Synthesis and structure of 1-tert-butyl-3-R-tetrazolium salts

Article abstract of DOI:10.1023/A:1012779315893

An effective method was developed for the synthesis of 1,3-disubstituted tetrazolium salts by the quaternization of 2-monosubstituted tetrazoles, including functionally substituted compounds, with tert-butanol in 72% perchloric acid. An X-ray diffraction

Full text of DOI:10.1023/A:1012779315893

Chemistry of Heterocyclic Compounds, Vol. 37, No. 8, 2001
SYNTHESIS AND STRUCTURE OF
1
-tert-BUTYL-3-R-TETRAZOLIUM SALTS
S. V. Voitekhovich, P. N. Gaponik, A. S. Lyakhov, and O. A. Ivashkevich
An effective method was developed for the synthesis of 1,3-disubstituted tetrazolium salts by the
quaternization of 2-monosubstituted tetrazoles, including functionally substituted compounds, with
tert-butanol in 72% perchloric acid. An X-ray diffraction investigation of examples of this series of
salts – 1-tert-butyl-3-(1-methylvinyl)- and 1,3-di-tert-butyltetrazolium perchlorates – was carried out.
Keywords: 1,3-disubstituted tetrazolium salts, 2R-tetrazoles, quaternization.
Tetrazolium salts have found the application in various regions of technology, biochemistry, medicine,
and chemical analysis and are promising as phase-transfer catalysts [1, 2]. Recently interest has arisen in the use
of tetrazolium salts as intermediates in organic synthesis [2], particularly for the production of mesoionic
tetrazoles [3] and various heterocyclic systems (benzoxazoles [4, 5], quinazolinediones [5], aziridines, tetrazines
[
6], etc.). The 5-unsubstituted tetrazolium salts are of considerable interest due to the possibility of their further
functionalization at the C(5) atom, the first examples of which were demonstrated in series of
1
1
,3-diaryltetrazolium salts [7]. The principal and the most accessible method for the synthesis of
,3-disubstituted tetrazolium salts includes the quaternization of 2-monosubstituted tetrazoles (2-MST) in
neutral or acidic media [1, 2]. The quaternization of 2-MST in acidic media was discovered recently and has
been studied little. It is known that 2-MST enter into reaction with tert-butanol in 48% HBF at room
temperature, leading to 1,3-disubstituted tetrazolium salts [8]. Higher yields of tetrazolium salts are obtained
during quaternization in perchloric acid, as we demonstrated for isolated examples of the quaternization of
4
2
-MST with diacetone alcohol [9]. Further investigation of quaternization in acidic media is of undoubted
interest, since this approach makes it possible to obtain salts that cannot be obtained by other methods.
In the present work we investigated N-tert-butylation of a series of 2-R-tetrazoles, including
functionally substituted compounds, in the presence of perchloric acid in order to develop effective methods of
synthesis and increase the set of 1,3-disubstituted tetrazolium salts. In the case of the reaction of tert-butanol
and 2-isopropyltetrazole (1a) in perchloric acid we studied the effect of the reagent ratio, the concentration of
acid, the addition of an organic phase, and the reaction time on the yield of tetrazolium salt 2a. The yield of the
salt is reduced by decrease in acidity of the medium and by decrease in the relative amount of acid (Table 1).
Additions of chloroform to 62% perchloric acid increase the quaternization rate, and this may be due to the
presence of a considerable proportion of the unprotonated form of the initial tetrazole 1a, which is clearly more
active towards the tert-butyl cation than the protonated tetrazole 1a. An important factor here is the good
solubility of both the initial tetrazole and the final product in chloroform.
_
_________________________________________________________________________________________
Scientific-Research Institute of Physicochemical Problems, Belorussian State University, Minsk; e-mail:
fhp@fhp.bsu.unibel.by. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1035-1046,
August, 2001. Original article submitted September 2, 1999.
