Benign and efficient preparation of thioethers by solvent-free S-alkylation of thiols with alkyl halides catalyzed by potassium fluoride on alumina

Article abstract of DOI:10.1080/17415993.2016.1150483

The preparation of thioethers by S-alkylation of various thiols with alkyl halides under solvent-free reaction conditions using potassium fluoride on alumina (KF/Al₂O₃) as a solid catalyst has been investigated in detail with respect to three different modes of reaction activation (ultrasound irradiation, microwave irradiation, and conventional heating) for obtaining maximum yield of the thioether. The importance of KF/Al₂O₃ as a particularly efficient catalyst was corroborated for all three modes of reaction activation, although the reaction time was found to be strongly dependent on the mode of activation. The yield of the thioethers was also found to depend on the amount of the solid catalyst relative to the equimolar amounts of the two reactants.

Full text of DOI:10.1080/17415993.2016.1150483

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Benign and efficient preparation of thioethers by
solvent-free S-alkylation of thiols with alkyl halides
catalyzed by potassium fluoride on alumina
Kha Ngoc Nguyen, Fritz Duus & Thi Xuan Thi Luu
To cite this article: Kha Ngoc Nguyen, Fritz Duus & Thi Xuan Thi Luu (2016): Benign
and efficient preparation of thioethers by solvent-free S-alkylation of thiols with alkyl
halides catalyzed by potassium fluoride on alumina, Journal of Sulfur Chemistry, DOI:
10.1080/17415993.2016.1150483
To link to this article: http://dx.doi.org/10.1080/17415993.2016.1150483
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Date: 25 February 2016, At: 07:28

JOURNAL OF SULFUR CHEMISTRY, 2016
http://dx.doi.org/10.1080/17415993.2016.1150483
Benign and efficient preparation of thioethers by solvent-free
S-alkylation of thiols with alkyl halides catalyzed by
potassium fluoride on alumina
a
b
a
Kha Ngoc Nguyen , Fritz Duus and Thi Xuan Thi Luu
a
Department of Organic Chemistry, University of Science of Ho Chi Minh City, Ho Chi Minh City, Vietnam;
Department of Science, Systems and Models, Roskilde University, Roskilde, Denmark
b
ABSTRACT
ARTICLE HISTORY
The preparation of thioethers by S-alkylation of various thiols with
alkyl halides under solvent-free reaction conditions using potassium
fluoride on alumina (KF/Al2O3) as a solid catalyst has been inves-
tigated in detail with respect to three different modes of reaction
activation (ultrasound irradiation, microwave irradiation, and con-
ventional heating) for obtaining maximum yield of the thioether. The
importance of KF/Al2O3 as a particularly efficient catalyst was cor-
roborated for all three modes of reaction activation, although the
reaction time was found to be strongly dependent on the mode of
activation. The yield of the thioethers was also found to depend on
the amount of the solid catalyst relative to the equimolar amounts of
the two reactants.
Received 25 July 2015
Accepted 1 February 2016
KEYWORDS
Potassium fluoride on
alumina; thioether;
ultrasound irradiation;
microwave irradiation;
solvent-free reaction
1. Introduction
Thioethers (sulfides) are the sulfur analogs of ethers and constitute an important class
of organosulfur compounds.[1,2] Thioethers have large applications, for example, as
potential hypocholesterolemic agents,[3] antagonists of leukocyte function-associated
antigen-1 (LFA-1),[4] nicotinic acetylcholine receptors,[5] precursors of sulfoxides and
sulfones,[6–8] and in general useful synthetic reagents and/or intermediates in organic
synthesis, agro-chemistry and heterocyclic chemistry.[9–12]
CONTACT Thi Xuan Thi Luu
ltxthi@hcmus.edu.vn
Department of Organic Chemistry, University of Science of
Ho Chi Minh City, 227 Nguyen Van Cu St., Dist. 5, Ho Chi Minh City, Vietnam
Supplemental data for this article can be accessed here. http://dx.doi.org/10.1080/17415993.2016.1150483
©
2016 Taylor & Francis

