United States Patent (19) 11 4,297,500 Finke et al. 45 Oct. 27, 1981

(54 CONVERSION OF LOW-BOILING 2,752,379 6/1956 Wagner et al...... 556/466 CONSTITUENTS FROM Primary Examiner-Paul F. Shaver ALKYL-CHLOROSLANE SYNTHESIS Attorney, Agent, or Firm-Sprung, Felfe, Horn, Lynch 75) Inventors: Ulrich Finke, Ettlingen; & Kramer Hans-Heinrich Moretto, Cologne, both of Fed. Rep. of Germany 57) ABSTRACT 73 Assignee: Bayer Aktiengesellschaft, A process for converting the low-boiling constituents Leverkusen, Fed. Rep. of Germany formed in the preparation of methylchlorosilane to the Miller-Rochow process and which consist essentially (21) Appl. No.: 209,932 of tetramethylsilane, dimethylmonochlorosilane and (22 Filed: Nov. 24, 1980 2-methylbut-2-ene into a product mixture consisting essentially of trimethylchlorosilane, dimethylchlorosi 30) Foreign Application Priority Data lane and C2-20 alkyldimethylchlorosilanes or C6-10 Dec. 14, 1979 IDE Fed. Rep. of Germany ...... 295.0402 aryldimethylchlorosilanes, comprising contacting the 51) Int. Cl...... C07F 7/08 low-boiling product mixture with AlCl3, AlOCl and/or 52 U.S. Cl...... 556/466; 556/478 AlBr3, together with hydrogen chloride, in the liquid 58) Field of Search ...... 556/466,478 phase at about 40 to +25° C. The mixture prior to conversion may be contacted with HCl and either 56) References Cited ZnCl2 or active charcoal and/or an olefin may be added U.S. PATENT DOCUMENTS thereto. 2,500,652 3/1950 Barry et al...... 556/466 2,628,243 2/1953 Barry et al...... 556/466 4 Claims, No Drawings 4,297,500 1 2 Offenlegungsschrift 2,546,919). Furthermore, the use of CONVERSION OF LOW-BOILING pure TMS or enriched TMS fractions (containing at CONSTITUENTS FROM ALKYL-CHLOROSILANE least 50 percent by weight) is a precondition of the SYNTHESIS known processes and is associated with considerable 5 expenditure and appears uneconomical. However, these The present invention relates to a process for con processes are suitably exclusively for the conversion of verting low-boiling constituents from the synthesis of tetramethylsilane, of which only relatively low concen alkylchlorosilanes into more valuable products by cata trations are frequently found, in addition to dimethyl lytic treatment in the liquid phase at low temperatures. monochlorosilane, 2-methylbut-2-ene and other com The preparation of methylchlorosilanes by direct 10 pounds, in the product mixture obtained. The reaction synthesis (Rochow-Miller process) results in the un conditions chosen in the processes mentioned are un avoidable formation of a considerable proportion of suitable for realizing the conversions described here. low-boiling products with a boiling point <40 C. (760 The conversion of Me2SiHCl (Me = CH3-) into di mm Hg), such as, for example, tetramethylsilane (TMS) methyldichlorosilane by means of AlCl3/HCl or and dimethylmonochlorosilane, in addition to the de 15 AlCl3/CH3Cl or C2H5Cl which is likewise effected sired products methyltrichlorosilane, dimethyldichloro according to the invention is also surprising since dis silane and trimethylchlorosilane. TMS is of no further proportionation of Me HSiCl in the presence of AlCl3 importance for silicone chemistry since it carries no into Me2SiH2 and Me2SiCl2 was to be expected accord functional group on the silicon. TMS has hitherto there ing to MacDiarmid-Organometallic Compounds of fore been destroyed. In contrast to TMS, dimethyl 20 the Group IV Elements, volume 2, page 238. monochlorosilane has functional groups on the silicon A further advantage of the process according to the and is thus capable of further reactions, but preparation invention is the possibility of producing alkyl- or aryl of this compound in a pure form from the product mix dimethylmonochlorosilanes (alkyl=CnH2n-1 in which ture presents considerable difficulties because of the n=2-20), in addition to trimethylchlorosilane and dim presence of 2-methyl-but-2-ene, which has virtually the 25 methyldichlorosilane. same boiling point. For this reaction, the product mixture intended for It is thus an object of the invention to convert the the AlCl3/HCl reaction is treated with AlCl3 (or AlOCl product mixture obtained into compounds useful in or AlBr3) attemperatures from - 40' to +25°C. In this silicone chemistry and hence of increasing the yield of treatment, in the presence of 2-methylbut-1-ene or 2 valuable chlorosilanes without first having to carry out 30 methylbut-2-ene the Me2HSiCl is converted into pen expensive separation processes. tyldimethylmonochlorosilane which is an important It has been found, surprisingly, that the conversion of product. Such product does not undergo further reac the compounds contained in the product mixture, such tion under the conditions later prevailing so expensive as tetramethylsilane, dimethylmonochlorosilane and separation thereof can be spared. 