0009-3122/01/3708-0949$25.00©2001 Plenum Publishing Corporation
949

TABLE 1. The Effect of the Quaternization Conditions of Tetrazole 1a on
the Yield of Tetrazolium Salt 2a
Molar ratio of reagents
Experiment
Holding time, h
Yield, %
tetrazole/acid*/alcohol
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1 : 1 : 1
1 : 2 : 2
1 : 2 : 1
1 : 2 : 1
1 : 2 : 1
1 : 2 : 1
1 : 2 : 1
1 : 2 : 1
1 : 2 : 1
1 : 2 : 1
1 : 2 : 1
1 : 2 : 1*2
48
48
48
2
57
93
96
23
43
75
96
5
12
50
66
31
39
48
63
5
24
48
2
5
0
1
2
3
4
5
24
48
5
12
24*3
48*4
2
1 : 2 : 1*
1 : 2 : 1*2
1 : 2 : 1*2
_
*
*
*
*
______
72% HClO
4
was used in expts. 1-7, 62% HClO in expts. 8-15.
4
2
Additional chloroform was added.
3
4
Vigorous agitation of the mixture for 12 h.
Vigorous agitation of the mixture for 24 h.
On the basis of the investigations we proposed the t-BuOH/72% HClO system as an effective
4
quaternization agent for the synthesis of 1-tert-butyl-3-R-tetrazolium salts 2 from 2-MST (Table 2). As a result
of the use of this system functionally substituted tetrazoles as well as alkyltetrazoles were submitted
successfully to tert-butylation; their functional groups were not affected. This quaternization system is more
effective than the t-BuOH/48% HBF
4
system, as shown by comparison of the yields of the respective salts
during the tert-butylation of tetrazoles 1b,e in 72% HClO
4
and 48% HBF [8].
4
Bu-t
N
N
N
t-BuOH
N
N
N
N
+
CH
CH
–
HClO
4
ClO4
N
R
R
1
a–h
2a–h
1
, 2 – a R = i-Pr, b R = Me, c R = Et, d R = t-Bu, e R = CH
2
CH=CH ,
2
f R = CH(Me)=CH , g R = CH(Me)CH Br, h R = CH CH COMe
2
2
2
2
An important factor affecting the quaternization rate and the yield of tetrazolium salt is the solubility of
the latter in the reaction mixture. This showed up significantly in the synthesis of the salt 2f. A high yield of the
latter (84%) is obtained after only 2 h of interaction of the reagents, whereas the yield of the product 2a under
analogous conditions amounts to only 23%. This difference is due to the low solubility of the salt 2f in the
reaction mixture – it starts to crystallize already 5-10 min after the reagents are mixed.
9
50

TABLE 2. The Characteristics of the Synthesized Compounds
Found, %
1Н NMR spectrum, ppm
Other signals
Com-
Empirical
formula
——————
Yield,
%
mp, °C
Calculated, %
pound
С
Н
N
Cl
НcyclС
t-Bu
2
2
2
2
a
b
c
С8H17ClN4O4
C6H13ClN4O4
С7H15ClN4O4
C9H19ClN4O4
130-131
150 (dec.)
133-135
36.01
6.40
6.34
20.95
20.90
13.12
13.06
10.49
10.48
10.51
10.49
1.70
1.72
1.73
1.73;
1.65 (d, 6Н, 2Me); 5.35 (m, 1Н, CH)
4.62 (s, 3Н, Me)
96
95
80
74
3
5.82
30.23
5.69
23.25
14.91
2
9.95
5.45
23.28
14.73
33.21
6.02
5.94
22.12
22.00
13.79
13.92
1.64 (t, 3Н, Me); 5.01 (q, 2Н, CH2)
—
3
3.01
d
120-122*
38.16
6.96
19.64
12.73
3
8.23
6.73
19.82
12.57
1
.78
2
2
2
2
3
3
e
f
С8H15ClN4O4
С8H15ClN4O4
С8H16BrClN4O4
С9H17ClN4O4
С11H24ClN4O5
С11H24ClN4O5
143-145
145 (dec.)
