The degradation of 4,5-dichloro-1,2,3-dithiazolium chloride in wet solvents

Article abstract of DOI:10.1016/j.tet.2009.06.086

4,5-Dichloro-1,2,3-dithiazolium chloride 1 (Appel salt) reacts in wet DCM, THF or MeCN to give elemental sulfur, dithiazole-5-thione 4, dithiazol-5-one 5 and thiazol-5-one 6. Furthermore the reaction of 2-phenylthiazol-5(4H)-one 12 with Appel salt 1 at ca

Full text of DOI:10.1016/j.tet.2009.06.086

Tetrahedron 65 (2009) 6859–6862
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The degradation of 4,5-dichloro-1,2,3-dithiazolium chloride in wet solvents
*
Andreas S. Kalogirou, Panayiotis A. Koutentis
Department of Chemistry, University of Cyprus, PO Box 20537, 1678 Nicosia, Cyprus
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 April 2009
Received in revised form 2 June 2009
Accepted 19 June 2009
Available online 25 June 2009
4,5-Dichloro-1,2,3-dithiazolium chloride 1 (Appel salt) reacts in wet DCM, THF or MeCN to give ele-
mental sulfur, dithiazole-5-thione 4, dithiazol-5-one 5 and thiazol-5-one 6. Furthermore the reaction
of 2-phenylthiazol-5(4H)-one 12 with Appel salt 1 at ca. 20 ꢀC gives 4-(4-chloro-5H-1,2,3-dithiazol-5-
ylidene)-2-phenylthiazol-5(4H)-one 13 (26%) while at ca. 82 ꢀC a new product 2,20-diphenyl-4,40-bi-
thiazol-ylidene-5,50-dione 14 (36%) is additionally isolated. Finally, 4,40-bithiazolylidene-5,50-dione 14
is prepared directly by treating 2-phenylthiazol-5(4H)-one 12 with N-chlorosuccinimide. All new
compounds are fully characterised and rational mechanisms are proposed for the formation of all key
compounds.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
salt 1 and aminotetrazole.12 The structure was solved by single
crystal X-ray crystallography but little was reported regarding the
4,5-Dichloro-1,2,3-dithiazolium chloride 1 (Appel salt), readily
prepared from chloroacetonitrile and disulfur dichloride,1,2 is an im-
portant reagent for the preparation of neutral 1,2,3-dithiazoles.1,3–5
Appel salt 1 condenses with either active methylenes, 1ꢀ anilines or
H2Stoafford 4-chloro-5H-1,2,3-dithiazolylidenes 2, dithiazolimines 3
or dithiazolethione 4 respectively in good yields. The chemistry of
Appel salt 1 and related 1,2,3-dithiazoles has been reviewed.6
compound’s origin.
CN
S
N
Cl
O
S
N
S
X
Cl
Cl
Cl
6
2 (X = CR2)
3 (X = NAr)
4 (X = S)
H2X
+ S
N
We have observed the formation of this thiazol-5-one 6 in
several unrelated Appel salt reactions, in particular when the re-
actions proceeded slowly. This suggested that thiazol-5-one 6 was
a degradation product of Appel salt alone and prompted an in-
vestigation studying the behaviour of Appel salt in a range of
solvents.
S
N
Cl_
S
S
1
1,2,3-Dithiazoles have uses in both biological and material sci-
ences: N-aryldithiazolimines show interesting antitumour,5 anti-
bacterial,7 antifungal,8 and herbicidal9 activities. A search for organic
conductors based on neutral radicals has led to the preparation of
two 1,2,3-dithiazolyl radicals10 and also a tetrathiadiazafulvalene
analogue11 has been prepared and studied.
Often the desired neutral dithiazoles are isolated in good to
excellent yields, however, the reactions mixtures normally contain
minor impurities, often unreported, which include elemental sul-
fur, dithiazolethione 4, and the dithiazolone 5. In one case Rees and
Sivadasan reported the isolation of the structurally unusual, ma-
roon coloured thiazol-5-one 6 from the reaction mixture of Appel
2. Formation of the thiazol-5-one 6 from Appel salt 1
Stirring a suspension of Appel salt 1 in either DCM, THF and
MeCN gave a good recovery of thiazol-5-one 6 while solvents such
as benzene, diethyl ether, MeOH or DMF gave little or no trace of
the compound. The behaviour of Appel salt 1 in DCM, THF and
MeCN was studied more closely (Table 1).
