Thermal reactions of dibenzyl disulfide and dibenzyl sulfide with metals: A new route to trans-stilbene and dibenzyl

Article abstract of DOI:10.1023/B:RUGC.0000045861.31805.e0

A procedure was developed for preparing stilbene by thermal desulfuring of dibenzyl disulfide and dibenzyl sulfide with metals (Fe, Zn). The major product of the similar reaction of dibenzyl disulfide with copper is dibenzyl.

Full text of DOI:10.1023/B:RUGC.0000045861.31805.e0

Russian Journal of General Chemistry, Vol. 74, No. 7, 2004, pp. 1043 1045. Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 7, 2004,
pp. 1132 1134.
Original Russian Text Copyright
2004 by Voronkov, Panova, Timokhina, Gromkova.
Thermal Reactions of Dibenzyl Disulfide and Dibenzyl Sulfide
with Metals: A New Route to trans-Stilbene and Dibenzyl
M. G. Voronkov, G. M. Panova, L. V. Timokhina, and R. A. Gromkova
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences, Irkutsk, Russia
Received July 4, 2002
Abstract A procedure was developed for preparing stilbene by thermal desulfuring of dibenzyl disulfide
and dibenzyl sulfide with metals (Fe, Zn). The major product of the similar reaction of dibenzyl disulfide
with copper is dibenzyl.
Thermal decomposition of dibenzyl sulfide I and
dibenzyl disulfide II is fairly well studied [1]. The
primary products of thermolysis of these compounds
at temperatures above 185 C were stilbene and hydro-
gen sulfide [2 4]; their further reaction gave tetra-
phenylthiophene and 2-phenylbenzothiophene. The
identified by-products of these reactions were toluene
and pentaphenylcyclopentadiene [3], erroneously iden-
tified earlier as 1,2,3,4-tetraphenylbutane [2]. Stilbene
is also one of the products of thermal reactions of I
and II with sulfur [4, 5]. When the reaction of II with
sulfur was performed at 150 C with distillation of the
forming stilbene in a vacuum, its yield reached 31%.
Stilbene was obtained in 17% yield in the reaction of
disulfide II with potassium tert-butylate in DMF at
Heating of II with copper powder was accompanied
by gradual darkening of the mixture, followed by fast
sintering at 200 215 C. No hydrogen sulfide evolved,
and the yield of trans-stilbene did not exceed 10%
(see table). In the reaction mixture, we identified by
GLC the degradation products: toluene, phenylmeth-
anethiol, dibenzyl, and sulfide I. When the reaction of
II with copper was performed at a lower temperature
(130 140 C), no stilbene was obtained. The major
reaction product was sulfide I (see table).
Heating of dibenzyl sulfide I with iron powder at
200 215 C for 20 h gave a mixture of trans-stilbene
(15%), dibenzyl (5%), and unchanged I (GLC data).
The reaction was accompanied by evolution of hydro-
gen sulfide and formation of iron sulfide. At a higher
temperature (230 235 C), the content of trans-stilbene
in the reaction mixture increased to 40% (see table).
On heating of I with zinc dust at 210 220 C for 32 h,
a mixture containing 50% unchanged I, 36% stilbene,
8
0 C [6].
With the aim to develop a convenient procedure for
preparing stilbene, we studied the thermal reactions of
readily available compounds I and II [7] with some
metals (activated Fe, Zn, Cu powders) in 1 : 4 molar
ratio.
4% II, and 2% dibenzyl was formed. After appropriate
work-up, the yield of trans-stilbene was 32% (see
table). At the reaction temperature was increased to
240 250 C, the yield of trans-stilbene was as high as
46%. A product of secondary transformation of stil-
bene, tetraphenylthiophene, was also detected (yield
3%). The process can be described by the equation
The reaction of II with iron powder was performed
at 200 215 C for 15 h in a continuous argon flow.
Longer heating was not appropriate because of tarring
of the reaction mixture. The reaction was accompa-
nied by evolution of H S and sublimation of the
2
forming trans-stilbene. From the residue, we isolated
an additional crop of stilbene by vacuum distillation.
The total yield of stilbene was 50% (see table). Heat-
ing of II with zinc dust under similar conditions gave
trans-stilbene in 40% yield (see table). The reactions
of II with Fe and Zn are described by the following
equation:
2
PhCH SCH Ph + M
2PhCH=CHPh + MS + H S,
2
2
2
I
M = Fe, Zn.
Dibenzyl sulfide I did not noticeably react with
copper powder at 160 165 C (5 h). At the tempera-
ture increased to 205 215 C and time, to 8 h, the con-
version of I appreciably grew, but the yield of the
reaction products remained poor (see table).
PhCH SSCH Ph + M
PhCH=CHPh + MS + H S,
2
2
2
II
M = Fe, Zn.
1
070-3632/04/7407-1043 2004 MAIK Nauka/Interperiodica