78-80
97-99
*2
35.91
5.88
5.64
21.20
21.05
13.29
13.16
10.51
10.61
10.64
10.50
10.57
11.25
1.73
1.75
1.73
1.72
1.80
1.80
5.50 (m, 2Н, СН2=); 5.64 (d, 2Н, СН2);
89
88
75
70
*3
3
6.09
6
.00 (d, 1Н, СН=)
36.13
5.83
21.13
12.99
2.45 (s, 3Н, Me); 5.81 (m, 1Н, СН2α=);
.30 (m, 1Н, СН2β=)
1.80 (d, 3Н, Me); 4.13 (m, 2Н, СН2);
.75 (m, 1Н, CH)
2.17 (s, 3Н, Me); 3.39 (t, 2Н, СН2CO);
.09 (d, 2Н, СН2N)
1.76 (s, 6Н, 2Me); 2.45 (s, 3Н, MeCO);
.39 (s, 2Н, СН2CO)
1.76 (s, 6Н, 2Me); 2.45 (s, 3Н, MeCO);
.39 (s, 2Н, СН2CO)
3
6.09
5.64
21.05
13.16
6
g
h
a
b
27.51
4.85
4.61
16.29
16.14
2
7.67
5
36.70
5.52
18.72
11.67
11.82
3
6.49
5.74
18.92
5
3
*2
*3
3
_
*
*
*
______
The characteristics of the salt coincide with data in [10].
2
3
The mixture obtained in the form of a viscous oil was not separated.
The total yield of the mixture of salts was 61%.

Prolonged holding of the reaction mixtures and also the individual compounds 2a,b in HClO
4
(up to
4
days) did not indicate the formation of the isomeric 1,4-disubstituted tetrazolium salts. This indicates the
absence of isomerization of 1-tert-butyl-3-R-tetrazolium salts to their 1,4 isomers by migration of substituent
from the N(3) position to N(4), like the behavior we observed earlier for 1-R-3-tert-butyltetrazolium salts [10]. An
essential condition for the isomerization of the compounds is clearly heterolysis of the N–Rmigrated bond and the
generation of a carbocation from it. Such groups as Me and i-Pr, unlike t-Bu, do not meet the given criteria and
do not migrate from N(3) to N(4). The corresponding salts do not therefore isomerize under the investigated
conditions. They are partly de-tert-butylated, since heterolysis of the N(1)–t-Bu bond occurs and the tert-butyl
cation is generated. Possible substrates for further attack by the tert-butyl cation can only be the 2-R-tetrazole
that forms and water, which leads to formation of the initial salt and tert-butanol respectively. The tert-butyl
cation can also be converted into isobutylene and the products of its polymerization.
Bu-t
N
+
N
N
N
N
N
HClO
4
N
N
CH
CH
_
R
ClO4
R
2
a,b
1a,b
In the case of the salt 2d (R = t-Bu) during heterolysis of the N–t-Bu bonds 1-tert-butyltetrazole is
formed together with 2-tert-butyltetrazole, and it can be attacked by the tert-butyl cation both at the N(3) atom
and at N(4) atom. The salt 2d therefore isomerizes in perchloric acid to 1,4-di-tert-butyltetrazolium perchlorate
[
10]. The perchlorate was not found under the conditions of the synthesis of the salt 2d. However, a mixture of
the isomeric 1-(1,1-dimethyl-3-oxobutyl)-3- and 1-(1,1-dimethyl-3-oxobutyl)-4-tert-butyltetrazolium salts 3a
and 3b with a predominance of the 1,3 salt 3a was obtained during the quaternization of 2-tert-butyltetrazole 1d.
Their ratio, determined from the intensities of the singlets of the protons at the C(5) atom of the tetrazole ring,
was 1:0.2.
H
CMe CH CMe
2
2
N
N
N
N
+
O
–
ClO
HClO4
Me C
4
3
1
d
+
Me
2
CCH
OH
CMe
2
3
a
H
O
Me C
CMe CH CMe
2 2
3
N
N
N
N
+
–
O
ClO4
3
b
The quaternization of 2-adamantyltetrazole by 1-adamantanol in sulfuric acid takes place in a similar
manner, and the 1,4-tetrazolium salt is mostly formed [11]. However, the process is much faster (2 h).
Experiments indicate a substantial effect of the nature of tetrazole, alcohol, and acid, and the concentration of
the latter on the isomerization transformations of tetrazolium salts. This must be taken into consideration during
the quaternization of 2-R-tetrazoles in the case of a group R capable of being eliminated in acidic media in the
form of a sufficiently stable carbocation.
