Mechanism of the zinc-catalyzed addition of azide ion to unsaturated compounds: Synthesis of 5-substituted 1Н-tetrazoles from nitriles and of 1-substituted 1Н-tetrazole-5-thiols from isothiocyanates

Article abstract of DOI:10.1134/S1070363217040119

The mechanism of the formation of 5-substituted 1H-tetrazoles from organic nitriles and thiocyanates in the presence of NaN₃ and ZnCl₂ in aliphatic alcohols was studied. The results of this study allowed efficient methods of synthesis of substituted tetrazoles from nitriles, thiocyanates, and isothiocyanates to be proposed.

Full text of DOI:10.1134/S1070363217040119

ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 4, pp. 731–738. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © L.V. Myznikov, S.V. Vorona, T.V. Artamonova, Yu.E. Zevatskii, 2017, published in Zhurnal Obshchei Khimii, 2017, Vol. 87, No. 4,
pp. 597–604.
Mechanism of the Zinc-Catalyzed Addition of Azide Ion
to Unsaturated Compounds: Synthesis of 5-Substituted
1Н-Tetrazoles from Nitriles and of 1-Substituted
1Н-Tetrazole-5-thiols from Isothiocyanates
L. V. Myznikova*, S. V. Voronaa, T. V. Artamonovaa, and Yu. E. Zevatskiia,b
a St. Petersburg State University of Technology and Design, ul. Bol’shaya Morskaya 18, St. Petersburg, 191186 Russia
*е-mail: myznikov_lv@mail.ru
b Ul’yanov (Lenin) State Electrotechnical University “LETI,” St. Petetrsburg, Russia
Received December 15, 2016
Abstract—The mechanism of the formation of 5-substituted 1H-tetrazoles from organic nitriles and thiocyanates
in the presence of NaN3 and ZnCl2 in aliphatic alcohols was studied. The results of this study allowed efficient
methods of synthesis of substituted tetrazoles from nitriles, thiocyanates, and isothiocyanates to be proposed.
Keywords: 5-substituted 1Н-tetrazoles, 1-substituted 1Н-tetrazole-5-thiols, [2+3]-cycloaddition, zinc salts, catalysis
DOI: 10.1134/S1070363217040119
Tetrazoles attract interest which increases with
expanding range of practical applications of these
compounds. Tetrazole derivatives are widely used as
components of pharmaceuticals, energetic materials,
gas-generating compositions, and in some other fields
[1–3].
allows successful synthesis at a lower temperature and
over a shorter time and, therefore, helps in approaching
the problem of the synthesis of tetrazoles from thermally
unstable thiocyanates and deactivated aliphatic nitriles.
The considerable advantages offered by the system
NaN3 + ZnCl2 in aliphatic alcohols led us to suggest
that detailed study of the role of each of its com-
ponents would make it possible to expand the applica-
tion field of this system.
At present 5-substituted 1Н-tetrazoles are syn-
thesized by reactions of hydrazoic acid salts with
nitriles and thiocyanates in the presence of various
reagents and catalysts like iodine [4], ammonium salts
[5], copper [6], and other metals in DMF and scandium
[7], bismuth [8], and zinc [9] in water. Lately a lot of
papers have been published on the use of recyclable
heterogeneous catalysts in the synthesis of tetrazoles
[10, 11]. Unfortunately, comparing the reaction condi-
tions in the mentioned and other recent publication we
can conclude that no essential progress has been made
in the synthesis of tetrazoles, because these methods
do not differ much both in reaction temperature and
time with the method of synthesis of tetrazoles in the
presence of ammonium chloride in DMF developed
over 50 years ago [12].
First, we studied the kinetic regularities of the
process by an example of the model reaction of benzyl
thiocyanate (1а) with NaN3 in the presence of ZnCl2
in isopropanol (heterogeneous process) at 50°С (reac-
tion (1)].
S
N
1a
ZnCl2, NaN3
H
(1)
At the same time we previously [13] showed that
the catalytic system NaN3 + ZnCl2 in aliphatic alcohols
сompares favorably with the catalytic systems commonly
used in the synthesis of 5-substituted tetrazoles since it
i-PrOH, 50oC, 1.5 h
S
N
N
N
N
2a
731

732
MYZNIKOV et al.
