Direct synthesis of sulfinic esters via ultrasound accelerated tandem reaction of thiols and alcohols with N-bromosuccinimide

Article abstract of DOI:10.1080/17415993.2021.1928669

The direct transformation of various thiols and simple alcohols with N-bromosuccinimide into sulfinic esters has been investigated by using different categories of base/acidic catalysts as well as co-solvents under varied reaction conditions. The reaction was found out to afford the sulfinic esters with high yields in the absence of catalysts, especially within the shorter time under the acceleration of ultrasonic irradiation than under the longer-lasting conventional stirring conditions.

Full text of DOI:10.1080/17415993.2021.1928669

Journal of Sulfur Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gsrp20
Direct synthesis of sulfinic esters via ultrasound
accelerated tandem reaction of thiols and alcohols
with N-bromosuccinimide
Lan-Anh Thi Nguyen, Tri-Nghia Le, Cong-Thang Duong, Chi-Tam Vo, Fritz
Duus & Thi Xuan Thi Luu
To cite this article: Lan-Anh Thi Nguyen, Tri-Nghia Le, Cong-Thang Duong, Chi-Tam Vo, Fritz
Duus & Thi Xuan Thi Luu (2021) Direct synthesis of sulfinic esters via ultrasound accelerated
tandem reaction of thiols and alcohols with N-bromosuccinimide, Journal of Sulfur Chemistry, 42:5,
519-528, DOI: 10.1080/17415993.2021.1928669
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JOURNAL OF SULFUR CHEMISTRY
2021, VOL. 42, NO. 5, 519–528
https://doi.org/10.1080/17415993.2021.1928669
Direct synthesis of sulfinic esters via ultrasound accelerated
tandem reaction of thiols and alcohols with
N-bromosuccinimide
Lan-Anh Thi Nguyena, Tri-Nghia Lea, Cong-Thang Duong a, Chi-Tam Voa, Fritz
Duusb and Thi Xuan Thi Luua
aFaculty of Chemistry, University of Science, Vietnam National University, Ho Chi Minh City, Vietnam;
bDepartment of Science, Systems and Models, Roskilde University Roskilde, Denmark
ABSTRACT
ARTICLE HISTORY
Received 2 September 2020
Accepted 4 May 2021
The direct transformation of various thiols and simple alcohols with
N-bromosuccinimide into sulfinic esters has been investigated by
using different categories of base/acidic catalysts as well as co-
solvents under varied reaction conditions. The reaction was found
out to afford the sulfinic esters with high yields in the absence of
catalysts, especially within the shorter time under the acceleration
of ultrasonic irradiation than under the longer-lasting conventional
stirring conditions.
KEYWORDS
Thiols; sulfinic esters;
N-bromosuccinimide;
tandem reaction; ultrasound
irradiation
1. Introduction
Sulfinic esters (general formula: R1-S(O)-O-R2), the esters of sulfinic acids, are interme-
diates in the organosulfur chemistry, especially in the synthesis of sulfoxides [1,2], sulfon-
amides [3,4], sulfonimidates [4], and sulfonyl isonitriles (TosMIC analogs) [5]. Moreover,
sulfinate salts are also used as efficient reagents in the electrochemical sulfonylation of
alkynes [6]; or in the radically alkylated electrophilic olefins with iridium(III)-complex
as a photocatalyst [7].
CONTACT Thi Xuan Thi Luu
ltxthi@hcmus.edu.vn
Faculty of Chemistry, University of Science, Vietnam
National University, 227 Nguyen Van Cu, District 5, HCMC, Ho Chi Minh City, Vietnam
This article has been republished with minor changes. These changes do not impact the academic content of the article.
Supplemental data for this article can be accessed here. https://doi.org/10.1080/17415993.2021.1928669
© 2021 Informa UK Limited, trading as Taylor & Francis Group

