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United States Patent Office Patented May 19, 1959 2 Other Objects of the Invention Will Become Apparent from the Following Description Thereof

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United States Patent Office Patented May 19, 1959 2 Other Objects of the Invention Will Become Apparent from the Following Description Thereof 2,887,501 United States Patent Office Patented May 19, 1959 2 Other objects of the invention will become apparent from the following description thereof. 2,887,501 All the foregoing objects and other advantages can be PREPARATION OF HIGHER ALKYLATED ALKYTL obtained if an alkyl halide is passed over silicon in contact HALOGENOSLANES with calcium in which the calcium comprises from 10-80% of the total weight of the latter and the silicon. Ben A. Bluestein, Schenectady, N.Y., assignor to General The alkyl halides employed in the present invention Electric Company, a corporation of New York may be any one of those employed in making alkyl halo No Drawing. Application December 26, 1956 genosilanes. Among these may be mentioned methyl Serial No. 630,460 10 chloride, ethyl chloride, methyl bromide, propyl bro mide, etc. 4 Claims. (C. 260-448.2) The calcium may be mechanically mixed with the sili con to form a mixed powder in which the particles of the silicon and calcium have average particle size diameters This invention is concerned with a process for prepar 5 of from 44 to 400 or more microns. Generally, it is de ing silanes containing a plurality of silicon-bonded alkyl sirable for many purposes that at least 90% of the silicon groups. More particularly, the invention relates to the and calcium particles range in average particle size diam preparation of alkyl halogenosilanes containing substan eter of from 105-250 microns; stated alternatively it is tial quantities of trialkyl halogenosilanes as well as tetra desirable that they have a mesh size of from about alkyl silanes, which comprises effecting reaction at an 100-200 when sifted through sieves of the United States elevated temperature in the presence of a hydrogen halide Standard Sieve Series (ASTM Standard) as is more par between a lower alkyl halide and a mixture of silicon and ticularly recited in Gilliam et al. Patent 2,466,413. Alter calcium, wherein the calcium comprises, by weight, from natively, the calcium and silicon may be employed in the 10 to 80% of the total weight of the calcium and the form of an alloy which is then crushed and powdered silicon. 25 to the desirable particle size suitable for carrying out In Rochow Patent 2,380,995, issued August 7, 1945, the reaction. Whether in the form of mixed powders or and assigned to the same assignee as the present inven as an alloy, the proportion of calcium, by weight, should tion, there is disclosed and broadly claimed a method of be within the range of from about 10-80% of the total preparing organohalogenosilanes by the reaction of an weight of the calcium and the silicon. organic halide and silicon. When an alkyl halide, for in 30 Various promoters for the reaction between the alkyl stance, methyl chloride, is passed over heated silicon or halide and the mixture of silicon and calcium are ad mixtures of silicon and copper as described in the afore vantageously incorporated including copper, zinc, and mentioned Rochow patent, there is obtained a complex mixtures of copper and zinc. When employing copper as mixture of products containing substantial quantities of the promoter it is desirable that the latter comprises, by methyltrichlorosilane and dimethyldichlorosilane, and 35 weight, from about 2 to 20% of the silicon. When using trace amounts of trimethylchlorosilane and other higher zinc as the promoter (which promoter is more particularly alkylated silanes such as tetramethylsilane. disclosed in Gilliam Patent 2,464,033 issued March 8, Higher alkylated alkyl silanes, such as trimethylchloro 1949), the zinc is advantageously present in an amount silane, triethylchlorosilane, tetramethylsilane, tetraethyl equal to from about 0.05 to 0.5%, based on the weight silane, tripropylbromosilane, etc., are in large demand. 40 of the silicon. Thus, the trimethylhalogenosilanes are useful in the prep The temperature at which reaction is effected is ad aration of organopolysiloxane lubricating fluids for vantageously above 250 C. up to the temperature of de chain-stopping purposes, for instance, to form trimethyl composition of the reactants and reaction products. Tem siloxy groups at the end of linear organopolysiloxanes peratures of about 275 to 400° C. are usually preferable employed as lubricating fluids. The preparation of such from an overall yield viewpoint. Anhydrous conditions chain-stopped organopolysiloxanes is more particularly are required in order to minimize loss of alkylsilanes due described in Patnode Patents 2,469,888 and 2,469,890, to hydrolysis of the silicon-bonded halogen by moisture both issued May 10, 1949, and assigned to the same as in the air. signee as the present invention. It has unexpectedly