Process for preparation of organodisilanes

A one-step process for the preparation of organodisilanes. The process comprises contacting magnesium metal with a mixture comprising diethylene glycol dibutyl ether, an organic halide, and a halodisilane at a temperature within a range of about 0.degree. C. to 250.degree. C. The process provides a high yield of organodisilane product that is easily recoverable. The present process is especially useful for converting halodisilanes in a high-boiling mixture resulting from the direct process for making organosilane monomers into hexaorganodisilanes.

BACKGROUND OF INVENTION 
The present invention is a one-step process for the preparation of 
organodisilanes. The process comprises contacting magnesium metal with a 
mixture comprising diethylene glycol dibutyl ether, an organic halide, and 
a halodisilane at a temperature within a range of about 0.degree. C. to 
250.degree. C. The process provides a high yield of organodisilane product 
that is easily recoverable. The present process is especially useful for 
converting halodisilanes in a high-boiling mixture resulting from the 
direct process for making organosilane monomers into hexaorganodisilanes. 
The reaction of organic halides with magnesium metal in the presence of 
solvents such as dialkyl ethers to form reactive complexes typically 
referred to as Grignard reagents is well known. The production and 
reactions of Grignard reagents has been the subject of books and numerous 
review articles. Such reviews are provided, for example, in Coates et al., 
ORGANOMETALLIC COMPOUNDS, Vol. 1, p. 76-103 (1967), Methuen and Co. LTD, 
London, U.K.; and in Kirk and Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, 
Vol. 10, 721-734 (1966), The Interscience Encyclopedia, Inc., N.Y., N.Y. 
The structure of the Grignard reagent has not been determined with 
certainty. However, it is generally believed that the Grignard reagent 
exists as a complex in solution and solvent can play a critical role in 
such complex formation. The unpredictable effect of solvent on the 
formation and reactivity of Grignard reagents is discussed in the above 
cited review articles. 
The reaction of Grignard reagents with halosilanes is also well known and 
many such reactions are described in Kharash et al., Grignard Reactions of 
Nonmetallic Substances, Prentice-Hall, Inc. N.Y., 1954, P. 1306-1331. 
Turk et al., Organic Synthesis, Vol. 27, 7-8, 1947, teach a process for 
preparing 1,5 hexadiene by the reaction of allyl chloride in anhydrous 
ether with magnesium turnings. Turk et al. teach that this reaction 
results in the formation of a thick slurry which becomes unstirrable. This 
unstirrable slurry is then treated with a hydrochloric acid solution until 
the magnesium chloride by-product is in solution and the slurry becomes 
sufficiently fluid to be stirred. 
Processes such as taught by Turk et al. are not generally acceptable as 
commercial processes. The formation of the non-stirrable slurry during 
conduct of the reaction can cause reduced mass transfer and heat transfer 
and therefore reduced yield of product. Furthermore, the nature of the 
slurry makes it necessary to treat the slurry in an additional step with a 
reagent to solubilize the slurry to allow isolation of the product. 
Typically, a major portion of the product is trapped within the 
non-stirrable slurry. In addition, the non-flowable nature of the slurry 
does not allow for the reaction to be run as a continuous process. 
Semenov et al., Russian Chem. Bulletin 44:927-930, 1995, report the 
reaction of Grignard reagents with polychloro-substituted disilanes in 
tetrahydrofuran (THF) or a THF-heptane mixture. 
Turnbull et al., U.S. Pat. No. 5,358,670, report the formation of alkyl 
Grignard reagents in diethylene glycol dibutyl ether (DEGDBE). Turnbull et 
al. reported that Grignard reagents prepared in the presence of DEGDBE 
have improved yield and stability. 
