The preparation and characterization of 5-substituted-4-chloro-1,2,3- dithiazolium salts and their conversion into 4-substituted-3-chloro-1,2,5- thiadiazoles

Article abstract of DOI:10.3390/10020346

A series of monosubstituted acetonitriles were treated with disulfur dichloride at room temperature in CH₂Cl₂ to afford 5-substituted-4-chloro-1,2,3-dithiazolium chlorides 1. Where the 5-substituent was not a good leaving group the chloride salts were converted into the corresponding perchlorate salts 2 which were sufficiently stable and soluble to provide both ¹H- and ¹³C-NMR and cyclic voltammetry data. Several of the dithiazolium chlorides were converted into their corresponding 4-substituted-3-chloro-1,2,5-thiadiazoles 13 on treatment with aqueous ammonia. Mechanisms for all reactions are proposed.

Full text of DOI:10.3390/10020346

Molecules 2005, 10, 346-359
molecules
ISSN 1420-3049
http://www.mdpi.org
The Preparation and Characterization of 5-Substituted-4-
chloro-1,2,3-dithiazolium Salts and their Conversion into 4-
Substituted-3-chloro-1,2,5-thiadiazoles
Panayiotis A. Koutentis*
Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus.
Tel. +35722892783, Fax +35722892809.
* Author to whom correspondence should be addressed; e-mail koutenti@ucy.ac.cy
Received: 29 November 2004 / Accepted: 16 December 2004 / Published: 28 February 2005
Abstract: A series of monosubstituted acetonitriles were treated with disulfur dichloride at
room temperature in CH2Cl2 to afford 5-substituted-4-chloro-1,2,3-dithiazolium chlorides 1.
Where the 5-substituent was not a good leaving group the chloride salts were converted into
the corresponding perchlorate salts 2 which were sufficiently stable and soluble to provide
1
both H- and 13C-NMR and cyclic voltammetry data. Several of the dithiazolium chlorides
were converted into their corresponding 4-substituted-3-chloro-1,2,5-thiadiazoles 13 on
treatment with aqueous ammonia. Mechanisms for all reactions are proposed.
Keywords: 1,2,3-Dithiazole, 1,2,5-thiadiazole, heterocycle, heteroaromatic, electro-
chemistry.
Introduction
The ready formation of 4,5-dichloro-1,2,3-dithiazolium chloride (1a) from chloroacetonitrile and
disulfur dichloride, S2Cl2, was described by Appel and coworkers, who also showed that the reactive
5-chlorine atom was smoothly displaced by a variety of nucleophiles [1]. This work has been widely
applied to heterocyclic synthesis by Kim [2] and Rees [3]. Intramolecular reactions and nucleophilic
opening of the dithiazole ring in derivatives of 1a have also added to the synthetic utility of salt 1a
[2,3]. Although 1,2,3-benzodithiazolium chlorides, ‘Herz salts’, are well known [4] surprisingly few
monocyclic 1,2,3-dithiazolium salts analogous to 1a have been reported. 4-Aryl-5-chloro-1,2,3-
dithiazolium chlorides have been generated from acetophenone oximes and S2Cl2, and the 5-chlorine
displaced by nucleophiles in situ [5]. 1,2,3-Dithiazolyl mono radicals can also be prepared by a one

Molecules 2005, 10
347
electron reduction of dithiazolium salts [6]. It could therefore be of interest to synthesize a wider range
of these salts with the 5-chlorine replaced by other groups so that nucleophilic attack would be
directed to the heterocyclic sulfur atoms with consequent ring opening. Thus we have studied the
reactions of derivatives of acetonitrile with S2Cl2 to see if salts analogous to 1a are formed, and to gain
insight into the mechanism of these reactions.
Results and Discussion
We started with malononitrile, which is inexpensive and highly reactive, since the analogous 5-
cyano-1,2,3-dithiazolium salt could be a versitile synthetic intermediate. Malononitrile has been
reported to react with S2Cl2 in the hot [7], and with thionyl chloride in the cold [8], to give some
tetracyanoethylene (TCNE). We hoped that under mild conditions, similar to those used for the
formation of Appel salt 1a, that this formation of TCNE could be minimised. A CH2Cl2 solution of
malononitrile and S2Cl2 at ca. 20 oC gave a precipitate of golden flakes of a new salt, C3Cl2N2S2
(20%), with very weak nitrile stretching in the IR spectrum at 2235 and 2191 cm-1. Because of its poor
solubility in organic solvents and instability in aqueous solvents no 13C NMR data was obtained. Slow
cooling of a hot solution of the salt in S2Cl2 gave single crystals of the 4-chloro-5-cyano-1,2,3-
dithiazolium chloride 1b which provided an X-ray structure that shows the cationic charge delocalized
and associated with both sulfur atoms [9].
