Aromatic hydrocarbon-catalyzed direct reaction of sulfur and sodium in a heterogeneous system: Selective and facile synthesis of sodium monosulfide and disulfide

Article abstract of DOI:10.1021/ic034084z

Sodium disulfide and monosulfide were selectively formed via the direct reaction of sulfur and an equimolar amount of sodium in 1,2-dimethoxyethane at 70 °C in the presence of a catalytic amount of aromatic hydrocarbons and ketone.

Full text of DOI:10.1021/ic034084z

Inorg. Chem. 2003, 42, 3712−3714
Aromatic Hydrocarbon-Catalyzed Direct Reaction of Sulfur and Sodium
in a Heterogeneous System: Selective and Facile Synthesis of Sodium
Monosulfide and Disulfide
,†
Toshikazu Takata,* Daisaku Saeki,† Yoshimasa Makita,† Nobuo Yamada,‡ and Nobuhiro Kihara†
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture UniVersity,
Sakai, Osaka 599-8531, Japan, and Research DiVision, DAISO Co. Ltd., Otakasu,
Amagasaki, Hyogo 660-0842, Japan
Received January 27, 2003
Sodium disulfide and monosulfide were selectively formed via the
direct reaction of sulfur and an equimolar amount of sodium in
1,2-dimethoxyethane at 70 °C in the presence of a catalytic amount
of aromatic hydrocarbons and ketone.
anhydrous sodium oligosulfides.7 However, it has not yet
been possible to control the number of sulfur atoms in the
oligosulfides. Thus, a great deal of effort was put into the
selective preparation of sodium oligosulfides. In this paper,
the selective synthesis of anhydrous sodium disulfide and
monosulfide is reported. Further, a novel catalyst system for
the reaction of elemental sulfur and sodium metal is also
described.
Sodium oligosulfide, generally prepared by the reaction
of elemental sulfur with sodium sulfide, is a key intermediate
for the synthesis of a variety of organic oligosulfanes.1 While
sodium sulfide is available as hydrate, its dehydration
requires immense heating to prepare anhydrous sodium
sulfide.2 The reduction of sodium sulfate with carbon also
requires considerable heating.3 Although the laboratory scale
synthesis of anhydrous sodium sulfide in liquid ammonia
has been reported, this method has not been practically
applied because of the use of liquid ammonia.4 Access to
anhydrous sodium oligosulfides has been rather difficult, and
the preparation of moisture sensitive organic oligosulfanes
has shown practical problems.5 Although the direct reaction
of molten sulfur and sodium has been used industrially,6 the
solution state synthesis of oligosulfides is desirable for further
use of sodium oligosulfide to prepare organic oligosulfanes.
Recently, we developed a reaction of elemental sulfur and
sodium metal in organic solvent that ensures easy access to
The reaction of sodium dispersion and powdery sulfur was
carried out in anhydrous 1,2-dimethoxyethane (DME) in
accordance with our previous report.7 For a prompt and
simple evaluation of the yield and composition of sodium
oligosulfides, and to confirm their applicability to the
synthesis of organic oligosulfanes, the reaction mixture was
quenched by slight excess of benzyl chloride to convert
sodium oligosulfide into dibenzyl oligosulfane.8 The organic
1
product was analyzed by GC-MS and H NMR spectra to
determine the yield and composition of the oligosulfanes.
Scheme 1
8 Na2Sn PhCH Cl8 PhCH2SnCH2Ph
2
2Na + (n/8)S8
DME, 70 °C
rt, 1 h
Although a mixture of oligosulfanes in which the average
sulfur content corresponded to the feed ratio of sulfur to
sodium (n) was obtained, most of our attempts to obtain
oligosulfide selectively were unsuccessful. However, when
sulfur was reacted with 1.1 atom equiv of sodium, dibenzyl
disulfane was obtained selectively. Namely, disulfane was
* Author to whom correspondence should be addressed. E-mail: takata@
chem.osakafu-u.ac.jp.
† Osaka Prefecture University.
‡ DAISO Co. Ltd.
(1) (a) Lange, L.; Triebel, W. Ullmann’s Encycl. Ind. Chem. 1994, A25,
443. (b) Steudel, R. Chem. ReV. 2002, 102, 3905.
(2) (a) Brown, A. P.; Battles, J. E. Synth. React. Inorg. Met.-Org. Chem.
1984, 14, 945. (b) Courtois, G.; C. R. Hebd. Seances Acad. Sci. 1938,
207, 1220. (c) Meller, J. W. Inorganic and Theoretical Chemistry;
Longmans and Green: London, 1961; Vol. II, p 991.
(3) Ullmann’s Encycl. Ind. Chem., 4th ed.; Wiley: Weinheim, 1979; 17,
167.
(7) Yamada, N.; Furukawa, M.; Nishi, M.; Takata, T. Chem. Lett. 2002,
454.
(8) The conversion of inorganic oligosulfide to organic oligosulfane was
investigated by various electrophiles including benzyl chloride, benzyl
bromide, methyl iodide, and propyl bromide, and no difference was
observed in the composition of oligosulfanes. Therefore, it was
assumed that the composition of dibenzyl oligosulfanes obtained by
the trapping experiments by benzyl chloride is well corresponded to
the composition of sodium oligosulfides in the solution. Further, the
yield of sodium oligosulfide can be evaluated by the yield of benzyl
oligosulfane because of both the high nucleophilicity of sulfur anion
and the high electrophilicity of benzyl chloride.
(4) Brandsma, L.; Wijers, H. E. Recl. TraV. Chim. Pays-Bas 1963, 82,
68.
(5) (a) Ranney, M. W.; Pagano, C. A. Rubber Chem. Technol. 1971, 44,
1080. (b) Deschler, U.; Kleinschmit, P.; Panster, P. Angew. Chem.,
Int. Ed. Engl. 1986, 25, 236. (c) Vondracek, P.; Hradec, M.;
Chvalovsky, V.; Khanh, H. D. Rubber Chem. Technol. 1984, 57, 675.
(6) Degussa, US 4640832, 1985.
3712 Inorganic Chemistry, Vol. 42, No. 12, 2003
10.1021/ic034084z CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/17/2003