Time, min
Time, min
Fig. 1. Kinetic curves of the consumption of (1) benzyl
thiocyanate and (2) accumulation of 5-(benzylsulfanyl)-1Н-
tetrazole in i-PrOH at 50°С in the reaction with a 1 : 1 : 1
benzyl thiocyanate : NaN3 : ZnCl2 molar ratio.
Fig. 2. Kinetic curves of the consumption of (1) benzyl
thiocyanate and (2) accumulation of 5-(benzylsulfanyl)-1Н-
tetrazole in i-PrOH at 50°С in the reaction with a 1 : 8 : 8
benzyl thiocyanate : NaN3 : ZnCl2 molar ratio.
The reaction was performed both with equimolar
mounts of reagents and with deficienty of benzyl
thiocyanate 1а. In the first case, the kinetic curves of
benzyl thiocyanate 1а consumption and product 2а
accumulation were linear (Fig. 1). The zero reaction
order in thiocyanate shows that the rate of the reagents
diffusion to the phase interface is lower than the
reaction rate. However, with a 8-fold molar excess of
NaN3 and ZnCl2 with respect to benzyl thiocyanate 1а
both mentioned kinetic curves were no longer linear
(Fig. 2). This result suggests a change in the rate-
limiting stage: the rate of chemical reaction of
compound 1а becomes lower that the diffusion rate of
the reagents to the phase interface. The reaction is now
first-order in benzyl thiocyanate.
plexometric titration showed that more than 90% of Zn
used in the reaction was present in the solution.
Thus, the rate-limiting stage of the synthesis of
tetrazoles in isopropanol is the reaction of ZnCl2 and
NaN3 to form NaCl and a reactive intermediate,
specifically, the mixed zinc salt ZnClN3, and the latter
enters cycloaddition with nitrile or thiocyanate [reac-
tion (2)].
i-PrOH
ZnCl2 + NaN3
(2)
ZnClN3 + NaCl↓.
50oC, 1.5 h
Further on we studied the kinetics of the model
reaction in ethylene glycol. The latter solvent provides
homogeneity of the system over the entire process. The
kinetic curves for the reaction of ZnCl2, NaN3, and
benzyl thiocyanate in ethylene glycol are presented in
Figs. 3 and 4. The calculated partial reaction order in
benzyl thiocyanate was 1 both with deficienty of thio-
cyanate and with equimolar amounts of the reagents,
implying that this reaction is not diffusion-controlled.
It was found that the rates of formation of 5-substituted
1Н-tetrazoles from compounds 1а–1f in ethylene
glycol were higher compared to the heterogeneous
process, but the yields of the reaction products in the
two processes were comparable [reaction (3), see the
table].
The obtained data show that the limiting stage of
the reaction in isopropanol at a 1 : 1 reagent molar
ratio involves the formation of a reactive species, and
the reaction kinetics depend on the solubility of the
reagents. Of all the reaction participants, the least
soluble in aliphatic alcohols is NaN3, and just its dis-
solution controls the overall reaction rate. The
evidence showing that the reaction is diffusion-con-
trolled is provided by the fact that all the 5-substituted
sulfanyl-1Н-tetrazoles obtained in [13], irrespective of
the substituent, formed within the same time (1.5 h).
It was found that the reaction of equimolar amounts
of NaN3 and ZnCl2 in isopropanol for 1.5 h at 50°С in
the absence of organic thiocyanate formed a pre-
cipitate. According to the results of argentometric
titration, this precipitate was a 95% NaCl. Com-
H
R
N
ZnCl2, NaN3
R
(3)
N
N
N
N
2a_2f
1a_1f
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MECHANISM OF THE ZINC-CATALYZED ADDITION OF AZIDE ION
733
Time, min
Time, min
Fig. 3. Kinetic curves of the consumption of (1) benzyl
thiocyanate and (2) accumulation of 5-(benzylsulfanyl)-1Н-
tetrazole in ethylene glycol at 50°С in the reaction with a
1 : 1 : 1 benzyl thiocyanate : NaN3 : ZnCl2 molar ratio.
Fig. 4. Kinetic curves of the consumption of (1) benzyl
thiocyanate and (2) accumulation of 5-(benzylsulfanyl)-1Н-
tetrazole in ethylene glycol at 50°С in the reaction with a
1 : 8 : 8 benzyl thiocyanate : NaN3 : ZnCl2 molar ratio.
It should be noted that in the synthesis of tetrazoles
from deactivated nitriles (compound 1f), which is a
rather long process, the fact that the reaction rate is no
longer controlled by diffusion does not have such a
strong accelerating effect.
