrazoles involving electrogene-
rated NaOCl using 3-amino-1-methyl-
1Н-pyrazole (1a) as a model compound
and studied a number of regularities of this
transformation.2 In particular, we found
that 3-aminopyrazole inhibited the oxida-
tion of Сl– anions, which dictates the necessity of a two-
step process with the isolation of NaOCl electrogeneration
in a particular step.
The purpose of the present work is to show that the
mentioned above and other regularities of electrosynthesis
of azopyrazoles from aminopyrazole 1a on treatment with
electrogenerated NaOCl2 are valid for rather wide range
of aminopyrazoles. In addition, we studied the possibility
of using electrogenerated NaOBr in similar processes.
At the equimolar ratios of aminopyrazoles 1a—с and
NaOCl (see Scheme 1 and Table 1, entries 1, 3, and 5),
the process results in azopyrazoles 2a—c, 4-chloroamino-
pyrazoles 3a—c (chlorination products of the initial
aminopyrazoles), and 4,4´-azopyrazoles 4a—c, which are
the products of oxidative transformation of the initial
aminopyrazoles.
Results and Discussion
The influence of the nature of substituents (donor,
acceptor) in the pyrazole cycle on the transformation of
3-aminopyrazoles 1a—d into azopyrazoles involving elec-
trogenerated sodium hypohalogenites was studied first. As
in the previous work,2 the first step of the process was the
Note that the total yield of chlorination products 3 and
4 is higher than that of azopyrazoles 2. This is due, most
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 164—170, January, 2021.
1066-5285/21/7001-0164 © 2021 Springer Science+Business Media LLC

N—N coupling of N-alkyl-3-aminopyrazoles
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 1, January, 2021
165
Scheme 1
1—6: R1 = Me, R2 = H (a); R1 = Et, R2 = H (b); R1 = R2 = Me (c); R1 = Me, R2 = CF3 (d)
Ti is a Ti cathode, and ORTA is an oxide ruthenium—titanium anode.
Table 1. Influence of the nature of N-alkyl-3-aminopyrazoles (PzNH2) and NaOCl : PzNH2 molar ratio on the
yields of azopyrazoles under the conditions of N—N coupling of PzNH2 on treatment with electrogenerated NaOCla
Entry
PzNH2
Molar ratio
NaOCl : PzNH2
Conversion
PzNH2 (%)
Products
Yieldb (%)
I
II
1c
2c
3
1a
1a
1b
1 : 1
2 : 1
1 : 1
171
100
194
2a
3а
4а
2a
3а
4а
2b
3b
4b
2b
4b
2c
3c
2c
3c
4c
2c
3c
4c
2d
26
30
4
40
7
40
37
40
17
41
46
1
76
1
63
32
2
37
42
6
40
7
40
39
43
18
41
46
1
79
1
63
32
2
4
5
6
1b
1c
1c
3 : 1
1 : 1
2 : 1
100
196
100
7
1c
1d
4 : 1
2 : 1
100
100
6
79
86
6
79
86
8
a Reaction conditions: PzNH2 (0.002 mol), 25 °С, 5 h.
b The yields of the product based on the initial aminopyrazole (I) and reacted aminopyrazole (II).
c Data of Ref. 2.

Lyalin et al.
166
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 1, January, 2021
likely, to a higher reactivity of the N atom of the pyrazole
cycle in 3-aminopyrazoles with respect to electrophiles
than that of the N atom of the NH2 group.5 This agrees
with the predominant formation of 4-chloroamine de-
rivative 3c by the oxidative transformation of 3-amino-
1,5-dimethyl-1Н-pyrazole (1c) (see Table 1, entry 5).
Evidently, the additional Me group in pyrazole 1c makes
it more reactive in electrophilic substitution.
the use of NaOBr excess in the reaction favors the forma-
tion of 4,4´-dibromoazopyrazoles 8 (see Table 2, entries
2, 4, and 6), and the presence of the acceptor substituent
at position 5 of the cycle (compound 1d) results in the
selective formation of azopyrazole 2d containing no brom-
ine atom in a yield of 93% (see Table 2, entry 7).
