Method for the preparation of an oximesilane compound

An efficient and safe method is proposed for the preparation of an oximesilane compound having a group of the general formula --O--N.dbd.CR.sup.2 R.sup.3, in which R.sup.2 and R.sup.3 are each a hydrogen atom or a monovalent hydrocarbon group, bonded to the silicon atom. The method consists of successive steps of which the first is for the reaction of a chlorosilane compound with ammonia and the second is for the reaction of the reaction mixture coming from the first step with an oxime compound to introduce the oxime groups as bonded to the silicon atom. Different from conventional methods in which formation of an explosive compound such as hydrochloride of an organic base or oxime compound is unavoidable, the inventive method does not involve formation of such an explosive by-product so that the desired oximesilane compound can be obtained without the danger of explosion.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for the preparation of an 
oximesilane compound. More particularly, the invention relates to an 
efficient method for the preparation of an oximesilane compound without 
the risk of forming an oxime hydrochloride having explosiveness and 
unavoidably formed in the prior art methods. 
An oximesilane compound, such as methyl tris(methyl ethyl ketoxime) silane 
of the formula MeSi(--O--N.dbd.CMeEt).sub.3 and vinyl tris(methyl ethyl 
ketoxime) silane of the formula ViSi(--O--N.dbd.CMeEt).sub.3, in which Me 
is a methyl group, Et is an ethyl group and Vi is a vinyl group, is a 
useful organosilicon compound to serve, for example, as a crosslinking 
agent in certain types of room temperature-curable organopolysiloxane 
rubber compositions. These oximesilane compounds are prepared in the prior 
art by the method disclosed, for example, in Japanese Patent Publication 
39-29837, according to which a chlorosilane compound such as methyl 
trichlorosilane MeSiCl.sub.3 is subjected to a dehydrochlorination 
reaction with an at least stoichiometrically equivalent amount of an oxime 
compound such as methyl ethyl ketoxime of the formula MeEtC.dbd.N--OH in 
the presence of an excess amount of an organic base such as pyridine as an 
acceptor of the hydrogen chloride produced by the dehydrochlorination 
reaction. A problem in this method is that, while it is necessary to 
isolate the desired oximesilane compound from the hydrochloride of the 
organic base, e.g., pyridine hydrochloride, by distillation, 
hydrochlorides of an organic base are sometimes explosive to cause serious 
explosion during the distillation procedure. 
It is also proposed in Japanese Patent Publication 1-21834 that the 
dehydrochlorination of a chlorosilane compound for the preparation of an 
oximesilane compound is performed in the presence of an oxime compound in 
an amount twice as large as the stoichiometrically equivalent amount and 
the excess of the oxime compound serves as an acceptor of the hydrogen 
chloride so that addition of a separate organic base compound is not 
required. This method is also not free from the danger of explosion during 
processing of the reaction mixture since hydrochlorides of an oxime 
compound are generally explosive. In addition, oxime compounds are 
generally expensive so that the hydrochloride thereof cannot be discarded 
as such necessitating facilities for the recovery and recycling of the 
oxime compound from the hydrochloride thereof. 
It is further proposed in Japanese Patent Kokai 63-227592 that the 
dehydrochlorination of a chlorosilane compound and an oxime compound is 
performed while ammonia gas is blown into the reaction mixture to serve as 
an acceptor of the hydrogen chloride so that an oximesilane compound can 
be prepared in a continuous process. A problem in this method is that the 
reaction must be performed under control of the temperature of the 
reaction mixture by using a non-inflammable halogenated hydrocarbon 
solvent such as perchloro fluorinated alkanes, trichlorotrifluoroethanes 
and the like, most of which are industrially banned due to the problem in 
the environmental pollution. 
SUMMARY OF THE INVENTION 
The present invention accordingly has an object to provide a novel and 
efficient method for the preparation of an oximesilane compound from a 
halogenosilane compound as the starting material without the above 
described disadvantages in the prior art methods, in particular, relative 
to the danger of explosion. 