The study indicated that some water (moisture) was necessary
for complete consumption of Appel salt 1. Protecting the reaction
mixture from atmospheric moisture by introducing a drying tube
containing anhydrous CaCl2 led to incomplete consumption of
Appel salt 1; after 24 h stirring ca. 50% of the Appel salt 1 was re-
covered from the reaction mixture by filtration. This implied that
* Corresponding author. Tel.: þ357 22 892783; fax: þ357 22 892809.
E-mail address: koutenti@ucy.ac.cy (P.A. Koutentis).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.06.086

6860
A.S. Kalogirou, P.A. Koutentis / Tetrahedron 65 (2009) 6859–6862
Table 1
CN
Reaction of Appel salt 1 (0.48 mmol) in various solvents (10 mL), at ca. 20 ꢀC
CN
S
N
S
Cl
Cl
Cl
+
Cl
S
N
O
+
+
H2O
S
Cl
O
Cl
Cl
S
N
S
N
S
N
S
S
O
S
_
1
S8
+
+
+
Cl
4
S
N
S
N
S
N
4
6
S
4
S
5
S
6
1
Solvent
Time (h)
Yieldsb (%)
Cl
Cl
Cl
_
Cl
1
S8
4
5
6
Cl
S
S
CN
Cl
1
_
DCM
24
24
6
24
1.5
24
2
0
52
48
0
0
0
0
0
0
0
7
7
5
2
6
13
2
2
3
1
14
15
7
8
8
8
6
17
12
15
10
31
46
32
39
17
28
12
35
35
53
32
24
21
24
5
23
25
13
12
15
13
Traces
SCl2
S
_
N
S
DCMa
DCMa
DCMa,c
THF
_
Cl
CN
HO
CN
Cl
S
S
Cl
H2O
Cl
Cl
7
8
9
10
THF
THFa,c
MeCN
MeCN
MeCNa,c
MeCNa,d
O
S
3
S
S
_
24
4.5
1
Cl
S
O
S
CN
CN
Cl
_
0
3
N
S
a
NC
With CaCl2 drying tube.
Based on recovered starting material.
1 equiv of water added.
N
N
b
c
Cl
+
Cl
HO
11
d
10 equiv of water added.
S
N
S
_
Cl
_
water was needed for the reaction to take place, however, the ad-
dition of excess water to the reaction mixture led to a reduced yield
of the thiazol-5-one 6. Of the three solvents examined DCM and
THF were superior to MeCN and gave yields as high as 25% (yields
are based on 4 equiv of Appel salt 1 for each thiazol-5-one 6, see
Scheme 1) while the latter solvent gave at best yields of 15%. Fur-
thermore the consumption of Appel salt 1 proceeded faster in THF.
Allowing the reaction mixture to stir for longer did not alter the
yield of the thiazol-5-one 6 although the yield of dithiazolone 5 did
improve in some cases. The addition (1 equiv) of a variety of ad-
ditives (S8, Bu4NCl, DMF, dithiazolone 5, dithiazolethione 4) in all
cases led to a reduced yield of thiazol-5-one 6 and so little addi-
tional information could be obtained from these studies.
Cl
NC
N
Cl
_
Cl
S
NC
Cl
Cl
N
O
Cl
S
Cl
S
S
S
N
Cl
S
6
_
_
_
N
Cl
+
Cl
O
Cl2
4
S
Cl2
S
N
S
_
Cl
Scheme 1.
Nevertheless, a close structural analysis of the product revealed
the carbon skeleton of at least three Appel salt molecules. In the
absence of any other reagent or incorporation of solvent molecule
(except H2O) in the structure, it can only be surmised that the
thiazol-5-one 6 was formed only from Appel salt 1 in wet solvent. A
tentative proposed mechanism involved a total of four equivalents
of Appel salt 1 (Scheme 1).
to give the (cyanothioformyl)(cyanoformyl)sulfane 11. Chloride,
which can add to activated nitrile bonds,14 could attack the cyano-
formyl nitrile triggering an intramolecular cyclisation. This chloride
induced cyclisation of the (cyanothioformyl)(cyanoformyl)sulfane
11 can give 4-chloro-2-cyanothiazol-5(H)-one but this would re-
quire the release of elemental sulfur, substantial quantities of which
were not isolated from the reaction mixture. To account for the poor
recovery of elemental sulfur an additional equivalent of Appel salt 1
was envoked to simultaneously assist this cyclisation step and ‘mop
up’ the sulfur. This additional equivalent of Appel salt 1 can then be
released as dithiazolethione 4 and finally after elimination of mo-
lecular chlorine afford the observed thiazol-5-one 6.