520
L.-A. NGUYEN ET AL.
Various indirect synthetic pathways of sulfinic acid esters from the sulfur(IV) derivatives
have been performed via the nucleophilic substitution of alcohols/alkoxytrimethylsilane
into sulfinyl chloride [8–13], sulfinamide [14–16], and sulfinyl sulfone [17]. Further-
more, the reaction of sulfinic acid with alcohols [18–20], the Brønsted/Lewis acid-
catalyzed sulfination of alcohols by using sulfinic acid sodium salts [21–22], or by using
p-toluenesulfonylmethyl isocyanide [23–25], the copper-catalyzed aerobic oxidative reac-
tion [26,27], the esterification of sulfonyl hydrazides with alcohols promoted by NaHSO3
[28], the decomposition of N–sulfonylhydrazones mediated by Wittig ylide [29], or DIPEA
(di-iso-propylethylamine) [30], as well as the in situ reduction of sulfonyl chlorides with
alcohols in the presence of excess trimethyl phosphite have been also developed for
the synthesis of sulfinic esters [31]. Recently, the alcoholysis of sulfinyl bromide in situ
formed from the C-S(O) bond cleavage of sulfone-bearing t-butyl group by using N-
bromosuccinimide was found out by Wei and co-workers [32]. Other popular pathways for
the syntheses of sulfinic esters from the sulfur (II) derivatives, e.g. disulfides have attracted
attention via the chlorination of disulfides in alcohols [33], and the oxidation of disulfides
in alcohols by using N-bromosuccinimide [34], and lead tetraacetate [35]. Unfortunately,
the sulfur (IV) derivatives are commercially available within limit, except for sulfinate salts.
In addition, the sulfur (II) derivatives as disulfides are popularly prepared via the oxidative
coupling of thiols by utilizing various oxidizing agents, e.g. N-bromosuccinimide [36].
In recent years, the direct transformations of thiols and alcohols to sulfinic esters have
become interesting topics, for instance they were performed with oxygen in the presence of
several catalysts, e.g. copper(I) iodide and 1,5,7-triazabicyclo[4.4.0]dec-5-ene [37], cobalt
nanocatalyst supported on N-SiO2-doped activated carbon [38], or performed with N-
bromosuccinimide at 0–25°C for several hours [5,39–40]. Furthermore, other processes
such as electrochemistry [41–44], and photochemistry [45] have also been introduced for
the direct synthesis of sulfinates.
Therefore, our intentions with this work were to improve and understand the synthetic
pathway of sulfinic esters via an ultrasonic-assisted tandem reaction of thiols and alco-
hols with N-bromosuccinimide to achieve maximum yield of the desired product with
respect also to the short reaction time at room temperature (Scheme 1). Although sulfinic
esters synthesized from the reactions of thiols and alcohol with NBS have been announced
[2,5,39–40], the impact factors such as the molar ratio of thiols, alcohols and NBS, the
amount of solvent, the type of co-solvent or catalyst, and the nature of thiols as well
Scheme 1. The transformation of thiols and alcohols into sulfinic esters in the presence of
N-Bromosuccinimide.

JOURNAL OF SULFUR CHEMISTRY
521
as alcohols have not been considered extensively to assimilate, illustrate the scope and
generality of this process.
2. Result and discussion
At the beginning of our work, the priority adding of reactants was investigated and selected
by sequentially dropping thiol (3 mmol) in methanol (5 mL), NBS (4.5 mmol) in methanol
(9 mL) and a specific volume of co-solvents e.g. dichloromethane, ethyl acetate, [Bmim]Br
or [Bmim]BF4 into the reaction flask at room temperature. The amount of NBS was delib-
erately used in the lower amount (6.0 mmol) than those in the previous literature [2,5],
so that the effects of catalyst or co-solvent on the reaction of thiophenol and methanol
with NBS were found out clearly. The results depicted in Entries 1–5, Table 1 showed
that the presence of [Bmim]BF4 led to a weight loss of product, and dichloromethane
as well as [Bmim]Br reduced the formation of sulfinate slightly in comparison with the
case of using only methanol. Among above co-solvents, ethyl acetate was selected as the
best co-solvent for this reaction. In the further experiments, inorganic solid supports such
as silica gel, alumina and Mont K-10 were alternatively tested for the reaction optimizat-
tion. The results showed that diphenyl disulfide was mainly formed instead of sulfinate
in the presence of above inorganic solid supports, exceptionally Mont K10. In the next
survey, acidic/base catalysts such as triethylamine, Amberlyst 26 and Amberlyst 15 used
have not increased efficiency in the product formation. Consequently, neither catalysts nor
inorganic solid supports were selected for the reaction of thiophenol and methanol with
N-bromosuccinimide (Entries 6–13, Table 1).
Table 1. Influence of reaction condition on the yield of methyl benzenesulfinate obtained by the
tandem reaction of thiophenol and methanol with N-Bromosuccinimide.
Yield (%)b
Entry
Reaction condition
Conv. (%)
4a
3a
1
2
3
4
5
6
7
8
NBS
98
96
52
46
64
52
26
23
2
0
6
64
60
58
60
26
24
14
33
13
52
73
85
46
30
27
26
24
NBS in CH2Cl2 (1 mL)s
NBS in EtOAc (1 mL)
NBS in [Bmim]Br (3 mmol)
NBS in [Bmim]BF4 (3 mmol)
NBS/SiO2 (wt. 25%) (3.203 g)
NBS/SiO2 (wt. 50%) (1.602 g)
NBS/SiO2 (wt. 75%) (1.068 g)
NBS/Al2O3 (wt. 25%) (3.203 g)
NBS/Mont K-10 (wt. 25%) (3.203 g)
NBS catalyzed by Et3N (1.5 mmol)
NBS catalyzed by Amberlyst 26 (1.5 mmol)
NBS catalyzed by Amberlyst 15 (1.5 mmol)
100
100
100
100
100
100
100
100
100
100
100
9
10
11
12
13
Note: The reaction of thiophenol (3 mmol), MeOH (5 mL), NBS (4.5 mmol) dissolved in an additional MeOH (9 mL) and a
specific co-solvent/catalyst was performed under magnetic stirring at room temperature for 5 h.