We then extended this salt-forming reaction to the acetonitrile derivatives shown in Table 1, using
the conditions for the dichloro salt 1a, with S2Cl2 in CH2Cl2 at room temperature.
Table 1 Reaction of substituted acetonitriles with S2Cl2 in CH2Cl2 at room temperature to give
1,2,3-dithiazolium chlorides 1
R
Cl
RCH2CN
S2Cl2
+
+
S
N
S
_
Cl
1
R
Reaction time
Product
Yield (%)
Cl
Br
12 h
12 h
4 h
1a
1a
1b
1c
1d
1e
1f
65
60a
20
70
80
85
61
NC
MeS
12 h
14 d
14 d
14 d
4-MeO.C6H4
C6H5
4-O2N.C6H4
a The product was the 5-chloro and not the 5-bromo derivative
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Molecules 2005, 10
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The reaction products were yellow to golden orange in colour with the exception of the 5-chloro
salt 1a which was dark green and the p-methoxyphenyl salt 1d which was deep red. The latter
presumably results from extended conjugation from the methoxy group to the dithiazolium ring. The
dark green colour of 1a was less expected and may result from impurities occluded in the crystals. The
addition of a catalytic amount (5%) of Adogen 464 was reported [10] to give a cleaner reaction for the
preparation of 1a, but we now find the reaction to proceed equally well without this addition.
Furthermore, the reaction mixture of chloroacetonitrile with S2Cl2 gave a more crystalline product if
left to stand without stirring [11] and we found this to apply to all the salts 1a-f in Table 1. These salts
could be separated from the reaction mixtures by rapid filtration under a blanket of nitrogen, and
washed with CH2Cl2, to give analytically pure compounds. An exception to this was the 5-phenyl
derivative 1e which was air sensitive and gave a poor microanalysis.
1,2,3-Dithiazolium perchlorates 2
Owing to poor solubility of the dithiazolium salts and their sensitivity to aqueous solvents, NMR
data was not obtained. To obtain salts more amenable to further study the dithiazolium chlorides 1
were converted into the corresponding perchlorates 2. By treating a suspension of the chlorides 1c-f in
acetonitrile with excess of aqueous perchloric acid (60%) at room temperature followed by filtration
and then dilution of the filtrate with diethyl ether, the 1,2,3-dithiazolium perchlorates 2c-f were
obtained in about 80% yield. Recrystallisation from acetonitrile-diethyl ether gave analytically pure
compounds. Attempts to exchange the anion of the 4,5-dichloro 1a and 4-chloro-5-cyano 1b chlorides
were unsuccessful. With the former the reaction became hot and deep red and hydrogen chloride was
evolved, no precipitate was formed on dilution with diethyl ether. With the latter, 1b, there was a
vigorous exothermic reaction upon addition of the perchloric acid, and only sulfur and ammonium
perchlorate could be isolated.
The stability of the perchlorates 2c-f in wet acetonitrile was sensitive to the C-5 substituent. As this
becomes more electron withdrawing the salts become more prone to decomposition, possibly by
hydrolysis at C-5, the order of stability being MeS = 4-MeO.C6H4 > C6H5 > 4-O2N.C6H4 as would be
expected. This reactivity could explain the failure to obtain the corresponding 5-chloro and
5-cyanodithiazolium perchlorates. The improved stability, crystallinity and solubility of the
dithiazolium perchlorates 2 allowed a more comprehensive spectroscopic study than was possible with
the chlorides 1.
R
Cl
c, R = MeS
d, R = 4-MeO.C6H4
e, R = C6H5
f, R = 4-O2N.C6H4
+
S
N
S
_
ClO4
2
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Molecules 2005, 10
349
Table 2 Selected properties for the 1,2,3-dithiazolium perchlorates 2
Compound
R
Colour
λ
maxnm (log ε)a 13C Chemical shift (ppm)b
mp (oC)c
C-4
C-5
2c
2d
2e
2f
MeS
yellow
red
395 (3.97)
479 (4.07)
399 (3.88)
377 (3.87)
150.6
154.6
156.4
157.7
193.2
181.3
182.1
178.7
205-215
179-183
210-220
216-220
4-MeO.C6H4
C6H5
yellow
cream
4-O2N.C6H4
a For acetonitrile solutions at room temperature. b For CD3CN solutions at 76 MHz. c Twice recrystallised
from acetonitrile-diethyl ether by vapour diffusion techniques.
The perchlorates have strong UV/vis absorption and the lowest energy bands correspond to their
colours (Table 2). The first absorption band of the 4-methoxyphenyl derivative 2d was shifted to the
red, indicating extended delocalisation from the methoxy group to the dithiazolium cation. The 13C
NMR data (Table 2) showed that the C-5 carbon resonances for all the perchlorates were at low field
suggesting that there is considerable positive charge associated with S-1 and S-2. The decrease in
chemical shift at C-5 in going from R = MeS to Ph to 4-O2N.C6H5 reflects the decreasing ability of
these substituents to stabilize the positive charge at S-1 and S-2. The C-5 resonance of the
4-MeO.C6H4 derivative 2d does not follow this trend and, in agreement with the UV/vis data, it
appears that delocalisation of charge directly affects the hybridisation of C-5 and hence its 13C
resonance. The chemical shift values obtained give a qualitative picture of the charge distribution in
the 1,2,3-dithiazolium perchlorates 2.