Thus, the method of the present invention for the preparation of an 
oximesilane compound represented by the general formula 
EQU R.sup.1.sub.4-n Si(--O--N.dbd.CR.sup.2 R.sup.3).sub.n, (I) 
in which R.sup.1 is an unsubstituted or substituted monovalent hydrocarbon 
group, R.sup.2 and R.sup.3 are each, independently from the other, a 
hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon 
group and the subscript n is 1, 2, 3 or 4, comprises the steps of: 
(a) introducing continuously a halogenosilane compound represented by the 
general formula 
EQU R.sup.1.sub.4-n SiX.sub.n, (II) 
in which R.sup.1 and n each have the same meaning as defined above and X is 
an atom of halogen, into a first reaction zone together with ammonia in a 
molar proportion of ammonia in the range from 1.55n to 2.1n moles per mole 
of the halogenosilane compound, precipitates of an ammonium halide being 
formed in the reaction mixture; 
(b) introducing the reaction mixture containing the precipitates of the 
ammonium halide continuously withdrawn from the first reaction zone into a 
second reaction zone together with an oxime compound represented by the 
general formula 
EQU R.sup.2 R.sup.3 C.dbd.N--OH, (III) 
in which R.sup.2 and R.sup.3 each have the same meaning as defined above, 
in a molar proportion of the oxime compound in the range from 1.0n to 1.1n 
moles per mole of the halogenosilane compound introduced into the first 
reaction zone to form an oximesilane compound by the reaction 
therebetween; 
(c) continuously withdrawing the reaction mixture containing the 
precipitates of the ammonium halide from the second reaction zone; and 
(d) removing the precipitates of the ammonium halide from the reaction 
mixture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As is described above, the inventive method comprises the four steps, of 
which the first step, i.e. step (a), is for the reaction of a starting 
halogenosilane compound of the general formula (II) with ammonia in a 
first reaction zone and the second step, i.e. step (b), is for the 
reaction of the reaction mixture withdrawn from the first reaction zone 
with an oxime compound of the general formula (III) to form the desired 
oximesilane compound represented by the above given general formula (I). 
The steps (c) and (d) are for the isolation of the oximesilane compound 
from the reaction mixture in the second reaction zone. 
The starting material used in the inventive method is a halogenosilane 
compound represented by the above given general formula (II). In the 
formula, R.sup.1 is an unsubstituted or substituted monovalent hydrocarbon 
group exemplified by alkyl groups such as methyl, ethyl, propyl and butyl 
groups, cycloalkyl groups such as cyclohexyl group, alkenyl groups such as 
vinyl, allyl and butenyl groups and aryl groups such as phenyl and tolyl 
groups as well as those substituted groups obtained by replacing a part or 
all of the hydrogen atoms in the above named hydrocarbon groups with 
halogen atoms such as chloromethyl and 3,3,3-trifluoropropyl groups. The 
symbol X denotes an atom of halogen which is preferably chlorine or 
fluorine or, more preferably, chlorine. The subscript n is 1, 2, 3 or 4. 
Particular examples of the halogenosilane compounds to which the inventive 
method is applicable include tetrachlorosilane, trimethyl chlorosilane, 
dimethyl dichlorosilane, methyl trichlorosilane, methyl ethyl 
dichlorosilane, ethyl trichlorosilane, diethyl dichlorosilane, triethyl 
chlorosilane, n-propyl trichlorosilane, isopropyl trichlorosilane, 
2-chloroethyl trichlorosilane, 3-chloropropyl trichlorosilane, triethyl 
chlorosilane, vinyl trichlorosilane, vinyl mehyl dichlorosilane, 
isopropenyl trichlorosilane, allyl trichlorosilane, phenyl 
trichlorosilane, benzyl trichlorosilane and the like, of which those in 
which the group R.sup.1 is a methyl or vinyl group and the subscript n is 
3 are most frequently used in the inventive method in view of the 
usefulness of the oximesilane compounds derived therefrom. 
The nature of the reaction taking place between the above defined 
halogenosilane compound and ammonia gas in step (a) of the inventive 
method is not well analyzed but it is presumable that the silicon-bonded 
halogen atoms are replaced with amino groups of the formula --NH.sub.2 or 
a silazane linkage .tbd.Si--NH--Si.tbd. is formed between the silicon 
atoms with formation of an ammonium halide as the by-product. 