The synthesized salts 2 were assigned to the 1,3-disubstituted tetrazolium salts on the basis of their
1
H NMR spectra, compared with the analogous spectra for related tetrazolium salts [8-10]. The chemical shifts
of the protons at the C(5) atom of the salts are extremely characteristic for identification of disubstituted
tetrazolium salts. For 1,3-dialkyl-substituted tetrazolium perchlorates these values lie in the region of
1
0.2-10.6 ppm, whereas for the isomeric 1,4 salts they are at 11.0-11.8 ppm (DMSO-d
6
).
9
52

1
-tert-Butyl-3-(1-methylvinyl)tetrazolium perchlorate 2f is of particular interest among the synthesized
salts. This compound belongs to an uninvestigated class of α-methylvinyl monomers with a quaternized
tetrazole ring. As well as at tert-butylation of 2-(1-methylvinyl)tetrazole 1f the salt 2f can also be obtained by
dehydrobromination of its synthetic precursor 2g.
Bu-t
Bu-t
N
N
N
N
N
N
H
+ CH
+ CH
NaOH, EtOH
NaBr, –H O
Me
Me
N
N
–
2
–
–
CH Br
ClO4
CH2
2f
ClO4
2
2
g
However, the reaction is unsuitable for preparative purposes on account of the low product yield, which
is probably due to cleavage of the salts 2f,g by the action of the base, leading (as known for
1
,3-dialkyltetrazolium salts [7]) to 1,3-disubstituted 3-cyanotriazenes.
In order to establish the structural features of 1,3-disubstituted tetrazolium salts, about the structure of
which there are no published data, an X-ray diffraction analysis was carried out on single crystals of compounds
2
d and 2f. Fragments of their structure, illustrating the mutual arrangement and conformation of the ions, are
shown in Fig. 1, 2. The bond lengths and bond angles in the tetrazolium cations are given in Tables 3, 4.
The tetrazole ring in the cations of salts 2d and 2f is planar (average departure of the ring atoms from
the mean-square plane 0.002 Å), and this is typical of tetrazole and its derivatives. As in the 1,3,5-trisubstituted
tetrazolium cations [12, 13], in the cation of salt 2f the N(2)–N(3) and N(4)–C(5) bonds are the shortest. The lengths
of the other C–N and N–N bonds are intermediate between the lengths of the corresponding single and double
2
bonds of aromatic compounds, where the carbon and nitrogen atoms have sp -hybridization [14]. In contrast to
the structure of 1-(1-adamantyl)-5-(1-methylvinyl)tetrazole [15], in the structure of compound 2f the torsion
Fig. 1. Fragment of the structure of salt 2f
disordering of the perchlorate ion and tert-butyl group is not shown).
(
9
53

Fig. 2. Fragment of the structure of salt 2d
one of the perchlorate ions is disordered with respect to two positions).
(
angles at the C(9)–N(3) bond deviate from 0° and 180° by no more than 10.6°. On the basis of these data it can be
concluded that the π-systems of the C=C bond and the tetrazole ring are conjugated, while the positive charge is
localized to a larger degree at the N(3) atom than at N(1), which is the quaternization center. The localization of
the charge at the N(3) atom is confirmed indirectly by the fact that the oxygen atoms of the perchlorate ions in
the structure are closest to this nitrogen atom (d[O(1)···N(3)] = 2.964(7) Å, d[O(2)···N(3)] = 2.965(7) Å, Fig. 1). The
conjugation of these fragments probably also gives rise to the difference in the values of the chemical shifts of
TABLE 3. The Bond Lengths (d) in the Cations of Salts 2d and 2f
Salt 2d
Bond
Salt 2f, d, Å
cation 1, d, Å
cation 2, d, Å
N
N
N
N
N
N
(1)–N(2)
1.316(3)
1.337(3)
1.299(3)
1.334(3)
1.300(4)
1.508(3)
1.531(6)
1.501(6)
1.485(6)
1.53(2)
1.54(3)
1.58(4)
1.440(3)
1.329(4)
1.440(5)
—
1.322(2)
1.334(3)
1.292(3)
1.330(3)
1.303(3)
1.510(3)
1.521(4)
1.508(4)
1.493(4)
—
1.316(3)
1.334(3)
1.290(3)
1.325(3)
1.314(3)
1.517(3)
1.517(4)
1.513(4)
1.511(4)
—
(1)–C(5)
(2)–N(3)
(3)–N(4)
(4)–C(5)
(1)–C(6)
C
C
C
C
C
C
(6)–C(7)
(6)–C(8)
(6)–C(9)
(6)–C(7')
(6)–C(8')
(6)–C(9')
—
—
—
—
N
(3)–C(10)
1.506(3)
1.498(4)
1.487(4)
1.515(4)
1.516(3)
1.508(5)
1.514(4)
1.517(4)
C
C
C
(10)–C(11)
(10)–C(12)
(10)–C(13)
9
54

TABLE 4. The Bond Angles (ω) in the Cations of Salts 2d and 2f
Salt 2d
Angle
Salt 2f, ω, deg.
