1,1-Dichloropolyfluoroalkanesulfenamides and their dehydrochlorination effected by triethylamine

Article abstract of DOI:10.1007/s11178-005-0155-5

Reactions of 1,1-dichloropolyfluoroalkanesulfenyl chlorides with ammonia afford 1,1-dichloropolyfluoroalkanesulfenamides that under the action of triethylamine are converted into 3,5-bispolyfluoroalkyl-1,2,4-thiadiazoles. 2005 Pleiades Publishing, Inc.

Full text of DOI:10.1007/s11178-005-0155-5

Russian Journal of Organic Chemistry, Vol. 41, No. 2, 2005, pp. 268-271. Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 2, 2005,
pp. 277-280.
Original Russian Text Copyright Ó 2005 by Timoshenko, Rudnichenko, Tkachenko, Shermolovich.
1,1-Dichloropolyfluoroalkanesulfenamides
and Their Dehydrochlorination Effected by Triethylamine
V.M. Timoshenko,A.V. Rudnichenko,A.V. Tkachenko, andYu.G. Shermolovich
Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Kiev, 02094 Ukraine
e-mail: sherm@bpci.kiev.ua
Received February 21, 2004
Abstract—Reactions of 1,1-dichloropolyfluoroalkanesulfenyl chlorides with ammonia afford 1,1-dichloro-
polyfluoroalkanesulfenamides that under the action of triethylamine are converted into 3,5-bispolyfluoroalkyl-
1,2,4-thiadiazoles.
Reactions of a-chloroalkanesulfenyl chlorides with
ammonia and amines are studied in detail only by an
example of trichloromethanesulfenyl chloride [1]. In
contrast to alkane- and arenesulfenamides arising in
reaction of the corresponding sulfenyl chlorides with
ammonia and primary amines, the trichloromethane-
sulfenamides are very unstable. For instance, CCl3SNH2
is stable only below –70°C [1]. In reaction of CCl3SCl
with primary alkyl- and arylamines form sulfenamides
CCl3SNHR that are stable below 0°C, decompose at room
temperature, and explode at heating [2]. However the
longer perchloroalkyl substituent as well as introduction
of fluorine into the molecule of sulfenamide result in
considerable stabilization of the molecule. For instance,
pentachloroetanesulfenamide C2Cl5SNH2 [3] and fluoro-
chloro-substituted sulfenamides CCl2FSNH2 and
CClF2SNH2 [4] are heat-resistant compounds.
The chlorination of sulfides III with gaseous chlorine
resulted in difficultly separable mixtures of sulfenyl
chlorides II and benzyl chloride. However passing excess
ammonia through the reaction mixture afforded sulfen-
amides I that were easily separated from benzyl chloride
by distillation. 1,1-Dichlorosulfenamides I in contrast to
their nonfluorinated analogs are thermally stable liquids
distillable in a vacuum.
We formerly obtained sulfenamides RFCCl2SNHR
treating 1,1-dichloropolyfluoroalkanesulfenyl chlorides
with primary aliphatic and aromatic amines.At dehydro-
chlorination of these compounds by lithium hexamethyl-
disilazide formed thermally stable C-Cl-sulfinimides
RFC(Cl)=S=NR [6, 7]. The latter proved to be valuable
initial compounds for preparation of fluorine-containing
heterocycles [7]. This fact prompted us to investigate
the dehydrochlorination of N-unsubstituted sulfenamides
I. It was expected that at the use of an equimolar amount
of a base would occur monodechlorination to afford
sulfinimide RFC(Cl)=S=NH.
We report here on the synthesis of 1,1-dichloro-
polyfluoroalkanesulfenamides I and their transformation
effected by triethylamine.
It turned out that unlike sulfenamides RFCCl2SNHR
whose dehydrichlorination requires the use of strong
bases, 1,1-dichloropolyfluoroalkanesulfenamides I under-
go dehydrochlorination already at treatment with triethyl-
amine. For instance, reaction of sulfenamides I with
triethylamine in benzene at room temperature gave rise
to 3,5-bis(polyfluoroalkyl)-1,2,4-thiadiazoles IVin 32–40%
yields.
We formerly described a synthesis of 1,1-dichloro-
2,2,3,3,4,4,-5,5-octafluoropentanesulfenyl chloride (IIb)
by chlorination of w-H-perfluoropentanal S,S-dibenzyl-
dithioacetal [5]. Other initial compounds for preparation
of 1,1-dichlorosulfenyl chlorides I are 1,1-dihydropoly-
fluoroalkyl benzyl sulfides III.
&O
5 &&O 6&O
5 &+ 6&+ 3K
,,, ꢀꢁ,,,E
,, ꢀꢁ,,E
6
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(W 1
5 &&O
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5 &&O 61+
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1
, ꢀꢁ,E
, ꢀꢁ,E
,9 ꢀꢁ,9E
RF = H(CF2)2 (a), H(CF2)4 (b)
RF = H(CF2)2 (a), H(CF2)4 (b)
1070-4280/05/4102-0268Ó2005 Pleiades Publishing, Inc.

