Amberlyst-15: An efficient heterogeneous reusable catalyst for selective anti-Markovnikov addition of thiols to alkenes/alkynes and for thiolysis of epoxides

Article abstract of DOI:10.1016/j.catcom.2013.06.032

The anti-Markovnikov addition of thiols to alkenes/alkynes and thiolysis of epoxides is described using Amberlyst-15 as a selective, commercially available, inexpensive and reusable catalyst. The products like diorganyl sulphides, β-hydroxy sulphides and phenyl(styryl)sulfanes were obtained in good to excellent yields in short reaction time and with high regio-selectivity. The catalyst was reused up to five consecutive recycles without any loss in its catalytic activity. The developed methodology is a metal free protocol for C-S bond formation reaction with high atom economy.

Full text of DOI:10.1016/j.catcom.2013.06.032

Catalysis Communications 41 (2013) 29–33
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Amberlyst-15©: An efficient heterogeneous reusable catalyst for
selective anti-Markovnikov addition of thiols to alkenes/alkynes and
for thiolysis of epoxides
⁎
Satish R. Lanke, Bhalchandra M. Bhanage
Department of Chemistry, Institute of Chemical Technology, Matunga, Mumbai, 400019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The anti-Markovnikov addition of thiols to alkenes/alkynes and thiolysis of epoxides is described using
Amberlyst-15© as a selective, commercially available, inexpensive and reusable catalyst. The products like
diorganyl sulphides, β-hydroxy sulphides and phenyl(styryl)sulfanes were obtained in good to excellent
yields in short reaction time and with high regio-selectivity. The catalyst was reused up to five consecutive
recycles without any loss in its catalytic activity. The developed methodology is a metal free protocol for
C–S bond formation reaction with high atom economy.
Received 26 March 2013
Received in revised form 14 June 2013
Accepted 28 June 2013
Available online 4 July 2013
Keywords:
Amberlyst-15©
β-hydroxy sulphides
Anti-Markovnikov addition
Thiol
© 2013 Elsevier B.V. All rights reserved.
Styrene
Phenyl(styryl)sulfanes
1. Introduction
The utility of conventional protocols which comprises the use of
non-greener homogeneous acid catalysis is limited as it suffers from
Thioethers, thioesters, β-hydroxy sulphides and phenyl(styryl)
sulfanes are important building blocks in several natural products, phar-
maceutically active compounds and various intermediates [1–4]. The
β-hydroxy sulphides are useful in the synthesis of benzoxathiepines
[5,6], benzodiazepines, [7,8] α-substituted α, β-unsaturated enones
[9,10], α-thioketones, [11] β-hydroxysulfoxides [12–14] and allylic alco-
hols [15]. The β-hydroxy sulphides are also important compounds in var-
ious intermediates and generally prepared via thiolysis of 1,2-epoxides
[16]. The synthesis of thioethers via nucleophilic addition of thiols to elec-
tron deficient alkenes is catalyzed by Lewis acid as well as protics [17–20].
The addition of thiols or thiolate anions to carbon–carbon double bonds
has a major drawback of polymerization of thiols under acidic condi-
tions [18]. Conventionally, these compounds are synthesized by the addi-
tion of thiols, thiolate anions to organic halides, alkenes and alkynes in the
presence of different reagents/catalysts. Markovnikov addition to sty-
one or more drawbacks like lower yield, longer reaction time, use of
expensive metal catalyst, lower selectivity and without consideration
of recyclability aspect. Hence, developing heterogeneous catalysis is
an attractive alternative to these conventional catalysis [28–33].
Furthermore, they can be recycled over a prolonged period without
any difficulty in handling and storage.
In this context, to develop an environmentally benign and reusable
protocol for the synthesis of thioethers, β-hydroxysulphides and one
pot synthesis of phenyl(styryl)sulfanes is obligatory. Herein, we report
catalytic efficiency of Amberlyst-15© as a metal-free protocol for the
anti-Markovnikov addition of thiol towards styrene and thiolysis of
1,2 epoxides (Scheme 1).