In carrying out the step (a), the halogenosilane compound and ammonia are 
continuously introduced into a first reaction zone. It is preferable that 
an organic solvent is also introduced into the first reaction zone 
separately or together with the halogenosilane compound with an object to 
ensure smooth proceeding of the reaction and decrease the consistency of 
the reaction mixture after the reaction in the first reaction zone which 
is in the form of a slurry containing the precipitates of the ammonium 
halide. Suitable organic solvents include toluene, hexane, petroleum ether 
and the like though not particularly limitative thereto. The rate of 
introduction of the ammonia into the first reaction zone should be such 
that from 1.55 n to 2.1 n moles or, preferably, from 1.60 n to 1.95 n 
moles of ammonia are introduced per mole of the halogenosilane compound. 
The rate of introduction of the organic solvent, when used, is preferably 
in the range from 1 to 20 times by weight relative to the halogenosilane 
compound. 
Though not critical, the above described reaction of the halogenosilane 
compound and ammonia is performed at room temperature or at a temperature 
in the range from 0.degree. to 100.degree. C. or, preferably, in the range 
from 25.degree. to 70.degree. C. but not to cause boiling of the reaction 
mixture. Needless to say, the reaction velocity can be increased as the 
temperature is increased although the reaction product would eventually be 
colored when the temperature is too high. Since the reaction proceeds 
exothermically, the reaction is performed in a reaction vessel equipped 
with a stirrer and provided with a cooling means such as a jacket for 
cooling water. It is preferable to use a vertical reactor and the 
halogenosilane compound, ammonia and organic solvent are introduced into 
the reactor at the bottom thereof and the reaction mixture is discharged 
from the top of the reactor. The staying time of the reaction mixture in 
the first reaction zone in such a vertical reactor is in the range from 
0.5 to 10 minutes or, preferably, from 1 to 5 minutes. 
The reaction mixture discharged out of the first reaction zone in the above 
described manner is then introduced in step (b) of the inventive method 
into a second reaction zone where it is reacted with an oxime silane 
compound concurrently introduced thereinto. The oxime compound is 
represented by the general formula (III) given before, in which R.sup.2 
and R.sup.3 are each, independently from the other, a hydrogen atom or an 
unsubstituted or substituted monovalent hydrocarbon group depending on the 
kind of the desired oximesilane compound as the final product. The 
monovalent hydrocarbon groups denoted by R.sup.2 and R.sup.3 can be 
methyl, ethyl, propyl, butyl, pentyl, hexyl, vinyl, butenyl, cyclopentyl, 
cyclohexyl, cyclooctyl, 3-methyl-1-hexenyl, cyclopentenyl, phenyl and 
tolyl groups though not particularly limitative thereto. 
Particular examples of the oxime compounds to which the inventive method is 
applicable include, though not particularly limitative, formaldoxime, 
acetaldoxime, acetone oxime, methyl ethyl ketoxime, diethyl ketoxime, 
cyclohexanoxime, 4-methylcyclohexanoxime, 4-chlorocyclohexanoxime, 
acetophenoxime, benzophenoxime, benzyl ethyl ketoxime, methyl cyclohexyl 
ketoxime, benzaldoxime and the like, of which formaldoxime, acetaldoxime, 
acetone oxime, methyl ethyl ketoxime, diethyl ketoxime and cyclohexanoxime 
are important and methyl ethyl ketoxime and acetone oxime are more 
important in respect of the usefulness of the oximesilane compounds 
derived therefrom. 
The rate of introduction of the oxime compound into the second reaction 
zone is preferably in the range from 1.0 n to 1.1 n moles or, more 
preferably, from 1.01 n to 1.06 n moles per mole of the halogenosilane 
compound introduced into the first reaction zone in step (a) since the 
reaction proceeds almost quantitatively. The second reaction zone is kept 
at a temperature in the range from 0.degree. to 100.degree. C. or, 
preferably, from 25.degree. to 75.degree. C. The reaction vessel in which 
the second reaction zone is formed is not required to be provided with a 
cooling means such as a jacket for cooling water since the reaction 
proceeding in this second reaction zone is not so highly exothermic as in 
the reaction of the step (a). The staying time of the reaction mixture in 
the second reaction zone is in the range from 5 to 60 minutes or, 
preferably, from 10 to 40 minutes although it is important to select the 
exact staying time in consideration of various factors such as the kinds 
of the reactants, kind and amount of the organic solvent, reaction 
temperature and so on. 
