High yielding protocol for direct conversion of thiols to sulfonyl chlorides and sulfonamides

Article abstract of DOI:10.1080/17415993.2019.1570196

In this paper, a new method for oxidative chlorination of thiols to sulfonyl chlorides and sulfonamides using H₂O₂ in the presence of TMSCl is reported. The excellent yields, short reaction times, excellent efficiencies, low costs, and easy separation of products are the most important advantages of this method.

Full text of DOI:10.1080/17415993.2019.1570196

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: https://www.tandfonline.com/loi/gsrp20
High yielding protocol for direct conversion of
thiols to sulfonyl chlorides and sulfonamides
Samira Sohrabnezhad, Kiumars Bahrami & Farahman Hakimpoor
To cite this article: Samira Sohrabnezhad, Kiumars Bahrami & Farahman Hakimpoor (2019): High
yielding protocol for direct conversion of thiols to sulfonyl chlorides and sulfonamides, Journal of
Sulfur Chemistry, DOI: 10.1080/17415993.2019.1570196
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JOURNAL OF SULFUR CHEMISTRY
https://doi.org/10.1080/17415993.2019.1570196
High yielding protocol for direct conversion of thiols to
sulfonyl chlorides and sulfonamides
Samira Sohrabnezhada, Kiumars Bahramib,c and Farahman Hakimpoora
aDepartment of Chemistry, Faculty of Science, Lorestan University, Khoramabad, Iran; bDepartment of
Organic Chemistry, Faculty of Chemistry, Razi University, Kermanshah, Iran; cNanoscience and
Nanotechnology Research Center (NNRC), Razi University, Kermanshah, Iran
ABSTRACT
ARTICLE HISTORY
Received 4 August 2018
Accepted 8 January 2019
In this paper, a new method for oxidative chlorination of thiols to
sulfonyl chlorides and sulfonamides using H2O2 in the presence of
TMSCl is reported. The excellent yields, short reaction times, excel-
lent efficiencies, low costs, and easy separation of products are the
most important advantages of this method.
KEYWORDS
Sulfonyl chlorides;
sulfonamides; oxidative
chlorination;
chlorotrimethylsilane;
hydrogen peroxide
1. Introduction
A large of group of physiologically active compounds based on various sulfonyl chlorides
have been synthesized [1]. Sulfonyl chlorides are also promising compounds as reagents or
intermediates in organic synthesis [2].
Sulfonamides are a class of significantly important compounds that have been widely
applied as building blocks in medical chemistry [3]. These compounds are found in many
remedial agents including drugs for the treatment of bacterial [4] and viral [5] putrefaction.
Sulfonamides are used as an anticancer agent [6], HIV protease inhibitory activities [7] and
in Alzheimer’s disease [8] (Figure 1).
CONTACT Kiumars Bahrami
kbahrami2@hotmail.com
This article makes reference to supplementary material available on the publisher’s website at https://doi.org/10.1080/
17415993.2019.1570196
© 2019 Informa UK Limited, trading as Taylor & Francis Group

2
S. SOHRABNEZHAD ET AL.
Figure 1. Examples of sulfonamide frameworks as drug candidates.
Due to significance sulfonyl chlorides, over the last several years many endeavors have
been made for the synthesis of these compounds using many different methods. Tra-
ditionally, sulfonyl chlorides can be prepared in several different ways [9–20]. Of these
and for years, the oxidative chlorination of sulfur compounds such as thiols, thioethers,
thioacetates, and thiocarbamates with aqueous chlorine [9] has been the most typical syn-
thetic methods used for the formation of sulfonyl chlorides. Although these methods are
efficient for the synthesis of sulfonyl chlorides, most of them suffer from one or several
disadvantages such as harsh and complex reaction conditions, poor yields, limitations in
starting materials, long reaction time, side reactions, slow reactivity, poor functional group
tolerability and tedious purification procedures.
Therefore, to overcome these problems it is highly desired to develop a novel and sus-
tainable method for the preparation of sulfonyl chlorides. In continuation of our work on
the use of TMSCl in organic transformation [21], herein, we report an efficient and rapid
method for the synthesis of sulfonyl chlorides from thiols by the TMSCl-H2O2 reagent
system (Scheme 1).
Chlorotrimethylsilane (TMSCl) is a chemical reagent with low toxicity, low cost, and
high reactivity, which has attracted considerable attention. However, currently no report
has been published utilizing TMSCl as promoter in the conversion of thiols to sulfonyl
chlorides.
Scheme 1. Synthesis of sulfonyl chlorides from thiols.

