Process for heat-fractionation or organosilanes

Abstract: A process is disclosed for the heat-fractionation of a mixture comprising an organosilane and a borane or borane forming compound. The presence of a tertiary organoamine or tertiary phosphorous compound at a concentration sufficient to reduce modification of the organosilane during the heat-fractionation process unexpectedly improves our process over the prior art.

Description: The present invention is a process for the heat-fractionation of a mixture comprising an organosilane and a borane or borane forming compound. The presence of a tertiary organoamine or tertiary phosphorous compound at a concentration sufficient to reduce modifications of the organosilane during the heat-fractionation process is an improvement over the art. Methods are known in the art for the production of organosilanes having one or more aryl or cycloalkyl substitutions on the silicon atom. Such processes typically involve the reaction of an aromatic compound or cycloalkane with a silicon hydride in the presence of a Lewis acid as catalyst. The preferred Lewis acid catalyst in such processes is a trihalide boron compound or an organoboron compound. We believe that in such processes the trihalide boron compound or organoboron compound is reduced to a borane by the silicon hydride to form the active catalytic specie. We also believe that, during conduct of subsequent heat-fractionation processes to isolate the desired organosilanes from the reaction product mixture, borane can act as a redistribution catalyst causing reduced yield of the desired product. Unexpectedly, we have found that, when mixtures comprising an organosilane and a borane or borane forming compound are heat-fractionated in the presence of a tertiary organoamine or tertiary organophosphorus compound, the redistribution of the reaction product mixture to less commercially desirable compounds is reduced. The patents of the general prior art are represented by US-A-2,572, 302; US-A-2,594,860; US-A-2,626,266; US-A-2,775,606 and US-A-5,118,829. Wright, J . Organometallic Chemistry 145: 307-314 (1978) discloses the reaction of benzene with trichlorosilane in the presence of boron trichloride to form phenyltrichlorosilane. Wright also discusses possible mechanisms for the catalytic activity of the boron trichloride in the process. The described art does not recognize that boranes, particularly in situ formed boranes, will act as a catalyst for detrimental processes in subsequent heat-fractionation steps to isolate the preferred organosilane products. Furthermore, this art does not appreciate that tertiary organoamines and tertiary organophosphorus compounds can reduce modification of organosilanes in mixtures comprising an organosilane and a borane or borane forming compound during a heat-fractionation process. The present invention is a process for heat fractionation of a mixture comprising (A) an organosilane described by formula R 1 a R 2 b SiX 4-a-b , where each R 1 is independently selected from cycloalkyls comprising 4 to 20 carbon atoms or aryls, each R 2 is independently selected from alkyls comprising one to 20 carbon atoms, X is halogen, a=1 or 2, b=0 to 3 and a+b=1 to 4, and (B) a borane or borane forming compound in the presence of (C) a tertiary amine or tertiary organophosphorus compound at a concentration sufficient to reduce modification of the organosilane during heat fractionation of the mixture. Herein, the term "heat fractionation" refers to those processes where heat is applied to the mixture to effect separation of the original mixture into two or more fractions, one fraction of which contains the organosilane. The heat fractionation process is for example a distillation process or a stripping process. This process is run as a continuous, semi-continuous or batch process. It is effected in standard apparatus suitable for contact with halosilanes. The mixture which is heat fractionated by our process comprises an organosilane as described by formula (1) R 1 a R 2 b SiX 4-a-b . Each R 1 is independently selected from aryls or cycloalkyls comprising four to 20 carbon atoms. R 1 can be an aryl such as phenyl, tolyl and xylyl. R 1 can also be a cycloalkyl such as