US3160647A - Alkylation of dialkoxy monohalo silanes - Google Patents

Description

United States Patent Ofl ice 3,166,647 Patented Dec. 8, 1964 3,16%,647 ALKYLATIGN F DIALKGXY MGNGHALG SELANES This invention relates to, and has as its chief objective, the provision of a novel alkylation process which is especially adapted for the preparation of alkyl trialkoxysilanes.

According to this invention alkyl trialkoxysilanes are prepared by maintaining a mixture of an alkali metahan alkyl halide and a tri-substituted silane at a temperature in the range of about 50 to about 200 C. suihcient to effect alkylation of the silane. The tri-substituted silanes which are used as one of the reactants in the present process can be represented by the formula I-iSi(0R) X wherein R is an alkyl group of up to about 12 carbon atoms, X is a halide, n is an integer from 2 to 3, inclusive, and m is an integer from 0 to 1, inclusive, n+m being equal to 3.

The alkali metals are generally useful in conducting this process. Hence, recourse may be had to lithium, sodium, potassium, rubidium, cesium and various alkali metal alloy mixtures such as sodium-potassium alloy and the like. Metallic sodium is the preferred alkali metal reagent because of its low cost and availability and because of the very good results obtained by its use. However, metallic potassium is also a very effective reagent, as are mixtures of sodium and potassium. When using lithium, sodium, potassium or various alloys thereof it is preferable to employ a temperature at which the alkali metal reagent is in the liquid state. However, if desired the alkali metal can be used in the form of a dispersion or sand.

A wide variety of alkyl halides can be used in the present process. Preferably these contain from 1 to about 12 carbon atoms although higher alkyl halides (e.g. compounds containing up to about 18 or more carbon atoms) can be used. The principles of this invention likewise extend to the use of cycloalkyl halides as these materials give generally equivalent results. Alkylfluorides and alkyliodides may be used but it is preferable to use alkyl halides of the middle halogensi'.e. alkyl chlorides and alkyl bromidessince these materials, especially the alkyl chlorides, provide the best results. The use of tertiary alkyl halides, preferably tertiary alkyl bromides and tertiary alkyl chlorides is likewise preferred because the resultant tertiary alkylated silane product is not only very useful in the chemical and allied arts but is produced in excellent yield.

A particularly desirable embodiment of this invention is to use metallic sodium and an alkyl chloride, especially a tertiary alkyl chloride. In this way the desired alkyl trialkoxysilanes are produced in the highest yields at the lowest cost.

Reference to the above general formula relative to the tri-substituted silane will show that there are two specific types thereof which are used pursuant to this invention. One type of tri-substituted silane has the formula HSi(OR) wherein R is an alkyl (or cycloalkyl) group, preferably containing up to about 12 carbon atoms.

The other type of tri-substituted silane has the formula HSi(OR) X wherein R is an a kyl (or cycloalkyl) group, preferably containing up to about 12 carbon atoms and X is a halide, preferably bromide or chloride, most preferably chloride.

From our experimental work it appears that the proportions of the several ingredients of our reaction mixture are not critical. However, when using the unhalogenated tri-substituted silane reagents the best yields of desired alkyl trialkoxysilanes are favored by using from about 2 to about 5 moles of such tri-substituted silanes per mole of the alkyl halide. When using the halogenated tri-substituted silane reagents the best yields of desired product occur when there is used at least about 1 mole (e.g. from about 1 to about 5 moles) of alkyl halide per mole of such halogenated tri-substituted silane. When using either type of tri-substituted silane reagent it is generally helpful to use an excess of alkali metal relative to the amount of alkyl halide employed. It will be understood, however, that departures from the foregoing ranges consistent with the principles of this invention may be made without departing from the spirit and scope thereof. Such permissive deviations will now be apparent to those skilled in the art.