It is an objective of the present invention to provide a one-step process 
for preparing organodisilanes using a Grignard-type reagent as an 
intermediate, where the process avoids many of the above discussed 
problems with Grignard type processes by creating a reaction mixture that 
is flowable and easily stirred. Thus, mass transfer and heat transfer can 
be improved in the reaction mixture providing for improved yield of 
organodisilane. In addition, the process provides for a two-phase system 
from which the organodisilane can be easily separated. The present process 
is especially useful for converting halodisilanes in a high-boiling 
mixture resulting from the direct process for making organosilane monomers 
into hexaorganodisilanes. The resulting hexaorganodisilanes can be further 
treated to form commercially desirable monomers such as 
allyltrimethylsilane. 
SUMMARY OF INVENTION 
The present invention is a one-step process for the preparation of 
organodisilanes. The process comprises contacting magnesium metal with a 
mixture comprising diethylene glycol dibutyl ether, an organic halide, and 
a halodisilane at a temperature within a range of about 0.degree. C. to 
250.degree. C. The process provides a high yield of organodisilane product 
that is easily recoverable. The present process is especially useful for 
converting halodisilanes in a high-boiling mixture resulting from the 
direct process for making organosilane monomers into hexaorganodisilanes. 
DESCRIPTION OF INVENTION 
The present invention is a one-step process for the preparation of 
organodisilanes. The process comprises contacting magnesium metal with a 
mixture comprising diethylene glycol dibutyl ether, an organic halide 
described by formula 
EQU R.sup.1 X, 
and a halodisilane described by formula 
EQU R.sup.2.sub.a Si.sub.2 X.sub.6-a 
at a temperature within a range of about 0.degree. C. to 250.degree. C.; 
where R.sup.1 is a monovalent hydrocarbon radical comprising about one to 
20 carbon atoms, each R.sup.2 is an independently selected monovalent 
hydrocarbon radical comprising about one to 20 carbon atoms, X is a 
halogen atom selected from a group consisting of bromine and chlorine, and 
a=0 to 5. 
In the present process, by the term "one-step" it is meant that it is not 
necessary to isolate an intermediate Grignard type reagent in the process 
and further react this Grignard type reagent with the halodisilane to form 
the organodisilane. Furthermore, it is not necessary to conduct a separate 
solubilization step on the resulting product mixture to facilitate 
recovery of the organodisilane. 
The process comprises reacting magnesium metal with an organic halid in the 
presence of a halodisilane and diethylene glycol dibutyl ether (DEGDBE). 
The method of preparing the magnesium metal and the physical form of the 
magnesium metal can be any of those known in the art. The magnesium metal 
can be, for example, in the form of powder, chips, or shavings. A 
preferred form of magnesium metal is in the form of shavings. 
Contact of the magnesium metal with the organic halide can be effected in 
standard reactors suitable for running Grignard type reactions. The 
reactor can be of a batch type, semi-batch type, or continuous-type. A 
preferred reactor is a continuous-type reactor. The environment in which 
the present process is run should be inert. Therefore, in a preferred 
process the reactor is purged and blanketed with an inert gas such as, for 
example, nitrogen or argon. 
The mole ratio of magnesium to organic halide fed to the reactor is not 
critical and can be varied within wide limits. In a batch process it is 
preferred that the mole ratio of magnesium to organic halide provide 
organic halide in sufficient excess to ensure essentially total conversion 
of the magnesium to magnesium salts. When the present process is conducted 
as a continuous process, the magnesium metal is typically present in 
excess in relation to the organic halide fed to the reactor. In such a 
case, the rate of feed of organic halide and halodisilane to the reactor 
can be controlled to assure acceptable levels of conversion of the organic 
halide to the organodisilane and minimal presence of unreacted organo 
magnesium halide complexes. The halodisilane feed may be split, with a 
portion being added after the magnesium bed to insure complete reaction of 
the organo magnesium halide complex. Excess organic halide and 
halodisilane added to the reactor can be recovered and recycled to the 
process. 
