Process for the production of trialkoxysilanes

Abstract: This invention is concerned with an improved process for producing trialkoxysilanes comprising (i) an activation step where metallic silicon and a copper catalyst are activated, (ii) a reaction step where an alcohol is contacted with metallic silicon and the copper catalyst to allow it to react with the metallic silicon and (iii) a purification step where reaction product obtained is separated and/or refined, which is characterized in that a halogenide is introduced into the reaction system and/or mixture in one or more of the above steps (i) to (iii). With the introduction of a halogenide, the lowering in the selectivity of trialkoxysilanes can be prevented, and the percentage of metallic silicon reacted can be increased. In addition, the trialkoxy­ silanes contained in the reaction product can be stabilized.

Description: This invention relates to a process for producing trialkoxysilanes. In particular, it relates to a process for producing trialkoxysilanes in which metallic silicon is reacted with an alcohol in the presence of a copper catalyst to obtain the desired products in a high yield. Trialkoxysilanes (e.g., trimethoxysilane, triethoxysilane, etc.) composed of a silicon atom bonded with three alkoxy groups and one hydrogen atom are highly unstable and reactive and, hence, undergo various reactions, such as addition, copolymerization, copolycondensation, disproportionation, etc., with other organic compounds, thereby yielding a variety of useful substances which can be utilized as raw materials for making silane coupling agents, coating agents, heat-resistant paints or silane gas to be used in the production of semiconductors. US-A-4088669 describes the preparation of organosilicon compounds by contacting activated silicon, a hydrocarbon ether and a halogen-containing catalyst in a closed system at elevated temperature. Known processes for producing trialkoxysilanes include the one in which trichlorosilane is reacted with an alcohol in accordance with the following equation: HSiCl₃ + 3ROH → HSi(OR)₃ + 3HCl (in which R represents an alkyl group) and the one in which metallic silicon is allowed to react with an alcohol in gas or liquid phase in the presence of a copper catalyst, whereby complicated reactions, including the following: (1) Si + 4ROH → Si(OR)₄ + 2H₂ (2) Si + 3ROH → HSi(OR)₃ + H₂ (3) Si + 2ROH → H₂Si(OR)₂ (4) Si + 2ROH → SiO₂ + 2RH (5) ROH + H₂ → RH + H₂O (6) Other products: (in which R represents an alkyl group) take place, depending on reaction conditions (see, e.g., Inorg. Chem., Vol. 9, No. 5, 1071-1075 (1970)). In the former process, desired trialkoxysilanes can be obtained only in a poor yield. The process also suffers from the problem that reactors used for the production are corroded by hydrogen halides produced as a by-product. It is thought that the corrosion occurs in accordance with the following mechanism: The by-product, i.e., hydrogen halides, react with alcohols to produce alkyl halides and water. The water so-produced hydrolyzes the raw material (trichlorosilane) and the products (tri- or tetra- alkoxysilanes), thereby forming polycondensation products. In the latter process, alcohols are used in general in an excessive amount in order to increase the reaction percentage (i.e., percentage reacted) and the reaction velocity of metallic silicon. In the case of a gas phase reaction, the reaction shown by the above formula (1) takes place predominantly, and reactions shown by the above formulas (4) (5) also take place because of high reaction temperature. Water formed in accordance with reaction formula (5) reacts with metallic silicon to form a film of silicic acid or silicon oxide (silica), or with the copper catalyst to form copper oxide. Because of this, both of them become inactive and the reactions terminate midway, thus causing the problems that the reaction percentage of metallic silicon becomes lower and that the desired trialkoxysilanes can be obtained in a poor yield. In cases where the latter process is carried out in a liquid phase, the reaction shown by formula (2) proceeds preferentially at the initial stage of the reaction and, hence, the desired trialkoxysilanes can be obtained with a good selectivity. However, with the progress of the reaction, the selectivity of trialkoxysilanes decreases gradually. It is therefore impossible to obtain the desired trialkoxysilanes in a satisfactorily high yield. The reason why the selectivity of trialkoxysilanes decreases with the progress of the reaction is not certain. It may however be explained as follows. Metallic silicon used in industries usually contains various impurities, for example, alkali metals and/or alkaline earth metals, in an amount not greater than ca. 1% by weight. Such impurites react with alcohols to form metal alcoholates which gradually accumulate with the progress of the reaction. With the increase in the quantity of accumulated metal alcoholates, the pH value of the reaction system gradually shifts from acidic to neutral or basic. Because of this, once formed trialkoxysilanes are converted into tetraalkoxysilanes. With regard to the yield, it is considered to be important to activate metallic silicon and copper catalysts to the highest level possible and to suppress the above-described reactions (4) and (5) to the lowest level possible, by carrying out the reaction at a relatively low temperature. The problems in the above liquid phase reaction can be solved by maintaining the acidity in the reaction system at a constant level, by using highly pure metallic silicon which is substantially free from the undesirable side reactions of alcohols with the impurities. However, purification of metallic silicon is highly time consuming and costly and, hence, it is virtually impossible to use highly pure metallic silicon which is pure enough not to cause the adverse effects in the production of trialkoxysilanes on a commercial scale. The process in which metallic silicon is directly reacted with alcohols in gas or liquid phase in the presence of a copper catalyst also suffers from the problem that the reaction percentage of the alcohols is not high enough and, hence, the resulting reaction mixture contains large quantitis of unreacted alcohols, together with the desired trialkoxysilanes and other alkoxysilanes, such as tetraalkoxysilanes, dialkoxysilanes, dialkoxyalkylsilanes, trialkoxyalkylsilanes and dimers of these. In addition, the unreacted alcohols contained in the reaction mixture react with the desired