Trifluoromethanesulfonic hydrazides

Article abstract of DOI:10.1023/B:RUJO.0000045884.87574.ec

We succeeded to observe at low temperature in reactions of trifluoromethanesulfonic anhydride and trifluoromethanesulfonyl chloride with hydrazine, phenyl hydrazine, and 1,1-dimethylhydrazine a formation of the corresponding trifluoromethanesulfonic hydra

Full text of DOI:10.1023/B:RUJO.0000045884.87574.ec

Russian Journal of Organic Chemistry, Vol. 40, No. 8, 2004, pp. 1071-1075. Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 8, 2004,
pp. 1119-1123.
Original Russian Text Copyright Ó 2004 by Shainyan, Tolstikova, Meshcheryakov, Danilevich.
Trifluoromethanesulfonic Hydrazides
B.A. Shainyan, L.L. Tolstikova, V.I. Meshcheryakov, and Yu.S. Danilevich
Faworsky Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences Irkutsk, 664033 Russia
å-mail: bagrat@irioch.irk.ru
Received November 3, 2003
Abstract— We succeeded to observe at low temperature in reactions of trifluoromethanesulfonic anhydride and
trifluoromethanesulfonyl chloride with hydrazine, phenyl hydrazine, and 1,1-dimethylhydrazine a formation of the
corresponding trifluoromethanesulfonic hydrazides that at heating to room temperature decomposed liberating
nitrogen and affording trifluoromethanesulfinic acid. 2-Phenyl-2H-1,2,3-triazole-4-carboxylic hydrazide reacted
with trifluoromethanesulfonic anhydride to furnish trifluoro-N'-(2-phenyl-2H-1,2,3-triazol-4-ylcarbonyl)methane-
sulfonic hydrazide that decomposed at heating with elimination of trifluoromethanesulfinic acid and nitrogen yielding
2
.
-phenyl-2H-1,2,3-triazole-4-carbaldehyde.
at 122 ppm with a coupling constant 1JCF 322.8 Hz. The
signal belonged to the trifluoromethanesulfonic
hydrazide CF SO NHNH (VII). The heating to room
Nitrogen derivatives of pentafluoroalkanesulfonic
acids, like amides R SO NH and their N-substituted
F
2
2
derivatives, or azides R SO N are successfully used in
F
2
3
3
2
2
the organic synthesis [1–5]. At the same time the
published information on perfluoroalkanesulfonic
hydrazides is relatively scanty. It was demonstrated that
perfluoroalkenasulfonyl halides were reduced with
hydrazine into perfluoroalkanesulfinic acids derivatives
temperature was accompanied with a vigorous nitrogen
evolution, and in the 13C NMR spectrum a quartet
1
appeared at 125–126 ppm with a coupling constant J
CF
350–360 Hz (depending on the solvent). The signal
belonged to the CF group of trifluoromethanesulfinic
3
1
9
[6–10] but in neither of these studies the intermediate
acid or its salt. The signal in the F NMR spectrum is
shifted at the same time upfield from –78 to –86 ppm.
Inasmuch as all trifluoromethanesulfonic acid derivatives
CF SO X (X = OH, OSO CF , Cl, NH , NR ,
hydrazides R SO NHNH were isolated as individual
F
2
2
compounds or at least characterized. Among the N-
substituted hydrazides R SO NHNHX only func-
F
2
3
2
2
3
2
2
tionally-substituted trifluoromethanesulfonic acid hydr-
NHSO CF , N ) regardless of X character possess signals
with a definite position in the C and F NMR spectra
2 3 3
1
3
19
azides CF SO NHNHX (X = PhCO, t-BuOCO) are
3
2
known that are used in oxidation of alkyl halides to the
correspondinghydrazonesofaldehydesandketones[11];
therewith the triflate group is also reduced to triflinate
one. No data were published on reactions between
prefluoroalkanesulfonic acids derivatives with alkyl- or
arylhydrazines.
(119...122 and –78...–79 ppm respectively), and the
1
corresponding coupling constants J are 319–321 Hz
CF
the resonances arising at heating can be unambiguously
ascribed to trifluoromethanesulfinic acid derivatives.
