Process for cycloalkyl substitution of hydrogen containing silanes

Abstract: The present invention is a process for substituting cycloalkyl substituents for a silicon bound hydrogen of a silane. The process employs a preformed organoborane compound as a catalyst to increase the apparent rate of the reaction and to increase the yield of desired cycloalkylsilanes

Description: The present invention is a process for substituting cycloalkyl substituents for a silicon bound hydrogen of a silane. The process employs an organoborane compound as a catalyst to increase the apparent rate of the reaction and to increase the yield of desired cycloalkyl substituted silanes. US-A-2,660,597 describes the preparation of alkylsilicon compounds by the direct reaction of an alkane with a chlorosilane, containing at least one Si-H bond, such as trichlorosilane (HSiCl 3 ) or dichlorosilane (H 2 SiCl 2 ) in the presence of a catalyst of the Friedel-Crafts type at a temperature in the range of from 300 to 500°C, e.g., 375°C. The Friedel-Crafts type catalysts recommended include boron trichloride, aluminum trichloride, boron trifluoride and aluminum tribromide, boron trichloride being preferred and the U.S. Patent stating that other catalysts of this type may be used. Journal of Organometallic Chemistry 145 (1978), pages 307-314 discusses the role of boron trichloride in the synthesis of phenyltrichlorosilane from benzene and trichlorosilane, and investigates the reaction between benzene and trichlorosilane with triphenylborane as a catalyst. The inventors have found that the presence of at least one organic substituent on boron compounds, described herein, provides a catalyst which can increase the apparent reaction rate and the product yield of the reaction of cycloalkanes with hydrogen containing halosilanes. The use of the organic substituted boron catalysts allows the process to be run at lower temperatures and shorter residence times, than those described by the above cited art. The shorter residence times and lower temperatures reduce undesirable reactions and the heat induced decomposition of reactants and products. The present invention is a process for substituting cycloalkyl substituents for a silicon bound hydrogen of a silane. The process employs an organoborane compound as a catalyst to increase the apparent rate of the reaction and to increase the yield of desired cycloalkylsilanes. The present invention is a process for preparing cycloalkylsilanes of formula R 1 a R 2 d H b-d SiX 4-a-b , where each R 1 is independently selected from a group consisting of alkyl radicals of 1 to 7 carbon atoms, aryl radicals and R 2 ; R 2 is a cycloalkyl radical of formula R 3 y C n H 2n-y-1 , where R 3 is selected from a group consisting of alkyl radicals of 1 to 7 carbon atoms and aryls, y=O or 1 and n is an integer from 4 to 7; each X is independently selected from a group consisting of chlorine, bromine and fluorine atoms, a=O or 1 , b=l or 2 , d is an integer in a range of 1 to b and a+b=l, 2 or 3 . The process comprises contacting a cycloalkane of formula R 3 y C n H 2n-y , where R 3 , n and y are as previously described; with a silane of formula R 1 a H b SiX 4-a-b , where R 1 , a, b and X are as previously described; in the presence of an organoborane catalyst of formula R 1 c BX 3-c , where R 1 and X are as previously described and c=l, 2 or 3 : at a temperature within a range of 200°C to 500°C and a pressure within a range of 6895 kPa to 34475 kPa (1000 psi to 5000 psi). The present process substitutes a cycloalkyl group for a hydrogen substituent of a silane The substitution is effected by contacting a cycloalkane with a silane in the presence of an organoborane catalyst. The cycloalkane can be, for example, cyclobutane, cyclopentane, cyclohexane and cycloheptane. The cycloalkane can be substituted with an organic radical, R 3 , where R 3 is selected from the group consisting of alkyl radicals of 1 to 7 carbon atoms and aryl radicals. R 3 can be, for example, methyl, ethyl, propyl, butyl, isobutyl, tert-butyl, heptyl, phenyl, tolyl and xylyl. The organic substituted cycloalkane can be, for example, methylcyclopentane or benzylcyclohexane. The silane can be a halosilane or an organohalosilane. The halosilane can be, for example, trichlorosilane, dichlorosilane, tribromosilane, dibromosilane or trifluorosilane. The organohalosilane is substituted with a hydrocarbon radical, R 1 , where R 1 is selected from a group consisting of alkyl radicals