Process for producing trialkoxysilanes

In a process for producing trialkoxysilanes by reaction of a metallic silicon and an alcohol having 1 to 4 carbon atoms, the reaction is effected (1) using as the metallic silicon one containing 0.30 to 0.37% by weight of aluminum, (2) using as the catalyst cuprous chloride prepared by a wet process, and (3) allowing aluminum and/or an aluminum compound to coexist, thereby securing a high conversion rate of metallic silicon, and accordingly decreasing the amount of unreacted metallic silicon and suppressing discharge of industrial wastes with eliminating environmental problems.

This invention relates to a process for efficiently producing 
trialkoxysilanes, which are useful as materials for silane-coupling agents 
and others. 
Alkoxysilanes are useful as materials for various silane-coupling agents 
and for insulating films. Particularly, trialkoxysilanes, which have an 
Si-H linkage in the molecule and are chemically stable as compared with 
monoalkoxysilanes and dialkoxysilanes, have been highly demanded, and 
their low-cost, efficient manufacturing method has been sought. 
Hitherto, a process using chlorosilanes and lower alkyl alcohols as 
materials has been known as the manufacturing method for trialkoxysilanes. 
However, it has some disadvantages due to high cost of chlorosilanes, 
difficulty in purification of the product owing to by-production of 
hydrochloric acid besides objective alkoxysilanes, and corrosion of the 
reaction apparatus. 
On the other side, a process, called "direct method", by the reaction of 
metallic silicon and an alkyl alcohol has been known. The process is 
carried out in gas or liquid phase in the presence of a copper catalyst, 
for example. This may be advantageous from the industrial and economical 
viewpoints, since trialkoxysilanes are obtained by one step reaction. 
However, it has yet a big problem in its low silicon conversion rate, and 
also provides another environmental problem because it discharges much 
amount of unreacted metallic silicon as industrial wastes. 
In view of such problems as mentioned above, the present inventors have 
made an intensive research for a process of producing trialkoxysilanes, 
which gives a high conversion rate of metallic silicon, a decreased amount 
of unreacted metallic silicon, and a suppressed amount of industrial 
wastes with eliminating environmental problems, and then has accomplished 
the present invention. 
The present invention relates to a process for producing trialkoxysilanes 
by reaction of a metallic silicon and an alcohol having 1 to 4 carbon 
atoms, in which the reaction is effected under at least one of the 
following conditions (1)-(3): 
(1) using as the metallic silicon one which contains 30 to 0.37% by weight 
of aluminum, 
(2) in the presence of a catalyst of cuprous chloride prepared by a wet 
process, and 
(3) allowing aluminum and/or an aluminum compound to coexist. 
Metallic silicon used as one of the materials in the present invention is 
suitably one having a purity of 80% by weight or more. Metallic silicon 
may contain up to about 1% by weight each of Al, Fe, Ca, and other 
impurities. A metallic silicon washed with fluoric acid or the like may 
also be used. 
Metallic silicon more suitably used in the present invention is one 
containing 0.30 to 0.37%, preferably 0.31 to 0.36%, particularly 0.32 to 
0.35%, by weight of aluminum. Conversion rate of metallic silicon is 
particularly improved when metallic silicon containing such an amount of 
aluminum is used. Aluminum contained in the metallic silicon may possibly 
be present in the form of metallic aluminum, an aluminum compound, an 
aluminum alloy or the like, and the aluminum content referred to in the 
present invention means a value calculated as aluminum atoms. 
To produce metallic silicon having a controlled amount of aluminum, a 
method in which, for example, ferrosilicon preferably containing about 92% 
by weight of silicon, is made react with an iron chloride solution in 
hydrochloric acid, is suitable. 
Metallic silicon used in the present invention is suitably granular. There 
is little limitation in granular size, but a granular diameter on average 
is preferably 2 mm or less, more preferably 25 to 500 .mu.m, most 
preferably 50 to 300 .mu.m. 
Lower alkyl alcohols having 1 to 4 carbon atoms, which are another raw 
material, may be either straight chain or branched chain, specifically, 
methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, 
isobutanol, tert-butanol, among which methanol and ethanol are preferred, 
and ethanol is the most preferred. 