trialkoxysilanes, thereby forming tetraalkoxysilanes, and the desired trialkoxysilanes undergo disproportionation to form dialkoxysilanes and tetralkoxysilanes in the course of purification or during storage before purification. As a result, the yield of trialkoxysilanes is markedly lowered. Various methods have been proposed to solve the above problems. For example, the reaction product is stored at a temperature lower than 0°C, or a certain amino acid is added to the reaction mixture for its stabilization (see Japanese Patent Application (Laid Open) No. 72,197/80); an amine is added to the reaction mixture and its pH is adjusted to 2.0 to 7.0 (see Japanese Patent Application (Laid Open) No. 118,592/82; or trivalent organic phosphates (Japanese Patent Application (Laid Open) No. 21,478/86) or epoxides (Japanese Patent Application (Laid Open) No. 1,694/86) are added to the reaction mixture. However, in cases where the temperature of the reaction mixture obtained is stored at 0°C or below, refrigerators or freezers are required for its cooling. This makes its storage quite costly. In addition, the reaction mixture must be heated at the time when it is to be refined by means of rectification, which most likely results in decomposition of trialkoxysilanes. In cases where amino acids, amines, trivalent organic phosphates or epoxides are used as a stabilizer, refined trialkoxysilanes obtained by the distillation of the reaction mixture tend to be contaminated by the stabilizers used. In addition to this, those stabilizers did not always perform satisfactorily in preventing the reaction of trialkoxysilanes with unreacted alcohols. Or the disproportionation of trialkoxysilanes at the time of rectification of the reaction product, could not be sufficiently suppressed by the use of those stabilizers. In any case, the known stabilizers are by no means satisfactory. In view of the above, the present inventors have conducted intensive investigations. As a result, it has now been found that, in the production of trialkoxysilanes comprising an activation step where metallic silicon and a copper catalyst are activated, a reaction step where an alcohol is contacted with metallic silicon and the copper catalyst so as to allow it to react with the metallic silicon and a purification step where the reaction mixture obtained is refined, the lowering in the selectivity of trialkoxysilanes can be prevented during the progress of the reaction, metallic silicon can be reacted at a high percentage and the trialkoxysilanes contained in the reaction mixture can be stabilized, by introducing a halide into, and allowing it to contact with, the reaction system and/or mixture in one or more of said steps. It is therefore an object of the invention to provide a process for producing trialkoxysilanes wherein not only metallic silicon can be reacted at a high percentage but also the selectivity of trialkoxysilanes can be enhanced, and hence trialkoxysilanes can be produced at a high yield. It is another object of the invention to provide a method for producing trialkoxysilanes wherein trialkoxysilanes contained in the reaction mixture can be stabilized and, hence, the reaction mixture can be easily rectified to give a highly pure trialkoxysilanes at a high yield. It is a further object of the invention to provide a process for producing trialkoxysilanes wherein, in its activation step, metallic silicon and a copper catalyst are brought into contact with a halide in a gas or liquid phase, in order to increase the percentage of metallic silicon reacted and to improve the selectivity of trialkoxysilanes through the activation of the metallic silicon and the catalyst. It is a still further object of the invention to provide a process for producing trialkoxysilanes wherein, in its reaction step where metallic silicon is reacted with an alcohol, a halide is introduced into the reaction system, so as to improve both the percentage of metallic silicon reacted and the selectivity of trialkoxysilanes. It is a further object of the invention to provide a process for producing trialkoxysilanes wherein, in its purification step, a halide is added to the reaction mixture containing unreacted alcohols, so as to stabilize trialkoxysilanes contained therein. Accordingly, there is provided by the invention a process comprising an activation step where metallic silicon and a copper catalyst are activated, a reaction step where an alcohol is contacted with metallic silicon and the copper catalyst so as to allow it to react with metallic silicon and a purification step where the reaction mixture obtained is purified, in which a halide is introduced into, and allowed to contact with, the reaction system and/or mixture in one or more of said steps. In the present invention, a halide can be introduced and contacted in one of the production steps, including said activation, reaction and purification steps, or in all of the steps. It can be preferable to activate metallic silicon and a copper catalyst by allowing a halide to contact with them in a gas or liquid phase in the activation step. It can also be preferable to add a halide to the reaction system in said reaction step or to add it to the reaction mixture that contains unreacted alcohols in said purification step. Metallic silicon to be used as a raw material in the process of the invention may have a purity of 80% by weight or above and may be in the form of granules having an average particle size not greater than 200 µm. It is possible to use, for example, commercially available low price products having a purity of from 80 to 99% by weight and an average particle size of 50 to 100 µm which may be produced by use of a vibrating mill, a ball mill, or the like. Usually, such a commercially available metallic silicon contains metals, such as Fe, Ca, Mg, Zn, Al, Ti, Cr, Ni, Mn, Ba, Cu and Zr, in an amount up to ca. 1% by weight, or at least in the order of parts per million. Alcohols to be used as a raw material in the process of the invention include alkyl alcohols. It can be preferable to use alkyl alcohols having 1 to 6 carbon atoms, for example, methyl alcohols ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, amyl alcohol and the like. These alcohols may have a purity of no less than 98% by weight, preferably 99.9% by weight or above and a water content not higher than 0.2% by weight, preferably not higher than 0.1% by weight. In ordinary cases, alcohols can be used in an amount of from 3 to 10 mol, per mol of metallic silicon. In order to improve the reaction percentage of metallic