cation 1, ω, deg.
cation 2, ω, deg.
N
N
N
(2)–N(1)–C(5)
(3)–N(2)–N(1)
(2)–N(3)–N(4)
108.9(2)
103.66(18)
114.54(19)
102.6(2)
110.3(2)
121.19(19)
129.9(2)
121.3(2)
124.2(2)
104.4(3)
105.5(3)
108.6(3)
112.7(4)
111.1(4)
113.9(5)
110.4(8)
106.1(10)
103.0(9)
115(2)
108.63(18)
103.73(17)
114.77(18)
102.56(19)
110.3(2)
119.30(18)
132.07(19)
121.68(18)
123.54(18)
107.4(2)
107.3(2)
107.6(2)
113.7(3)
111.8(3)
108.7(3)
—
109.2(2)
103.84(19)
114.73(19)
102.9(2)
109.3(2)
122.3(2)
128.5(2)
123.4(2)
121.9(2)
106.6(2)
108.0(2)
106.8(2)
111.6(3)
111.7(3)
111.8(3)
—
C
(5)–N(4)–N(3)
(4)–C(5)–N(1)
(2)–N(1)–C(6)
N
N
C
(5)–N(1)–C(6)
N
N
N
N
N
(2)–N(3)–C(10)
(4)–N(3)–C(10)
(1)–C(6)–C(7)
(1)–C(6)–C(8)
(1)–C(6)–C(9)
C
C
C
N
N
N
(9)–C(6)–C(8)
(9)–C(6)–C(7)
(8)–C(6)–C(7)
(1)–C(6)–C(7')
(1)–C(6)–C(8')
(1)–C(6)–C(9')
—
—
—
—
—
—
—
—
C
C
C
(7')–C(6)–C(8')
(7')–C(6)–C(9')
(8')–C(6)–C(9')
109(2)
113(3)
—
—
(3)–C(10)–C(11)
(3)–C(10)–C(12)
(3)–C(10)–C(13)
117.1(3)
114.1(2)
—
128.8(3)
—
107.3(2)
106.5(2)
106.6(2)
113.0(3)
110.6(3)
112.4(3)
108.0(2)
106.0(2)
106.2(2)
111.5(3)
112.5(3)
112.1(3)
—
1
the protons at the C(5) atom in the H NMR spectrum of salt 2f and salts 2a,e. For the salt 2f the signal of the
given proton is shifted downfield by ~0.1 ppm. However, in spite of the fairly high mobility of this proton, there
is no clearly defined C–H···O interaction between them and the oxygen atoms of the perchlorate ion. The
shortest distance between the hydrogen atom at C(5) and the oxygen atoms of the perchlorate anion amounts to
2.276(4) Å (d(C(5)···O(2')) = 3.145(7) Å, ω(C(5)–H···O(2')) = 153(3)°), which is somewhat shorter than the
analogous value for 1-(2-methyl-4-oxopentan-2-yl)-4-methyltetrazolium perchlorate [9] [2.37(3) Å]. However,
these values are in the critical region of lengths of intermolecular contacts giving rise to the greatest discussions
concerning crystallographic evidence for the presence or absence of hydrogen bonds [16]. Meanwhile, the data
in [16] apply to C–H···O contacts of intermolecular type, while in the salts that we investigated there is ion–ion
interaction. Therefore the regions for the existence of hydrogen bonds may be somewhat different. The position
of the vinyl group in relation to the heterocycle in the crystal structure corresponds to the s-trans(N )
2
conformation, which agrees with the high population of this conformation (72.1%) in the unquaternized
tetrazole 1f (according to the data from nonempirical calculation in the 6-31G**//STO-3G basis set) and
provides further evidence for the insignificant effect of the substituent (by virtue of its remoteness) on the
stereochemical structure of 2-alkenyltetrazoles [17].