JOURNAL OF SULFUR CHEMISTRY
3
2. Results and discussion
To investigate the effects of various amounts of H2O2 and TMSCl in acetonitrile at room
temperature, 4-bromothiophenol was selected as a sample for optimization of the reaction
conditions. According to Table 1, the best yield (97%) was achieved by performing the
reaction with three equivalents of H2O2 in the presence of one equivalent of TMSCl for
2 min. Using a lower amount of H2O2 resulted in lower yields, while higher amounts did
not affect the reaction time and yield.
To select the best solvent, the oxidative chlorination of 4-bromothiophenol was done
under the same conditions using various organic solvents such as chloroform, toluene,
acetonitrile and 1,4-dioxane. In this step of work, acetonitrile gave the best results and
was chosen for this purpose.
Investigation of the reactions of different thiols was performed using the above-
mentioned optimized reaction conditions. As seen in Table 2, aromatic thiols carrying
either electron-donating or electron-withdrawing substituents led to excellent yields of
products in high purity as proved by NMR spectroscopy. Moreover, aliphatic thiols like
cyclohexanethiol and 1-octanethiol led to the formation of sulfonyl chlorides in excellent
Table 1. Effect of increasing the amounts of H2O2 and TMSCl on the oxidative
chlorination of 4-bromothiophenol.
Entry
TMSCl (mmol)
30%H2O2 (mmol)
Yield (%)a
1
2
3
4
5
6
7
0
4
4
4
4
2
3
4
0
51
63
80
74
97
97
0.5
0.7
0.8
1
1
1
Note: Reaction conditions: 4-bromothiophenol (1 mmol), 3 min, 25 °C.
aIsolated yields.
Table 2. Oxidative chlorination of thiol derivatives.
2a: R = C6H5; 96% (2 min); oil [39]
2b: R = 4-MeC6H4; 97% (2 min); mp = 68–69 [39]
2c: R = 4-MeOC6H4; 93% (4 min); mp = 39 [40]
2d: R = 4-ClC6H4; 97% (3 min); mp = 48–51 [39]
2e: R = 4-BrC6H4; 95% (3 min); mp = 70 [40]
2f: R = 4-FC6H4; 96% (3 min); mp = 34 [40]
2g: R = 3-MeOC6H4; 90% (4 min); oil [41]
2h: R = 4-O2NC6H4; 90% (2 min); mp = 71–72 [42]
2i: R = 2-Naphthyl; 93% (3 min); mp = 73–75 [39]
2j: R = Benzyl; 96% (3 min); mp = 91 [43]
2k: R = 2-Benzoimidazole; 0% (10 min); mixture of products [44]
2l: R = Cyclohexyl; 90% (10 min); oil [45]
2m: R = n-Octyl; 92% (10 min); oil [43]
Notes: The products were characterized by comparison of their
spectroscopic and physical data with authentic samples syn-
thesized by reported procedures. Yields refer to pure isolated
products.

4
S. SOHRABNEZHAD ET AL.
yields (2 l and 2 m). This reaction was also compatible with other functional groups such
as halogens, nitro, and ether linkages (Table 2).
The heterocyclic thiol, 2-mercaptobenzimidazole was examined under the same con-
ditions and failed to produce the desired sulfonyl chloride (2k). According to a reported
paper [22], benzimidazole-2-sulfonyl chloride is unstable at room temperature and rapidly
decomposes to 2-chlorobenzimidazole and 2-hydroxybenzimidazole as detected by com-
parison to commercial samples.
We also studied the oxidative chlorination of thiols in the presence of alcohol and oxime
(Scheme 2). The findings confirm that this procedure can be employed for the oxidative
chlorination of thiols in the presence of alcohol and oxime functional groups in multi-
functional molecules.
These observations can be rationalized by the reaction mechanism proposed in Scheme
3. The reactions proceed, in general, via the intermediacy of disulfide 6 and thiosulfonate 9
which produces sulfonyl chloride 3. Formation of 9 via 8 from 7 has been well substantiated
and acknowledged [23].
An investigation confirmed the presence of the corresponding disulfide as the
main intermediate in this reaction. Thus, the reaction of thiophenol (1 mmol) with
H2O2/TMSCl in 1:1 molar ratio for 1 min produced diphenyl disulfide in high yield (see
supporting information).
Various synthetic methods have been reported for the preparation of sulfonamides
[24–29], but the most traditional method is the reaction of an amine with a sulfonyl
chloride in the presence of a base in an aprotic solvent [30]. Although, this procedure
is sufficient, its utility is limited by the formation of undesired disulfonamides with pri-
mary amines, and to need for harsh reaction conditions for less nucleophilic amines such
as anilines [31] and also the availability of sulfonyl chlorides, some of which are difficult to
handle or store.
In view of the importance of sulfonamides in chemistry and biology, the synthesis of
these compounds is of great interest in synthetic and medicinal chemistry.
Scheme 2. Reagents and conditions: molar ratio of substrates: H2O2: TMSCl (1:1:3:1), CH3CN, 25 °C.