2-methylbut-2-ene into the compounds which are im 35 If the product unavoidably obtained contains a molar portant in silicone chemistry, that is to say trimethyl excess of Me2SiHCl relative to olefin (which is fre chlorosilane, dimethyldichlorosilane and alkyldime quently the case), it is advantageous to add olefins for thylchlorosilanes, can be effected in a simple manner by example 2-methylbut-2-ene or any other olefin suitable reacting the product mixture with AlCl3, AIOCl and/or for this reaction, as required, in order to increase the AlBr3 and HCl in the liquid phase. yield of the desired alkyl- or aryl-dimethylmono The present invention therefore relates to a process chlorosilanes. for converting the low-boiling constituents which are Any fraction obtained in the Rochow-Miller process formed in the preparation of methylchlorosilane (Mill which has a boiling point of less than 40 C. can be er-Rochow process) and which essentially consist of employed in the process according to the invention as tetramethylsilane, dimethylmonochlorosilane and 2 45 the product unavoidably obtained. These fractions as a methylbut-2-ene into product mixtures essentially con rule contain tetramethylsilane, dimethylmonochlorosi sisting of trimethylchlorosilane, dimethylchlorosilane lane, 2-methylbut-1-ene and 2-methylbut-2-ene as the and alkyldimethylchlorosilanes (alkyl radical with 2 to main constituents. CH3Cl, ethyl chloride, 2-methylbu 20 C atoms) or aryldimethylchlorosilanes (aryl radical tane, SiCl3H and SiCl4 and other compounds are also with 6 to 10 Catoms), which is characterized in that the 50 present as by-products. The composition can vary low-boiling product mixture is brought into contact greatly and depends on the procedure in the Rochow with AlCl3, AlOCl and/or AlBr3, together with hydro synthesis and on the composition of the catalyst in this gen chloride, in the liquid phase at -40 C. to +25 C. process. In addition to the substances already mentioned, The amount of hydrogen chloride employed in the which essentially form the mixture, the starting mixture 55 process according to the invention can be determined can also contain methyl chloride, ethyl chloride, 2 by analysis of the content of the product mixture which methylbutane, silicon tetrachloride, silicochloroform reacts with HCl, that is to say tetramethylsilane, dime and 2-methylbut-2-ene. However, relatively small thylmonochlorisilane and in certain circumstances 2 amounts of these products are present. The end prod methylbut-2-ene. Molar amounts are required in each ucts can therefore also contain, for example, the follow 60 case. It is advantageous to use a slight excess of hydro ing compounds: hydrogen, methane, ethane and 2 gen chloride. The catalyst concentration depends on methylbutane. the desired procedure. In the case of a discontinuous It is particularly surprising that the reaction of tet procedure, a catalyst amount of about 0.1 to 1% by ramethylsilane with hydrogen chloride and AlCl3, weight, relative to the reaction mass, of AlCl3 (or AlOCl or AlBr3 to give trimethylchlorosilane also pro 65 AlOCl3 or AlBr3) is sufficient. In the case of continuous ceeds attemperatures of -40°C., since this reaction has operation, it is advantageous to use relatively high cata hitherto been carried out only at relatively high temper lyst concentrations in order to achieve high space/time atures (compare U.S. Pat. No. 2,802,852 and German yields. 4,297,500 3 4. The temperature at which the process according to relative to Me2HSiCl. the invention is carried out is preferably about - 40 C. Other reaction products are, inter alia, hydrogen, to +25° C., in particular about -30° C. to +20° C. methane and 2-methylbutane. The process according to the invention is preferably carried out under the pressure of the surrounding atmo- 5 Example 2 sphere. If desired, however, higher or lower pressures The unavoidably obtained product as in Example 1 is can also be applied. added dropwise to a mixture, cooled to 0°C., of 1 g of The conversions achieved in the process according to AlCl3 and 10g of pentane, without passing in HCl (max the invention are in general 90-100 mol%, in each case imum temperature: + 10 C.). When the exothermic relative