The reaction taking place in the second reaction zone between the reaction 
mixture coming from the first reaction zone and the oxime compound, which 
is introduced into the reaction vessel preferably through an in-liquid 
dropping tube, in step (b) of the inventive method is a replacement 
reaction of the Si--NH.sub.2 linkage with the Si--(--O--N.dbd.CR.sup.2 
R.sup.3) linkage producing ammonia as a by-product of the reaction. The 
ammonia thus produced would react with any trace amount of the unreacted 
halogenosilane compound remaining in the reaction mixture coming from the 
first reaction zone so as to prevent formation of an oxime salt of a 
halogen-containing acid along with the effect of preventing coloration of 
the desired oximesilane compound by the halogenosilane compound. It is a 
preferable process that the ammonia produced in the second reaction zone 
is introduced into and absorbed by the organic solvent to be introduced 
into the first reaction zone. 
The oximesilane compound as the desired product is isolated from the 
reaction mixture after step (b) in a conventional procedure. Namely, the 
reaction mixture containing the precipitates of ammonium halide and 
continuously discharged out of the second reaction zone is first filtered 
to remove the precipitates and the filtrate is subjected to distillation 
to recover the organic solvent and the unreacted oximesilane compound, if 
any. It is important that the temperature of the reaction mixture in the 
distillation does not exceed 90.degree. C. because the product oximesilane 
compound is sometimes colored when the temperature of the distillation is 
too high. In this regard, the distillation is performed preferably under 
reduced pressure. 
Following is a brief description of the inventive method making reference 
to the accompanying drawing. The figure in the accompanying drawing 
illustrates a schematic block diagram of the typical apparatus system to 
perform the inventive method in a semi-continuous process. In this 
reaction system, the starting halogenosilane compound and the organic 
solvent are continuously introduced into the vertical reactor column 1, 
which is equipped with a stirrer and provided with a jacket for cooling 
water, at the bottom thereof through the lines 2 and 3, respectively, 
while ammonia gas is introduced also continuously into the reactor column 
1 at the bottom through the line 4 simultaneously as the silane compound 
and solvent. The reaction between the halogenosilane and ammonia proceeds 
while the reaction mixture ascends from the bottom to the top of the 
vertical reactor column 1 with a staying time of 1 to 5 minutes. The space 
inside the reactor column 1 above the liquid phase is filled with a dry 
inert gas to ensure an anhydrous condition. 
The reaction mixture containing the precipitates of ammonium halide after 
the reaction in the vertical reactor column 1 is discharged out of the 
reactor column 1 through the line 6 and introduced into the reaction 
vessel 5 for the second reaction zone to effect the reaction with an oxime 
compound. The oxime compound to be reacted with the reaction mixture 
coming from the reactor column 1 is introduced into the reaction vessel 5 
through the line 7 concurrently with introduction of the reaction mixture 
thereinto. As is mentioned before, ammonia is produced as a by-product in 
the reaction taking place in this reaction vessel 5 and discharged out of 
the line 8. The ammonia gas can be recycled to the first reaction zone. 
After completion of the reaction in the second reaction zone, the reaction 
mixture containing the precipitates of ammonium halide in the reaction 
vessel 5 is discharged through the line 10 and introduced into the slurry 
reservoir 9 from which it is transferred through the duct 12 to the 
filtering machine 11 where it is filtered and, if necessary, the cake is 
washed with an organic solvent coming through the line 13. The cake of the 
ammonium halide is discharged from the filtering machine 11 through the 
line 14 while the filtrate is introduced through the line 16 into the 
reservoir 15. The filtrate in the reservoir 15 is sent through the line 17 
to the stripping column 18 where the filtrate is stripped under reduced 
pressure to be freed from the organic solvent and other volatile matters 
contained therein as the distillate discharged from the line 20 while the 
oximesilane compound as the desired product is obtained from the line 19. 
