CA1133499A - Process for preparing acyloxysiloxanes - Google Patents
Process for preparing acyloxysiloxanesInfo
- Publication number
- CA1133499A CA1133499A CA385,475A CA385475A CA1133499A CA 1133499 A CA1133499 A CA 1133499A CA 385475 A CA385475 A CA 385475A CA 1133499 A CA1133499 A CA 1133499A
- Authority
- CA
- Canada
- Prior art keywords
- column
- carboxylic acid
- acyloxysiloxanes
- weight
- chlorosilane
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ABSTRACT OF THE DISCLOSURE
An improved process is provided for preparing acyloxysiloxanes.
The acyloxysiloxanes are prepared by conducting an aliphatic carboxylic acid in vapour form upwards from the bottom of a column countercurrent to the flow of chlorosilane, in which the carboxylic acid is introduced into the column at such a rate that the carboxylic acid does not exceed 1.3 mol per gram of Si-bonded chlorine in the column, while introducing up to 10 percent by weight of water based on the weight of the carboxylic acid into the column and removing the acyloxysiloxane from the bottom of the column. The process is carried out in the absence of iron or iron complexing agents, is conducted in the absence of solvents, with very short reaction times with excellent yields of acyloxysiloxanes. These products may be mixed with diorganopolysiloxanes to prepare compositions storable under anhydrous conditions but which cure upon exposure to water to elastomeric solids.
An improved process is provided for preparing acyloxysiloxanes.
The acyloxysiloxanes are prepared by conducting an aliphatic carboxylic acid in vapour form upwards from the bottom of a column countercurrent to the flow of chlorosilane, in which the carboxylic acid is introduced into the column at such a rate that the carboxylic acid does not exceed 1.3 mol per gram of Si-bonded chlorine in the column, while introducing up to 10 percent by weight of water based on the weight of the carboxylic acid into the column and removing the acyloxysiloxane from the bottom of the column. The process is carried out in the absence of iron or iron complexing agents, is conducted in the absence of solvents, with very short reaction times with excellent yields of acyloxysiloxanes. These products may be mixed with diorganopolysiloxanes to prepare compositions storable under anhydrous conditions but which cure upon exposure to water to elastomeric solids.
Description
1133~99 The present invention relates to the preparation of siloxanes and more particularly to a process for preparing acyloxysiloxanes.
Ihis application is a division of Serial No. 319,545 filed January 12, 1979.
Acyloxysiloxanes are well known and have been prepared heretofore by reacting in a column at an eleva-ted temperature, a chlorosilane and an aliphatic carboxylic acid.
A process is described in Chemical Abstracts, Volume 77, 1972, page 70 (153525q) for preparing acyloxysiloxanes which comprises partially hydrolyzing acyloxysilanes in the presence of tetrahydrofuran.
An object of a broad aspect of this invention is to provide an improved process for preparing acyloxysiloxanes.
~ n object of still another aspect of this invention is to pro-vide an improved process for preparing acyloxysiloxanes in the substantial absence of organic solvents.
An object of a further aspect of this invention is to provide an improved process for preparing acyloxysiloxanes in a single step from chlorosilanes and carboxylic acids.
An object of a still further aspect of this invention is to pro-vide an improved process for prep~ring acyloxysiloxanes in the absence ofiron and iron complexing agents.
In accordance with a broad aspect of this invention, an improved process is provided for preparing acyloxysiloxanes by reacting chloro-silanes with aliphatic carboxylic acids in a packed column at an elevated temperature, the improvement involving passing an aliphatic carboxylic acid in vapour phase upwards from the bottom of the column countercurrent to the flow of the chlorosilane; introducing the aliphatic carboxylic acid into the column at such a rate that it does not exceed 1.3 mol per gram atom of Si-bonded chlorine in the column; and simultaneously - 1 - .
1133~99 introducing, into the column~ up to 10 percent by weight of water based on the weight of the aliphatic carboxylic acid, and removing the acyloxy-siloxane from the bottom of the column.
In comparison to prior art processes, the process of an aspect of this invention can be carried out in the absence of iron or iron com-plexing agents. In addition, the process of an aspect of this invention can be conducted in the absence of expensive solvents and with a very short reaction time. Moreover, acyloxysiloxanes prepared in accordance with the process of an aspect of this invention have the advantage that they are not contaminated with iron compounds which have a tendency to impart discolorations thereto.
In further contrast to the process described in Chemical Abstracts, the process of an aspect of this invention has the advantage that it does not require the use of tetrahydrofuran and it does not require the preparation of the acyloxysilane in a separate step prior to the formation of the acyloxysiloxanes.
