Methylation of benzene with dimethyl disulfide

Article abstract of DOI:10.1134/S1070428015120118

Dimethyl disulfide reacts with benzene at 250-350°C over a period of 1-20 s in the presence of catalysts containing strong Br?nsted and Lewis acid centers to give a mixture of methylbenzenes, viz. toluene, isomeric xylenes, mesitylene, and durene.

Full text of DOI:10.1134/S1070428015120118

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2015, Vol. 51, No. 12, pp. 1729–1732. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © A.V. Mashkina, L.N. Khairulina, 2015, published in Zhurnal Organicheskoi Khimii, 2015, Vol. 51, No. 12, pp. 1763–1766.
Methylation of Benzene with Dimethyl Disulfide
A. V. Mashkina and L. N. Khairulina
Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences,
pr. Akad. Lavrent’eva 5, Novosibirsk, 630090 Russia
e-mail: amash@catalysis.ru
Received May 18, 2015
Abstract—Dimethyl disulfide reacts with benzene at 250–350°C over a period of 1–20 s in the presence of
catalysts containing strong Brønsted and Lewis acid centers to give a mixture of methylbenzenes, viz.
toluene, isomeric xylenes, mesitylene, and durene.
DOI: 10.1134/S1070428015120118
Methylbenzenes are important solvents and starting
compounds for the synthesis of various valuable prod-
ucts. Methylbenzenes can be obtained by catalytic
methylation of benzene using methanol, dimethyl
ether, halomethanes, or dimethyl sulfate as alkylating
agents. At present, oil and gas processing facilities
produce huge amounts of lower dialkyl disulfides R2S2
cleavage of the S–S and C–S bonds with formation of
CH and CH S fragments. The formation of methyl
3
3
species is favored by elevated temperature and long
contact time [2, 5]. It may be expected that under
certain conditions methyl species generated from 1
will react with activated benzene to form methyl-
benzenes.
(
R = C –C ) among which dimethyl disulfide (1) is the
1 4
The goal of the present work was to find out
whether benzene can be methylated with dimethyl
disulfide (1) in the presence of solid acid catalysts. We
studied the reaction of 1 with benzene over a number
of solid acid catalysts whose properties were examined
previously [5, 6]. The reactions were carried out at
major one; however, these compounds have found
limited application [1]. Studies are now performed to
explore the possibilities for using dimethyl disulfide in
catalytic syntheses of a number of organic compounds
such as thiols, sulfides, thiophene, sulfoxides, sulfones,
sulfonic acids, and sulfonyl-substituted heterocycles
3
00°C, the time of contact was 3.1–3.5 s, and the
[
2]. The liquid-phase reaction of 1 with benzene in the
molar ratio 1–PhH was (4–5):1.
presence of aluminum chloride at 82°C in 5–60 min
afforded 40–90% of thioanisole [3], but no methyl-
benzenes were detected.
Silica-supported phosphoric acid (H PO /SiO )
containing only weak Brønsted centers turned out to be
inactive. Catalysts possessing only strong Brønsted
3
4
2
Benzene is activated when contacted with Brønsted
acid centers on a catalyst [4]. Dimethyl disulfide
readily decomposes over active sites of catalyst via
centers (HSiW/SiO ), predominantly strong Lewis
2
centers and very weak Brønsted centers (γ-Al O ),
2
3
strong Brønsted and weak Lewis centers (Cr/SiO ), or
2
Table 1. Reaction of dimethyl disulfide (1) with benzene in the presence of different acid catalysts; 300°C, contact time 3.1–
.5 s, molar ratio 1–PhH (4–5):1
3
Yield, mol %
Conversion
of benzene, %
Catalyst
toluene (2)
xylenes (3)
mesitylene (4)
durene (5)
HSiW/SiO
2
05
06
07
09
15
18
0.0
0.2
0.3
0.2
0.2
0.4
3.6
1.5
3.6
4.8
8.4
9.0
1.2
1.0
0.1
3.0
4.7
6.5
0.0
1.5
3.0
1.1
1.2
2.1
γ-Al
Cr
AlSi
2
O
3
2
O
3
/SiO
2
HNaY
HZSM-5
1
729