2
K. N. NGUYEN ET AL.
Many categories of thioethers are mainly synthesized by S-alkylation of thiols/thiolates
with alkyl halides,[13–25] or with alcohols,[26–37] S-arylation (Ullmann cross-coupling)
of thiols and aryl halides catalyzed by KF/alumina as base [38–40] or promoted by metal
compounds/complexes,[41–48] and cleavage of disulfides to react with alkyl halides or
alkyl tosylate.[49–53] However, the base-promoted S-alkylation of thiols with alkyl halides
is the classical and most common method to produce thioethers. The previous works on
the catalyst-free S-alkylation of thiols and alkyl halides illustrated that the presence of a
catalyst is necessary in order to reduce the reaction time.[13] A variety of inorganic or
organic base catalysts in the presence of phase transfer catalyst,[14–17] or solid supports
have been investigated in solvent media.[18,19] Moreover, solvent-promoted S-alkylation
of thiols by alkyl halides can take place in the presence of Zn powder.[20] In recent years,
solvent-free S-alkylation of thiols with alkyl halides by using Mg–Al Hydrotalcite,[21]
KF/Al O ground in a mortar as primary tests,[22] or magnetic iron oxide nanopar-
2
3
ticles has been developed.[25] In addition, the application of ionic liquid [pmIm]Br
as a catalyst and reaction medium for the conversion of thiols to thioethers has been
investigated.[23,24]
Solid-phase organic syntheses are preferable due to simple handling, cheaper opera-
tion, easy product isolation (avoiding the removal of the polar organic solvent at the work
up step), highly efficient catalyst recycling, and especially of importance in the chemical
industry.[54–56] Since the invention of ultrasound and microwave irradiation, many cat-
egories of solid phase syntheses or heterogeneous reactions accelerated by ultrasound or
microwave irradiation have been launched in order to reduce the reaction time, generate
fewer by-products, giving higher yield of the main products, or produce other products
incidentally compared with reactions under the conventional methods (stirring or thermal
heating methods).[57–61]
In this work, we report the influences of ultrasound or microwave irradiation on
the solvent-free S-alkylation of thiols with alkyl halides catalyzed by potassium fluo-
ride absorbed on alumina (KF/Al O ) to form the corresponding thioethers (Scheme 1).
2
3
KF/Al O was introduced as a useful base reagent by Ando et al. in 1979. Subsequently,
2
3
the applications of KF/Al O in organic synthesis became popular and widely used in
2
3
the formation of carbon–carbon bonds, carbon–oxygen bonds, carbon–nitrogen bonds,
carbon–phosphor bonds,[62,63] carbon–sulfur bonds via solvent S-alkylation of thiols
with alkyl halides,[19] or solvent-free Ullmann cross-coupling,[38–40] and sulfur–sulfur
bonds.[64]
Scheme 1. S-alkylation of thiols with alkyl/aryl halides catalyzed by KF/Al2O3.

JOURNAL OF SULFUR CHEMISTRY
3
2. Result and discussion
At the beginning of this research, p-thiocresol was arbitrarily selected as the test sub-
stance in order to find the most efficient reaction molar ratios. A series of experiments was
performed under microwave irradiation, in which the molar ratio between p-thiocresol, 1-
chlorobutane and the amount of catalyst (KF/Al O ) was varied. Obviously, an increasing
2
3
amount of KF/Al O affected the reaction conversion and hence the reaction yield more
2
3
drastically than excessive amounts of the alkyl halide and the thiol. However, an exces-
sive amount of KF/Al O catalyst led to an increase in the formation of the disulfide from
2
3
the self-coupling reaction of the thiol (Figure 1). This observation is comparable with the
observation of E. J. Lenardão et al. on the synthesis of symmetrical disulfide from thiols
by using KF/Al O as the base, although the self-coupling reaction of thiols occurred only
2
3
slowly.[60] Further experiments demonstrated that the appropriate amount of KF/Al O -
2
3
promoted solvent-free S-alkylation of p-thiocresol into 4-(butylthio)toluene to take place
most efficiently is 0.6 g.
Altogether nine thiols were subjected to solvent-free S-alkylation with three alkyl
halides under three different reaction conditions. In the first series of solvent-free S-
alkylation reactions, the mixture of reactants was allowed to react under the assistance
of ultrasound irradiation (Method A, Table 1). Some experiments on the effects of ultra-
sound irradiation were compared with magnetic stirring at room temperature. The results
showed that the yields obtained by the heterogeneous reactions between p-thiocresol
and 1-chlorobutane with KF/Al O catalyst was 77% after 2 h of ultrasound irradiation,
2
3
while it was 63% after 5 h of magnetic stirring. Thus, ultrasound irradiation is selected
to activate the further experiments of solvent-free S-alkylation of thiols with alkyl halides.
The second series of solvent-free S-alkylation reaction was performed under the assistance
Figure 1. Influence of the catalyst amount in the S-alkylation of p-thiocresol into 4-(butylthio)toluene
under solvent-free reaction conditions and assistance by microwave irradiation (50° 4 W, 6 min, p-
thiocresol: 1.5 mmol, 1-chlorobutane: 1.5 mmol).