In one variant of this process, the amount of the carboxylic acid introduced in the column is controlled by a temperature-governing device which is located in the lower one-third of the column.
By another variant, the reaction between the chlorosilane and the aliphatic carboxylic acid is carried out at 50 to 300 mm Hg (abs).
By a further variant, the water is mixed with the carboxylic acid.
Chlorosilanes which may be used in the process of an aspect of this invention are those of the general formula:
RaSiC14 a where R represents the same or different substituted and unsubstituted hydrocarbon radicals having from 1 to 8 carbon atoms, and a is 0, 1, 2 or 3.
~133~99 Examples of hydrocarbon radicals represented by R according to a variant thereof are alXyl radicals, e.g., the methyl, ethyl, isopropyl, sec-butyl and 2-ethylhexyl radicals; alkenyl radicals, e.g., the vinyl and allyl radicals, as well as the hexadienyl radicals; cycloalkyl radicals, e.g., the cyclopentyl and the cyclohexyl radicals; cycloalkenyl radicals, e.g., cyclopentenyl, cyclohexenyl and ethylcyclohexenyl radicals; aromatic hydrocarbon radicals, e.g., thephenyl radical; aralkyl radicals, e.g., the benzyl and phenylethyl radicals; and al~caryl radicals, e.g., the tolyl and dimethylphenyl radicals. Examples of substituted hydrocarbon 10 radicals represented by R are halogenated hydrocarbon radicals, e.g., the chloromethyl, 3-chloropropyl and 3,3,3-trifluoropropyl radicals.
Gther chlorosilanes which may be employed in the process of other aspects of this invention are those of the general formula:
C13 bSiRbR RbSiC13-b where R is the same as above, Rl represents a bivalent hydrocarbon radical, for example, an ethylene or phenylene radical and b is 1 or 2.
The carboxylic acids used in the process of yet other aspects of this invention may be acetie acid, propionie acid, butyric acid or dimethyl-acetic acid. The aliphatic carbc~ylic acid is preferably employed in an 20 amount of at least 1 mol per gram atom of Si-bonded chlorine in the chloro silane .
The column used for carrying out the process of an aspect of this invention may be any packed column which can also be used for frac-tionation distaillations. It is preferred according to a variant thereof that the ehlorosilane be introduced at a point in the column at least 90 cm above the point where the c arboxylic acid is introduced. This means that the column is preferably at least 90 em in height. The upper limit of the column's height is limitedsolely by economic considerations.
In the process of another aspect of this invention, the reaction ~13;~
of the chlorosilane with aliphatic carboxylic acid may be carried out at atmospheric pressure, i.e., at 760 mm Hg (abs) or approximately 760 mm Hg (abs). However, in order to obtain acyloxysiloxanes which are substan-tially free of unreacted carboxylic acid and hydrogen chloride, it is pre-ferred according to a variant thereof that the reaction is carried out at 10 to 600 mm Hg (abs) and, more preferably, from 50 to 300 mm Hg (abs).
The chlorosilane is preferably, according to a variant thereof, reacted with the aliphatic carboxylic acid ata temperature which corres-ponds or substantially corresponds to the boiling point of the carboxylic acid used under the~prevàiling conditions of pressure.
When water is employed in the process of an aspect of this invention to prepare acyloxysiloxanes, then it may be introduced into the column at any location in which solid hydrolyzates will not form. However, it is according to a variant thereof that the water be mixed with the carboxylic acid. When water is used in the process of an aspect of this invention, then it is preferably employed at the rate of at least 0.5 percent by weight, based on the weight of the carboxylic acid.
The use of solvent which is inert to the reactants is neither desirable nor required, but it is by no means to be excluded. Examples of solvents which may be used with the process of an aspect of this inven-tion are toluene and methylene chloride.
It is preferred that the process of an aspect of this invention be carried out as a continuous process.
Acyloxysilanes having the general formula:
RaSi(OcoR )4-a are prepared by the process of an aspect of this invention using chloro-silanes of the fornula RaSiC14 a where R and a are the same as above and R' represents the methyl, ethyl, ~133499 propyl or isopropyl radicals.
The acyloxysiloxanes prepared in accordance with the process of an aspect of this invention may be employed in all applications where acyloxysiloxanes have been used heretofore, i.e., they may be mixed with diorganopolysiloxanes having terminal Si-bonded hydroxyl groups to prepare compositions which may be stored under anhydrous conditions but which, when exposed to water at room temperatur~e, cure to elastomeric solids.