However, contrary to our expectations, the replace-
ment of NaOCl by NaOBr did not increase the efficiency
of the process (cf. entries 1, 3, and 5 in Tables 1 and 2).
Probably, this is explained by a higher reactivity of the
N atom of the pyrazole cycle (unlike the N atom of the
NH2 group) toward the electrophile. In this case, hypo-
bromous acid HOBr formed by hydrolysis of NaOBr in an
aqueous medium acts as an electrophile.
As in the case of aminopyrazole 1a,2 an excess of
NaOCl over aminopyrazoles 1b and 1c favor the N—N
coupling of 4-chloroaminopyrazoles 3 to form 4,4´-di-
chloroazopyrazoles 4. For example, in entries 2, 4, 6, and
7 (see Table 1), the yields of 4,4´-dichloroazopyrazoles
4a—c were 40—70%.
It is important that the reaction of electrogenerated
NaOCl with aminopyrazole containing an acceptor sub-
stituent in the cycle, for example, with 3-amino-1-methyl-
5-trifluoromethyl-1Н-pyrazole (1d), is selective and gives
1,2-bis(1-methyl-5-trifluoromethyl-1Н-pyrazol-3-yl)di-
azene (2d) in a yield of 86% in the complete absence of
chlorination products of the initial aminopyrazole (see
Scheme 1). This result is consistent with our earlier data6
on a decrease in the chlorination rate of pyrazoles if the
cycle contains acceptor substituents.
It has previously2 shown that the reaction of NaOCl
with 3-amino-1,4-dimethyl-1Н-pyrazole (1e) is selective
and gives the corresponding N—N coupling product 2e
containing no chlorine atom in the cycle in a yield of 66%.
Developing these studies, we found that the reactions of
aminopyrazoles 1e and 7a substituted at position 4 of the
cycle with NaOBr also selectively afford the correspond-
ing azopyrazoles 2e and 8a (see Scheme 2 and Table 2,
entries 8 and 9).
The aforementioned formation of 4,4´-dihaloazopyr-
azoles 4 and 8 by the transformation of aminopyrazoles
unsubstituted at position 4 of the cycle into azopyrazoles
on treatment with NaOCl or NaOBr (see Tables 1 and 2)
is due to the hydrolysis of NaOHal to form hypohaloid
acids HOHal (see Scheme 1), which are highly efficient
halogenating agents. It could be expected that the sup-
pression of hydrolysis of NaOHal by the addition of NaOH
to solutions of sodium hypohalites would allow one to
selectively synthesize azopyrazoles containing no halogen
atoms in the heterocycle. The results of these studies are
presented in Table 3.
N-Bromoamines are known7 to be more reactive than
N-chloroamines. Therefore, it could be expected that the
replacement of NaOCl by NaOBr would increase the ef-
ficiency of azopyrazole synthesis. It turned out that the
reactions of N-alkyl-3-aminopyrazoles 1a—c unsubstituted
at position 4 with NaOBr* proceeded similarly to the
reactions with NaOCl (see Scheme 1) and resulted in
a mixture of the corresponding azopyrazoles 2a—c,
4-bromoaminopyrazoles 7a—c, and 4,4´-dibromoazopyr-
azoles 8a—c (Scheme 2, Table 2). As in the case of NaOCl,
It turned out that in the reaction of aminopyrazole 1a
with NaOCl in the presence of NaOH (molar ratio
PzNH2 : NaOCl : NaOH = 1 : 1 : 1) the yield of azopyr-
* NaOBr was preliminarily synthesized by the undivided galvano-
static electrolysis of an aqueous solution of NaBr (ORTA anode,
Ti cathode, ja = 100 mA cm–2, 20—25 °С).