COMMUNICATION
Table 1. Preparation of Sodium Disulfidea
the direct reaction method. When elemental sulfur was
reacted with 2.2 atom equiv of sodium at 70 °C for 4 h,
dibenzyl sulfane and disulfane were obtained in 21% and
44% yields, respectively, after treatment with benzyl chloride.
The reduction of disulfide to monosulfide was thus very slow.
However, when the reaction was carried out in the presence
of phenanthrene (18 mol % toward sodium), 68% of dibenzyl
sulfane was obtained with 96% selectivity. To further
increase the selectivity, the reaction with benzyl chloride was
carried out in refluxing DME for 5 h. Monosulfane was
obtained in 87% yield, and only traces of disulfane were
observed (selectivity >95%). Because of the low solubility
of sodium sulfide in DME, the yield of sulfane increased
under refluxing conditions.
yieldc/%
n ) 1 n ) 2 disulfide/%
selectivity of
run temp/°C time/h
catalystb
none
none
none
none
none
naphthalene
anthracene
phenanthrene
benzophenone
none
1
2
3
4
5
6
7
8
9
70
70
70
70
70
70
70
70
70
rt
2
4
8
12
24
4
4
4
4
4
1
2
4
3
2
4
6
1
2
3
6
25
40
64
66
20
78
73
82
83
5
95
96
94
96
92
91
92
99
98
63
92
10
11
rt
4
anthracene
65
a Elemental sulfur was reacted with 1.1 atom equiv of sodium dispersion
in DME before treatment with 1.5 equiv of benzyl chloride at room
temperature for 1 h. b 0.18 equiv toward sodium. c Yields of sodium
oligosulfides were evaluated after benzylation followed by GC analyses
using tetradecane as an internal standard.
The reduction potential of sulfur to sulfide and disulfide
anions is reported to be -0.476 and -0.428 V, respectively.9
Although the reduction potential of oligosulfides with three
or more sulfur atoms is unknown, it is expected to be higher
in accordance with the number of sulfur atoms, because of
reduced electrostatic repulsion between two negative charges
in oligosulfides. Therefore, not only the atom ratio of sodium
to sulfur but the gaps of reduction potential between these
oligosulfides were attributed to the selective reduction of
sulfur to disulfide and monosulfide. Thus, selective reduction
to either disulfide or sulfide was achieved in this system
because the gaps of reduction potential between sulfide,
disulfide, and oligosulfides are rather big. Meanwhile,
aromatic compounds were reduced by sodium to form radical
anions that then reduced sulfur. The aromatic compounds
mediated the electron transfer between the solid substrates
to reveal remarkable catalytic activity. The difference in
catalytic activity among the aromatic compounds tested can
presumably be accounted for by the electron-releasing ability
of the radical anion formed as an intermediate and its
interacting ability with the sulfur molecule or oligosulfide
anions.
Table 2. Preparation of Sodium Monosulfidea
yieldc/%
selectivity of
monosulfide/%
catalystb
none
naphthalene
anthracene
phenanthrene
benzophenone
phenanthrene
n ) 1
n ) 2
21
41
13
68
26
87d
44
5
4
3
30
<1
32
89
76
96
46
>99
a Elemental sulfur was reacted with 2.2 atom equiv of sodium dispersion
in DME before treatment with 1.5 equiv of benzyl chloride at room
temperature for 1 h. b 0.18 equiv toward sodium. c Yields of sodium
oligosulfides were evaluated after benzylation followed by GC analyses
using tetradecane as an internal standard. d Reaction with benzyl chloride
was carried out under reflux for 5 h.