cyclopentyl, cyclohexyl and cycloheptyl. Preferred is when R 1 is phenyl. In formula (1), subscript a has a value of one or two. Subscript b has a value of zero to three, with the preferred value being zero or one. The preferred organosilane is selected from methylphenyldichlorosilane and diphenyldichlorosilane. In addition to organosilane, the mixture which is heat fractionated by our claimed process must include a borane or borane forming compound which facilitates rearrangement of the organosilane during the process. This borane includes, for example, B 10 H 14 , B 2 H 6 , B 4 H 10 , B 5 H 9 , B 5 H 11 , B 6 H 10 and H 2 C 2 B 10 H 10 . The borane may contain alkyl, cycloalkyl, aryl or silyl groups substituted on the boron atom, for example, compounds such as B 5 H 8 (SiCl 3 ), B 5 H 7 (SiCl 3 ) 2 and B 5 H 8 (C 6 H 5 ). By borane forming compound, it is meant those compounds that are reduced by a silicon hydride to a borane in situ during our heat fractionation process. The borane forming compound is, for example, a boron trihalide described by formula BX 1 3 , where each X 1 is an independently selected halogen. The trihalide is, for example, boron trichloride, boron trifluoride and boron dichlorobromide. The borane forming compound is, for example, an organoboron compound such as triphenylboron, phenylboron dichloride and trimethyl boron or an organoboron compound such as described by the formula The source of the mixture comprising the organosilane and the borane or borane forming compound is not critical to our invention. The mixture can be the reaction product resulting from the reaction of a benzenoid hydrocarbon with an organodichloromonohydrosilane in the presence of a boron trihalide as described in U.S. Patent 2,572,302. Or, the mixture can be the reaction product resulting from the contact of a cycloalkane with a silicon hydride in the presence of an organoboron catalyst as claimed in U.S. Patent 5,118,829. Other reaction product mixtures which can be separated by our heat fractionation process include, for example, those described in US-A-2,626,266; US-A-2,775,606; US-A-2,594,860 and in Wright, J . of Organometallic Chemistry 145 :307-314 (1978). A preferred mixture is the reaction product resulting from the reaction of benzene with trichlorosilane, phenyldichlorosilane or methyldichlorosilane in the presence of boron trichloride. In addition to the desired organosilane (i.e., phenyltrichlorosilane, diphenyldichlorosilane and methylphenyldichlorosilane respectively), the mixture may contain other silanes as well as unreacted feed compounds. The separation and recovery of organosilane compounds from mixtures by heat-fractionation processes is well known in the art. However, the yield of desirable organosilane compounds from such heat-fractionation processes is reduced in the presence of a borane which can act as a catalyst to effect modification of the organosilanes by such processes as redistribution, rearrangement and degradation at temperatures above 130°C. We have surprisingly found that adding a tertiary organoamine or tertiary organophosphorus compound to the mixture comprising the organosilane and borane or borane forming compound during the heat-fractionation process will reduce the undesirable modification of the organosilanes present in the mixture. We believe that the added tertiary organoamine or tertiary organophosphorus compound forms a stable complex with borane thereby reducing the ability of borane to act as a catalyst to effect the modification of the organosilanes. Therefore, any tertiary amine or tertiary organophosphorus compound capable of forming a stable complex with the borane under our heat-fractionation process conditions may be used in the present process. The tertiary organoamine is, for example, described by formula R 3 3 N, where each R 3 is an independently selected hydrocarbon radical comprising one to 20 carbon atoms. R 3 is also, for example, an alkyl such as methyl, ethyl, t-butyl, octyl and dodecyl; an aryl such as phenyl and tolyl; or a aralkyl such as benzyl and beta-phenylethyl. The tertiary organoamine is a diamine such as N,N,N',N'-tetramethylethylenediamine. The tertiary organoamine can also be a higher organoamine described by, for