Electrochemical Study of the 1,2,3-dithiazolium perchlorates 2c-f
In light of the stability of the perchlorate salts and the interest in 1,2,3-dithiazolyl radicals [6] we
submitted dithiazolium perchlorates (2c-f)+ to cyclic voltammetry and found reversible redox
.
behavior, with formation of the corresponding dithiazolyl radicals (2c-f) . A second reduction process
-
was also observed and tentatively indicated the formation of the dithiazolide anions (2c-f) .
R
Cl
R
Cl
R
Cl
_
_
+ 1e
+ 1e
_
_
_
_
_
.
+
S
1e
1e
S
N
S
N
S
N
S
S
-
2+
2.
2
This second process was apparently irreversible and may indicate that the reduced anionic species
-
2 undergoes a further and rapid reaction on the CV time-scale (seconds); possibly the reduced species
+
-
2 is rapidly quenched by dithiazolium cations 2 in the bulk solution to give two equivalents of the
.
radical species 2 .
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Molecules 2005, 10
350
R
Cl
R
N
+
S
+
S
S
N
N
S
_
_
ClO4
AsF6
2+
3+
Table 3 The E1/2(red) valuea for the 1,2,3-dithiazolium perchlorates 2c-f and
for the 1,2,3,5-dithiadiazolium salts 3a-c.
R
Compound
E1/2(red)/V
Compound
E1/2(red)/Vb
2c
2d
2e
2f
- 0.22
- 0.22
- 0.14
+ 0.02
-
-
MeS
3a
3b
3c
+ 0.19
+ 0.22
+ 0.295
4-MeO.C6H4
C6H5
4-O2N.C6H4
a Referenced vs ferrocene as internal standard at 0 V in CH3CN at ca. 273 K.
b Original values referenced to a standard calomel electrode but have been
adjusted (- 0.38 V) to a ferrocene zero for comparison.
The half-wave reduction potentials, E1/2(red) [12], for the dithiazolium cations were calculated and
compared to those published for the 1,2,3,5-dithiadiazolium salts (Table 3). The more positive the
value for the half wave reduction potential the more easily an electron can be introduced into the
cation to form the radical species. As the substituent R at C-5 becomes more electron withdrawing the
values for the reduction potential become more positive as expected. The 1,2,3-dithiazolium salts 2+
are more difficult to reduce than the 1,2,3,5-dithiadiazolium salts 3+ and this possibly arises from the
presence of one nitrogen atom in the dithiazolium salts 2+ compared to two in the latter salts 3+.
Nitrogen is strongly electronegative and may help in the formation of the radical species. Interestingly,
changing the substituent on the aryl ring from MeO to H to NO2 has a greater effect (more than
double) on the half wave reduction potential for the dithiazolium salts 2+ than for the dithiadiazolium
salts 3+ suggesting that the former are more sensitive to the electronic effects than the latter. The
insensitivity of compounds 3+ to the substituent at C-5 has been attributed to a node at C-5 in the
LUMO state which effectively isolates the dithiadiazolium ring from the substituent at C-5 [13]. The
quality of the CV spectra for the dithiazolium perchlorates 2+ became steadily worse with each scan
cycle. New peaks were observed to form and to increase steadily on successive scans whilst those
peaks attributed to the reversible reduction process became steadily less intense. The acetonitrile
solution became slowly cloudy and a pale precipitate was observed. Furthermore a pale cream
coloured film was deposited on the platinum electrode. Due to the fairly rapid decomposition of the
compound under the scan conditions, an investigation of the deposition onto the platinum electrode
was not continued.
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Molecules 2005, 10
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Mechanism of Dithiazole Ring Formation.
Various mechanisms can be envisaged for the conversion of RCH2CN into the dithiazolium salts 1,
but there is no firm evidence available. The first step could be chlorination of the acetonitrile by S2Cl2,
as demonstrated for acetonitrile itself [1] and for phenylacetonitrile [14]. This could be followed by
addition of S2Cl2 to the cyano group and cyclisation and ionisation as shown in Scheme 1, or
chlorination could occur later in the sequence.
Scheme 1
R
Cl
Cl
Cl
H
RCH2CN
S2Cl2
R
CH CN
+
S
N
Cl
S
Cl
S
Cl
S
Cl
Cl
R
R
S
1
N
N
S
Cl
H
However, dimethylacetonitrile is reported to react with S2Cl2 to give the substitution products 4
and 5, without addition to the cyano group [15]; similarly when 1-cyanomethylcyclopentene 6 was
treated with S2Cl2 and Hünig’s base the cyclopenta-1,2-dithiole 7 was formed with the cyano group
intact [16] (Scheme 2).
