3,704,261 United States Patent Office Patented Nov. 28, 1972 2 materials and are not recovered from the reaction medium 3,704,261 since they form stable complexes with the alkali metal PREPARATION OF SELCON HYDRDES halides generated in the reaction. The formation of these Abe Berger, Schenectady, and Frederick M. Lewis, Buriat Hills, N.Y., assignors to General Electric Company complexes emits heat thereby requiring that the reaction No Drawing. Filed Oct. 18, 1971, Ser. No. 90,401. be closely monitored. In addition, it is generally neces in C, COTf I7/08 sary to employ corrosion resistant reaction vessels since U.S. C. 260-448.2 E 5 Claims corrosion causing materials are emitted in the reaction when alkyl aluminum halides are employed. The present invention provides a process for converting ABSTRACT OF THE DISCLOSURE 10 organosilicon halides to the corresponding hydrides which A method is provided for converting organosilicon is effective and safe. Moreover, the process of the present halides, for example, halosilanes and bis(halosilyl) hydro invention is economically feasible for commercial opera carbons, to the corresponding hydrides. Silicon halide re tions. Also the method of the present invention does duction is effected by utilizing certain organometallic not require extra-ordinary safety precautions. hydrides. SUMMARY OF THE INVENTION The process of the present invention comprises re BACKGROUND OF THE INVENTION acting: Prior to the present invention, various methods were (A) an effective amount of organometallic hydride known for reducing silicon halides as illustrated by the 20 having the structural formula: equation, ( 2 ) L (MeHR)y (1) (EI) RaSiX4-a - RaSiH4 wherein L is an alkali metal or an alkaline earth metal; y is the valence of L; Me is a metal from group III-A of where R is selected from monovalent hydrocarbon radicals 25 the periodic table; each R2 individually is a monovalent and halogenated monovalent hydrocarbon radicals, X is hydrocarbon radical such as alkyl, alkaryl, aryl, aralkyl, a halogen radical, and a is an integer equal to from 1 to 3, and cycloalkyl; and z is a whole number integer from 1 inclusive. One method that can be used to reduce silicon to 3, inclusive; and halides involves the use of lithium aluminum hydride in (B) organosilicon halide selected from organohalo an ether Solvent. Although this procedure can be satis 30 factorily employed for making a variety of silicon hydrides, silanes of formula: those skilled in the art know that it is not economically (3) RaH Six (4-a-b) feasible to utilize lithium aluminum hydride in com or bis(halosilyl) hydrocarbons of the formula: mercial operations. Other methods are shown by Jenkner, Pats. 3,043,857 and 3,100,778. These patents show the 35 (4) (3-c-d)XHRdSiR'SiReFX(3-e-r) reduction of halides of certain Group IV elements, for where R, X, and a are defined above; R is a divalent example, organohalosilanes, by the employment of sodium hydrocarbon radical; b is a whole number which has a hydride utilizing hydrogen gas under pressure, or a value equal to 0 to 2, inclusive; c is a whole number combination of sodium hydride and a promoter in the which has a value equal to 0 to 2, inclusive; d is a whole form of a metallic organic compound such as an alkyl 40 number which has a value equal to form 0 to 2, inclusive; aluminum. These methods achieve effective results but e is a whole number which has a value equal to 0 to 2, have many limitations. For example, the employment of inclusive; f is a whole number which has a value equal to in situ sodium hydride utilizing hydrogen gas under 0 to 2, inclusive; the sum of a and b has a value equal to pressure in combination with sodium metal, requires the 1 to 3, inclusive; the sum of c and d has a value equal use of high pressure equipment. Such equipment can be 45 to 0 to 2, inclusive; and the sum of e and f has a value expensive and present a safety hazard. Alternatively, equal to 0 to 2, inclusive. although the alkyl aluminum can be employed effectively to reduce organohalosilanes substituted with monovalent DESCRIPTION OF PREFERRED EMBODIMENTS hydrocarbon radicals, the use of alkyl aluminums often The present invention provides a method for preparing present problems of contamination. For example, in 50 organosilicon hydrides selected from silanes of the form instances where the boiling points of the resulting silicon ula: hydride and alkyl aluminum overlap, separation