1,1-DICHLOROPOLYFLUOROALKANESULFENAMIDES
269
Scheme.
6
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(W 1
5
1
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1
6
&&O
6
1+
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6
1+
5
5
5
5
1+
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&O
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,
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1
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To elucidate the path of thiadiazoles formation the
dehydrochlorination was monitored by 19F NMR spectro-
scopy. In reaction at room temperature with 2 mol of
Et3N sulfenamide was not completely consumed even
within 3 days. At the use of 3 mol of Et3N the signals of
the initial sulfenamide disappear from the 19F NMR
spectrum of the reaction mixture in 24 h. After disappear-
ance of the sulfenamide signals the pattern of the
19F NMR spectrum of the reaction mixture did not change
even within 24 h. It is presumable that the limiting reaction
stage is the primary proton abstraction from sulfenamide
I and the arising anion quickly undergoes further
transformations. Therewith it is possible that form both
sulfinimide Aand its isomer cyclic product B which readily
undergoes further dehydrochlorination affording thiazirine
C. The latter exists in an equilibrium with nitrile sulfide
D [8]. Nitrile sulfides are known to be very unstable and
to lose easily the sulfur to give nitriles [9]. At the same
time the nitrile sulfides as active 1,3-dipoles enter into
the cycloaddition reactions with nitriles. It is therefore
presumable that thiadiazoles IV originate from nitrile
sulfide addition to its decomposition product, nitrile (see
the Scheme). The rate of cycloaddition is lower than that
of nitrile sulfide decomposition as shows the presence in
the 19F NMR spectra of the reaction mixtures of signals
belonging to the corresponding polyfluoroalkylnitriles, and
the low-boiling nitrile H(CF2)2CN (bp. 14°C [10]) was
distilled from the reaction mixture and identified by the
19F NMR spectrum.
with tert-butyl hypochlorite of thioamides Va and Vb that
we prepared by introducing sulfur into the corresponding
polyfluoroalkanecarboxamides VIa and VIb furnished
thiadiazoles IVa and IVb in 54–62% yields. The physical
and spectral characteristics of thus obtained compounds
were identical to those of dehydrochlorination products
prepared from sulfenamides I.
3 6
5 &ꢀ2ꢁ1+
5 &ꢀ6ꢁ1+
9, ꢀꢁ9,E
9 ꢀꢁ9E
6
1
5
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5
1
,9 ꢀꢁ,9E
It is known that sulfinimides (of A type), same as nitrile
sulfides (of D type), can react as 1,3-dipoles in the cyclo-
addition reactions [7, 12]. We attempted to trap the
possible intermediates of the dehydrochlorination under
study in the form of cycloaddition adducts. However the
reactions carried out in the presence of various dipolaro-
philes (styrene, ethyl vinyl ether, dimethyl acetylenedicarb-
oxylate) did not provide any new products as shown by
the 19F NMR spectra of the reaction mixtures. Thus the
transformations of the dehydrochlorination products occur
faster than the cycloaddition to the trapping agents
applied.
The analogous cycloaddition of intermediately formed
nitrile sulfide and nitrile was suggested as one of the
possible ways of thiadiazoles formation in thioamides
oxidation with tert-butyl hypochlorite [11]. We chose this
reaction as a procedure for independent synthesis of
thiadiazoles IV in order to confirm the structure of products
obtained at sulfenamides I dehydrochlorination. Reactions
EXPERIMENTAL
1H and 19F NMR spectra were registered on a spectro-
meter Varian VXR-300 at operating frequencies 299.943
and 282.203 MHz respectively. As internal standards
served for H spectra the signals of residual protons in
deuterochloroform (dH 7.26 ppm) and for 19F spectra
1
RUSSIAN JOURNALOF ORGANIC CHEMISTRY Vol. 41 No. 2 2005