Scheme 2
CN
Me2C
CN
Me2C CN
S2Cl2
R
CH2 CN
+
+
CMe2
S
S
S
SCl
4
5
CN
Cl
Cl
CN
S2Cl2
Cl
S
+
S
6
7
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Molecules 2005, 10
352
We must therefore consider an alternative mechanism for the salt formation in which RCH2CN is
first substituted by S2Cl2 to give 8 which can cyclise by addition of chloride to the cyano group or its
ketenimine tautomer, or by further reaction of 7 with S2Cl2, as shown in Scheme 3.
Scheme 3
_
Cl
NH
C
R
C
S
R
CH2 CN
+
S2Cl2
S
Cl
R
CH CN
S
SCl
S2Cl2
S2Cl2
8
_
Cl
R
Cl
H
S
Cl
R
N
SSCl
NH
C
S
R
N
SSCl
S
C
S
S
S
Cl
Cl
R
Cl
N
R
Cl
S
S
S
+
S
S
N
Cl
S
_
Cl
A Route to 1,2,5-Thiadiazoles 13
To further characterise the 1,2,3-dithiazolium salts we proceeded to investigate their response to
aqueous ammonia. Since 1,2-dithiolium salts 9 on treatment with ammonia afford isothiazoles 10
through a formal exchange of one ring sulfur by nitrogen [17], and treatment of 4-alkyl-5-chloro-1,2,3-
dithiazolium chlorides 11 with aniline gave 4-alkyl-2-phenyl-3H-1,2,5-thiadiazol-3-thiones 12 [18]
(Scheme 4), we anticipated the formation of 4-substituted 3-chloro-1,2,5-thiadiazoles 13 [19].
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Molecules 2005, 10
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Scheme 4
Ph
Ph
NH3 (g), EtOH
20-80 oC, 1.5 h
+
S
N
S
S
_
ClO4
9
10, 88 %
Cl
+
R
N
S
R
PhNH2
S
N
N
S
Ph
S
_
Cl
11
12
Treatment of an acetonitrile solution of the 1,2,3-dithiazoles with aqueous ammonia gave in three
cases the corresponding 1,2,5-thiadiazoles 13 (Scheme 5). The derivatives 13c and 13a (R=MeS and Cl
respectively) were not observed possibly as these compounds were very volatile and difficult to isolate.
Scheme 5
R
Cl
R
Cl
a, R = Cl, 0 %
b, R = CN, 7 %
c, R = SMe, 0 %
d, R = Ph, 36 %
e, R = 4-NO2.C6H4, 26 %
NH4OH, MeCN
20-80 oC, 2 h
+
S
N
N
N
S
S
_
Cl
1
13
A mechanism for the the S-N exchange leading to the formation of the 1,2,5-thiadiazoles 13 from
the dithiazolium salts 1 is tentatively based closely on that proposed for the transformation of
1,2-dithiolium salts into their corresponding isothiazoles under analogous conditions [17]. The amine
14 presumably suffers ring opening to give the imine 15 which undergoes subsequent ring closure to
afford thiadiazole 13 with evolution of H2S (Scheme 6).
Scheme 6
R
Cl
R
S
Cl
R
Cl
_
H2N
H2S
HN
N
N
S
N
N
S
S
SH
15
13
14
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Molecules 2005, 10
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Conclusions
A series of substituted acetonitriles give on treatment with disulfur dichloride the corresponding
5-substituted-4-chloro-1,2,3-dithiazolium chlorides 1. Where the 5-substituent is not a good leaving
group, these chloride salts can be converted into their perchlorate analogues 2 on treatment with
perchloric acid in acetonitrile. Treatment of dithiazolium chlorides with ammonia afford the
1,2,5-thiadiazoles 12 albeit in low to moderate yields. Whilst the preparation of fully unsaturated
1,2,5-thiadiazoles from 1,2,3-dithiazolium salts has not previously been reported [19], further work, is
required to find optimal reaction conditions which may afford the thiadiazoles in good yield. The
conversion also highlights the electrophilic and labile nature of 1,2,3-dithiazolium salts and suggests
new uses of 1,2,3-dithiazolium salts as precursors in heterocyclic synthesis and this is now under
investigation by our research group.
Acknowledgements
I wish to thank N. J. Shirtcliffe for performing the cyclic voltammetry studies at Imperial College,
Professor C. W. Rees for valuable discussions and the EPSRC for a Research Studentship (P. A. K.).
MDL Information Systems (UK) Ltd for financial support and the Wolfson Foundation for establishing
the Wolfson Centre for Organic Chemistry in Medicinal Science at Imperial College.
Experimental
General
Commercial compounds and solvents were used without further treatment except where noted.