example, formula R 3 2 N{(CH 2 ) x NR 3 } y (CH 2 ) x NR 3 2 ; where R 3 is as previously described, subscript x is one to 20 and subscript y is one to 20. Preferred is when x is 2 and y is one. Thus, the tertiary organoamine is triphenylamine, tribenzylamine, triethylamine, trimethylamine, trioctylamine and tridodecylamine. Preferred is when the tertiary organoamine has a pK a value greater than 10. Even more preferred is when the tertiary organoamine as a pK a value greater than 11. It is preferred that the tertiary organoamine have a boiling point temperature greater than that of the organosilane, to reduce carry-over during our heat-fractionation process. When the major organosilane compound in the mixture is methylphenyldichlorosilane, the preferred tertiary organoamine is trioctylamine. When the major organosilane compound in the mixture is diphenyldichlorosilane the preferred tertiary organoamine is tridodecylamine. Tertiary organophosphorus compounds useful in our claimed process are, in general, of the same type as described for the tertiary organoamine, where the phosphorous atom is substituted for the nitrogen atom in the compound. The tertiary organophosphorus compound is, for example, of formula R 3 3 P, where R 3 is as previously described. The tertiary organophosphorus compound can also be a compound containing more than one phosphorous atom such as 1,2-bis(diphenylphosphino)ethane. It is preferred that the tertiary organophosphorus compound also have a boiling point temperature greater than that of the organosilane to reduce carry-over during the heat-fractionation process. The tertiary organoamine or tertiary organophosphorus compound is added to our heat-fractionation process at a concentration sufficient to reduce modification of the organosilane during process performance. The useful concentration of tertiary organoamine or tertiary organophosphorus compound will depend upon such factors as the chemical composition of the tertiary organoamine and tertiary organophosphorus compounds and the type and concentration of the borane present in the mixture. In general, adding the tertiary organoamine or tertiary organophosphorus compound to provide a nitrogen to boron (N/B) mole ratio or phosphorous to boron (P/B) mole ratio of 0.1 to 10 is useful. More preferred is when the tertiary organoamine or tertiary organophosphorus compound is added at a concentration providing a N/B mole ratio or P/B mole ratio within a range of 0.1 to five. Most preferred is when tertiary organoamine or tertiary organophosphorus compound is added at a concentration providing a N/B mole ratio or P/B mole ratio of about one. Example 1 (Comparative, outside scope of present invention) A crude product mixture containing diphenyldichlorosilane was prepared by heating at a temperature of 250°C and a pressure of 8.3 MPa a mixture comprising dichlorosilane, trichlorosilane and benzene in the presence of boron trichloride as catalyst. Next, 83.3 g of the crude product mixture containing 32 g of diphenyldichlorosilane was placed in a flask. The mixture was stripped at 101.3 kPa (1 atm) of pressure and up to a temperature of 300°C. The volatiles were condensed and analyzed by gas chromatography using a thermal conductivity detector (GC-TCD). The collected liquid comprised 10.8 g of diphenyldichlorosilane (yield of 32 percent, where yield is based upon the weight recovery of diphenyldichlorosilane present in the crude product mixture), 3.4 g of phenyldichlorosilane, 37.8 g of phenyltrichlorosilane and 13.8 g of benzene. Example 2 Triethylamine (3.9 g) was added to a flask containing 83.3 g of the crude product mixture described in Example 1. This mixture was stripped by the process described in Example 1. The volatiles were condensed and analyzed by GC-TCD. Then, 77.4 g of a liquid was recovered comprising 24.7 g of diphenyldichlorosilane (yield of 77 percent), 1.4 g of phenyldichlorosilane, 24.5 g of phenyltrichlorosilane and 10.1 g of benzene. Example 3 6.3 g of Ph 2 PCH 2 CH 2 PPh 2 was placed in a flask containing 128 g of the crude product mixture described in Example 1. This mixture was stripped at 101.3 kPa (1 atm) of pressure and up to a temperature of 330°C. The volatiles were condensed and analyzed by GC-TCD. The collected liquid comprised 36 g of diphenyldichlorosilane (yield of 80 percent) and 33.7 g of phenyltrichlorosilane. Example 4 225 g of a crude product mixture prepared by the process described in Example 1 and containing 94 g of diphenyldichlorosilane was added into a flask equipped with a distillation head, a 30 cm distillation column and a thermometer. 