of the silicon hydride free of alkyl aluminum often can be ex (5) RaSiH4 a tremely difficult. In addition, when alkyl aluminums are and bis(silyl) hydrocarbons of the formula: employed to promote the reduction of organohalosilane, 55 reaction times can often exceed 24 hours or more and (6) (8-d)HRdSiR'SiRH(3-e) yields of the corresponding silicon hydride are low. where R, R., a, d, and e are as defined above. A recent method for reducing silicon halides wherein Radicals included by R of Formula 1 are, for example, an alkali metal hydride and an alkyl aluminum halide aryl radicals and halogenated aryl radicals, such as phenyl, are employed to reduce the silicon halides is described 60 chlorophenyl, napthyl, chloronapthyl, etc.; aliphatic in U.S. Pat. 3,496,206. Although the process described radicals such as for example, methyl, ethyl, n-propyl, iso in U.S. Pat. 3,496,206 overcomes many of the problems propyl, n-butyl, sec-butyl, tert-butyl, amyl, hexyl, hepty, previously encountered when converting organosilicon octyl, dodecyl, pentadecyl, octadecyl; alkenyl radicals such halides to the corresponding hydrides, it has a few as vinyl, 1-propenyl, allyl etc.; cycloalkyl radicals such as limitations. For example, alkyl aluminum halides must 65 cyclohexyl, cycloheptyl, etc.; haloalkyl radicals such as be carefully handled since they are unstable and ignite chlorobutyl, chloroamyl, chlorooctyl, chlorodecyl, etc. on exposure to oxygen or water. Also, the alkyl aluminum Radicals included by R are arylene radicals such as phen halides when contacted with the skin cause severe blister ylene, naphthylene, anthrylene, etc.; alkylene radicals such ing. Moreover, such halides are difficult to handle since as methylene, ethylene, propylene, butylene, pentylene, they are quite volatile. In addition, the use of the alkyl 70 etc. aluminum halides in such reactions is quite expensive. Organohalosilanes included by Formula 3 are, for ex The alkyl aluminum halides are relatively expensive raw ample, methyltrichlorosilane, methylphenyldichlorosilane, 3,704,261 3 4. methyldichlorosilane, ethyltrichlorosilane, ethylchlorosil hydride; sodium ethyl aluminum trihydride; sodium tri ane, n-propyltrichlorosilane, n-butyltrichlorosilane, n ethyl aluminum hydride; sodium dimethyl aluminum di amyltrichlorosilane, n-amyldichlorosilane, n-amylchloro hydride; sodium methyl ethyl aluminum dihydride; sodi silane, n-hexyltrichlorosilane, n-hexyldichlorosilane, n um triethyl aluminum hydride; sodium trimethyl alumi hexylchlorosilane, phenyltrichlorosilane, chlorophenyltri num hydride; sodium methyl aluminum trihydride, sodi chlorosilane, isopropyldichlorosilane, diphenyldichlorosil um dimethyl boron dihydride, sodium diphenyl aluminum ane, diphenylchlorosilane, n-propyl n-octyldichlorosilane, dihydride, sodium diphenyl boron dihydride, sodium di tri-n-propylchlorosilane, etc. cyclobutyl aluminum dihydride, sodium dicyclohexyl alu Bis(halosilyl) hydrocarbons included by Formula 4 are minum dihydride, sodium ethyl phenyl aluminum dihy for example, bis(chlorodimethylsilyl)methane, bis(trichlo O dride, lithium diethyl aluminum dihydride, lithium di rosilyl)methane, 1,2-bis(trichlorosilyl)ethane, 1,2-bis(di methyl aluminum dihydride, lithium diethyl boron dihy chlorosilyl)ethane, 1,3-bis(trichlorosilyl)propane, 1,4-bis dride, lithium dimethyl boron dihydride, potassium di (methyldibromosilyl)butane, 1,8-bis(dichlorosilyl)octane, ethyl aluminum dihydride, potassium dimethyl aluminum p-bis(dichlorosilyl)benzene, etc. dihydride, calcium-bis-(diethyl aluminum dihydride), and The organometallic hydrides suitable in the present in 5 magnesium-bis(diethyl aluminum dihydride). It is of vention have the following structural formula: course, understood that mixtures of such compounds can be employed in the process of the present invention. (2) L(MeH,R), Methods for preparing the aforementioned organometallic hydrides can be found in E. L. Ashby et al., Inorganic wherein L is an alkali metal or an alkaline earth metal; y 20 Chemistry, volume No. 2, page 499, 1963. is the valence of L; Me is a metal from Group II-A of The reaction between the organosilicon halides and the periodic table; each Rindividually is an alkyl radical the organometallic hydrides can achieve yields as high and/or aryl radical and/or cycloalkyl radical and/or ar as 95% in reaction times as little as a hour or less alkyl and/or alkaryl; and z is a whole number integer