Verifying this proposed mechanism, by preparing the chloro-
thioformyl cyanides 9 was not within the capabilities of our labo-
ratory owing to the molecules precarious synthesis.13 Furthermore
it should be noted that the introduction of the necessary oxygen
atom could occur at different stages of the reaction mechanism.
Nevertheless, an analogue of the thiazol-5-one 6 was prepared
from the readily prepared 2-phenylthiazol-5(4H)-one 12, which on
treatment with Appel salt 1 gave the maroon-red 4-(4-chloro-
5H-1,2,3-dithiazol-5-ylidene)-2-phenylthiazol-5(4H)-one 13 (26%)
together with traces of other products. At higher reaction temper-
atures (ca. 82 ꢀC) the yield of thiazol-5-one 13 decreased (17%) and
the bright orange coloured 2,20-diphenyl-4,40-bithiazolylidene-
5,50-dione 14 was additionally isolated in moderate yield (36%). The
formation of 4,40-bithiazolylidene 14 in the reaction mixture
While Appel salt 1 is normally represented in its ionic form it
could be considered to be in equilibrium with the covalent 4,5,5-
trichloro-1,2,3-dithiazole 7, and it is worthy of note that 4-chloro-
5,5-difluoro-1,2,3-dithiazole is a distillable oil.1 Owing to the
reduced aromaticity of the 4,5,5-trichloro-1,2,3-dithiazole 7 the
S–N bond could be sufficiently weak to cleave in the presence of
nucleophilic chloride to afford the thiosulfenyl chloride 8. This
cleavage could also be thermodynamically driven by the release of
a new nitrile triple bond. Similar chloride mediated S–S bond
cleavage of the thiosulfenyl chloride 8 can lead to the formation of
chlorothioformyl cyanide 9.13 This unusual small molecule can
surprisingly be prepared by pyrolysing trichloroacetonitrile in the
presence of elemental sulfur, and was reportedly stable at room
temperature; however, except for its polymerisation on cooling,
nothing has been reported regarding its chemistry.13 It would not be
unreasonable to assume that this species, being highly electrophilic,
could react with any moisture in the reaction mixture to afford
cyanomethanethioic O-acid 10 which could go on to react via the
thione with an additional equivalent of chlorothioformyl cyanide 9

A.S. Kalogirou, P.A. Koutentis / Tetrahedron 65 (2009) 6859–6862
6861
required oxidation. A pure solution of thiazol-5-one 12 in MeCN at
ca. 82 ꢀC open to the atmosphere gave no formation of the dimer
14. This indicated that Appel salt 1 or one of its decomposition
products acted as an oxidizing agent.
spectrometer with a Pike Miracle Ge ATR accessory and strong, me-
dium and weak peaks are represented by s, m and w respectively. 1H
and 13C NMR spectra were recorded on a Bruker Avance 300 machine
(at 300 and 75 MHz, respectively). Deuterated solvents were used for
homonuclear lock and the signals are referenced to the deuterated
solvent peaks. Low resolution (EI) mass spectra were recorded on
a Shimadzu Q2010 GCMS with direct inlet probe. 4,5-Dichloro-1,2,3-
dithiazolium chloride 11 and 2-phenylthiazol-5(4H)-one 1217 were
prepared according to literature procedures.
Ph
S
Ph
+
O
S
N
S
Cl
N
N
O
N
4.2. Reactions of Appel salt 1 with various solvents: typical
procedure (see Table 1)
1
+
N
O
Ph
O
Ph
S
12
S
13
S
14
Toa stirredsolutionofTHF(10 mL) at ca. 20 ꢀC, 4,5-dichloro-1,2,3-
dithiazolium chloride 1 (100 mg, 0.48 mmol) was added and the
reaction was left open to an air atmosphere. After 1.5 h no 4,5-
dichloro-1,2,3-dithiazolium chloride 1 remained. Chromatography
(hexane) gave sulfur (1.5 mg, 5%) and further elution (hexane/DCM,
8:1) gave 4-chloro-5H-1,2,3-dithiazole-5-thione 4 (3.7 mg, 9%) as red
needles, mp 75–76 ꢀC (lit.,1 78–79 ꢀC) (from pentane) identical to an
authentic sample. Further elution (hexane/DCM, 2:1) gave 4-chloro-
5H-1,2,3-dithiazol-5-one 5 (11.7 mg, 16%) as pale yellow plates, mp
35–36 ꢀC (lit.,1 39 ꢀC) (from pentane) identical with that reported. A
final elution (hexane/DCM, 2:3) gave (4E)-4-(4-chloro-5H-1,2,3-
dithiazol-5-ylidene)-4,5-dihydro-5-oxothiazole-2-carbonitrile 6
(7.2 mg, 23%) as dark red crystals, mp (DSC onset) 220 ꢀC (decomp.)
