Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2001-09-26
2002-05-07
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06384257
ABSTRACT:
The present invention relates to the catalytic hydrogenolysis of Si—X bonds (X=halogen, preferably Cl) present in compounds of the alkylhalosilane (ahs) type, for example methylchlorosilane, for the purpose of converting these ahs into alkylhydrohalosilanes (ahhs), for example methylhydrochlorosilane. In particular, the hydrogenolysis to which the invention relates is of the type that employs gaseous hydrogen and a metallic catalyst with production of hydrogen halide.
More particularly still, the invention relates to the value enhancement of byproducts of the direct synthesis (or Müller-Rochow synthesis) permitting the, production of methylchlorosilanes (MCS), which are base monomers for the manufacture of silicones by hydrolysis of Si—Cl bonds and creation, by polycondensation, of polysiloxanes containing siloxyl units “D” (—Me
2
SiO
2/2
—), “M” (—Me
3
SiO—), “T” (—MeSiO
3/2
—), “Q” (—SiO
4/2
—). The direct synthesis takes place by reaction between metallic silicon and methyl chloride at a temperature of between 250 and 300° C. in the presence of a catalyst based on copper, zinc or tin. This synthesis leads to a mixture in which dimethylchlorosilane Me
2
SiCl
2
is predominant (approximately 90%), but also to heavier products consisting primarily of disilanes (approximately 8%) of formula Me
p
Cl
3−p
—Si—Si—Cl
3−q
Me
q
(p, q=1 or 2). Other, so-called “light” MCS are also formed at the outcome of this direct synthesis. These light MCS are produced in allow proportion. They comprise in particular MeSiCl
3
(7-18%), MeSiCl
2
(0.5%) and, in even smaller quantities, Me
2
HSiCl, MeHSiCl
2
, Me
4
Si. HSiCl
3
, and isopentane. The light MCS are present in the stream emerging from the head of one or more distillation columns. This distillation operation makes it possible to separate the various products of the direct synthesis.
Among the light MCS, MeSiCl
2
constitutes the building block for the formation of polysiloxane chains containing units D (—Me
2
SiO—); Me
3
SiCl serves as a chain-end blocker; MeSiCl
3
permits the crosslinking of the polymer; and the compounds MeHSiCl
2
and Me
2
HSiCl enable the functionalization of the polymer through the use of the Si—H bond. Me
2
HSiCl, which does not possess an Si—Cl bond, permits selective chain-end functionalization, which is particularly desired. Consequently, the relative value of the MCS in relation to Me
2
HSiCl
2
(reference=1) is as follows:
Me
2
HSiCl (10-100)>Me
3
SiCl (2-3)>MeHSiCl
2
(0.5-1.5)) >MeSiCl
3
(0.1-0.2).
Industrially, the production of MeSiCl
3
far outstrips demand. The desire of those involved in industry would therefore be to enhance the value of MeSiCl
3
. Since the hydromethylchlorosilanes Me
2
HSiCl and MeHSiCl
2
are greatly desired, it is possible to envisage producing them from the methylchlorosilanes Me
2
SiCl
2
and MeSiCl
3
, respectively, which are widely available and inexpensive.
Accordingly, a number of processes have been proposed for hydrogenolyzing Si—Cl bonds present in ahs by molecular hydrogen, in accordance with the following reactions:
Me
2
SiCl
2
+H
2
⇄Me
2
ClSiH+HCl
Me
2
SiCl
3
+H
2
⇄MeCl
2
SiH+HCl
These reactions are catalyzed by at least one metallic compound.
Among the known processes of hydrogenating alkylhalosilanes, especially methylchlorosilanes, mention may be made of that described in the U.S. Pat. No. 5,329,038, wherein dimethyldichlorbsilane is hydrogenated using hydrogen gas in the presence of aluminum and a catalyst selected from the group consisting of copper, tin, zinc and derivatives of these metals.