silicon (or percentage of metallic silicon reacted), it is preferable to use an excess of alcohol, preferably 4 to 8 mol, per mol of metallic silicon. In the process of the invention, there can be used known copper catalysts, including, e.g., powders of metallic copper, and compounds of copper, such as cuprous chloride, cupric chloride, cuprous bromide, cupric bromide, cuprous iodide, cupric iodide, cuprous fluoride, copper formate, acetylacetonatocopper, cuprous acetate, cupric acetate, cuprous oxide, cupric oxide, and the like. These catalysts can be used individually, or two or more of these can be used in combination. In usual cases, the copper catalysts are used in an amount of from 0.005 to 0.5 mol, preferably from 0.01 to 0.1 mol, per mol of metallic silicon. When the amount of copper catalysts is less than 0.005 mol, a lowering in the reaction percentage of metallic silicon will be resulted, whereas even if a copper catalyst is used in an amount exceeding 0.5 mol, no improvements will be attained in the reaction percentage of metallic silicon and in the selectivity of trialkoxysilanes, which is disadvantageous from economic view point. The copper catalysts may be premixed with metallic silicon and then subjected, prior to their use, to a heat treatment in nitrogen atmosphere at a temperature of from 200 to 600 °C, preferably from 200 to 400 °C, or in an appropriate solvent at a temperature of from 100 to 500 °C, preferably from 200 to 400 °C, for the purpose of their activation. Halides to be used in the process of the invention may be either organic halides or inorganic halides. It can however be preferable to use organic halides. As examples of usable organic halides, mention may be made of alkyl halides, such as methyl chloride, methyl bromide, methyl fluoride, methyl iodide, ethyl chloride, ethyl bromide, ethyl fluoride, ethyl iodide, n-propyl chloride and n-propyl bromide; alkenyl halides, such as dichloromethane and dichloroethane; aryl halides, such as chlorobenzene and dichlrobenzene; and other organic acid halides, such as chloroform, carbon tetrachloride, acetyl chloride, and the like. As examples of usable inorganic halides, mention may be made of hydrogen halogenides, such as hydrogen chloride, hydrogen bromide, hydrogen fluoride and hydrogen iodide ammonium halides, such as ammonium chloride, ammonium bromide, ammonium fluoride and ammonium iodide; other organic compounds, such as trimethylamine hydrochloride, trimethylamine hydrobromide, triethylamine hydrochloride,triethylamine hydrobromide; halogenated quaternary alkyl ammoniums such as tetramethylammonium chloride and tetramethylammonium bromide; and choline chloride and choline bromide. It is preferred to use an organic halide which is an alkyl halide having an alkyl group identical to that of the trialkoxysilane used. The amount of halides to be used varies, depending on the step where it is to be introduced. In the case where metallic silicon and a copper catalyst are subjected to activation in a gas or liquid phase, by allowing them to contact with a halide, the halide is used in usual cases in an amount of from 0.0001 to 1 mol, preferably from 0.001 to 0.5 mol, per mol of metallic silicon. When the amount is less than 0.0001 mol, the metallic silicon and copper catalyst will not be activated sufficiently. In addition to this, alcoholates of alkali and alkaline earth metals, which are contained as impurities in metallic silicon, will be formed in greater amounts, thus making the reaction system basic and, hence, causing a lowering in the selectivity of trialkoxysilanes. On the other hand, when the amount of halide used is greater than 1 mol, the reaction system becomes excessively acidic, and a lowered selectivity of trialkoxysilanes will be resulted. It is also disadvantageous from economic view point. In the case where a halide is introduced in the reaction step, the halide is used usually in an amount of from 0.0001 to 1 mol, preferably from 0.001 to 0.5 mol, per mol of alcohol. When the amount is less than 0.0001 mol, alcoholates of alkali or alkaline earth metals, which are contained as impurities in metallic silicon, are formed, thus making the reaction system neutral or basic and, hence, causing a lowering in the amount of trialkoxysilanes formed. On the other hand, when the amount is greater than 1 mol, the reaction system becomes excessively acidic, and a lowered selectivity of trialkoxysilanes will be resulted. It is also disadvantageous from economic view point. In cases where a halide is introduced in the activation or reaction step, it can be employed in a pure form. It can however be advantageous, with regard to convenience in handling and in the control of volume, to introduce a halide in the form of a mixture with an inactive gas (e.g., nitrogen gas) or hydrogen gas. In the case where a halide is added to the reaction mixture containing unreacted alcohols, the halide is used usually in an amount of from 0.0001 to 20% by weight, preferably from 0.001 to 10% by weight, more preferably from 0.01 to 6% by weight, based on the weight of the reaction mixture obtained. When the amount of halide used is less than 0.0001 %, it will not be possible to attain a sufficient stabilization effect, whereas when it is used in an amount greater than 20% by weight, no additional stabilizing effect will be attained. It is disadvantageous from economic view point. In the case where the process of the invention is carried out in a liquid phase, any solvent can be used if it is stable in the reaction system and can be heated to the required reaction temperature. As examples of usable solvents, mention may be made of various hydrocarbons, including paraffinic hydrocarbons, such as octane, decane, dodecane, tetradecane, hexadecane, octadecane, eicosane, etc.; hydrocarbons of alkylbenzene series, such as ethylbenzene, trimethylbenzene, cymene, diethylbenzene, butylbenzene, butyltoluene, octylbenzene, dodecylbenzene, didodecylbenzene, etc., and hydrogenated derivatives thereof; hydrocarbons of diphenyl series, such as diphenyl, diphenyl ether, monoethyldiphenyl, diethyldiphenyl, triethyldiphenyl, etc., and hydrogenated derivatives thereof; hydrocarbons of alkylnaphthalene series and hydrogenated derivatives thereof; hydrocarbons of triphenyl series and hydrogenated derivatives thereof; and the like. It is possible to use one single solvent or to use more than one solvent in combination. Of these solvents, those which do not generate foams in the course of the reaction and have a boiling point of from 100 to 