However, we could not obtain any experimental
evidence for the formation of imino ethers, and there-
fore, to substantiate this hypothesis, therefore we per-
formed quantum-chemical calculations using the
example of acetonitrile. It was found that the limiting
stage of the formation of 5-substituted 1H-tetrazole
from acetonitrile and ZnClN3 is the nucleophilic
substitution of the ether group in the imino ether
intermediate by the azido group to form an imidoyl
azide intermediate with the activation energy of
45.24 kJ/mol. At the same time in the absence of
Lewis acid, when alcohol does not add to unactivated
nitrile, the limiting stage of the formation of 5-substi-
tuted 1H-tetrazole from MeCN and NaN3 is the addi-
tion of the azide ion to nitrile to form an imidoyl azide
intermediate with the activation barrier of 96.19 kJ/mol.
Earlier we showed [13] that the yield of 5-
substituted 1Н-tetrazoles depended on the nature of the
alcohol: the yields both in the sterically compact
MeOH and in the sterically bulky tert-butanol proved
to be much lower than in ethanol, isopropanol, n-propanol,
and n-butanol. Therewith, the solvents traditionally
used in tetrazole synthesis (DMSO, DMF, MeCN,
H2O) were inefficient at such a low temperature.
The above findings suggest that alcohol in the
synthesis of 5-substituted 1H-tetrazoles acts not only
as a solvent but also as a reagent. As known, organic
nitriles can react with alcohols to form imino ethers.
We assumed that in our case zinc compounds present
in the reaction mixture favor the formation of an imino
ether intermediate [reaction (4)].
In summary, the obtained data allow us a sugges-
tion of the following mechanism of the [2+3]-cycloaddi-
tion of NaN3 to organic nitriles and thiocyanates in the
presence of ZnCl2 in aliphatic alcohols (Scheme 1).
The mixed zinc salt ZnClN3 formed in situ in the reac-
tion of NaN3 and ZnCl2 acts both as a source of azide
ions and as a Lewis acid. The latter favors polarization
of the CN bond, resulting in the alcohol addition to
nitrile to form the intermediate imino ether. Further on,
the intermediate reacts with azide ion to form the
intermediate imidoyl azide, because the energy barrier
for the nucleophilic substitution of the ether by azido
group is much lower than for the addition of the azide
ion to a unactivated nitrile. The resulting imidoyl azide
intermediate undergoes cyclization to form zinc salt of
5-substituted 1H-tetrazole, which is then decomposed
with alkali and acidified to isolate the target product.
R1
C
N
R1
C
N
R2OH, ZnClN3
50oC
R1
C
O
(4)
NH
R2
Under these conditions the lower efficiency of the
reaction in methanol is due to the high stability of the
imino ether intermediate, which originates from the
comparable nucleophilicity of the methoxy group and
azide ion. In the case of tert-butanol, the yield of the
product decreased by steric reasons.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 4 2017

734
MYZNIKOV et al.
Synthesis of 5-substituted 1Н-tetrazoles in heterogeneous (monoatomic aliphatic alcohols) and homogeneous (ethylene
glycol) conditions
Time, h
Comp. no.
Tetrazole
Т, °С
ROH [13]
HO(CH2)2OH
0.50
1а
50
1,5
(i-PrOH)
H
N
S
N
N
N
1b
50
1,5
(i-PrOH)
0.25
H
S
N
C6H11
N
N
N
1c
95
95
2
1.00
0.67
H
N
(p-PrOH)
N
N
N
1d
1
(p-PrOH)
H
N
N
N
N
1e
1f
95
95
1
0.33
7.00
SH
N
HN
(p-PrOH)
N
N
N
N
HN
N
7
H3CO
(p-PrOH)
H
N
N
N
N
We suggested that the in situ formation of the
reactive mixed zinc salt ZnClN3 could also drive other
cycloaddition reactions. Among the most common
cycloaddition reactions of inorganic azides an
important role belongs to the synthesis of 1-substituted
1Н-tetrazole-5-thiols from organic isothiocyanates,
which usually requires prolonged boiling in water [14].
R
NaN3, ZnCl2, MeCN
80oC, 1 h
N
(5)
R
N
C
S
N
N
N
3а_3f
4а_4f (65_99%)
R = allyl (а), PhCH2 (b), Ph (c), (2-COOMe)C6H4 (d),
(2-F2HCO)C6H4 (e), 1-naphthyl (f).
