New method of dimethyl sulfi de synthesis

Article abstract of DOI:10.1134/S1070428011050046

The synthesis of dimethyl sulfide consists in the reaction of dimethyl disulfide with methanol in the presence of solid catalyst, aluminum γ-oxide. The yield of dimethyl sulfide grows with growing temperature, contact time, and content of methanol in the reaction mixture. At 350-400°C, molar ratio methanol-dimethyldisulfide 2.0-2.5, and total conversion of the reagents the yield of dimethyl sulfide reached 95 mol%. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S1070428011050046

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 5, pp. 678−681. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.V. Mashkina, 2011, published in Zhurnal Organicheskoi Khimii, 2011, Vol. 47, No. 5, pp. 677−679.
New Method of Dimethyl Sulfide Synthesis
A. V. Mashkina
Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences
Novosibirsk, 630090 Russia; e-mail: amash@catalysis.ru
Received December 2, 2009
Abstract—The synthesis of dimethyl sulfide consists in the reaction of dimethyl disulfide with methanol in the
presence of solid catalyst, aluminum γ-oxide. The yield of dimethyl sulfide grows with growing temperature, contact
time, and content of methanol in the reaction mixture. At 350–400°C, molar ratio methanol–dimethyldisulfide
2.0–2.5, and total conversion of the reagents the yield of dimethyl sulfide reached 95 mol%.
DOI: 10.1134/S1070428011050046
Dimethyl sulfide is used as extraction reagent, odorant
for gases, and as initial raw material for production of
dimethyl sulfoxide [1].
products at 350°C and molar ratio methanol–dimethyl-
disulfide 0.5 and 2.6.
At low content of methanol in the reaction mixture
alongside the dimethyl sulfide formed the other sulfur-
containing products: methanethiol, hydrogen sulfide,
carbon disulfide, and also traces of carbon oxysulfide;
among the reaction products also methane, ethylene, and
carbon oxides were found. The increase in the contact
time resulted in the growth of dimethyl disulfide conver-
sion and of the yield of dimethyl sulfide and hydrogen
sulfide, but virtually did not affect the yields of the other
reaction products.
A promising source of raw material for preparation
of dimethyl sulfide may be dimethyl disulfide, manufac-
tured at the purification of sulfur-containing hydrocarbon
mixtures [2]. It was found earlier [3] that in the presence
of a series of solid catalysts at the atmospheric pressure
and 190–350°C the decomposition of dimethyl disulfide
in an inert medium resulted in dimethylsulfide but the
process was accompanied with the formation of side prod-
ucts: methanethiol, hydrogen sulfide, carbon disulfide,
methane, ethane, and other substances. Consequently the
selectivity of dimethyl sulfide formation from dimethyl
disulfide does not exceed 56%, and it is not possible to
improve it by varying the catalyst composition and the
reaction conditions.
At excess methanol with respect to dimethyl disulfide
its decomposition proceeded giving mainly dimethyl
sulfide, and as the side product methanethiol formed in
a small yield. The yield of dimethyl sulfide grew with the
increase in the contact time and at the total conversion of
methanol and dimethyl disulfide the yield attained 95%.
At varying contact time the yield of dimethyl sulfide
was close to the conversion of dimethyl disulfide. The
variation of the degree f conversion of dimethyl disulfide
virtually did not affect the selectivity of the dimethylsul-
fide formation.
In this study with the goal to increase the selectivity
with respect to dimethyl sulfide the decomposition of
dimethyl disulfide was carried out on a solid catalyst
(γ-Al2O3) in the presence of methanol that methoxylated
the surface of the catalyst easier than dimethyl disulfide
[4].
The conversion of dimethyl disulfide with addition
of various amounts of methanol was investigated at the
contact time providing the dimethyl disulfide conversion
in the range 30–98%. For example the figure illustrates the
effect of the contact time on the conversion of dimethyl
disulfide and on the yields of the main sulfur-containing
Conversion, %
Selectivity, %
34 41 60 70 82 94 97
93 95 94 95 96 93 95
From the kinetic curves of the runs at 350°C and
different molar ratios methanol– dimethyl disulfide we
678