1044
VORONKOV et al.
Products of thermal reactions of dibenzyl sulfide I and dibenzyl disulfide II with metals
Reagent conversion, Stilbene yield,
Reagent Metal
T,
C
, h
Other reaction products (yield, %)a
%
%
II
II
II
II
I
I
I
I
I
Fe
Zn
Cu
Cu
Fe
210 215
210 220
210 215
130 140
200 215
230 235
210 220
240 250
160 165
205 215
15
18
0.5
5
20
20
32
35
5
94
95
100
56
70
88
58
90
13
56
48
38
7
R2S (9)
R2S (12)
RH (4), RSH (2), R (39), R S (28)
2
2
R (5), R S (23)
2
2
15
40
32
46
R2 (5)
R2 (10)
Fe
Zn
Zn
Cu
Cu
R (1), R S (2)
2 2 2
R (2), R S (5), tetraphenylthiophene (3)
2 2 2
RSH (5), R (2)
RH (1), RSH (8), R (7), R S (4)
2
I
8
2
2
2 2
a
R = PhCH .
2
EXPERIMENTAL
To monitor the reaction progress and analyze the
of the inorganic residue with dilute HCl results in
evolution of H S, suggesting the presence of iron
2
sulfide.
products, we used TLC (Silufol UV-254 plates, eluent
hexane benzene, 10 : 1) and GLC (Tsvet-500 chroma-
tograph, thermal conductivity detector, 3 2000-mm
stainless steel column, liquid phase 5% XE-60 on
Chromaton N-AW-HMDS, 0.25 0.315 mm; linear
heating from 40 to 220 C at a rate of 12 deg min ;
carrier gas He). All the reactions were performed
under Ar.
Reaction of dibenzyl disulfide II with zinc. A
mixture of 4.18 g of II and 4.4 g of zinc dust was
heated at 210 220 C for 18 h. This was accompanied
by evolution of H S and sublimation of stilbene. The
2
1
yield of stilbene after recrystallization from ethanol
was 1.16 g (38%). The remaining reaction mixture,
according to TLC, contained a minor amount of stil-
bene, dibenzyl disulfide II, dibenzyl sulfide I, elemen-
tal sulfur, and tars.
Dibenzyl disulfide II was prepared according to [8],
mp 71 C. Dibenzyl sulfide I was of analytically pure
grade. Iron, zinc, and copper powders were activated
according to [9].
Desulfuring of dibenzyl disulfide II with copper.
a. A mixture of 4.3 g of disulfide II and 4.4 g of cop-
per powder was heated to 200 C. The mixture gradu-
ally darkened, and at 210 215 C its rapid sintering
started. No hydrogen sulfide evolved. The mixture
was kept at 210 215 C for an additional 15 min,
cooled, and treated with benzene. The insoluble re-
sidue was filtered off, the benzene solution was evap-
orated, and the residue (2.4 g) was analyzed by GLC.
The mixture of reaction products contained 5% tolu-
ene, 3% phenylmethanethiol, 8% stilbene, 39% diben-
zyl, and 45% dibenzyl sulfide I.
Thermal reaction of dibenzyl disulfide II with
iron. A mixture of 4.93 g of disulfide II and 4.48 g
of iron powder was stirred for 15 h at 210 215 C.
Hydrogen sulfide evolved [reaction with a Pb(OAc)2
solution], and the forming stilbene sublimed and
deposited on cold walls of the reactor. The reaction
was stopped because of extensive tarring of the reac-
tion mixture. The sublimed trans-stilbene after re-
crystallization from ethanol [yield 1.3 g (36%)] had
mp 122 123 C (published data [10]: mp 123 124 C).
The remaining mixture was treated with hot benzene.
The dark yellow residue after removing the solvent
was distilled in a vacuum. A fraction (1.1 g) distilling
in the range 160 230 C (12 15 mm Hg) was col-
lected; according to GLC, it contained 40% trans-
stilbene, 35% dibenzyl sulfide I, and 25% dibenzyl
disulfide II, which was consistent with the results of
its elemental analysis. Found, %: C 80.32; H 6.91; S
b. The same amounts of reactants were kept at
30 140 C for 15 h. The mixture was worked up as
1
in procedure a. The residue after removal of benzene
was vacuum-distilled, and a broad fraction distilling
in the range 130 190 C (7 8 mm Hg) was isolated
in the amount of 2.95 g. According to GLC and ele-
mental analysis, it consisted of 65% disulfide II, 30%
sulfide I, and 5% dibenzyl. Found, %: C 72.29; H
5
2
.80; S 19.67. Calculated, %: C 72.53; H 6.06; S
1.41.
1
1.99. Calculated, %: C 81.86; H 6.39; S 11.75. From
this mixture, we isolated 0.43 g of trans-stilbene.
Total yield of trans-stilbene 1.73 g (48%). Treatment
Reaction of dibenzyl sulfide I with iron. a. A
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 7 2004