Indeed, aromatic and aliphatic isocyanates 3а–3f
reacted with NaN3 in the presence of ZnCl2 in MeCN
to form 1-substituted 1Н-tetrazole-5-thiols 4а–4f within
a short time at a fairly low temperature [reaction (5)].
The yields of tetrazole-5-thiols in aliphatic alcohols
proved to be lower than in MeCN, probably, because
of O-thiocarbamate formation. It should be noted that
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 4 2017

MECHANISM OF THE ZINC-CATALYZED ADDITION OF AZIDE ION
735
Scheme 1.
R1
R1
ZnClN3
R1
C
R2OH
C
O
NH
R2
C
N
+
N
_R2OH
N3
R1
R1
(1) OH−
(2) H+
+
C N
N ZnCl
C NH
ZnCl
N
N
N
N
N
in the absence of ZnCl2 no formation of 1-substituted
1Н-tetrazole-5-thiols from isothiocyanates in MeCN
was observed.
The precipitate that formed was filtered off, washed
with water, and dried in air. Yield 1.17 g (91%),
colorless crystals, mp 135–137°C (EtOH) (mp 134–
135°C [15]). IR spectrum, ν, cm–1: 2895 (CH2), 1532
Thus, the key stage that controls the cycloaddition
of the azide ion to nitriles (thiocyanates) and
isothiocyanates is the in situ formation of the mixed
salt ZnClN3. The use of the NaN3–ZnCl2 system much
decreases the time and temperature of the synthesis of
1-substituted 1Н-tetrazole-5-thiols from isothio-
cyanates. In the case of nitriles, the formation of the
intermediate imino ether additionally decreases the
activation energy, which, together with the fact that the
reaction in ethylene glycol is no longer diffusion-
controlled, allows us to consider the proposed
procedure as the presently most efficient synthetic
approach to 5-substituted 1Н-tetrazoles.
1
(C=N), 1454 (Ph), 1079 (C–N), 704 (C–S). Н NMR
spectrum, δ, ppm: 4.47 s (2H, CH2), 7.20–7.28 m (3H,
H-Ar), 7.35–7.37 m (2H, H-Ar). 13С NMR spectrum,
δС, ppm: 36.51 (CH2), 128.20 (Ph), 129.09 (Ph),
129.45 (Ph), 137.22 (Ph), 154.23 (C–N). Found, %: C
49.87; H 4.35; N 29.00; S 16.79. C8H8N4S. Calculated,
%: C 49.98; H 4.19; N 29.14; S 16.68.
Compounds 2b–2f were prepared in a similar way.
5-(Hexylsulfanyl)-1Н-tetrazole (2b). Yield 1.03 g
(79%), colorless crystals, mp 85–87°C (CCl4) (mp 85°C
[15]). IR spectrum, ν, cm–1: 2948 (CH3), 2857 (CH2),
1
1522 (C=N), 1041 (C–N), 718 (C–S). Н NMR spec-
trum, δ, ppm: 0.80 t (3H, CH3, J = 12.0 Hz), 1.18–1.22
m (4H, CH2CH2), 1.28–1.36 m (2H, CH2), 1.58–1.65
m (2H, CH2), 3.18 t (2H, CH2, J = 12.0 Hz). 13С NMR
spectrum, δС, ppm: 14.35 (CH3), 22.47 (CH2), 28.02
(CH2), 29.54 (CH2), 31.15 (CH2), 32.46 (CH2), 154.63
(C–N). Calculated, %: C 45.13; H 7.58; N 30.08; S
17.21. C7H14N4S. Found, %: C 45.01; H 7.50; N 29.99;
S 17.06.
EXPERIMENTAL
The IR spectra were registered on a Shimadzu
FTIR-8400S spectrometer in KBr pellets. The Н and
1
13С NMR spectra were obtained on a JEOL JNM-ECX
400A spectrometer (400 and 100 MHz, respectively) in
DMSO-d6, internal reference residual proton signals of
the solvent. Elemental analysis was performed on a
LECO CHNS-932 analyzer. The melting points were
measured on a Koeffler heating block. The purity and
individuality of the synthesized compounds were
controlled by TLC on Silufol UV-254 plates.