In conducting the present process it is unnecessary to employ a reaction solvent or diluent. In other words, excellent results have been achieved simply by co-mingling the several reagents and maintaining them under the conditions described above. it is thereupon a relatively simple matter to recover the desired alkyl trialkoxysilane from the reaction mixture by standard separation techniques, as for example, fractional distillation, solvent ex traction, chromotography, or like procedures. However, Where greater control of temperature is desired recourse may be had to inert organic solvents or diluents. For this purpose hydrocarbons which are liquid under the reaction conditions are generally preferable although use can be made of inert ethers and related materials. Of the preferred hydrocarbon diluents it is desirable to use compounds which are generally inert to alkali metals under the conditions of this process, and thus effective use can be made of paraflinic hydrocarbons, cycloparaffins and inert aromatics (e.g. benzene, tert.-butyl benzene, etc). Petroleum ethers, hexanes, heptanes, octanes, nonanes, decane, undecanes, dodecanes, cyclohexanes, cycloneptanes, cyclooctanes, and the like, serve as examples of the preferred paraflins or cycloparaflins.

As described above, the process of this invention'is conducted at a temperature in the range of about 50 to about 200 C. suflicient to effect alkylation of the trisubstituted silane reagent. In general, the process tends to be somewhat exothermic and, therefore, in some instances it is unnecessary to apply heat to the reaction mixtures. However, when somewhat higher temperatures are desired the reaction can be readily controlled by the application of heat. The precise temperature for optimum results is in general a function of the nature of the several reagents employed in formulating our reaction systems. For example, when using lithium and the relatively less reactive alkyl halides it is desirable to employ temperatures approaching the upper end of the range described. Conversely, when using the more reactive alkali metal species, notably sodium or potassium, and the more reactive alkyl halides, e.g. the chlorides,

lower temperatures can be. used to good advantage. Those skilled in the art will now understand the principles to be followed relative .to the. temperature conditions for use in achieving the maximum benefits of this invention. As a rule of thumb, however, very excellent resultshave been achieved at temperatures of about to about C. especially when using sodium and tertiary alkyl chlorides. For this reason these particular temperatures are preferred.

Our work has shown that benefits are achieved by agitating the reaction mixture so as to provide good mixing of and contact among the reactants. For example we have found it desirable to equip the reaction vessel with stirring means operated at speeds of as high as 5,000 r.p.m. Nevertheless this agitation procedure is unnecessary as the reaction will proceed even when the reactants are maintained in a relatively quiescent state.

This invention will be still further understood by reference to the following specific examples in which all percentages are by weight.

EXAMPLE I To 19.5 g. (0.85 mole) of molten sodium in 172.2 g. (1.05 moles) of triethoxysilane was added 32.3 g. (0.35 mole) of tert.-butyl chloride. Rapid stirring (5,000 r.p.m.) was employed, and the temperature of the reaction mixture was maintained at 110 C. by the rate of addition. After the addition was complete, the reaction mixture was heated at 110 C. for one-half hour and filtered. There was no condensate in the Dry Ice-acetone trap. Distillation gave no distillate boiling in the triethoxysilane range, Bl. 134 C. The boiling point of the material collected was 160-169 C. Gas chromatography revealed that 41.0 g. (53.3 percent yield) of tert.-butyl triethoxysilane had been produced, the identity of this product having been established by comparison with an authentic sample of tert.-butyl triethoxysilane prepared in an independent synthesis. A lesser quantity of tetraethoxysilane was also detected in the product.

Repetition of the above general procedure using in one instance tert.-butyl bromide and potassium metal and in another instance tert.-butyl iodide and cesium metal in place of the tert.-butyl chloride and sodium metal results in the formation of the same principal productviz. tert.- butyl triethoxysilane. Similarly, substitution of the equivalent amounts of 2-chloro-2,3-dimethylbutane, n-amyl bromide, n-decyl iodide and isopropyl bromide for the tert.-butyl chloride in the above procedure results in the formation respectively of 1,1,2-trimethylpropyl triethoxysilane, amyl triethoxysilane, decyl triethoxysilane and isopropyl triethoxysilane.

EXAMPLE II The general procedure of Example 1 was repeated using 0.15 mole of triethoxysilane, 0.15 mole of tert.-butyl chloride and 0.40 mole of sodium as the reactants. In this instance 2,2,5-trimethylhexane was used as reaction diluent. The reaction was conducted primarily at a temperature of 110 C. Tert.-buty1 triethoxysilane was produced in 22 percent yield.