500 °C, preferably from 200 to 400 °C, at ordinary pressure can be preferable. Although it is possible to use different solvents for the activation step and for the reaction step, it is preferable to use the same solvent for both of the steps since it can be advantageous to carry out those two steps continuously. In cases where a halide is allowed to contact with metallic silicon and a copper catalyst in a liquid phase, so as to effect their activation, the process of the invention can be carried out, for example, in the following manner. Into a reactor equipped with a stirrer, an alcohol introduction tube, a halide introduction tube, a product flow-out tube and a thermometer are charged metallic silicon, a copper catalyst and a reaction solvent. While an inactive gas (e.g., nitrogen) or hydrogen gas is being blown, if necessary, into the reactor, a halide or a mixture of a halide and an inactive gas or hydrogen gas is introduced thereinto with stirring at the boiling point of the solvent (usually which is in the range of from 100 to 500 °C), preferably at a temperature of from 200 to 400 °C, whereby the metallic silicon and the copper catalyst are allowed to contact with the halogenide for a certain period of time, for the purpose of their activation. If desired, the heating is continued under an atmosphere of an inactive gas or hydrogen gas for their ripening. After the completion of the activation treatment, an alcohol is introduced into the reactor at a constant rate through the alcohol introduction tube, so as to allow it to react with the metallic silicon, and the reaction products that flow out of the product flow-out tube are cooled by a condenser connected to the outlet thereof, to collect the desired trialkoxysilanes and unreacted alcohols. It can be preferable to use, in this step, an alcohol containing a small quantity of halide or to introduce, through the halide introduction tube, a small quantity of halide, which may or may not be diluted with an inactive gas or hydrogen gas, so as to maintain the pH of the reaction system and the desired trialkoxysilanes flowing out of the reactor in the range of from 1 to 6, preferably from 2 to 4. This makes it possible to further improve the selectivity of trialkoxysilanes. In cases where metallic silicon and a copper catalyst are allowed to contact with a halide in a gas phase in order to effect the activation thereof, there can be used known vertical-type or horizontal-type reactors in accordance with conventional methods. In this case, the activation treatment can be effected by introducing a halide, which may or may not be diluted with an inactive gas or hydrogen gas, into a reactor charged with metallic silicon and a copper catalyst and heated to a temperature of from 150 to 650 °C, preferably from 200 to 400 °C. It can be preferable to continue the heating with continued introduction of an inactive gas or hydrogen gas for a predetermined period of time, so as to ripen the contents of the reactor. When the metallic silicon is consumed by the reaction with an alcohol following the activation step, it is possible to charge into the reactor an additional amount of metallic silicon (and an additional amount of copper catalyst may also be charged thereinto although it is not required in ordinary cases), and the same activation and reaction steps can be repeated, so as to repeatedly produce desired trialkoxysilanes in the same reactor. In cases where a halide is added to the reaction system, the process of the invention can be carried out, for example, in the following manner. Into a reactor equipped with a stirrer, an alcohol introduction tube, an organic halide introduction tube, a product flow-out tube and a thermometer are charged powders of metallic silicon, a solvent and a copper catalyst. If desired, the powders of the metallic silicon and the copper catalyst can be ripened by allowing them to contact each other with stirring under nitrogen atmosphere for a predetermined period of time at a temperature of from 100 to 300 °C. Thereafter, an alcohol and an organic halide are introduced into the reactor through the alcohol introduction tube and the halide introduction tube, respectively, at a constant rate, and the reaction products that flow out of the product flow-out tube are cooled by a condenser connected to the outlet thereof, so as to collect the desired trialkoxysilanes and unreacted alcohols. In cases where a halide is added in the purification step to the resulting reaction mixture containing unreacted alcohols, the process of the invention can be carried out, for example, in the following manner. After the completion of the reaction of metallic silicon with an alcohol which is carried out in the presence of a copper catalyst, a certain amount of halide is added to the resulting reaction mixture, and desired trialkoxysilanes are purified by distilling the reaction mixture in the presence of the halide. The halide can be added to the reaction mixture either immediately after the completion of the reaction of the metallic silicon with the alcohol, or just before the distillation of the reaction mixture. It can however be preferable to add it into the reaction mixture immediately after the completion of the reaction. It is presumed that reactions set forth below take place in the system when metallic silicon and a copper catalyst are subjected to activation through contact with a halide. CuCl + Si → SiCl₄ + Cu 2Cu + RCl → CuCl + RCu 3(Si + 2RCl) → R₂SiCl₂ + RSiCl₃ + R₃SiCl Because of the above reactions, metallic silicon and copper catalysts can be activated, and their reactivity with alcohols can be enhanced. In addition, undesirable side reactions can be suppressed and, hence, the reaction percentage of metallic silicon and the selectivity of trialkoxysilanes can be improved. Moreover, alcoholates which may be generated by the reaction of alcohols with alkali metals and/or alkaline earth metals, which are contained in metallic silicon as impurities, can be neutralized by halide or by the combination of metallic silicon, copper catalyst and halide. Accordingly, the reaction system can always be maintained in an acidic state. This prevents once formed trialkoxysilanes to be converted into tetraalkoxysilanes and contributes to maintain the selectivity of trialkoxysilanes to a high level. In addition, the stability of the reaction products can also be improved, although the reason for the stabilization effect has not been theoretically elucidated. Taking the above into consideration, it is assumed that reactions as set