Scheme 2
Compound 1a—c
and 2a—c
1a, 2a
R1
R2
R3
Compound 1d,e,
R1
R2
R3
2d,e, and 7a
1d, 2d
1e, 2e
7a
Me
Et
Me
H
H
Me
H
H
H
Me
Me
Me
CF3
H
H
H
Me
Br
1b, 2b
1c, 2c
7, 8: R1 = Me, R2 = H (a); R1 = Et, R2 = H (b); R1 = R2 = Me (c)

N—N coupling of N-alkyl-3-aminopyrazoles
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 1, January, 2021
167
Table 2. Influence of the nature of N-alkyl-3-aminopyrazoles (PzNH2) and NaOBr : PzNH2 molar ratio on the
yields of azopyrazoles under the conditions of N—N coupling of PzNH2 on treatment with electrogenerated NaOBra
Entry
PzNH2
Molar ratio
NaOCl : PzNH2
Conversion
PzNH2 (%)
Products
I
Yieldb (%)
II
1
2
3
1a
1a
1b
1 : 1
2 : 1
1 : 1
158
100
182
2a
7a
8a
2a
7a
8a
2b
7b
8b
2b
8b
2c
7c
8c
2c
7c
8c
2d
2e
8a
20
20
6
34
34
10
34
22
48
22
43
15
23
42
11
69
28
11
39
47
93
70
62
34
22
48
18
36
12
23
42
11
59
24
11
39
47
93
70
62
4
5
1b
1c
3 : 1
1 : 1
100
185
6
1c
2 : 1
100
7
8
9
1d
1e
7a
2 : 1
1 : 1
1 : 1
100
184
189
a Reaction conditions: PzNH2 (0.002 mol), 25 °С, 5 h.
b The yields of the product based on the initial aminopyrazole (I) and reacted aminopyrazole (II).
azole 2a containing no chlorine atom in the cycle increased
from 37 to 49% (based on unreacted aminopyrazole). The
total yield of the chlorination products of aminopyrazole
1a, namely, chloroaminopyrazole 3а and 4,4´-dichloro-
azopyrazole 4a, simultaneously decreases from 48 to 29%
(cf. entries 1 in Tables 1 and 3), and the conversion of
aminopyrazole 1a is 87% (see Table 3, entry 1). An increase
in the NaOH : NaOCl molar ratio from 1 : 1 to 3 : 1 is
accompanied by an increase in the yield of azopyrazole
2a to 70% and a decrease in the total yield of chlorination
products 3a and 4a by 14% (cf. entries 1 and 2 in Table 3).
However, the conversion of aminopyrazole 1a decreased
by 27%. To avoid this decrease, NaOCl excess was used
(molar ratio NaOCl : PzNH2 = 3 : 1) with the retention
of the molar ratio NaOH : NaOCl = 3 : 1. This resulted
in an almost complete conversion of aminopyrazole 1a
(96%) and formation of azopyrazole 2a in a high yield
(75% based on loaded aminopyrazole). In this case, the
total yield of chlorination products 3a and 4a did not
exceed 19% (see Table 3, entry 3). Thus, a higher selectiv-
ity of the process was achieved in the presence of NaOH.
The use of NaOH additives in the transformation of
3-amino-1-ethyl-1Н-pyrazole (1b) into azopyrazole 2b
also favors the yield of the target product (cf. entries 4 in
Tables 1 and 3). However, the efficiency of NaOH addi-
tives in the transformation of 3-amino-1,5-dimethyl-1Н-
pyrazole (1c) into azopyrazole 2c is low. The major reac-
tion product is chloroaminopyrazole 3c, the yield of which
is 67% (based on unreacted aminopyrazole), whereas the
yield of azopyrazole 2c is only 14% (see Table 3, entry 5).
Probably, this is explained by a higher halogenation rate
of aminopyrazole 1c caused by two donor substituents
(Me groups) in the cycle along with the NH2 group. In
this case, even the use of a much larger amount of NaOH
(molar ratio NaOH : NaOCl = 15 : 1) did not result in the
predominant formation of azopyrazole 2с: the yields of
azopyrazole 2c and chloroaminopyrazole 3c were 30 and
70%, respectively (see Table 3, entry 6).