Thus the hydrazine reaction with acyl chloride V
proceeded along equation (1) with elimination of
CF SO H molecule from the intermediate hydrazide VII
In this study we investigated reactions of hydrazine
3
2
yielding either free acid VIII, or at large hydrazine excess
(I), phenyl hydrazine (II), 1,1-dimethylhydrazine (III),
+
–
its salt N H CF SO .
and 2-phenyl-2H-1,2,3-triazole-4-carboxylic hydrazide
2
5
3
2
(
(
(
IV) with trifluoromethanesulfonyl chloride CF SO Cl
3 2
V), and/or trifluoromethanesulfonic anhydride
CF SO ) O (VI) aiming at preparation of the
ꢀꢁ&) 62 &Oꢁꢁꢀꢁꢁꢂꢁ1 +
&) 62 1+1+ꢁ
3
2 2
9,,
corresponding trifluoromethanesulfonic hydrazides and
their characterization. Acyl chloride V reacted with
excess hydrazine (I) in anhydrous THF at –50°C without
nitrogen liberation, and in the 13C NMR spectrum
ꢀ
ꢁ&) 62 +ꢁꢁꢀꢁꢁꢀꢁ1 + &Oꢁꢁꢀꢁꢁ1
(1)
9,,,
The above spectral criteria of distinction between
triflate or triflinate derivatives were applied to
recorded at –30°C a quartet of CF group was observed
3
1070-4280/04/4008-1071Ó2004 MAIK “Nauka/Interperiodica”

1072
SHAINYAN et al.
1
investigation of reactions between trifluoromethane-
sulfonic anhydride and trifluoromethanesulfonyl chloride
with substituted hydrazines II and III. The reaction of
phenylhydrazine (II) with acyl chloride V was carried
out under various conditions: without solvent, in
dichloromethane, carbon tetrachloride, or in DMSO-d6
directly in an NMR tube at the reagents ratio from 1 : 1
to 2 : 1, at –78°C and room temperature. In all cases the
reaction proceeded according to equation:
121.10 ppm with a coupling constant J 321.8 Hz, and
CF
the signal in the 19F NMR spectrum is observed at
–77.76 ppm In the IR spectrum of salt X the very strong
band of stretching vibrations of SO group is present
2
1
9
which lacks in the IR spectrum of salt IX. The F NMR
spectrum of the residue after separation of salt X contains
a main signal at –85.54 ppm belonging to salt IX (50%),
and also two signals in the “triflate” region at –77.75 ppm
(
30%) and –75.59 ppm (20%). The first one corresponds
to salt X, whereas the second belongs presumably to an
intermeiate trifluoromethanesulfonic N'-phenyl-
hydrazide (XI). Benzenesulfonic N'-phenylhydazide
ꢀ
ꢁ3K1+1+ ꢁꢁꢀꢁꢁ&) 62 &O
ꢀ
ꢁ3K1+1+ &) 62 ꢀꢁꢁ& + ꢁꢁꢀꢁꢁ1
PhSO NHNHPh is known to eliminate benzenesulfinic
acid at treatment with alkali yielding phenyldiimide
2
3K1+1+ &O
,
;
(
2)
C H N=NH that decomposes further into benzene and
6
5
Benzene formation was revealed by appearance of a
nitrogen [14].Apparently the N'-phenylhydrazide of the
stronger trifluorometahesulfonic acid suffers
spontaneous decomposition.
1
singlet at 7.33 ppm in the H NMR spectrum and of a
1
3
singlet at 129.89 ppm in the C NMR spectrum of the
reaction mixture. In contrast to hydrochloride 2-phenyl-
hydrazinium triflinate (IX) is soluble in ether, and thus
these two salts may be separated. The structure of salt
The reaction of acyl chloride V with 1,1-dimethyl-
hydrazine (III) in anhydrous THF at room temperature
13
also occurred with nitrogen evolution. The C NMR
1
3
IX is confirmed by the presence in its C NMR spectrum
spectra of reaction mixtures contain two quartetes of CF
3
alongside the signals from the benzene ring also a quartet
1
groups: at 121 ppm with a coupling constant J
CF
1
at 125 ppm with a coupling constant J 350–360 Hz
1
CF
322 Hz, and at 125 ppm with a coupling constant J
CF
(
depending on the solvent), and by a singlet at –86.04
3
4
56 Hz, and also two methyl group signals at 34 and
7 ppm. In the H NMR spectrum the corresponding
ppm in its 19F NMR spectrum; the composition of the
salt was proved by elemental analysis. The triflates are
additionally distinguished from triflinates by the absorp-
tion bands in the IR spectra corresponding to the
1
singlets from NMe groups appear at 2.5 and 2.8 ppm.