522
L.-A. NGUYEN ET AL.
Figure 1. Influence of the methanol amount on the tandem reaction of thiophenol and methanol with
N-bromosuccinimide to obtain methyl benzenesulfinate under magnetic stirring at room temperature
(5 h, thiophenol: 3.0 mmol, NBS: 4.5 mmol, EtOAc: 1 mL).
In the next series of experiments, the volume of methanol was studied in order to get
the higher yield of methyl benzenesulfinate. The results, depicted in Figure 1, also demon-
strated that the amount of methanol influenced slightly on the yield of methyl sulfinate and
finally was selected at 14 mL for the next investigation (Figure 1).
Subsequently, the influences of the molar ratios between thiophenol and
N-bromosuccinimide were investigated. The results displayed that when the amount of N-
bromosuccinimide varied from 4.5 mmol to 6.0 mmol, the yield of methyl benzenesulfinate
was achieved from 64% (Entry 3, Table 1) to 87% after 5 h-stirring at room temperature
in MeOH (14 mL) and EtOAc (1 mL). In the next experiments, the factor of reaction time
was studied in four activation methods: stirring method, ultrasound irradiation, conven-
tional heating and microwave irradiation. Consequently, the ‘one-pot’ synthesis of methyl
benzenesulfinate has not achieved a good yield at temperature more than 60°C under
microwave irradiation as well as conventional heating owing to the decomposition of reac-
tion mixture. While the best yield was obtained at 94% after eight-hour stirring at room
temperature (Fig. 1S, Supplementary) and at 90% after 30-minute ultrasonic irradiation
(Fig. 2S, Supplementary). Thus, two activation methods, stirring at room temperature and
ultrasonic irradiation, were selected for further experiments on the scope of thiols and
alcohols.
Altogether four simple alcohols, e.g. methanol, ethanol, n-propyl alcohol, isopropyl
alcohol and n-butanol were subjected to a tandem reaction of thiophenol or 4-
methylthiophenol with N-bromosuccinimide by using two efficient methods. In the first
series of tandem reactions, where the reactions were carried out under magnetic stirring at
room temperature (Method A). The next series of reactions were performed as described in
Method A (Experimental), but under the acceleration of ultrasonic irradiation (Method B).
Summarily, the yields of the products were not remarkably different in both above methods,
however the reaction time in Method B was reduced considerably (Table 2). The significant

