Process for preparing isocyanatoorganosilanes

Abstract

The invention relates to a process for preparing isocyanato-functional organosilanes.

Description

Methods for the production of isocyanatoorganosilanes The invention relates to a process for the production of isocyanate-functional organosilanes. Organosilanes that possess both an isocyanate function and a reactive alkoxysilyl group can be reacted with almost any hydroxyl-functional polyol via their isocyanate function. Because of this property, they are important starting materials for the production of alkoxysilane-functional polymers. These polymers are products that can be cured via condensation reactions of their alkoxysilyl groups upon contact with atmospheric moisture and therefore represent ideal binders used in a wide variety of adhesives, sealants, and coatings. Of particular importance are alkoxysilane-terminated polypropylene glycols, which are accessible through a reaction of the isocyanate-functionalized alkoxysilanes with long-chain polypropylene glycols. The name hybrid polymers has now become established for this product group. If so-called α-isocyanatomethyl alkoxysilanes are used, i.e., compounds in which the reactive alkoxysilyl group is separated from the isocyanate function only by a methyl group, the corresponding α-alkoxysilane-terminated polymers are obtained. These are characterized by extremely high reactivity towards atmospheric moisture and—unlike most conventional silane-functional polymers—do not require tin catalysts for rapid reaction. Curing occurs at room temperature. Therefore, α-isocyanoatom ethyl alkoxysilanes are of particular importance. Various processes for the production of isocyanate-functional alkoxysilanes are known from the prior art. Suitable processes are described, among others, in EP 3221324, EP 3546465 or EP 3546468. In these processes, the corresponding amine-functional alkoxysilanes of formula (1) are reacted in a first reaction step. optionally reacted with dialky carbonate (EP 3221324 & EP 3546465) or a mixture of urea and an alcohol (EP 3546468) to give the corresponding carbamate-functional silanes (2). In a second reaction step, the respective isocyanate-functional silane (3) is then produced from the latter by thermolytic alcohol elimination. A disadvantage of these processes, however, is that the aminoalkyl alkoxysilanes required as starting materials are usually significantly more expensive than the corresponding chloralkyl alkoxysilanes. Furthermore, only 3-aminopropyl alkoxysilanes are commercially available in sufficiently large quantities, which limits the industrial applicability of these processes to isocyanate-functional silanes that also possess a propyl spacer between the isocyanate and alkoxysilyl functional groups. The aforementioned α-isocyanatomethyl alkoxysilanes, which are required for the production of highly reactive hybrid polymers, are currently not accessible on an industrial scale using these processes due to the lack of commercial availability of cc-aminomethyl alkoxysilanes. Only the corresponding oc-chloromethyl-alkoxysilanes are available on an industrial scale. Therefore, a method is desirable that would allow access to a wider range of different isocyanate-functional silanes, especially the og α-isocyanatomethyl-alkoxysilanes, starting from the corresponding chloroalkylsilanes. The first process step, the preparation of carbamate-functional silanes starting from the corresponding chloroalkyl silanes, has already been described, for example in EP 2455385. Here, the chloroalkyl alkoxysilanes are heated under reflux with potassium cyanate and an alcohol of the formula Dimethylformamide is preferably used as the solvent. The corresponding carbamatoalkyl alkoxysilanes and potassium chloride are formed as a coproduct. The solvent is then removed by distillation and the salt is filtered off. Preferably, a nonpolar solvent is added prior to the filtration step. Salts with poor solubility, e.g., toluene, are added and removed by distillation after the filtration step. In the examples of EP 2455385, this process is used both for the preparation of 3-carbamatopropyl alkoxysilanes, i.e., compounds of formula (2), and for the preparation of α-carbamatomethyl alkoxysilanes of formula (4). It is therefore logical that the carbamatoalkyl alkoxysilanes produced in this way can also be further processed to the corresponding isocyanate-functional alkoxysilanes using the known methods for thermolytic alcohol elimination. The corresponding α-isocyanate ethyl alkoxysilanes of formula (5) would also be accessible from the cc-carbamatomethyl alkoxysilanes of formula (4). However, a disadvantage of the process described in EP 2455385 for the preparation of carbamate-functional silanes of formulas (2) or (4) is the long reaction time required to achieve a high yield. This is all the more detrimental because the reaction must be carried out in a solvent that occupies a significant part of the reaction volume, which further reduces the space-time yield of this process step. In order to limit the scope of the description of the present invention to a reasonable extent, only the preferred embodiments of the individual features are listed