The 47 ppm resonance in the 13C NMR spectrum and
1
the respective signal at 2.8 ppm in the H NMR spectrum
stretching vibrations of the SO groups: In the IR spectra
belong to methyl groups in the 1,1-dimethylhydrazin-
2
+
13
of all triflates appear strong bands of symmetric (1220–
ium ion [Me NHNH ] as prove the C NMR spectra of
2 2
–
1
-1
1
160 cm ) and antisymmetric (1440–1357 cm )
1,1-dimethylhydrazinium chloride, triflate, and triflinate
that have been independently prepared by treating di-
methylhydrazine with hydrochloric or trifluoromethane-
sulfonic acid, or from 1,1-dimethylhydrazinium chloride
and sodium triflinate respectively. In the IR spectrum of
vibrations of SO group. In the spectra of triflinates only
2
–
1
a band in the 1010–1150 cm region is observed [6, 12,
3]. The lack of the high-frequency band in the IR
1
spectrum of salt IX confirms its triflinate structure.
2
,2-dimethylhydrazinium triflinate (XII) lacks the
The reaction of phenylhydrazine with trifluoro-
methanesulfonic anhydride (VI) in dichloromethane
afforded as the main product phenylhydrazinium triflate
–
1
vibration band n SO in the region 1440–1357 cm as
has been observed in the spectrum of salt IX.
as
O
In reactions carried out below–30 C no nitrogen
(
X) identical to a sample obtained directly from
1
3
evolution occurred, and in the C NMR of the reaction
mixture appeared only signals at 34 and 120 ppm from
trifluoromethanesulfonic 2,2-dimethylhydrazide
phenylhydrazine and trifluoromethanesulfonic acid.
ꢀ
ꢁ3K1+1+ ꢁꢁꢀꢁꢁꢂ&) 62 ꢃ 2
K1+1+
3K1+1+ &) 62
1
5
CF SO NHN(CH ) (XIII). In the N NMR spectrum
3
2
3 2
;
the resonances from this compound are observed at
3
1
–
286.4 (NH) and –356.9 ppm (NMe ), and in the H
ꢀ
>3K1+1+62 &) @
;ꢁꢁꢀꢁꢁ& + ꢁꢁꢀꢁꢁ1
(3)
2
NMR spectrum is present only the signal of non-
protonated methyl group at 2.5 ppm.
;
,
1
3
The CF quartet in the C NMR spectrum of salt
The cleavage of trifluoromethanesulfinic acid from
3
X appears in the region characteristic of triflates, at
hydrazide XIII in contrast to hydrazides VII and XI
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 8 2004

TRIFLUOROMETHANESULFONIC HYDRAZIDES
1073
ꢀ
ꢁ0H 1+1+ ꢁꢁꢀꢁꢁ&) 62 &O
H 1+1+ &O ꢀꢁꢁ0H 11+62 &)
,,,
H 11+
&220H
1
&21+1+
+ ꢀ+ 2
0
1
1
1
1
;
1
1
B
0
& + ꢁꢁꢁ1
3K
3K
,9
;
9,
0H 1+1+ &O ꢀꢁ&) 62 1D
0H 1+1+ &) 62
,,
1D&O
;
&
21+1+62 &)
(
4)
ꢁ
&) 62 ꢂ 2
1
1
can proceed solely as 1,1-elimination affording dimethyl-
1
aminonitrene (Me NN:) that should either dimerize into
2
3
K
tetramethyltetrazene or decompose into ethane and
nitrogen [15]. The vigorous evolution of gaseous products
and triflinate formation at heating the reaction mixture
to room temperature confirms that the reaction occurs in
conformity to equation (4). However the concomitant
;
9,,
&
+2
'
(
5)
ꢀ
1 ꢁꢀꢀ&) 62 +
1
1
formation of tetramethyltetrazene Me NN=NNMe or
2
2
1
its salts cannot be excluded. In some runs on treating the
evaporated reaction mixture with methanol we observed
additional signals in the NMR spectra at the following
3
K
;
9,,,
9,,,
1
13
chemical shifts: 3.3 ppm ( H), 57 ppm ( C), and 69.8
1
5
and –230.0 ppm ( N). These signals may be assigned to
tetramethyltetrazene salt. To clear out this possibility
cation formed through akkylation of hydrazide XIII with
intermediate methyl trifluoromethysulfonate.