forth below take place in the system. (1) Si + 2RCl → RSiCl₃ + R₂SiCl₂ + R₃SiCl (in which R is an alkyl group, such as methyl, ethyl, etc.) (2) (RSiCl₃ + R₂SiCl₂ + R₃SiCl) + ROH → R x Si(OR) y Cl z + yHCl (in which x, y and z are 1, 2 or 3) (3) RCl + MOR → MCl + ROH (in which M is a metal, such as Ca, Al, Zn, Mg, Na, K, Ni, Ba, etc.) (4) 2Cu + RCl --- CuCl + RCu The invention will further be explained by way of examples and comparative examples. Example 1 Into a 500 ml reactor equipped with a stirrer, an alcohol introduction tube, a halide introduction tube, a product flow-out tube and a thermometer were charged 150 g of metallic silicon having a purity of 98 wt% and an average particle size of ca. 50 µm [impurities: Fe, 0.83 wt%; Ca, 0.35 wt%; Mg, 150 ppm; Zn, 320 ppm; Al, 0.60 wt%; Ti, 860 ppm; Cr, 40 ppm; Ni, 43 ppm; Mn, 240 ppm; Ba, 50 ppm; Cu, 32 ppm; and Zr, 180 ppm (determined by ICP emission spectral analysis)], 300 ml of hydrocarbons of alkylbenzene series having boiling points of from 280 to 300 °C (AB-HL marketed by Mitsubishi Petrochemical Co., Ltd.) and 7.5 g of cuprous chloride. A condenser was attached to the outlet of the flow-out tube. While being stirred, the contents of the reactor were heated up to 200 °C over a period of 60 minutes, during which nitrogen gas was introduced into the reactor at a rate of 30 ml/min. Subsequently, 20 ml/min of nitrogen gas and 10 ml/min of gaseous methyl chloride were introduced thereinto at a temperature of from 200 to 260 °C for a period of 10 hours, and then the introduction of methyl chloride was stopped and the contents were ripened at a temperature of 200 to 230 °C for a period of 4 hours, with continued introduction of nitrogen gas at a rate of 20 ml/min. After the activation of the metallic silicon and the cuprous chloride, liquid methyl alcohol of 99.9 wt% purity or above was introduced into the reactor through the alcohol introduction tube at a rate of 25 g/hr and, at the same time, 2 ml/min of gaseous methyl chloride and 10 ml/min of nitrogen gas were introduced thereinto through the halide introduction tube, during which the reaction temperature was maintained at 160 to 170 °C. This reaction was continued for 40 hours, and the reaction product flowing out of the product flow-out tube was cooled by the condenser connected to its outlet. There was obtained 980 g of reaction product. The thus obtained reaction product contained 46.4 wt% of desired trimethoxysilane, 9.5 wt% of tetramethoxysilane, 39.1 wt% of unreacted methyl alcohol, 0.2 wt% of dimethoxysilane, 0.6 wt% of methyldimethoxysilane, 1.1 wt% of methyltrimethoxysilane, a total of 1.1 wt% of three different kinds of dimers, and 3.0 wt% of the solvent (determined b) gas chromatography). The reaction percentage of the metallic silicon (i.e., percentage of metallic silicon reacted) was 81.0% by weight, and the selectivity of trimethoxysilane was 88.2% by mol. The reaction product was charged into a container and tightly sealed. After being allowed to stand for 15 days at 20 °C, it was again analyzed by gas chromatography. There was observed no change in its composition. This proves that the reaction product is highly stable. Comparative Example 1 Example 1 was repeated, except that metallic silicon and cuprous chloride were not subjected to the activation treatment using methyl chloride. There was obtained 970 g of reaction product. The thus obtained reaction product contained 25.1 wt% of desired trimethoxysilane, 24.2 wt% of tetramethoxysilane, 46.1 wt% of unreacted alcohol, and 4.6 wt% of other compounds. The reaction percentage of the metallic silicon was 66.3% by wegiht, and the selectivity of trimethoxysilane was 56.7% by mol. Example 2 Into a Pyrex glass tube of 30 mm diameter were charged 150 g of metallic silicon and 7.5 g of cuprous chloride, both the metallic silicon and the cuprous chloride used being the same as those used in Example 1. It was heated by a band heater up to 250 °C over 2 hours, during which nitrogen gas was passed therethrough at a rate of 20 ml/min. Subsequently, 20 ml/min of nitrogen gas and 10 ml/min of gaseous methyl chloride were introduced thereinto at a temperature of from 250 to 300 °C for a period of 4 hours. Then, the heating and the introduction of gaseous methyl chloride were stopped, and the contents were ripened for 3 hours with introduction of 20 ml/min of nitrogen gas, during which the temperature of the contents was dropped to 50 °C. The thus obtained metallic silicon and cuprous chloride were placed in a reactor, and methyl alcohol was introduced under the same conditions as in Example 1. There was obtained 990 g of reaction product. The thus obtained reaction product contained 44.5 wt% of desired trimethoxysilane, 10.3 wt% of tetramethoxysilane, 37.6 wt% of unreacted methyl alcohol, and 2.2 wt% of other compounds (determined by gas chromatography). The reaction percentage of the metallic silicon was 80.4% by weight, and the selectivity of trimethoxysilane was 84.3% by mol. Example 3 Into an 8 liter stainless steel reactor similar to the one used in Example 1 were charged 2 kg of metallic silicon, 100 g of cuprous chloride and 4 liters of hydrocarbons of alkylbenzene series, the three components used being the same as those used in Example 1. While being stirred, 20 ml/min of nitrogen gas and 10 ml/min of gaseous methyl chloride were introduced into the reactor at a temperature of 200 to 260 °C for a period of 6 hours, and then 30 ml/min of nitrogen gas and 10 ml/min of gaseous methyl chloride were introduced thereinto at a temperature of 200 to 230 °C for a period of 6 hours. The heating and the introduction of methyl chloride were stopped, and the contents were ripened for 2 hours with continued introduction of 30 ml/min of nitrogen gas, during which the temperature of the contents was dropped to 160 °C. After the activation of the metallic silicon and the cuprous chloride, liquid methyl alcohol was introduced into the reactor at a rate of 145 g/hr and, at the same time, 3 ml/min of gaseous methyl chloride and 20 ml/min of nitrogen gas were introduced thereinto through the halide introduction tube, during which the reaction temperature was maintained at 160 to 170 °C. This reaction was allowed to continue for 40 hours to obtain 5,750 g of product for the first reaction. The thus obtained product contained 71.0 wt% of trimethoxysilane, 18.5 wt% of tetramethoxysilane, 5.1 wt% of unreacted methyl alcohol, and 4.5 wt% of other compounds (determined by gas chromatography). The reaction percentage of the metallic silicon