TCCA-promoted solvent-free chemoselective synthesis of thiosulfonates on grinding

Article abstract of DOI:10.3184/030823410X12744466896732

Trichloroisocyanuric acid (TCCA) is an inexpensive and efficient reagent for solvent-free chemoselective synthesis of thiosulfonates by grinding, providing a metal-free new methodology for the oxidation of disulfides. The important features of this method are that it is reasonably fast, very clean, high yielding, has a simple workup and is environmentally benign.

Full text of DOI:10.3184/030823410X12744466896732

358 RESEARCH PAPER
JUNE, 358–360
JOURNAL OF CHEMICAL RESEARCH 2010
TCCA-promoted solvent-free chemoselective synthesis of thiosulfonates
on grinding
Yali Xua, Yong Penga, Junhui Suna, Jiuxi Chena*, Jinchang Dinga,b and Huayue Wua
aCollege of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035, P. R. China
bWenzhou Vocational andTechnical College, Wenzhou, 325035, P. R. China
Trichloroisocyanuric acid (TCCA) is an inexpensive and efficient reagent for solvent-free chemoselective synthesis of
thiosulfonates by grinding, providing a metal-free new methodology for the oxidation of disulfides. The important
features of this method are that it is reasonably fast, very clean, high yielding, has a simple workup and is environ-
mentally benign.
Keywords: trichloroisocyanuric acid (TCCA), disulfides, thiosulfonates, solvent-free synthesis
Thiosulfonates, with strong sulfenylating power, have found
wide industrial applications both in polymer production and
in photographic processes.1 One of the most practically and
widely used routes for the synthesis of thiosulfonates involves
the direct oxidation of disulfides in the presence of various
promoting agents, such as benzenesulfinate/bromine,2 sodium
trifluoromethanesulfinate/[bis(trifluoroacetoxy) iodo]benzene3
and dinitrogen tetroxide/charcoal.4 In another method, thiosul-
fonates have been prepared by tandem reaction of thiols under
oxidative conditions.5 Some other methods include selective
reduction of arenesulfonyl chlorides promoted by samarium
metalin DMF.6 However, these methods usually suffer from
one or more limitations such as use of volatile organic solvents
and strong oxidizing agents, drastic reaction conditions, expen-
sive reagents, unsatisfactory yields, tedious workup proce-
dures, and co-occurrence of several side reactions. Therefore,
the introduction of new methods to overcome these limitations
is an important experimental challenge.
Trichloroisocyanuric acid (TCCA), an inexpensive, easily
available reagent, having low toxicity, has been widely used in
organic reactions,10,11 but it has not been carefully studied as a
promotor in the synthesis of thiosulfonates until now.
As a part of our continuing interest in the synthesis of sulfur-
containing compounds using green chemistry,9,12,13 we report
here a new and simple TCCA-promoted solvent-free chemose-
lective synthesis of thiosulfonates by oxidation of disulfides
under mild conditions.
To optimise the reaction conditions, initial studies were con-
centrated on treatment of disulfides 1a with TCCA as a model
reaction. Different reaction media were tested to find the
optimised conditions. As shown in Table 1, silica gel was
determined to be the more suitable medium, which afforded
the desired product 2a with excellent yield (Table 1, entry 5).
Using 0.7 equiv. of TCCA the reaction gave the highest
yield (99%) (Table 1, entry 13). However, when the amount
of TCCA was more than 0.7 equiv. or less than 0.7 equiv., the
yields were unsatisfactory (Table 1, entries 6–12). Neverthe-
less, a trace of product was obtained in the absence of TCCA,
which also further proved that TCCA does play an important
role in this reaction (Table 1, entry 14).
In recent years, significant articles have appeared reporting
solid-state reactions by grinding.7–9 Most of these reactions
were carried out at room temperature in an absolutely solvent-
free environment using only a mortar and pestle, and a common
merit of these processes is that they are efficient, economical,
and environmentally friendly.
In the light of these results, subsequent studies were carried
out under the following optimized conditions with 0.7 equiv.
Table 1 Optimisation of reaction conditions for the oxidation of PhSSPha
Entry
Media
TCCA/equiv.
Time/min
Yield/%b
1
2
Acidic Al2O3
Neutral Al2O3
Basic Al2O3
Basic Al2O3
Silica gel
Silica gel
Silica gel
Silica gel
Silica gel
Silica gel
Silica gel
Silica gel
Silica gel
Silica gel
0.8
0.8
0.8
0.8
0.8
0.8
1.0
1.5
1.2
1.1
0.4
0.7
0.7
–
10
10
5
10
10
5
10
10
10
10
10
5
72
78
3
79
4
86
5
95
6
64
7
94
8
42
9
57
10
11
12
13
14
63
61
78
10
30
99
trace
a Reactions conditions: PhSSPh 1a (0.5 mmol) and media (0.5 g) in the presence of TCCA on grinding at room temperature under
solvent-free conditions.
b Isolated yields.
* Correspondent. E-mail: jiuxichen@wzu.edu.cn