below. The expert reader should understand this type of revelation to mean that every combination of different levels of preference is explicitly revealed and explicitly desired. The object of the present invention was therefore to develop a process for the production of isocyanate-functional organosilanes that no longer exhibits the disadvantages of the prior art. The invention relates to a process for the production of isocyanatoalkyl alkoxysilanes (SI) of general formula (6), OCN-R 2 -Si(R 3 ) 3-x (OR 4 )x (6) by a multi-stage process, with a 1st process step in which a haloalkyl alkoxysilane (SH) of general formula (7), XR 2-Si(R 3 ) 3-x (OR 4 )x (7) with a metal cyanate (MOCN) and an alcohol (A) of general formula (8), R 1 OH (8) to a carbamatoalkyl alkoxysilane (SC) of general Formula (9) R 1 O-CO-NH-R 2 -Si(R 3 ) 3-x (OR 4 ) x(9) is carried out, provided that this reaction is carried out partly or completely in the presence of a component (K) that increases the solubility of anions in the organic reaction mixture and is present in the reaction mixture in an amount of 0.05 to 5 wt% based on the mass of the total reaction mixture, a second process step in which the carbamatoalkyl alkoxysilane (SC) is purified by distillation, wherein distillation takes place in an evaporation unit (VD) in which the silane (SC) is evaporated in a layer thickness of no more than 5 cm, at a pressure of no more than 80 mbar and at temperatures of no more than 200°C, and a third process step in which the isocyanatoalkyl alkoxysilane (SI) is produced by thermolytic elimination of alcohol from the silane (SC), wherein R 1 , R 3 and R 4independently of each other, an unsubstituted or halogen-substituted hydrocarbon residue with 1-10 C atoms, R 2 a divalent unsubstituted or halogen-substituted hydrocarbon residue with 1-10 C atoms, which may be interrupted by non-adjacent oxygen atoms, X represents a halogen atom, and x represents a value of 0, 1, 2 or 3. Process steps 1 to 3 are carried out sequentially in the specified order. Naturally, the process according to the invention can also include further process steps in addition to process steps 1 to 3, e.g., further processing steps of the silane (SC) that take place between process steps 1 and 2. The remains R 1 , R 3 and R 4 They can be the same or different. Preferably, the residues are R. 1 in alcohol (A) and R 4in the halogen alkyl alkoxysilane (SH) of general formula (7) identical, because otherwise an exchange of the R groups would occur during the first process step. 4 can occur at the silicon atom. This would result in a mixture of different silanes (SC) of the general formula (9), in which the individual silane molecules have different R groups. 1 and different residues R 4 exhibiting, which is possible, but usually not desirable. Provided that halogen substituents are attached to the R groups 1 , R 2 , R 3 and R 4 If these are available, they are preferably selected from fluorine and chlorine. Preferably, the R groups are 1 , R 2 , R 3 and R 4 However, it is halogen-free. R 3 R preferably represents a methyl, ethyl, iso, or n-propyl group, with a methyl group being particularly preferred. 4preferably means for a methyl, ethyl, iso- or n-propyl group, with a methyl or ethyl group being particularly preferred. R 2 R preferably represents a propylene or, more preferably, a methylene residue. 1 preferably represents a methyl, ethyl, iso- or n-propyl group, with a methyl or ethyl group being particularly preferred. The variable x preferably represents 2 or 3, and in the case of the silanes (S-H) of general formula (7), X preferably represents a chlorine atom. The component (K) used in the first process step is preferably a crown ether and / or so-called phase transfer catalysts, with the use of phase transfer catalysts being particularly preferred. The component (K) can consist of a single or several individual compounds. Preferably, all individual compounds of component (K) are crown ethers and / or phase-transfer catalysts, in particular exclusively phase-transfer catalysts. Crown ethers are cyclic ethers whose schematic structure, consisting of a sequence of ethyleneoxy units (-CH2-CH2-O-) and / or cyclohexane-1,2-diol units, resembles a crown. Typical crown ethers consist of 4 ethyleneoxy units (

[0012] Crown-4), 5 ethyleneoxy units (

[0015] crown-5) or 6 ethyleneoxy units (

[0018] crown-6) . As a representative of a crown ether which, in addition to ethyleneoxy units, also has cyclohexane-1,2-diol units, dicyclohexano-

