Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2000-08-11
2001-06-12
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06245926
ABSTRACT:
The present invention relates to the production of alkylmonohydrosilanes, which are starting materials particularly prized in organosilicon chemistry. More specifically, the invention relates to the separation of these alkylmonohydrohalosilanes (AHHSs) within complex mixtures obtained on conclusion of double exchange (or redistribution) reactions of alkyl and halogen substituents between halogenated silanes which may or may not result from direct synthesis, at least one of these silanes being a hydrosilane. This separation is carried out by distillation and the present invention is more specifically an improvement to this stage.
Without this being limiting, the present invention is targeted very specially at purifying a dialkylhydrochlorosilane produced by redistribution from a chlorinated alkylhydrosilane and an optionally chlorinated alkylsilane. This mono- or dialkylhydrochlorosilane is a synthetic agent which is particularly valued in very numerous and varied applications, for example in the preparation of organosilicon monomers or of more condensed base compounds.
The starting materials for this redistribution are obtained by direct synthesis. This technique consists in reacting alkyl chloride with silicon in the presence of a copper catalyst in order to form alkylchlorosilanes. The main product from this synthesis is dialkyldichlorosilane. The other coproducts are: monoalkylhydrodichlorosilane, dialkylhydrochlorosilane, trialkylchlorosilane and alkyltrichlorosilane.
It would have been possible to imagine isolating mono- and dialkylhydrochlorosilanes by distillation from the reaction mixture produced by direct synthesis. However, in so far as this mono- and this dialkylhydrochlorosilane are minor coproducts of the direct synthesis, it is clear that this route for obtaining them is not advantageous.
It follows that to produce mono- and dialkylchlorosilanes (e.g. Me
2
HSiCl), it is preferable, in accordance with the present invention, to recover these products from the crude mixture originating from the redistribution between an alkylhydrodichlorosilane and a trialkylchlorosilane or between an alkylhydrodichlorosilane and a tetraalkylsilane.
The redistribution between the alkyl, chlorine and hydrogen substituents of the silicons is carried out in the presence of catalysts, such as Lewis acids.
Throughout the present account, Me denotes the monovalent radical CH
3
.
French Patent FR-A-2,119,477 gives a good illustration of this technique for the preparation of dialkylhydrochlorosilanes by redistribution. The process disclosed in this document consists in reacting methylhydrodichlorosilane and trimethylchlorosilane in an MeHSiCl
2
/Me
3
SiCl molar ratio of the order of 0.5 in the presence of a catalyst formed by AlCl
3
.
The reaction mixture is placed in a reactor under an autogenous pressure of 3 to 5×10
5
Pa. The reaction takes place for several hours at a temperature of between 85 and 170° C. This redistribution results in Me
2
HSiCl and in numerous byproducts. On completion of the distillation, it is apparent that the yield for separation of Me
2
HSiCl is abnormally low, since it peaks at approximately 71%. Such results must be regarded as unsatisfactory with regard to industrial profitability.
To improve this state of the art, provision has been made by the Applicant in French Patent Application No. 9607569 of Jun. 12, 1996, which has not yet been published, to employ inhibition of the redistribution catalyst as soon as it has fulfilled its role in the reaction under consideration. This provision makes it possible to decrease, indeed even to eliminate, an interfering phenomenon induced by the AlCl
3
catalyst during the distillation, namely the dismutation of the chlorinated dialkyl(methyl)hydrosilane which it is desired to purify. It is clear that such a dismutation phenomenon is entirely harmful to the yield of Me
2
HSiCl.
The inhibitors provided in this improvement are polyorganosiloxanes or (poly)silanes which are provided in the fluid form or in the resin form and which are optionally alkoxylated. The metal of the catalyst/oxygen of the inhibitor molar ratio is chosen within a range of values which are less than 0.9.
These improvements have made it possible to significantly increase the yields of dialkylhydrochlorosilane. Thus, after redistribution, a distillate is obtained composed of a mixture of redistribution products rich in dialkylhydrohalosilane (e.g. Me
2
HSiCl), since the interfering dismutation has been eradicated.
However, when attempts are made to isolate the alkylhydrohalosilane(s) from the crude redistribution mixture by distillation, a substantial loss in AHHS (e.g. Me
2
HSiCl) is observed.
Confronted with this technical problem of loss of mono- or dialkylhydrochlorosilanes during distillation, the Applicant Company has set itself the essential objective of solving it.
Another essential objective of the present invention is to provide a process for the preparation of alkylmonohydrohalosilanes (e.g. Me
2
HSiCl or MeHSiCl
2
) which resolves the problem targeted above and which is particularly simple to employ and economical.
Another essential objective of the invention is to provide a process for the preparation of alkylmonohydrohalosilanes (e.g. Me
2
HSiCl or MeHSiCl
2
) which resolves the problem targeted above, which is as defined above and which makes it possible in particular to obtain these products with high levels of purity.
In order to be able to achieve these objectives, inter alia, the Applicant Company has had the credit of demonstrating a problem specific to the use of the process for the preparation of alkylmonohydrochlorosilanes and more particularly still to the distillation phase characteristic of this process. This is because the Applicant Company has been able to show that the distillation columns can be the site of undesirable dismutation reactions of alkylmonohydrochlorosilanes because of the presence of traces of aluminium-comprising products which can be aluminium chloride and/or organoaluminium compounds and/or silicon/aluminium compounds and/or organosilicon/aluminium compounds. These traces of aluminium-comprising products (e.g. AlCl
3
) promote the conversion of the redistribution products to byproducts of the optionally chlorinated organosilane and organohydrosilane type. Thus it is that, for example, Me
2
HSiCl is converted to Me
2
SiH
2
and to Me
2
SiCl
2
because of this interfering dismutation. It is clear that the latter seriously interferes with this separation phase of the process for the preparation of organohydrohalosilanes (AHHSs).
In addition to updating the technical problem, the inventive step of the Applicant Company has been complemented and enriched by the development of provisions which consist in choosing the appropriate temperature variables and in deactivating the compounds present in the distillation circuit with the AHHSs which are capable of acting as dismutation catalysts for the latter. It follows that the present invention relates to an industrial and continuous process for the preparation of alkylmonohydrohalosilanes (AHHSs) which are liable to be subject to a dismutation catalysed by at least one Lewis acid,
this process being of the type of those comprising the following essential stages:
(a) redistribution between at least one first compound of formula (1): (R)
a
(H)
b
SiX
4-a-b
, and at least one second compound of formula (2): (R′)
c
SiX
4-c
, (1) and (2) being formulae in which:
* a=0, 1, 2 or 3; b =1, 2 or 3; c 1, 2, 3 or 4 and a+b <3;
* R and R′ are radicals which are identical to and/or different from one another and which are chosen from alkyls and/or aryls (preferably methyl, ethyl, propyl or phenyl);
* the X substituents are identical to or different from one another and correspond to a halogen, preferably Cl, with the condition according to which at least one X atom is present in at least one of the two compounds of formulae (1) and (2), the said redistribution taking place in the presence of a catalyst chosen from Lewis acids, preferably from
Charrin Jean-Jacques
Colin Pascale
Guinamard Raphael
Igersheim Francoise
Margeriat Gilbert
Rhodia Chimie
Seugnet Jean-Louis
Shaver Paul F.
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