9
55

4
TABLE 5. The Coordinates (in Unit Cell Fractions, ×10 ) and Equivalent
Isotropic Temperature Factors of the Atoms in the Structure of Salt 2d
2
3
Atom
x/a
y/b
z/c
U(eq) (Å × 10 )
N
N
N
N
(1)
(2)
(3)
(4)
6588(2)
5732(2)
6548(2)
7894(2)
7889(2)
5999(3)
4626(4)
5710(5)
7037(4)
5997(3)
4520(4)
6123(6)
6893(5)
9374(2)
9286(2)
8603(2)
8239(3)
8731(3)
10120(3)
9132(3)
10453(4)
11427(3)
8233(3)
8612(4)
6678(3)
9063(5)
5788(1)
6154(3)
6105(6)
6514(5)
4393(4)
8463(1)
9209(7)
7359(5)
9312(9)
7798(8)
9019(16)
7850(70)
9455(18)
8244(16)
2340(2)
2536(2)
2459(2)
2214(2)
2134(3)
2381(3)
3408(4)
1140(4)
2652(6)
2617(2)
3420(4)
1337(3)
3273(5)
6892(2)
7152(2)
8322(2)
8849(2)
7919(2)
5602(2)
5250(3)
4711(3)
5715(4)
9051(3)
8138(4)
9666(3)
10004(4)
6373(1)
7224(2)
5209(3)
6333(4)
6778(5)
8556(1)
9035(8)
9515(4)
7780(8)
7815(8)
8248(13)
9430(40)
8960(20)
7490(9)
4202(1)
3511(1)
2646(1)
2728(2)
3722(2)
5322(2)
5171(3)
6054(3)
5725(3)
1639(2)
1627(3)
1747(4)
648(3)
46(1)
47(1)
44(1)
59(1)
58(1)
57(1)
C
C
C
C
C
C
C
C
C
(5)
(6)
(7)
(8)
(9)
97(1)
107(1)
121(2)
52(1)
(10)
(11)
(12)
(13)
99(1)
118(2)
104(1)
50(1)
N
(1')
N
(2')
N
(3')
N
(4')
1800(2)
762(2)
382(2)
51(1)
51(1)
69(1)
66(1)
58(1)
78(1)
88(1)
90(1)
61(1)
85(1)
85(1)
109(1)
62(1)
1109(2)
2011(2)
2577(2)
3616(2)
2007(3)
2806(3)
-800(2)
-1348(3)
-727(3)
-1335(3)
1730(1)
1981(2)
2572(3)
746(3)
1598(5)
4778(1)
5126(9)
4282(6)
4264(6)
5748(6)
5696(9)
3960(30)
3860(17)
4821(16)
C
C
C
C
C
C
C
C
C
(5')
(6')
(7')
(8')
(9')
(10')
(11')
(12')
(13')
Cl(1)
O
(1)
O
(2)
O
(3)
O
(4)
89(1)
169(2)
163(2)
194(2)
66(1)
173(4)
133(3)
161(3)
201(4)
103(4)
501(17)
187(11)
112(6)
Cl(1')
O
O
O
O
O
O
O
O
(1')
(2')
(3')
(4')
*
*
*
*
*
*
*
*
2
2
2
2
(1'A)
(2'A)
(3'A)
(4'A)
_
*
*
______
Population of position 0.726(9).
2
Population of position 0.274(9).
