Alkyne hydrosilation using cycloalkadiene as catalyst modifier

Abstract: A process is disclosed for hydrosilating alkynes with hydridosilane in the presence of a platinum catalyst, selected from platinum halides or the reaction product of platinum halides, with organosilicon compounds having terminal aliphatic unsaturation. The process uses a cycloalkadiene comprising 6 to 20 carbon atoms as a catalyst modifier to reduce formation of the bis-silated adduct of the alkynes.

Description: The present invention is a process for hydrosilating alkynes with hydridosilanes in the presence of a platinum catalyst, selected from platinum halides or the reaction product of platinum halides with organosilicon compounds having terminal aliphatic unsaturation. This process uses a cycloalkadiene comprising 6 to 20 carbon atoms as a catalyst modifier to reduce formation of the bis-silated adduct of the alkynes. Virtually any compound which contains a ≡SiH group is reacted with compounds containing aliphatic unsaturation in the presence of a platinum compound, such as chloroplatinic acid, to effect a reaction typically referred to as hydrosilation or hydrosilylation. U.S. Patent 2,823,218 discusses such hydrosilation reactions in greater detail. U.S. Patent 3,419,593 describes a group of catalysts that are the reaction product of chloroplatinic acid with organosilicon compounds having terminal unsaturation that are particularly useful in hydrosilation processes. U.S. Patent 4,292,434 discloses a hydrosilation catalyst obtained by dissolving a platinum halide in at least 20 parts by weight of an olefin, such as 1,5-cyclooctadiene, for each part by weight of platinum halide, and subsequently heating and mixing the solution obtained with from 0.5 to one mole of a primary or secondary amine for each gram atom of platinum. The catalyst is reported useful in the reaction of acetylene with methyldichlorosilane to produce vinylmethyldichlorosilane. A common problem associated with the hydrosilation of an alkyne with a hydridosilane, in the presence of a platinum halide or platinum olefin complex as catalyst, is the formation of the bis-silated adduct of the alkyne as a by-product. Typically, such hydrosilation processes are run under high pressure to increase the concentration of alkyne in the reaction mixture, relative to the alkenyl substituted product, thereby minimizing the formation of the bis-silated adduct. However, alkynes such as acetylene are explosive at high pressures, thereby making those processes dangerous. We have surprisingly found that in processes where an alkyne is silated with a hydridosilane in the presence of a platinum catalyst, selected from platinum halides or the reaction product of platinum halides with organosilicon compounds having terminal aliphatic unsaturation, the presence of 0.1 to 5 moles of cycloalkadiene, comprising 6 to 20 carbon atoms per g·atom of platinum will reduce the amount of the bis-silated adduct formed. This allows such processes to be run at near normal atmospheric pressure while still providing an acceptable ratio of alkenyl substituted product to bis-silated by-product. The present invention is a process for hydrosilation of an alkyne. The process comprises contacting at a temperature within a range of 40 to 150°C. an alkyne described by formula R 1 C≡CH (1) where R 1 is selected from hydrogen atom or alkyl groups comprising one to ten carbon atoms; with a hydridosilane described by formula (R 2 ) n HSiX 3-n (2) where R 2 is selected from alkyl groups comprising one to 20 carbon atoms or aryl groups, each X is an independently selected halogen atom and n=0 to 3; in the presence of a platinum catalyst selected from platinum halides or the reaction products of platinum halides with organosilicon compounds having terminal aliphatic unsaturation and 0.1 to 5 moles of a cycloalkadiene comprising 6 to 20 carbon atoms per g·atom of platinum provided by said catalyst. The alkyne is contacted with the hydridosilane in standard low-pressure type reactors suitable for reacting such compounds. The pressure at which our process is conducted is not critical and is varied within a wide range. However, the present process is unexpectedly advantageous in that it is conducted at near normal atmospheric pressure while still providing an acceptable ratio of alkenyl-substituted product to bis-silated by-product. Therefore, it is preferred that the process is conducted at a pressure within a range of 10.1 to 303.9 kPa (0.1 to 3 