Method for preparing organomonochlorosilane

An organodisiloxane represented by the general formula: R.sup.1 R.sup.2 R.sup.3 SiOSiR.sup.4 R.sup.5 R.sup.6 is reacted with thionyl chloride in the presence of an ammonium salt represented by the general formula: R.sup.7 R.sup.8 R.sup.9 R.sup.10 NX wherein R.sup.1 to R.sup.5 and R.sup.10 may be the same or different and each represents a monovalent hydrocarbon group or a hydrogen atom; R.sup.7 to R.sup.9 may be the same or different and each represents a monovalent hydrocarbon group; and X represents a monovalent anion. Thus, organomonochlorosilanes represented by R.sup.1 R.sup.2 R.sup.3 SiCl and R.sup.4 R.sup.5 R.sup.6 SiCl can be obtained.

BACKGROUND OF THE INVENTION 
The present invention relates to a novel method for preparing an 
organomonochlorosilane which serves as an intermediate material for the 
preparation of silylating agents or other various kinds of organosilicon 
compounds. 
As methods for preparing organomonochlorosilanes represented by the 
formula: R.sup.1 R.sup.2 R.sup.3 SiCl starting from organodisiloxanes, 
there have conventionally been known, for instance, a method disclosed in 
Japanese Patent Provisional Publication No. 52-65226 in which an 
organodisiloxane is reacted with a dialkyldichlorosilane in the presence 
of hexamethylphosphoric acid triamide as a catalyst. 
This method which makes use of dialkyldichlorosilanes accompanies formation 
of polysiloxanes as by-products. The polysiloxane is quite viscous and 
accordingly, when isolating, by distillation, the organomonochlorosilane 
as the subject product from the reaction solution, it is needed to 
extremely raise the temperature of the reaction vessel for distillation. 
Moreover, a viscous oily product remains in the reaction vessel after the 
distillation. This makes the post-treatment of the reaction vessel quite 
difficult. In addition, hexamethylphosphoric acid triamide used as the 
catalyst is one of carcinogens and, therefore, handling of the starting 
materials and treatment of waste liquor must be carefully carried out. 
SUMMARY OF THE INVENTION 
The object of the present invention is generally to solve the foregoing 
problems associated with the conventional methods for preparing 
organomonochlorosilanes and more specifically to a method for preparing an 
organomonochlorosilane in which the purification of the subject product 
can be performed without extremely raising the temperature of a reaction 
vessel, which makes the handling of reagents, products and waste liquor 
easy and highly safe and which makes the post-treatment of the reaction 
vessel easy. 
The method for preparing organomonochlorosilane according to the present 
invention comprises the step of reacting an organodisiloxane represented 
by the general formula: R.sup.1 R.sup.2 R.sup.3 SiOSiR.sup.4 R.sup.5 
R.sup.6 with thionyl chloride in the presence of an ammonium salt 
represented by the general formula: R.sup.7 R.sup.8 R.sup.9 R.sup.10 NX. 
In the foregoing general formulas, R.sup.1 to R.sup.6 and R.sup.10 may be 
the same or different and each represents a monovalent hydrocarbon group 
or a hydrogen atom; R.sup.7 to R.sup.9 may be the same or different and 
each represents a monovalent hydrocarbon group; and X represents a 
monovalent anion. 
According to the method of the present invention, it is not necessary to 
use hexamethylphosphoric acid triamide. The method does not accompany the 
formation of any viscous oily product as a by-product which results in a 
substantial increase of the temperature for the distillation of the 
reaction solution. The method accompanies the generation of sulfur dioxide 
gas as a by-product, but the by-product is a gaseous substance capable of 
being easily handled. The method does not require the use of other 
dangerous reagents and does not accompany the formation of any dangerous 
product. 
As has been described above, the method does not accompany the formation of 
a viscous oily substance. This permits substantial reduction of the 
distillation temperature during the isolation of highly pure 
organomonochlorosilane from the reaction solution. Moreover, the method 
accompanies the generation of sulfur dioxide as a by-product, but the 
by-product is a gaseous substance. Therefore, the by-product does not 
remain in the reaction vessel at all, can easily be discharged from the 
reaction system and accordingly, the post-treatment of the reactor is very 
easy. As a result, the organomonochlorosilane can be recovered from a 
constant volume of the reaction solution in an amount greater than those 
obtained according to the conventional methods (an improvement of the pot 
yield). The method can easily be handled and has high safety since the 
method does not require the use of dangerous reagents and does not 
accompany the formation of dangerous products and/or by-products.

DETAILED EXPLANATION OF THE INVENTION 
If the substituents R.sup.1 to R.sup.6 bonded to the silicon atoms of the 
organodisiloxane which undergoes a reaction with thionyl chloride are 
monovalent hydrocarbon groups, they may be saturated or unsaturated 
groups. They may be noncyclic hydrocarbon groups or cyclic hydrocarbon 
groups. These monovalent hydrocarbon groups may be unsubstituted or 
substituted with substituents such as halogen atoms and/or cyano group. 