[0018] crown-6 is mentioned. Crown ethers form very stable and soluble complexes with cations such as potassium or sodium in organic media, and when these complexes dissolve, the corresponding counter-anions inevitably also dissolve from the organic matrix. Phase transfer catalysts are salts whose cations possess organic residues and thus exhibit good or at least moderate solubility in organic media. Due to the good solubility of the cation, an anion is inevitably dissolved along with it. In this process, the anion contained in the original salt can be exchanged for other anions. Phase-transfer catalysis typically describes a chemical process in which a reactant in an organic phase reacts with an anion that exists as part of a salt in an aqueous phase immiscible with the organic phase. The presence of the phase-transfer catalyst allows the anion to pass through the phase boundary from the aqueous to the organic phase, where the actual chemical reaction then takes place. Examples of phase transfer catalysts are - Ammonium salts, such as tetrabutylammonium chloride, methyltributylammonium chloride, methyltrioctylammonium chloride, dimethyldioctadecylammonium chloride, cetyltrimethylammonium chloride, tribenzylmethylammonium chloride, benzyltriethylammonium chloride, alkylbenzyldimethylammonium chlorides or tricaprylylmethylammonium chloride, as well as the corresponding ammonium bromide iodides and hydroxides, and - Phosphonium salts such as tetrabutylphosphonium chloride or hexadecyltributylphosphonium bromide, as well as the corresponding phosphonium bromides, iodides and hydroxides. Preferably, component (K) is added to the reaction mixture in a total amount of 0.01 to 10 wt.%, particularly preferably in a total amount of 0.1 to 5 wt.%, and especially preferably in a total amount of 0.3 to 3 wt.%, in each case based on the total mass of the reaction mixture. Component (K) can be added before or during the ongoing reaction; however, it is preferably added from the beginning of the reaction. Particularly preferred is one or more phase transfer catalysts and / or one or more crown ethers, in particular One or more phase transfer catalysts are added to the reaction mixture in the above-mentioned preferred, especially preferred, total amounts. Preferably, the first process step according to the invention is carried out in an anhydrous reaction system, i.e., a system which, unlike the usual implementation of a phase transfer catalysis, does not contain an aqueous salt phase. In principle, cyanates of all monovalent or divalent metal ions can be used as metal cyanates (MOCN), with alkaline earth cyanates and especially alkali cyanates being preferred. Sodium and especially potassium cyanate are particularly preferred. Preferably at least 0.8 mol, particularly preferably at least 0.9 mol, in particular at least 1 mol of cyanate ions, and preferably at most 2 mol, particularly preferably at most 1.5 mol and in particular at most 1.2 mol of cyanate ions are used per mol of haloalkyl alkoxysilane (SH) of general formula (7). The alcohols (A) preferably used are methanol, ethanol, iso- or n-propanol, with methanol and ethanol being particularly preferred. Preferably at least 0.8 mol, particularly preferably at least 0.9 mol, in particular at least 1 mol of alcohol (A), and preferably at most 2 mol, particularly preferably at most 1.5 mol and in particular at most 1.2 mol of alcohol (A) per mol of silane (SH) of general formula (7) are used. Preferably, the first process step according to the invention is carried out in the presence of at least one aprotic solvent (L). The solvent (L) preferably has a boiling point of at least 140 °C, particularly preferably at least 150 °C, and preferably at most 240 °C, particularly preferably at most 220 °C, in each case at 0.1 MPa. Suitable solvents (L) include, for example, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, N-methylimidazole, sulfolane, diethylformamide, dimethylacetamide, diethylacetamide, acetylacetone, acetoacetic ester, hexamethylphosphoric triamide, nitriles such as acetonitrile or butyronitrile, as well as ethers and / or esters with at least two ether or ester groups per molecule. Preferred solvents (L) are dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, sulfolane, and diethylformamide, with dimethylformamide being particularly preferred. Preferably, the solvent is used in amounts such that at least 0.1 and at most 1.5 parts by weight of solvent (L) are used per part by weight of the total amount of reactant. The total amount of reactant consists of the amount of silane (S-H), metal cyanate (MOCN), and alcohol (A). Preferably, the solvent is used in amounts such that at least 0.2 parts by weight, and particularly preferably at least 0.3 parts by weight of solvent (L) are used per part by weight of the total amount of reactant. Preferably, the solvent is used in amounts such that at most 1 part by weight, and particularly preferably at most 0.7 parts by weight of solvent (L), are used per part by weight of the total amount of reactant. In carrying out the first process step according to the invention, the various reactants, substances for accelerating the reaction, solvents and optionally also other auxiliary substances can be placed at the beginning of the reaction or dosed only during the reaction. In a preferred variant for carrying out the first process step, all solids including the metal cyanate (MOCN) and component (K) are placed in a solvent (L), while the haloalkyl alkoxysilane (SH) and the alcohol (A) are added wholly or at least partially only during the reaction. The haloalkyl alkoxysilane (SH) is preferably added at a minimum of 80% by weight only during the reaction. The advantage of this preferred method lies in the improved reaction safety, as the significantly exothermic reaction can thus be controlled and, if necessary, stopped by regulating the dosage of the silane (SH). Dosing the liquid silane (SH) is usually much more convenient than the solid metal cyanate (MOCN), which is also theoretically possible. Controlling the exothermicity solely by adjusting the dosage of the alcohol (A) is not possible, however, because cyanate (MOCN) and haloalkyl alkoxysilane (SH) can undergo significantly exothermic reactions, forming byproducts, even in the absence of the alcohol (A). A preferred variant of the first process step according to the invention is in which the total amount of alcohol (A) to be used is divided such that at least 5% and particularly preferably at least 8% of the total amount of alcohol is already present in the reaction mixture before the reaction begins. and preferably at least 50% and particularly preferably at least 70% of the total amount of alcohol is added to the reaction mixture only during the reaction. In a particularly preferred embodiment of the first process step, the amount of alcohol (A) in the receiving flask and the dosing rate of the remaining amount of alcohol (A) are controlled via the boiling point of the reaction mixture. Preferably, enough alcohol is supplied such that the reaction mixture has a boiling point >110 °C and particularly preferably >120 °C before the alcohol is added. The upper limit of the boiling point is preferably at least 5 °C, and particularly preferably at least 10 °C, below the boiling point of the solvent (L). During the first process step according to the invention, the alcohol (A) is preferably dosed so rapidly that the reaction mixture has a boiling point >110 °C and particularly preferably >120 °C throughout the entire reaction duration. The upper limit of the boiling point is preferably at least 5 °C, and particularly preferably at least 10 °C, below the boiling point of the solvent (L) throughout the entire reaction duration. The first process step according to the invention is preferably carried out under reflux. The preferred method described, in which the alcohol dosage during the process step according to the invention is controlled by the reaction temperature, is based on the surprising discovery that this method makes it possible to combine a high reaction rate with a high yield. Thus, an excessively rapid dosage of the alcohol leads to... (A) If the boiling point of the reaction mixture falls below the preferred or particularly preferred limits, the reaction will slow down considerably. Conversely, excessively high temperatures or non-refluxing reactions will lead to increased formation of oligomeric and / or polymeric impurities. At the same time, controlling the dosing rate of the alcohol (A) via the reflux temperature of the reaction mixture offers the person skilled in the art a simple way to keep the alcohol concentration in the reaction mixture in an optimal range throughout the entire duration of the reaction in order to achieve the best possible results in terms of both reaction rate and yield. Optionally, further substances can be used during the reaction to accelerate it. A preferred example is the addition of a metal iodide, preferably an alkali metal iodide, and particularly preferably potassium iodide. Preferably at least 0.01 parts by weight, particularly preferably at least 0.1 parts by weight, in particular at least 0.5 parts by weight of metal iodide, and preferably at most 5 parts by weight, particularly preferably at most 3 parts by weight and in particular at most 2 parts by weight of metal iodide are used per 100 parts by weight of metal cyanate. The solids can be easily separated after completion of the first process step, preferably by filtration. Preferably, at least 70% and especially preferably at least 85% of the solvent (L) is removed by distillation before the separation of the metal halides formed as by-products and any remaining metal cyanate residues. In a particularly preferred embodiment of the process according to the invention, at least one solvent (L1) with a lower dipole moment than solvent (L) is added to the reaction mixture before the solids are separated, which is carried out in particular by filtering off the metal salts. If solvent (L1) has a higher boiling point than solvent (L), the addition of solvent (L1) can take place before or after the distillative removal of solvent (L) according to the invention. Preferably, however, the at least one solvent (L1) is added only after the distillative removal of solvent (L), regardless of the respective boiling points of solvents (L) and (L1). Preferably, after the distillative removal of the solvent (L) according to the invention, at least 0.3, in particular at least 0.5 parts by weight and at most 3, in particular at most 1.5 parts by weight of one or more solvents (Ll) are added to the reaction mixture for each part by weight of solvent (L) previously removed. After filtration, the filter cake is preferably washed with the same solvent (Ll) that was added to the reaction mixture after removal of the solvent (L). Preferably, the filtrates are then combined and the solvent (Ll) is removed by distillation. The solvent (LI) is preferably aromatic and / or aliphatic hydrocarbons (e.g., the various stereoisomers of