N-bromosuccinimide/HCl mediated reduction of sulfoxides to sulfides

Article abstract of DOI:10.1080/10426507.2020.1871348

An efficient reduction of sulfoxides to sulfides mediated by N-bromosuccinimide (NBS)/HCl system has been developed. This protocol shows good functional group compatibility as well as broad substrates scope with operational simplicity.

Full text of DOI:10.1080/10426507.2020.1871348

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gpss20
N-bromosuccinimide/HCl mediated reduction of
sulfoxides to sulfides
Jianqiang Wang, Fangmin Shi, Dongyan Dai, Liping Xiong & Yongpo Yang
To cite this article: Jianqiang Wang, Fangmin Shi, Dongyan Dai, Liping Xiong & Yongpo Yang
(2021) N-bromosuccinimide/HCl mediated reduction of sulfoxides to sulfides, Phosphorus, Sulfur,
and Silicon and the Related Elements, 196:5, 439-443, DOI: 10.1080/10426507.2020.1871348
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PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
2021, VOL. 196, NO. 5, 439–443
https://doi.org/10.1080/10426507.2020.1871348
N-bromosuccinimide/HCl mediated reduction of sulfoxides to sulfides
Jianqiang Wang , Fangmin Shi, Dongyan Dai, Liping Xiong, and Yongpo Yang
School of Chemical Engineering, Zhejiang International Maritime College, Zhoushan, Zhejiang, P. R. China
ABSTRACT
ARTICLE HISTORY
Received 11 November 2020
Accepted 30 December 2020
An efficient reduction of sulfoxides to sulfides mediated by N-bromosuccinimide (NBS)/HCl system
has been developed. This protocol shows good functional group compatibility as well as broad
substrates scope with operational simplicity.
KEYWORDS
Deoxygenation; reduction;
sulfoxides; N-
GRAPHICAL ABSTRACT
bromosuccinimide; sulfides
Introduction
bromine-catalyzed reduction of sulfoxide to sulfide by
hydrogen chloride as a cheap reductant.
The reduction of sulfoxide to sulfide is a key transformation
in organic synthesis[1] as well as biochemistry.[2] As such,
many combinations of metal and reductant, including M/
H2,[3] M/borane,[4] Ru/isopropanol,[5] Mo/phosphite,[6] Mo/
pinacol[7] and M/silane,[8] have been developed for this
transformation. Alternatively, transition-metal free proce-
dures, including I2/NaHSO3,[9] PPh3/SOCl2,[10] I2/NaBH4,[11]
NBS/TABCO (2,4,4,6-tetrabromo-2,5-cyclohexadienone),[12]
NaSH/HCl[13] as well as photoredox catalyst[14] allows the
reduction of sulfoxide to sulfide efficiently. In addition,
hydrogen iodide[15] and its salt[16] have been known as a
reductant in this transformation for a long time, due to the
low standard oxidation potential of I2/Iꢀ (0.5355 V).
Meanwhile, bromides also acted as ideal promoters to
Results and discussion
With this idea in mind, we started our study by using the
reduction of diphenyl sulfoxide as a model reaction in the
presence of N-iodosuccinimide (NIS, 0.2 equiv) and hydro-
gen chloride (2.0 equiv, 12 M) under N2. The sulfide 2a was
isolated in 11% yield (Table 1, entry 1). Replacing NIS with
N-chlorosuccinimide (NCS) increased the yield to 53%
(Table 1, entry 2). N-bromosuccinimide (NBS, 0.2 equiv)
provided 3a in a quantitative yield (Table 1, entry 3).
However, decreasing the loading of NBS (0.1 equiv)
decreased the reaction efficiency (67%, Table 1, entry 4),
whereafter, the yield decreased to 21% in the absence of
NBS (Table 1, entry 5). Under an atmosphere of air, an
identical yield was obtained (Table 1, entry 7); while the
yield slightly decreased at 110 ꢁC (87%, Table 1, entry 6).
Other acids, such as H2SO4 (2.0 equiv, 18 M) and HOAc
(2.0 equiv) were tested, but they were both ineffective for
this transformation (Table 1, entries 8 and 9), which indi-
cated the chloride anion should take part in this transform-
ation. Further studies showed that this reaction efficiently
proceeded in the presence of bromine (0.2 equiv) and HCl
(2 equiv) (Table 1, entry 10, 99% yield). This result indi-
cated that bromine cation may serve as a real catalyst in this
transformation.
reduce sulfoxide (standard oxidation potential Br2/Brꢀ
¼
1.087 V).[17] In comparison with bromide and iodide ana-
logues, chloride was cheaper and more abundant (standard
oxidation potential Cl2/Clꢀ ¼ 1.396 V). However, to date, its
application for such transformation was limited to diaryl[18]
and specific cyclic sulfoxides,[19] along with the undesired
formation chloration side products in some cases.[20] This
may ascribe to the high standard oxidation potential of Cl2/
Clꢀ. Thus, developing reduction of sulfoxide by HCl with a
broad scope of substrates is beneficial in organic
transformations.
According to the electrode equation, the oxidation poten-
tial E1 in eq 1 would increase in the presence of proton,
while E2 decreases by the extrusion or consumption of Cl2
(Scheme 1). Thus, E1 and E2 may be reversed under acidic
conditions, providing the possibility of reduction of sulfox-
With the optimized conditions in hand, the substrates
scope and limitation of sulfoxides were studied, as shown in
Figure 1. This procedure was not limited to diaryl sulfoxides
ides by the chloride anion. Herein, we wish to report the (2a–2h), as benzyl aryl and alkyl aryl analogues both
CONTACT Jianqiang Wang
wangjianqiang_88@163.com
School of Chemical Engineering, Zhejiang International Maritime College, Zhoushan, Zhejiang
316021, P. R. China.
Supplemental data for this article is available online at https://doi.org/10.1080/10426507.2020.1871348.
ß 2021 Taylor & Francis Group, LLC