THERMAL REACTIONS OF DIBENZYL DISULFIDE AND DIBENZYL SULFIDE WITH METALS 1045
mixture of 2.7 g of sulfide I and 2.8 g of iron powder
was heated at 200 215 C for 20 h. Hydrogen sulfide
evolved. After cooling, the dark yellow mixture was
treated with benzene. The benzene solution was evap-
orated, and the residue was vacuum-distilled. A frac-
tion distilling at 183 187 C (15 mm Hg) was col-
lected (0.96 g); according to GLC and elemental anal-
ysis, it contained 80% dibenzyl sulfide I, 15% stil-
bene, and 5% dibenzyl. Found, %: C 81.49; H 7.35;
S 11.91. Calculated, %: C 81.42; H 6.61; S 11.97.
b. The same amounts of the reactants were heated
at 205 215 C for 8 h; the resulting mixture was
worked up as in procedure a. In vacuum distillation
(8 mm Hg), we collected the fractions distilling at
130 160 and 160 165 C. By GLC, we identified
(yield, %) dibenzyl (7), phenylmethanethiol (8), stil-
bene (2), dibenzyl disulfide (4), and unchanged diben-
zyl sulfide (44).
REFERENCES
b. A mixture of 5.4 g of dibenzyl sulfide I and
.6 g of iron powder was stirred at 230 235 C for
0 h. The mixture gradually became dark and viscous,
and hydrogen sulfide evolved. The mixture was
worked up as in procedure a. In vacuum distillation,
a fraction distilling at 130 150 C (5 7 mm Hg) was
collected (1.3 g); according to GLC and elemental
analysis, it contained 50% dibenzyl sulfide I, 40%
stilbene, and 10% dibenzyl. Found, %: C 86.18; H
1
2
. Voronkov, M.G. and Deryagina, E.N., Usp. Khim.,
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5
2
2
. Fromm, E. and Achert, O., Ber., 1903, vol. 36,
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5
. Voronkov, M.G. and Pereferkovich, A.N., Khim.
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6
.91; S 7.40. Calculated, %: C 85.81; H 6.71; S 7.48.
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tions of Sulfur with Organic Compounds), Voron-
kov, M.G., Ed., Novosibirsk: Nauka, 1979.
Reaction of dibenzyl sulfide I with zinc. A mix-
ture of 8.6 g of sulfide I and 10.4 g of zinc dust was
stirred at 240 250 C for 35 h. The sublimed stilbene
6
7
. Wallace, T.J., Pobiner, H., Hofmann, J.E., and
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(
1.3 g) was separated, and the remaining mixture was
worked up as in the reaction with Fe. In vacuum
distillation, we collected fractions distilling at 125
. Voronkov, M.G., Pereferkovich, A.N., and Mikhailo-
va, S.V., Zh. Prikl. Khim., 1969, vol. 42, no. 5,
p. 1155.
1
40 C (8 mm Hg) and 170 176 C (5 mm Hg), from
which we isolated 2.0 g of stilbene, 0.5 g of dibenzyl
disulfide II, 0.3 g of elemental sulfur, and 0.3 g of
tetraphenylthiophene. The latter compound was iden-
tified by elemental analysis and IR spectroscopy.
8. Voronkov, M.G., Deryagina, E.N., Turchaninova, L.P.,
Panova, G.M., and Korchevin, N.A., USSR Inventor’s
Certificate no. 1361139, 1986, Byull. Izobret., 1987,
no. 47.
Desulfuring of dibenzyl sulfide I with copper.
a. A mixture of 4.3 g of sulfide I and 5.1 g of copper
powder was heated at 160 165 C for 5 h, cooled, and
worked up as in the previous examples. Vacuum
distillation gave 3.8 g (87%) of unchanged sulfide I,
9
. Karyakin, Yu.V. and Angelov, I.I., Chistye khimiches-
kie veshchestva (Pure Chemicals), Moscow: Khimiya,
1
987.
0
.1 g (2%) of dibenzyl, and 0.2 g (5%) of phenyl-
10. Beilsteins Handbuch der organischen Chemie, 1964,
methanethiol.
vol. 5, p. 1954.
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