4
K. N. NGUYEN ET AL.
Table 1. Yields of sulfides obtained by the solvent-free alkylation of thiols by various methods.a
b
c
Yield of 3 (time )
Entry
1
R1-SH
R2-X
Method Ad
72 (120)
Method Bd
85 (13)
Method Cd
63 (13); 72 (60)
2
82 (120)
88 (8)
64 (8); 86 (60)
e
e
e
e
3
4
72 (120)
75 (13)
52 (13); 63 (60)
77 (120)
89 (120)
89 (7)
40 (7); 70 (60)
5
95 (8)
58 (8); 92 (60)
e
e
e
e
6
7
71 (120)
71 (13)
42 (13); 62 (60)
e
e
e
72 (120)
70 (13)
68 (60)
e
e
e
8
9
80 (120)
82 (13)
73 (60)
e
e
e
75 (180)
77 (16)
60 (90)
e
e
e
10
76 (150)
78 (14)
64 (75)
1
1
2
96 (90)
97 (90)
95 (12)
98 (12)
96 (45)
97 (45)
1
1
3
96 (120)
92 (120)
97 (13)
96 (13)
98 (60)
96 (60)
14
a
Ratio of thiol : alkyl/aryl halides : KF/Al2O3 = 1.5 mmol : 1.5 mmol : 0.6 g.
b
c
Yields were calculated based on GC/MS.
Time = reaction time in minutes.
d
e
Method A: ultrasound irradiation; Method B: Microwave irradiation at 4 W, 50°C; Method C: Conventional heating at 50°C.
Yields of isolated products.

JOURNAL OF SULFUR CHEMISTRY
5
Figure 2. Influence of the catalyst cycles on the S-alkylation of thiophenol into 1-(phenylthio)butane
under solvent-free reaction conditions and assistance by microwave irradiation (50°C, 4 W, 8 min, thio-
phenol: 1.5 mmol, 1-bromobutane: 1.5 mmol).
of microwave irradiation (Method B, Table 1). A series of experiments on testing reaction
temperatures from room temperature to 40°C, 50°C, 60°C and 70°C was carried out. The
results of the experiments clearly demonstrated that a conveniently increased reaction tem-
perature (50°C) could shorten the time of the solvent-free S-alkylation. Consequently, the
yields of the products were comparable to those of experiments on Method A, but the
reaction times appeared shortened drastically from some hours down to some minutes at
5
0°C. Microwave irradiation inevitably affects the temperature rise of the reaction mix-
ture, and it would be of interest to check whether the drastically shortened reaction times
could be affected simply by the higher reaction temperatures. A series of experiments was
performed under conventional heating (Entries 1–6, Method C, Table 1) at the same reac-
tion times and temperatures with those under microwave irradiation. The results showed
that microwave irradiation affected considerably the yields of the thioethers and reaction
times owing to the efficient internal heating of microwave irradiation by direct coupling of
microwave energy with molecules present in the reaction mixture.
With advantages of KF/Al O on enhanced reactivity, a straightforward work-up pro-
2
3
cedure and milder reaction conditions, the reusability of KF/Al O was paid attention
2
3
and needs to be examined. The KF/Al O collected after filtration from the previous
2
3
reaction was washed sequentially with diethyl ether, ethyl acetate and acetone at room
temperature, subsequently dried in an oven at 100°C for 1, 2 and 3 h. The structure of the
recovered catalyst after 2-h drying was comparable with that of the fresh KF/Al O by the
2
3
X-ray diffraction pattern. The recycled KF/Al O was used for solvent-free S-alkylation
2
3
of thiophenol with 1-bromobutane under microwave irradiation as that of the optimized
experiment presented in Entry 2, Table 1. The catalytic efficiency of KF/Al O did not drop
2
3
significantly even after four cycles of being reused and recycled (Figure 2).
3. Experimental
3
.1. Instrumentation and chemicals
3.1.1. Instrumentation
Microwave irradiations were performed by means of a CEM Discover microwave oven.
Ultrasound irradiation was performed by means of a BRANSON 1510 ultrasonic bath,