we synthesized along procedure [16] tetramethyltetrazene
We expected that 2-phenyl-2H-1,2,3-triazole-4-
carboxylic hydrazide (IV) which we had prepared by
treating methyl 2-phenyl-2H-1,2,3-triazole-4-carboxylate
XVI) with hydrazine hydrate would react with
trifluoromethanesulfonic anhydride or trifluoromethane-
sulfonyl chloride similarly to the described reactions of
functionally-substituted hydrazides XNHNH (X =
PhCO, t-BuOCO) [11] affording trifluoro-N'(2-phenyl-
H-1,2,3-triazol-4-ylcarbonyl)methanesulfonic hydr-
1
(
XIV), prepared its triflate salt XV, and recorded H,
1
3
15
C, and N spectra of both compounds. In the NMR
spectra of tetramethyltetrazene recorded in DMSO-d
were observed the following signals: 2.73 ppm ( H),
6
(
1
1
3
15
4
0.83 ppm ( C), and two signals in the N NMR
spectrum in the regions characteristic of NMe and N=N
1
13
2
groups. In the H and C NMR spectra of salt XV
prepared in situ by adding trifluoromethanesulfonic acid
2
to a solution of compound XIV in DMSO-d directly in
6
azide (XVII).Actually the mixed hydrazide XVII proved
to be more stable that the above mentioned hydrazides
VII, XI, and XIII lacking electron-withdrawing groups,
and it was prepared by reaction between compound IV
and anhydride VI. However at the attempt to purify
hydrazide XVII by sublimation it suffered thermal
degradation with nitrogen evolution and formation of
2-phenyl-2H-1,2,3-triazole-4-carbaldehyde (XVIII) and
trifluoromethanesulfinic acid (VIII).
an NMR tube the corresponding signals underwent
downfield shifts to 3.08 and 42.29 ppm respectively.
These results showed that no tetrazene XIV or its salt
1
XV formed in reaction (4). The signals at 3.3 ppm ( H)
1
3
and 57 ppm ( C) were alternatively suggested to belong
to methylation product of the intermediate hydrazide
XIII, 1,1,1-trimethyl-2-[(trifluoromethyl)sulfonyl)]hydr-
+
azinium cation CF SO NHN Me . This assignment is
3
2
3
confirmed by coincidence of these chemical shifts with
1
13
15
the known data on H, C, and N spectra of 1,1,1-tri-
methylhydrazonium salts [17]. Inasmuch as the esters of
sulfonic acids were known to be able to behave as
alkylating agents and taking into account that the signals
of 1,1,1-trimethyl-2-[(trifluoromethyl)sulfonyl)]hydr-
azinium cation were observed only if the reaction mixture
was treated with methanol it was presumable that the
The formation of aldehyde XVIII was proved by
1
chromatography with an authentic sample. In the H
NMR spectrum appeared singlets at 9.13 and 10.20 ppm
in 1:1 ratio belonging to trifluoromethanesulfinic acid
(VIII) and aldehyde XVIII. The singlet of aldehyde
proton in the spectrum of authentic aldehyde XVIII is
also observed at 10.20 ppm.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 8 2004

1074
SHAINYAN et al.
(Cp), 120.79 (CF3, JCF 321.9 Hz), 128.77 (Cm), 149.78
1
EXPERIMENTAL
1
19
(
C ). F NMR spectrum, d, ppm: –77.63. Found, %:
IR spectra were recorded on spectrophotometer IKS-
C 32.69; H 3.66; F 21.99; N 11.25; S 12.42.
C7H9F3N2O3S. Calculated, %: C 32.56; H 3.51; F 22.07;
N 10.85; S 12.42.
2
9 from thin film on CaF plates or from samples
2
pelletized with KBr. NMR spectra were registered on a
spectrometer Bruker DPX-400 at operating frequencies
Reaction of trifluoromethanesulfonic acid with
phenylhydrazine. To 1.08 g (0.01 mol) of phenyl-
hydrazine cooled to –78°C was added dropwise a
solution of 1.50 g (0.01 mol) of trifluoromethanesulfonic
acid in 0.9 ml of distilled water maintaining the
temperature of the reaction mixture at –78°C. Then the
cooling was removed, and the reaction mixture was left
standing for 24 h at –12°C On evaporation we obtained
2.57 g (quantitative yield) of 2-phenylhydrazinium
triflate (X), mp 160°C.