to the reactants employed in the smallest 10 reaction has ended, HCl is passed in, while still cooling. amount. The reaction is ended when the reaction mixture takes The selectivity can be 90-100% for the conversion of up no further HCl. Consumption of HCl: ~0.58 mol. tetramethylsilane into trimethylchlorosilane. Yield: 98% of (CH3)3SiCl, relative to TMS, 20% of The selectivity for the conversion of Me2SiHCl into (CH3)2SiCl2, relative to Me2SiHCl and 98% of (CH3)2 dimethyldichlorosilane is between 90 and 98% in the 15 Pent SiCl, relative to 2-methylbut-2-ene reaction with AlCl3/HCl. The selectivity can be in creased to 100% if, according to a particular embodi CH3 CH3 ment of the process according to the invention, the product unavoidably obtained is simply treated with (Pent sa CH3-CH-CH ). ZnCl/HCl or active charcoal/HCl at temperatures of 2O up to about 40 C. before the reaction with AlCl3 or Example 3 AlCl3/HCl. No splitting of TMS into trimethyl 5 g of ZnCl2 are added to 100 g of the product un chlorosilane, as described in U.S. Pat. No. 2,802,852, avoidably obtained, and 0.2 mol of HCl is passed in. The takes place in this case. The process step of treatment 25 reaction temperature should not exceed 40° C. AlCl3 is with ZnCl2/HCl or active charcoal/HCl furthermore then added, while adding further HCl and cooling to enables Me2SiHCl which is free from 2-methylbut-2-ene -- 10 C. The amount of HCl to be added is about 0.58 to be separated off by distillation, the 2-methylbut-2-ene mol. being converted into amyl chloride, which has a lower Yield: 98.5% of (CH3)3SiCl, relative to TMS, 98% of volatility. Me2SiHCl can therefore be separated offin a (CH3)2SiCl2, relative to Me2HSiCl, and 0% of simple manner as required. The reaction products obtained in the process ac cording to the invention can be distilled in a simple th SH: (H, manner together with the methylchlorosilanes obtained Hic---ic in the reaction of silicon with methylchlorosilanes. H H CH3 The process according to the invention can be carried 35 out with or without solvents, as desired. Examples of In all the examples, HCl is added at a rate of about suitable solvents are saturated hydrocarbon fractions of 10-15 l/hour. which the boiling range does not lie within the boiling It will be appreciated that the instant specification range of the product or of a starting component which 4 and examples are set forth by way of illustration and not can be recovered. Low-boiling or high-boiling paraffin limitation, and that various modifications and changes oils, for example, can be employed. may be made without departing from the spirit and GENERAL INSTRUCTIONS scope of the present invention. We claim: The following reactions are carried out in the absence 45 1. A process for converting the low-boiling constitu of oxygen and moisture in a 0.5 four-necked flask with ents formed in the preparation of methylchlorosilane in an internal thermometer, a reflux condenser with a gas the Miller-Rochow process and which consist essen outlet, a dropping funnel and a gas inlet tube: tially of tetramethylsilane, dimethylmonochlorosilane and 2-methylbut-2-ene into a product mixture consisting Example 1 50 essentially of trimethylchlorosilane, dimethylchlorosi 100 g of a product which is unavoidably obtained and lane and C2-20 alkyldimethylchlorosilanes or C6-10-aryl contains 46% of TMS, 20% of MeSiHCl. 12% of 2 dimethylchlorosilanes, comprising contacting the low methylbut-2-ene and 3% SiCl3H, 1% CH3Cl, 13% Me boiling product mixture with AlCl3, AlOCl and/or SiCl2.H and 5% 2-methylbutane are added dropwise to AlBr3, together with hydrogen chloride, in the liquid a mixture of 1 g of AlCl3 in 10 ml of pentane, which is 55 phase at about 40 to +25 C. cooled to 0 and continuously saturated with HCl 2. A process according to claim 1, wherein the prod through the gas inlet tube, at a rate such that the tem uct mixture is contacted with the AlCl3, AlOCl and/or perature does not exceed 10° C. (cooling). The amount AlBr3 at about 40” to +25° C. in the liquid phase and of HCl added is 0.75 mol. the HCl is then added. Yield: 98% of Me3SiCl, relative to TMS, 96.5% of 60 3. A process according to claim 1, wherein a com Me2SiCl2, relative to Me2HSiCL, and 1.5% of pound with a C=C double bond is added to the product mixture before the conversion. CH3 CH 4. A process according to claim 1, wherein the prod Me uct mixture is contacted with HCl and at least one of HC-C-C-SiCl, Me 6S ZnCl2 and active charcoal at a temperature up to about H H - 40 C. before conversion. sk