Direct synthesis of organochlorosilanes by the reaction of metallic silicon with hydrogen chloride and alkene/alkyne

Article abstract of DOI:10.1039/a800121i

Organosilicon compounds were directly synthesized from metallic silicon, alkene/alkyne and HCl, EtHSiCl₂ being obtained with 47% selectivity from Si, C₂H₄ and HCl at 513 K, and CH₂=CHSiHCl₂ and EtHSiC

Full text of DOI:10.1039/a800121i

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Direct synthesis of organochlorosilanes by the reaction of metallic silicon with
hydrogen chloride and alkene/alkyne
Masaki Okamoto, Satoshi Onodera, Yuji Yamamoto, Eiichi Suzuki and Yoshio Ono*†
Department of Chemical Engineering, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152, Japan
0.3
0.2
0.1
0.0
50
40
Organosilicon compounds were directly synthesized from
metallic silicon, alkene/alkyne and HCl, EtHSiCl2 being
obtained with 47% selectivity from Si, C2H4 and HCl at 513
K, and CH2NCHSiHCl2 and EtHSiCl2 with 39 and 23%
selectivity, respectively, when C2H2 was used in place of
C2H4.
(e)
30
20
10
0
(a)
Methylchlorosilanes, especially dimethyldichlorosilane, are
produced industrially by the reaction of metallic silicon with
MeCl using a copper catalyst.1 The direct synthesis of
dimethyldichlorosilane is the key step for synthesizing silicone
polymers. Various mechanisms have been proposed for this
direct synthesis.2 We carried out the reaction in the presence of
butadiene as a silylene trapping agent and found that an
appreciable amount of silacyclopent-3-enes was formed to-
gether with methylchlorosilanes.3 This indicates the inter-
mediacy of silylene-type species in this heterogeneous reaction.
It was presumed that the silylene species are formed on the
surface of a silicon–copper alloy, through which silicon atoms
diffuse out to the surface from the phase of metallic silicon. The
intermediacy of the silylene species has also been proposed for
the selective formation of trialkoxysilanes in the direct reactions
of metallic silicon with alcohols.4
HCl also reacts with metallic silicon to afford chlorosilanes,
mainly trichlorosilane.5 We presume that the surface silylene is
also an intermediate for the selective formation of tri-
chlorosilane.
It is well known that the addition of silylenes to alkenes gives
vinylsilanes via silacyclopropane intermediates.6,7 It is very
plausible that silylene species at the surface also react with
alkenes to form silacyclopropanes. In previous work, we have
reported that ethylmethoxysilanes are obtained by the reaction
of metallic silicon, MeOH and C2H4.8 When allyl propyl ether
was used instead of C2H4, allyldimethoxysilane was obtained in
38% selectivity.9
In this work, we report that alkylsilanes are directly prepared
by the reaction of metallic silicon and HCl in the presence of
C2H4 or propene. Organosilanes are also obtained by the
reaction of metallic silicon, HCl and C2H2.
The reactions were carried out in a fixed-bed flow reactor.
The mixture of metallic silicon (8.9 mmol) and copper(i)
chloride (0.79 mmol) as a catalyst was placed in a quartz tube
reactor (id 10 mm) and preheated at 723 K for 10 min. Then,
HCl (3 mmol h21) and C2H4 (12 mmol h21) was fed to the
reactor at 513 K. The reactor effluents were analyzed every 10
min by GC.
Fig. 1 shows the time courses of the rates of formation of
products and cumulative conversion of silicon. Ethyldichloro-
silane and trichlorosilane were obtained as the main products.
The rates of formation of these products increased to the
maximum with reaction time and then decreased. Small
amounts of dichlorosilane and tetrachlorosilane were also
formed. The cumulative conversion of silicon reached 36% in
12 h. Though the reaction was stopped at 12 h in the experiment
in Fig. 1, further increases in silicon conversion would be
attained on further extending reaction time. The overall
selectivity for ethyldichlorosilane for 12 h was 47%. The
(c)
(b)
(d)
0
2
4
6
t / h
8
10
12
Fig. 1 Time courses of formation rates of the products and cumulative
conversion of silicon in the reaction of silicon, HCl and C2H4. Preheating:
723 K for 10 min; reaction: 513 K, Si: 8.9 mmol, CuCl: 0.79 mmol. Feed:
HCl (3 mmol h21) and C2H4 (12 mmol h21). Rates of formation of (a)
ethyldichlorosilane, (b) dichlorosilane, (c) trichlorosilane, (d) tetrachlor-
osilane and (e) conversion of silicon.
selectivities for dichlorosilane, trichlorosilane and tetrachlor-
osilane were 6, 45 and 2%, respectively.
Note that ethyldichlorosilane was the sole organosilane
produced. To explain this fact, we propose the following
reaction scheme involving surface silylene 1 as shown in
Scheme 1. In the absence of C2H4, the surface silylene reacts
with HCl. The subsequent reactions through surface species 2
and 3 lead to the formation of HSiCl3 as the main product. The
formation of HSiCl3 by the addition of HCl to dichlorosilylene
has been reported.10 The silylene intermediate 1 reacts with
C2H4 to form silacyclopropane species 4. The species 4 is
converted into the surface species 5 by attack of HCl. Finally
attack of HCl on the species 5 leads to the cleavage of the two
Si–Cu bonds to form ethyldichlorosilane.
Use of propene instead of C2H4 under similar conditions
resulted in the formation of propyldichlorosilane and iso-
propyldichlorosilane with the selectivities of 10 and 24%,
respectively, together with chlorosilanes.
When C2H2 was used instead of alkenes, vinyldichlorosilane
and ethyldichlorosilane were produced. After preheating the
Cl
Cl
Cl
H
Cl
Cl
Cl
HCl
HCl
–H2
HCl
HCl
Si
Si
Si
Si
Si
H
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
1
2
3
H2C CH2
Si
Et
Cl
Cl
Et
Cl
C2H4
HCl
Si
Si
H
Cu
Cu
Cu
Cu
1
4
5
Scheme 1
Chem. Commun., 1998
1275

