(7)
Table 4 The silicon conversion and the product distribution in the
tert-butyldichlorosilane. Since the isobutyl group is primary a
reactions of silicon with butyl chlorides
smaller amount of hydrogen chloride is probably formed than
that using sec- or tert-butyl chloride. This causes a lower silicon
conversion. The formation rate of tert-butyl chloride was below
0.02 mmol hϪ1, indicating no reaction of silicon, hydrogen
chloride and tert-butyl chloride to afford tert-butyldichloro-
silane. Thus, isobutene and hydrogen chloride formed from
isobutyl chloride take part in the formation of tert-butyl-
dichlorosilane.
Taken in total, it is concluded that alkyldichlorosilane is
formed both by the reaction of silicon, hydrogen chloride and
alkyl chloride and by the reaction of silicon, hydrogen chloride
and alkene.
Selectivity (%)
Butyl
chloride
Silicon
(%)
(C4H9)HSiCl2 (C4H9)SiCl3 HSiCl3 SiCl4
n
29
66
68 (n)
3 (n)
18
40
0
2
11 (sec)
39 (tert)
18 (iso)
16 (sec)
3 (tert)
iso
1 (tert)
sec
tert
82
79
0
0
79
81
5
16
The parentheses represent the kinds of butyl group in butyldichloro-
silanes or butyltrichlorosilanes. Catalyst amount 5 wt%, amount of
silicon charged 7.1 mmol, pretreatment at 723 K for 10 min, flow rates
of helium and butyl chloride 10 and 5 mmol hϪ1, respectively.
Conclusion
Alkyl- or vinyl-dichlorosilane was synthesized by the reaction
of silicon, hydrogen chloride and alkene/alkyne. A silicon–
carbon bond is formed mainly by the reaction of a surface
silylene intermediate with alkene or alkyne. During the reaction
a small part of the alkene undergoes hydrochlorination to yield
alkyl chloride, which subsequently reacts with the surface
silylene to form the silicon–carbon bond. The reaction of
silicon with propyl or butyl chloride also gave alkyldichloro-
silane as a main organosilicon product. Alkyl chloride is
dehydrochlorinated over the copper surface, and hydrogen
chloride formed participates in the formation of the silicon–
hydrogen bond. Alkyldichlorosilane is formed not only by the
reaction of silicon, hydrogen chloride and alkyl chloride but by
the reaction of silicon, hydrogen chloride and alkene.
chloride were not completely converted. The amounts of
butenes formed from iso- and n-butyl chloride were 2.5 and 1.0
mmol hϪ1, respectively. These results are compatible with both
the zwitterion stability and the butyl chloride stability over
copper metal.
The reaction mechanism is shown in eqn. (7). Butyl chloride
reacts with surface silylene 1 to form surface species 11. If the
reaction a proceeds butyldichlorosilane is formed via inter-
mediate 12. Reaction b leads to the formation of butene and
species 2, the latter reacting with hydrogen chloride originating
from butyl chloride to give trichlorosilane finally. Among
various butyl chlorides, tert-butyl chloride gave the highest
selectivity for trichlorosilane. This result is in agreement with
the highest yield of hydrodisilane in the reaction of phenyl-
(trimethylsilyl)silylene with tert-butyl chloride and with easy
formation of hydrogen chloride from tert-butyl chloride over
the copper surface. Comparing the silicon conversion for 5 h in
the reactions of silicon with various butyl chlorides, use of
n-butyl chloride resulted in the lowest silicon conversion,
because it is not easy to form hydrogen chloride by decom-
position of butyl chloride over copper.
The reaction with n-butyl chloride resulted in the formation
of sec-butyldichlorosilane together with n-butylchlorosilanes.
The sec-butyldichlorosilane formation may be caused by the
reaction of silicon, hydrogen chloride and 1-/2-butene formed
from n-butyl chloride and/or by the reaction of silicon, hydro-
gen chloride and sec-butyl chloride formed by isomerization
of n-butyl chloride. Actually, the formation of ca. 0.2 mmol hϪ1
of sec-butyl chloride was observed during the reaction.
References
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Elsevier, Amsterdam, 1967.
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Catalyzed Direct Reactions of Silicon, eds. K. M. Lewis and D. G.
Rethwisch, Elsevier, Amsterdam, 1993, pp. 333–440 and references
therein.
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therein; K. M. Lewis, D. McLeod, B. Kanner, J. L. Falconer and
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5 R. C. Bracken, U. S. Pat., 3 565 590, 1971.
6 P. S. Skell and E. J. Goldstein, J. Am. Chem. Soc., 1964, 86, 1442;
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Chem., 1979, 178, 105.
In the case of isobutyl chloride, tert-butyldichlorosilane was
mainly formed with a 39% selectivity, and the selectivity for
isobutyldichlorosilane was about a half (18%) that for the
J. Chem. Soc., Dalton Trans., 2001, 71–78
77