2. Experimental
renes is
a
common reaction [21], whereas H-rho-zeolite and
2.1. Materials
benzene-reflux [22,23], silica nano particles [24], CeCl3 [25], InI [26]
and acidic ionic liquids [27] are known to lead anti-Markovnikov
products. The synthesis of thioethers and β-hydroxysulfides is usu-
ally carried out by using thiols under basic or acidic conditions or in the
presence of promoters and/or catalysts.
All chemicals and reagents were procured from Sigma Aldrich, S.D.
Fine chemical, Lancaster (Alfa-Aesar), all other reagents and solvents
were of analytical grade and were used without further purification.
2.2. Characterization methods
⁎
Corresponding author. Tel.: +91 22 33611111; fax: +91 22 33611020.
E-mail addresses: bhalchandra_bhanage@yahoo.com, bm.bhanage@gmail.com
The products were characterized using 1H NMR spectra (Varian
Mercury 300 NMR Spectrometer) and IR (Perkin-Elmer FT-IR)
(B.M. Bhanage).
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.06.032

30
S.R. Lanke, B.M. Bhanage / Catalysis Communications 41 (2013) 29–33
S
R'
R'
R
S
SH
Amberlyst-15©
R"
Toluene
R
R
80oC, 3 hr
R= H, CH3,
OCH3,
C(CH3)3,
Cl, Br
R', R"= -Ph
OH
R"
O
S
80oC
R"
-H2O, 12 hr
R
Scheme 1. Amberlyst-15© catalyzed anti-Markovnikov addition of thiols to alkenes and thiolysis of epoxides.
spectroscopic techniques. The reaction progress was monitored using GC
analysis (Perkin-Elmer, Clarus 400) (BP-10 GC column, 30 m × 0.32 mm
ID, film thickness 0.25 mm) equipped with flame ionization detector
(FID) or thin layer chromatography using the Merck silica gel 60 F254
plates. The yields reported in Tables 1, 2 and 4 are GC yields and were cal-
culated using external standard method, Tables 3 and 5 are isolated yield.
The products were confirmed by GC-MS (Shimadzu GC-MS QP 2010
Rtx-17, 30 m × 25 mm ID, film thickness 0.25 μm df) (column flow
2 mLmin−1, 80 °C to 240 °C at 10 °C/min rise). Some representative
products were also confirmed by 1H and 13C NMR. All products are
known in the literature.
backbone like Indion-130 and non-porous perfluorinated resin sulfonic
acid (Nafion-NR50) were examined for the entitled reaction (Table 2,
entries 1–4). It can be seen that Amberlyst-15© was the most active cat-
alyst for anti-Markovnikov addition of thiols to styrene as compared to
other ion exchange resins. It is also observed that Nafion-NR50, inspite
Table 1
Optimization of reaction parameters for anti-Markovnikov addition of thiol with
styrene.a
Entry Catalyst
Solvent
neat
Temp Time Conv. (%)b Yield (%)b
(°C)
(h)
Catalyst screening
2.3. General experimental procedure for anti-Markovnikov addition of
thiol with alkene and thiolysis of epoxides
1
2
3
4
p-TSA
80
80
80
80
6
6
6
6
50
48
78
70
–
Amberlyst-15© neat
100
100
n. r.
Mont K-10
none
neat
neat
Toluene (2 ml), alkene (0.5 mmol) and thiol (2.0 mmol)/
epoxide(0.5 mmol) and thiol (1.2 mmol), and Amberlyst-15© (30 wt%)
were added to a 10 ml sealed tube. The reaction mixture was heated to
80 °C for a desired time and after completion of reaction, it was cooled
to room temperature. 10% NaOH (5 ml) was added to the reaction mix-
ture. The catalyst (Amberlyst-15©) was separated by normal filtration
technique and product was extracted with ethyl acetate (3 × 5 ml).
Alkene/epoxide conversion and product formation were monitored
using gas chromatography. The residue obtained was purified by column
chromatography (silica gel, 60–120 mesh; PE–EtOAc, 95:05) to afford
desired thioethers, β-hydroxy sulphides and phenyl(styryl)sulfanes prod-
ucts. The structures of the products were confirmed by GC-MS, 1H NMR,
and IR spectroscopic techniques. The purity of compounds was deter-
mined by GC-MS analysis (see supporting information).