of 1 to 7 carbon atoms, aryl radicals and the cycloalkyl radical R 2 . The alkyl hydrocarbon radical may be, for example, methyl, ethyl, propyl, butyl, isobutyl, tert-butyl or heptyl. The aryl hydrocarbon radical may be, for example, phenyl, tolyl or xylyl. The cycloalkyl radical, R 2 , may be, for example, cyclobutyl, cyclopentyl, methylcyclopentyl, cyclohexyl benzylcyclohexyl or cycloheptyl. The mole ratio of cycloalkane to silane employed in the process will depend upon the number of hydrogens substituted on the silicon atom of the silane and the desired substitution. In general, it is preferred that the mole ratio of cycloalkane to hydrogen bound to the silicon of the silane be within a range of 0.5 to 6.0. More preferred is when the mole ratio of cycloalkane to hydrogen bound to the silicon of the silane is within a range of 1.0 to 1.1. A lower mole ratio of reactants may be employed, but may result in unacceptably low yields of cycloalkyl substituted silanes. A higher mole ratio than 6.0 may be employed, but to no perceived advantage. The catalyst employed in the present invention is an organoborane compound containing one, two or three hydrocarbon radicals, R 1 , as previously described. The organoborane compound may be preformed or formed in situ. The organoborane catalyst may contain one or two halogen atoms, X, selected from the group consisting of chlorine, bromine and fluorine. The organoborane catalyst may be, for example, methyldichloroborane, dimethychloroborane, trimethylchloroborane, methyldibromoborane, dimethylbromoborane, ethyldichloroborane, diethylchloroborane, triethyldichloroborane, phenyldichloroborane, diphenylchloroborane, triphenylborane, phenyldibromoborane, diphenybromoborane, diphenylfluoroborane, methylpentyldichloroborane, benzylhexyldichloroborane or tricyclopentylborane. The hydrocarbon radical(s) substituted on the organoborane catalyst can be the same or different than the hydrocarbon radical(s) to be substituted on the silane by reaction with the cycloalkane. Preferred, is when the hydrocarbon radical(s) substituted on the organoborane catalyst is the same as that to be substituted on the silane by reaction with the cycloalkane. An effective concentration of organoborane catalyst is within a range of 0.1 to 6.0 weight percent, based upon the combined weights of the cycloalkane, the silane and the organoborane catalyst fed to the reactor. A preferred concentration for the organoborane catalyst is within a range of about 1.0 to 3.0 weight percent. The temperature at which the process can be run is within a range of from 200°C to 500°C A preferred temperature for running the process is within a range of from 275°C to 375°C. The temperature can be controlled by standard means for heating reactors, for example, a heating mantle or a heating jacket through which a heat transfer fluid is circulated. The present process must be run under sufficient pressure to ensure that at least a portion of the cycloalkane, silane and organoborane catalyst are in the liquid phase. A usable pressure for running the process is within a range of from 6895 to 34475 kPa (1000 psi to 5000 psi). A preferred pressure for running the process is within a range of from 6895 kPa to 1379 kPa (1000 psi to 2000 psi). The present process can be run as a batch process or as a continuous process, in standard high pressure reactors. Preferred is a continuous process. When the process is run as a batch process, residence times for the reaction to occur are within a range of 0.1 to 6.0 hours. A preferred residence time for the batch process is within a range of 0.25 to 3.0 hours. When the present process is run as a continuous process, the residence time may be shortened by as much as a factor of two to ten, in comparison with the batch process. A preferred embodiment of the present process is when the process is run as a continuous process, with a residence time within a range of from one minute to 15 minutes. More preferred is when the present process is run as a continuous process employing a coiled-tube reactor. Examples of cycloalkyl substituted silanes that may be made by the present process are: cyclobutylchlorosilane, cyclopentylchlorosilane, cyclohexylchlorosilane, cycloheptylchlorosilane, cyclobutyldichlorosilane, cyclopentyldichlorosilane, cyclohexyldichlorosilane, cycloheptyldichlorosilane, cyclobutyltrichlorosilane, cyclopentyltrichlorosilane, cyclohexyltrichlorosilane, cycloheptyltrichlorosilane, dicyclobutyldichlorosilane, dicyclopentyldichlorosilane, dicyclohexyldichlorosilane, dicycloheptyldichlorosilane, cyclopentylbromosilane, cyclohexylbromosilane, cyclopentyltrichlorosilane, cyclohexyltribromosilane, cyclobutylmethylsilane, cyclopentylmethylsilane, cyclohexylmethylsilane, cycloheptylmethylsilane, cyclopentylmethylchlorosilane, cyclohexylmethylchlorosilane, cyclopentylmethyldichlorosilane, cyclohexyldichlorosilane, dicyclopentylmethylsilane, dicyclohexylmethylsilane, dicyclohexylmethylchlorosilane, cyclopentylethylsilan, cyclohexylethylchlorosilane, dicyclobutylethylsilane, cyclopentylphenylsilane, cyclohexylphenylsilane, dicyclopentylphenylchlorosilane, tricyclohexylchlorosilane, methylcyclopentytrichlorosilane or benzylcyclohexyltrichlorosilane. The following examples are offered to facilitate understanding of the present process. These examples are not meant to be limiting on the scope of the claims herein. Example 1 The reaction of cyclohexane with trichlorosilane in the absence of phenyldichloroborane was evaluated. A mixture containing 39 weight percent cyclohexane and 61 weight percent trichlorosilane was placed in a series of glass tubes and the tubes sealed. The tubes were heated to 350°C at an estimated internal pressure of 10342 kPa (1500 psi), for times of 30, 90 and 260 minutes. At the end of each time period, the tubes were cooled and the contents analyzed by gas chromatography using a flame ionization detector (GC-FID). No significant quantities of cyclohexyl substituted silane products were detected. Example 2 A mixture containing by weight 37.5% cyclohexane, 61.0% trichlorosilane and 1.5% phenyldichloroborane was placed in a series of glass tubes and the tubes sealed. The tubes were heated to 350°C at an estimated internal pressure of 10342 kPa (1500 psi), for the times given in Table 1. At the indicated time, the tubes were cooled and the contents analyzed by GC-FID. The results are presented as percentage area under the curve, as defined by the GC-FID analysis. Phenyldichloroborane Catalyzed Reaction of Cyclohexane With Trichlorosilane GC-FID Area Percent Time (Min) (C 6 H 11 )HSiCl 2 C 6 H 11 )SiCl 3 (C 6 H 11 ) 2 SiCl 2 C 6 H 12 0 0.00 0.00 0.00 99.70 30 0.87 14.72 0.10 79.65 60 1.50 25.62 0.87 50.48 120 1.22 26.16 0.90 41.25 180 1.01 27.46 1.08 37.05 The data demonstrate the short residence time required to achieve an equilibrium limited amount of cyclohexyltrichlorosilane when using phenyldichloroborane as catalyst. Example 3 The effectiveness of various boron compounds as catalyst for the reaction of cyclohexane with trichlorosilane was evaluated. The process was conducted in sealed glass tubes as described in Example 2. Each tube contained by weight 37.5% cyclohexane, 61.0% trichlorosilane and 1.5% boron compound. The process was conducted at 310°C and approximately 10342 kPa (1500 psi) pressure. The results are presented in Table 2. Effectiveness of Selected boron Compounds as Catalyst for The Reaction of Cyclohexane With Trichlorosilane Boron Compound BCl 3 (PhBCl 2 ) (C 6 H 11 ) 3 B Time GC-FID Area percent (C 6 H 11 )SiCl 3 0 0 0 0 15 0 - 14 30 10 15 28 60 22 26 30 90 22 30 30 The data presented in Table 2 demonstrate that organic substituted boron compounds can increase both the rate of production of cyclohexyltrichlorosilane and the yield of cyclohexyltrichlorosilane, in comparison with trichloroborane as catalyst. Example 4 Using a procedure similar to that described in Example 2, a mixture containing by weight 44.6% cyclooctane, 53.9% trichlorosilane and 1.5% phenyldichloroborane was heated for 60 minutes at 350°C at 10342 kPa (1500 psi) pressure. Negligible cyclooctyltrichlorosilane was observed by GC-FID. Example 5 Using a procedure similar to that described in Example 2, a mixture containing by weight 33.5% cyclopentane, 64.8% trichlorosilane and 1.8% phenyldichloroborane was heated at 350°C and 10342 kPa (1500 psi) pressure, for the times presented in Table 3. The results are presented in Table 3. Phenyldichloroborane Catalyzed Reaction of Cyclopentane With Trichlorosilane GC-FID Area Percent Time (Min.) C 5 H 9 SiCl 3 (C 5 H 9 ) 2 SiCl 2 15 0.8 - 30 10.2 0.7 60 24.6 1.2 Example 6 The effectiveness of phenydichloroborane as a catalyst for the reaction of cyclohexane with methyldichlorosilane was evaluated. The procedure was as described in Example 2. A mixture containing by weight 41.5% cyclohexane, 56.7% methyldichlorosilane and 1.8% phenyldichloroborane was heated at 350°C and 10342 kPa (1500 