Repetition of the procedure of Example 11 using in one instance tripropoxysilane and in another instance tridecoxysilane instead of the triethoxysilane results in the formation respectively of tert.-butyl tripropoxysilane and tert.-butyl tridecoxysilane.

A feature of the above embodiment in which a trialkoxysilane (HSi(OR) isused as a reactant is our finding that the product is of an entirely diiferent type as compared with the product produced when conducting the analogous reaction employing a tetra-substituted silane of the formula R'Si(OR) (R being an alkyl and R an alkyl or aryl group). In the latter instance an alkoxy group of the tetra-substituted silane is replaced by the alkyl group of the alkyl halide. This is demonstrated by the following comparative examples.

V COMPARATIVE EXAMPLE A To 19.5 g. (0.85 mole) of molten sodium and 207.9 g. (1.05 moles) of phenyltrirnethoxysilane in 200 ml. of 2,2,5-trimethylhexane was added slowly 32.3 g. (0.35 mole) of tert.-butyl chloride. The reaction mixture was was added at a rate that wouldmaintain a temperature of stirred rapidly (5,000 r.p.m.), and the tert.-butyl chloride 4 C. in the reaction mixture. After the addition was complete, the reaction mixture was maintained at C. for one-half hour. Filtration of the reaction mixture followed by distillation gave 162 g. of material distilling between 110124 C. at mm. Redistillation of this fraction gave a product boiling in the range of 220224 C. and containing 0.6 percent chlorine. Analysis of this distillate by gas chromatography gave 20 mole percent of starting material-ire. phenyl trimethoxysilane (identified by an authentic sample)-1and 80 mole percent of phenyl tert.- butyl dimethoxysilane (identified by its infrared spectrum). I

COMPARATIVE EXAMPLE B The same general procedure of Comparative Example A was repeated several times except that an approximately equivalent quantity of methyl trimethoxysilane, methyl trie'thoxysilane, or methyl triisopropoxysilane was used instead of the phenyl trimethoxysilane. The respective products of these runs were found to be tert.-'outyl methyl dimethoxysilane, tert.-butyl methyl diethoxysilane and tert.-butyl methyl diisopropoxysilane.

As seen from Comparative Examples A and B the use of tetra-substituted silane resulted in the replacement of an alkoxy group by an alkyl group from the alkyl halide alkylating agent; In contrast, the process of this invention results in the replacement of the hydrogen of the trisubstituted silane by the alkyl group, thereby producing an entirely different class of product.

EXAMPLE III The general procedure of Example I was repeated using 9.2 g. (0.4 mole) of sodium, 23.2 g. (0.15 mole) of chlorodiethoxysilane, and 13.9 g. (0.15 mole) of tert.- butyl chloride. Tert.-butyl triethoxysilane, 26.5 percent yield, was obtained as determined by gas chromatography analysis.

Repetition of the procedure described in Example III using in one instance bromodibutoxysilane and in another instance chlorodihexoxysilane instead of the chlo-' rodiethoxysilane produces tert.-butyl tributoxysilane and tert.-butyl trihexoxysilane respectively.

A feature of the above embodiment of this invention in which a halo tri-substituted silane (HSi(OR) X) is used as the silane reactant is that a rearrangement occurs in such a way as to produce a significant yield of the desired alkyl trialkoxysilane product. Another feature of this embodiment is the fact that when a halo tetrasubstituted silaneRSi(OR) X-is used in place of the halo tri-substituted' silaneHSi(OR) X-no reaction occurs. This is borne out by the Work summarized in the following table.

Tabie.Attempted Alkylation of Methyl Dialkoxy Halo 1 Sodium was employed as a dispersion. No tert.-butyl silicon product was detected in the reaction mixtures of Runs 1-3, inclusive. We conclude, there fore, that in the embodiment of this invention in which a halo tri-substituted silane is used (i.e. I-ISi(OR) X) the presence of the silicon-hydrogen bond is essential in order to effect the desired monoalkylation.

