Process for the preparation of halogenosilanes

Halogenosilanes are prepared from an organohalogenosilane and an organopolysiloxane as the starting materials by subjecting them to an intermolecular redistribution reaction in the presence of a monohydrochloride of a hexaalkylphosphotriamide. The thus prepared halogenosilanes, which are different from the starting halogenosilane reactant, are very useful in the silicone industry.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for preparing halogenosilanes by 
a redistribution reaction. There are known methods in which two different 
silicon compounds are subjected to a redistribution reaction in the 
presence of an amine, such as stearyl amine or aniline or a Lewis acid, 
such as aluminum chloride or iron(III) chloride to obtain a valuable 
silicon compound which is different from either of the starting silicon 
compounds (see U.S. Pat. Nos. 3,065,252 and No. 3,101,361). The prior art 
methods are disadvantaged, for example, by that the reaction must be 
carried out under pressure at a high temperature over 150.degree. C. Such 
reaction conditions cause complicated side reactions to take place 
simultaneously and, as a result, the yields of the intended silicon 
compounds will be reduced, while the separation and recovery of the 
products from the reaction mixtures will sometimes be very difficult. 
Furthermore, a redistribution reaction has been proposed between a siloxane 
reactant and a chlorosilane in the presence of a hexaalkylphosphotriamide 
(see, for example, U.S. Pat. No. 3,646,088), in which the cleavage of a 
silicon-oxygen bond takes place and one fragment of the siloxane is 
combined with the chlorine atom from the chlorosilane, while the other 
fragment of the siloxane is combined with the residue of the chlorosilane. 
When this process is employed as a means for preparing the desired 
chlorosilane, however, it is disadvantaged by low yields because only one 
fragment of the siloxane is converted to the chlorosilane. 
SUMMARY OF THE INVENTION 
It is the object of the present invention to provide an effective means to 
obtain organohalogenosilanes, which are very useful and highly demanded in 
the silicone industry, from an organopolysiloxane and an 
organohalogenosilane as the starting materials. 
As the result of our research relating to processes of producing, from an 
organopolysiloxane and a halogenosilane, a valuable halogenosilane product 
different from the starting halogenosilane, it has been discovered that 
when these two kinds of the starting silicon compounds are subjected to a 
redistribution reaction in the presence of a hydrochloride of a 
hexaalkylphosphotriamide, the intended halogenosilane can easily be 
obtained in a high yield, without the above-described disadvantages 
involved in the conventional processes. 
Thus, the present invention provides a process for the preparation of an 
organohalogenosilane product expressed by the general formula 
EQU R.sup.1.sub.a SiX.sub.4-a 
where R.sup.1 is a hydrogen atom or a substituted or unsubstituted 
monovalent hydrocarbon group, a is 1, 2 or 3 and X is a halogen atom, by 
a reaction between an organohalogenosilane reactant expressed by the 
general formula 
EQU R.sup.2.sub.b SiX.sub.4-b (I) 
where R.sup.2 is a substituted or unsubstituted monovalent hydrogen group, 
X is the same as defined above, and b is 0, 1, or 2, always being smaller 
than the value of the above-defined a and an organopolysiloxane reactant 
represented by the average unit formula 
EQU (R.sup.1.sub.3 SiO.sub.0.5).sub.p (R.sup.1.sub.2 SiO).sub.q (R.sup.1 
SiO.sub.1.5).sub.r (SiO.sub.2).sub.s (II) 
where each R.sup.1, which may be the same or different, is the same as 
defined above and p, q, r and s each are numbers satisfying the 
requirements of 0 .ltoreq. p .ltoreq. 1, 0 .ltoreq. q .ltoreq. 1, 0 
.ltoreq. r .ltoreq. 1, 0 .ltoreq. s &lt; 1 and (p+q+r+s)=1, to bring about a 
redistribution reaction wherein the reaction is carried out in the 
presence of a monohydrochloride of a hexaalkylphosphotriamide represented 
by the general formula 
##STR1## 
where R.sup.3 and R.sup.4, which may be the same or different, are alkyl 
groups having 1 to 6 carbon atoms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The organohalogenosilanes as one of the starting substances expressed by 
formula (I) above are exemplified by dimethyldichlorosilane, 
methyltrichlorosilane, diphenyldichlorosilane, phenyltrichlorosilane, 
vinyltrichlorosilane, methylethyldichlorosilane, ethyltrichlorosilane and 
tetrachlorosilane. 