8 g of triphenylamine were added to the flask. This mixture was distilled at 9.3 kPa (70 mm Hg) pressure up to a temperature of 270°C. When the temperature reached 200°C., 111 g of liquid had been collected from the column. The collected liquid was analyzed by GC-TCD. This liquid fraction comprised 3 g of diphenyldichlorosilane, 80 g of phenyltrichlorosilane and 21 g of benzene. The total liquid collected from the column between the temperatures of 200°C. and 210°C. was 85 g, of which diphenyldichlorosilane was 83 g. Distillation was continued up to a temperature of 270°C. The total recovery of diphenyldichlorosilane was 92 percent. Example 5 (Comparative, outside scope of present invention) The process described in Example 4 was repeated in the absence of the triphenylamine. A total of 62 g of diphenyldichlorosilane was recovered, as determined by GC-TCD (yield of 66 percent). Example 6 228 g of the crude product mixture described in Example 4 and containing 10 g of triphenylamine was distilled at a pressure of 2.7 kPa (20 mm Hg). The distillation apparatus was the same as described in Example 4. Initially, the mixture was heated to 200°C. to remove benzene. The distillation apparatus was then evacuated to 2.7 kPa (20 mm Hg) and distillation continued until the solution temperature of the flask reached 250°C. The liquid collected at a temperature less than 160°C. comprised 1.3 g of diphenyldichlorosilane, 3.3 g phenyldichlorosilane and 71.4 g phenyltrichlorosilane, as determined by GC-TCD. The liquid collected at a temperature between 160°C. and 187°C. comprised 89 g of diphenyldichlorosilane and 1 g of phenyltrichlorosilane. The yield of diphenyldichlorosilane was 96 percent. Example 7 (Comparative, outside scope of present invention) The process described in Example 6 was repeated in the absence of the triphenylamine. 76 g of diphenyldichlorosilane was recovered, as determined by GC-TCD (yield of 81 percent). Example 8 A crude product mixture comprising methylphenyldichlorosilane was prepared by contacting a reaction mixture comprising methyldichlorosilane and benzene in the presence of boron trichloride catalyst at a temperature of 270°C. and a pressure of 8.3 MPa. 1600 g of a crude product mixture containing 17 GC-TCD area percent methylphenyldichlorosilane was placed in a flask equipped with a thermometer and a 10 tray bubble-cap distillation column. Then, 52 g of distilled tri-n-octylamine was added to the flask. The content of the flask was heated at a temperature below 210°C. to remove low boilers comprising primarily methyldichlorosilane and benzene. The temperature of the flask was then heated to 210°C. and kept at this temperature for 48 hours. The content of the flask was distilled at a pressure of 2.7 kPa (20 mm Hg) and a distillation head temperature of 104°C. 240 g of methylphenyldichlorosilane (99.3 GC-TCD area percent) was collected (yield of 88%), having a purity of 99%+ and nitrogen content of 10 ppm. Example 9 (Comparative, outside scope of present invention) The process described in Example 8 was repeated in the absence of the tri-n-octylamine. After the low boilers were removed by distillation, the solution was heated at 160°C. for 24 hours. The resulting mixture was analyzed by GC-TCD and found to contain only five percent by weight of methylphenyldichlorosilane. Example 10 18.8 g of tridodecylamine was placed in a flask containing 352 g of the crude product mixture described in Example 1. The mixture was heated up to a temperature of 210°C. for 48 hours to remove low-boilers. Phenyltrichlorosilane was removed by distillation at a temperature of 100°C. and 2.7 kPa (20 mm Hg). The residual solution was heated at 210°C. for another 48 hours. Diphenyldichlorosilane was recovered by distillation at a temperature of 185°C. and 2.7 kPa (20 mm Hg) and the yield determined by GC-TCD to be 80 percent. Example 