The lower alkyl alcohols are preferably of a purity of 95% by weight or 
more, and are more preferably those treated with a dehydrating agent to 
have a water content of not more than 2,000 ppm, preferably not more than 
500 ppm. 
Feeding rate of the lower alkyl alcohol to the reaction system is 
preferably 10 to 1,000 millimols/hour, more preferably 50 to 500 
millimols/hour, per 1 mole of metallic silicon. Within such ranges, 
economically good results are secured with a high conversion rate of 
metallic silicon and a small amount of unreacted lower alkyl alcohol. 
The lower alkyl alcohol may be supplied as it is, or after diluted with a 
dilution gas. The dilution gas is not specifically limited so far as it 
does not react with the materials and trialkoxysilanes. Nitrogen, argon, 
hydrogen, or the like may be exemplified. 
Catalysts used in the invention are not specifically restricted and may be 
those conventionally used, such as copper catalysts, zinc catalysts, 
nickel catalysts and the like, among which copper catalysts are preferred. 
Specifically, copper salts, such as cuprous chloride, cupric chloride, 
copper bromide, copper iodide, copper fluoride, copper carbonate, copper 
sulfate, copper acetate, copper oxalate, copper thiocyanate and the like; 
copper-containing inorganic compounds, such as cuprous hydroxide, cuptic 
hydroxide, copper cyanide, copper sulfide, copper oxide and the like; 
organic copper compound, such as methylcopper, ethylcopper, and the like; 
and metallic copper, may be illustrated. Among them, cuprous chloride is 
more preferable, and, particularly, cuprous chloride prepared by a wet 
process is preferred. Hereinafter, the invention will be explained with 
respect to such cuprous chloride. 
Cuprous chloride prepared by a wet process (hereinafter referred to as "wet 
process cuprous chloride") means one prepared through steps of 
crystallization and separation from a solution and drying. Specifically, a 
preparing method in which copper flakes are added to an aqueous cupric 
chloride solution and the resulting cuprous chloride crystals are 
separated and dried; or a preparing method in which copper sulfate, 
hydrochloric acid, copper and sodium chloride are subjected to a solution 
reaction, and the crystals of the resulting cuprous chloride are separated 
and dried, is illustrated. 
Wet process cuprous chloride is clearly distinct from cuprous chloride 
prepared by a dry process, namely that prepared using metallic copper and 
chlorine gas as the materials. 
As for the wet process cuprous chloride, one having a purity not less than 
90% by weight is preferred, by which metallic silicon conversion rate can 
be increased. 
Granular diameter of the wet process cuprous chloride is preferably less 
than 40 .mu.m, more preferably less than 2 .mu.m. Use of wet process 
cuprous chloride of such a granular diameter much more increases the 
reaction rate and increases the conversion rate of metallic silicon. 
The granular size of wet process cuprous chloride can be controlled by 
modifying the preparation conditions. If it is too fine, efficiencies in 
crystallization and drying steps in the preparing process are lowered, and 
the surface of the granules tends to be deactivated by heat, moisture, 
etc. As a particularly suitable process, therefore, a method is 
illustrated in which wet process cuprous chloride is so prepared as to be 
of a granular diameter not less than 20 .mu.m, and then the granules are 
pulverized to a diameter of less than 2 .mu.m by means of ball mill or the 
like. The pulverization is preferably conducted in air with least 
moisture, more preferably in nitrogen. 
The catalyst may be fed to the reaction system, separately from metallic 
silicon, or in the form of a mixture with metallic silicon or in the form 
carried on metallic silicon, preferably after the catalyst has been 
activated. For activation, a heat-treatment at a temperature of 
100.degree. C. to 600.degree. C., more preferably 130.degree. C. to 
230.degree. C., is preferred. At a temperature lower than 100.degree. C., 
it is not efficient since it needs a longer activation period of time, 
and, at a temperature higher than 600.degree. C., it might cause 
deactivation of the catalyst. In case of liquid phase reaction, the 
catalyst may be activated before added to a solvent or in a solvent while 
an inert gas is blown into it. 
Amount of the catalyst used is preferably 0.5 to 50 parts, more preferably 
5 to 30 parts, by weight based on 100 parts by weight of metallic silicon. 