The European patent application No. 717 900 describes the vapor-phase catalytic hydrogenation of alkylhalo(chloro)silanes to produce alkylhydrohalo(chloro)silanes in the presence of a metallic catalyst selected from the group consisting of palladium, platinum, ruthenium, optionally supported on active carbon and/or on aluminum oxide and/or on titanium oxide and/or on silicone oxide. More specifically, this European application describes the conversion of Me
2
SiCl
2
into Me
2
HSiCl, MeHSiCl
2
and Me
3
SiCl. The catalysts employed in the examples are, respectively, palladium on active carbon, platinum on active carbon, and ruthenium on alumina. The gaseous hydrogen is mixed into the Me
2
SiCl
2
, which is also in gaseous form. The reaction temperatures are 340 and 400° C. under pressures of 2, 6 and 10 bar. It should be noted that, in order to obtain a selectivity for MeHSiCl
2
of the order of 50%, it is necessary, according to this process, to employ pressures of 6 and 10 bar, which are relatively difficult to manage at the industrial level.
The European patent application No. 714 901 possesses the same content as the application EP No. 714 900 studied above, except that in this case the hydrogenation catalyst employed is hexachloroplatinic acid.
Within such a state of the art, one of the essential objectives of the present invention is to provide a process for preparing alkylhydrohalosilanes ahhs, in particular monosilanes of the methylhydrochlorosilane kind, by catalytic hydrogenation of alkylhalosilanes (ahs) of the methylchlorosilane type in the presence of a metallic catalyst, the purpose of such a process being to permit the obtention of high selectivities for alkylhydrohalosilanes (especially for methylhydrochlorosilanes) without, moreover, it being necessary to utilize conditions which are drastic and poorly suited to use in industry (high pressure).
Another essential objective of the present invention is to provide a process for catalytic hydrogenation in vapor phase of alkylchlorosilanes, especially methylchlorosilanes, to give alkylhydrohalosilanes, especially methylhydrochlorosilanes, which is simple to carry out and cost effective.
Another essential objective of the invention is to provide a process for enhancing the value of MeSiCl
3
by catalytic hydrogenation in vapor phase of this byproduct of the direct synthesis, for the purpose of obtaining MeHSiCl
2
which may be usefully exploited in the production of graftable siloxyl units D or else converted into MeHSiCl by chlorine redistribution starting from Me
3
SiCl (FR No. 96 07 559 and 97 16 047).
Another essential objective of the present invention is to provide a process for preparing alkylhydrohalosilanes (e.g., methylhydrochlorosilanes) by hydrogenating an alkylhalosilane (e.g., methylchlorosilane) using hydrogen gas in the presence of a metallic catalyst featuring particularly high performance and selectivity for MeH and further featuring a low cost price and obtainability on the industrial scale in a homogeneous form.
Another essential object of the invention is to provide a process for preparing ahhs by catalytic hydrogenation of ahs in the presence of a metal catalyst, the purpose of said process being to overcome the disadvantages of the prior art processes.
Given these objectives, among others, the inventors had the merit to select, after long and laborious research and experimentation, a specific ruthenium/tin catalyst which permits all of the abovementioned objectives to be attained, especially as regards selectivity for alkylhydrohalosilanes (MeHSiCl
2
).
The present invention accordingly provides a process for preparing alkylhydrohalosilanes (ahhs) of formula (I):
R
4−m−n
SiH
m
X
n
(I)
in which
R represents independently a C
1
-C
6
alkyl, preferably linear or branched, and more preferably still a methyl,
X represents independently a halogen, preferably chlorine,
m, n=1 or 2 and m+n≦3
by catalytic hydrogenation of alkylhalosilanes (ahs) of formula (II):
—R
(4−f)
Si
f
(II)
where f=1, 2 or 3in accordance with the reaction:
R(
4−p
) Si X
p
+H
2
→R
4−m−n
SiH
m
X
n
+H
m′
X
n′
where n′+n=p and m′=0 or 1
in the presence of a metallic catalyst, characterized in that the catalyst comprises a bimetallic ruthenium/tin catalytic agent.
One of the fundaments of the present invention is
Colin Pascale
Jacquot Roland
Morel Philippe
Burns Doane Swecker & Mathis L.L.P.
Rhodia Chimie
Shaver Paul F.
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