Solvent study
5
6
7
Amberlyst-15© CH3CN
80
6
6
6
n. r.
n. r.
100
–
Amberlyst-15© 1, 4-dioxane 80
–
Amberlyst-15© toluene
80
90
Effect of catalyst loading
8c
Amberlyst-15© toluene
80
80
80
6
6
6
80
100
100
78
90
90
9d
Amberlyst-15© toluene
Amberlyst-15© toluene
10e
Effect of temperature
11
12
13
14
Amberlyst-15© toluene
60
80
100
RT
6
6
6
6
90
85
90
90
–
Amberlyst-15© toluene
Amberlyst-15© toluene
Amberlyst-15© toluene
100
100
n. r.
Effect of mole ratio
15f
16g
17h
18i
19j
Amberlyst-15© toluene
80
80
80
80
80
6
6
6
6
6
100
100
100
100
100
75
98
58
90
15
3. Results and discussion
Amberlyst-15© toluene
Amberlyst-15© toluene
Amberlyst-15© toluene
Amberlyst-15© toluene
3.1. Anti-Markovnikov addition of thiol with alkene
Initially, anti-Markovnikov addition of thiols to styrene was selected
as a model reaction and the influence of reaction parameter such as cata-
lyst screening, solvent effect, catalyst loading, the mole ratio of substrates,
reaction temperature and time was studied (Table 1). Various acid cata-
lysts such as p-TSA, Amberlyst-15©, Montmorillonite K-10 and neat
were screened (Table 1, entries 1–4). We observed that Amberlyst-15©
provides 78% yield of the desired product (Table 1, entry 2) under screen-
ing conditions. The reaction was also carried out in the absence of a cata-
lyst; however no product formation was observed. This confirms the
necessity of Amberlyst-15© to catalyze the reaction with higher yields
(Table 1, entry 4).
Time study
20
21
22
23
Amberlyst-15© toluene
80
80
80
80
6
2
0.5
0.16
100
100
100
100
98
98
98
95
Amberlyst-15© toluene
Amberlyst-15© toluene
Amberlyst-15© toluene
a
Reaction conditions: styrene (0.5 mmol), thiol (1.5 mmol), catalyst (30 wt%),
temperature (80 °C).
b
GC yield.
Catalyst (10 mg).
Catalyst (15 mg).
Catalyst (20 mg).
Styrene:Thiol (1:2).
Styrene:thiol (1:4).
Styrene:Thiol (1:1).
Styrene:Thiol (1:3).
c
d
e
f
g
Considering the activity of Amberlyst-15©, we checked the effect
of different types of commercially available ion exchange resins like
gel type (Amberlite-IR120), macroreticular porous having polystyrene
h
i
j
Styrene:Thiol (4:1).

S.R. Lanke, B.M. Bhanage / Catalysis Communications 41 (2013) 29–33
31
Table 2
Effect of various ion exchange resins on anti-Markovnikov addition of thiol with styrene.a
+
Entry
Catalyst
H
capacity (meq/g)
Surface area (m2/g) (Langmuir)
Particle size (micron)
Average pore dia (A˚)
Yieldb (%)
1
2
3
4
Amberlite-IR120
Amberlyst-15©
Nafion-NR50
Indion-130
4.4
4.7
0.8
4.8
–
–
–
45
78
76
54
44
b0.02
–
600–800
–
260
–
420–1200
–
a
Reaction conditions: Styrene (0.5 mmol), Thiol (1.5 mmol), Catalyst (30 wt%), Temperature (80 °C).
GC yield.
b
of its surface area and lower H+ exchange capacity gives comparatively
similar results as that of Amberlyst-15©. (Table 2, entries 2–3) Nafion-
NR50 is a type of perfluorinated resin sulfonic acids with a very high
acidity values, e.g. Hammet acidity function in the range of −11 to
−13 (equivalent to 100% sulfuric acid) whereas Amberlyst-15© is a
resin composed of styrene/divinylbenzene copolymer with sulfonic
acid type functionality, and the probable reason for its higher activity
can be explained on the basis of its physical properties, such as reason-
ably good surface area (Langmuir 44 m2/g, and BET 29.52 m2/g) and
excellent H+ capacity (4.7 meq/g based on Hammet scale) [29,30]. Con-
sidering the higher cost of Nafion-NR50, Amberlyst-15© was chosen
and used for further studies.