In contrast to salt 2f, in the unit cell of salt 2d there are two structurally nonequivalent tetrazolium
cations and two perchlorate anions. Comparison of data from structural analysis of the salts 2f and 2d indicates
that the nature of the substituents has little effect on the parameters of the 1,3-disubstituted tetrazole ring. The
bond lengths and the values of the corresponding angles in the cations of salt 2d differ little and are close to the
analogous characteristics of the salt 2f. In the rings of the cations of compound 2d the shortest is the N(2)–N(3)
9
56

4
TABLE 6. The Coordinates (in Unit Cell Fractions, ×10 ) and Equivalent
Isotropic Temperature Factors of the Atoms in the Structure of Salt 2f
2
3
Atom
x/a
y/b
z/c
U(eq) (Å × 10 )
N
N
N
N
(1)
(2)
(3)
(4)
5367(2)
5273(3)
3809(3)
2936(3)
3953(4)
6926(4)
6048(9)
7992(11)
7968(9)
6590(30)
8620(30)
6880(70)
3208(4)
1861(5)
4207(6)
7465(1)
7123(7)
5795(11)
8970(16)
7822(13)
7240(40)
6260(40)
8490(20)
8340(40)
3762(2)
2690(2)
2546(2)
3468(2)
4220(2)
4292(2)
5074(6)
4860(7)
3424(4)
5526(19)
4000(60)
3730(40)
1464(2)
1400(3)
589(2)
2615(1)
1980(5)
3097(9)
3265(11)
1800(5)
2140(20)
3293(13)
3539(10)
2090(20)
3467(1)
3559(1)
3931(2)
4081(2)
3787(2)
3080(2)
2319(6)
3901(5)
2671(6)
2940(30)
3770(40)
2090(30)
4145(2)
4653(3)
3784(3)
6145(1)
6985(5)
5800(8)
6290(9)
5429(5)
6779(14)
5657(13)
6580(12)
5650(20)
50(1)
50(1)
51(1)
65(1)
62(1)
C
C
C
C
C
C
C
C
C
C
C
(5)
(6)
(7)
(8)
(9)
63(1)
*
*
*
104(3)
123(3)
99(2)
2
2
2
(7')
(8')
(9')
*
*
*
87(9)
190(30)
160(20)
66(1)
(10)
(11)
(12)
100(1)
106(1)
64(1)
Cl(1)
3
3
3
3
4
O
O
O
O
O
O
O
O
(1)
(2)
(3)
(4)
*
*
*
*
81(2)
116(3)
157(4)
97(2)
203(13)
140(8)
98(5)
(1')
(2')
(3')
(4')
*
4
4
4
*
*
*
191(11)
_
*
*
*
*
______
Population of position 0.82(2).
2
Population of position 0.18(2).
Population of position 0.67(2).
Population of position 0.33(2).
3
4
bond, and this once again demonstrates that the centers of quaternization and localization of the positive charge
in the tetrazole ring do not coincide and also that there is substantial conjugation in the N(1)–N(2)=N(3) fragment.
Further evidence for this can be obtained from the fact that exhaustive tert-butylation of tetrazole, 1-tert-
butyltetrazole [10], and 2-tert-butyltetrazole gave salts having identical spectral and physicochemical
characteristics and not giving melting point depressions in mixed melting tests.
EXPERIMENTAL
1
The H NMR spectra were recorded on a Tesla BS 567A spectrometer at 100 Hz (DMS0-d
6
). The initial
tetrazoles were obtained by the familiar procedures: 2-isopropyl- and 2-tert-butyltetrazoles – according to [18];
2
2
-(1-methylvinyl)- and 2-(2-bromo-1-methylethyl)tetrazole – [19]; 2-(3-oxobutyl)tetrazole – [20]. 2-Methyl-,
-ethyl-, and 2-allyltetrazoles were obtained by alkylation of tetrazole with alkyl halides according to the
method [21].
9
57

Procedure for the Synthesis of Salts 2. To solution of tetrazole 1 (0.045 mol) in 7.4 ml of 72%
perchloric acid we added 4 ml (0.045 mol) of tert-butanol. The mixture was kept at room temperature for 48 h.
The final product 2 was precipitated by the addition of 40 ml of water, the solution was cooled to 0°C, and the
product was recrystallized from ethanol. If 62% perchloric acid was used its volume was 9.4 ml. The
quaternization of tetrazole with diacetone alcohol was conducted similarly. The yields of the salts are reported
in Tables 1 and 2.