The following experiments illustrate the process of preparing the precursor acyloxysilane which may be reacted in situ to form an acyl-oxysiloxane whose preparation is shown in the following example;Experiment 1 A 3.5 meter long glass tube having an inside diameter of 100 mm, which is filled with 8 mm Raschig rings, is used as a column. The top of the column is connected to a reflux condenser which is cooled with an aqueous solution of sodiumchloride having a temperature of -20C. 400 ml per hour of ethyltrichlorosilane is introduced into the center of the column. Slightly above the bottom of the column, 550 ml per hour of glacial acetic acid is introduced into the column and a control element which is connected to a temperature sensing device operates a pump which supplies the glacial acetic acid to the column so as to maintain the tem-perature in an electrically heated forced circulation evaporator at approximately 135C. The pressure in the column is 120 mm Hg (abs) so that the glacial acetic acid evaporates as soon as it enters the column and rises against the flow of ethyl trichlorosilane. Ethyltriacetoxysilane is continuously removed from the bottom of the column.
Yield:98 percent of theoretical Ethytriacetoxysilane content:94 weight percent Acetic acid content:2 weight percent HCl content:less than 50 ppm by weight Experiment 2 Ihe process described in Experiment 1 is repeated, except that the glacial acetic acid is contaminated with 100 ppm of FeC13. The yield is again 98 weight percent of theoretical. The ethyltriacetoxysilane con-tent of the product has decreased slightly, i.e., to 92.5 percent by weight.
A 3.5 meter long glass tube having an inside diameter of 100 mm, which is filled with 8 mm Raschig rings is used as a column. The top of the column is connected to a reflux condenser which is cooled with an aqueous solution of sodium chloride having a temperature of -20C. 250 ml per hour of methyltrichlorosilane is introduced approximately at the center of the column. 220 ml per hour of acetic acid containing 4 percent by weight of water based on the weight of acetic acid is introduced at a point slightly above the bottom of the column. A control element which is connected to a temperture sensing device controls the pump which pumps the acetic acid into the column so as to maintain the temperature in an elec-trically operated forced circulation evaporator at approximately 130C.
Pressure within the column is approximately 135 mm Hg (abs) so that the acetic acid evaporates immediately after it enters the column and rises against the methyltrichlorosilane.
A mixture of methylacetoxysiloxanes which does not crystallize at room temperature and whose principal component is 1,3-dimethyl-1,1,3,3-tetraacetoxydisiloxane is continuously removed from the bottom of the column.
Ihis application is a division of Serial No. 319,545 filed January 12, 1979.
Acyloxysiloxanes are well known and have been prepared heretofore by reacting in a column at an eleva-ted temperature, a chlorosilane and an aliphatic carboxylic acid.
A process is described in Chemical Abstracts, Volume 77, 1972, page 70 (153525q) for preparing acyloxysiloxanes which comprises partially hydrolyzing acyloxysilanes in the presence of tetrahydrofuran.
An object of a broad aspect of this invention is to provide an improved process for preparing acyloxysiloxanes.
~ n object of still another aspect of this invention is to pro-vide an improved process for preparing acyloxysiloxanes in the substantial absence of organic solvents.
An object of a further aspect of this invention is to provide an improved process for preparing acyloxysiloxanes in a single step from chlorosilanes and carboxylic acids.
An object of a still further aspect of this invention is to pro-vide an improved process for prep~ring acyloxysiloxanes in the absence ofiron and iron complexing agents.
In accordance with a broad aspect of this invention, an improved process is provided for preparing acyloxysiloxanes by reacting chloro-silanes with aliphatic carboxylic acids in a packed column at an elevated temperature, the improvement involving passing an aliphatic carboxylic acid in vapour phase upwards from the bottom of the column countercurrent to the flow of the chlorosilane; introducing the aliphatic carboxylic acid into the column at such a rate that it does not exceed 1.3 mol per gram atom of Si-bonded chlorine in the column; and simultaneously - 1 - .
1133~99 introducing, into the column~ up to 10 percent by weight of water based on the weight of the aliphatic carboxylic acid, and removing the acyloxy-siloxane from the bottom of the column.
In comparison to prior art processes, the process of an aspect of this invention can be carried out in the absence of iron or iron com-plexing agents. In addition, the process of an aspect of this invention can be conducted in the absence of expensive solvents and with a very short reaction time. Moreover, acyloxysiloxanes prepared in accordance with the process of an aspect of this invention have the advantage that they are not contaminated with iron compounds which have a tendency to impart discolorations thereto.
In further contrast to the process described in Chemical Abstracts, the process of an aspect of this invention has the advantage that it does not require the use of tetrahydrofuran and it does not require the preparation of the acyloxysilane in a separate step prior to the formation of the acyloxysiloxanes.