1
13
15
19
4
00 ( H), 100 ( C), 40 ( N), and 376 MHz ( F) in
DMSO-d (if not other indicated), internal refernce
6
HMDS, chemical shifts are reported with respect to TMS
1
13
15
19
(
H, C), CH NO ( N), and CCl F ( F). The chemical
3 2 3
1
5
shifts for N were determined from two-dimensional
spectra 2D( H– N) with the use of gradient probe in
hmbcgp mode.
1
15
Reaction of trifluoromethanesulfonyl chloride
with phenylhydrazine At cooling to –78°C and stirring
to a solution of 2.16 g (0.02 mol) of phenylhydrazine in
2
-Phenyl-2H-1,2,3-triazole-4-carboxylic hydrazide
IV). A mixture of 3 g (0.015 mol) of methyl 2-phenyl-
H-1,2,3-triazole-4-carboxylate (XVI) [18] and 10 ml
1
0 ml of dichloromethane was added dropwise a solution
(
2
of 1.69 g (0.01 mol) trifluoromethanesulfonyl chloride
in 11 ml of dichloromethane. The reaction mixture was
stirred at room temperature and stored for 24 h at–12°C,
then evaporated, treated with anhydrous ethyl ether, the
precipitate of 2-phenylhydrazine hydrochloride (0.96 g,
of hydrazine hydrate was heated at stirring to 110–115°C
for 1 h. The separated precipitate was filtered off, washed
with water, and dried. We obtained 2.72 g (90.7%) of
1
hydrazide IV, mp 181–182°C. H NMR spectrum, d, ppm:
6
6%) was separated, washed with anhydrous ether (4´10
ml), the ether and arising benzene was distilled off. We
4
8
.60 br.s (2H, NH ), 7.44 t (1H, H ), 7.56 t (2H, H ),
2 p m
5
.05 d (2H, H ), 8.40 s (1H, H ), 9.85 br.s (1H, NHCO).
O
obtained 1.6 g (66%) of 2-phenylhydrazinium triflinate
13
C NMR spectrum, d, ppm: 118.73 (C ), 128.17 (C ),
29.44 (C ), 135.70 (C ), 138.78 (C ), 143.12 (C ),
–
1
o
p
4
(
2
8
IX), mp 78–80°C. IR spectrum, n, cm : 3200, 3050–
5
1
1
1
m
830, 2700, 1600, 1580, 1500, 1150, 1030, 980, 900,
58.52 (C=O). Found, %: C 53.89; H 5.04; N 34.74.
1
50, 690, 600. H NMR spectrum, d, ppm: 6.97 t (1H,
C H N O. Calculated, %: C 53.20; H 4.46; N 34.47.
9
9
5
H ), 7.26 d (2H, H ), 7.47 t (2H, H ), 9.83 br.s (4H,
p
O
m
1
3
Trifluoro-N'-(2-phenyl-2H-1,2,3-triazol-4-yl-
NH). C NMR spectrum, d, ppm: 114.49 (C ), 121.67
o
1
carbonyl)methanesulfonic hydrazide (XVII). To a
solution of 1.88 g (0.067 mol) of trifluoromethane-
sulfonic anhydride in 50 ml of dichloromethane at cooling
with solid carbon dioxide was added in small portions
while stirring 2.71 g (0.0133 mol) of 2- phenyl-2H-1,2,3-
triazole-4-carboxylic hydrazide (IV). Then the reaction
mixture was heated to room temperature (it turned thick
in the process). The mixture was stirred for 1 h, the
solvent was evaporated, 20 ml of anhydrous ether was
added, after stirring the hydrazide IV triflate was filtered
off, and the filtrate was evaporated to obtain 1.13 g (50%)
of compound XVII. After column chromatography on
silica gel (eluent hexane–ether, 2:1) we obtained colorless
(
(
3
C ), 125.03 (CF , J 356.0 Hz), 129.07 (C ), 145.52
p
3
CF
m
1
19
C ). F NMR spectrum, d, ppm: –86.04. Found, %: C
4.31; H 3.84; F 22.82; N 11.22; S 13.85. C H F N O S.