was 56.7 % by weight, and the selectivity of trimethoxysilane was 82.7 % by mol. Subsequently, liquid methyl alcohol was introduced into the reactor at a rate of 94 g/hr for a period of 30 hours under the same conditions as above, to obtain 2,680 g of product for the second reaction. The thus obtained product contained 51.2 wt% of desired trimethoxysilane, 33.8 wt% of tetramethoxysilane, 9.8 wt% of unreacted methyl alcohol, and 0.5 wt% of other compounds (determined by gas chromatography). The overall reduction percentage of the metallic silicon for the first and second reaction was 80.7 % by weight, and the overall selectivity of trimethoxysilane was 65.5 % by mol. After the completion of the second reaction, 1.5 Kg of metallic silicon was charged into the reactor (no additional copper catalyst was charged), and the contents were subjected to the same activation treatment as above. Thereafter, liquid methyl alcohol was introduced thereinto at a rate of 140 g/hr and, at the same time, gaseous methyl chloride and nitrogen gas were introduced at a rate of 3 ml/min and 20 ml/min, respectively, during which the reaction temperature was maintained at 160 to 180 C. This reaction was continued for 30 hours to obtain 4,100 g of reaction product for the third reaction. The thus obtained product contained 68.0 wt% of desired trimethoxysilane, 21.0 wt% of tetramethoxysilane, 7.8 wt% of unreacted methyl alcohol, and 3.2 wt% of other compounds (determined by gas chromatography). The reaction percentage of the metallic silicon was 53.2% by weight (based on the quantity of the additional metallic silicon), and the selectivity of trimethoxysilane was 80.1% by mol. Subsequently, liquid methyl alcohol was introduced into the reactor at a rate of 90 g/hr for a period of 25 hours under the same conditions as above, to obtain 2,140 g of product for the fourth reaction. The thus obtained reaction product contained 50.0 wt% of trimethoxysilane, 31.0 wt% of tetramethoxysilane, 11.6 wt% of unreacted methyl alcohol, and 7.4 wt% of other compounds. The overall reaction percentage of the metallic silicon for the third and fourth reactions was 78.4% by weight (based on the quantity of the additional metallic silicon), and the overall selectivity of trimethoxysilane was 67.3% by mol. Comparative Example 2 The first and second reactions of Example 3 were repeated under the same conditions, except that methyl chloride was not introduced in the activation treatment of metallic silicon and cuprous chloride and the reaction temperature was maintained at 200 °C. There were obtained 5,680 g of product in the first reaction and 2,590 g of product in the second reaction. The product of the first reaction contained 29.0 wt% of desired trimethoxysilane, 33.4 wt% of tetramethoxysilane, 32.5 wt% of unreacted methyl alcohol, and 5.1 wt% of other compounds, and the product of the second reaction contained 21.2 wt% of desired trimethoxysilane, 31.4 wt% of tetramethoxysilane, 39.4 wt% of unreacted methyl alcohol, and 8.0 wt% of other compounds. The overall reaction percentage of the metallic silicon for the first and second reactions was 50.2% by weight, and the selectivity of trimethoxysilane was 46.4% by mol. Example 4 Example 1 was repeated, except that ethyl alcohol was used in place of methyl alcohol and ethyl chloride was used in place of methyl chloride, said ethyl alcohol being supplied at a rate of 25 g/min and the temperature of the reaction being maintained at 200 to 220 °C. There was obtained 940 g of reaction product. The thus obtained product contained 43.2 wt% of desired triethoxysilane, 15.4 wt% of tetraethoxysilane, 35.3 wt% of unreacted ethyl alcohol, and 6.1 wt% of other compounds (determined by gas chromatography). The reaction percentage of the metallic silicon was 60.2% by weight, and the selectivity of triethoxysilane was 78.4% by mol. Comparative Example 3 Example 4 was repeated, except that ethyl chloride was not introduced in the activation step. There was obtained 930 g of reaction product. The thus obtained product contained 17.1 wt% of triethoxysilane, 21.0 wt% of tetraethoxysilane, 54.8 wt% of unreacted ethyl alcohol, and 7.1 wt% of other compounds (determined by gas chromatography). The reaction percentage of the metallic silicon was 35.0% by weight, and the selectivity of triethoxysilane was 50.3% by mol. Example 5 Example 1 was repeated, except that hydrogen chloride was used in place of methyl chloride for the activation of metallic silicon and cuprous chloride. There was obtained 955 g of reaction product. The thus obtained product contained 45.5 wt% of desired trimethoxysilane, 10.6 wt% of tetramethoxysilane, 38.5 wt% of unreacted methyl alcohol, and 5.4 wt% of other compounds (determined by gas chromatography). The reaction percentage of the metallic silicon was 78.9% by weight, and the selectivity of trimethoxysilane was 84.2% by mol. Example 6 Into a 500 ml reactor equipped with a stirrer, an alcohol introduction tube, an organic halogenide introduction tube, a product flow-out tube and a thermometer were charged 150 g of metallic silicon having an average particle size of ca. 50 µm, 300 ml of hydrocarbons of alkylbenzene series and 7.5 g of cuprous chloride, as in Example 1. A condenser was attached to the outlet of the product flow-out tube. While being stirred, the contents of the reactor was heated to 200 to 250 °C and the metallic silicon was allowed to contact with the cuprous chloride for a period of 5 hours, during which nitrogen gas was introduced at a rate of 100 ml/min. Thereafter, liquid methyl alcohol of 99.9 wt% purity or above was introduced into the reactor at a rate of 30 ml/hr through the alcohol introduction tube, and gaseous methyl chloride at a rate of 20 ml/min through the halide introduction tube, thereby maintaining the reaction temperature at 180 °C. This reaction was continued for 40 hours, and the reaction product flowing out of the product flow-out tube was cooled by the condenser connected to its outlet. There was obtained 1,040 g of reaction product. The composition of the thus obtained product was analyzed by gas chromatography. It contained 44.33 wt% of desired trimethoxysilane, 8,75 wt% of tetramethoxysilane, and 46.92 wt% of unreacted methyl alcohol. The reaction percentage of the metallic silicon was 81% by weight, and the selectivity of trimethoxysilane was 86% by mol. The reaction product was charged into a container and tightly sealed. After being allowed to stand for 4 days at 18 °C, it was again analyzed by gas chromatography. There was observed