In one variant of this process, the amount of the carboxylic acid introduced in the column is controlled by a temperature-governing device which is located in the lower one-third of the column.
By another variant, the reaction between the chlorosilane and the aliphatic carboxylic acid is carried out at 50 to 300 mm Hg (abs).
By a further variant, the water is mixed with the carboxylic acid.
Chlorosilanes which may be used in the process of an aspect of this invention are those of the general formula:
RaSiC14 a where R represents the same or different substituted and unsubstituted hydrocarbon radicals having from 1 to 8 carbon atoms, and a is 0, 1, 2 or 3.
~133~99 Examples of hydrocarbon radicals represented by R according to a variant thereof are alXyl radicals, e.g., the methyl, ethyl, isopropyl, sec-butyl and 2-ethylhexyl radicals; alkenyl radicals, e.g., the vinyl and allyl radicals, as well as the hexadienyl radicals; cycloalkyl radicals, e.g., the cyclopentyl and the cyclohexyl radicals; cycloalkenyl radicals, e.g., cyclopentenyl, cyclohexenyl and ethylcyclohexenyl radicals; aromatic hydrocarbon radicals, e.g., thephenyl radical; aralkyl radicals, e.g., the benzyl and phenylethyl radicals; and al~caryl radicals, e.g., the tolyl and dimethylphenyl radicals. Examples of substituted hydrocarbon 10 radicals represented by R are halogenated hydrocarbon radicals, e.g., the chloromethyl, 3-chloropropyl and 3,3,3-trifluoropropyl radicals.
Gther chlorosilanes which may be employed in the process of other aspects of this invention are those of the general formula:
C13 bSiRbR RbSiC13-b where R is the same as above, Rl represents a bivalent hydrocarbon radical, for example, an ethylene or phenylene radical and b is 1 or 2.
The carboxylic acids used in the process of yet other aspects of this invention may be acetie acid, propionie acid, butyric acid or dimethyl-acetic acid. The aliphatic carbc~ylic acid is preferably employed in an 20 amount of at least 1 mol per gram atom of Si-bonded chlorine in the chloro silane .
The column used for carrying out the process of an aspect of this invention may be any packed column which can also be used for frac-tionation distaillations. It is preferred according to a variant thereof that the ehlorosilane be introduced at a point in the column at least 90 cm above the point where the c arboxylic acid is introduced. This means that the column is preferably at least 90 em in height. The upper limit of the column's height is limitedsolely by economic considerations.
In the process of another aspect of this invention, the reaction ~13;~
of the chlorosilane with aliphatic carboxylic acid may be carried out at atmospheric pressure, i.e., at 760 mm Hg (abs) or approximately 760 mm Hg (abs). However, in order to obtain acyloxysiloxanes which are substan-tially free of unreacted carboxylic acid and hydrogen chloride, it is pre-ferred according to a variant thereof that the reaction is carried out at 10 to 600 mm Hg (abs) and, more preferably, from 50 to 300 mm Hg (abs).
The chlorosilane is preferably, according to a variant thereof, reacted with the aliphatic carboxylic acid ata temperature which corres-ponds or substantially corresponds to the boiling point of the carboxylic acid used under the~prevàiling conditions of pressure.
When water is employed in the process of an aspect of this invention to prepare acyloxysiloxanes, then it may be introduced into the column at any location in which solid hydrolyzates will not form. However, it is according to a variant thereof that the water be mixed with the carboxylic acid. When water is used in the process of an aspect of this invention, then it is preferably employed at the rate of at least 0.5 percent by weight, based on the weight of the carboxylic acid.
The use of solvent which is inert to the reactants is neither desirable nor required, but it is by no means to be excluded. Examples of solvents which may be used with the process of an aspect of this inven-tion are toluene and methylene chloride.
It is preferred that the process of an aspect of this invention be carried out as a continuous process.
Acyloxysilanes having the general formula:
RaSi(OcoR )4-a are prepared by the process of an aspect of this invention using chloro-silanes of the fornula RaSiC14 a where R and a are the same as above and R' represents the methyl, ethyl, ~133499 propyl or isopropyl radicals.
The acyloxysiloxanes prepared in accordance with the process of an aspect of this invention may be employed in all applications where acyloxysiloxanes have been used heretofore, i.e., they may be mixed with diorganopolysiloxanes having terminal Si-bonded hydroxyl groups to prepare compositions which may be stored under anhydrous conditions but which, when exposed to water at room temperatur~e, cure to elastomeric solids.