Amounts less than 0.5 part and more than 50 parts by weight tend to cause 
a decrease in conversion rate of silicon. 
For the purpose of further increasing the silicon conversion rate, in the 
present invention, it is desirable to allow aluminum and/or an aluminum 
compound (hereinafter generally called as "aluminums") to coexist in the 
reaction system. The aluminums referred to herein should be understood to 
be distinct from aluminum contained in metallic silicon. 
As the aluminums, aluminum metals, such as metallic aluminum, aluminum 
alloys with Si, Mg and Ca; aluminum halides, such as aluminum chloride, 
aluminum bromide, aluminum fluoride, aluminum iodide and the like; 
aluminum salts, such as aluminum carbonate, aluminum sulfate and the like; 
other aluminumcontaining inorganic compounds, such as aluminum hydroxide, 
aluminum sulfide and the like; and aluminum-containing organic compounds, 
such as aluminum acetate, aluminum oxalate, trialkoxyaluminums and the 
like, may be illustrated, among which aluminum metals, such as metallic 
aluminum and aluminum alloys, are preferred. The aluminums may be used 
singly or in a combination of two or more kinds. 
The aluminums are preferably used in an amount of 0.01 to 10 parts, more 
preferably 0.1 to 2 parts, by weight based on 100 parts by weight of 
metallic silicon. Within such ranges, significant increase in silicon 
conversion rate is secured. 
In case of using aluminum alloys as the aluminums, those containing not 
less than 50% by weight of aluminum are preferred. Those containing not 
less than 85% by weight are more preferred. 
The aluminums may be fed to the reaction system, singly or as a mixture 
with metallic silicon or the catalyst. 
The reaction of the present invention can be conducted in gas or liquid 
phase, but a liquid phase reaction is much preferred. Hereinafter, the 
invention will be further explained with respect to the liquid phase 
reaction as examples. 
There is no limitation for the shape of a reactor, so far as metallic 
silicon is kept in a well-dispersed state in the reactor. It may have an 
outside jacket for cooling or heating, or inside fins or coils for 
improving heat transmission. 
The reactor is suitably equipped with a tube for feeding the reactants, 
namely material silicon and alcohols; a tube for discharging a liquid 
reaction product containing trialkoxysilane as a main component and other 
silicon compounds and unreacted alcohols as by-products; and an outlet for 
discharging the residue after reaction. 
Material for the reactor may be chosen within the broad range of kinds, 
such as quartz, glass, metals and the like. 
System of the reaction may be either in batch wherein the whole amounts of 
metallic silicon and the catalyst are initially fed, or continuous wherein 
metallic silicon and the catalyst are continuously fed during the course 
of reaction. 
In case of liquid phase reaction, a solvent is used. There is no specific 
limitation for the solvent, so far as it is inert to metallic silicon, the 
catalyst and trialkoxysilanes. However, stable solvents having a 
relatively high boiling temperature are preferred. For example, paraffinic 
hydrocarbons, such as octane, decane, dodecane, tetradecane, hexadecane, 
octadecane, eicosane and the like; alkylbenzene hydrocarbons, such as 
diethylbenzene, trimethylbenzene, cymene, butylbenzene, butyltoluene, 
octylbenzene, dodecylbenzene and the like, and hydrogenated products 
thereof; diphenyl hydrocarbons, such as diphenyl, diphenyl ether, 
monoethyldiphenyl, diethyldiphenyl, triethyldiphenyl and the like, and 
hydrogenated products thereof; alkylnaphthalene hydrocarbons and 
hydrogenated products thereof; and triphenyl hydrocarbons and hydrogenated 
products thereof, are illustrated, among which alkylbenzene hydocarbons 
are preferred, and dodecylbenzene hydrocarbons are more preferred. These 
may be used singly or in a combination of two or more kinds. 
Suitable ratio of metallic silicon to solvent is preferably 0.1 kg to 1 kg, 
more preferably 0.3 kg to 0.7 kg of metallic silicon to one liter of 
solvent. 
The reaction temperature is preferably 100.degree. C. to 300.degree. C., 
more preferably 150.degree. C. to 230.degree. C. At a temperature lower 
than 100.degree. C., the conversion rate of metallic silicon is not 
increased. At a temperature higher than 300.degree. C., the lower alkyl 
alcohol is decomposed by contact with metallic silicon or the catalyst, 
and the generated moisture tends to deactivate the catalyst. 