pentane, hexane, heptane, octane, etc., cyclopentane, cyclohexane, methylcyclohexane, cycloheptane, etc., benzene, toluene, the various xylene, etc.), substituted aromatics (e.g., chlorobenzene), heterocyclic aromatics (e.g., pyridine, furan, etc.), ethers (e.g., diethyl ether, methyl tert-butyl ether, tetrahydrofuran, dibutyl ether, anisole, etc.), esters (e.g., ethyl acetate, methyl acetate, butyl acetate, alkyl benzoates, dialkyl maleates, dialkyl phthalates, etc.), ketones (e.g., acetone, butanone, etc.) or alcohols (e.g., tert-butanol). Aromatic and / or aliphatic hydrocarbons are particularly preferred, such as the various cyclic or non-cyclic pentane, hexane, heptane or octane isomers, as well as toluene or xylene. The preferential use of a second solvent (LI) significantly improves the filterability of the suspension obtained in the first process step according to the invention. Furthermore, the amount of salt remaining in dissolved form in the filtrate is significantly reduced, which is advantageous for the subsequent second process step, since less or ideally no salt can precipitate from the bottom during distillation according to the invention. The evaporator unit (VD) used in the second process step according to the invention can be any evaporator unit known to date, such as a thin-film, falling-film or short-path evaporator, with the three evaporator types mentioned being preferred. In the second process step of the process according to the invention, the preferred layer thickness of the reaction mixture is preferably in Form of a liquid film in the evaporator unit (VD) preferably at a maximum of 2 cm, particularly preferably at a maximum of 1 cm, particularly at a maximum of 0.5 cm, most preferably at a maximum of 0.3 cm. Preferably, the second process step according to the invention is carried out in the evaporator unit (VD) at a pressure of at most 20 mbar, particularly preferably at at most 10 mbar, especially at at most 5 mbar. Preferably, the second process step according to the invention is carried out in the evaporator unit (VD) at a temperature of at most 180°C, particularly preferably at at most 160°C, especially at at most 140°C. Preferably, the second process step according to the invention is carried out such that the reaction mixture in the evaporation unit (VD) has an average residence time of at most 20 minutes, particularly preferably at most 10 minutes, and especially preferably at most 5 minutes. All process steps according to the invention are preferably carried out in a protective gas atmosphere, preferably argon or nitrogen. The second process step according to the invention is based on several discoveries. The discovery that component (K), which increases the solubility of anions in the organic reaction mixture, cannot be separated by filtration carried out after the first process step was foreseeable. The same naturally applies to the anion whose solubility in organic media is improved by component (K). Surprisingly, the carbamatoalkyl alkoxysilane (SC), which was not freed from the component (K) and the associated anion, could no longer be thermolytically cleaved to the desired carbamatoalkyl alkoxysilane (SI). Equally surprising was the fact that the carbamatoalkylalkoxysilane (SC) could not be separated from component (K) and its corresponding anion by conventional distillation. For the sake of simplicity, such a conventional distillation could have been carried out directly after the distillative separation of the solvent (L1) by lowering the pressure and / or increasing the temperature in the distillation sump. However, it turned out that this was not possible because, under these conditions, large proportions, i.e., typically 30–50%, of the carbamatoalkylalkoxysilane (SC) produced in the first reaction step were converted into various low-volatility compounds, dramatically reducing the isolable yield of this silane. The carbamatoalkyl alkoxysilanes (SC) produced according to the invention preferably have a purity >90%, particularly preferably >95%, and especially >98% after the second process step according to the invention. The thermolytic alcohol elimination from the carbamatoalkyl alkoxysilanes (SC) taking place in the third process step according to the invention can be carried out in various ways. Preferably, the carbamatoalkyl alkoxysilanes (SC) are heated to high temperatures >200 °C, particularly preferably >250 °C, optionally even >280 °C, whereby an alcohol molecule is eliminated from the carbamate group and the isocyanatoalkyl alkoxysilane (SI) is formed. The cleavage can, of course, be carried out relatively simply in a flask or kettle, with the more volatile reaction products being removed by distillation. However, more complex procedures, such as those described in EP 3221324 or EP 3546465, are usually more efficient. Particularly preferred are processes such as those described in EP 3221324, in which the cleavage of the carbamatoalkyl alkoxysilanes takes place continuously in a thin-film or short-path evaporator at a pressure >100 mbar, preferably >500 mbar, in the presence of a catalyst (K). This process has the advantage that the reaction products evaporate particularly quickly and thus can only undergo undesired subsequent reactions to a limited