The organopolysiloxanes useful as the other of the starting substances in 
accordance with the present invention are represented by formula (II), in 
which the monovalent hydrocarbon groups denoted by R.sup.1 include 
saturated and unsaturated aliphatic hydrocarbon groups, aryl groups and 
aralkyl groups as well as the substituted groups thereof by halogen atoms, 
cyano groups and other substituents. Further, in formula (II), p,q,r and 
s, being numbers satisfying the specified requirements, represent mole 
fractions of respective siloxane units. 
Illustrative of the organopolysiloxanes are hexaorganodisiloxanes; 
octaorganotrisiloxanes; linear organopolysiloxanes having at least 4 
silicon atoms, each terminal group of which is a triorganosilyl group; 
cyclic organopolysiloxanes, such as hexaorganocyclotrisiloxanes and 
octaorganocyclotetrasiloxanes; branched and crosslinked oranopolysiloxanes 
having siloxane units represented by the formulas R.sup.1.sub.3 
SiO.sub.0.5, R.sup.1.sub.2 SiO and R.sup.1 SiO.sub.1.5 ; branched and 
crosslinked organopolysiloxanes having siloxane units represented by the 
formula SiO.sub.2 in addition to the above siloxane units; and 
organohydrogenpolysiloxanes derived from the foregoing organopolysiloxanes 
by replacing part of the organic groups bonded directly to the silicon 
atoms with hydrogen atoms. As specific examples of such 
organopolysiloxanes, there can be mentioned hexamethyldisiloxane, 
1,1,3,3-tetramethyl-1,3-divinyldisiloxane, 1,1,3,3-tetramethyldisiloxane, 
1,1,3,3-tetramethyl-1,3 -di-n-butyldisiloxane, 
1,1,3,3-tetramethyl-1,3-diethynyldisiloxane, 
1,1,3,3-tetraphenyl-1,3-dimethyldisloxane, 1,1,3,3-tetramethyl- 
1,3-diphenyldisiloxane, octamethyltrisiloxane, 
1,1,3,3-tetramethyldisiloxane, hexamethylcyclotrisiloxane and 
octamethylcyclotetrasiloxane. 
The redistribution reaction in accordance with the present invention is 
carried out in the presence of a hydrochloride of a 
hexaalkylphosphotriamide expressed by formula (III) above, which serves as 
a catalyst to accelerate the reaction. The charge of the catalyst into a 
reaction vessel can be carried out in the following manners. For example, 
the prepared hydrochloride is introduced into the reaction vessel together 
with the two starting compounds. As another example, the 
hexaalkylphosphotriamide is introduced into the reaction vessel together 
with the two starting compounds, followed by addition of hydrogen chloride 
or hydrochloric acid as a hydrochloride-forming agent. As a further 
example, the hexaalkylphosphotriamide is introduced into the reaction 
vessel together with the two starting compounds, followed by addition of 
water, an alcohol, an inorganic or organic acid or amine as a 
hydrochloride-forming agent to generate hydrogen chloride in situ by the 
partial decomposition of the starting halogenosilane. 
The amount of the hydrochloride as the catalyst is not narrowly critical 
and may range from 0.001 to 80% by weight based on the total weight of the 
starting siloxane and silane. Preferably from 0.1 to 10% of the catalyst 
based on the total weight of the siloxane and silane is employed. 
Hexaalkylphosphotriamides can form two kinds of hydrochlorides, i.e., 
monohydrochloride and dihydrochloride, by reaction with 1 or 2 moles of 
hydrogen chloride, of which the former hydrochloride is especially 
suitable in the redistribution reaction of the present invention. 