The reaction may be conducted under an atmospheric, pressurized or 
depressurized condition, but the reaction under atmospheric pressure is 
preferred because of its economical advantages rendered from the simple 
apparatus. 
Trialkoxysilanes obtained by the present invention have the alkoxyl groups 
corresponding to lower alkyl alcohols that have been used as a material. 
Specifically, trimethoxysilane, triethoxysilane, tri-n-propoxysilane, 
triisopropoxysilane, tri-n-butoxysilane, tri-sec-butoxysilane, 
triisobutoxysilane, tri-tert-butoxysilane, and the like, are illustrated. 
As trioxysilanes produced according to the present invention, preferred 
are trimethoxysilane and triethoxysilane, and the most preferred is 
triethoxysilane. 
The liquid reaction product contains a trialkoxysilane in a high 
concentration, besides a tetraalkoxysilane and other by-products, as well 
as an unreacted alcohol. The objective trialkoxysilane can be readily 
isolated from the liquid product according to a conventional procedure, 
such as distillation. 
The reaction solvent that has been separated from the trialkoxysilane stays 
as a reddish brown slurry containing copper powder formed during the 
reaction, and unreacted metallic silicon. According to the process of the 
invention, amount of the reaction residue is small, because there remains 
little unreacted metallic silicon, so that the residue can be readily 
separated by filtration, centrifugation or similar means. The separated 
solid reaction residue is almost composed of copper powder, with little 
unreacted metallic silicon. The solvent recovered by filtration may be 
recycled.

The present invention will more fully be explained with respect to the 
following working and comparative examples, which are, however, only 
illustrative and never construed to be limitative. 
In this specification, values in selectivity of trialkoxysilanes and in 
conversion rate of metallic silicon are those calculated according to the 
following equations: 
##EQU1## 
EXAMPLE 1 
Into a 500 ml glass reactor equipped with a tube for feeding materials, a 
thermometer, a stirrer, a cooler and an outlet of coolant, was fed 300 ml 
of dodecylbenzene as solvent. Then, 150 g of metallic silicon (containing 
99.1% by weight of silicon, 0.29% by weight of aluminum and 0.2% by weight 
of iron, with a granular diameter on average of 100 .mu.m) and wet process 
cuprous chloride (95% purity) were fed thereto. While nitrogen (30 ml/min) 
was fed, the mixture was stirred and heated at 200.degree. C. for 10 hours 
for catalyst activation treatment. The above wet process cuprous chloride 
had been prepared by subjecting copper sulfate, hydrochloric acid, copper 
and sodium chloride to a solution reaction, separating the 
thus-crystallized cuprous chloride, and drying it to obtain solid cuprous 
chloride, which was then pulverized by ball mill to a granular diameter of 
0.06 to 1.48 .mu.m. 
While the reactor was kept at 180.degree. C. under stirring with nitrogen 
(30 ml/min) being supplied, vaporized ethanol was fed through the feeding 
tube into the solvent at a rate of 50 g/hour for reaction. 
Five minutes after commencement of the reaction, a liquid product began 
distilling out of the cooler. The composition of the distilled liquid 
product was occasionally analyzed by gas chromatography, and change in the 
composition with elapse of time was observed. The reaction was considered 
to finish when the ethanol content reached 100%. 
The reaction finished after 23 hours from the commencement, and a liquid 
product containing objective triethoxysilane was obtained. Analytical 
results of the composition of the whole liquid product, as well as the 
corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 1. 
The content remaining in the reactor after separation of the 
trialkoxysilane was a reddish brown slurry. The solid reaction residue 
separated by filtration was almost copper powder with little amount of 
unreacted silicon. The solvent recovered by filtration was colorless and 
clear, which was able to be reused. 
EXAMPLE 2 
The reaction was repeated in the same manner as in Example 1, except that 
wet process cuprous chloride (prepared as in Example 1, but the ball mill 
treatment was omitted; 0.12 to 28 .mu.m granular diameter) was used. The 
reaction finished after 22 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 1. 