obtained with a small amount of dibenzyl sulfane (selectivity
∼96%) as shown in Table 1. Only traces of oligosulfanes
with three or more sulfur atoms were detected. Since
heterogeneous reaction conditions were used to suppress the
explosive direct reaction of sodium and sulfur, the reaction
proceeded rather slowly. The yield of disulfane gradually
increased up to 66% in 12 h while selectivity remained high,
but the prolonged reaction decreased both yield and selectiv-
ity (runs 1-5). The reaction with solvent may cause the
decomposition of sodium disulfide.
Since a similar reaction in liquid ammonia gave sodium
sulfide in quantitative yield,4 effective electron transfer from
sodium to sulfur is presumably necessary to enhance the
reaction. Therefore, additives that can mediate the electron
transfer from sodium were explored. It was found that
aromatic hydrocarbons and ketone such as naphthalene,
anthracene, phenanthrene, and benzophenone showed high
catalytic activity to facilitate the formation of sodium
disulfide without decreasing selectivity (runs 6-9). Thus,
83% yield of disulfane was obtained with 98% selectivity
when a catalytic amount of benzophenone was added to the
system. Although only a 5% yield of disulfane was obtained
with 63% selectivity when the reaction was carried out at
room temperature without a catalyst, a 65% yield of disulfane
was obtained with 92% selectivity in the presence of
anthracene as a catalyst (runs 10, 11). Encouraged by the
effective catalytic activity of the aromatic compounds, we
further investigated the synthesis of sodium monosulfide by
In summary, we have demonstrated the selective synthesis
of sodium disulfide and monosulfide by the direct reaction
of elemental sulfur and sodium metal in organic solvent under
heterogeneous conditions. We evaluated the yields of sodium
disulfide and monosulfide by reacting these products with
benzyl chloride in order to convert them to the corresponding
organic di- and monosulfanes. Aromatic hydrocarbons and
ketone were quite effective catalysts to enhance both the yield
and the selectivity of sodium oligosulfides. The advantage
of the present method is the simple and direct preparation
of anhydrous sodium oligosulfides as a solution in organic
solvent under mild conditions. While organic disulfanes have
been prepared via the oxidation of thiols, the alkylation of
sodium disulfide has not been paid much attention.10
However, the method described above was proven as simple
and effective as the conventional oxidation method. This
(9) . CRC Handbook of Chemistry and Physics, 76th ed.; Lide, D. R.,
Ed.; CRC Press: New York, 1995; pp 8-25.
(10) (a) Miller, E.; Crossley, F. S.; Moore, M. L. J. Am. Chem. Soc. 1942,
64, 2322. (b) Field, L. Disulfides and Polysulfides. In Organic
Chemistry of Sulfur; Oae, S., Ed.; Plenum: New York, 1977. (c) Shin
Jikken Kagaku Koza; Maruzen: Tokyo, 1977; Vol. 14-3, Chapter 8.
Inorganic Chemistry, Vol. 42, No. 12, 2003 3713

COMMUNICATION
method’s strong feature is that it does not require stinky thiol
for the preparation of disulfane.
11793008) from the Ministry of Education, Science, Sports
and Culture.
Acknowledgment. We acknowledge financial support by
a Grant-in-Aid for University and Society Collaboration (No.
IC034084Z
3714 Inorganic Chemistry, Vol. 42, No. 12, 2003