11 7.22 g of N,N,N',N'-tetramethylethylenediamine was placed in a flask containing 436 g of the crude product mixture described in Example 1. The mixture was heated up to a temperature of 210°C. for 48 hours to remove low-boilers. Phenyltrichlorosilane was removed by distillation at a temperature of 100°C. at 2.7 kPa (20 mm Hg). The residual solution was heated at 210°C. for another 96 hours. Diphenyldichlorosilane was recovered by distillation at a temperature of 190°C. and 2.7 kPa (20 mm Hg) and the yield determined by GC-TCD to be 70 percent. Example 12 4.45 g of pentethylenehexamine was placed in a flask containing 495 g of the crude product mixture described in Example 1. The mixture was heated up to a temperature of 210°C. for 48 hours to remove low-boilers. Phenyltrichlorosilane was removed by distillation at a temperature of 100°C. and 2.7 kPa (20 mm Hg). The residual solution was heated at 210°C. for another 96 hours. Diphenyldichlorosilane was recovered by distillation at a temperature of 185°C. and 2.7 kPa (20 mm Hg) and the yield determined by GC-TCD to be 70 percent. Example 13 11 g of 1,2-bis(diphenylphosphino)ethane was placed in a flask containing 495 g of the crude product mixture described in Example 1. The mixture was heated up to a temperature of 210°C. for 48 hours to remove low-boilers. Phenyltrichlorosilane was removed by distillation at a temperature of 100°C. and 2.7 kPa (20 mm Hg). The residual solution was heated at 210°C. for another 96 hours. Diphenyldichlorosilane was recovered by distillation at a temperature of 190°C. and 2.7 kPa (20 mm Hg) and the yield determined by GC-TCD to be 60 percent.

Claims: A process for heat fractionation of a mixture comprising (A) an organosilane described by formula R 1 a R 2 b SiX 4-a-b , where each R 1 is independently selected from cycloalkyls comprising 4 to 20 carbon atoms or aryls, each R 2 is independently selected from alkyls comprising one to 20 carbon atoms, X is halogen, a=1 or 2, b=0 to 3 and a+b=1 to 4, and (B) a borane or borane forming compound; in the presence of (C) a tertiary amine or tertiary organophosphorus compound at a concentration sufficient to reduce modification of the organosilane during heat fractionation of the mixture. A process according to claim 1 where the organosilane is selected from methylphenyldichlorosilane or diphenyldichlorosilane. A process according to claim 1 where the borane is selected from a group consisting of B 10 H 14 , B 2 H 6 , B 4 H 10 , B 5 H 9 , B 5 H 11 , B 6 H 10 , B 5 H 8 (SiCl 3 ), B 5 H 7 (SiCl 3 ) 2 , B 5 H 8 (C 6 H 5 ) and H 2 C 2 B 10 H 10 . A process according to claim 1 where the borane forming compound is selected from boron trichloride; organoboron and triphenylboron. A process according to claim 1 where the mixture comprising the organosilane and the borane or borane forming compound results from the reaction of benzene with a chlorosilane selected from the group consisting of trichlorosilane, phenyldichlorosilane and methyldichlorosilane in the presence of boron trichloride. A process according to claim 1 where the tertiary organoamine is described by formula R 3 3 N, where each R 3 is an independently selected hydrocarbon radical comprising one to 20 carbon atoms. A process according to claim 1 where the tertiary organoamine is selected from the group consisting of triphenylamine, tribenzylamine, triethylamine, trimethylamine, trioctylamine and tridodecylamine. A process according to claim 1 where the tertiary organoamine is N,N,N',N'-tetramethylethylene-diamine. A process according to claim 1 where the tertiary organoamine has a pK a value greater than 10. A process according to claim 1 where the tertiary organophosphorus compound is 1,2-bis(diphenylphosphino)ethane. A process according to claim 1 where the tertiary organoamine or tertiary organophosphorus compound is added to the process in an amount sufficient to provide a nitrogen to boron mole ratio or phosphorous to boron mole ratio of 0.1 to 10.

Inventors: CANNADY JOHN PATRICK, GOHNDRONE JOHN MICHAEL, TZOU MING-SHIN, CANNADY, JOHN PATRICK, GOHNDRONE, JOHN MICHAEL, TZOU, MING-SHIN
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1996
Main classification: C07F7
IPC codes: C07F7, C07F5