atmospheres). More preferred is when the process is conducted at 101.3 to 303.9 kPa (1 to 3 atmospheres). The present process is conducted in either a gas or liquid phase. However, it is preferred that the process is conducted in a liquid phase using a liquid hydrocarbon solvent in which the alkyne and hydridosilane are soluble. It is preferred that the liquid hydrocarbon solvent have a boiling point greater than the boiling point of the alkenyl substituted product of our process to facilitate separation of the product from the solvent. The solvent is, for example, an aromatic hydrocarbon such as xylene or a mixture of the isomers of xylene, toluene or benzene. A demonstration of such a liquid phase process is provided in the examples herein. The present process is conducted at a temperature within a range of 40 to 150°C. A preferred temperature is 60 to 100°C. The optimal temperature for conducting our process will depend upon such factors as the alkyne and hydridosilane to be reacted. For example, when acetylene is reacted with methyldichlorosilane a preferred temperature for conducting the process is within a range of 70 to 80°C. Alkynes useful in the present process are described by formula (1), where R 1 is selected from hydrogen atoms or alkyl groups comprising one to ten carbon atoms. R 1 is methyl, ethyl, propyl, tert-butyl and decyl. Preferred is when R 1 is hydrogen atom, thereby making the alkyne acetylene. Hydridosilanes useful in our process are described by formula (2), where R 2 is selected from alkyl groups comprising one to 20 carbon atoms or aryl groups, each X is an independently selected halogen atom and n has a value of zero, one, two or three. R 2 is, for example, alkyl groups such as methyl, ethyl, propyl and tert-butyl; halogen substituted alkyl groups such as chloromethyl or 3,3,3-trifluoropropyl; aryl groups such as phenyl, tolyl and xylyl; and halogen substituted aryl groups such as chlorophenyl. Preferred is when R 2 is methyl. Also preferred is when X is a chlorine atom. The preferred hydridosilane is selected from methyldichlorosilane or dimethylchlorosilane. In the present process, it is preferred that the mole ratio of the alkyne to the hydridosilane fed to the process is within a range of 0.5:1 to 3:1. Preferred is when the mole ratio of alkyne to hydridosilane is within a range of 1:1 to 1.3:1. The present process is conducted in the presence of a platinum catalyst, selected from platinum halides or the reaction product of platinum halides, with organosilicon compounds having terminal aliphatic unsaturation. Platinum halides useful in the present invention include platinum dichloride, platinum dibromide, platinum tetrachloride, chloroplatinic acid (H 2 PtCl 6 .6H 2 O) and dipotassium tetrachloroplatinate (K 2 PtCl 4 ). The preferred platinum halide is chloroplatinic acid. Platinum catalysts useful in the present invention also include the reaction product of a platinum halide with an organosilicon compound having terminal aliphatic unsaturation. Such catalysts are more fully described in U.S. Patent 3,419,593 which teaches platinum catalysts useful in the present process. The platinum catalyst is, for example, the reaction product of a solution of chloroplatinic acid in 2-propanol with methylvinyldichlorosilane as described in our examples herein or the reaction products of platinum dichloride or chloroplatinic acid with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane. The concentrations of platinum catalyst used in the present process are varied within wide limits. In general, when our process is run as a batch process in the liquid phase, the catalyst concentration in the liquid phase is that providing 1 to 20,000 parts per million (ppm) platinum. Preferred is 20 to 10,000 ppm of platinum in the liquid phase. The present process requires the presence of 0.1 to 5 moles of a cycloalkadiene comprising 6 to 20 carbon atoms per each g·atom of platinum added to the process as catalyst. Preferred is when 0.5 to 3 moles of a cycloalkadiene comprising 6 to 20 carbon atoms is added to the process per each g·atom of platinum added as catalyst. Even more preferred is when 1 to 2.5 moles of a cycloalkadiene comprising 6 to 20 carbon atoms is added to the process per each g· atom of platinum added as catalyst. Preferred is when the cycloalkadiene comprises 6 to 10 carbon atoms. The cycloalkadiene is, for example, a cyclohexadiene, cycloheptadiene, cyclooctadiene or cyclodecadiene. The preferred cycloalkadiene is 1,5-cyclooctadiene. The following examples are provided to illustrate the present invention. The platinum catalyst used in our examples and designated as "CPA/IPA/MeViSiCl 2 ", was prepared by the following method. A 500 mL, round-bottom flask, equipped with a stirring bar, was flushed with nitrogen and charged with 296.3 g of distilled methylvinyldichlorosilane. 