Acetonitrile was freshly distilled from phosphorus pentoxide. Monosulfur dichloride was freshly
distilled from phosphorus trichloride. All reactions were protected from moisture by a calcium
chloride drying tube. Anhydrous magnesium sulphate was used for drying organic extracts and
volatiles were removed under reduced pressure. Ether refers to diethyl ether and petrol refers to light
petroleum bp 60-80 oC. All reactions and column eluents were monitored by TLC using commercial
aluminium-backed thin-layer chromatography (TLC) plates (Merck Kieselgel 60 F254). The plates were
observed under UV light at 254 and 350 nm. The technique of dry flash chromatography was used
throughout for all non-TLC scale chromatographic separations using Sorbsil C60 M40 silica. Melting
points were determined using a Reichert Kofler hot-stage apparatus. Where samples were
recrystallised, the solvents used are indicated after the melting point. UV spectra were obtained using a
Perkin Elmer Lambda II spectrometer and inflections are identified by the abreviation “inf”. IR spectra
were recorded on a Perkin-Elmer 1710FT spectrometer and strong, medium and weak peaks are
1
represented by s, m or w respectively. H- and 13C-NMR spectra were measured on a Brucker
AM300WB machine at 300 and 76 MHz, respectively. Deuterated solvents were used for homonuclear
lock and the signals are referenced to the deuterated solvent peaks. Mass spectra were recorded on a
VG micromass 7070E or a VG Autospec “Q” mass spectrometer. FAB spectra were obtained using a
glycerol matrix and CI were carried out using ammonia for ionisation. Microanalyses were carried out
on a Perkin-Elmer 2400 CHN Analyser.
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Molecules 2005, 10
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Cyclic voltammetry of the 1,2,3-dithiazolium perchlorates 2c-f
The 1,2,3-dithiazolium perchlorates 2c-f were dissolved in acetonitrile (25 mL) together with
enough tetrabutylammonium tetrafluoroborate to make a 0.1M solution. All solutions were degassed
with argon and stored under a blanket of argon. The cell was held at 0 oC using an ice/water bath.
Cyclic voltammetry was performed on the salt solutions. A 7 mm diameter platinum electrode (Oxford
Electrics) was the working electrode with a Ag/AgNO3 in acetonitrile reference (Russel Electrodes).
The counter electrode was a platinum gauze. Potential sweeps were performed between +0.5 and -1.5
V beginning at the higher potential, with a sweep rate of 20 mV s-1, (see Table 3).
1,2,3-Dithiazolium chlorides (1) (see Table 1)
Typical procedure: To a solution of chloroacetonitrile (16.8 mL, 0.265 mol) in CH2Cl2 (50 mL) at ca.
20 oC, disulfur dichloride (50 ml, 0.62 mol) was added and the mixture was agitated manually for a
few seconds. On standing a black precipitate was formed and after 12 h this was separated by filtration
and washed copiously with CH2Cl2 to give 4,5-dichloro-1,2,3-dithiazolium chloride 1a (35 g, 65%),
identical with an authentic specimen [1].
4-Chloro-5-cyano-1,2,3-dithiazolium chloride (1b). Similar treatment of propanedinitrile with disulfur
dichloride gave compound 1b (20%) as golden plates, mp 115-120 oC dec. (from disulfur dichloride):
Found: C, 18.3; N, 13.9. C3Cl2N2S2 requires C, 18.2; N, 14.1%; IR νmax (Nujol)/cm-1 2235w and
2191w (CN), 1703w, 1614w, 1537w, 1360s, 1343s, 1327m, 1308m, 1168m, 1140w, 986w, 936m,
889w, 856s, 828w, 745w, 723w, 647m; MS m/z (EI) 198 (M+, 1%), 163 (M+-Cl, 61), 128 (9), 104 (10),
+
102 (100), 96 (9), 93 (CClNS+, 11), 76 (6), 70 (76), 64 (S2 , 14), 45 (12); HRMS Found: M+,
197.8877. C3Cl2N2S2 requires M, 197.8880.
4-Chloro-5-methylthio-1,2,3-dithiazolium chloride (1c). Similar treatment of (methylthio)acetonitrile
with disulfur dichloride gave 1c (70%) as yellow crystals, mp 180-190 oC; Found: C, 16.2; H, 1.4; N,
6.1. C3H3Cl2NS3 requires C, 16.4; H, 1.4; N, 6.4%; IR νmax (Nujol)/cm-1 1674w, 1427s, 1311m, 1279m,
1225s, 1086s, 992w, 978m, 917w, 895s, 803s, 711w, 639m; MS m/z (FAB) 184 (M+-Cl, 100%) ;
HRMS Found: M+-Cl, 183.9104. C3H3ClNS3 requires M-Cl, 183.9116.