440
J. WANG ET AL.
Scheme 1. The possibility of sulfoxide reduction by chloride.
Table 1. Screening the optimal conditions.a
Entry
Catalyst (equiv.)
Acid (2.0 equiv)
Yield (%)b
1
2
3
4
5
6
7
8
9
10
NIS (0.2)
NCS (0.2)
NBS (0.2)
NBS (0.1)
–
NBS (0.2)
NBS (0.2)
NBS (0.2)
NBS (0.2)
Br2 (0.2)
HCl
HCl
HCl
HCl
HCl
HCl
HCl
H2SO4
HOAc
HCl
11
53
99
67
21
87c
99d
23d
17d
99d
aReaction conditions: 1a (0.2 mmol) in 1,4-dioxane (2.0 mL) at 120 ꢁC for 10 h under N2, NBS ¼ N-bromosuccinimide, NCS ¼ N-chloro-
succinimide, NIS ¼ N-iodosuccinimide.
bIsolated yield.
cAt 110 ꢁC.
dUnder air atmosphere.
transformed smoothly leading to the corresponding sulfides reagent; and (2) enhancing the oxidation potential of sulfox-
in moderate to excellent yields (2i–2t). Notably, ortho-sub-
stituted substrates worked well in the procedure and 2d was
isolated in 56% yield. Importantly, the procedure tolerated
chloro, bromo, cyano, amino, hydroxy, nitro and formyl
group well. Dialkyl sulfoxide 1v was also evaluated, albeit in
a relative lower yield (2v, 37%). However, substrate 1w bear-
ing a pyridine ring showed rather poor activity, providing
the corresponding product 2w in trace yield.
ides by proton. Since both Br2 and NBS are effective for this
reaction, it is believed that bromine cation may serve as the
real catalyst. During the reaction, HOBr can directly react
with substrate 1 to give intermediate 3 (path a). Moreover,
HOBr can react with succinimide anion to regenerate NBS
(path b).
The oxidation potential of phenyl sulfoxide (2 ꢂ 10ꢀ3 M)
in water was tested by cyclic voltammetry with a reductive
peak at 0.461 V. The oxidation potential increased in the
presence of HCl (0–1.0 equiv); while the oxidation potential
decreased with HCl (1.0–2.0 equiv), with a minimized peak
0.47 V with 2.0 equiv of HCl. This result indicated the for-
mation of a new species, which was probably [PhSþOH]Clꢀ.
After that, the oxidation potential increased steadily as the
increasing of HCl (2.0–10.0 equiv) (Figure 2).
Conclusion
In conclusion, we developed a simple bromine-catalyzed
procedure for the reduction of sulfoxide to sulfides.
Hydrogen chloride was applied as reductant reagent via
increasing the oxidation potential of sulfoxide by proton.
This procedure showed broad substrates scope and good
functional groups compatibility.
Experimental
A tentative mechanism was outlined in Scheme 2. Firstly,
NBS is attacked by the corresponding sulfoxide to generate
intermediate 3 and succinimide anion. Secondly, the reac-
tion of intermediate 3 with hydrogen chloride provides
intermediate 4 and HOBr. Finally, the reaction between
intermediate 4 and chloro anion takes place, providing sul-
fide and Cl2. Hydrogen chloride plays dual roles in this
Method and apparatus
Unless otherwise noted, all chemicals were purchased from
commercial suppliers (Adamas, Aladdin and Aldrich) and
used without further purification. H NMR and 13C NMR
1
spectra were recorded at ambient temperature on a Bruker
transformation: (1) the chloride anion serving as reductant DPX-300 (1H: 300 MHz; 13C: 75 MHz), a Varian Unity

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
441
Figure 1. The substrates scope of sulfoxides. Reaction conditions: 1 (0.2 mmol), NBS (0.2 equiv) and hydrogen chloride (2.0 equiv, 12 M) in 1,4-dioxane (2.0 mL) at
120 ꢁC for 10 h under air atmosphere. Isolated yield.[8h, 16e, 21–30]
Inova 400 spectrometer (1H: 400 MHz; 13C: 100 MHz) or a using EM Silica gel 60 (300–400 mesh). Mass spectra were
Bruker AVANCE III 500 spectrometer (1H: 500 MHz; 13C: performed on a GCMS-QP2010 SE spectrometer. Melting
125 MHz). Chemical shifts are reported in d units, parts per points (m.p.) are determined with an Optimelt MPA 100
million (ppm), and were referenced to CDCl3 (7.26 or apparatus and are not corrected. All the products are known
77.0 ppm) as the internal standard. The coupling constants J compounds and were identified by comparing of their phys-
are given in Hz. Column chromatography was performed ical and spectra data with those reported in the literature.

442
J. WANG ET AL.
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Diphenylsulfane 2a.[21] Colorless oil; 1H NMR (CDCl3,
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100 MHz): d 135.7, 130.9, 129.1, 126.9; MS (EI): 186 (Mþ).
ORCID
Jianqiang Wang
http://orcid.org/0000-0001-7500-1612
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