6
K. N. NGUYEN ET AL.
operating at frequency 40 kHz. GC/MS analyses were performed on a Hewlett Packard
890 GC series II, apparatus of MS 5975C with Triple-Axis detector equipped with a J&W
6
DB-5MS capillary column (30 m, 0.25 mm i.d., 0.25 μm film thickness) and a Hewlett
Packard 7683B autosampler. HPLC analyses were performed on a micrOTOF-QII (Bruker)
with UV/VIS and MS detector, the heated capillary of iron trap mass spectrometer was set
to 350°C, reverse colume ACE 3C18 (5 μm × 4.6 × 150 mm) and ESI (electrospray ioniza-
tion): μQTOF Bruker. NMR spectra were recorded on a Bruker 500 NMR spectrometer at
1
13
500 MHz ( H) and 125 MHz ( C).
3.1.2. Chemicals
All commercially available chemicals used were from Aldrich and analyzed for authenticity
and purity by GC/MS before being used.
w
3
.1.3. Preparation of base catalyst KF/Al O (40% / )
2
3
w
KF (20 g) was dissolved completely in de-ionized water (150 mL, pH of solution: 6.5). Neu-
tral Al O (30 g) was stirred regularly in de-ionized water (150 mL) for around 5 min.
2
3
Then the KF solution was poured into the solution containing Al O under continuous
2
3
stirring for 30–45 min, until the pH of the mixture of the solutions was 11.5–11.7. Subse-
quently, water was removed from the solution mixture by rotatory evaporation, until the
weight of the remaining solid mass was 53–55 g. The wet solid mass was dried at 100–110°C
for 6 h. Finally, the obtained solid mass (50.5–51.5 g) was ground in a mortar into a fine
powder.
3.2. Typical procedures
3
.2.1. S-alkylation of thiols into corresponding thioethers by KF/Al O under
2
3
solvent-free reaction conditions assisted by ultrasound irradiation (Method A).
A suitable quantity of alkyl halide (1.5 mmol) and KF/Al O (0.6 g) was added to the
2
3
5
mL round-bottom flask containing thiol (1.5 mmol). The flask was placed into an ultra-
sound bath where the mixture of reactants was exposed to ultrasound irradiation for a
specific period of time (Table 1). Subsequently, the reaction mixture was extracted with
dichloromethane (4 × 15 mL). The combined extracts were filtered, washed with water
until neutral, and then dried by anhydrous Na SO . After removal of the solvent by
2
4
rotary evaporation, the remaining crude product was analyzed by GC/MS and NMR
spectroscopy.
3
.2.2. S-alkylation of thiols into corresponding thioethers by KF/Al O under
2 3
solvent-free reaction conditions assisted by microwave irradiation (Method B)
A suitable quantity of alkyl halides (1.5 mmol) and KF/Al O (0.6 g) was added to a specific
2
3
test tube (h = 9 cm, d = 1.5 cm) containing the thiol (1.5 mmol). The test tube was placed
into a Discover CEM microwave oven. For each of the thiols, an irradiation program was
fixed to operate at power of oven (4 W), reaction temperature (50°C) and reaction time
(minutes), see Table 1. After cooling, the reaction mixture was worked up as described in
method A.