JOURNAL OF SULFUR CHEMISTRY
523
Table 2. Yields of alkyl alkanesulfinates/arenesulfinates obtained by the tandem reaction of thiols,
alcohols with NBS by various methods.a
Yield (%) (Timeb)
Entry
R1
R2
Product
Method Aa
Method Ba
1
2
3
4
5
6
7
8
C6H5
C6H5
C6H5
C6H5
C6H5
CH3
CH3CH2
CH3CH2CH2
(CH3)2CH
CH3(CH2)2CH2
CH3
CH3CH2
CH3CH2CH2
CH3
4a
4b
4c
94 (8)
79 (8)
67 (8)
69 (9)
2 (8)
98 (8)
81 (8)
69 (8)
98 (8)
82 (8)
74 (8)
92 (8)
83 (8)
96 (8)
94 (8)
90 (30)
78 (40)
65 (40)
70 (40)
No trace
91(30)
80 (40)
66 (40)
96 (30)
86 (20)
78 (30)
94 (30)
94 (30)
97 (30)
88 (20)
4d
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
C6H5CH2
p-MeOC6H5
p-ClC6H4
n-C4H9
n-C8H17
c-C6H11
MeOC(O)CH2-CH2
4e
4f
4g
4h
4j
4k
4l
4m
4n
4p
9
10
11
12
13
14
15
CH3
CH3
CH3
CH3
CH3
CH3
aThe reaction of thiol (3 mmol), alcohol (5 mL), NBS (6.0 mmol) dissolved in an additional alcohol (9 mL) and EtOAc (1 mL)
was performed under magnetic stirring at room temperature (Method A) and ultrasound irradiation (Method B).
bTime = reaction time in hours for the method A; time = reaction time in minutes for the method B.
influence of ultrasound irradiation on the reaction time was dependent on the cavitation
collapse to increase the interfacial contact area [46].
Further experiments showed that the structures of thiols did not influence consider-
ably the reaction yields; while the longer carbon chains of alcohols were used, the lower
yields of sulfinic esters were obtained, for instance, the yield of n-butyl benzenesulfinate
was obtained either 2% after eight-hour magnetic stirring or 0% after 30-minute ultra-
sonic irradiation. Moreover, sulfinic esters have not appeared from the reaction of benzyl
alcohol or phenol with thiophenol and NBS at optimized reaction condition. The analysis
results reported by gas chromatography-mass spectrometry showed that the oxidation of
benzyl alcohol into benzaldehyde (2%) by using N-bromosuccinimide occurred similarly
to the previous literatures [47]. The aromatic substitution of bromine was not detected
in the case of benzyl alcohol, however, it occurred at the ortho postion (2%) and the
para position of phenol (12%). In addition, the formation and existence of disulfides were
recognized in most optimized reaction conditions with the range of yields from 1% to
23%, particularly in case of phenylmethanethiol (Entry 9, Table 2). The long carbon chain
of alcohols affected considerably to the presence of disulfide (18−23%) in the product
mixture.
The introduced protocol for the synthesis of simple sulfinic esters offers many advan-
tages in terms of high product yield, catalyst-free and shorter reaction time under mild
and ultrasound-supported reaction conditions, compared to the reported methods in the
different reaction conditions as well as catalysts (Table 3).

524
L.-A. NGUYEN ET AL.
Table 3. Comparison of previous methods for direct synthesis of sulfinic ester from the reaction of thiols
and alcohols.
Catalyst/Reactant
Solvent
Condition
Time (h)
18
Yield (%)
CuI (5 mol%); 1,5,7-
triazabicyclo[4.4.0]dec-
5-ene (TBD)
THF (1 mL, 0.5 M)
Stirred at 65°C under
1 atmosphere of
oxygen
56–91 [30]
(10 mol%)
Co/N-SiO2-AC (1.46 mol%);
K2CO3 (0.1 mmol)
excess alcohol
CH2Cl2
Stirred at 60–80°C
under O2
atmosphere
24
20
45–91 [31]
58–90 [32]
Undivided cell with platinum
electrodes and nBu4NBF4
(0.2 M) as the electrolyte
Electrocatalyzed at
room temperature
under nitrogen
atmosphere
Eosin Y (2.0 mol%); green LEDS
(2.50 W, λ = 535 nm)
N-Bromosuccinimide (2-3 eq)
excess alcohol
Photocatalyzed under
air atmosphere
0.5–2
1–15
51–90 [33]
alcohol:CH2Cl2
(V/V = 1:1) or
excess alcohol
Stirred at 0°C or 25°C
after NBS was added
at 0°C
42–98 [5, 39–40]
N-Bromosuccinimide (2 eq)
excess alcohol;EtOAc
(1 mL)
Irradiated at room
temperature in
ultrasonic bath
20–40 min
65–97 [our work]
3. Experimental
3.1. Instrumentation and chemicals
3.1.1. Instrumentation
The reactions were carried out by means of a magnetic stirrer IKA Ret Basic C, speed-
ing at 250 rpm and a BRANSON 1510 ultrasonic bath, operating at frequency 40 kHz with
a power output of 70 W. The progress of the reaction was monitored by GC-FID Agilent
6890N apparatus equipped with capillary column (30 m × 320 μm × 0.25 μm), detector
and injector temperature at 250°C. LC/MS analyses were performed on a micrOTOF-
QII-ESI-Qq-TOF (Bruker Daltonics, D-28359 Bremen, Germany) with UV/VIS and MS
detector, the heated capillary of iron trap mass spectrometer was set to 350°C, reverse col-
umn ACE 3C18 (5 μm × 4.6 × 150 mm) and ESI (electrospray ionization): μQTOF Bruker.
NMR spectra were recorded on a Brüker Advance DPX 500 MHz spectrometer at 500 MHz
(1H) and 125 MHz (13C).
3.1.2. Chemicals
All commercially available chemicals used were from Aldrich and analyzed for authenticity
and purity by GC/MS (gas chromatography/mass spectrometry) before being used.
3.2. Typical procedures
3.2.1. The tandem reaction of thiols, alcohols with N-bromosuccinimide (4a-4p)
under magnetic stirring (Method A) [2]
A solution of N-bromosuccinimide (6 mmol, 1.068 g) dissolved in simple alcohol (5 mL)
and ethyl acetate (1 mL) was added slowly into the 25 mL two-neck round flask contain-
ing a solution of thiol (3 mmol) in simple alcohol (5 mL) and then 4 mL of alcohol was