(lit.,12 252–254 ꢀC) (from cyclohexane) identical with that reported.
While several 4,40-bithiazolylidene-5,50-diones have been
reported15 to our knowledge this 2,20-diphenyl derivative 14 was
new. Interestingly the isomeric 2,20-diphenyl-5,50-bithiazolylidene-
4,40-dione 15 was known16 anditspostulatedformationvia5-chloro-
2-phenylthiazol-4(5H)-one, suggested
a possible independent
synthesis. As such treatment of 2-phenylthiazol-5(4H)-one 12 with
NCS (1 equiv) gave 4,40-bithiazol-ylidene 14 in 51% yield.
S
N
Ph
O
Ph
O
NCS (1 equiv.)
MeCN, 82 °C
N
S
12
N
S
O
Ph
O
Ph
S
N
4.3. (4E)-4-(4-Chloro-5H-1,2,3-dithiazol-5-ylidene)-2-
phenylthiazol-5(4H)-one 13
14 (51%)
15
3. Conclusion
To a stirred solution of 2-phenylthiazol-5(4H)-one 12 (17 mg,
0.10 mmol) in dry MeCN (2 mL) at ca. 20 ꢀC, 4,5-dichloro-1,2,3-
dithiazolium chloride 1 (20 mg, 0.10 mmol) was added in one
portion. After 18 h no 4,5-dichloro-1,2,3-dithiazolium chloride 1
Appel salt 1 degrades in wet solvents to give sulfur, dithiazole-
thione 4, dithiazolone 5 and the unusal thiazol-5-one 6. A tentative
mechanism for the formation of the latter was proposed. Water
thus complicates the formation and isolation of desired neutral
1,2,3-dithiazoles. The exclusion of moisture from the reaction sol-
vent, or the atmosphere could lead to cleaner Appel salt reactions.
Finally, the thiazol-5-one 13 was prepared by condensing 2-phenyl-
thiazol-5-one 12 with Appel salt 1 which demonstrated a logi-
cal synthetic route to this unusual class of dithiazolylidenes.
remained and pyridine (16 mL, 0.20 mmol) was added. The mixture
was stirred for 2 h and then adsorbed onto silica. Chromatography
(hexane/DCM, 1:1) gave the title compound 13 (8.4 mg, 26%) as dark
red needles, 234–235 ꢀC (from benzene); (Found: C, 42.3; H, 1.6; N,
8.9. C11H5ClON2S3 requires C, 42.2; H, 1.6; N, 9.0%); lmax (DCM)/nm
230 (log 3 3.22), 298 inf (3.30), 307 (3.33), 361 (2.72), 385 inf (2.57),
487 inf (3.35), 512 (3.40), 551 inf (3.16); nmax/cmꢁ1 1601s (C]N),
1582m, 1526s, 1485s, 1476m, 1447w, 1431s, 1315w, 1302w, 1283w,
1248s, 1238m, 1206w, 1150s, 1099w, 1076w, 1061w, 1028w, 1001w,
957s, 920w, 891s, 829s, 777w and 758s; dH (300 MHz; CDCl3) 8.02–
7.99 (2H, m, Ph H), and 7.53–7.46 (3H, m, Ph H); dC (75 MHz; CDCl3)
189.45 (C]O), 155.8 (dithiazole C-5), 146.4, 146.2, 133.0, 131.7 (Ph
CH), 129.3 (Ph CH) and 127.0 (Ph CH); dC (75 MHz; DEPT-135; CDCl3)
131.7 (Ph CH), 129.3 (Ph CH) and 127.0 (Ph CH); m/z (EI) 314 (Mþþ2,
51%), 312 (Mþ, 100), 277 (2), 153 (2), 121 (C7H5Sþ, 73), 103 (1), 77
(C6Hþ5 , 11), 51 (2).
4. Experimental
4.1. General
Solvents DCM, MeCN and THF were freshly distilled from CaH2
under argon. Reactions were protected from atmospheric moisture
by CaCl2 drying tubes. Anhydrous Na2SO4 was used for drying or-
ganic extracts, and all volatiles were removed under reduced pres-
sure. All reaction mixtures and column eluents were monitored by
TLC using commercial glass backed thin layer chromatography (TLC)
plates (Merck Kieselgel 60 F254). The plates were observed under UV
light at 254 and 365 nm. The technique of dry flash chromatography
was used throughout for all non-TLC scale chromatographic sepa-
rations using Merck Silica Gel 60 (less than 0.063 mm). Melting
points were determined using a PolyTherm-A, Wagner & Munz,
Koefler-Hotstage Microscope apparatus. Decomposition points
(decomp.) and mp>250 ꢀC were determined using a TA Instruments
DSC Q1000 with samples hermetically sealed in aluminium pans
under an argon atmosphere; using heating rates of 5 ꢀC/min. Sol-
vents used for recrystallization are indicated after the melting point.