5-Benzyl-1H-tetrazole (2c). Yield 1.14 g (83%),
colorless crystals, mp 123–124°C (EtOAc) (mp 123–
124°C [16]). IR spectrum, ν, cm–1: 2852 (CH2), 1596
1
(C=N), 1494 (Ph), 1176 (C–N). Н NMR spectrum, δ,
ppm: 4.26 s (2H, CH2), 7.20–7.32 m (5H, H-Ar), 16.18
s (1H, NH). 13С NMR spectrum, δС, ppm: 29.43 (CH2),
127.55 (Ph), 128.67 (Ph), 129.19 (Ph), 136.45 (Ph),
155.77 (C–N). Found, %: C 60.14; H 5.17; N 35.05.
C8H8N4. Calculated, %: C 59.99; H 5.03; N 34.98.
5-(Benzylsulfanyl)-1Н-tetrazole (2a). Sodium azide,
0.52 g (8.0 mmol), and 1.10 g (8.0 mmol) of ZnCl2
were added to 30 mL of ethylene glycol. The mixture
was heated with stirring at 50°C, after which 1 g
(6.7 mmol) of benzyl thiocyanate was added. The
reaction mixture was stirred for 0.5 h, and the solvent
was then removed in a vacuum. The residue was
treated with 5% aqueous NaOH (50 mL) with stirring
for 20 min, and the resulting suspension was filtered.
The aqueous layer was acidified with conc. HCl to рН 1.
5-Phenyl-1H-tetrazole (2d). Yield 1.18 g (83%),
colorless crystals, mp 214–216°C (EtOAc) (mp 215–
216°C [9]). IR spectrum, ν, cm–1: 1564 (C=N), 1483
1
(Ph), 1163 (C–N). Н NMR spectrum, δ, ppm: 7.49–
7.50 m (3H, H-Ar), 7.98–8.00 m (2H, H-Ar), 15.78 s
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 4 2017

736
MYZNIKOV et al.
(1H, NH). 13С NMR spectrum, δС, ppm: 124.67 (Ph),
127.47 (Ph), 129.82 (Ph), 131.63 (Ph), 155.81 (C–N).
Found, %: C 57.42; H 4.19; N 38.23. C7H6N4.
Calculated, %: C 57.53; H 4.14; N 38.34.
1-Benzyl-1Н-tetrazole-5-thiol (4b). Yield 0.84 g
(65%), colorless crystals, mp 142–144°C (H2O) (mp
144°C [14]). IR spectrum, ν, cm–1: 2930 (CH2), 2556
(SH), 1504 (C=N), 1452 (Ph), 1183 (C–N), 708 (C–S).
1Н NMR spectrum, δ, ppm: 5.38 s (2Н, СH2), 7.24–
7.30 m (3H, Н-Ph), 7.36–7.38 m (2H, Н-Ph). 13С NMR
spectrum, δС, ppm: 49.7 (CH2), 128.3 (Ph), 128.7 (Ph),
129.1 (Ph), 134.8 (Ph), 164.8 (С–S). Found, %: C
50.08; H 4.02; N 29.07; S 16.82. C8H8N4S. Calculated,
%: C 49.98; H 4.19; N 29.14; S 16.68.
5,5'-Benzene-1,2-diylbis(1H-tetrazole) (2e). Yield
1.54 g (92%), colorless crystals, mp 230–232°C (EtOH)
(mp 228–230°C [9]). IR spectrum, ν, cm–1: 1546 (C=N),
1
1469 (Ph), 1064 (C–N). Н NMR spectrum, δ, ppm:
7.74–7.78 m (2H, H-Ar), 7.88–7.92 m (2H, H-Ar). 13С
NMR spectrum, δС, ppm: 125.03 (Ar), 131.32 (Ar),
131.82 (Ar), 155.24 (C–N). Found, %: C 45.02, H
2.77; N 52.39. C8H6N8. Calculated, %: C 44.86; H 2.82
N 52.32.
1-Phenyl-1Н-tetrazole-5-thiol (4c). Yield 1.31 g
(99%), colorless crystals, mp 148–150°C (H2O) (mp
150°C [14]). IR spectrum, ν, cm–1: 2549 (SH), 1510
1
(C=N), 1457 (Ph), 1153 (C–N), 725 (C–S). Н NMR
5-(4-Methoxyphenyl)-1H-tetrazole (2е). Yield
1.21 g (91%), colorless crystals, mp 232–234°C
(EtOAc) (231–232°C [9]). IR spectrum, ν, cm–1: 2984
(CH3), 1501 (C=N), 1443 (Ph), 1265 (C–O–C=), 1183
spectrum, δ, ppm: 7.44–7.54 m (3Н, H-Ph), 7.89–7.92
m (2H, Н-Ph). 13С NMR spectrum, δС, ppm: 124.0
(Ph), 129.3 (Ph), 134.8 (Ph), 164.1 (С–S). Found, %: C
47.29; H 3.50; N 31.56; S 18.11. C7H6N4S. Calculated,
%: C 47.18; H 3.39; N 31.44; S 17.99.