JOURNAL OF SULFUR CHEMISTRY
5
Scheme 3. A proposed mechanism for the preparation of sulfonyl chloride from a thiol with the H2O2-
TMSCl reagent system.
Scheme 4. Conversion of thiols to sulfonamides.
In recent work, we have shown H2O2 in combination with SOCl2 [32], ZrCl4 [33] and
POCl3 [34] as an efficient system for the direct conversion of thiols into sulfonamides. As an
extension of this work and also in continuation of our program directed to the development
of efficient reagents for use under mild conditions [35–38] herein, we report a new mild
and efficient synthesis of such compounds via the reaction of amines (1 mmol) and thiols
(1 mmol) in the presence of H2O2 (3 mmol), TMSCl (1 mmol) and pyridine (0.5 mL) in
acetonitrile at room temperature. To the best of our knowledge, such a reagent system for
the preparation of sulfonamides has not been described in the literature. The route for the
preparation of sulfonamides from thiols is shown in Scheme 4.
According to Scheme 4, the reaction of structurally and electronically diverse thiols
and amines were evaluated by using optimized reaction conditions. The data in Table 3
show that all reaction performed efficiently and the desired sulfonamides were formed in
excellent yields and high purity (detected by NMR spectroscopy). As can be seen, aryl thi-
ols carrying either electron-donating or electron-withdrawing substituents reacted very
well. In addition, it was discovered that amines are insensitive to substitution and pri-
mary (4a) and secondary (4n) alkyl amines, as well as ammonia (4j), undergo this reaction
with the same efficiency. As shown in Table 3, this method proved to be very useful even
for sterically hindered amines such as diphenylamine and piperidine, the corresponding
sulfonamides were obtained in 92% and 93% yields, respectively (4e and 4k). Furthermore,