extent. In addition, the rapid evaporation causes a continuous shift of the reaction equilibrium in favor of the products. The catalyst (K) is preferably added to the carbamatoalkyl-alkoxysilane (SC) before the start of the reaction. The catalyst (K) is particularly preferred to be liquid or soluble in the carbamatoalkyl-alkoxysilane (SC). Preferred catalysts (K) include all compounds used in polyurethane chemistry for catalyzing condensation reactions of isocyanates and alcohols. Examples include commonly used organic tin compounds such as dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetylacetonate, dibutyltin diacetate, or dibutyltin dioctoate, etc. Divalent tin catalysts such as tin diacetate or tin dilaurate can also be used. Furthermore, organic bismuth and / or zinc compounds, e.g., the various catalysts from Borcherts such as Borchi-Kat 22, Borchi-Kat 24 or Borchi-Kat 0244, and organic titanium compounds such as titanates, can also be used. e.g. titanium (IV) isopropylate or titanium (IV) acetylacetonate, organic iron compounds, e.g. iron (III) acetylacetonate, iron (II) acetylacetonate or other metal compounds such as zirconium (IV) acetylacetonate, cobalt (III) acetylacetonate or manganese acetylacetonate. Combinations of several catalysts (K) can, of course, also be used. Non-volatile or only slightly volatile catalysts, in particular the metal complexes mentioned above, are preferred, with tin (IV), tin (II), and iron (III) complexes being especially preferred. The catalyst (K') is preferably used in concentrations of 1–10,000 ppm, with concentrations of 10–5,000 ppm and 100–2,000 ppm being particularly preferred. In a preferred embodiment of the invention, an inert gas stream, e.g., of argon, hydrogen, or nitrogen, is passed through this evaporation unit during the evaporation process. This gas is preferably heated before being introduced into the evaporation unit, particularly in industrial processes. The hot carrier gas stream assists in the heating and evaporation of the reaction mixture. Nitrogen is the preferred gas. Preferably, the evaporated reaction products are then fractionally condensed, with the eliminated alcohol preferably being separated in gaseous form, and the isocyanatoalkylalkoxysilane (SI) and the optionally also partially evaporated carbamatoalkylalkoxysilane (SC) being condensed together or optionally separately one after the other. The separation of the alcohol prevents a reverse reaction of the formed isocyanatoalkylalkoxysilane (SI). Preferably, the separation of the alcohol takes place in a condenser or a a simple separation column is used, in which the alcohol is withdrawn in gaseous form and silanes (SI) and (SC) are condensed together. The isocyanatoalkyl-alkoxysilane (SI) is then preferably purified by distillation, which can be carried out either continuously or batchwise, with the former being preferred. The carbamatoalkyl-alkoxysilane (S-C) separated in this process is preferably recycled back into the thermolytic manufacturing process. The process according to the invention has the advantage that it is suitable for the preparation of all isocyanatoalkyl alkoxysilanes (SI) for which the corresponding haloalkyl alkoxysilanes (SH) are available. This applies in particular to the α-isocyanatomethyl alkoxysilanes, which are of particular interest due to their high reactivity. The inventive method has the advantage that it delivers very good yields and is therefore comparatively cost-effective. The process according to the invention has the advantage that in the carbamatoalkyl alkoxysilane (SC) produced as an intermediate according to the invention, only a small amount of by-products are present after the 2nd process step, which can lead to disturbances in the 3rd process step, e.g. through the formation of deposits. The method according to the invention has the advantage of being very simple and robust. All the symbols in the above formulas have their meanings independently of one another. In all formulas, the silicon atom has a tetravalent valence. The following examples describe the basic feasibility of the present invention, without, however, limiting it to the contents disclosed therein. In the following examples, unless otherwise stated, all quantities and percentages are based on weight, all pressures are 0.10 MPa (abs.) and all temperatures are 20°C. Example 1a Implementation of the first process step according to the invention: Synthesis of N-(methyldimethoxysilylmethyl)-O-methylcarbamate In a 4000 mL four-necked flask equipped with a reflux condenser, KPG stirrer, and thermometer, a suspension of 584 g (7.2 mol) potassium cyanate, 5.8 g potassium iodide, and 30 g tetrabutylammonium bromide in 921 g dimethylformamide and 24 g (0.75 mol) methanol is heated to 125 °C. Then, a solution of 1067 g (6.9 mol) 1-chloromethylmethyldimethoxysilane and 210 g (6.6 mol) methanol is added. The reaction is carried out under reflux, and the addition rate is controlled by the boiling point of the reaction mixture, so that this temperature remains constant within a very narrow range between 123 °C and 127 °C. Reducing the addition rate increases the boiling point, and vice versa. The dosing time is 90 minutes. After