JOURNAL OF SULFUR CHEMISTRY
7
3
.2.3. S-alkylation of thiols into corresponding thioethers by KF/Al O under
2 3
solvent-free reaction conditions assisted by conventional heating (Method C)
A test tube (h = 18 cm, d = 2 cm) containing a suitable quantity of thiols, alkyl halides
and KF/Al O (following the molar ratio as in Table 1) was placed in an oil bath heated to
2
3
the temperature applied for the reactions under microwave irradiation. The test tube was
kept in the oil bath for a period of time corresponding exactly to that found at optimum in
Method B or for a period of time to optimize the reaction yields. After cooling, the reaction
mixture was worked up as described in Method A.
3
.3. Spectroscopic data
The identity and purity of all of the thioethers synthesized were ensured by H and 13C
1
1
13
NMR spectroscopy as well as by GC/MS or HPLC/ESI. The observed data of H, C NMR
spectroscopic and mass spectra for the 12 thioethers synthesized are listed below, and most
of them were found compatible with those reported in the literature.[65–68]
1
-(Phenylthio)butane
1
(
Entry 1 or 2, Table 1): H NMR (CDCl ): δ = 7.14–7.33 (m, 5H), 2.93 (t, J = 7.5 Hz,
3
H
2
H), 1.64 (quintet, J = 7 Hz, 2H), 1.45 (sextet, J = 7.5 Hz, 2H), 0.92 (t, J = 7.5 Hz, 3H).
1
3
C NMR (CDCl ): δ = 137.04, 128.85 (2C), 128.78 (2C), 125.60, 33.26, 31.21, 21.93,
3
C
+
13.60. MS: m/z = 166[M] , 123, 110.
Benzylthiobenzene
1
(
(
3
Entry 3, Table 1): H NMR (CDCl ): δ = 7.19–7.34 (m, 10H), 4.14 (s, 2H). 13C NMR
3
H
CDCl ): δ = 137.46, 136.37, 129.84 (2C), 128.79 (4C), 128.44 (2C), 127.13, 126.31,
3
C
+
9.05. MS: m/z = 200[M] , 91, 65.
4
-Butylthiotoluene
1
(
(
(
1
1
Entry 4 or 5, Table 1): H NMR (CDCl ): δ = 7.25 (d, J = 8.0 Hz, 2H), 7.09
3
H
d, J = 8.0 Hz, 2H), 2.88 (t, J = 7.5 Hz, 2H), 2.32 (s, 3H), 1.61 (quintet, J = 7 Hz, 2H), 1.44
13
sextet, J = 7.5 Hz, 2H), 0.91 (t, J = 7.5 Hz, 3H). C NMR (CDCl ): δ = 135.81, 133.14,
3
C
+
29.77 (2C), 129.58 (2C), 34.04, 31.34, 21.91, 20.96, 13.62. MS: m/z = 180[M] , 137,
24, 91.
4
-Benzylthiotoluene
1
(
Entry 6, Table 1): H NMR (CDCl ): δ = 7.24–7.32 (m, 7H), 7.09 (d, J = 8.0 Hz, 2H),
3
H
1
3
4
1
.10 (s, 2H), 2.34 (s, 3H). C NMR (CDCl ): δ = 137.78, 136.50, 132.49, 130.68 (2C),
3
C
+
29.56 (2C), 128.79 (2C), 128.38 (2C), 127.01, 39.76, 20.98. MS: m/z = 214[M] , 123, 91.
2
-Butylthiobenzimidazole
1
(
(
2
1
1
Entry 7, Table 1): H NMR (CDCl ): δ = 9.06 (s, 1H), 7.52–7.55 (m, 2H), 7.18–7.21
3
H
m, 2H), 3.33 (t, J = 7.5 Hz, 2H), 1.72 (quintet, J = 7.5 Hz, 2H), 1.39 (sextet, J = 7.5 Hz,
1
3
H), 0.86 (t, J = 7.5 Hz, 3H). C NMR (CDCl ): δ = 150.99, 139.17 (2C), 122.25 (2C),
3
C
+
+
13.98 (2C), 32.47, 31.56, 21.75, 13.48. MS (ESI ): m/z = 207.0986 ([M+H] , 6%),
51.0378 (100%).