COMATIVE EXAMPLE 1 
The reaction was repeated in the same manner as in Example 1, except that 
cuprous chloride prepared by a dry process from metallic copper and 
chlorine gas (subjected to ball milling; 0.04-1.63 .mu.m granular 
diameter) was used. The reaction finished after 23 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
metallic silicon, are shown in Table 1. 
COMATIVE EXAMPLE 2 
The reaction was repeated in the same manner as in Example 1, except that 
dry process cuprous chloride (prepared as in Comparative Example 1, but 
the ball mill treatment was omitted; 0.10 to 24 .mu.m granular diameter) 
was used. The reaction finished after 21 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
metallic silicon, are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Time until Selectivity 
Conversion 
Catalysts finish of 
Composition of product (wt 
of tri- 
rate of 
Preparation 
Ball mill 
Granular size 
the reaction 
Tri- Tetra- Unreacted 
compound 
metallic Si 
process 
treatment 
(.mu.m) 
(hr) compound*.sup.1 
compound*.sup.2 
alcohol 
(mol 
(wt 
__________________________________________________________________________ 
%) 
Example 1 
wet yes 0.06-1.48 
23 54.2 6.7 39.1 91 87.5 
Example 2 
wet no 0.12-28 
22 56.5 5.3 38.3 83 81.8 
Comparative 
dry yes 0.04-1.63 
23 46.1 9.7 44.2 86 76.3 
Example 1 
Comparative 
dry no 0.10-24 
21 44.9 3.7 51.4 94 61.8 
Example 2 
__________________________________________________________________________ 
*.sup.1 Tricompound: triethoxysilane 
*.sup.2 Tetracompound: tetraethoxysilane 
EXAMPLE 3 
The reaction was repeated in the same manner as in Example 1, except that 
metallic silicon containing 98.9% by weight of silicon, 0.38% by weight of 
aluminum and 0.43% by weight of iron and having a granular diameter on 
average of 100 .mu.m was used, and, further, 1 g of powdered aluminum was 
allowed to coexist. The reaction finished after 23 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectiveity of triethoxysilane and conversion rate 
of metallic silicon, are shown in Table 2. 
The content remaining in the reactor after separation of the 
trialkoxysilane was a reddish brown slurry. The solid reaction residue 
separated by filtration was almost copper powder with little amount of 
unreacted silicon. The solvent recovered by filtration was colorless and 
clear, which was able to be reused. 
EXAMPLE 4 
The reaction was repeated in the same manner as in Example 3, except that 1 
g of aluminum silicon (containing 10% by weight of silicon) was used in 
place of the powdered aluminum. The reaction finished after 31 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 2. 
EXAMPLE 5 
The reaction was repeated in the same manner as in Example 4, except that 
the amount of aluminum silicon used was 0.5 g. The reaction finished after 
23 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Time until Selectivity 
Conversion 
finish of 
Composition of product (wt %) 
of rate of 
Aluminum the reaction 
Tri- Tetra- Unreacted tri-compound 
metallic Si 
Kinds Amounts 
(hr) compound*.sup.1 
compound*.sup.2 
alcohol 
Others*.sup.3 
(mol %) 
(wt 
__________________________________________________________________________ 
%) 
Example 3 
aluminum 
1.0 g 
23 55.2 14.0 28.7 1.1 83 99.8 
powder 
Example 4 
aluminum 
1.0 g 
31 43.2 14.7 41.2 1.0 79 99.7 
silicon 
(Si content 
10 wt %) 
Example 5 
aluminum 
0.5 g 
23 42.5 21.2 35.1 1.2 72 96.5 
silicon 
(Si content 
10 wt %) 
__________________________________________________________________________ 
*.sup.1 Tricompound: triethoxysilane 
*.sup.2 Tetracompound: tetraethoxysilane 
*.sup.3 Mainly diethoxysilane 
EXAMPLE 6 
The reaction was repeated in the same manner as in Example 1, except that 
metallic silicon (containing 99% by weight of silicon, 0.32% by weight of 
aluminum and 0.37% by weight of iron, with a granular diameter on average 
of 100 .mu.m) prepared by a reaction of ferrosilicon containing 92% by 
weight of silicon and an iron chloride solution in hydrochloric acid was 
used. The reaction finished after 26 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 3. 