under atmospheric conditions. For complete conversion from 1 to 3, inclusive. Some alkali metals and alkaline earth metals which are 25 of the silicon halide to the corresponding silicon hydride, suitable constiutents of the organometallic hydrides of it is preferred that the organometallic hydride be em Formula 2 above include sodium, potassium, lithium, ployed in an amount so as to provide at least about one rubidium, cesium, magnesium, calcium, strontium, and mole of chemically combined hydrogen per mole of barium. Preferably sodium is employed as the alkali metal halogen chemically bonded to silicon metal. The present or alkaline earth metal substituents of the organometallic 30 reaction is quite useful since the organosilicon hydrides hydrides of Formula 2. can be recovered from the reaction medium free from Some metals of Group III-A of the periodic table contamination due to the organometallic hydride by which are suitable components of the organometallic hy vaporization and subsequent condensation. An organo drides employed in the present invention include boron, metallic halide corresponding to the organometallic hy aluminum, gallium, and indium. The preferred Group 35 dride reactant is formed in the reaction. The halide III-A metals employed as substituents of the organo formed in the reaction can be readily regenerated to form metallic hydrides of Formula 2 are boron and aluminum the relatively non-volatile organometallic hydride re with aluminum being the most preferred. actant by simple reduction with a relatively inexpensive R2 in Formula 2 above is a monovalent organic radical alkali metal hydride such as sodium hydride, thereby which may be an alkyl radical, an aryl radical, a cyclo 40 facilitating recovery of the organosilicon hydride free alkyl radical, an aralkyl or an alkyaryl. Generally the alkyl from contamination due to the organometallic hydride. radicals contain from 1 to about 18 carbon atoms, and Moreover, this renders the reaction quite feasible from preferably from about 1 to 10 carbon atoms. Some suit a commercial and economic viewpoint since the organo able alkyl radicals include methyl, ethyl, isopropyl, iso metallic hydride unlike the previously employed reactants butyl, amyl, 2-ethyl hexyl, nonyl, decyl, and octadecy. 45 or promoters for such reduction reactions can be re The most preferred alkyl radicals are methyl and ethyl. covered and reused. The aryl radicals suitable in the present invention include Although the advantages of the present invention are mononuclear and polynuclear radicals. Some suitable aryl readily attainable by the reaction between only the or radicals include phenyl, naphthyl, phenanthryl, and an ganosilicon halide and the organometallic hydride, it is thracyl, of which phenyl is the most preferred. Generally 50 preferred that the reaction further be carried out in the the aryl radicals contain from about 6 to 14 carbon atoms. presence of an alkali metal hydride. This modification The cycloalkyl radicals suitable as R2 in Formula 2 of the present invention is particularly advantageous usually contain from about 3 to about 12 carbon atoms, since the organometallic halide surprisingly functions as and preferably from about 4 to 8 carbon atoms. In a promoter for the reduction of the organosilicon halide cluded among such cycloalkyl radicals are cyclopropyl, 55 by the alkali metal hydride. Accordingly, the quantity cyclobutyl, cyclopenty, cyclohexyl, cycloheptyl, cyclo of the relatively expensive organometallic hydride can octyl, and cyclododecyl. be significantly reduced as compared to those reactions Generally the aralkyl radicals contain from 7 to about carried out in the absence of the alkali metal hydride with 18 carbon atoms. Included among such aralkyl radicals out a loss in the yield of desired organosilicon hydride. are phenylethyl and naphthylethyl. Usually the alkaryl 60 Furthermore, the regeneration of the organometallic hy radicals suitable as R2 in Formula 2 contain from 7 to dride is effected in situ during the reaction when an about 18 carbon atoms. Included among such alkaryl radi alkali metal hydride is present. cals are xylyl, tolyl and cumyl. Included by the alkali metal hydrides that can be em Most preferably R in Formula 2 is an alkyl radical and ployed in the present invention are, for example, sodium is methyl or ethyl. It is understood, of cource, that com 65 hydride, potassium hydride, lithium hydride, rubidium