JOURNAL OF SULFUR CHEMISTRY
525
added into the reaction mixture. The reaction mixture was stirred for eight hours at room
temperature (Method A, Table 2). After the reaction completed, the reaction mixture was
extracted with dichloromethane (4 × 10 mL). The combined extracts were neutralized by
a saturated solution of sodium bicarbonate, washed with water until neutral (pH = 7) and
dried by anhydrous Na2SO4. After the removal of the solvent by rotary evaporation, the
remaining crude product was analyzed by GC-FID to control the reaction conversion and
the product selectivity. The crude product was purified by column chromatography (silica
gel 60, 0.04–0.06 mm, Scharlau, as static phase) using eluent as a mixture of n-hexane and
ethyl acetate and identified the structure by HRMS and NMR spectroscopy.
3.2.2. The tandem reaction of thiols, alcohols with N-bromosuccinimide (4a-4p)
under ultrasonic irradiation (Method B)
A test tube (h = 20.0 cm, d = 3.0 cm) containing a pertinent quantity of thiol (3 mmol),
N-bromosuccinimide (6 mmol, 1.068 g) dissolved in simple alcohol (14 mL) and ethyl
acetate (1 mL) was placed into an ultrasonic bath and irradiated for the necessary period
of reaction time (Method B, Table 2). After the reaction completed, the reaction mixture
was worked up as in Method A.
3.3. Spectroscopic data
The structure elucidation of all products reported was measured by 1H NMR, 13C NMR
and HRMS. The unknown NMR spectroscopic data are described below and well-known
spectra of compounds (4a [32]; 4b, d-g [22]; 4c, 4n [41]; 4p [48]; and 4j, 4k [38,41] 4 l
[39,40]) have been found compatible with those reported in the literature.
Methyl phenylmethanesulfinate (4 h).
1
Hexane:ethyl acetate (9:1) Rf = 0.53; colorless liquid, H NMR (500 MHz, CDCl3)
δ(ppm) = 7.32-7.37 (m, 3H), 7.29 (d, J = 7.5 Hz, 2H), 4.03 (d, J = 13 Hz, 1H), 3.94 (d,
J = 13 Hz, 1H), 3.72 (s, 3H)[5]. 13C NMR (125 MHz, CDCl3) δ(ppm) = 130.50, 128.93
(2C), 128.89, 128.39, 64.16, 54.68. HRMS-ESI: m/z [M + Na]+ calcd for C8H10O2S,
193.0294; found, 193.0334.
Methyl 1-octanesulfinate (4 m).
1
Hexane:ethyl acetate (9:1) Rf = 0.62; colorless liquid, H NMR (500 MHz, CDCl3)
δ(ppm) = 3.72 (s, 3H), 2.63-2.72 (m, 2H), 1.61-1.67 (m, 2H), 1.33-1.38 (m, 2H), 1.22-
1.26 (m, 8H), 0.85 (t, J = 7.0 Hz, 3H). 13C NMR (125 MHz, CDCl3) δ(ppm) = 57.07,
54.44, 31.83, 29.28, 29.08, 28.87, 22.70, 21.35, 14.15. HRMS-ESI: m/z [M + Na]+ calcd for
C9H20O2S, 215.1076; found, 215.1089.
4. Conclusion
A direct synthesis from thiols and simple alcohols with N-bromosuccinimide to produce
sulfinic esters has been developed under magnetic stirring and ultrasound irradiation.
Ultrasound irradiation is regarded as green and remarkable accelerator for this transforma-
tion. Moreover, the utilization of heterogeneous and homogeneous acidic and base catalysts
has illustrated their influences on the selectivity of reaction, in some cases the formation
of disulfide in priority. Furthermore, the catalyst-free reactions of thiols and alcohols also
get benefit from the addition of ethyl acetate as co-solvent in place of dichloromethane.

526
L.-A. NGUYEN ET AL.
Acknowledgements
We acknowledge Thanh-Phu Chau, Mong-Hang Thi Tran and Ngoc-Lan Thi Nguyen (Ho Chi Minh,
University of Science) for technical assistance.
Disclosure statement
No potential conflict of interest was reported by the author(s).
ORCID
Cong-Thang Duong http://orcid.org/0000-0002-3753-5389
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