270
TIMOSHENKO et al.
hexafluorobenzene (dF –162.9 ppm). The column
chromatography was performed on silica gel Merck 60
(40–63 mm). Sulfide IIIa was prepared as described in
[13], sulfide IIIb and sulfenyl chloride IIb by procedure
from [5].
(2F, CF2), –117.8 m (2F, CF2), –129.5 m (2F, CF2),
–136.6 d.m (2F, HCF2, 2JFH 52.0 Hz). Found, %: C 18.22;
H 0.89; Cl 22.59; S 9.85. C5H3Cl2F8NS. Calculated, %:
C 18.08; H 0.89; Cl 21.35; S 9.66.
Reaction of sulfenamides (I) with Et3N. To a
solution of 0.01 mol of sulfenamide I in 20 ml of benzene
was added dropwise 4.2 ml (0.03 mol) of triethylamine,
and the mixture was stirred for 24 h monitoring the
completion of the reaction by disappearance in the
19F NMR spectrum of the reaction mixture of the signals
of the initial sulfenamide. The precipitate was filtered off,
the filtrate was washed with a saturated water solution
of NH4Cl, dried over Na2SO4, and benzene was
evaporated. The residue was subjected to fractional
distillation in a vacuum. Thiadiazoles IV were additionally
purified by column chromatography on silica gel, eluent
petroleum ether, monitoring byTLC Silufol UV-254 plates,
development in a iodine chamber.
1,1-Dichloro-2,2,3,3-tetrafluoropropanesulfenyl
chloride (IIa). Through a solution of 11.9 g (0.05 mol)
of sulfide IIIa in 40 ml of chloroform at 10°C was passed
a stream of gaseous chlorine for 4 h. The chloroform
was distilled off on a Vigreux column first at the atmo-
spheric pressure, then the residue was distilled in a vacuum
(20 mm Hg) collecting the fraction boiling within 50–60°C.
On repeated distillation the fraction was collected boiling
at 50–52°C (20 mm Hg) was collected; we obtained 10 g
of sulfenyl chloride IIa, containing 10% of benzyl chloride
(according to 1H NMR spectrum). Yield 72%. 1H NMR
spectrum (CDCl3), d, ppm: 4.59 s (PhCH2Cl), 6.26 t.t
(1H, HCF2, 2JHF 52.2, 3JHF 5.4 Hz), 7.36 m (PhCH2Cl).
19F NMR spectrum (CDCl3), d, ppm: –116.1 m (2F, CF2),
–132.5 d.m (2F, CF2H, 2JFH 52.2 Hz).
3,5-Bis(2,2,3,3-tetrafluoroethyl)-1,2,4-thiadi-
azole (IVa). Colorless liquid, yield 40%, bp 51–53°C
1
1,1-Dichloro-2,2,3,3,4,4,5,5-octafluoropentane-
sulfenyl chloride (IIb) was prepared in the same way
as sulfenyl chloride IIa by chlorination of sulfide IIIb.
The solvent was distilled off, the residue was distilled in a
vacuum (12 mm Hg) on a Vigreux column collecting the
fraction boiling at 60–65°C. Sulfenyl chloride IIb thus
prepared contained 35% of benzyl chloride.
(10 mm Hg), Rf 0.72. H NMR spectrum (CDCl3), d,
ppm: 6.31 t.t (1H, HCF2, 2JHF 52.8, 3JHF 4.0 Hz), 6.35 t.t
(1H, HCF2, 2JHF 52.8, 3JHF 4.4 Hz). 19 F NMR spectrum
(CDCl3), d, ppm: –111.3 m (2F, CF2), –116.3 (2F, CF2),
2
–136.5 d.m (2F, CF2, JFH 52.8 Hz), –137.5 d.m (2F,
CF2H, 2JFH 52.8 Hz). Found, %: C 25.36; H 0.68; N 9.62;
S 11.00. C6H2F8N2S. Calculated, %: C 25.18; H 0.70;
N 9.79; S 11.21.
1,1-Dichloro-2,2,3,3-tetrafluoropropanesulfen-
amide (Ia). Through a solution of 16 g of a mixture of
sulfenyl chloride IIa and benzyl chloride in 200 ml of ether
gaseous ammonia was passed at –10°C for 0.5 h. The
reaction mixture was stirred while gradually warmed to
room temperature under continuous stream of ammonia.
To the mixture 75 ml of water was added, the ether layer
was separated, dried over Na2SO4, and the solvent was
evaporated. The residue was subjected twice to a vacuum
distillation. Yellow liquid.Yield 72%, bp 60–61°C (10 mm
Hg). 1H NMR spectrum (CDCl3), d, ppm: 3.43 br.s (2H,
3,5-Bis(2,2,3,3,4,4,5,5-octafluorobutyl)-1,2,4-
thiadiazole (IVb). Colorless liquid, yield 32%, bp 45–
47°C (0.06 mm Hg), Rf 0.64. 1H NMR spectrum (CDCl3),
2
3
d, ppm: 6.10 t.t (1H, HCF2, JHF 51.9, JHF 5.1 Hz),
6.11 t.t (1H, HCF2, JHF 52.1, JHF 5.3 Hz). 19F NMR
spectrum (CDCl3), d, ppm: –107.5 m (2F, CF2–C3),
–112.3 m (2F, CF2–C5), –124.3 m (2F, CF2), –125.2 m
(2F, CF2), –129.6 m (2F, CF2), –130.6 m (2F, CF2),
–138.2 m (4F, 2´CF2H). Found, %: C 24.87; H 0.59;
F 61.79; N 5.68; S 6.43. C10H2F16N2S. Calculated, %:
C 24.70; H 0.41; F 62.52; N 5.76; S 6.60.
2
3
2
3
SNH2), 6.25 t.t (1H, CHF2, JHF 52.8, JHF 5.7 Hz).
19F NMR spectrum (CDCl3), d, ppm: –117.7 m (2F, CF2),
–133.2 d.m (2F, CF2H, 2JFH 52.8 Hz). Found, %: C 15.34;
H 1.52; Cl 30.49; S 13.96. C3H3Cl2F4NS. Calculated, %:
C 15.53; H 1.30; Cl 30.56; S 13.82.
Synthesis of thioamides V. General procedure.
To a dispersion of 0.05 mol of amide VI in 100 ml of
toluene was added 26.68 g (0.06 mol) of P4S10 and 6.7 g
(0.05 mol) of hexamethyldisiloxane. The mixture was
heated to 80°C under vigorous stirring for 20 h with com-
pound VIa or for 12 h with compound VIb. The precipi-
tate was filtered off and washed on the filter with 20 ml
of ether. The solvents were removed in a vacuum (10–
20 mm Hg), the residue was diluted with ether (100 ml).
The ether solution was washed in succession with a satu-
1,1-Dichloro-2,2,3,3,4,4,5,5-octafluoropentane-
sulfenamide (Ib) [14] was prepared similarly to
sulfenamide Ia. Yellow liquid, yield 78%, bp 89–91°C
1
(10 mm Hg). H NMR spectrum (C6D6), d, ppm:
2.58 br.s (2H, SNH2), 5.27 t.t (1H, HCF2, 2JHF 52.0, 3JHF
5.4 Hz). 19F NMR spectrum (C6D6), d, ppm: –107.6 m
RUSSIAN JOURNALOF ORGANIC CHEMISTRY Vol. 41 No. 2 2005