Therefore, when the in situ formation of the hydrochloride is intended as 
described above, the amount of the hydrochloride-forming agent, e.g., 
hydrogen chloride, hydrochloric acid, water or an alcohol, should be 
limited so that the formation of the dihydrochloride may be avoided. 
In practicing the process of the invention as described above, it may be 
possible that the hexaalkylphosphotriamide which has not been converted to 
the hydrochloride is present in the reaction vessel. The reaction 
temperature may range from 0.degree. to 200.degree. C, preferably from 
20.degree. to 150.degree. C. Under these reaction conditions, the intended 
redistribution reaction can proceed rapidly. The molar ratio of the 
starting reactants may be appropriately chosen depending on the kinds of 
the starting reactants and according to the stoichiometry of the intended 
redistribution reaction. 
The following examples are illustrative of the practice of the present 
invention and are not intended for limitation. In the examples, 
percentages are all by weight. 
EXAMPLE 1 
To a mixture consisting of 48.7 g of hexamethyldisiloxane, 30.0 g of 
methyltrichlorosilane and 2.6 g (0.0145 mole) of hexamethylphosphotriamide 
was added 0.20 g (0.0111 mole) of water, and the resulting mixture was 
heated at 80.degree. C for 4 hours. Here, part of the 
methyltrichlorosilane was hydrolyzed by the added water to generate 
hydrogen chloride, which in turn formed the monohydrochloride of the 
hexamethylphosphotriamide. The resultant reaction mixture was analyzed and 
it was found that 57.4 g of trimethylchlorosilane was produced with 88% 
yield based on the hexamethyldisiloxane. 
For comparison, a similar procedure was repeated except that the addition 
of water was omitted and, as a result, the yield of trimethylchlorosilane 
based on the hexamethyldisiloxane was 40 %. 
EXAMPLE 2 
To a mixture consisting of 93.2 g of 1,1,3,3-tetramethyl-1, 
3-divinyldisiloxane, 64.5 g of dimethyldichlorosilane and 4.7 g of 
hexaethylphosphotriamide was added 0.40 g of water, and the resulting 
mixture was heated at 100.degree. C for 4 hours. The reaction mixture was 
then analyzed and it was found that 102.6 g of dimethylvinylchlorosilane 
was produced with 91% yield based on the 1,1,3,3-tetramethyl-1, 
3-divinyldisiloxane. 
EXAMPLE 3 
To a mixture consisting of 134.3 g of 1,1,3,3-tetramethyldisiloxane, 129.0 
g of dimethyldichlorosilane and 8.0 g of hexamethylphosphotriamide was 
added 0.66 g of water, and the resulting mixture was heated at 40.degree. 
C for 4 hours. The reaction mixture was then analyzed and it was found 
that 113 g of dimethylchlorosilane was produced with 60 % yield based on 
the 1,1,3,3-tetramethyldisiloxane. pg,10 
EXAMPLE 4 
To a mixture consisting of 147.9 g of 1,1,3,3-tetramethyl-1, 
3-di-n-butyldisiloxane, 80.6 g of phenyltrichlorosilane and 6.9 g of 
hexamethylphosphotriamide was added 0.57 g of water, and the resulting 
mixture was heated at 130.degree. C for 6 hours. The reaction mixture was 
then analyzed and it was found that 150 g of n-butyldimethylchlorosilane 
was produced with 83% yield based on the 1,1,3,3-tetramethyl-1, 
3-di-n-butyldisiloxane. 
EXAMPLE 5 
To a mixture consisting of 54.7 g of 1,1,3,3-tetramethyl-1, 
3-diethynyldisiloxane, 42.3 g of phenyltrichlorosilane and 2.9 g of 
hexamethylphosphotriamide was added 0.24 g of water, and the resulting 
mixture was heated at 60.degree. C for 4 hours. The reaction mixture was 
then analyzed and it was found that 67.7 g of dimethylethynylchlorosilane 
was produced with 95% yield based on the 1,1,3,3-tetramethyl-1, 
3-diethynyldisiloxane. 