Specific examples of such organodisiloxanes are 
pentamethyl-t-butyl-disiloxane: [(CH.sub.3).sub.3 C](CH.sub.3).sub.2 
SiOSi(CH.sub.3).sub.3, 1,3-dimethyl-1,1,3,3-tetraphenyl-disiloxane: 
(C.sub.6 H.sub.5).sub.2 (CH.sub.3)SiOSi(CH.sub.3)(C.sub.6 H.sub.5).sub.2, 
1,1,3,3-tetramethyl-disiloxane: (CH.sub.3).sub.2 HSiOSiH(CH.sub.3).sub.2, 
1,3-di-(cyanoethyl)-1,1,3,3-tetramethyl-disiloxane: [(CN)C.sub.2 H.sub.4 
](CH.sub.3).sub.2 SiOSi(CH.sub.3).sub.2 [C.sub.2 H.sub.4 (CN)], 
1,1,3,3-tetramethyl-1,3-diisopropyl-disiloxane: [(CH.sub.3).sub.2 
CH](CH.sub.3).sub.2 SiOSi(CH.sub.3).sub.2 [CH(CH.sub.3).sub.2 ], 
1,3-dicyclohexyl-1,1,3,3-tetramethyl-disiloxane: (C.sub.6 
H.sub.11)(CH.sub.3).sub.2 SiOSi(CH.sub.3).sub.2 (C.sub.6 H.sub.11), 
hexamethyl-disiloxane: (CH.sub.3).sub.3 SiOSi(CH.sub.3).sub.3, 
1,3-divinyl-1,1,3,3-tetramethyl-disiloxane: (CH.sub.2 CH)(CH.sub.3).sub.2 
SiOSi(CH.sub.3).sub.2 (CHCH.sub.2) and 
1,3-diallyl-1,1,3,3-tetramethyl-disiloxane: (CH.sub.2 
CHCH.sub.2)(CH.sub.3).sub.2 SiOSi(CH.sub.3).sub.2 (CH.sub.2 CHCH.sub.2). 
These compounds may be used alone or in any combination. Among these 
compounds, particularly preferred are, for instance, 
pentamethyl-t-butyl-disiloxane, hexamethyl-disiloxane and 
1,3-divinyl-1,1,3,3-tetramethyl-disiloxane. 
The substituents R.sup.7 to R.sup.10 of the ammonium salt represented by 
Formula: R.sup.7 R.sup.8 R.sup.9 R.sup.10 NX used as the catalyst for the 
reaction may be the same monovalent hydrocarbon group defined above in 
connection with the substituents R.sup.1 to R.sup.6, provided that 
R.sup.10 may be a hydrogen atom. The substituent X in the ammonium salt 
represents a monovalent anion such as a chloride ion, a bromide ion, a 
sulfate ion or a perchlorate ion. Specific examples of such ammonium salts 
include tertiary ammonium salts such as trimethylamine hydrochloride: 
(CH.sub.3).sub.3 NHCl, triethylamine hydrochloride: (C.sub.2 
H.sub.5).sub.3 NHCl, tributylamine hydrochloride: [CH.sub.3 
(CH.sub.2).sub.3 ].sub.3 NHCl, N,N-dimethyl-phenylamine hydrobromide: 
(C.sub.6 H.sub.5)(CH.sub.3).sub.2 NHBr, N,N-diethyl-phenylamine 
hydrobromide: (C.sub.6 H.sub.5)(C.sub.2 H.sub.5)NHBr and 
N-ethyl-diphenylamine hydrobromide: (C.sub.6 H.sub.5).sub.2 (C.sub.2 
H.sub.5)NHBr; and quaternary ammonium salts such as tetrabutylammonium 
chloride: [CH.sub.3 (CH.sub.2).sub.3 ].sub.4 NCl, tetrabutylammonium 
bromide: [CH.sub.3 (CH.sub.2).sub.3 ].sub.4 NBr and tetramethylammonium 
sulfate: [(CH.sub.3).sub.4 N].sub.2 SO.sub.4. These ammonium salts may be 
used alone or in any combination. 
The intended organomonochlorosilane can be obtained by reacting the 
foregoing organodisiloxane with thionyl chloride in the presence of the 
ammonium salt. The reaction scheme will be given below: 
##STR1## 
Specific examples of the organomonochlorosilane obtained by the foregoing 
reaction are t-butyl-dimethyl-chlorosilane: [(CH.sub.3).sub.3 
C](CH.sub.3).sub.2 SiCl, trimethyl-chlorosilane: (CH.sub.3).sub.3 SiCl, 
vinyl-dimethyl-chlorosilane: (CH.sub.2 CH)(CH.sub.3).sub.2 SiCl, 
allyl-dimethyl-chlorosilane: (CH.sub.2 CHCH.sub.2)(CH.sub.3).sub.2 SiCl, 
ethynyl-dimethyl-chlorosilane: (HCC)(CH.sub.3).sub.2 SiCl, 
(cyanoethyl)-dimethyl-chlorosilane: [(CN)C.sub.2 H.sub.4 ](CH.sub.3).sub.2 
SiCl, methyl-diphenyl-chlorosilane: (C.sub.6 H.sub.5).sub.2 (CH.sub.3)SiCl 
and diisopropyl-chlorosilane: [(CH.sub.3).sub.2 CH].sub.2 HSiCl. 