8
K. N. NGUYEN ET AL.
2
-Benzylthiobenzimidazole
1
(
Entry 8, Table 1): H NMR (DMSO-d ): δ = 12.55 (s, 1H), 7.09–7.57 (m, 9H), 4.55 (s,
6
H
1
3
2
1
1
H). C NMR (CDCl ): δ = 149.68, 143.61, 137.66, 135.44, 128.81 (2C), 128.45 (2C),
3
C
+
+
27.29, 121.65, 121.13, 117.40, 110.32, 35.13. MS (ESI ): m/z = 241.0769 ([M] , 100%),
98.0791 (34%), 150.0339 (18%).
2
-Butylthio-4,5-dihydrothiazole
1
(
Entry 9, Table 1): H NMR (CDCl ): δ = 4.20 (t, J = 7.5 Hz, 2H), 3.36 (t, J = 8.0 Hz,
3
H
2
0
1
H), 3.09 (t, J = 7.5 Hz, 2H), 1.66 (quintet, J = 7.5 Hz, 2H), 1.41 (sextet, J = 7.5 Hz, 2H),
13
.91 (t, J = 7.5 Hz, 3H). C NMR (CDCl ): δ = 166.34, 64.10, 35.19, 32.52, 31.23, 21.82,
3
C
+
+
3.52. MS (ESI ): m/z = 176.0537 ([M] , 98%).
2
-Butylthio-4-phenylimidazole
1
(
Entry 10, Table 1): H NMR (CDCl ): δ = 7.68 (dm, J = 8 Hz, 2H), 7.34 (tm,
3
H
J = 7.25 Hz, 3H), 7.23 (tt, J = 7.5 Hz, J = 1 Hz, 1H), 6.52 (s, 1H), 3.00 (t, J = 7.5 Hz,
2
H), 2.18 (s, 1H), 1.58 (quintet, J = 7.5 Hz, 2H), 1.35 (sextet, J = 7.5 Hz, 2H), 0.85 (t,
1
3
J = 7.5 Hz, 3H). C NMR (CDCl ): δ = 141.13, 139.57, 132.19, 128.69 (2C), 127.06,
3
C
+
+
1
24.80 (2C), 117.86, 34.84, 31.96, 21.67, 13.53. MS (ESI ): m/z = 233.1144 ([M] , 9%),
1
77.0581 (100%).
1
-(Benzylthio)butane
1
(
(
2
1
Entry 11, Table 1): H NMR (CDCl ): δ = 7.30–7.33 (m, 4H), 7.22–7.27 (m, 1H), 3.71
3
H
s, 1H), 2.43 (t, J = 7.0 Hz, 2H), 1.56 (quintet, J = 7.0 Hz, 2H), 1.38 (sextet, J = 7.0 Hz,
1
3
H), 0.90 (t, J = 7.0 Hz, 3H). C NMR (CDCl ): δ = 138.69, 128.83(2C), 128.44(2C),
3
C
+
26.85, 36.31, 31.34, 31.07, 22.03, 13.68. MS: m/z = 180[M] , 91, 77, 65, 45.
1
-(Benzylthio)octane
1
(
(
(
3
Entry 12, Table 1): H NMR (CDCl ): δ = 7.29–7.33 (m, 4H), 7.22–7.26 (m, 1H), 3.71
3
H
s, 1H), 2.41 (t, J = 7.0 Hz, 2H), 1.56 (quintet, J = 7.0 Hz, 2H), 1.22–1.37 (m, 10H), 0.89
13
t, J = 7.2 Hz, 3H). C NMR (CDCl ): δ = 138.72, 128.84(2C), 128.45(2C), 126.86,
3
C
+
6.34, 31.82, 31.45, 29.26, 29.20, 29.18, 28.91, 22.66, 14.10 . MS: m/z = 236[M] , 145,
9
1, 69.
Benzylthiocyclohexane
1
(
(
1
4
Entry 13, Table 1): H NMR (CDCl ): δ = 7.29–7.35 (m, 4H), 7.22–7.26 (m, 1H), 3.75
3
H
s, 1H), 2.54–2.60 (m, 1H), 1.94–1.97 (m, 2H), 1.75–1.77 (m, 2H), 1.60–1.75 (m, 1H),
1
3
.24–1.33 (m, 5H). C NMR (CDCl ): δ = 138.97, 128.76(2C), 128.44(2C), 126.77,
3
C
+
2.93, 34.61, 33.39(2C), 26.00, 25.89(2C). MS: m/z = 206[M] , 115, 91, 67.
2
-Benzylthio-2-methylpropane
1
(
Entry 14, Table 1): H NMR (CDCl ): δ = 7.20–7.36 (m, 5H), 3.77 (s, 2H), 1.36 (s, 9H).
3
H
1
3
C NMR (CDCl ): δ = 138.61, 128.96(2C), 128.45(2C), 126.76, 42.87, 33.45, 30.92(3C).
3
C
+
MS: m/z = 180[M] , 124, 91, 77, 57.

JOURNAL OF SULFUR CHEMISTRY
9
Conclusion
Comprehensive experimental work has made it possible for us to introduce an fast and
efficient synthetic method for the preparation of thioethers in fair to high yields by solvent-
free S-alkylation of thiols with alkyl halides by means of KF/Al O as a green catalyst (safety
2
3
for use and high recyclability) under the assistance of ultrasound or microwave irradiation,
subsidiarily also under the influence of conventional heating.
Funding
We are grateful to Vietnam National Foundation for Science and Technology Development (NAFOS-
TED) under grant number [104.01-2011.40] for financial support.
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