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Description  |
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FIELD OF THE INVENTION
The present invention relates to a method of producing
dimethylpolysiloxanes and, more particularly, to a method of selectively
producing either linear dimethylpolysiloxanes alone both ends of which are
blocked with chlorine atoms or cyclic dimethylpolysiloxanes alone.
BACKGROUND OF THE INVENTION
A synthesis method for linear methylchloropolysiloxanes has already been
reported by Winton Patnode and Donald F. Wilcock in J. Am. Chem. Soc.,
volume 68, page 358 (1946).
In the above-cited method, a mixture of purified water and dioxane is
introduced into dimethyldichlorosilane dissolved in a large quantity of
diethyl ether. However, using a large quantity of diethyl ether is
dangerous in handling and impairs the production efficiency per unit
volume. Therefore, that method has a defect of having no suitability for
production on an industrial scale.
In addition, the foregoing report describes experimental results such that
a mixture of linear methylchloropolysiloxanes with cyclic
dimethylpolysiloxanes is produced when purified water by itself is
introduced into dimethyldichlorosilane alone, the linear product and the
cyclic product thus obtained are hard to separate because their boiling
points are very close to each other, and the linear
methylchloropolysiloxanes, which are more useful than the cyclic product,
are produced therein in low yields.
In order to solve the above-described problems, therefore, we have made
intensive studies. As a result, it has been found out that in hydrolyzing
dimethyldichlorosilane by introducing thereinto a water solution
containing a water-soluble oxygen-containing organic compound, linear
dimethylpolysiloxanes alone, having both ends blocked with chlorine atoms,
can be selectively produced when the water solution introduced is rendered
acidic and the quantity of water introduced into the hydrolysis system is
controlled properly; while cyclic dimethylpolysiloxanes alone can be
selectively produced by properly controlling the quantity of water
introduced into the hydrolysis system and, if desired, the water solution
is rendered acidic; thereby achieving the present invention.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide a
dimethylpolysiloxane-producing method which enables selective production
of linear dimethylpolysiloxanes alone, having both ends blocked with
chlorine atoms, or cyclic dimethylpolysiloxanes alone.
The above-described object of the present invention is attained with by a
method of producing dimethylpolysiloxanes which comprises carrying out
hydrolysis by introducing into dimethyldichlorosilane a water solution
containing a water-soluble oxygen-containing organic compound.
BRIEF DESCRIPTION OF DRAWING
FIG. 1 shows an apparatus used for the synthesis reactions according to the
present invention.
Therein, the numeral 1 represents a reaction flask, the numeral 2 a
condenser, the numeral 3 a thermometer, the numeral 4 a tube for
introduction of water, the numeral 5 a magnetic stirrer, the numeral 6 a
microfeeder, the numeral 7 a sampling capillary, the numeral 8 a trap, and
the numeral 9 a hydrogen chloride absorber.
DETAILED DESCRIPTION OF THE INVENTION
Suitable examples of a water-soluble oxygen-containing organic compound
include alcohols such as methanol, ethanol, etc., ketones such as acetone,
methyl ethyl ketone, etc., and cyclic ethers such as 1,3-dioxane,
1,4-dioxane, tetrahydrofuran, etc. Of these compounds, acetone,
1,4-dioxane and tetrahydrofun are particularly preferred over the others
since they do not react with dimethyldichlorosilane as a starting
material.
These compounds may be used alone or as a mixture of two or more thereof.
When they are used as a mixture, however, it becomes difficult to separate
the solvent from the reaction product. Accordingly, it is desirable for
them to be used independently.
In order to render the water solution acidic, ordinary acids such as
hydrochloric acid, sulfuric acid, acetic acid and so on can be used
properly. From the industrial point of view, however, hydrochloric acid is
especially preferred because of its readiness in recovery.