Table 3
Amberlyst-15© catalyzed anti-Markovnikov addition of thiophenol to alkene/alkyne.a
Entry
Thiols
Product
Time
(h)
Yieldb(%)
Reactions of styrene with various thiols
1
0.5
96
2
3
1
1
93
95
Initially, the reaction was performed without any solvent and it
gave 78% yield for the Amberlyst-15© catalyst. We also checked the
effect of various solvents. We did not observe any conversion in acetoni-
trile as well as in 1, 4-dioxane (Table 1, entries 5–6). In case of toluene
the reaction was more favourable and gave 90% yield of desired product
(Table 1, entry 7). In an attempt to determine the optimum catalyst load-
ings, various catalyst loadings ranging from 20 wt% to 40 wt% were used
(Table 1, entries 8–10). The optimum results were observed with 30 wt%
of catalyst (90% yield) and further increase in the catalyst loading had
no significant impact on the yield of anti-Markovnikov addition product
(Table 1, entry 9). To check the role of reaction temperature, we
performed the reactions at various temperatures and was observed
that the reaction works smoothly at 80 °C with an appreciable yield
(Table 1, entries 15–19). The substrate ratio of styrene:thiol (1:4) was
found to be optimum for the higher yields of desired product (Table 1,
entries 11–14). The reaction parameters such as reaction time was also
studied and observed to work within 0.5 h (Table 1, entries 20–23).
Hence, the optimum reaction conditions for anti-Markovnikov addition
of thiols with styrene are: catalyst- Amberlyst-15© (30 wt %), solvent-
toluene (2 ml), at 80 °C for 0.5 h.
4
5
2
3
91
84
Reactions of 4-ter-butyl styrene with various thiols
6
1
1
2
81
91
80
7
8
Reactions of α-methyl styrene with various thiols
9
1.5
1.5
79
81
10
Reactions of 4-vinylpyridine with various thiols
Several substituted thiophenols possessing various electron-
withdrawing and electron-donating groups, including styrene deriva-
tives were investigated for anti-Markovnikov addition reaction with
styrene and were found to furnish good to excellent yields of the
desired products (Table 3, entries 1–18) under optimum reaction con-
ditions. We observed that the additions were regioselective and anti-
Markovnikov in nature (Table 3, entries 1–5). Furthermore, the reaction
of styrene derivatives such as 4-tert-butyl styrene and α-methyl styrene
with different substituted thiophenols were also examined and was
found to afford the respective thioethers in 79–91 % yield of desired
products (Table 3, entries 6–10).
11
2
2
2
93
92
97
12
13
14
15
3
3
87
81
We have also studied the applicability of the developed catalytic sys-
tem for the anti-Markovnikov addition of 4-vinyl pyridine with different
substituted thiophenols including both electron-donating and electron-
withdrawing group. We observed good to excellent yields of desired
products under present reaction conditions (Table 3, entries 11–15).
Alkene such as 1-octene was found to react with thiophenol to provide
the octyl(phenyl)sulfane as a linear thioether in high yields (Table 3,
entry 16). However, the addition of thiophenol with methyl acrylate
goes into a Michael type addition mode to furnish the methyl
3-(phenylthio)propanoate as a addition product in excellent yield
(Table 3, entry 17). Moreover, Amberlyst-15© effectively catalyzed the
addition of thiophenol with phenyl acetylene was highly selective in
Reactions of oct-1-ene with thiophenol
16
2
2
2
84
94
93
Reactions of methyl acrylate with thiophenol
17
Reactions of phenyl acetylene with thiophenol
18
a
Reaction conditions: Alkene/Alkyne (0.5 mmol), Thiol (2.0 mmol), Amberlyst-15©
(30 wt%), Toluene (2 mL), temperature (80 °C).
b
Isolated yield.

32
S.R. Lanke, B.M. Bhanage / Catalysis Communications 41 (2013) 29–33
Scheme 2. Amberlyst-15© catalyzed epoxides ring opening by thiols.
nature, which achieved 93% yield of (E)-phenyl(styryl)sulfane within
2 h (Table 3, entry 18).