NEW METHOD OF DIMETHYL SULFIDE SYNTHESIS
(a) (b)
679
The effect of contact time on dimethyl disulfide conversion (X, %) (1), yields of sulfur-containing products (у, %): dimethyl sulfide (2),
methanethiol (3), hydrogen sulfide (4), carbon disulfide (5) in the presence of aluminum oxide at 350°C and molar ratio methanol–di-
methyl disulfide 0.5 (a) and 2.6 (b).
selected the contact time corresponding to the dimethyl
disulfide conversion of 70–73% and determined the yield
of reaction products in this point (see the table). At the
molar ratio methanol–dimethyl disulfide 0.1–0.2 the com-
position of sulfur-containing reaction products was the
same as at the decomposition of pure dimethyl disulfide,
but the yield of dimethyl sulfide and the selectivity of
its formation were a little better. With the growing ratio
methanol– dimethyl disulfide up to 0.5–1.0 the yield
of dimethyl sulfide and the selectivity of its formation
notably increased, and at the double and larger methanol
excess the main product was dimethyl sulfide, namely,
the reaction proceeded as follows:
[H+]
(CH3)2S2 + 2CH3OH
2(CH3)2S + 2H2O,
where [H+] were the protons on the catalyst surface.
The effect of the temperature of the experiment on
the parameters of the process was examined at the molar
ratio methanol–dimethyl disulfide 2 : 1.At different tem-
perature the contact time required to obtain the dimethyl
Decomposition of dimethyl disulfide in the presence of various content of methanol. Catalyst γ-Al2O3, 350°C, dimethyl disulfide
conversion 70–73%
Yield, %
Selectivity with
respect to dimethyl
Molar ratio methanol– Contact time,
hydrogen
carbon
disulfide
dimethyl disulfide
s
dimethyl sulfide metanethiol
sulfide , %
sulfide
0
0.04
0.14
0.16
0.24
0.62
0.75
1.10
1.15
1.2
25
27
28
34
46
60
64
65
66
23
16
18
19
11
7
11
17
11
9
12
11
13
9
36
38
40
47
66
85
91
95
94
0.12
0.24
0.50
1.0
1.4
2.0
2.5
2.8
4
8
3
1
5
0
0
5
0
0
4
0
0
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 5 2011

MASHKINA
680
disulfide conversion of 70–73% was different.
conversion virtually did not affect the selectivity with
respect to dimethyl sulfide, but it grew with temperature
from 250 to 400°C and somewhat decreased at higher
temperature due to the partial decomposition of dimethyl
sulfide [5].
Temperature, °C
Contact time, s
250 300 325 350 375 390 400 420 450
9.0 3.5 1.7 1.1 0.6 0.3 0.25 0.16 0.06
70 78 82 90 93 94 95 93 86
Selectivity with
respect to dimethyl
sulfide, %
Taking into consideration the data on adsorption
of reagents and the results of their transformations on
catalysts with diverse acid-base properties of the surface
[3, 4, 6–9] it is presumable that the reaction proceeds
through the stages of the decomposition of dimethyl di-
sulfide to methanethiol and the dehydration of methanol
resulting in the formation of surface CH3 groups that
further react with the formation of dimethyl sulfide.
The mechanism of this reaction is evidently similar to
that described in [6] for the formation of dimethyl ether
from methanol.
The formation of dimethyl sulfide was observed al-
ready at 250°C, but the reaction required a long contact.
With growing temperature the process accelerated, and
the required contact time decreased: At the temperature
growth from 250 to 450°C the contact time decreased 150
times. At the constant temperature the variation in the
contact time and consequently in the dimethyl disulfide
H3C
S S
CH3
. .
H H
.
.
.
H
.
H
H
(CH3)2S2
2CH3SH +
O
O Al
O Al O
O O
Al
H3C
H
O
O
CH3OH
O
O Al
O Al
CH3
.
.
S
H
.
.
.
.
H3C
O
H
H
CH3SH
CH3
.
.
.
.
.
O
O Al
+
(CH3)2S
.
O
O Al
O
O
Al
The prevailing formation of methoxy groups from
methanol impedes the proceeding of the side processes
of dimethyl disulfide decomposition thus increasing the
selectivity with respect to dimethylsulfide.
with the specific surface 275 m2/g was used as the
catalyst. The catalyst was dispersed till the size of
grains 0.25–0.5 mm and before use it was calcined in
the flow of dry air for 5 h at 500°C. The experiments
were performed in an installation of flow type at the
atmospheric pressure. The glass reactor was filled
with catalyst and placed into a tubular electric oven.
Methanol and dimethyl disulfide were poured into two
different saturators that were at temperature control. At
a desired velocity the helium flow was passed through
the saturators, then the gas was passed into a mixer
and afterwards into the reactor. The initial mixture
and reaction products were sampled intermittently for
chromatographic analysis. The GLC was performed
on a chromatograph LKhM-8MD equipped with the
katharometer, column 2 m × 3 mm packed with Paro-
pack R+Q (1 : 1), carrier gas helium.
As showed the study of the effect of the reaction con-
ditions on the parameters of the process, the preparative
synthesis of dimethyl sulfide from dimethyl disulfide and
methanol should be carried out at the atmospheric pres-
sure, temperature of 350–400°C, molar ratio methanol–
dimethyl disulfide 2.0–2.5, and contact time 2.5–4.0 s.
Under these conditions at the total conversion of reagents
dimethyl sulfide forms in 95 mol% yield.
EXPERIMENTAL
Methanol and dimethyl disulfide used in the study
were of “pure” grade. A ready sample of γ-Al2O3
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 5 2011

NEW METHOD OF DIMETHYL SULFIDE SYNTHESIS
681
vol. 39, p. 371.
The contact time was calculated as the ratio of the
catalyst volume to the velocity of the gas flow (cm3/s at
the room temperature and the atmospheric pressure. The
conversion of dimethyl disulfide, yield of the products,
and the selectivity of dimethyl sulfide formation equal to
the ratio of its yield to the conversion of dimethyl disulfide
were calculated.
3. Mashkina, A.V. and Khairulina, L.N., Kinetika, Kataliz,
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 5 2011