For the acidic water solution, it is desirable that the ratio of an acid to
water (the acid/water ratio by weight) be in the range of 0.001 to 0.35,
particularly 0.005 to 0.25. When the acid/water ratio is increased beyond
0.35, the solution is difficult to handle, e.g., in the case of using
hydrochloric acid as the acid. This is because the hydrochloric acid in
the water solution is gasified at ordinary temperature under ordinary
pressure. When the ratio is decreased below 0.001, on the other hand, the
water solution has no appreciable effect on the hydrolysis.
As for the amount of the water-soluble oxygen-containing organic compound
used, it is desirable that the ratio of the compound to water (the ratio
of the weight of the water-soluble oxygen-containing organic compound to
the weight of water in the water solution) be in the range of 0.1 to 10,
particularly 0.5 to 2.0. This is because an economical advantage is not
produced when the compound is used in a ratio greater than 10, while the
organic compound cannot achieve its solvent effect when it is used in a
ratio smaller than 0.1.
In carrying out the hydrolysis, it is desirable that the foregoing water
solution be introduced into dimethyldichlorosilane at a rate of 0.1 to 0.8
g/min per 100 g of dimethyldichlorosilane. When the introduction rate is
too high, heat evolution becomes intense, and so it becomes difficult to
control the temperature inside the reaction tank. When the introduction
rate is too low, on the other hand, it is undesirable from an economical
point of view because of its low production efficiency.
When the amount of water added to dimethyldichlorosilane is strictly
controlled in the present method, it becomes possible to selectively
produce only linear dimethylpelysiloxanes the both ends of which are
blocked with chlorine atoms, which are represented by the following
general formula (I), and also to selectively produce only cyclic
dimethylpolysiloxanes represented by the following general formula (II):
##STR1##
wherein n is a natural number including 0, preferably from 0 to 12, and
particularly preferably from 0 to 2;
##STR2##
wherein m is an integer of at least 3, preferably from 3 to 14, and
particularly preferably from 4 to 6.
In order to produce only linear dimethylpolysiloxanes having both ends
blocked with chlorine atoms, or in other words, in order not to produce
cyclic dimethylpolysiloxanes at all, it is required to add water in a
proportion of at most 0.5 mole per mole of dimethyldichlorosilane and
further to render the water solution acidic.
When the proportion of water is increased beyond the value specified above,
the produced dimethylpolysiloxanes having both ends blocked with chlorine
atoms are rapidly converted into cyclic siloxanes.
In addition, the value n in general formula (I) can be controlled by
keeping the reaction system homogeneous and properly choosing the amount
of water added and the reaction temperature.
In order to produce cyclic dimethylpolysiloxanes alone, on the other hand,
it is required to add water in a proportion of from 1.0 to 1.2 mole per
mole of dimethyldichlorosilane. When the proportion is increased beyond
1.2, there are produced undesirable high-molecular methylpolysiloxanes
containing hydroxyl groups as end groups.
In addition, the value m in general formula (II) can be controlled by
properly choosing the amount of water added and the reaction temperature.
Preferably, the reaction temperature ranges from 1.degree. C. to
101.degree. C., particularly from 3.degree. C. to 30.degree. C. This is
because it sometimes happens that the reaction temperature lower than
1.degree. C. causes the freezing of the water solution introduced, while
the reaction temperature higher than 101.degree. C. causes the
vaporization of the water solution introduced.
Further hydrolysis makes it possible to eliminate chlorine atoms from the
linear dimethylpolysiloxanes represented by general formula (I), and
thereby to produce dimethylpolysiloxanes having higher polymerization
degrees. Furthermore, the hydrolysis product undergoes the an
equilibration reaction with hexamethyldisiloxane in the presence of an
acidic catalyst such as sulfuric acid, thereby being converted into the
polysiloxanes containing the group (CH.sub.3).sub.3 SiO-- as the end
groups.
The thus obtained polysiloxanes are inert chemically, and so they can be
used as heat-resisting silicone oil.