7
9
3
2
2
Calculated, %: C 34.71; H 3.74; F 23.53; N 11.57;
S 13.24.
Reaction of trifluoromethenesulfonic anhydride
with phenylhydrazine.At cooling to –78°C and stirring
to a solution of 2.16 g (0.02 mol) of phenylhydrazine in
1
0 ml of dichloromethane was added dropwise a solution
of 2.82 g (0.01 mol) of triluoromethanesulfonic anhydride
in 10 ml of dichloromethane. The reaction mixture was
left standing for 24 h at –12°C, evaporated, treated with
anhydrous ethyl ether, the 3.86 g of precipitate was
separated, washed with dichloromethane (4´10 ml), and
dried in a vacuum. We obtained 2.03 g (79%) of 2-pheny-
lhydrazinium triflate (X), mp 160°C. IR spectrum, n,
O
1
crystals, mp 210 C. H NMR spectrum, d, ppm: 7.50 t
1H, H ), 7.62 t (2H, H ), 8.09 d (2H, H ), 8.59 s (1H,
(
p
m
o
5
13
H ), 11.37 s (1H, NHCO). C NMR spectrum, d, ppm:
119.16 (CO), 119.24 (CF3, JCF 322.6 Hz), 128.90 (Cp),
129.81 (C ), 137.07 (C ), 138.72 (C ), 141.35 (C ),
159.33 (C=O). F NMR spectrum, d, ppm: –76.33.
–
1
1
cm : 3300, 3200–2970, 1600, 1500, 1220, 1160, 1020,
1
5
1
4
7
(
50, 680, 640. H NMR spectrum, d, ppm: 6.28 br.s
m
1
9
4H, NH), 6.74 t (1H, H ), 6.85 d (2H, H ), 7.18 t (2H,
p
o
1
3
H ). C NMR spectrum, d, ppm: 112.70 (C ), 118.74
Found, %: C 36.49; H 2.39; F 16.84; N 20.48; S 10.05.
m
o
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 8 2004

TRIFLUOROMETHANESULFONIC HYDRAZIDES
1075
C H F N O S. Calculated, %: C 35.83; H 2.41; F 17.00;
N 20.89; S 9.56.
7. Harzdorf, C., Meu²doerffer, J-N., Niederprum, H., and
1
0
8
3
5
3
Wechsberg, M., Lieb. Ann., 1973, p. 33.
8
9
. US Patent 2950317, 1960; Ref. Zh. Khim., 1961, 17L103.
. German Patent 2148597, 1973. Chem. Abstr., 1973, vol.
Compound XVII (1 g) was heated in a vacuum (1–
3
mm Hg) in a device for sublimation in a vacuum. In
7
8, 158922.
1
the cooling trap settled out colorless crystals whose H
NMR spectrum was identical to that of an authentic
1
0. Hendrickson, J.B., Bair, K.W., Bergeron, R., Giga, A.,
Skipper, P. L., Sternbach, D.D., and Wareing, J.A., Org.
Prep. Proc. Int., 1977, vol. 9, p. 173.
2
-phenyl-2H-1,2,3-triazole-4-carbaldehyde (XVIII) in
CDCl , d, ppm: 7.44 t (1H, H ), 7.53 t (2H, H ), 8.13 d
3
p
m
11. Hendrickson, J.B. and Sternbach, D.D., J. Org. Chem.,
1975, vol. 40, p. 3450.
(
2H, H ), 8.25 s (1H, CH), 10.21 s (1H, CHO).
O
The authors are grateful to L.I.Larina for recording
12. Haszeldine, R.N. and Kidd, J.M., J. Chem. Soc., 1955, no.
8, p. 2901.
the 15N NMR spectra, and to M.A.Kuznetsov (St.
Petersburg State University) for helpful discussion of
results.
1
3. Fernandez, L.E., Ben, Altabef, A., Fantoni, A.C., and
Varetti, E.L., Spectr. Acta, A, 1997, vol. 53, p. 189.
14. Dhar, M.L., Hughes, E.D., Ingold, C.K., Mandour,A.M.M.,
Maw, G.A., and Woolf, L.I., J. Chem. Soc., 1948, p. 2093.
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