pounds corresponding to Formula 2 may include mixtures hydride, and cesium hydride. Preferably, sodium hydride of monovalent hydrocarbon radicals as the R2 portion of is employed in the method of the present invention. the compound. When the reaction includes an alkali metal hydride, desirable results can be achieved if there is utilized in z is a whole number from 1 to 3, inclusive, and preferably 70 the reaction mixture sufficient organometallic hydride is 2. to provide from 0.01 mole to 1 mole, and preferably y is the valence of L which is either 1 or 2. from about 0.05 mole to about 0.7 mole of chemically Some specific compounds which correspond to Formula combined hydrogen per mole of halogen chemically 2 and are suitable in the present invention include sodium bonded to silicon metal. Desirable results can be achieved diethyl aluminum dihydride; sodium diethyl boron di 75 also if there is utilized in the reaction mixture sufficient 3,704,261 5 6 alkali metal hydride to provide for at least 1 mole and What is claimed is:. generally up to about 1.1 moles of chemically combined 1. A method for making silicon hydrides which com hydrogen per mole of halogen chemically bonded to prises reacting: silicon metal. Although amounts in excess of the about (A) an effective amount of organometallic hydride hav 1.1 moles can be employed, there is usually no advantage ing the structural formula: in doing so. Although the order of addition of the various reactants L (MeHR) y is not especially crucial, it is preferred to add the or ganosilicon halide to the organometallic hydride and the wherein L is selected from the group consisting of alkali metal hydride, if employed. O alkali metals and alkaline earth metals; y is the va During the addition, agitation of the mixture can be lence of L; Me is a Group III-A metal; R2 is a mono employed as well as the use of a solvent. In certain in valent hydrocarbon radical selected from the group stances, the organosilicon halide can be employed as a consisting of alkyl radicals, aryl radicals, cycloalkyl solvent. It is preferred, however, to employ a substan radicals, aralkyl radicals and alkaryl radicals, and mix tially inert organic solvent such as ethers such as tetra 5 tures thereof; and z is a whole number integer from hydrofuran; aliphatic hydrocarbons such as hexane, 1 to 3; and heptane, mineral oil and hexadecane; aromatic hydro (B) silicon halide selected from the class consisting of carbons such as benzene, toluene, and xylene; etc. A sub organohalosilanes of the formula: stantially inert organic solvent is a solvent which is substantially inert to the reactants under reaction condi 20 RaSiHX(4-a-b) tions. A temperature in the range of between about -20 and bis(halosilyl) hydrocarbon of the formula C. to 150° C. can be employed. It is preferred, however, (3-c-d)XHRdSiR'SiReHX(3-e-f) to utilize a temperature between 100° C. to 150° C. Depending upon such factors as the conditions utilized, 25 where R is selected from monovalent hydrocarbon proportions of reactants, etc., a reaction time of as little radicals and halogenated monovalent hydrocarbon as a hour or less, to 3 hours or more, will not be un radicals; R is a divalent hydrocarbon radical; X is usual. The course of the reaction can be followed by ex a halogen radical; a is an integer equal to from 1 to amining samples of the reaction mixture periodically by 3, inclusive; b is a whole number which has a value by use of a vapor phase chromatograph. The resulting 30 equal to 0 to 2, inclusive; c is a whole number which organosilicon hydride is recovered from the mixture by has a value equal to 0 to 2, inclusive; d is a whole distillation, etc. number which has a value equal to from 0 to 2, in In order that those skilled in the art will better under clusive; e is a while number which has a value equal stand the present invention, the following nonlimiting to 0 to 2, inclusive; f is a whole number which has 35 a value equal to 0 to 2, inclusive; the sum of a and examples are given wherein all parts are by Weight unless b has a value equal to 1 to 3, inclusive; the sum of the contrary is stated: c and d has a value equal to 0 to 2, inclusive; and EXAMPLE 1. the sum of e and f has a value equal to 0 to 2, in clusive. To a slurry containing 9.6 parts of sodium hydride as 40 2. The method of claim 1 which further includes the a 57% suspension in mineral oil, and 50 parts of Xylene presence of an alkali