The following experiments illustrate the process of preparing the precursor acyloxysilane which may be reacted in situ to form an acyl-oxysiloxane whose preparation is shown in the following example;Experiment 1 A 3.5 meter long glass tube having an inside diameter of 100 mm, which is filled with 8 mm Raschig rings, is used as a column. The top of the column is connected to a reflux condenser which is cooled with an aqueous solution of sodiumchloride having a temperature of -20C. 400 ml per hour of ethyltrichlorosilane is introduced into the center of the column. Slightly above the bottom of the column, 550 ml per hour of glacial acetic acid is introduced into the column and a control element which is connected to a temperature sensing device operates a pump which supplies the glacial acetic acid to the column so as to maintain the tem-perature in an electrically heated forced circulation evaporator at approximately 135C. The pressure in the column is 120 mm Hg (abs) so that the glacial acetic acid evaporates as soon as it enters the column and rises against the flow of ethyl trichlorosilane. Ethyltriacetoxysilane is continuously removed from the bottom of the column.
Yield:98 percent of theoretical Ethytriacetoxysilane content:94 weight percent Acetic acid content:2 weight percent HCl content:less than 50 ppm by weight Experiment 2 Ihe process described in Experiment 1 is repeated, except that the glacial acetic acid is contaminated with 100 ppm of FeC13. The yield is again 98 weight percent of theoretical. The ethyltriacetoxysilane con-tent of the product has decreased slightly, i.e., to 92.5 percent by weight.
A 3.5 meter long glass tube having an inside diameter of 100 mm, which is filled with 8 mm Raschig rings is used as a column. The top of the column is connected to a reflux condenser which is cooled with an aqueous solution of sodium chloride having a temperature of -20C. 250 ml per hour of methyltrichlorosilane is introduced approximately at the center of the column. 220 ml per hour of acetic acid containing 4 percent by weight of water based on the weight of acetic acid is introduced at a point slightly above the bottom of the column. A control element which is connected to a temperture sensing device controls the pump which pumps the acetic acid into the column so as to maintain the temperature in an elec-trically operated forced circulation evaporator at approximately 130C.
Pressure within the column is approximately 135 mm Hg (abs) so that the acetic acid evaporates immediately after it enters the column and rises against the methyltrichlorosilane.
A mixture of methylacetoxysiloxanes which does not crystallize at room temperature and whose principal component is 1,3-dimethyl-1,1,3,3-tetraacetoxydisiloxane is continuously removed from the bottom of the column.
Claims (4)
1. In a process for preparing acyloxysiloxanes by reacting a chlorosilane with an aliphatic carboxylic acid in a packed column at an elevated temperature, the improvement which comprises: passing an ali-phatic carboxylic acid in the vapour phase upwards from the bottom of the column countercurrent to the flow of the chlorosilane; introducing said aliphatic carboxylic acid into the column at such a rate that the carboxy-lic acid does not exceed 1.3 mol per gram atom of Si-bonded chlorine in the column; and simultaneously introducing, into the column, up to 10 percent by weight of water based on the weight of the aliphatic carboxylic acid; and removing the acyloxysiloxane from the bottom of the column.
2. The process of claim 1, wherein the amount of said carboxylic acid introduced in the column is controlled by a temperature-governing device which is located in the lower one-third of the column.
3. The process of claim 1, wherein the reaction between said chlorosilane and said aliphatic carboxylic acid is carried out at 50 to 300 mm Hg (abs).
4. The process of claim 1, wherein said water is mixed with said carboxylic acid.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA385,475A CA1133499A (en) | 1978-01-17 | 1981-09-09 | Process for preparing acyloxysiloxanes |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19782801780 DE2801780A1 (en) | 1978-01-17 | 1978-01-17 | PROCESS FOR MANUFACTURING ACYLOXYSILANES AND, IF APPLICABLE, ACYLOXYSILOXANES |
| DEP2801780.3 | 1978-01-17 | ||
| CA000319545A CA1137100A (en) | 1978-01-17 | 1979-01-12 | Process for preparing acyloxysilanes |
| CA385,475A CA1133499A (en) | 1978-01-17 | 1981-09-09 | Process for preparing acyloxysiloxanes |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1133499A true CA1133499A (en) | 1982-10-12 |
Family
ID=27166043
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA385,475A Expired CA1133499A (en) | 1978-01-17 | 1981-09-09 | Process for preparing acyloxysiloxanes |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1133499A (en) |
-
1981
- 1981-09-09 CA CA385,475A patent/CA1133499A/en not_active Expired
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| MKEX | Expiry |