UV spectra were obtained using a Perkin–Elmer Lambda-25 UV/vis
spectrophotometer and inflections are identified by the abbreviation
‘inf’. IR spectra were recorded on a Shimadzu FTIR-NIR Prestige-21
4.4. 2,20-Diphenyl-4,40-bithiazolylidene-5,50-dione 14
To a stirred solution of 2-phenylthiazol-5(4H)-one 12 (17 mg,
0.10 mmol) in dry MeCN (2 mL), 4,5-dichloro-1,2,3-dithiazolium
chloride 1 (20 mg, 0.10 mmol) was added in one portion and the
mixture was heated at ca. 82 ꢀC. After 0.5 h no 4,5-dichloro-1,2,3-
dithiazolium chloride 1 remained. The mixture was adsorbed onto
silica and chromatography (hexane/DCM, 1:1) gave (4E)-4-(4-
chloro-5H-1,2,3-dithiazol-5-ylidene)-2-phenylthiazol-5(4H)-one
13 (5.5 mg, 17%) as dark red needles, mp 234–235 ꢀC (from ben-
zene) identical with that described above. Further elution (hexane/
DCM, 3:7) gave the title compound 14 (6.1 mg, 36%) as orange
needles, mp (DSC onset) 290 ꢀC (from 1,2-dichloroethane); (Found:
C, 61.7; H, 2.8; N, 7.95. C18H10N2O2S3 requires C, 61.7; H, 2.9; N,

6862
A.S. Kalogirou, P.A. Koutentis / Tetrahedron 65 (2009) 6859–6862
8.0%); lmax (DCM)/nm 230 (log
3
3.27), 267 inf (3.02), 304 (3.34),
References and notes
314 inf (3.33), 349 (3.23), 452 inf (3.46), 479 (3.61), 507 inf (3.49);
nmax/cmꢁ11726m, 1701s (C]O), 1595m, 1504s, 1481s, 1447s, 1317m,
1283s, 1233w, 1194s, 1182m, 1161w, 1130w, 1099w, 1074w, 1051s,
1026s, 1001s, 955s, 922m, 845w, 804w, 762s and 704m; dH
(300 MHz; CD2Cl2) 8.14–8.11 (4H, m, Ph H), 7.70–7.65 (2H, m, Ph H)
and 7.61–7.55 (4H, m, Ph H); m/z (EI) 350 (Mþ, 9%), 121 (C7H5Sþ,
100), 77 (C6Hþ5 , 25), 69 (2), 51 (7).
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2. Koutentis, P. A. Molecules 2005, 10, 346.
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4.5. Independent synthesis of 2,20-diphenyl-4,40-
bithiazolylidene-5,50-dione 14
To a stirred solution of 2-phenylthiazol-5(4H)-one 12 (20 mg,
0.11 mmol) in dry MeCN (1 mL), N-chlorosuccinimide (15.1 mg,
0.11 mmol) was added in one portion and the mixture was heated
at ca. 82 ꢀC for 3.5 h until no thiazolone 12 remained (TLC). The
mixture was then allowed to cool to ca. 20 ꢀC, adsorbed onto silica
and chromatographed (hexane/DCM, 3:7) to afford the title com-
pound 14 (9.9 mg, 51%) as orange needles, mp (DSC onset) 290 ꢀC
(from 1,2-dichloroethane) identical with that reported above.
9. Mayer, R.; Foerster, E. DD Pat. 212,387, 1984.
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1 2002, 1535.
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The authors wish to thank the Cyprus Research Promotion
Foundation [Grant No. NEAYPODOMH/NEKYP/0308/02] and the
following organisations in Cyprus for generous donations of chem-
icals and glassware: the State General Laboratory, the Agricultural
Research Institute and the Ministry of Agriculture. Furthermore we
thank the A.G. Leventis Foundation for helping to establish the NMR
facility in the University of Cyprus.
15. Parrod, J. C.R. Hebd. Seances Acad. Sci. 1951, 232, 740; Wilkinson, J. H.; Wiggins,
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