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HC CH
Si
the C2H2 :HCl ratio increases, the reactivity of metallic silicon
decreases. The selectivity for organosilanes was highest at a
C2H2 :HCl ratio of 0.26.
The reactions of silicon, HCl and alkene/alkyne offer a new
method for synthesizing organosilanes directly from metallic
silicon.
CH2 CH Cl
Si
CH2 CH Cl
Si
C2H2
HCl
HCl
Si
H
Cl
Cu
Cu
Cu
Cu
Cu
Cu
1
H2
H2C CH2
Si
Et
Cl
Cl
Et
Cl
HCl
HCl
Si
Si
H
Cu
Cu
Cu
Cu
Notes and References
Scheme 2
Table 1 Effect of C2H2 :HCl ratio on the Si–HCl–C2H2 reactiona
† E-mail: yono@o.cc.titech.ac.jp
1 R. J. H. Voorhoeve, Organohalosilanes: Precursors to Silicones,
Elsevier, Amsterdam, 1967.
Si
(C2H3)-
2 D. H. Hurd and E. G. Rochow, J. Am. Chem. Soc., 1945, 67, 1057; A.
L. Klebansky and V. S. Fikhtengolts, J. Gen. Chem. USSR, 1956, 26,
2795; R.J. H. Voorhoeve and J. C. Vlugter, J. Catal., 1965, 4, 220; I. M.
Podgornyi, S. A. Golubtsov, K. A. Andrianov and E. G. Mangalin, J.
Gen. Chem. USSR, 1974, 44, 739; M. P. Clarke, J. Organomet. Chem.,
1989, 376, 165, and references therein; K. M. Lewis, D. McLeod, B.
Kanner, J. L. Falconer and T. Frank, in Catalyzed Direct Reactions of
Silicon, ed. K. M. Lewis and D. G. Rethwisch, Elsevier, Amsterdam,
1993, pp. 333–440, and references therein.
3 M. Okamoto, S. Onodera, T. Okano, E. Suzuki and Y. Ono, J.
Organomet. Chem., 1997, 531, 67.
4 M. Okamoto, E. Suzuki and Y. Ono, J. Catal., 1994, 145, 537; M.
Okamoto, K. Yamamoto, E. Suzuki and Y. Ono, J. Catal., 1994, 147,
15.
C2H2 :HCl conversion HSiCl2
EtHSiCl2 H2SiCl2 HSiCl3 SiCl4
ratio
(%)
(%)
(%)
(%)
(%)
(%)
0.33
0.26
0.2
0.13
0.07
0
15
16
31
37
67
85
27
34
23
22
10
—
15
21
11
11
3
4
0
4
5
11
6
53
45
61
62
76
93
1
0
1
1
1
1
—
a Preheating: 723 K for 10 min; reaction: 513 K for 5 h, Si: 8.9 mmol, Cu:
0.20 mmol, HCl: 15 mmol h21
.
silicon–CuCl mixture at 723 K, only HCl (15 mmol h21) was
fed at 513 K for 10 min. During this period, 1% of silicon
charged in the reactor was consumed to form chlorosilanes, the
main product being HSiCl3. Then, the feed of HCl was changed
to a mixture of HCl (15 mmol h21) and C2H2 (4 mmol h21).
Vinyldichlorosilane and ethyldichlorosilane were produced
together with chlorosilanes. The overall selectivities in the 5 h
reaction for vinyldichlorosilane and ethyldichlorosilane were
39 and 23%, respectively, these two organosilanes accounting
for 62% of the products. About 13% of silicon charged in the
reactor was consumed in 5 h. A plausible mechanism for the