3.77 g of a solution comprising chloroplatinic acid in 2-propanol and containing 4.39 percent by weight of platinum, obtained from Johnson-Matthey, Ward Hill, MA, were slowly added to the flask. This mixture was stirred for 15 hours under nitrogen and then transferred to a clean, stoppered glass bottle for storage. The apparatus set-up for running the examples is as follows. Commercially acquired acetylene was purified to remove stabilizing agents. The purified acetylene was introduced via a coarse glass-frit gas dispersion tube into a 500 mL, 3-neck, round-bottom flask containing liquid hydridosilane. This flask, termed the "SiH reservoir", was fitted with a thermometer and equipped with Teflon™ adapters at the necks for entry of delivery and exit tubes. The exit tube from the SiH reservoir was a 6 mm outside diameter (O.D.) polypropylene tube leading to a 500 mL flask used as a safety trap between the SiH reservoir and the reaction flask. The tubing exiting the safety trap was a 3 mm O.D. Teflon™ tube. This exit tube was connected to a second gas dispersion tube which entered a l L, 3-neck, round-bottom flask termed the "reactor". The reactor was equipped with a stirring bar and fitted with a thermometer at one neck and a claisen adapter on the center neck. The straight neck of the claisen adaptor was equipped with a rubber septum for the periodic withdrawal of samples from the reactor for analysis by gas chromatography using a thermal conductivity detector (GC-TCD). The second neck of the claisen adapter was fitted with a dewar condenser cooled with a dry ice/isopropyl alcohol (IPA) bath. The Tygon™ tubing exiting this condenser led to a mineral oil double-bubbler via a dry ice/IPA trap. Provisions were made for blanketing and or purging the apparatus from just before the SiH reservoir to between the last dry ice/IPA trap and the bubbler. The experimental procedure for running the examples was as follows. Hydridosilane was added to the SiH reservoir, which was maintained at a constant temperature of 18°C. A preweighed quantity of catalyst and catalyst modifier was added to the reactor. Based on approximately one g-mol of product formed during a run, the amount of catalyst used provided a final Pt/SiH mole ratio of 6 X 10 -5 :1 in each example. Methylvinyldichlorosilane (as a means of varying the average amount of vinylsilane concentration in the reactor) and xylenes in the amounts described in each example were transferred to the reactor under a slow nitrogen purge. The reaction apparatus was purged with acetylene and then the gas dispersion tube in the SiH reservoir was slowly lowered into the hydridosilane to bubble acetylene through the hydridosilane. The acetylene flow rate was maintained at 115 to 120 mL minute to yield approximately 120 to 170 g of vinylsilane product in a three to four hour run time. The gas exiting the SiH reservoir comprised acetylene and hydridosilane at a molar ratio within a range of 1.2:1 to 1.25:1. The gaseous mixture was passed into the stirring catalyst solution in the reactor. Within three minutes, an exotherm was evident. The temperature of the reactor was controlled by means of a silicone oil bath to maintain the temperatures reported for each example. The exotherm usually peaked in 30 to 45 minutes. The reaction temperature was then maintained at a constant temperature as reported for each example for the remainder of the run. When the level of liquid in the reactor reached a preset mark on the flask corresponding to the approximate product weight as described in each example, the gas dispersion tube in the SiH reservoir was raised above the liquid level to stop any further hydrosilation. Acetylene flow was continued for an additional two to five minutes. The reactor was cooled to room temperature under nitrogen atmosphere and the product mixture was removed under nitrogen pressure into a preweighed bottle. The weight of all products formed was obtained by subtracting the weight of the initial reaction mixture (i.e. catalyst, catalyst modifier, vinylsilane and xylenes) from that of the final product mixture. Analysis of the mixture was performed by GC-TCD. In