On the other hand, when the chlorine-eliminated polysiloxanes undergo
polymerization in the presence of a basic catalyst such as sodium
hydroxide, the polysiloxanes obtained come to have very high molecular
weights. Further, when the thus obtained polysiloxanes undergo a
cross-linking reaction by heating in the presence of a peroxide, such as
benzoyl peroxide, as a catalyst, they are converted into polymers having
structural stability. The thus produced polysiloxanes can serve as
silicone rubber having excellent heat resistance and weather resistance.
In accordance with the present method of producing dimethylpolysiloxanes,
either the linear dimethylpolysiloxanes alone having both ends blocked
with chlorine atoms or cyclic dimethylpolysiloxanes alone can be
selectively produced. Therefore, the present method has advantages in that
(1) it has a capability of realizing a process in which dimethylcyclics
are produced without requiring any cracking step, (2) it does not require
the separation of waste acid, and so it can have a high pot yield, (3) it
enables a considerably great reduction of cost in production on an
industrial scale, (4) it can provide linear oligomers serving as
intermediates applicable for various purposes, and so on.
Now, the present invention is illustrated below in greater detail by
reference to the following examples and comparative examples. However, the
invention should not be construed as being limited to these examples.
EXAMPLES
All the synthesis reactions were carried out using a reaction apparatus
shown in FIG. 1.
The flask 1 used therein had a volume of 500 ml and was equipped with a
condenser 2, a thermometer 3, a water introduction tube 4 and a magnetic
stirrer 5. Dimethyldichlorosilane was placed in the flask, and a water
solution containing a water-soluble oxygen-containing organic compound
and, if needed, an acid (preferably hydrochloric acid) was introduced into
the flask from a microfeeder 6 as the reaction temperature was controlled
with a means placed outside the flask.
The quantity of an intended methylchloropolysiloxane produced was examined
by collecting a small volume of reaction mixture through a sampling tube 7
and analyzing it by gas chromatography.
When hydrogen chloride gas was evolved as a by-product, it was passed
through the condenser 2, cooled with methanol-dry ice, passed through a
trap 8, and then trapped with an absorber 9 in which water was charged.
Example 1
A water solution to be introduced was prepared by mixing 49 g of dioxane, 1
g of hydrogen chloride and 50 g of water. This solution was injected at a
speed of 0.5 g/min into 185 g of the dimethyldichlorosilane placed in the
flask. The reaction temperature was kept within the range of 6.degree. to
10.degree. C. by the external control.
Synthesis reactions were carried out under the same condition as described
above, except that the content of water in the water solution introduced
was changed variously. More specifically, the ratios of the water to the
dimethyldichlorosilane in these reactions were 0.257, 0.500, 0.600, 0.820,
1.200 and 1.500, respectively, by mole. A small volume of the reaction
product in each reaction was collected, and analyzed by gas
chromatography. The thus determined yields of the reaction products and
the water/dimethyldichlorosilane ratios (by mole) corresponding thereto
are summarized in Table 1.
TABLE 1
__________________________________________________________________________
Yield (%) of Reaction Product
Linear Siloxane
H.sub.2 O/(CH.sub.2).sub.2 SiCl.sub.2
2,2-
2,2-
2,2- Cyclic Siloxane
Ratio (by mole)
Dimer
Trimer
Tetramer
D.sub.3
D.sub.4
D.sub.5
D.sub.6
Note
__________________________________________________________________________
0.257 75 20 5 0 0
0
0 Invention
0.500 51 29 20 0 0
0
0 Invention
0.600 30 20 33 0 10
7
0 Comparison
0.820 12 18 40 0 15
15
0 Comparison
1.000 0 0 0 0 65
30
5 Invention
1.200 0 0 0 0 65
29
6 Invention
1.500* 0 0 0 0 45
25
10 Comparison
__________________________________________________________________________
*When the H.sub.2 O/(CH.sub.3).sub.2 SiCl.sub.2 ratio was 1.500,
highmolecular methylpolysiloxanes containing hydroxyl groups as end group
were produced in a 20% yield.