1
730
MASHKINA, KHAIRULINA
Table 2. Methylation of benzene with dimethyl disulfide (1) over HZSM-5; molar ratio 1–PhH (4–5):1
Yield, mol %
Temperature,
Conversion
of benzene, %
Contact time, s
12.1
°C
toluene (2)
xylenes (3)
mesitylene (4)
durene (5)
2
00
07
10
12
19
31
15
14
15
27
39
45
14
20
28
34
0.1
0.2
0.4
0.6
0.9
0.4
0.5
0.5
0.7
0.8
0.9
0.1
0.2
0.4
0.5
02.0
03.0
02.4
04.5
09.3
06.3
05.4
06.1
11.3
16.5
19.8
06.8
09.7
13.4
16.1
01.4
02.1
06.2
09.5
13.0
03.8
04.1
04.2
07.3
10.5
11.3
00.2
00.4
00.3
00.5
03.1
04.5
02.5
04.2
08.0
04.7
04.2
03.7
07.9
12.5
13.2
07.0
09.8
13.6
17.0
2
0.0
2
50
03.0
0
1
7.2
5.1
3
3
00
50
02.5
a
a
0
0
0
1
2
2.3
2.4
5.8
4.1
0.0
b
b
01.1
0
0
0
2.0
4.7
8.8
a
b
Molar ratio 1–PhH: 1:1; 8.4:1.
strong Brønsted and strong Lewis centers (amorphous
aluminosilicates and H-zeolites HNaY and HZSM-5)
were active in the methylation of benzene with di-
methyl disulfide (Table 1). The products were toluene
Benzene remained almost unchanged in the absence
of dimethyl disulfide (the conversion did not exceed
2%). At low temperature and short contact time, pure
disulfide 1 over HZSM-5, as well as in the presence of
other acid catalysts [2, 6], was converted mainly into
methanethiol which then underwent partial dispro-
portionation to give dimethyl sulfide and hydrogen
sulfide. At elevated temperature and long contact time,
severe decomposition of both initial disulfide 1 and
methanethiol and dimethyl sulfide derived therefrom
was observed with formation of hydrogen sulfide,
sulfur, carbon disulfide, and ethylene. Analogous trans-
(
2), isomeric xylenes (3) in approximately equal
amounts, mesitylene (4), and durene (5). High-silicon
zeolite characterized by increased acidity showed the
highest catalytic activity. Therefore, the effects of
reaction conditions [200–350°C, contact time 1–20 s,
molar ratio 1–PhH (1.1–8.4) : 1] on the yield of
methylbenzenes were studied with the use of HZSM-5
as catalyst.
3
5
6
4
2
0
0
0
6
4
2
0
0
0
3
5
4
4
2
2
0
0
0
10
20
30
40
250
300
350
Benzene conversion, %
Temperature, °C
Fig. 1. Selectivity of formation of toluene (2), xylenes (3),
mesitylene (4), and durene (5) in the reaction of benzene
with dimethyl disulfide (1) at different benzene conversions.
Catalyst HZSM-5, 300°C, molar ratio 1–benzene (4–5):1.
Fig. 2. Temperature effect on the selectivity of formation of
toluene (2), xylenes (3), mesitylene (4), and durene (5) in the
reaction of benzene with dimethyl disulfide (1). Catalyst
HZSM-5, molar ratio 1–benzene (4–5):1.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 12 2015