A wide variety of tri-substituted silanes and alkyl (or cycloalkyl) halides of the type described above are available for use in practicing the process of this invention.

Inasmuch as the nature of these materials is well known to those skilled in the art it would serve no useful purpose to set forth additional exemplifications thereof. Suffice it to say that when the various reactants of the type defined herein are combined and subjected to the reaction conditions noted above, the results characterizing this invention are accomplished.

While this invention has been discussed in relation to the use of an alkyl halide, and alkali metal and a trisubstituted silane as reactants, it will be understood that a preformed alkyl (or cycloalkyl) alkali metal compound (RM, R being an alkyl or cycloalkyl group of up to about 12 carbon atoms and M being an alkali metal) can be used along with the tri-substituted silane. In short, instead of using the combination of an alkali metal and an alkyl halide one can use an equivalent amount of the corresponding organo alkali metal compound. Thus in place of tert.-butyl chloride and metallic sodium use can be made of tert.-butyl sodium for reaction with the various tri-substituted silanes in order to produce the corresponding tert.-butyl trialkoxy silanes.

The silanes produced by our process have, inter alia, the various utilities described in US. Patent 2,985,678, the entire disclosure of which is incorporated herein by the foregoing reference. For example, the alkyl trialkoxysilanes can be used in the production of siloxanes and other valuable silicon-containing compounds and/ or polymers. Consequently, the products formed by the present process are useful in the manufacture of engine and industrial lubricants and hydraulic fluids, heat exchange media and the like.

We claim:

1. A process of preparing alkyl trialkoxysilanes which comprises maintaining a mixture of an alkali metal, an alkyl halide and a tri-substituted silane at a temperature in the range of about 50 to about 200 C. sutficient to effect alkylation of said silane and recovering said alkyl trialkoxysilane from the reaction mixture; said silane reactant being characterized by having the formula HSi(OR) X wherein R is an alkyl group of up to about 12 carbon atoms and X is a halide, said process being further characterized in that at least about one mole of said alkyl halide is used per mole of said silane.

2. A process according to claim 1 wherein said alkali metal is sodium.

3. A process according to claim 1 wherein said alkyl halide is an alkyl chloride.

4. A process according to claim 1 wherein said alkali metal is sodium and said alkyl halide is an alkyl chloride.

5. A process according to claim 1 wherein said alkyl halide is a tert.-alkyl halide.

6. A process according to claim 1 wherein said alkali metal is sodium and said alkyl halide is a tort-alkyl chloride.

7. A process of preparing tert.-butyl triethoxysilane which comprises reacting sodium, tert.-butyl chloride and diethoxychlorosilane at a temperature in the range of about to about C., and recovering said tort.- butyl triethoxysilane from the reaction system, said process being further characterized in that about one mole of tert.-butyl chloride is used per mole of diethoxychlorosilane.

References Cited in the file of this patent UNITED STATES PATENTS 2,444,784 Meals July 6, 1948 2,521,267 Tiganik Sept. 5, 1950 FOREIGN PATENTS 573,906 Great Britain Dec. 12, 1945 OTHER REFERENCES Friedel et al.: Annalen der Chemie, vol. 143, 1867, pages 124-7.

Chappelow et a1: Jour. of Organic Chem, vol. 27, April 1962, pages 1409-14.

Eaborn: Organosilicon Compounds, Academic Press Inc., New York, publ., 1960, pages 19-31.

Peake et a1.: Jour. Am. Chem. 800., vol. 74 (1952), pp. 1526-8.

Claims (1)

1. A PROCESS OF PREPARING ALKYL TRIALKOXYSILANES WHICH COMPRISES MAINTAINING A MIXTURE OF AN ALKALI METAL, AN ALKYL HALIDE AND A TRI-SUBSTITUTED SILANE AT A TEMPERATURE IN THE RANGE OF ABOUT 50 TO ABOUT 200*C. SUFFICIENT TO EFFECT ALKYLATION OF SAID SILANE AND RECOVERING SAID ALKYL TRIALKOXYSILANE FROM THE REACTION MIXTURE; SAID SILANE REACTANT BEING CHARACTERIZED BY HAVING THE FORMULA