JOURNAL OF CHEMICAL RESEARCH 2010 359
TCCA, 0.5 g silica gel, grinding, at room temperature under
solvent-free conditions. Next, to extend the scope and general-
ity of this method, a variety of aromatic disulfides were oxi-
dised to give various thiosulfonates by grinding and the results
are summarised in Table 2.
As shown in Table 2, a series of aromatic disulfides were
investigated. Disulfides containing electron-donating groups,
such as the dimethyl substituted diphenyldisulfides (1b–d)
and the 4,4′-dimethoxydiphenyldisulfide (1e) afforded the cor-
responding thiolsulfonates in 92%, 98%, 92% and 89% yields,
respectively (Table 2, entries 2–5). Similarly, disulfides con-
taining electron-withdrawing groups, such as 4,4′-difluoro-
diphenyl disulfide (1f), 4,4′-dichlorodiphenyl disulfide (1g),
4,4′-dibromodiphenyl disulfide (1h) afforded the correspond-
ing thiosulfonates in 95%, 95%, and 99% yields respectively
(Table 2, entries 6–8), which showed no obvious electronic
effect. Again the high yields of 2c and 2d from substrates with
steric constraints indicate an absence of large steric effects
(Table 2, entries 3 and 4).
To the best of our knowledge, it was little reported that a
reaction could be conducted within 10 min; except, Iranpoor5
reported TBAO/Im/Mn(TPP)OAc promoted synthesis of thio-
sulfonates. Compared to the reaction carried out by TBAO/Im/
Mn(TPP)OAc, this procedure is completely free from organic
solvents and does not use any additives during the reaction.
In conclusion, we have developed a highly efficient and
facile method for the synthesis of thiosulfonates on grinding
under solvent-free conditions. Good yields, short reaction
times and neat conditions are the notable advantages of this
method. We believe that this method provides improved scope
in the synthesis of thiosulfonates and might be a more practical
alternative to existing methods for other organic reactions.
Investigations for the application of the protocol are underway
in our laboratory.
Table 2 Preparation of thiosulfonates from disulfidesa
Entry
1
Substrate (1)
Product (2)
Yield/%b
99
2
3
92
98
4
5
6
7
8
92
89
95
95
99
a Reactions were carried out on a 0.5-mmol scale with TCCA (0.7 equiv.) and silica gel (0.5 g) by grinding at room temperature under
solvent-free conditions.
b Isolated yields.

360 JOURNAL OF CHEMICAL RESEARCH 2010
S-4-Fluorophenyl 4-fluorobenzenesulfonothioate (2f): Solid, m.p.
66–67 °C, (lit.16 70–71 °C). 1H NMR (300 MHz, CDCl3): δ 7.01–7.13
Experimental
Chemicals were purchased and used without further purification.
Melting points were recorded on Digital Melting Point Apparatus
WRS-1B and are uncorrected. NMR spectroscopy was performed on
a Bruker-300 spectrometer or Bruker-500 spectrometer using CDCl3
as the solvent with tetramethylsilane (TMS) as an internal standard
at room temperature. Chemical shifts are given in δ relative to TMS,
the coupling constants J are given in Hz. Mass spectra (MS) were
measured with a Thermo Finnigan LCQ-Advantage. Column chroma-
tography was performed using EM Silica gel 60 (300–400 mesh).
(m, 4H, ArH), 7.32–7.36 (m, 2H, ArH), 7.54–7.59 (m, 2H, ArH). 13
C
NMR (125 MHz, CDCl3): δ 116.1, 116.2, 116.8, 117.0, 123.1, 123.2,
130.3, 130.4, 138.65, 138.67, 138.7, 138.8, 163.8, 164.5, 165.8, 166.5.
ESI-MS: m/z (%): 286 ([M+H]+, 100).
S-4-Chlorophenyl 4-chlorobenzenesulfonothioate (2g): Solid, m.p.
130–131 °C, (lit.14 134–136 °C). 1H NMR (300 MHz, CDCl3): δ 7.29–
7.36 (m, 4H, ArH), 7.40–7.43 (m, 2H, ArH), 7.50–7.53 (m, 2H, ArH).
13C NMR (125 MHz, CDCl3): δ 125.0, 127.9, 128.3, 128.9, 136.7,
137.5, 139.5, 140.3.
S-4-Bromophenyl 4-bromobenzenesulfonothioate (2h): Solid, m.p.
150–152 °C, (lit.17 157–158 °C). 1H NMR (300 MHz, CDCl3): δ 7.21–
7.23 (m, 2H, ArH), 7.41–7.86 (m, 6H, ArH). 13C NMR (125 MHz,
CDCl3): δ 126.6, 127.1, 129.0, 129.2, 132.3, 133.0, 137.9, 141.9.
Typical procedure for preparation of thiosulfonates
The following components were added to the glass mortar: silica gel
(200–300mesh, 500 mg), diphenyldisulfide 1a (109 mg, 0.5 mmol)
and TCCA (81.4 mg, 0.35 mmol). Then the mixture was ground at
room temperature with a glass pestle in the glass mortar. The reaction
was monitored by TLC. After completion of the reaction, the mixture
was transferred into ethyl acetate. The combined organic solvent was
removed under vacuum. The pure product 2a was obtained by silica
gel column chromatography. The physical and spectra data of the
compounds 2a–h are as follows.
We are grateful to the National Key Technology R&D Program
(No. 2007BAI34B00) and the Natural Science Foundation of
Zhejiang Province (No. Y4080107) for financial support.
Received 7 April 2010; accepted 10 May 2010
Paper 1000055 doi: 10.3184/030823410X12744466896732
Published online: 2 July 2010
S-Phenyl benzenesulfonothioate (2a): Solid, m.p. 38–40 °C, (lit.14
1
41–42 °C). H NMR (300 MHz, CDCl3): δ 7.33–7.45 (m, 7H, ArH),
7.55–7.58 (m, 3H, ArH). 13C NMR (125 MHz, CDCl3): δ 127.6, 127.9,
128.8, 129.5, 131.4, 133.7, 136.6, 143.0. ESI-MS: m/z (%): 250
([M+H]+, 100).
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