4. Conclusion
In summary, we have developed a clean, safe and highly efficient
metal free protocol for the anti-Markovnikov addition of thiols to alkenes
and ring opening of epoxides by thiols catalysed by Amberlyst-15© in tol-
uene under milder reaction conditions. Under same reaction conditions
3.2. Amberlyst-15© catalyzed epoxides ring opening by thiol
Encouraged with the successful application of the developed
catalytic system for anti-Markovnikov addition of thiophenols with
alkenes, we focused our attention for thiolysis of epoxides under
the similar reaction conditions (Scheme 2) and we observed that the
expected β-hydroxysulphides as a corresponding products with excel-
lent yield. We also optimized the mole ratio of the styrene oxide:thiol
and only 1.2 equivalent of thiol is necessary for the reaction (Table 4,
entry 2), further increase in mole ratio does not affect the yield of
β-hydroxysulphides (Table 4, entries 3–4). Considering the results
obtained, we then explored the developed methodology for the thiolysis
of various epoxides (Table 5).
Table 5
Amberlyst-15© catalysed epoxides ring opening by various thiols.a
Entry
Thiols
Product
Time (h)
Yieldb(%)
92
Reactions of 2-phenyloxirane with various thiols
1
4
2
5
88
We used present methodology for several substituted thiophenols
possessing various electron-withdrawing and electron-donating groups,
including various epoxides derivatives for thiolysis reaction and observed
good to excellent yields of the desired products (Table 5, entries 1–10).
Styrene oxide was treated under the optimized reaction conditions with
various thiophenol derivatives, β-hydroxysulphides as a thiolysis product
obtained regioselectivly and gave excellent yields (Table 5, entries 1–4)
but it required longer reaction time as compared to anti-Markovnikov
addition. Furthermore, we screened various electron donating as well as
withdrawing thiophenols with 1,2-epoxycyclohexane gives a compara-
tively better yield within 4–5 hours (Table 5, entries 5–8). We have also
extended the protocol for epichlorohydrin and gives very good results
β-hydroxysulphides (Table 5, entries 9–10).
3
4
4
4
91
83
Reactions of 1,2-epoxycyclohexane with various thiols
5
4
91
6
7
4
4
83
82
Furthermore, we run the reactions of various thiols with styrene
oxide and epoxycyclohexane for longer reaction time and got a selective
dehydration of β-hydroxysulphides to phenyl (styryl) sulfane with an
excellent yield (Table 5, entries 11–16). This indicates that the method-
ology is applicable for the one pot synthesis of phenyl(styryl)sulfane.
8
5
84
Reactions of epichlorohydrin with various thiols
9
6
5
95
83
3.3. Recyclability of catalyst
10
To make the protocol more economical and greener at established
optimized reaction conditions, catalyst can be separated easily from
the reaction mixture by simple filtration, wash with methanol and
water and recycled further. It was observed that the catalyst can be
efficiently recycled for five consecutive cycles with the same activity.
There is no significant decrease in yield during the four recycles was
observed. The yield declined up to 92% for the fifth cycle (Fig. 1).
Reactions of 2-phenyloxirane with various thiols
11
12
86
12
13
14
12
12
12
84
85
80
Table 4
Effect of mole ratio on Amberlyst-15© catalysed epoxides ring opening by thiol.a
Reactions of 1,2-epoxycyclohexane with various thiols
15
Entry
Styrene oxide: Thiol
(mmol)
Solvent
Temp
(°C)
Time
(h)
Conv.
(%)b
Yield
(%)b
12
12
86
80
1
2
3
4
1:1
1:1.2
1:2
neat
neat
neat
neat
80
80
80
80
6
6
6
6
91
100
100
100
88
95
96
96
16
1:4
Reaction conditions: epoxide (0.5 mmol), thiol (0.6 mmol), Amberlyst-15© (30 wt%),
a
a
Reaction conditions: catalyst (Amberlyst-15© -30 wt%), temperature (80 °C).
GC yield.
toluene (2 mL), temperature (80 °C).
b
b
Isolated yield.

S.R. Lanke, B.M. Bhanage / Catalysis Communications 41 (2013) 29–33
33
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Appendix A. Supplementary data
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Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2013.06.032.