Organic halides useful in the present method are described by formula 
R.sup.1 X, where R.sup.1 is a monovalent hydrocarbon radical comprising 
about one to 20 carbon atoms and X is a halogen selected from a group 
consisting of bromine and chlorine. R.sup.1 can be, for example, an alkyl 
such as methyl, ethyl, propyl, tert-butyl, and eicosyl; a cycloalkyl such 
as cyclopentyl and cyclohexyl; an alkenyl such as vinyl, allyl, and 
hexenyl; a cycloalkenyl such as pentenyl and hexenyl; an aryl such as 
phenyl, tolyl, and naphthyl; and an aralkyl such as benzyl, 
beta-phenylethyl, and gamma-tolylpropyl. Preferred is when R.sup.1 is 
methyl. Preferred is when the halogen substituent of the organic halide is 
chlorine. The preferred organic halide is methyl chloride. 
Halodisilanes useful in the present process are described by formula 
R.sup.2.sub.a Si.sub.2 X.sub.6-a, where each R.sup.2 is an independently 
selected monovalent hydrocarbon radical comprising about one to 20 carbon 
atoms, X is a halogen selected from a group consisting of bromine and 
chlorine, and a=0 to 5. R.sup.2 can be, for example, an alkyl such as 
methyl, ethyl, propyl, tert-butyl, and eicosyl; a cycloalkyl such as 
cyclopentyl and cyclohexyl; an alkenyl such as vinyl, allyl, and hexenyl; 
a cycloalkenyl such as pentenyl and hexenyl; an aryl such as phenyl, 
tolyl, and naphthyl; and an aralkyl such as benzyl, beta-phenylethyl, and 
gamma-tolylpropyl. Preferred is when R.sup.2 is methyl. Preferred is when 
the halogen substituent of the halodisilane is chlorine. The preferred 
halodisilane is selected from a group consisting of 1,2-dimethyl- 
1,1,2,2-tetrachlorodisilane, 1,1,2-trimethyl-1,2,2-trichlorosilane, 
1,1,2,2-tetramethyl-1,2-dichlorodisilane, and 
1,1,1,2-tetramethyl-2,2-dichlorodisilane. 
The present process is especially useful for converting halodisilanes in a 
high-boiling mixture resulting from the direct process for making 
organosilane monomers into hexaorganodisilanes. The so called "direct 
process" for making organosilanes involves the contact of an organic 
halide with elemental silicon in the present of suitable catalysts at a 
temperature of about 300.degree. C. to 350.degree. C. Typically during 
conduct of the direct process gaseous products, unreacted organic halide, 
and fine particulates are continuously removed from the process. The 
removed materials are subsequently distilled to recover monosilanes, 
leaving a high-boiling mixture comprising halodisilanes. This high-boiling 
mixture has limited commercial value and therefore it is desirable to 
convert it to more useful monosilanes. The present process can convert the 
halodisilanes into organodisilanes and preferably into hexaorganodisilanes 
which can then be cleaved by standard methods to form organosilane 
monomers. A preferred halodisilane containing high-boiling mixture for use 
in the present process is one with a boiling point above about 70.degree. 
C. resulting from the distillation of monosilanes from the reaction 
product of methyl chloride with elemental silicon. Such a high-boiling 
mixture may comprising as much as 50 to 60 weight percent halodisilanes. A 
typical composition for such a halodisilane containing high-boiling 
mixture is described, for example, in Ferguson et al., U.S. Pat. No. 
5,430,168, which is incorporated by reference for its teaching of such 
compositions. In some instances, it may be desirable to pre-treat the 
high-boiling mixture by a process such as filtration to remove 
particulates. 
The mole ratio of organic halide to halodisilane can be varied within a 
range of about 0.1 to 10 moles of organic halide per each mole of halogen 
substituted on the silicon atoms of the halodisilane. Preferred is when 
the mole ratio of organic halide to halodisilane is within a range of 
about 1 to three moles of organic halide per each mole of halogen 
substituted on the silicon atoms of the halodisilane. In a preferred 
process the magnesium is added to the process in excess to the organic 
halide forming an organo magnesium halide intermediate. In such a 
preferred process the preferred mole ratio of halogen substituted on the 
silicon atoms of the halodisilane to the organic magnesium halide 
intermediate is less than one. 