4-Chloro-5-(4-methoxyphenyl)-1,2,3-dithiazolium chloride (1d). Similar treatment of (4-methoxy-
phenyl)acetonitrile with disulfur dichloride gave 1d (80%) as red crystals, mp 180-190 oC dec.; Found:
C, 38.4; H, 2.6; N, 4.8. C9H7Cl2NOS2 requires C, 38.7; H, 2.5; N, 5.0%; IR νmax (Nujol)/cm-1 3103m,
3080w and 3058w (Ar CH), 1598m, 1526s, 1515s, 1492w, 1407w, 1342s, 1312s, 1289m, 1265m,
1206s, 1182w, 1115m, 1106m, 1008m, 991w, 975w, 925w, 864m, 854m, 836s, 754m, 719m, 693m,
662w; MS m/z (FAB) 244 (M+-Cl, 100%); HRMS Found: M+-Cl, 243.9665. C9H7ClNOS2 requires M-
Cl, 243.9658.
4-Chloro-5-phenyl-1,2,3-dithiazolium chloride (1e). Similar treatment of phenylacetonitrile with
disulfur dichloride gave 1e (85%) as yellow needles, mp 80-90 oC; Found: C, 36.3; H, 1.9; N, 5.2.
3(C8H5Cl2NS2).CH2Cl2 requires C, 36.1; H, 2.05; N, 5.05%; IR νmax (Nujol)/cm-1 1675w, 1590m,
1350s, 1320s, 1254w, 1231w, 1201s, 1174m, 1078m, 1027m, 999m, 966m, 909m, 856m, 843m, 825m,
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Molecules 2005, 10
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775m, 769m, 759m, 722w, 686s; MS m/z (EI) 214 (M+-Cl, 14%), 192 (4), 178 (4), 115 (26), 160 (9),
+
147 (16), 131 (42), 121 (37), 105 (100), 90 (5), 77 (C6H5 , 39), 69 (17); HRMS Found: M+-Cl,
213.9552. C8H5ClNS2 requires M-Cl, 213.9552.
4-Chloro-5-(4-nitrophenyl)-1,2,3-dithiazolium chloride (1f). Similar treatment of (4-nitro-
phenyl)acetonitrile with disulfur dichloride gave 1f (61%) as yellow/orange plates, mp > 180 oC dec.;
Found: C, 32.6; H, 1.4; N, 9.3. C8H4Cl2N2O2S2 requires C, 32.65; H, 1.4; N, 9.5%; IR νmax (Nujol)/cm-1
3103m, 3080w and 3058w (Ar CH), 1598m, 1526s, 1515s, 1492w, 1407w, 1342s, 1312s, 1289m,
1265m, 1206s, 1182w, 1115m, 1106m, 1008m, 991w, 975w, 925w, 864m, 854m, 836s, 754m, 719m,
693m, 662w; MS m/z (EI) 259 (M+-Cl, 36%), 236 (6), 213 (25), 192 (78), 176 (11), 162 (20), 146 (45),
136 (20), 120 (21), 102 (19), 90 (6), 69 (100), 55 (11); HRMS Found: M+-Cl, 258.9418.
C8H4ClN2O2S2 requires M-Cl, 258.9403.
1,2,3-Dithiazolium perchlorates (2): Typical procedure
To a suspension of 4-chloro-5-methylthio-1,2,3-dithiazolium chloride 1c (500 mg, 2.28 mmol) in
acetonitrile (50 mL) at ca. 20 oC, 60% aqueous perchloric acid (1 mL) was added. The mixture became
hot and the chloride salt dissolved. The mixture was filtered and then diluted with ether until a cloudy
suspension had formed. On standing this formed crystals and filtration gave 4-chloro-5-methylthio-
1,2,3-dithiazolium perchlorate (2c, 516mg, 80%) as yellow needles, mp 205-215 oC (from
acetonitrile/ether); Found: C, 12.9; H, 0.8; N, 4.8. C3H3Cl2NO4S3 requires C, 12.7; H, 1.1; N, 4.95%;
UV λmax(CH3CN)/nm 223 (log ε 3.65), 240 (3.52), 279 (3.35), 340 inf (3.50), 395 (3.97); IR
1
νmax(Nujol)/cm-1 1438m, 1235s, 1104s and 1060s (ClO4), 978w, 917w, 835m, 622m; H-NMR
(CD3CN) 3.23 (3H, s, CH3S); 13C-NMR (CD3CN) 193.20 (C-5), 150.62 (C-4), 23.76 (CH3S); MS m/z
(FAB) 184 (M+-ClO4, 100%); HRMS Found: M+-ClO4, 183.9096. C3H3ClNS3 requires M-ClO4,
183.9116.
4-Chloro-5-(4-methoxyphenyl)-1,2,3-dithiazolium perchlorate (2d). Similar treatment of 4-chloro-5-(4-
methoxyphenyl)-1,2,3-dithiazolium chloride (1d) with 60% aqueous perchloric acid and ether gave 2d
(75%) as red needles, mp 179-183 oC (from acetonitrile/ether); Found: C, 31.8; H, 2.1; N, 4.1.