formation of vinyl- and ethyl-dichlorosilane is shown in
Scheme 2.
5 I. Shiihara and J. Iyoda, Bull. Chem. Soc. Jpn., 1959, 32, 636; B. Kanner
and K. M. Lewis, in Catalyzed Direct Reactions of Silicon, ed. K. M.
Lewis and D. G. Rethwisch, Elsevier, Amsterdam, 1993, pp. 1–66, and
references therein; W. C. Breneman, in Catalyzed Direct Reactions of
Silicon, ed. K. M. Lewis and D. G. Rethwisch, Elsevier, Amsterdam,
1993, pp. 441–457.
6 P. S. Skell and E. J. Goldstein, J. Am. Chem. Soc., 1964, 86, 1442; V. J.
Tortorelli, M. Jones, Jr., S. Wu and Z. Li, Organometallics, 1983, 2,
759; M. Ishikawa, K. Nakagawa and M. Kumada, J. Organomet. Chem.,
1979, 178, 105.
7 P. P. Gaspar, in Reactive Intermediates, ed. M. Jones, Jr., and R. A.
Moss, Wiley, New York, 1981, vol. 2, pp. 335–385, and references
therein; Y.-N. Tang, in Reactive Intermediates, ed. R. A. Abramovitch,
Plenum Press, New York, 1982, vol. 2, pp. 297–366, and references
therein.
The silylene intermediate 1 reacts with C2H2 to form a
silacyclopropene surface species, which is attacked by HCl to
form a surface species containing a vinyl group. Silacyclopro-
pene intermediates are often postulated in the reaction of
silylenes with alkynes, though normally only dimeric products,
1,4-disilacyclohexa-2,5-dienes are obtained.7,11 The exclusive
formation of monomeric products indicates the silylene species
do not exist in the vapor phase, but are located on the surface.
Formation of ethyldichlorosilane indicates that the hydro-
genation of the intermediate(s) occurs on the surface.
8 M. Okamoto, N. Watanabe, E. Suzuki and Y. Ono, J. Organomet.
Chem., 1995, 489, C12.
9 M. Okamoto, E. Suzuki and Y. Ono, J. Chem. Soc., Chem. Commun.,
1994, 507.
10 R. C. Bracken, U.S. Patent 3 565 590, 1971.
11 T. J. Barton, J. A. Kilgour, J. Am. Chem. Soc., 1974, 96, 7150; E. A.
Chernyshev, N. G. Komalenkova, S. A. Bashkirova and V. V. Sokolov,
Zh. Obshch. Khim., 1978, 48, 830; E. A. Chernyshev, N. G.
Komalenkova and S. A. Bashkirova, Zh. Obshch.Khim., 1971, 41, 1175;
M. Ishikawa, K. Nakagawa and M. Kumada, J. Organomet. Chem.,
1977, 131, C15; W. H. Atwell, D. R. Weyenberg, J. Am. Chem. Soc.,
1968, 90, 3438.
Table 1 shows the effect of the C2H2 :HCl molar ratio on the
product distribution. Without C2H2, high conversion of metallic
silicon is attained, giving trichlorosilane as a main product. As
Received in Cambridge, UK, 5th January 1998; 8/00121I
1276
Chem. Commun., 1998