been found that when passing the The tetra-alkyl silanes are desirable because they can alkyl halide over the mixture of the silicon and calcium, be readily redistributed in the presence of suitable catalysts it is necessary to activate the latter materials before any with phenylhalogenosilanes to give the very desirable alkyl detectable yields of alkyl halogenosilanes are obtained phenylhalogenosilanes, which have been found to be an by passing a hydrogen halide (preferably in the gaseous advantageous intermediate in the preparation of high and anhydrous state) over the metallic powder. Among temperature organopolysiloxane resins and lubricating 55 the hydrogen halides which may be employed are, for fluids. instance, hydrogen chloride, hydrogen bromide, etc. It The primary object of the present invention is to pro is desirable that the halogen of the hydrogen halide be vide a process for producing mixtures of alkylhalogeno the same as the halogen of the alkyl halide in order to silanes containing substantial quantities of the trialkyl avoid obtaining alkyl halogenosilanes in which the silicon derivative as well as increased amounts of the tetra-alkyl 60 has attached thereto different halogens. The amount of silane. hydrogen halide used in the reaction will vary depend Another object of the invention is to provide a method ing upon such factors as the concentration of the calcium, for increasing the yield of trialkyl halogenosilanes such as temperature of the reaction, presence or absence of pro trimethylchlorosilane, trimethylbromosilane, triethyl moters, etc. In general, I have found that where the tem chlorosilane, etc., obtained from the reaction of a lower 65 perature during the course of the reaction is well above alkyl halide such as methyl chloride, methyl bromide, 300 C., the amount of hydrogen halide used may vary ethyl chloride, etc., and silicon preferably in the presence from about 5-25%, by weight, of the alkyl halide. Where of a metallic catalyst for the silicon-alkyl halide reaction. temperatures below 300° C. are employed, care should Another object of the invention is to obtain increased be exercised that the activation of the calcium-silicon 70 mixture should be effected by the use of adequate amounts yields of tetra-alkyl silanes from the reaction of a lower of the hydrogen halide. In general, once activation of alkyl halide and silicon. the calcium-silicon mixture has taken place by passage 2,887,501 3. 4 of the hydrogen halide over the latter mixture (whether chloride were used. The following Table I shows the it constitutes a mixture of calcium and silicon powders, temperature of the reaction, the amounts of methyl chlo or an alloy of calcium and silicon), the passage of the ride and hydrogen chloride used, as well as the yields of hydrogen halide may be discontinued. The passage of the various methyl silanes obtained in the reaction the hydrogen halide may occur simultaneously with the 5 product. Table I 1 Percent Yields Test No. Temp., Parts Parts o C. CHCl HCl (OH)4Si (CH)SiCl (CH3)2SiCl, CHSiCls CESiHC 1---------------- 325 3. 2 8,8 44.2 30.8 9, 6 1.6 2---------------- 300 9. 5 7.6 6, 6 3, 7. 9 4.8 1 in the above table, the balance of the reaction product comprised SiCl, HSiCl3, and snail amounts of other silanes. passage of the alkyl halide by bringing effluent streams It will of course be apparent to those skilled in the art, of gasses of the two materials together and passing then that in place of the alkyl halide described above, other simultaneously over the calcium-silicon mixture. alkyl halides many examples of which have been given In order that those skilled in the art may better under- 20 above, may be employed without departing from the stand how the present invention may be practiced, the scope of the invention. In place of the alloy of silicon following examples are given by way of illustration and and calcium one may employ mixtures of powders of sili not by way of limitation. All parts are by weight. con and calcium as well as other proportions of the cal In the following examples, the calcium and silicon cium and silicon in whatever physical state used. Like employed were in the form of an alloy crushed to about 25 wise, the temperatures of reaction and proportions of -60 mesh (average particle size diameter of about 149- ingredients may be varied within wide limits without de 250 microns) in which the calcium comprised about 31 parting from the scope of the invention. At tempera percent and the silicon 61 percent of the alloy, the re- tures of from 200-250 C., reaction proceeds much more mainder being small amounts of impurities. Anhydrous slowly than at temperatures of around 300-400 C. In conditions were maintained throughout. 30 addition it will be understood by those skilled in the art, EXAMPLE 1. that metallic catalysts other than copper may be em ployed to accelerate or control the course of the reaction In this example 63 parts of the calcium-silicon alloy in between the alkyl halide and the silicon.
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