It was mentioned when studying the influence of alkali
additives on the transformation of aminopyrazoles in the
presence of NaOBr that the yield of azopyrazoles 2 lack-
ing the halogen atom in the cycle was higher than that in
the reaction with NaOCl. For example, in the case of
aminopyrazole 1a, the yield of azopyrazole 2a increased
from 70 to 88% with a decrease in the yields of bromina-
tion products 7a and 8a from 15 to 1% (cf. entries 2 and
8 in Table 3). A similar situation is observed for amino-
pyrazole 1b (cf. entries 4 and 9 in Table 3). An increase in
the efficiency of NaOBr in the presence of NaOH additives
in the N—N coupling of aminopyrazoles can be explained
by a higher reactivity in the target process of N-bromoamines
compared to N-chloroamines 5 (see Scheme 1) under the
conditions of suppression of aminopyrazole halogenation
by alkali additives. At the same time, for the transforma-

Lyalin et al.
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Russ. Chem. Bull., Int. Ed., Vol. 70, No. 1, January, 2021
Table 3. Influence of the nature of N-alkyl-3-aminopyrazoles (PzNH2) and experimental conditions on the yields
of azopyrazoles containing no halogen atom in the heterocycle of the N−N coupling of aminopyrazoles on treatment
with sodium hypohalogenites (NaOHal) in the presence of NaOH additivesa
Entry
PzNH2
NaOHal
NaOH : NaOHal
Molar ratio
PzNH2 (%)
Conversion
I
Products
II
Yieldb (%)
1
1a
NaOCl
1 : 1
187
2a
3а
4а
2a
3а
2a
3а
4а
2b
3b
4b
2c
3c
2c
3c
2a
7a
8a
2a
7a
2b
7b
8b
2c
7c
8c
43
49
24
15
70
15
78
15
15
65
24
19
11
83
30
70
16
11
18
88
11
78
12
16
16
66
18
21
14
42
19
75
15
14
43
16
16
14
67
30
70
60
10
17
72
11
73
12
16
12
48
13
2
1a
1a
NaOCl
NaOCl
3 : 1
3 : 1
160
196
3с
4
1b
NaOCl
3 : 1
166
5
6
7
1c
1c
1a
NaOCl
NaOCl
NaOBr
3 : 1
15 : 1
1 : 1
181
100
190
8
9
1a
1b
NaOBr
NaOBr
3 : 1
3 : 1
182
194
10
1c
NaOBr
3 : 1
173
a Reaction conditions: PzNH2 (0.002 mol), molar ratio NaOHal : PzNH2 = 1 : 1, 25 °С, 5 h.
b The yields of the product based on the initial aminopyrazole (I) and reacted aminopyrazole (II).
c Molar ratio NaOCl : PzNH2 = 3 : 1.
tion of aminopyrazole 1c into azopyrazole 2c, the use of
NaOH additives to a solution of NaOBr also turned out
to be inefficient as for the use of NaOCl (cf. entries 5 and 10
in Table 3).
of azopyrazoles. The N—N coupling of 4-substituted
3-aminopyrazoles involving electrogenerated NaOBr is
shown to result in the corresponding azopyrazoles in yields
of 62—70%.