1,1-DICHLOROPOLYFLUOROALKANESULFENAMIDES
271
rated solution of NaHCO3 till the end of gas evolution
(4´50 ml), with a saturated solution of NaCl (2´100 ml),
and with water (2´100 ml). The water layer was addi-
tionally extracted with ether (2´100 ml). The combined
ether solution was dried with Na2SO4, the ether was re-
moved in a vacuum (10–20 mm Hg), and the thioamides
V were obtained as a residue.
roform was distilled off, and the residue was distilled in
a vacuum. Yield of thiadiazole IVa 54%, of thiadiazole
IVb 62%.
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2,2,3,3-Tetrafluorothiopropionamide (Va). Yellow
liquid, yield 40%, bp 45–50°C (0.07 mm Hg). 1H NMR
spectrum (CDCl3), d, ppm: 6.42 t.t (1H, HCF2, 2JHF 53.4,
3JHF 5.5 Hz), 7.78 br.s (1H, NH), 8.00 br.s (1H, NH).
19F NMR spectrum (CDCl3), d, ppm: –120.5 m (2F, CF2),
–139.7 d.m (2F, CF2H, 2JFH 53.4 Hz). Found, %: C 22.29;
H 1.75; N 8.52; S 20.10. C3H3F4NS. Calculated, %:
C 22.36; H 1.88; N 8.69; S 19.90.
2,2,3,3,4,4,5,5-Octafluorothiovaleramide (Vb).
Colorless crystals, yield 89%, mp 38–41°C (from hex-
1
ane). H NMR spectrum (CDCl3), d, ppm: 6.12 t.t (1H,
2
3
HCF2, JHF 52.0, JHF 5.3 Hz), 7.44 br.s (1H, NH),
7.91 br.s (1H, NH). 19F NMR spectrum (CDCl3), d, ppm:
–111.8 m (2F, CF2), –123.8 m (2F, CF2), –130.3 m (2F,
CF2), –138.3 d.m (2F, CF2H, 2JFH 52.0 Hz). Found, %:
C 22.49; H 1.05; N 5.48; S 12.33. C5H3F8NS. Calcu-
lated, %: C 23.00; H 1.16; N 5.36; S 12.28.
11. El-Wassimy, M.T.M, Jorgensen, K.A., Lawesson, S.O.,
Tetrahedron, 1983, vol. 39, p. 1729.
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Shermolovich, Yu.G., and Markovskii, L.N., Zh. Org. Khim.,
1997, vol. 33, p. 70.
Synthesis of thiadiazoles IV from thioamides V.
General procedure. To a solution of 5.4 mmol of
thioamide V in 10 ml of chloroform was added 0.32 ml
(2.7 mmol) of tert-butyl hypochlorite, and the reaction
mixture was stirred at room temperature for 24 h. The
precipitate of elemental sulfur was filtered off, the chlo-
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1994.
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