6
S. SOHRABNEZHAD ET AL.
Table 3. Direct formation of sulfonamides from thiols.
4a: R = C6H5; Rꢀ = H; Rꢀꢀ = C6H5; 99% (8 min); mp = 109–110 [46]
4b: R = 4-MeC6H4; Rꢀ = H; Rꢀꢀ = 4-MeC6H4; 98% (8 min); mp = 112–114 [46]
4c: R = 4-BrC6H4; Rꢀ = H; Rꢀꢀ = 3-O2NC6H4; 95% (10 min); mp = 119–120 [32]
4d: R = 1-Naphthyl; Rꢀ = H; Rꢀꢀ = C6H5; 95% (9 min); mp = 158–159 [47]
4e: R = C6H5; Rꢀ = C6H5; Rꢀꢀ = C6H5; 92% (11 min); mp = 123–125 [48]
4f: R = C6H5; Rꢀ = H; Rꢀꢀ = 1-Naphthyl; 95% (9 min); mp = 165–166 [49]
4g: R = 4-BrC6H4; Rꢀ = H; Rꢀꢀ = C6H11; 97% (9 min); mp = 99 [33]
4h: R = ClSO2(CH2)3; Rꢀ = H; Rꢀꢀ = 4-MeC6H4; 91% (11 min); mp = oil [34]
4i: R = C6H11NHSO2(CH2)3; Rꢀ = H; Rꢀꢀ = C6H11; 94% (10 min); mp = oil [31]
4j: R = Benzyl; Rꢀ = H; Rꢀꢀ = H; 95% (9 min); mp = 97–98 [50]
4k: R = 4-MeC6H4; Rꢀ . . . ..Rꢀꢀ = CH2(CH2)4CH2; 93% (11 min); mp = 92 [34]
4l: R = 4-MeC6H4; Rꢀ = H; Rꢀꢀ = H; 96% (9 min); mp = 137–139 [51]
4m: R = 4-MeC6H4; Rꢀ = H; Rꢀꢀ = C6H5NH; 93% (8 min); mp = 156–157 [52]
4n: R = C6H5; Rꢀ = Ethyl; Rꢀꢀ = Ethyl; 97% (10 min); mp = 42 [53]
Notes: The products were characterized by comparison of their spectroscopic
and physical data with authentic samples synthesized by reported procedures.
Yields refer to pure isolated products.
1-naphthyl amine (4f) transformed into the desired sulfonamide with 95% yield. Moreover,
this procedure worked efficiently in the sulfonylation of phenylhydrazine (4 m) to provide
an excellent yield of the product without the formation of any side products. Interest-
ingly, propan-1,3-dithiol worked well in this method and monosulfamide and disulfamide
products were obtained in excellent yields with high selectivity (4h and 4i).
To assess the probability of applying this procedure on a preparative scale, we performed
the reaction of 4-methylthiophenol with 4-methylaniline on a 20 mmol scale. As expected,
the reaction proceeded smoothly, similar to the case in a smaller scale (Table 3, entry 4b),
and the desired product was obtained in 96% isolated yield.
3. Conclusions
In summary, a new and simple oxidative chlorination method using the H2O2-TMSCl
system is described and found to be very practical for the direct conversion of thiol com-
pounds into the desired sulfonyl chlorides in excellent yields and short reaction times.
This reagent system was also found to be an effective reagent system for the direct synthe-
sis of sulfonamides from thiols in excellent yields. The notable advantages offered by this
protocol are simplicity in operation, general applicability, mild reaction conditions, high
regioselectivity, compatibility of a wide range of functionalities, which includes the ether,
alcohol; and oxime moieties, very short reaction times, and the high yield of products.
Further utilization of this procedure is in progress in our laboratory.
4. Experimental
4.1. Materials and physical measurements
The starting materials for this work were purchased from the Merck chemical company.
Products are known compounds and were characterized by comparison of their spectral

JOURNAL OF SULFUR CHEMISTRY
7
data (NMR) and physical properties (melting point) with reported samples. The spectra
were recorded on Bruker NMR spectrometer (200 and 300 MHz) in CDCl3. Thin layer
chromatography (TLC) was carried out on silica gel polygrams SIL G/UV 254 plates.
All melting points were corrected and determined with the open capillary method using
Gallen. Kamp melting point apparatus. Yield refers to the isolated pure products.
4.2. General procedure for the conversion of thiols to sulfonyl chlorides
To a mixture of appropriate thiol (2 mmol) and TMSCl (2 mmol) in CH3CN, was added
30% H2O2 (6 mmol, 0.6 mL), and stirred at room temperature for the times mentioned
in Table 2. On completion of the reaction followed by TLC, H2O (10 mL) was added
and the mixture was then extracted with ethyl acetate (4 × 5 mL). The extract was dried
using MgSO4. After filtration and removal of the solvents under reduced pressure, the pure
product was obtained in excellent yield.
4.3. General procedure for the preparation of sulfonamides from thiols
To a soln of thiol compound (2 mmol) and TMSCl (2 mmol) in CH3CN, was added H2O2
(30%, 6 mmol, 0.6 mL) and stirred at room temperature. The progress of the reaction was
followed by TLC examination (n-hexane:ethyl acetate, 6:2). At the end of the reaction,
appropriate amine (2 mmol) in pyridine (1 mL) was added and the stirring was contin-
ued until the starting material was disappeared (Table 3). The reaction mixture was then
acidified by aqueous 2N HCl and extracted using ethyl acetate. After washing organic
layer with H2O and brine, the mixture was dried over MgSO4. After filtration, the sol-
vents were removed under vacuum to afford the desired sulfonamide in excellent yield.
Recrystallization from a mixture of ethanol and water produces a more pure final product.
Disclosure statement
No potential conflict of interest was reported by the authors.
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