To conclude, in this work we studied the regularities
of the two-step oxidative transformation of N-alkyl-3-
aminopyrazoles into azopyrazoles on treatment with
electrogenerated sodium hypohalogenites (NaOCl or
NaOBr). Under these conditions, aminopyrazoles contain-
ing donor substituents bearing the hydrogen atom at posi-
tion 4 of the cycle were found to give a mixture of the
corresponding azopyrazoles and 4,4´-dihaloazopyrazoles
in yields of 1—40% and 20—79%, respectively, depending
on the aminopyrazole structure. It is shown using 3-amino-
1-methyl-5-trifluoromethyl-1Н-pyrazole as an example
that an acceptor substituent in the cycle favors the forma-
tion of azopyrazoles in high yields. It is found that the
addition of NaOH to the reaction system of aminopyr-
azoles lacking substituents at position 4 of the cycle inter-
acting with sodium hypohalogenites favors the formation
Experimental
1H and 13С NMR spectra were recorded on a Bruker Avance 300
instrument (300.13 (1H) and 75.47 MHz (13C)) in CDCl3 us-
ing Me4Si as the standard. High-resolution mass spectra (HRMS)
were obtained on a Bruker micrOTOF II instrument using elec-
trospray ionization (ESI). Plates purchased from Merck were
used for thin-layer chromatography. Melting points were deter-
mined on a Koffler heating stage. Petroleum ether, EtOAc,
CHCl3, silica gel (0.035—0.070 mm, 60 Ǻ) for column chroma-
tography, and 3-amino-1-methyl-1Н-pyrazole (1a) were com-
mercially available products (Acros Organics). 3-Amino-4-
bromo-1-methyl-1Н-pyrazole (7a), 3-amino-1-ethyl-1Н-pyr-
azole (1b), 3-amino-1,5-dimethyl-1Н-pyrazole (1c), 1-methyl-
5-trifluoromethyl-1Н-pyrazole (1d) and 3-amino-1,4-dimeth-
yl-1Н-pyrazole (1e) were provided by UAB Crea-Chim (Lithuania).

N—N coupling of N-alkyl-3-aminopyrazoles
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 1, January, 2021
169
Electrochemical preparation of a neutral aqueous solution of
NaOCl. A 4 М aqueous solution of NaCl (100 mL) was placed
in an undivided cell equipped with the oxide ruthenium—tita-
nium anode (ORTA) and (S = 7.8 cm2) and the Ti cathode
(S = 10 cm2). Electrolysis was carried out at a current of 1260 mA
and temperature 20—25 °С passing 588—1764 C electricity. After
the end of electrolysis, solutions containing 0.002—006 mol NaOCl,
depending on the amount of passed electricity, were obtained.
The content of the target product was determined by iodometric
analysis.8
Electrochemical preparation of a neutral aqueous solution of
NaOBr. A 2 М aqueous solution of NaBr (100 mL) was placed
in a cell, and electrolysis was carried out as described above
at a current as 780 mA. After passing 661—1983 C electricity, solu-
tions containing 0.002—0.006 mole of NaOBr, depending on
the amount of passed electricity, were obtained (iodometric
analysis data).
Reaction of 3-amino-1-ethyl-1Н-pyrazole (1b) with a neutral
solution of NaOCl (see Table 1, entry 3). Aminopyrazole 1b
(0.22 g, 0.002 mol) was added to a neutral solution of NaOCl
(0.002 mol) preliminarily prepared as described previously. The
reaction mixture was stirred for 5 h and analyzed by TLC using
a petroleum ether—ethyl acetate (1 : 1) mixture as an eluent.
Then concentrated HCl were added (to рН ≈ 3), and the products
were extracted with CHCl3 (3×30 mL). The extracts were com-
bined, dried over anhydrous MgSO4, and evaporated in vacuo.
Column chromatography on silica gel (petroleum ether—ethyl
acetate (1 : 2) mixture as eluent) gave 1,2-bis(1-ethyl-1Н-pyr-
azol-3-yl)diazene (2b) (0.081 g, 37% yield, identified by m.p.
180—181 °С (cf. Ref. 3: m.p. 180 °С)) and previously described3
1Н NMR spectra) and 1,2-bis(4-chloro-1-ethyl-1Н-pyrazol-3-
yl)diazene) (4b) (0.049 g, 17% yield, identified by NMR spectro-
scopy and HRMS). The aqueous solution remained after extrac-
tion was concentrated in vacuo, NaOH was added (to рН ≈ 10)
with stirring, and the mixture was worked up as described above.
3-Amino-4-chloro-1-ethyl-1Н-pyrazole (3b) (0.012 g, 40% yield,
identified using NMR spectroscopy and HRMS) and unreacted
aminopyrazole 1b (0.013 g, 94% conversion, identified using
TLC and NMR spectroscopy) were isolated.
1,2-Bis(1,5-dimethyl-1Н-pyrazol-3-yl)diazene (2c) was iden-
tified by m.p. 252—253 °С (cf. Ref. 3: m.p. 252 °С) and previ-
ously described3 1Н NMR spectra.