EXAMPLE 6 
To a mixture consisting of 23.7 g of octamethyltrisiloxane, 44.8 g of 
methyltrichlorosilane and 3.4 g of hexamethylphosphotriamide was added 
0.068 g of water, and the resulting mixture was heated at 80.degree. C for 
4 hours. The reaction mixture was then analyzed and it was found that 16.2 
g and 9.6 g of trimethylchlorosilane and dimethyldichlorosilane, 
respectively, were produced with yields of 74.8% and 74.5%, respectively, 
based on the octamethyltrisiloxane. 
EXAMPLE 7 
To a mixture consisting of 48.7 g of hexamethyldisiloxane, 30.0 g of 
methyltrichlorosilane and 2.6 g of hexamethylphosphotriamide was added 
0.50 g of methanol, and the resulting mixture was heated at 80.degree. C 
for 4 hours. Here, part of the methyltrichlorosilane was alcoholyzed by 
the added methanol to generate hydrogen chloride, which in turn formed the 
monohydrochloride of the hexamethylphosphotriamide. The reaction mixture 
was then analyzed and it was found that 53.5 g of trimethylchlorosilane 
was produced with 82% yield based on the hexamethyldisiloxane. 
EXAMPLE 8 
To a mixture consisting of 14.8 g of octamethylcyclotetrasiloxane, 37.4 g 
of methyltrichlorosilane and 2.6 g of hexamethylphosphotriamide was added 
0.52 g of water, and the resulting mixture was heated at 80.degree. C for 
4 hours. The reaction mixture was then analyzed and it was found that 19.6 
g of dimethyldichlorosilane was produced with 76% yield based on the 
octamethylcyclotetrasiloxane. 
EXAMPLE 9 
Hydrogen chloride gas was passed through 50 g of hexamethylphosphotriamide 
(HMPA) in a flask, to form a white crystalline precipitate, which was then 
taken out of the reaction mixture by filtration. The amount of thus 
obtained precipitate was 12.5 g. (This precipitate is hereinafter called 
crystalline salt I). 
From the filtrate obtained above, a second white crystalline matter was 
precipitated by addition of n-hexane. The amount of this second 
precipitate separated by filtration was 16.4 g. (This second precipitate 
is called crystalline salt II, and the filtrate obtained by the second 
filtration is called liquid III). Crystalline salts I and II were dried in 
a desiccator under reduced pressure. 
The elementary analyses, including the determination of chlorine, gave the 
results that the crystalline salts I and II and liquid III were, 
respectively, dihydrochloride of HMPA, i.e., HMPA.(HCl).sub. 2 ; 
monohydrochloride of HMPA, i.e., HMPA.HCl; and HMPA diluted with n-hexane. 
Using each of these compounds as the catalyst, i.e., (a) crystalline salt 
I, (b) crystalline salt II, (c) liquid III and (d) mixture of liquid III 
and water, in an amount as indicated in the following table, a 
redistribution reaction was conducted between 93.2 g of 
1,1,3,3-tetramethyl-1, 3-divinyldisiloxane and 64.5 g of 
dimethyldichlorosilane with heating at 100.degree. C for 4 hours. As a 
result, dimethylvinylchlorosilane was obtained with the yields as 
indicated also in the table. 
Table 
______________________________________ 
Catalyst Amount* Yield** 
______________________________________ 
(a) Crystalline salt I 
5.0 % 26 % 
(b) Crystalline salt II 
5.0 % 92 % 
(c) Liquid III ***5.0 % 35 % 
(d) Mixture of: 
Liquid III ***5.0 % 
Water 0.25 % 90 % 
______________________________________ 
*Based on the total amount of 1,1,3,3-tetramethyl-1, 3-divinyldisiloxane 
and dimethyldichlorosilane. 
**Based on 1,1,3,3-tetramethyl-1, 3-divinyldisiloxane. 
***AS non-diluted HMPA.