The content remaining in the reactor after separation of the 
triethoxysilane was a reddish brown slurry. The solid reaction residue 
separated by filtration was almost copper powder with little amount of 
unreacted silicon. The solvent recovered by filtration was colorless and 
clear, which was able to be reused. 
EXAMPLE 7 
The reaction was repeated in the same manner as in Example 6, except that 
metallic silicon (containing 99.0% by weight of silicon, 0.31% by weight 
of aluminum and 0.30% by weight of iron, with a granular diameter on 
average of 100 .mu.m) was used. The reaction finished after 30 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 3. 
EXAMPLE 8 
The reaction was repeated in the same manner as in Example 6, except that 
metallic silicon (containing 99.0% by weight of silicon, 0.36% by weight 
of aluminum and 0.39% by weight of iron, with a granular diameter on 
average of 100 .mu.m) was used. The reaction finished after 27 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 3. 
EXAMPLE 9 
The reaction was repeated in the same manner as in Example 7, except that 1 
g of aluminum silicon (containing 10% by weight of silicon) was 
additionally fed to the reactor. The reaction finished after 30 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 3. 
EXAMPLE 10 
The reaction was repeated in the same manner as in Example 7, except that 
metallic silicon (containing 99.3% by weight of silicon, 0.25% by weight 
of aluminum and 0.22% by weight of iron, with a granular diameter on 
average of 100 .mu.m) was used. The reaction finished after 25 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 3. 
EXAMPLE 11 
The reaction was repeated in the same manner as in Example 6, except that 
metallic silicon (containing 98.9% by weight of silicon, 0.38% by weight 
of aluminum and 0.43% by weight of iron, with a granular diameter on 
average of 100 .mu.m) was used. The reaction finished after 18 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 3. 
EXAMPLE 12 
The reaction was repeated in the same manner as in Example 7, except that 
metallic silicon (containing 98.9% by weight of silicon, 0.41% by weight 
of aluminum and 0.50% by weight of iron, with a granular diameter on 
average of 100 .mu.m) was used. The reaction finished after 16 hours. 
Analytical results of the composition of the whole liquid product, as well 
as the corresponding selectivity of triethoxysilane and conversion rate of 
silicon, are shown in Table 3. 
TABLE 3 
__________________________________________________________________________ 
Reaction system 
Aluminum Time until 
Silicon content Selectivity 
Conversion 
content of finish of 
of aluminum 
Composition of product (wt %) 
of tri- 
rate of 
metallic Si the reaction 
silicon used 
Tri- Tetra- Unreacted compound 
metallic Si 
(wt %) (hr) (wt %) compound*.sup.1 
compound*.sup.2 
alcohol 
Others*.sup.3 
(mol 
(wt 
__________________________________________________________________________ 
%) 
Example 6 
0.32 26 -- 49.5 5.7 44.0 0.8 91.6 96.7 
Example 7 
0.31 30 -- 44.0 12.2 44.0 0.9 83.3 89.1 
Example 8 
0.36 27 -- 44.4 9.0 43.4 1.0 86.2 90.0 
Example 9 
0.31 30 10 43.6 9.2 46.5 0.7 85.7 99.7 
Example 10 
0.25 25 -- 44.9 14.6 39.4 1.1 91.8 79.6 
Example 11 
0.38 18 -- 59.3 10.2 29.3 1.2 88.0 76.4 
Example 12 
0.41 16 -- 55.0 7.2 35.8 1.4 90.7 62.8 
__________________________________________________________________________ 
*.sup.1 Tricompound: triethoxysilane 
*.sup.2 Tetracompound: tetraethoxysilane 
*.sup.3 Mainly diethoxysilane 
Thus, the present invention is to provide a process for producing 
trialkoxysilanes by the reaction of a metallic silicon and an alcohol 
having 1 to 4 carbon atoms in the presence of a catalyst, in which the 
operation of using metallic silicon containing 0.30 to 0.37% by weight of 
aluminum, using cuprous chloride prepared by a wet process as catalyst, or 
allowing aluminum and/or an aluminum compound to coexist, are employed. 
The present process secures a high conversion rate of metallic silicon, 
and accordingly decreases the amount of unreacted metallic silicon, and 
suppresses discharge of industrial wastes with eliminating environmental 
problems.