As can be seen from Table 1, linear siloxanes alone were produced when the
H.sub.2 O/(CH.sub.3).sub.2 SiCl.sub.2 ratio was 0.500 or lower, while they
were not produced at all when the H.sub.2 O/(CH.sub.3).sub.2 SiCl.sub.2
ratio was 1.000 or higher.
Additionally, the reaction products designated by 2,2-dimer, 2,2-trimer,
2,2-tetramer, D.sub.3, D.sub.4, D.sub.5 and D.sub.6 are the compounds
represented by the following structural formulae (i), (ii), (iii), (iv),
(v), (vi) and (vii), respectively.
##STR3##
Example 2
Synthesis reactions were carried out in the same manner as in Example 1,
except that hydrogen chloride was not used at all. The reaction products
obtained under the water/dimethyldichlorosilane ratios of 0.257, 0.500,
0.820 and 1.000 respectively were each sampled, and analyzed by gas
chromatography. The thus determined yields of the reaction products and
the water/dimethyldichlorosilane ratios (by mole) corresponding thereto
are summarized in Table 2.
TABLE 2
__________________________________________________________________________
Yield (%) of Reaction Product
Linear Siloxane
H.sub.2 O/(CH.sub.3).sub.2 SiCl.sub.2
2,2-
2,2-
2,2- Cyclic Siloxane
Ratio (by mole)
Dimer
Trimer
Tetramer
D.sub.3
D.sub.4
D.sub.5
D.sub.6
Note
__________________________________________________________________________
0.257 72 19 4 0 3 1 1 Comparison
0.500 47 28 15 0 7 2 1 Comparison
0.820 10 17 34 0 20 19 1 Comparison
1.000 0 0 0 0 65 32 3 Invention
__________________________________________________________________________
The data shown in Table 2 indicate that when the water solution introduced
was not acidic the cyclic siloxanes (D.sub.4, D.sub.5, D.sub.6), though
the yields thereof were low, were produced even when the H.sub.2
O/(CH.sub.3).sub.2 SiCl.sub.2 ratio was not higher than 0.500 by mole. On
the other hand, cyclic siloxanes alone were produced at the H.sub.2
O/(CH.sub.3).sub.2 SiCl.sub.2 ratio of 1.000 even when the water solution
introduced was not acidic.
Comparative Example 1
Synthesis reactions were carried out in the same manner as in Example 1,
except that dioxane was not used at all. The reaction products obtained
under the water/dimethyldichlorosilane ratios of 0.257, 0.500, 0.820 and
1.000 respectively were each sampled, and analyzed by gas chromatography.
The thus determined yields of the reaction products and the
water/dimethyldichlorosilane ratios (by mole) corresponding thereto are
summarized in Table 3.
TABLE 3
______________________________________
Yield (%) of Reaction Product
Linear Siloxane
H.sub.2 O/(CH.sub.3).sub.2 SiCl.sub.2
2,2- 2,2- 2,2- Cyclic Siloxane
Ratio (by mole)
Dimer Trimer Tetramer
D.sub.3
D.sub.4
D.sub.5
D.sub.6
______________________________________
0.257 32 12 2 0 41 10 3
0.500 24 10 2 0 49 11 4
0.820 17 16 3 0 48 12 4
1.000 16 18 2 0 46 12 6
______________________________________
The data shown in Table 3 indicate that the cyclic siloxanes (D.sub.4,
D.sub.5, D.sub.6) were produced to a considerable extent even when the
ratio of the water in the introduced water solution to the
dimethyldichlorosilane was low in value by mole.
Comparative Example 2
Synthesis reactions were carried out in the same manner as in Example 1,
except that neither dioxane nor hydrogen chloride was used at all. The
reaction products obtained under the water/dimethyldichlorosilane ratios
of 0.257, 0.500, 0.820 and 1.000 respectively were each sampled, and
analyzed by gas chromatography. The thus determined yields of the reaction
products and the water/dimethyldichlorosilane ratios (by mole)
corresponding thereto are summarized in Table 4.