Treatment of Salts 2a,b in Perchloric Acid. Solution of the salt (0.018 mol) in 72% perchloric acid
(
20 ml) was kept at room temperature for 4 days. The product was precipitated by the addition of water (60 ml),
and the solution was then cooled to 0°C. The yields of the salts 2a,b were 52 and 44% respectively. In the case
of the salt 2a tetrazole 1a was isolated with a yield of 40% by further extraction of the aqueous solution with
chloroform and distillation of the latter. Its characteristics agreed with published data [18].
Dehydrobromination of Salt 2g. To solution of the salt 2g (8.4 g, 0.024 mol) in ethanol (150 ml) we
added dropwise solution of sodium hydroxide (1 g, 0.025 mol) in ethanol (150 ml). The mixture was stirred at
room temperature for 1 h. Ethanol was removed under vacuum. The residue was recrystallized from isopropyl
alcohol. Yield of the salt 2f 3.0 g (0.011 mol, 47%).
X-ray Diffraction Investigation of Compound 2d. Single crystals of the salt 2d were obtained by
crystallization from ethanol at 298 K. A prismatic crystal (0.78 × 0.76 × 0.56 mm in size) was selected for X-ray
crystallographic analysis. A three-dimensional set of X-ray diffraction data was obtained on a Nicolet R3m
automatic four-circle diffractometer with MoKα radiation, a graphite monochromator, a θ/2θ scan, and
2
θ
= 55°. The total number of measured reflections was 7274, and the number of unique reflections was 6674
max
(Rint = 0.0098). The compound crystallizes in the triclinic system in space group P1. The parameters of the unit
cell were as follows: a = 10.280(3), b = 12.374(3), c = 13.534(4) Å; α = 64.02(2), β = 76.49(2), γ = 69.74(2)°;
3
3
-1
V = 1445.0(7) Å ; Z = 4; dX-ray = 1.300 g/cm ; μ = 2.77 cm . The structure of the compound was interpreted by
the direct method (SIR97 [22]). The positions of the hydrogen atoms were calculated by geometry. Refinement
(
SHELX-97 [23]) was made by full-matrix least-squares treatment with allowance for the anisotropy of the
thermal vibrations of the nonhydrogen atoms. The hydrogen atoms were refined using the "rider" model. The
final values of the uncertainty factors were: R = 0.0593, wR = 0.1772 (I > 2σ(I)); R = 0.0777, wR = 0.1936
all data); goodness of fit, GOOF = 1.080. Absorption was not taken into account. The coordinates and the
equivalent isotropic temperature factors of the atoms are given in Table 5.
1
2
1
2
(
X-ray Crystallographic Investigation of Compound 2f. Single crystals of the salt 2f were obtained by
crystallization from ethanol at 298 K. A prismatic crystal (0.60 × 0.52 × 0.48 mm in size) was selected for X-ray
crystallographic analysis. In view of its instability in air the crystal was sealed in a glass capillary. A three-
dimensional set of X-ray diffraction data was obtained on a Nicolet R3m automatic four-circle diffractometer
with MoKα radiation, a graphite monochromator, a θ/2θ scan, and 2θ = 55°. The total number of measured
max
reflections was 3184, and the number of unique reflections was 2863 (Rint = 0.0183). The compound crystallizes
in the monoclinic system, space group P2 /n. The unit cell parameters were as follows: a = 7.514(3),
1
3 3 -1
b = 12.192(4), c = 14.367(6) Å; β = 97.86°; V = 1303.8(9) Å ; Z = 4; dX-ray = 1.359 g/cm ; μ = 3.03 cm . The
structure was interpreted by the direct method (SIR97 [22]). Refinement (SHELX-97 [23]) was made by full-
matrix least-squares treatment with allowance for the anisotropy of the thermal vibrations of the nonhydrogen
atoms. The hydrogen atoms were treated as for the compound 2d. The final values of the uncertainty factor
were: R
1
= 0.0651, wR
2
= 0.1777 (I > 2σ(I)); R
1
= 0.0866, wR = 0.1989 (all data); goodness of fit,
2
GOOF = 1.025. Absorption was not taken into account. The coordinates and the equivalent isotropic
temperature factors of the atoms are given in Table 6.
The authors express their gratitude to the Russian Fundamental Research Fund for financial support in
payment for the license to use the Cambridge structural data bank (project 96-07-89187) during analysis of the
results obtained in the present work.
9
58

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959