the addition is complete, the mixture is stirred for another 120 minutes, during which the reflux temperature remains between 125 and 130 °C, initially with a slight upward trend. After that, the starting material, 1-chloromethyl-methyldimethoxysilane, is only detectable by gas chromatography in trace amounts <0.1% of the amount of product formed. The mixture is cooled to approximately 50 °C, and a total of 1040 g is distilled off through a Vigreux column approximately 20 cm long. The pressure is gradually reduced from an initial 14 mbar to 9 mbar. The bottom temperature rises from 55 °C to 100 °C, while the top temperature initially remains largely constant between 46 and 48 °C, but increases sharply towards the end of the distillation. Distillation is terminated at a top temperature of 80 °C. The distillate consists primarily of dimethylformamide, which also contains excess, unreacted methanol, a small amount (approximately 2%) of the by-product methyl trimethoxysilane, and approximately 5% product. After removal of the low-boiling components methanol and methyl trimethoxysilane, it can be used again without problems, thus also returning the product contained in the distillate to the production process. After distillation, the reaction mixture is cooled to approximately 30 °C. Then, 1000 g of toluene are added and stirred for 30 minutes at room temperature. Subsequently, all solids are filtered off using a pressure filter press with a Seitz K900 filter at an overpressure of 0.2 bar. Filtration proceeds smoothly and is completed within approximately 20 minutes. The filter cake is replenished twice with 500 g of toluene, which is also completed within approximately 20 minutes. The filtrates are then combined. Finally, the toluene is removed by distillation at a pressure of approximately 30 mbar and a bottom temperature that rises from 30 to 70 °C during distillation. Approximately 95% of the The amount of toluene used was recovered with a purity of >95%. The distilled toluene can be reused without any problems. At the end of the distillation, the pressure is reduced to 1 mbar and the bottom temperature is increased to 130 °C for 10 minutes. The resulting distillate volume of approximately 47 ml contains essentially the dimethylformamide and toluene residues that remained in the reaction mixture up to that point. 1234 g remain in the distillation residue. This crude product is processed by means of 1 The product was analyzed by 1H NMR. The product purity can be determined, for example, by integrating the CH3O-CO-NH-CH2-Si(CH3)(OCH3)2 signal and comparing this integral value with the signal integrals of an added internal standard such as trimethyl benzene tricarboxylate. The crude product analyzed using this method exhibits a purity of 92.8%. The crude product is a pale yellow, clear liquid. Example 1b Implementation of the first process step according to the invention: Synthesis of N-(methyldimethoxysilylmethyl)-O-methylcarbamate The procedure is the same as in Example 1a, except that instead of 30 g of tetrabutylammonium bromide, exactly the same weight of tetrabutylammonium chloride is used. All other process parameters remain unchanged. This means that the reaction is also carried out under reflux, and the dosing rate is controlled by the boiling point of the reaction mixture, so that this temperature remains constant within the same temperature range of 123 °C to 127 °C. The dosing time is 105 minutes. After the addition is complete, the mixture is stirred under reflux at 125–130 °C for a further 120 minutes. The work-up of the reaction mixture is also carried out exactly as described in Example 1a. Within the limits of measurement accuracy, the results are identical to those of Example 1a. Example 1c Implementation of the first process step according to the invention: Synthesis of N-(methyldimethoxysilylmethyl)-O-methylcarbamate The procedure is the same as in example aa, however, instead of 30 g of tetrabutylammonium bromide, exactly the same weight of tetrabutylphosphonium bromide is used. All other process parameters remain unchanged. That is, here too the reaction is carried out under reflux and the dosing rate is controlled by the boiling point of the reaction mixture, so that this temperature remains constant within the same temperature range of 123 °C to 127 °C. The dosing time is 95 min. After the addition is complete, unlike in example aa, stirring is only carried out under reflux at 125–130 °C for 60 min. The processing of the reaction mixture is also carried out exactly as described in Example 1a. Within the limits of measurement accuracy, the results are largely identical to those of Example 1a; however, the purity of the crude product is slightly lower at approximately 91.9%. Example 1d Implementation of the first process step according to the invention: Synthesis of N-(methyldimethoxysilylmethyl)-O-methylcarbamate The procedure is the same as in example aa, however, instead of 30 g of tetrabutylammonium bromide, exactly the same weight of triphenylmethylammonium chloride is used. All other process parameters remain unchanged. This means that the reaction is also carried out under reflux, and the dosing rate is controlled by the