metal hydride. and under a nitrogen atmosphere are added all at once 3. The process of claim 2 wherein the amount of said 16 parts of a 25% solution of sodium aluminum diethyl organometallic hydride provides from about 0.01 mole to hydride in xylene. The reaction mixture is then heated by about 1 mole of chemically combined hydrogen per mole an external source to 110° C. There is then added drop 45 of halogen chemically bonded to silicon metal. wise 50.6 parts of diphenyldichlorosilane. A very strong 4. The process of claim 2 wherein said alkaline metal exotherm occurs and the external heat source is removed. hydride is sodium hydride. The temperature is controlled by the rate of addition 5. The process of claim 4 wherein said organometallic of the diphenyldichlorosilane and is maintained between hydride is sodium diethyl aluminum hydride. 130 and 145° C. Towards the end of the addition, the 50 6. The method of claim 1 wherein Me is aluminum or temperature begins to drop and ends up at 125 C. After boron. this, heat is applied for an additional two hours to main 7. The method of claim 1 wherein L is sodium. tain the reaction temperature at 125 C. The reaction 8. The method of claim 1 wherein said organometallic mixture is then distilled, collected, and condensed. The hydride is sodium diethyl aluminum hydride. product as determined by the method of preparation, I.R. 55 9. The method of claim 1 wherein R is selected from spectrum, and VPC analysis is 93% diphenylsilane, 4% the group consisting of alkyl radicals of 1 to about 18 car diphenylmonochlorosilane and 2% diphenyldichlorosilane. bon atoms, aryl radicals of from about 6 to 14 carbon atoms, cyclo-alkyl radicals of from about 3 to 12 carbon EXAMPLE 2 atoms, aralkyl radicals of from 7 to about 18 carbon To a slurry containing 7.2 parts of sodium hydride as 60 atoms, and alkaryl radicals of from 7 to about 18 carbon a 49% suspension in mineral oil, and 50 parts mineral atoms, and mixtures thereof. oil and under a nitrogen atmosphere are added all at once 10. The process of claim wherein an inert organic sol 8 parts of a 25% solution of sodium aluminum diethyl vent is employed. hydride in xylene. No reaction was evident. The reaction 11. The process of claim 1 wherein said inert organic mixture is then heated by an external source to 110° C. 65 solvent is an aromatic hydrocarbon. There is then added dropwise 21.9 parts of hexyltrichloro 12. A method is accordance with claim 1 where the or silane. A very strong exotherm occurs and the external ganosilicon halide is an organohalosilane of the formula: heat source is removed. The temperature is controlled by the rate of addition of the chlorosilane and is maintained RaHSiX(4-a-b) between 95-115° C. Toward reaction completeness, ex 70 ternal heat is applied to maintain the reaction tempera where R is selected from monovalent hydrocarbon radi ture at 115° C. for two additional hours. Upon fractiona cals and halogenated monovalent hydrocarbon radicals;X tion there is obtained 10.4 parts hexyl silane at a boiling is a halogen radical; a is an integer equal to from 1 to 3, point between 118-122° C. This is a 90% yield. Its iden inclusive; b has a value equal to 0 to 2, inclusive; and the tification is confirmed by infrared analysis. 75 sum of a and b has a value equal to 1 to 3, inclusive. 3,704,261 7 8 13. A method in accordance with claim 1 wherein the References Cited organosilicon halide is a bis(halosilyl) hydrocarbon of the UNITED STATES PATENTS formula: 3,439,008 4/1969 Berger ------260-448.2 E X 3,496,206 2/1970 Berger ------260-448.2 E where R is selected from monovalent hydrocarbon radi 3,499,020 3/1970 Robinson ------260-448.2 E cals and halogenated monovalent hydrocarbon radicals; 3,607,896 9/1971 Michael ------260-448.2 E R’ is a divalent hydrocarbon radical; X is a halogen radi 3,607,897 9/1971 Michael ------260-448.2 E cal; c has a value equal to 0 to 2, inclusive; d has a value equal to from 0 to 2, inclusive; e has a value equal to 0 to 10 JAMES E. POER, Primary Examiner 2, inclusive; f has a value equal to 0 to 2, inclusive; the P. F. SHAVER, Assistant Examiner sum of c and d has a value equal to 0 to 2, inclusive; and the sum of e and f has a value equal to 0 to 2, inclusive. U.S. C. X.R. 14. The method of claim 1 wherein said organosilicon halide is diphenyldichlorosilane. 260-448.2 H. 15. The method of claim 1 wherein said organosilicon 5 halide is hexyl trichlorosilane.