the examples, the following labels apply. "Catalyst" is the type catalyst used, as previously described; "Catalyst Conc" is the g·atom of platinum added to the reactor per mole of SiH provided by addition of the hydridosilane; "Additional MeViSiCl 2 " is the weight of methylvinyldichlorosilane added to the reactor to control the average concentration of methylvinyldichlorosilane in the reactor; "Xylenes" is the amount of a mixture of xylene isomers added to the reactor; "Temperature Range" describes the temperature range of the reactor that occurred from initiation of the exotherm to temperature stabilization; "Hold Temp." is the constant temperature the content of the reactor was held at after temperature stabilization. "Average MeViSiCl 2 Conc" is the average concentration by weight of the compound in the reactor during a run; "Weight MeViSiCl 2 " is the weight of methylvinyldichlorosilane made by the process, as determined by GC-TCD and corrected for any such compound initially added to the reactor; "Weight Bis-Silated Derivative" is the amount of the bis-silated acetylene adduct made during conduct of the process; "P/B Weight Ratio" is the weight ratio of product MeViSiCl 2 to bis-silated acetylene adduct; "Me" is methyl and "Vi" is vinyl. Example 1 (Reference Example) Catalyst CPA/IPA/MeViSiCl 2 Catalyst Conc 6 X 10 -5 g·atom Pt/mole SiH 1,5-Cyclooctadiene 0.0 g Additional MeViSiCl 2 127.3 g Xylenes 148.0 g Temperature Range 67-79°C. Hold Temperature 77°C. Average MeViSiCl 2 Conc 58 Wt% Weight Product MeViSiCl 2 164.7 Weight Bis-Silated Derivative 10.7 g P/B Weight Ratio 15.4:1 Example 2 Catalyst CPA/IPA/MeViSiCl 2 Catalyst Conc 6 X 10 -5 g·atom Pt/mole SiH 1,5-Cyclooctadiene 0.0134 g Additional MeViSiCl 2 126.4 g Xylenes 148.8 g Temperature Range 69-77.5°C. Hold Temperature 75°C. Average MeViSiCl 2 Conc 58 Wt% Weight Product MeViSiCl 2 154.7 g Weight Bis-Silated Derivative 6.6 g P/B Weight Ratio 23.6:1 Example 3 (Reference example) Catalyst CPA/IPA/MeViSiCl 2 Catalyst Conc 6 X 10 -5 g·atom Pt/mole SiH 1,5-Cyclooctadiene 0.3 g Additional MeViSiCl 2 126.2 Xylenes 148.7 Under the process conditions described above, this mixture did not react thereby demonstrating the inhibiting effect of the high concentration of 1,5-cyclooctadiene on the process.

Claims: A process for hydrosilation of an alkyne, the process comprising contacting at a temperature within a range of 40 to 150°C. an alkyne described by formula R 1 C≡CH, where R 1 is selected from hydrogen atom or alkyl groups comprising one to ten carbon atoms; with a hydridosilane described by formula (R 2 ) n HSiX 3-n , where R 2 is selected from alkyl groups comprising 1 to 20 carbon atoms or aryl groups, each X is an independently selected halogen atom and n=0 to 3; in the presence of a platinum catalyst, selected from platinum halides or reaction products of platinum halides with organosilicon compounds having terminal aliphatic unsaturation and 0.1 to 5 mole of a cycloalkadiene comprising 6 to 20 carbon atoms per g·atom of platinum present as catalyst. A process according to claim 1 where the contacting is conducted at a pressure within a range of 10.1 to 303.9 kPa (0.1 to 3 atmospheres). A process according to claims 1 or 2 where the contacting is conducted in a liquid phase using a liquid hydrocarbon solvent in which the alkyne and hydridosilane are soluble. A process according to claims 1 or 2 where the alkyne is acetylene. A process according to claims 1 or 2 where the hydridosilane is selected from methyldichlorosilane or dimethylchlorosilane. A process according to claims 1 or 2 where the hydridosilane is methyldichlorosilane and the alkyne is acetylene and the mole ratio of acetylene to methyldichlorosilane is within a range of 0.5:1 to 3:1. A process according to claims 1 or 2 where the platinum catalyst is selected from a group consisting of chloroplatinic acid, reaction product of chloroplatinic acid with methylvinyldichlorosilane, reaction product of chloroplatinic acid with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane and reaction product of platinum dichloride with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane. A process according to claim 3 where the liquid phase comprises one to 20,000 ppm of platinum. A process according to claims 1 or 2 where the cycloalkadiene is 1,5-cyclooctadiene.

Inventors: ROY AROOP KUMAR, ROY, AROOP KUMAR
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1997
Main classification: C07F7
IPC codes: B01J27, C07F7, C07B61