C9H7Cl2NO5S2 requires C, 31.5; H, 2.0; N, 4.1%; UV λmax(CH3CN)/nm 262 (log ε 3.80), 289 (3.67),
479 (4.07); IR νmax (Nujol)/cm-1 3040w (Ar CH), 1594m, 1448m, 1352s, 1211s, 1187m, 1051s br
(ClO4), 928m, 859s, 763s, 692s, 625s; 1H-NMR (CD3CN) 8.12 (2H, d, J 9.0 Hz, Ar H-3), 7.28 (2H, d,
J 9.0 Hz, Ar H-2), 4.00 (3H, s, CH3O); 13C-NMR (CD3CN) 181.26 (C-5), 167.00 (Ar C-4), 154.61 (C-
4), 134.64 (Ar C-2), 119.50 (Ar C-1), 116.20 (Ar C-3), 56.33 (CH3O); MS m/z (FAB) 244 (M+-ClO4,
100%); HRMS Found: M+-ClO4, 243.9669. C9H7ClNOS2 requires M-ClO4, 243.9658.
4-Chloro-5-phenyl-1,2,3-dithiazolium perchlorate (2e). Similar treatment of 4-chloro-5-phenyl-1,2,3-
dithiazolium chloride (1e) with 60% aqueous perchloric acid and ether gave 2e (82%) as yellow
needles, mp 210-220 oC (from acetonitrile/ether); Found: C, 30.9; H, 1.7; N, 4.5. C8H5Cl2NO4S2
requires C, 30.7; H, 1.6; N, 4.5%; UV λmax(CH3CN)/nm 233 (log ε 3.83), 271 inf (3.44), 399 (3.88); IR
νmax (Nujol)/cm-1 3040w (Ar CH), 1594m, 1448m, 1352s, 1211s, 1187m, 1051s br (ClO4), 928m, 859s,
763s, 692s, 625s; 1H-NMR (CD3CN) 8.01 (2H, m, Ar H-2), 7.91 (1H, m, Ar H-4), 7.76 (2H, m, Ar H-
3); 13C-NMR (CD3CN) 182.08 (C-5), 156.37 (C-4), 135.51 (Ar C-4), 131.54 (Ar C-2), 130.09 (Ar C-
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3), 126.22 (Ar C-1); MS m/z (FAB) 214 (M+-ClO4, 100%); HRMS Found: M+-ClO4, 213.9562.
C8H5ClNS2 requires M-ClO4, 213.9552.
4-Chloro-5-(4-nitrophenyl)-1,2,3-dithiazolium perchlorate (2f). Similar treatment of 4-chloro-5-(4-
nitrophenyl)-1,2,3-dithiazolium chloride (1f) with 60% aqueous perchloric acid and ether gave 2f
(78%) as cream coloured needles, mp 216-220 oC (from acetonitrile/ether) (Found: C, 27.0; H, 1.15; N,
7.8. C8H4Cl2N2O6S2 requires C, 26.8; H, 1.1; N, 7.8%); λmax(CH3CN)/nm 263 (log ε 4.00), 373 (3.87);
νmax(Nujol)/cm-1 3107m, 3074w and 3049w (Ar CH), 1599m, 1521s, 1490w, 1464s, 1456s, 1410w,
1349s, 1316m, 1291m, 1253w, 1235w, 1215s, 1187w, 1110s, 1061s, 1014m, 992w, 979w, 936m,
869m, 849s, 833m, 751s, 719w, 691s, 666w, 626s; 1H-NMR (CD3CN) 8.51 (2H, d, J 8.9 Hz, Ar H-3),
8.16 (2H, d, J 8.9 Hz, Ar H-2); 13C-NMR (CD3CN) 178.70 (C-5), 157.65 (C-4), 151.22 (Ar C-4),
132.83 (Ar C-2), 131.72 (Ar C-1), 124.63 (Ar C-3); m/z (FAB) 259 (M+-ClO4, 100%), (Found: M+-
ClO4, 258.9415. C8H4ClN2O2S2 requires M-ClO4, 258.9403).
Reaction of 4-chloro-5-cyano-1,2,3-dithiazolium chloride (1b) with aqueous perchloric acid.
To a suspension of 4-chloro-5-cyano-1,2,3-dithiazolium chloride (1b, 500 mg, 2.53 mmol) in
acetonitrile (50 mL) at ca. 20 oC 60% aqueous perchloric acid (1 mL) was added. The mixture became
hot (> 80 oC) and brown. On cooling a cream coloured precipitate was deposited. This was filtered and
washed with CH2Cl2. The washings were concentrated under reduced pressure and a little sulfur was
identified. The precipitate was identified as ammonium perchlorate (139mg, 23%) as colourless
needles, mp > 300 oC (from acetone/ether); Found: H, 3.0; N, 11.8. Calc. for NH4ClO4: H, 3.4; N,
11.9%), identical with an authentic specimen.