In the following, the method of the present invention is described in more 
detail by way of examples. 
EXAMPLE 1 
Into a reactor column having an inner diameter of 80 mm and a height of 110 
mm equipped with a Teflon-made stirrer and provided with a jacket for 
cooling water were continuously introduced vinyl trichlorosilane and 
toluene at the bottom of the column at rates of 934 g/hour and 5887 
g/hour, respectively, with concurrent introduction of ammonia gas at a 
constant rate of 700 liters (N.T.P.)/hour. The rate of introduction of 
ammonia gas corresponded to 5.4 moles per mole of the silane compound. The 
reaction mixture in the reactor column was kept at a temperature of 
60.degree. to 75.degree. C. The staying time of the reaction mixture in 
the reactor column was 4 minutes. 
The reaction mixture discharged from the reactor column at the top thereof 
was introduced into a Teflon-made reaction vessel of 10 liters capacity 
along with concurrent introduction of methyl ethyl ketoxime at a rate of 
1555 g/hour corresponding to a rate of 3.09 moles per mole of the silane 
compound introduced into the reactor column. The staying time of the 
reaction mixture, which was kept at a temperature of 60.degree. to 
65.degree. C., in the reaction vessel was 40 minutes. 
The reaction mixture discharged out of the reaction vessel was introduced 
into a slurry reservoir and collected over 5 hours of the reaction 
continued in the above described manner. The reaction mixture was 
transferred into a pressurizable filtering machine and freed from the 
precipitates of ammonium chloride. The filtrate was subjected to stripping 
of volatile matters at 75.degree. to 80.degree. C. under a pressure of 30 
mmHg or below. The residual liquid in the stripper still was gas 
chromatographically analyzed to find that the principal constituent 
thereof was vinyl tris(methyl ethyl ketoxime) silane and the purity 
thereof was 95.1%. The yield of this product was 93% of the theoretical 
value taking the amount of the vinyl trichlorosilane as the base. 
EXAMPLE 2 
The experimental procedure was substantially the same as in Example 1 
excepting modification of the rates of introduction of the reactants and 
solvent into the respective reactors which were the same as used in 
Example 1. Namely, vinyl trichlorosilane, toluene and ammonia gas were 
introduced into the reactor column at rates of 1870 g/hour, 9350 g/hour 
and 1268 liters (N.T.P.)/hour, respectively, while methyl ethyl ketoxime 
was introduced into the reaction vessel at a rate of 3173 g/hour. The 
rates of introduction of the ammonia gas and the oxime compound 
corresponded to 4.89 moles and 3.15 moles, respectively, per mole of the 
silane compound. The staying times of the reaction mixture in the first 
and the second reaction zones were 2.4 minutes and 20 minutes, 
respectively. The yield of vinyl tris(methyl ethyl ketoxime) silane as the 
product was 91% of the theoretical value taking the amount of the vinyl 
trichlorosilane as the base. 
EXAMPLE 3 
The experimental procedure was substantially the same as in Example 1 
excepting replacement of vinyl trichlorosilane as the starting reactant 
with methyl trichlorosilane and modification of the rates of introduction 
of the reactants and solvent into the respective reactors which were the 
same as used in Example 1. Namely, methyl trichlorosilane, toluene and 
ammonia gas were introduced into the reactor column at rates of 1313 
g/hour, 6171 g/hour and 1091 liters (N.T.P.)/hour, respectively, while 
methyl ethyl ketoxime was introduced into the reaction vessel at a rate of 
2337 g/hour. The rates of introduction of the ammonia gas and the oxime 
compound corresponded to 5.55 moles and 3.06 moles, respectively, per mole 
of the silane compound. The staying times of the reaction mixture in the 
first and the second reaction zones were 3.6 minutes and 34 minutes, 
respectively. The yield of methyl tris(methyl ethyl ketoxime) silane as 
the product was 94% of the theoretical value taking the amount of the 
methyl trichlorosilane as the base.