3-Amino-4-chloro-1,5-dimethyl-1Н-pyrazole (3c). White
crystals. M.p. 108 °С. Rf 0.23 (petroleum ether—ethyl acetate
(1 : 2) as eluent). 1Н NMR, δ: 2.15 (s, 3 H, Me); 3.51—3.58
(m, 5 H, Me + NH2). 13С NMR, δ: 11.2 (СМе), 37.8 (NMe),
94.4 (ССl), 135.8 (CMe), 149.3 (CNH2). MS, found: m/z
146.0477 [M]+. Calculated for C5H8ClN3: 146.0480.
1,2-Bis(4-chloro-1,5-dimethyl-1Н-pyrazol-3-yl)diazene (4c).
Yellow crystals. M.p. 248—249 °С. Rf 0.71 (chloroform—methanol
(10 : 1) as eluent). 1Н NMR, δ: 2.34 (s, 6 H, CH3); 3.90 (s, 6 H,
CH3). 13С NMR, δ: 10.0 (2 СМе), 38.5 (2 NMe), 95.2 (2 CCl),
138.6 (2 CMe), 156.3 (2 CN). MS, found: m/z 287.0572 [M]+.
Calculated for C10H12Cl2N6: 287.0573.
1,2-Bis(1-methyl-5-trifluoromethyl-1Н-pyrazol-3-yl)diazene
(2d). Yellow crystals. M.p. 145—147 °С. Rf 0.83 (petroleum
ether—ethyl acetate (1 : 2) as eluent). 1Н NMR, δ: 4.14 (s, 6 H,
CH3); 7.06 (s, 2 Н, СН). 13С NMR, δ: 38.9 (2 NMe), 97.2
1
(2 CН), 119.5 (q, 2 СF3, JCF = 269.4 Hz); 133.9 (q, 2 CCF3,
2JCF = 39.2 Hz), 161.7 (2 CN). MS, found: m/z 327.0786
[M + H]+. Calculated for C10H8F6N6: 327.0787.
Reactions of aminopyrazoles 1a—e and 7а with a neutral solu-
tion of NaOBr (general procedure) (see Table 2, entries 1, 3, 5,
and 7—9). Aminopyrazole 1a—c,e or 7a (0.002 mol) was added
to the preliminarily prepared as described above neutral solution
of NaOBr (0.002 mol). In entry 7, 0.004 mole of NaOBr and
0.002 mole of aminopyrazole 1d were used. The reaction mixture
was stirred, worked up, and analyzed as described above for the
reaction of compound 1b with NaOCl.
3-Amino-4-bromo-1-methyl-1H-pyrazole (7a) was identified
by m.p. 97 °С (cf. Ref. 9: m.p. 97—98 °С) and previously de-
scribed9 1Н NMR spectra.
1,2-Bis(4-bromo-1-methyl-1Н-pyrazol-3-yl)diazene (8a) was
identified by m.p. 212 °С (cf. Ref. 9: m.p. 211—213 °С) and
previously described9 1Н NMR spectra.
3-Amino-4-bromo-1-ethyl-1H-pyrazole (7b). Oil. The prod-
uct was identified by previously described9 1Н and 13С NMR
spectra.
3-Amino-4-chloro-1-ethyl-1Н-pyrazole (3b). Oil. Rf 0.80
(petroleum ether—ethyl acetate (1 : 2) as eluent). 1Н NMR,
δ: 1.41 (t, 3 Н, Me, J = 7.1 Hz); 3.53 (br.s, 2 Н, NH2); 3.94
(q, 2 Н, СН2, J = 7.1 Hz); 7.18 (s, 1 Н, СН). 13С NMR, δ:
14.9 (Me), 46.7 (CH2), 95.0 (CCl), 126.4 (CH), 150.2 (CNH2).
MS, found: m/z 146.0480 [M]+. Calculated for C5H8ClN3:
146.0480.