psi) pressure. The results are presented in Table 4. Phenyldichloroborane Catalyzed Reaction of Cyclohexane With Methyldichlorosilane GC-FID Area Percent Time (Min.) (C 6 H 11 )MeSiCl 2 (C 6 H 11 ) 2 MeSiCl 15 3.5 0.2 30 4.1 0.2 60 4.8 0.3 Example 7 The effectiveness of phenyldichloroborane as a catalyst for the reaction of methylcyclopentane with trichlorosilane was evaluated. A mixture containing by weight 54.8% methylcyclopentane, 44.l% trichlorosilane and 1.1% phenyldichloroborane was heated at 330°C and 10342 kPa (1500 psi) pressure, for 60 minutes, in a sealed glass tube. The contents of the seal tube were cooled and analyzed by GC using a thermal conductivity detector (TCD). Methylcyclopentyltrichlorosilane comprised 3.6% of the area under the curve, as defined by the GC-TCD analysis. Example 8 The effectiveness of phenyldichloroborane as a catalyst for the reaction of cycloheptane with trichlorosilane was evaluated. A mixture containing by weight 58.6% cycloheptane, 40.4% trichlorosilane and 1.0% phenyldichloroborane was heated at 330°C and 10342 kPa (1500 psi) pressure, for 120 minutes, in a sealed glass tube. The contents of the seal tube were cooled and analyzed by GC-TCD. Cyclopentyltrichlorosilane comprised 1.6% of the area under the curve, as defined by the GC-TCD analysis. Example 9 The effectiveness of phenyldichloroborane as a catalyst for the reaction of cyclohexylbenzene with trichlorosilane was evaluated. A mixture containing by weight 69.8% benzylcyclohexane, 29.5% trichlorosilane and 0.7% phenyldichloroborane was heated at 330°C and 10342 kPa (1500 psi) pressure, in sealed glass tubes, for the times presented in Table 5. At the end of the appropriate heating period, the contents of the sealed tubes were cooled and analyzed by GC-TCD. The results are presented in Table 5 as percentage area under the curve, as defined by the GC-TCD analysis. Phenyldichloroborane Catalyzed Reaction of Benzylcyclohexane With Trichlorosilane GC-TCD Area Percent Time (Min.) Benzylcyclohexyltrichlorosilane 60 0.9 120 6.5 210 9.5 Example 10 The effectiveness of phenyldichloroborane as a catalyst for the reaction of cyclohexane with trichlorosilane was evaluated in a continuous process. A mixture containing by weight 37.8% cyclohexane, 60.9% trichlorosilane and 1.3% phenyldichloroborane was prepared. The mixture was fed to a continuous flow reactor comprising a heated 6.35 mm (1/4 inch) stainless steel tube. The reactor was maintained at a temperature of 350°C and a pressure of 11032 kPa (1600 psi). Residence time of the feed within the reactor was 1.5 minutes, for each pass. Product and unreacted feed materials were collected in a cold trap upon exit from the reactor. The collected materials were recycled through the reactor until equilibrium of the reaction mixture was reached. The contents of the cold trap were analyzed after each pass by GC-FID. The results are presented in Table 6 as percentage area under the curve, as defined by the GC-FID analysis. Phenyldichloroborane Catalyzed Reaction of Cyclohexane With Trichlorosilane in a Continuous Process GC-FID Area Percent Time (Min.) (C 6 H 11 )SiCl 3 (C 6 H 11 ) 2 1.5 1.6 0.1 3.0 12.5 0.7 4.5 24.7 1.3 6.0 26.1 1.6 7.5 29.7 2.1 9.0 29.2 2.1

Claims: A process for preparing cycloalkylsilanes of formula R 1 a R 2 d H b-d SiX 4-a-b , where each R 1 is independently selected from a group consisting of alkyl radicals of 1 to 7 carbon atoms, aryl radicals and R 2 ; R 2 is a cycloalkyl radical of formula R 3 y C n H 2n-y-1 , where R 3 is selected from a group consisting of alkyl radicals of 1 to 7 carbon atoms and aryls, y=O or 1 and n is an integer from 4 to 7; each X is independently selected from a group consisting of chlorine, bromine and fluorine atoms, a=O or 1 , b=l or 2 , d is an integer in a range of 1 to b and a+b=l, 2 or 3 ; the process comprising contacting a cycloalkane of formula R 3 y C n H 2n-y , where R 3 , n and y are as previously described; with a silane of formula R 1 a H b SiX 4-a-b , where R 1 a, b and X are as a previously described; in the presence of an organoborane catalyst of formula R 1 c BX 3-c , where R 1 and X are as previously described and c=l, 2 or 3; at a temperature within a range of 200°C to 500°C and a pressure within a range of 6895 kPa to 34475 kPa (1000 psi to 5000 psi).

Inventors: GOHNDRONE JOHN MICHAEL, GOHNDRONE, JOHN MICHAEL
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1992
Main classification: C07F7
IPC codes: C07F7, C07B61, B01J31