1
(C–N). Н NMR spectrum, δ, ppm: 3.77 s (3H, CH3),
7.08 d (2H, H-Ar, J = 4.0 Hz), 7.93 d (2H, H-Ar, J =
12.0 Hz), 16.47 s (1H, NH). 13С NMR spectrum, δС,
ppm: 55.88 (CH3), 115.27 (Ar), 116.79 (Ar), 129.13
(Ar), 155.24 (C–N), 161.95 (C–O). Found, %: C
54.50; H 4.57; N 31.82. C8H8N4O. Calculated, %: C
54.59; H 4.66; N 31.89.
Methyl 2-(5-mercapto-1Н-tetrazol-1-yl)benzoate
(4d). Yield 0.76 g (62%), colorless crystals, mp 144–
146°C (EtOH). IR spectrum, ν, cm–1: 2913 (CH3),
2566 (SH), 1719 (COO), 1601 (C=N), 1491 (Ar), 1191
1
(C–N), 703 (C–S). Н NMR spectrum, δ, ppm: 3.70 s
(3H, CH3), 7.56 d (1H, H-Ar, J = 8.0 Hz), 7.69 t (1H,
H-Ar, J = 16.0 Hz), 7.79 t (1H, H-Ar, J = 16.0 Hz),
8.05 d (1H, H-Ar, J = 8.0 Hz). 13С NMR spectrum, δС,
ppm: 52.8 (CH3), 128.3 (C Ar), 129.3 (Ar), 131.1 (Ar),
131.6 (Ar), 132.4 (Ar), 133.7 (Ar), 164.4 (C–S), 167.3
(C=O). Found, %: C 45.61; H 3.58; N 23.79; S 13.40.
C9H8N4O2S. Calculated, %: C 45.75; H 3.41; N 23.72;
S 13.57.
1-Allyl-1Н-tetrazole-5-thiol (4a). Sodium azide,
0.79 g (12.1 mmol), and 1.65 g (12.1 mmol) of ZnCl2.
were added to 30 mL of MeCN. The mixture was
heated with stirring until boiling (80°C), and then 1 g
(10.1 mmol) of allyl isothiocyanate was added. The
reaction mixture was stirred for 1 h at 80°C, and the
solvent was then removed in a vacuum. The residue
was treated with 5% aqueous NaOH (50 mL) with
stirring for 20 min. The suspension was filtered, and
the filtrate was treated with chloroform (2×10 mL) to
remove impurities. The aqueous layer was acidified
with conc. HCl to рН 1. The precipitate that formed
was filtered off, washed with water, and dried in air.
Yield 0.97 g (68%), yellowish crystals, mp 67–69°C
(EtOH) (mp 69°C[14]). IR spectrum, ν, cm–1: 2937
(CH2), 2560 (SH), 1645 (C=C), 1504 (C=N), 1182
1-[2-(Difluoromethoxy)phenyl]-1Н-tetrazole-5-
thiol (4e). Yield 0.98 g (81%), colorless crystals, mp
134–136°C (EtOH). IR spectrum, ν, cm–1: 2927 (CH),
2561 (SH), 1605 (C=N), 1492 (Ar), 1281 (=C–O–C),
1
1181 (C–N), 1054 (CF2), 721 (C–S). Н NMR spec-
trum, δ, ppm: 6.97 t (1H, CHF2, J = 12.0 Hz), 7.39–
7.44 m (2H, H-Ar), 7.54–7.62 m (2H, H-Ar). 13С NMR
spectrum, δС, ppm: 113.8 (Ar), 116.4 (Ar), 120.1 (Ar),
125.9 (Ar), 130.1 (Ar), 147.1 (Ar), 164.4 (C–S), 167.3
(CHF2). Found, %: C 39.21; H 2.59; N 23.11; S 13.01.
C8H6F2N4OS. Calculated, %: C 39.34; H 2.48; N
22.94; S 13.13.