The present process is conducted in the presence of diethylene glycol 
dibutyl ether (DEGDBE). About one to fifteen moles of DEGDBE can be added 
to the process per mole of organic halide. Preferred is when about three 
to ten moles of DEGDBE is added to the process per mole of organic halide. 
Even more preferred is when about 1.5 to five moles of DEGDBE is added to 
the process per mole of organic halide. 
The present process can be run at a temperature within a range of about 
0.degree. C. to 250.degree. C. It is preferred that the present process be 
run at a temperature within a range of about 30.degree. C. to 170.degree. 
C. The pressure at which the present process is run is not critical and 
can be ambient to about 200 psig. A preferred pressure is within a range 
of from about 0 psig to 125 psig. 
The product of the present process is an organodisilane where one or more 
of the halogen atoms substituted on the silicon atoms of the halodisilane 
are replaced with an organic substituent. Those skill in the art will 
recognize that the amount of such substitution can be controlled, for 
example, by controlling the ratio of the moles of organic halide to the 
moles of halogen substituted on the silicon atoms of the halosilanes. For 
example, the present process can be conducted with the ratio of the number 
of moles of organic halide to moles of halide substituted on the silicon 
atoms of the halodisilane being greater than about 1:1 and with a=0 to 4. 
The preferred product of the present process is a hexaorganodisilane, where 
all of the halogen substituents on the silicon atoms of the halodisilane 
have been replaced by an organic group. The preferred hexaorganodisilane 
prepared by the present process is hexamethyldisilane. 
The mixture resulting from conduct of the present process on standing 
separates into two-phases, with one phase comprising the organodisilane in 
DEGDBE and the other phase comprising a magnesium dihalide complex 
solubilized in DEGBDE. The organodisilane can be separated from the DEGDBE 
by, for example, distillation. The DEGDBE may be recovered from one or 
both of these phases and recycled to the method.

The following example is provided to illustrate the present invention. The 
example is not intended to limit the scope of the present claims. 
Example 1. The reaction of magnesium metal, methyl chloride, and 
methylchlorodisilanes containing high-boiling mixture resulting from a 
direct process for making methylsilanes, in diethylene glycol dibutyl 
ether (DEGDBE) was evaluated. The halodisilane content of the high-boiling 
mixture is provided in Table 1. Magnesium turnings (0.41 mol), DEGDBE 
(1.24 mol), and 30.7 g of the high-boiling mixture described in Table 
1were loaded into a glass flask equipped with a reflux condenser, addition 
funnel, air stirrer, heating mantle, and nitrogen inlet port. The flask 
was purged with nitrogen and then heated to 85.degree. C. Methyl chloride 
was then sparged into the reactor until the magnesium was consumed. An 
exotherm was observed, with the temperature rising to about 130.degree. C. 
The reaction mixture was cooled in an ice bath to a temperature of about 
85.degree. C. and stirring continued for an additional 3.5 hours. As the 
reaction proceeded the reaction mixture was observed to separate into 
two-phases. The reaction mixture was transferred to a separatory funnel 
and allowed to cool and separate into two-phases. The top-phase was 
analyzed by gas chromatography using a flame ionization detector (GC-FID) 
and found to comprising 9.4 area % hexamethyldisilane (area %= percent of 
total area under the GC-FID trace), 84 area % DEGBDE, and a minor amount 
of tetramethylsilane. No unreacted methylchlorodisilanes were detected in 
the top-phase. 
TABLE 1 
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Halodisilane Composition of High-Boiling Mixture 
Halodisilane GC-FID Area % 
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MeCl.sub.2 SiSiMeCl.sub.2 
24.7 
Me.sub.2 ClSiSiMeCl.sub.2 
25.4 
Me.sub.2 ClSiSiMe.sub.2 Cl 
11.6 
Me.sub.3 SiSiMeCl.sub.2 
2.8 
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