Reaction of 1,2,3-dithiazolium chlorides (1) with aqueous ammonia: Typical procedure
To a stirred suspension of 4-chloro-5-phenyl-1,2,3-dithiazolium chloride (1e, 124.5 mg, 0.5 mmol)
in acetonitrile (30 mL) at ca. 20 oC 33% aqueous ammonia (0.4 mL) was added. After 1 h at ca. 20 oC
the mixture was heated to reflux (80 oC) for a further 1 h and on cooling to ca. 20 oC was diluted with
water (30 mL), extracted with petrol (5x10 mL) and with CH2Cl2 (2x10 mL). The combined organic
fractions were separated, dried, filtered and the volatiles were removed. Chromatography
(petrol:CH2Cl2, 3:1) of the residue gave 3-chloro-4-phenyl-1,2,5-thiadiazole (13d, 35 mg, 36%) as
colourless needles, mp 32-33 oC (lit., [20] 33 oC) (from pentane); IR νmax(neat)/cm-1 3064w (Ar CH),
1680w (C=N), 1579w (C=C), 1463m, 1442m, 1359s, 1289w, 1259m, 1163s, 1076w, 1034w, 1002w,
1
979s, 922w, 841m, 773s, 745w, 715m, 693s, 656m; H-NMR (CD3CN) 7.89 (2H, m, Ar H-2), 7.48
13
(3H, m, Ar H-3 and 4); C-NMR (CD3CN) 157.82 (C-4), 143.24 (C-3), 130.78 (Ar C-1), 130.28 (Ar
C-4), 128.72 (Ar C-3), 128.65 (Ar C-2); MS m/z (EI) 196 (M+, 82%), 135 (M+-CClN, 100), 103 (M+-
CClNS, 20), 93 (CClNS+, 38), 77 (C6H5 , 25), 64 (11), 51 (22); HRMS Found: M+, 195.9860.
+
C8H5ClN2S requires M, 195.9862.
3-Chloro-4-(4-nitrophenyl)-1,2,5-thiadiazole (13e). Similarly,. treatment of 4-chloro-5-(4-nitro-
phenyl)-1,2,3-dithiazolium chloride (1f) with 33% aqueous ammonia gave 13e (31 mg, 26%) as
colourless needles, mp 103 oC (from cyclohexane); Found: C, 40.0; H, 1.45; N, 17.3. C8H4ClN3O2S
requires C, 39.8; H, 1.7; N, 17.4%; UV λmax(CH2Cl2)/nm 299 (log ε 4.30); IR νmax (Nujol)/cm-1 3120w
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Molecules 2005, 10
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and 3087w (Ar CH), 1600m (C=N), 1521s (NO2), 1412w, 1353s (NO2), 1334m, 1317m, 1301m,
1
1264w, 1167m, 1112w, 1014w, 985m, 864m, 856m, 839m, 831m, 760w, 720m, 686m; H-NMR
13
(CD3CN) 8.37 (2H, d, J 9.0 Hz, Ar H-3), 8.17 (2H, d, J 9.1 Hz, Ar H-2); C-NMR (CD3CN) 155.96
(C-4), 148.78 (Ar C-4), 143.72 (C-3), 136.65 (Ar C-1), 129.85 (Ar C-2), 123.82 (Ar C-3); MS m/z
(EI) 241 (M+, 100%), 225 (M+-O, 3), 211 (M+-NO, 29), 195 (M+-NO2, 25), 183 (M+-CNO2, 16), 168
(9), 160 (20), 151 (5), 137 (6), 133 (10), 122 (12), 118 (8), 108 (9), 102 (8), 93 (CClNS+, 12), 75 (9),
63 (7); HRMS Found: M+, 240.9704. C8H4ClN3O2S requires M, 240.9713.
3-Chloro-4-cyano-1,2,5-thiadiazole (13b). Similarly, treatment of 4-chloro-5-cyano-1,2,3-dithiazolium
chloride (1b) with 33% aqueous ammonia gave the title compound 13b (5 mg, 7%) as a colourless oil;
IR νmax(neat)/cm-1 2247w and 2211w (CN), 1453m, 1354s, 1313w, 1291m, 1257w, 1080s, 928s, 846s,
831m, 756w, 728w, 701s; MS m/z (EI) 145 (M+, 85%), 119 (M+-CN, 13), 93 (CClNS+, 100), 84 (M+-
CClN, 80), 58 (CNS+, 15), 46 (NS+, 25); HRMS Found: M+, 144.9498. C3ClN3S requires M, 144.9501.
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16. Rakitin, O. A.; Rees, C. W.; Williams, D. J.; Torroba, T. J. Org. Chem. 1996, 61, 9178-9185.
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Sample Availability: Available from the author.
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