The reaction of the organodisiloxane with thionyl chloride is preferably 
carried out, for instance, in the following manner. An organodisiloxane 
and an ammonium salt as a catalyst are introduced into a reaction vessel 
and then thionyl chloride is dropwise added to the mixture with stirring. 
The amount of the ammonium salt to be charged in general ranges from 0.1 
to 10 moles and preferably 2 to 7 moles per 100 moles of the 
organodisiloxane. The reaction temperature ranges from 0.degree. to 
200.degree. C. and preferably 10.degree. to 90.degree. C. It is preferred 
that water be dropwise added to the reaction vessel along with thionyl 
chloride. An acid may be added to the reactor in combination with or in 
place of water. In any case, the reaction rate can be improved. 
If water or an acid is introduced into the reaction vessel, a tertiary 
amine such as tributylamine can, in fact, be substituted for the ammonium 
salt. More specifically, if an acid is introduced into the reactor, the 
acid forms a tertiary ammonium salt through the reaction with a tertiary 
amine in the reactor and the resulting tertiary ammonium salt serves as a 
catalyst. On the other hand, if water is introduced into the reactor, it 
forms an acid through the reaction with thionyl chloride and the resulting 
acid undergoes a reaction with a tertiary amine in the reactor. 
The organomonochlorosilane of high purity can be obtained by distilling the 
crude product prepared according to the foregoing method. Thus, according 
to the method of the present invention, organomonochlorosilanes of high 
purity can be obtained in a high yield by reacting organodisiloxanes with 
thionyl chloride. Sulfur dioxide is simultaneously formed during the 
reaction as a by-product. It is externally discharged from the reaction 
vessel and can be recovered using a scrubber (washing collector) which 
makes use of an alkali aqueous solution such as an aqueous sodium 
hydroxide solution. 
The present invention will hereinafter be explained with reference to the 
following Examples, but the present invention is by no means limited to 
these specific Examples. 
EXAMPLE 1 
To a 200 ml volume reaction vessel equipped with a stirring machine, a 
reflux condenser, a dropping funnel and an inlet pipe for hydrogen 
chloride gas, there were added 51.1 g (0.25 mole) of 
pentamethyl-t-butyl-disiloxane and 4.16 g (0.015 mole) of 
tetrabutylammonium chloride and 41.6 g (0.35 mole) of thionyl chloride was 
charged in the dropping funnel. 
The reaction system was stirred at room temperature while dropwise adding 
thionyl chloride through the dropping funnel. In this manner, 
pentamethyl-t-butyl-disiloxane was reacted with thionyl chloride while 
dropwise adding the latter and supplying hydrogen chloride gas to the 
reaction solution. After stirring the reaction solution over 4 hours, it 
was distilled at 125.degree. C. to give 31.3 g (yield 83.2%) of 
t-butyldimethylchlorosilane and 21.4 g (yield 79.0%) of 
trimethylchlorosilane. There was not observed the formation of any viscous 
oily substance, the distillation temperature during the purification could 
substantially be decreased and the post-treatment of the reaction vessel 
was very easy. 
EXAMPLE 2 
To a 1.0 l volume reaction vessel equipped with a stirring machine, a 
reflux condenser, a dropping funnel and an inlet pipe for hydrogen 
chloride gas, there were added 204 g (1.0 mole) of 
pentamethyl-t-butyl-disiloxane and 9.25 g (0.050 mole) of tributylamine 
and 143 g (1.2 mole) of thionyl chloride was introduced into the dropping 
funnel. Pentamethyl-t-butyl-disiloxane was reacted with thionyl chloride 
at room temperature by dropwise adding thionyl chloride through the 
dropping funnel while supplying hydrogen chloride gas to the reaction 
solution. After stirring over 4 hours, the reaction solution was distilled 
at 125.degree. C. to give 130 g (yield 86.4%) of 
t-butyldimethylchlorosilane and 87.0 g (yield 80.2%) of 
trimethylchlorosilane. There was not observed the formation of any viscous 
oily substance, the distillation temperature during the purification could 
substantially be decreased and the post-treatment of the reaction vessel 
was very easy. 
EXAMPLE 3 
The same procedures used in Example 2 were repeated except that a 500 ml 
volume reaction vessel was substituted for the 1.0 l volume reaction 
vessel, that 186 g of 1,3-divinyl-1,1,3,3-tetramethyl-disiloxane was 
substituted for 204 g of the pentamethyl-t-butyl-disiloxane and that the 
distillation temperature was set at 85.degree. C. to give 198 g (yield 
82.0%) of dimethylvinylchlorosilane. There was not observed the formation 
of any viscous oily substance, the distillation temperature during the 
purification could substantially be decreased and the post-treatment of 
the reaction vessel was very easy.