Chemistry Letters 2002
455
methyl iodide, similar results were obtained.
and reactive solid surface kept by dissolving the product Na2Sn
formed on the surface.15
Financial support by a Grant-in-Aid for University and
Society Collaboration from the Ministry of Education, Culture,
Sports, Science, and Technology of Japan (11793008) is grate-
fully acknowledged. The authors thank Professor Shinji Kato of
Gifu University, Japan, for his helpful discussion concerning with
the reactions of sodium oligosulfides.
Feed ratio change of Na and S resulted in the shift of the
oligomer distribution as expected (Table 1, runs 1–5). It is known
that trisulfide and higher oligosulfides are in equilibrium with the
related higher and lower oligosulfides in solution.12 Therefore,
the products obtained by this method also displayed a certain
oligosulfide distribution. An initial distribution observed in the
case of 2 : 2 ratio (Table 1, run 1) are changed to be astringent to
disulfide by the prolonged reaction (run 6). This result is
consistent with that the equilibrium of the oligosulfide inter-
conversion takes some time to be settled. Meanwhile, similar
experiment with 2 : 3 ratio of Na and S did not cause such
astringency even by prolonged reaction (runs 2 and 7), being
consistent with the typical behavior of oligosulfide in solution.12
The results obtained suggest the possible selective synthesis of
disulfides.
References and Notes
1
L. Lange and W. Triebel, Ulmann’s Encyclopedia of Industrial
Chemistry, A25, 443 (1994).
2
a) M. W. Ranney and C. A. Pagono, Rubber Chem. Tech., 44, 1080
(1971). b) R. W. Cruse, M. H. Hofstetter, L. M. Panzer, and R. J.
Pickwell, 150th Meeting of the Rubber Division of the American
Chemical Society, Louisville, June (1996), Abstr. p 75. c) U.
Deschler, P. Kleinschmit, and P. Panster, Angew. Chem. Int. Ed.
Engl., 25, 236 (1986). d) P. Vondracek, M. Hradec, V. Chvalovsky,
and H. D. Khanh, Rubber Chem. Tech., 57, 675 (1984).
F. Feher and H. J. Berthold, Z. Anorg. Allg. Chem., 273, 144 (1953).
P. Janssen and K. D. Steffen, German Offen DE 2306471 (1975);
Chem. Abstr., 83, 114633 (1976).
3
4
Several organic halides such as ester and allyl group-
containing halides as well as simple primary and secondary alkyl
halides were promptly converted to the respective oligosulfides
with Na2Sn (averaged n ¼ 4:0) (Figure 2).
5
a) A. P. BrownandJ. E. Battles, Synth. React. Inorg. Met. Org. Chem.,
14, 945 (1984). b) K. Maeda, European Patent 0361998 (1981);
Chem. Abstr., 113, 117915 (1982).
6
7
G. Courtois and C. R. Hebd, Seaceses Acad. Sci., 207, 1220 (1938).
J. W. Meller, ‘‘Inorganic and Theoretical Chemistry,’’ Longmans and
Green Co. Ltd., London (1961), Vol. II, p 991.
8
9
Notice: The violent explosive reaction took place, when the mixture
of Na and S8 in most solvents was heated over or around the melting
point of Na.
The initial mixture of oligosulfides moves to a mixture with an
appropriate distribution during the equilibrium in solution. The result
obtained by quenching with organic electrophiles to organic
oligosulfides should reflect the distribution of Na2Sn in solution,
because the product ratio was not largely changed by the concentra-
tion change of the electrophile added, and further the nucleophilic
substitution with thiolate anion is sufficiently fast compared to the
‘‘slow’’ equilibrium between the oligosulfides.
Figure 2. Substrate (top), yield (middle) and averaged S-content
(bottom).
With anhydrous Na2Sn by the present method, synthesis of
the silane coupling agent was carried out. To a Na2Sn (averaged
n ¼ 4:0) solution in dry DME freshly prepared using S8 and
sodium dispersion was added an equivalent of 3-(triethoxysilyl)-
propyl chloride. The mixture was refluxed for1 h. The pale yellow
product13 obtained quantitatively by filtration had 98% purity as
determined by HPLC and 1H NMR. Content of free sulfur in the
product was also determined by HPLC to be less than 1%. There
was no gelated product which would be derived by influence of
water contaminated in the system, indicating the formation of
completely dry Na2Sn. Large scale synthesis (more than 1 kg)
with sodium dispersion14 was readily accomplished in similar
yield, purity, and oligomer distribution.
10 Both the reaction yielding Na2Sn (step 1) and the reaction with
electrophile (step 2) are very clean and the yield should be nearly
quantitative, like the case of the silane coupling agent. The reduced
yield in the case of benzyl chloride would be attributed to the
occurrence of the oversulfurization reaction11 and/or some secondary
reaction of oligosulfides with benzyl halide forming sulfonium
species. In fact, treatment of benzyl chloride with excess Na2Sn
(averaged n ¼ 3:8) in DME afforded high yield of dithiobenzoate. No
attempt is done to collect the sulfonium derivatives at present time.
11 F. Becke and H. Hagen, German Offen DE1274121 (1969); Chem.
Abstr., 70, 3573v (1969).
12 E. E. Reid, ‘‘Organic Chemistry of Bivalent Sulfur, Vol. III,’’
Chemical Publishing, New York (1960), Chap. 7, p 363.
13 The structure of the silane coupling agent and its oligomer
distribution were determined by the 1H NMR in comparison with
the authentic samples. All oligomers (n ¼ 2 ꢀ 8) were separable by
HPLC.
14 Very small amount of sodium or sulfur remained unreacted at the end
of the reaction. Therefore, sodium dispersion prepared in toluene was
used for the preparation of oligosulfides. Actually, the consumption
of both solid materials was somewhat accelerated and the yield of the
product was improved by a few percent.
15 The mechanism of theformationof Na2Sn can besimply explained by
the successive one-electron reduction of sulfur with sodium causing
the S8 ring cleavage in a random fashion leading to the formation of a
variety of Na2Sn. On the other hand, Na2Sn thus formed can attack
nucleophilically at sulfur atom of S8 bringing about the ring cleavage
and eventually yields higher sulfur-content Na2Sn.
In summary, we have demonstrated the novel practical
synthetic method of anhydrous sodium oligosulfides from metal
and elemental sulfur, with which various organic oligosulfides
were synthesized in high yields. The method can be characterized
by the simple procedure, high yield, large scale synthesis, easy
successive reaction, and so on. This development would be indebt
to the unprecedent choice of ethereal (aprotic) solvent, which
unambiguously promotes the reaction progress due to the clean