METHYLATION OF BENZENE WITH DIMETHYL DISULFIDE
1731
Scheme 1.
Me
2
Me
Me
Me
Me
Me
+
+
Me
+
Me S
2
2
3
Me
Me
1
Me
4
Me
Me
Me
Me
5
formations of disulfide 1 occurred in the presence of
benzene, but their rate was lower.
with XE-60 on Chromaton AW-LMCS; carrier gas
helium).
The yields and ratio of methylbenzenes in the reac-
tion of 1 with benzene depended on the contact time
and temperature (Table 2). Increase of the time of
contact, the temperature and reactant concentrations
being constant, resulted in increased conversion of
benzene and higher yields of methylbenzenes. The
yield of toluene was always lower than the yields of
the other methylbenzenes. Variation of the reactant
ratio at constant temperature and contact time almost
did not affect the results. When the time of contact was
varied at a constant temperature, the selectivity for
compounds 2–5 remained virtually unchanged as the
conversion of benzene increased (Fig. 1).
Reagents of pure grade were used. The catalysts
2
2
were γ-Al O (S = 200 m /g), SiO (S = 360 m /g),
2
3
sp
2
sp
2
amorphous aluminosilicate AlSi (S = 430 m /g),
H-zeolites HNaY (Ssp = 800 m /g) and HZSM-5
(SiO /Al O , commercial product, S = 500 m /g). The
sp
2
2
2
2
3
sp
catalysts were calcined for 5 h at 300–530°C in
a stream of dry air prior to use. Supported catalysts
were prepared by impregnation of preliminarily cal-
cined silica with aqueous solutions of phosphoric or
silicotungstic acid (HSiW) or chromium(III) oxide.
The impregnated samples were dried for 5 h at 110°C
in air and were then calcined for 5 h. The concentra-
tions of H PO , HSiW, and Cr O in the catalysts were
3
4
2
3
3
0, 25, and 2.5 wt %, respectively. The reactions were
carried out in a flow setup with a fixed bed of catalyst
grain size 0.25–0.5 mm) under atmospheric pressure.
These findings indicated that all benzene methyla-
tion products are formed independently (Scheme 1).
The selectivity for toluene (2) was low (1–3%)
throughout the examined temperature range, the selec-
tivity for xylenes 3 and durene (5) attained the maxi-
mum value at 350°C (~50%), and 50% selectivity for
mesitylene (4) was observed at 250°C (Fig. 2).
(
A fresh portion of catalyst was used in each run. The
system was heated to a required temperature, helium
was supplied from a high-pressure cylinder into satura-
tors charged with dimethyl disulfide and benzene, and
the gas saturated with the reactants was fed into a cata-
lytic reactor heated to a required temperature. High-
boiling products were trapped in a cooled receiver.
The duration of each run was about 2 h. Samples of
the gaseous phase were withdrawn intermittently to
analyze gaseous products. Their concentration was cal-
culated as the mean value from 2–3 samples if the
difference did not exceed 10%. The activity of the
catalyst almost did not change over a period of 2 h.
EXPERIMENTAL
The reaction mixtures were analyzed by GC/MS
on an Agilent 7000 GC/MS Triple Quad instrument
(
HP-5MS capillary column, 30 m×0.25 mm). Methyl-
benzenes were quantitated by chromatography on
an LKhM-8MD chromatograph equipped with a ther-
mal conductivity detector (2 m×3-mm column packed
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 12 2015

1
732
MASHKINA, KHAIRULINA
The contact time was calculated as the ratio of the
catalyst volume (cm ) and the gas flux (cm /s) at room
temperature and atmospheric pressure. The yields
2. Mashkina, A.V., Russ. Chem. Rev., 2014, vol. 83, p. 733.
3
3
3
4
5
. Senaratne, K.P.A., Everly, C.R., and Park, W.S., US
Patent no. 5902906, 1999.
(
mol %) were determined as the ratio of the product
. Volodin, A.M., Doctoral (Chem.) Dissertation, Novo-
sibirsk, 1996.
concentration and initial substrate concentration, and
the selectivity was calculated as the ratio of the prod-
uct yield and benzene conversion.
. Mashkina, A.V., Chem. Sustainable Dev., 2012, vol. 20,
p. 181.
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gennom kislotno-osnovnom katalize (Infrared Spectro-
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sibirsk: Nauka, 1992.
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. Sharipov, A.Kh., Chem. Technol. Fuels Oils, 2002,
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 12 2015