1
(C–N), 741 (C–S). NMR spectrum Н, δ, ppm: 4.78 d
(2Н, СН2, J = 8.0 Hz), 5.25 d (2Н, СН2, J = 12.0),
5.87–5.97 m (1Н, СH). NMR spectrum 13С, δС, ppm:
48.7 (СH2), 119.9 (CH2), 130.5 (CH), 164.5 (С–S).
Found, %: C 33.60; H 4.41; N 39.49; S 22.43.
C4H6N4S. Calculated, %: C 33.79; H 4.25; N 39.40; S
22.55.
1-(Naphthalen-1-yl)-1Н-tetrazole-5-thiol (4f). Yield
0.97 g (79%), colorless crystals, mp 146–148°C
(EtOH). IR spectrum, ν, cm–1: 2553 (SH), 1504 (C=N),
1466 (Ar), 1183 (C–N), 727 (C–S). 1Н NMR spectrum,
δ, ppm: 7.39 d (1H, H-Ar, J = 8.0 Hz), 7.51–7.57 m
Сompounds 4b–4f were prepared in a similar way.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 4 2017

MECHANISM OF THE ZINC-CATALYZED ADDITION OF AZIDE ION
737
(2H, H-Ar), 7.63–7.67 m (2H, H-Ar), 8.00 d (1H, H-
Ar, J = 8.0 Hz), 8.09–8.11 m (1H, H-Ar). 13С NMR
spectrum, δС, ppm: 122.8 (Ar), 125.5 (Ar), 126.3 (Ar),
126.7 (Ar), 127.2 (Ar), 128.8 (Ar), 129.2 (Ar), 130.3
(Ar), 131.5 (Ar), 134.4 (Ar), 164.4 (C–S). Found, %: C
57.70; H 3.72; N 24.68; S 14.15. C11H8N4S. Cal-
culated, %: C 57.88; H 3.53; N 24.54; S 14.05.
(1 : 1); as a result, the precipitate dissolved completely.
The resulting solution was heated at 50°С. Samples for
HPLC analysis were taken in 5, 10, 15, 20, 25, 30, 40,
50, 60, 70, 80, 100, and 120 min after start of heating
(for the reaction with a 1 : 1 : 1 benzyl thiocyanate :
NaN3 : ZnCl2 molar ratio) and in 5, 10, 15, 20, 25, 30,
40, 50, 60, 75, and 90 min (for the reaction with a 1 :
8 : 8 benzyl thiocyanate : NaN3 : ZnCl2 molar ratio).
Kinetic measurements were performed on a
Shimadzu Prominence LC-20 chromatograph with diode
array, column Luna 5μm C18(2)100A 250×3 mm,
eluent MeCN–[90% Н2О (pH 3, H3PO4) + 10%
MeCN], 65:35; column temperature 35°С, flow rate
0.4 mL/min, λ 243 nm.
Sample preparation for the reaction in ethylene
glycol. Sodium azide was added to a hot (50°С)
solution of benzyl thiocyanate and ZnCl2 in ethylene
glycol. This moment was taken as the reaction start
time. In definite time intervals, 25-μL samples were
taken from the reaction mixture and diluted with 2 mL
of a solution containing H2O (pH 3, H3PO4) and
i-PrOH (1 : 1). Aliquots of the resulting solution were
analyzed by HPLC.
Two series of model reactions were used for kinetic
measurements, one in isopropanol (heterogeneous
process) and the other in ethylene glycol (homo-
geneous process). The reactions were performed at 50°С
under the following conditions:
Quantum-chemical calculations were performed
using GAMESS (developer the Quantum
Chemistry Group, Iowa State University,
http://www.msg.chem.iastate.edu/gamess/index.html).
The enthalpies of formation were obtained by the DFT
B3LYP/6-31G calculations. Solvent (ethanol) effects
were included by the PCM method. The calculated
energies were corrected for zero-point vibrational
energies.
– reaction in isopropanol with equimolar amounts
of the reagents: benzyl thiocyanate 0.10 g (0.67 mmol),
NaN3 0.04 g (0.67 mmol), ZnCl2 0.09 g (0.67 mmol),
isopropanol 10 mL;
– reaction in isopropanol with a 8-fold molar excess
of NaN3 and ZnCl2 with respect to benzyl thiocyanate:
benzyl thiocyanate 0.10 g (0.67 mmol), NaN3 0.34 g
(5.37 mmol), ZnCl2 0.73 g (5.37 mmol), isopropanol
10 mL;
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