TABLE 4
______________________________________
Yield (%) of Reaction Product
Linear Siloxane
H.sub.2 O/(CH.sub.3).sub.2 SiCl.sub.2
2,2- 2,2- 2,2- Cyclic Siloxane
Ratio (by mole)
Dimer Trimer Tetramer
D.sub.3
D.sub.4
D.sub.5
D.sub.6
______________________________________
0.257 22 2 0 0 50 20 6
0.500 13 6 0 0 58 19 4
0.820 10 9 1 0 57 18 5
1.000 8 11 2 0 57 14 8
______________________________________
The data shown in Table 4 indicate that the cyclic siloxanes (D.sub.4,
D.sub.5, D.sub.6) were produced in higher yields than the linear siloxanes
even when the ratio of the water in the introduced water solution to the
dimethyldichlorosilane was low in value by mole.
Example 3
Synthesis reactions were performed in the same manner as in Example 1,
except that the introduction speed of the water solution was changed to
0.4 g/min and the reaction temperature was kept within the range of
10.degree. to 15.degree. C. In analogy with Example 1, the reaction
products obtained under the water/dimethyldichlorosilane ratios of 0.257,
0.500, 0.820 and 1.000 respectively were each sampled, and analyzed by gas
chromatography. The thus determined yields of the reaction products and
the water/dimethyldichlorosilane ratios (by mole) corresponding thereto
are summarized in Table 5.
TABLE 5
__________________________________________________________________________
Yield (%) of Reaction Product
Linear Siloxane
H.sub.2 O/(CH.sub.2).sub.2 SiCl.sub.2
2,2-
2,2-
2,2- Cyclic Siloxane
Ratio (by mole)
Dimer
Trimer
Tetramer
D.sub.3
D.sub.4
D.sub.5
D.sub.6
Note
__________________________________________________________________________
0.257 70 20 10 0 0
0
0 Invention
0.500 48 28 24 0 0
0
0 Invention
0.820 11 15 35 0 20
19
0 Comparison
1.000 0 0 0 0 65
30
5 Invention
__________________________________________________________________________
Example 4
A water solution to be introduced was prepared by mixing 49 g of acetone, 5
g of hydrogen chloride and 50 g of water. This solution was injected at a
speed of 0.3 g/min into 185 g of the dimethyldichlorosilane placed in the
flask. The reaction temperature was kept within the range of 0.degree. to
5.degree. C. by the external control.
Synthesis reactions were carried out under the same condition as described
above, except that the content of water in the water solution introduced
was changed variously. More specifically, the ratios of the water to the
dimethyldichlorosilane in these reactions were 0.257, 0.500, 0.820 and
1.000, respectively, by mole. A small volume of the reaction product in
each reaction was collected, and analyzed by gas chromatography. The thus
determined yields of the reaction products and the
water/dimethyldichlorosilane ratios (by mole) corresponding thereto are
summarized in Table 6.
TABLE 6
__________________________________________________________________________
Yield (%) of Reaction Product
Linear Siloxane
H.sub.2 O/(CH.sub.2).sub.2 SiCl.sub.2
2,2-
2,2-
2,2- Cyclic Siloxane
Ratio (by mole)
Dimer
Trimer
Tetramer
D.sub.3
D.sub.4
D.sub.5
D.sub.6
Note
__________________________________________________________________________
0.257 74 21 5 0 0
0
0 Invention
0.500 50 30 20 0 0
0
0 Invention
0.820 11 20 39 0 15
14
1 Comparison
1.000 0 0 0 0 68
27
5 Invention
__________________________________________________________________________
It can be concluded that all the experimental results set forth above prove
the validity of the present method.
* * * * *
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Description |
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