no change in its composition. This proves that the reaction product is highly stable. Example 7 In a porcelain mill, 500 g of powders of metallic silicon and 25 g of cuprous chloride were pulverized and admixed for 8 hours, both the metallic silicon and the cuprous chloride being the same as those used in Example 6. The resulting mixture was charged into a silica tube and heated at 600 °C for 3 hours under nitrogen atmosphere, thereby using an electric furnance. Into a stainless steel reactor having a diameter of 10 cm and a height of 23 cm and equipped with a stirrer, an alcohol introduction tube, an organic halide introduction tube, a product flow-out tube and a thermometer were charged the mixture of the metallic silicon and the cuprous chloride prepared above, and 900 ml of hydrocarbons of alkyl benzene series having a boiling point of 280 ∼ 300 °C, the same solvent as the one used in Example 6. Liquid methyl alcohol of 99.9 wt% purity or above was introduced into the reactor at a rate of 30 ml/hr and, at the same time, gaseous methyl chloride was introduced thereinto at a rate of 30 ml/min,during which the reaction temperature was maintained at 180 °C as in Example 6. This reaction was continued for 100 hours, and the product flowing out of the product flow-out tube was cooled by a condenser connected to its outlet. There was obtained 2,350 g of reaction product. The composition of the thus obtained reaction product was analyzed as in Example 6. It contained 57.45 wt% of desired trimethoxysilane, 12.38 wt% of tetramethoxysilane, and 30.17 wt% of unreacted methyl alcohol. The reaction percentage of the metallic silicon was 72% by weight, and the selectivity of trimethoxysilane was 85% by mol. After being allowed to stand in a tightly sealed container at 16 °C for 5 days, the product was again analyzed by gas chromatography. There was observed no change in its composition. This proves that the reaction product is highly stable. Comparative Example 4 Example 6 was repeated, except that methyl chloride was not introduced at all. There was obtained 1,050 g of reaction product. The composition of the thus obtained reaction product was analyzed as in Example 6. It contained 11.52 wt% of desired trimethoxysilane, 23.33 wt% of tetramethoxysilane, and 65.15 wt% of unreacted methyl alcohol. The reaction percentage of the metallic silicon was 49% by weight, the selectivity of trimethoxysilane was 38% by mol. After being allowed to stand in a tightly sealed container at 18 °C for 4 days, the composition of the reaction product was again analyzed by gas chromatography. The content of desired trimethoxysilane decreased to 5.06% by weight, and the content of tetramethoxysilane increased to 29.81% by weight. Comparative Example 5 Example 7 was repeated, except that methyl chloride was not introduced at all. There was obtained 2,460 g of reaction product. The composition of the thus obtained reaction product was analyzed as in Example 6. It contained 16.87 wt% of desired trimethoxysilane, 39.84 wt% of tetramethoxysilane, and 43.29 wt% of unreacted methyl alcohol. The reaction percentage of the metallic silicon was 55% by weight, and the selectivity of trimethoxysilane was 35% by mol. After being allowed to stand in a tightly sealed container at 16 °C for 5 days, the composition of the reaction product was again analyzed by gas chromatography. The content of desired trimethoxysilane decreased to 8.33% by weight, and the content of tetramethoxysilane increased to 48.34% by weight. Example 8 In a porcelain mill, 100 g of powders of metallic silicon and 5 g of cuprous chloride were pulverized and admixed for 8 hours, both the metallic silicon and cuprous chloride being the same as those used in Example 6. The resulting mixture was charged into a silica tube and heated at 600 °C for 3 hours under nitrogen atmosphere, thereby using an electric furnance. Into a 500 ml reactor equipped with a stirrer, an alcohol introduction tube, an organic halide introduction tube, a product flow-out tube and a thermometer were charged the mixture of the metallic silicon and the cuprous chloride prepared above, and 300 ml of hydrocarbons of alkylbenzene series having a boiling point of from 280 to 300 °C, the same solvent as the one used in Example 6. A liquid ethyl alcohol containing 2.5% by weight of ethyl chloride was introduced into the reactor at a rate of 30 ml/hr, during which the temperature inside of the reactor was maintained at 200 °C. This reaction was continued for 20 hours, and the product flowing out of the product flow-out tube was cooled by a condenser connected to its outlet. There was obtained 400 g of reaction product. The composition of the reaction product obtained was analyzed as in Example 6. It contained 35 wt% of desired triethoxysilane, 11 wt% of tetraethoxysilane, and 40 wt% of unreacted ethyl alcohol. The reaction percentage of the metallic silicon was 30% by weight, and the selectivity of triethoxysilane was 80% by mol. Comparative Example 6 Example 6 was repeated, except that ethyl chloride was not introduced at all. There was obtained 420 g of reaction product. The composition of the thus obtained reaction product was analyzed as in Example 6. It contained 7 wt% of desired triethoxysilane, 24 wt% of tetraethoxysilane, and 71 wt% of unreacted ethyl alcohol. The reaction percentage of the metallic silicon was 18% by weight, and the selectivity of triethoxysilane was 26% by mol. Example 9 In a porcelain mill, 500 g of metallic silicon having an average particle size of 200 µm and 25 g of cuprous chloride were pulverized and admixed for 2 hours. The resulting mixture was charged into a silica tube and heated at 600 °C for 3 hours under nitrogen atmosphere, thereby using an electric furnance. Into a stainless steel reactor having a diameter of 10 cm and a height of 23 cm and equipped with a stirrer, an alcohol introduction tube, a nitrogen introduction tube, a product flow-out tube and a thermometer were charged the mixture of metallic silicon and the cuprous chloride prepared above, and 1,000 liters of the same hydrocarbons of alkylbenzene series as the one used in Example 1. The reaction was allowed to proceed for 80 hours at a temperature of from 170 to 180 °C, during which 30 ml/hr of methyl alcohol having a purity of 99.9 wt% or above and 20 ml/min of nitrogen gas were introduced into the reactor, and 2,280 g of reaction mixture was recovered through the product flow-out tube. The reaction mixture contained 13.3 wt% of methanol, 60.8 wt% of trimethoxysilane, 21.5.wt% of