1,2-Bis(4-chloro-1-ethyl-1Н-pyrazol-3-yl)diazene (4b). Yellow
crystals. M.p. 163—164 °С. Rf 0.23 (petroleum ether—ethyl
acetate (1 : 2) as eluent). 1Н NMR, δ: 1.54 (t, 6 Н, Me, J = 7.1 Hz);
4.24 (q, 4 Н, СН2, J = 7.1 Hz); 7.50 (s, 2 Н, СН). 13С NMR,
δ: 15.2 (2 Me), 48.7 (2 CH2), 105.62 (2 CCl), 128.9 (2 CH),
156.3 (2 CN). MS, found: m/z 146.0771 [M]+. Calculated for
C10H12Cl2N6: 146.0480.
Reactions of aminopyrazoles 1c and 1d with a neutral solution
of NaOCl (general procedure) (see Table 1, entries 6 and 8).
Aminopyrazole 1c or 1d (0.002 mol) was added to the preliminar-
ily prepared as described above neutral solution of NaOCl
(0.004 mol). The reaction mixture was stirred, worked up, and
analyzed as described above for the reaction of compound 1b
with NaOCl.
1,2-Bis(4-bromo-1-ethyl-1Н-pyrazol-3-yl)diazene (8b) was
identified by m.p. 156 °С (cf. Ref. 9: m.p. 154—156 °С) and
previously described9 1Н NMR spectra.
3-Amino-4-bromo-1,5-dimethyl-1Н-pyrazole (7c) was iden-
tified by m.p. 111 °С (cf. Ref. 9: m.p. 111—113 °С) and previ-
ously described9 1Н NMR spectra.
1,2-Bis(4-bromo-1,5-dimethyl-1Н-pyrazol-3-yl)diazene (8c)
was identified by m.p. 248 °С (cf. Ref. 9: m.p. 247—249 °С) and
previously described9 1Н NMR spectra.
1,2-Bis(1,4-dimethyl-1Н-pyrazol-3-yl)diazene (2e) was iden-
tified by m.p. 190 °С (cf. Ref. 2: m.p. 190 °С) and previously
described2 1Н NMR spectra.
Reactions of aminopyrazoles 1a—c with an aqueous solution
of NaOCl containing NaOH (general procedure) (see Table 3,
entries 2, 4, and 5). Aminopyrazole 1a—c (0.002 mol) and NaOH
(0.006 mol) were added to the preliminarily prepared as described
above neutral solution of NaOCl (0.002 mol). The reaction
mixture was stirred, worked up, and analyzed as described above
for the reaction of compound 1b with NaOCl.
Reactions of aminopyrazoles 1a—c with an aqueous solution
of NaOBr containing NaOH (general procedure) (see Table 3,

Lyalin et al.
170
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 1, January, 2021
entries 8—10). Aminopyrazole 1a—e (0.002 mol) and NaOH
(0.006 mol) were added to the preliminarily prepared as described
above neutral solution of NaOBr (0.002 mol). The reaction
mixture was stirred, worked up, and analyzed as described above
for the reaction of compound 1b with NaOCl.
5. J. Catalán, M. Menéndez, J. Laynez, R. M. Claramunt,
M. Bruix, J. De Mendoza, J. Elguero, J. Heterocycl. Chem.,
1985, 22, 997.
6. B. V. Lyalin, V. A. Petrosyan, B. I. Ugrak, Russ. J. Electrochem.,
2008, 44, 1320.
7. R. Zawalski, P. Kovacic, J. Org. Chem, 1979, 44, 2130.
8. I. M. Kolthoff, R. Belcher, V. A. Stenger, G. Matsuyama,
Volumetric Analysis, Vol. 3, Intersci. Publ., New York—
London, 1957, 714 pp.
9. B. V. Lyalin, V. L. Sigacheva, V. A. Kokorekin, T. Yu. Dutova,
G. M. Rodionova, V. A. Petrosyan, Russ. Chem. Bull., 2018,
67, 510.
References
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Received February 3, 2020;
in revised form March 12, 2020;
accepted August 31, 2020