tetramethoxysilane, and 4.4 wt% of other compounds (determined by gas chromatography). The reaction percentage of the metallic silicon was 81.g % by weight, and the selectivity of trimethoxysilane was 77.9% by mol. The thus obtained reaction mixture was divided into two portions. To one portion (Mixture A) was added 23 g (ca. 2% by weight) of methyl chloride, whereas nothing was added to the other portion (Mixture B). The Mixtures A and B were separately fractionated, by means of distillation, into initial fraction (which had a boiling point up to 60 °C), main fraction (which had a boiling point of from 79 to 81 °C), post fraction (which had a boiling point of from 120 to 122 °C), and residue. Each of them were analyzed by gas chromatography. Results of the fractionation are shown in Table 1, and the results of the chromatographic analysis are shown in Table 2. Example 10 To a reaction mixture obtained in a similar manner as in Example 9 was added methyl chloride, to obtain a mixture having the following composition: trimethoxysilane, 50 wt%; tetramethoxysilane, 20 wt%; unreacted methyl alcohol, 25 wt%; methyl chloride, 1.5 wt%; and other compounds, 3.5 wt%. The resulting mixture was charged into a stainless steel container fitted with a calcium chloride cylinder at its gas outlet. It was allowed to stand in a room maintained at a temperature of 15 to 20 °C. The composition of the mixture was analyzed by gas chromatography at an interval of 10 days, in order to examine the changes, with the lapse of time, in the content of trimethoxysilane and tetramethoxysilane. Results obtained are shown in Table 3. Test Example 1 A sample mixture was prepared by adding 32 g of methyl alcohol and 4.6 g (2.9 wt%) of methyl chloride to 122 g of trimethoxysilane of 99 wt% purity. The changes, with the lapse of time, in the content of trimethoxysilane and tetramethoxysilane were determined as in Example 10. Results obtained are shown in Table 3. Test Example 2 A sample mixture was prepared in a similar manner as in Test Example 1, except that methyl chloride was not added at all. The changes in the content of trimethoxysilane and tetramethoxysilane were determined with the lapse of time. Results obtained are shown in Table 3. Test Example 3 A sample mixture was prepared by adding 46 g of ethyl alcohol and 6.3 g (2.9 wt%) of ethyl chloride to 164 g of triethoxysilane of 99 wt% purity. The changes, with the lapse of time, in the content of triethoxysilane and tetraethoxysilane were determined as in Example 10. Results obtained are shown in Table 3. Test Example 4 A sample mixture was prepared in a similar manner as in Test Example 3, except that ethyl chloride was not added at all. The changes in the content of triethoxysilane and tetraethoxysilane were determined with the lapse of time. Results obtained are shown in Table 3.

Claims: A process for producing trialkoxysilanes comprising an activation step where metallic silicon and a copper catalyst are activated, a reaction step where an alcohol is contacted with metallic silicon and the copper catalyst so as to allow it to react with the metallic silicon and a purification step where the reaction mixture obtained is purified, in which a halide is introduced into, and allowed to contact with, the reaction system and/or mixture in one or more of said steps. A process for producing trialkoxysilanes as defined in claim 1, wherein said metallic silicon and said copper catalyst are activated in said activation step by allowing them to contact with a halide in a liquid or gas phase. A process for producing trialkoxysilanes as defined in claim 2, wherein said activation is carried out in a liquid phase at a temperature of 100 to 500 °C. A process for producing trialkoxysilanes as defined in claim 2, wherein said activation is carried out in a gas phase at a temperature of 150 to 650 °C. A process for producing trialkoxysilanes as defined in claim 2, wherein said halide is an organic halide. A process for producing trialkoxysilanes as defined in claim 5, wherein said organic halide. is a member selected from the group consisting of alkyl halides, alkenyl halides and aryl halides. A process for producing trialkoxysilanes as defined in claim 2, wherein said halide is an inorganic halide. A process for producing trialkoxysilanes as defined in claim 7, wherein said inorganic halide is a hydrohalide. A process for producing trialkoxysilanes as defined in claim 2, wherein said halide is used in an amount of 0.0001 to 1 mol, per mol of said metallic silicon. A process for producing trialkoxysilanes as defined in claim 1, wherein a halide is added to the reaction system in said reaction step where said metallic silicon is reacted with said alcohol. A process for producing trialkoxysilanes as defined in claim 10, wherein said halide is an organic halide. A process for producing trialkoxysilanes as defined in claim 11, wherein said organic halide is a member selected from the group consisting of alkyl halides, alkenyl halides and aryl halides. A process for producing trialkoxysilanes as defined in claim 10, wherein said halide is used in an amount of 0.0001 to 1 mol, per mol of said alcohol. A process for producing trialkoxysilanes as defined in claim 1, wherein said halide is added in said purification step to said reaction mixture containing unreacted alcohol. A process for producing trialkoxysilanes as defined in claim 14, wherein said halide is an organic halide. A process for producing trialkoxysilanes as defined in claim 15, wherein said organic halide is one or more members selected from the group consisting of alkyl halides, alkenyl halides, aryl halides and halogenated quaternary alkyl ammoniums. A process for producing trialkoxysilanes as defined in claim 16, wherein said organic halide is an alkyl halide of which alkyl group is identical with the alkyl group of said trialkoxysilanes. A process for producing trialkoxysilanes as defined in claim 14, wherein said halide is used in an amount of 0.0001 to 20% by weight, based on the amount of said reaction mixture. A process for producing trialkoxysilanes as defined in any of claims 1 to 18, wherein said alcohol is a lower alcohol. A process for producing trialkoxysilanes as defined in any of claims 1 to 18, wherein said reaction of said metallic silicon with said alcohol is carried out at a temperature of 100 to 300 °C.

Inventors: OHTA YOSHIRO, YOSHIZAKO MAMORU, OHTA, YOSHIRO, YOSHIZAKO, MAMORU
Applicants: TAMA CHEMICALS CO LTD, TAMA CHEMICALS CO., LTD.
Application year: 1988
Main classification: C07F7
IPC codes: C07F7