boiling point of the reaction mixture, so that this temperature remains constant within the same temperature range of 123 °C to 127 °C. The dosing time is 140 minutes. After the addition is complete, the mixture is stirred under reflux at 125–130 °C for a further 120 minutes. The processing of the reaction mixture is also carried out exactly as described in Example 1a. Within the limits of measurement accuracy, the results are largely identical to those of Example 1a; however, the purity of the crude product is slightly lower at approximately 91.1%. Comparative example V1a Non-inventive implementation of the first process step: Synthesis of N-(methyldimethoxysilylmethyl)-O-methylcarbamate. The procedure is the same as in Example 1a, however, the addition of a phase-transfer catalyst, i.e., the addition of tetrabutylammonium bromide, is omitted entirely. All other process parameters remain unchanged. This means that the reaction is also carried out under reflux, and the dosing rate is controlled by the boiling point of the reaction mixture, so that this temperature remains constant within the same temperature range of 123 °C to 127 °C. The dosing time is 350 minutes. After the addition is complete, the mixture is stirred under reflux for another 120 minutes, during which time the temperature rises from an initial 123 °C to 125 °C. The work-up of the reaction mixture is also carried out exactly as described in Example 1a. The purity of the final product is lower at 85.7% than in Example 1a. All other results are comparable. Comparison example V1b Non-inventive execution of the first process step: Synthesis of N-(methyldimethoxysilylmethyl)-O-methylcarbamate The procedure is the same as in Example VI, however, instead of 24 g of methanol, only 10 g of methanol are used at the beginning of the reaction. This reaction is then also carried out under reflux, and the dosing rate is controlled by the boiling point of the reaction mixture. However, the dosing rate is such that this temperature remains constant within a range of 135 to 140 °C. The dosing time is 230 minutes. After the addition is complete, the mixture is stirred under reflux for another 120 minutes at 130 °C. The work-up of the reaction mixture is also carried out exactly as described in example 1a. However, the purity of the final product, at 81%, is significantly lower than in the previous examples. Example 2a Implementation of the second process step according to the invention: Distillation of N-(methyldimethoxysilylmethyl)-O-methylcarbamate via a short-path evaporator 400 g of N-(methyldimethoxysilylmethyl)-O-methylcarbamate, prepared according to Example 1, are passed through a short-path evaporator with Teflon wipers and an internal cooling loop at a dosing rate of 720 ml / h. The short-path evaporator has a diameter of 8 cm and a length of 28 cm. The wall temperature of the short-path evaporator is 125 °C and the applied pressure is 1 mbar. The residue is a yellow liquid that becomes very viscous at room temperature but contains no precipitated solids. The final product is in The distillate runoff from the short-path evaporator was collected. It is a light yellow liquid. The distillate yield is 368 g, which corresponds to 92.0%. The purity of the product was determined by GC and is 96.3%, with dimethylformamide (2.0%), methyl trimethoxysilane (0.2%), methanol (0.3%), and toluene (0.2%) being the most significant impurities. GC-MS was used to specifically search for possible decomposition products of the phase-transfer catalyst. Tributylamine (0.003%) was detected. Elemental analysis determined the bromine content to be 2 ppm. Example 2b Implementation of the second process step according to the invention: Distillation of N-(methyldimethoxysilylmethyl)-O-methylcarbamate via a short-path evaporator 400 g of N-(methyldimethoxysilylmethyl)-O-methylcarbamate, prepared according to Example 1b, are distilled as described in Example 2a. The wall temperature of the short-path evaporator is again 125 °C and the applied pressure is 1 mbar. The residue is a yellow liquid that becomes very viscous at room temperature but contains no precipitated solids. The final product is collected in the distillate outlet of the short-path evaporator. It is a colorless liquid. The yield is 370 g, or 92.5%. The purity of the product is 96.1%, with dimethylformamid (1.9%), methyl trimethoxysilane (0.1%), methanol (0.1%) and toluene (0.2%) being the most important impurities. Example 2c Implementation of the second process step according to the invention: Distillation of N-(methyldimethoxysilylmethyl)-O-methylcarbamate via a short-path evaporator 400 g of N-(methyldimethoxysilylmethyl)-O-methylcarbamate, prepared according to Example 1c, are distilled as described in Example 2a. However, the wall temperature of the short-path evaporator is only 100 °C and the applied pressure is 1 mbar. The residue is a yellow liquid containing no solids and remains low-viscosity even upon cooling to room temperature. The final product is collected in the distillate outlet of the short-path evaporator. It is a colorless liquid. The yield is 329 g, or 82.3%. The product purity is 97.2%, with dimethylformamide (1.8%), methyl trimethoxysilane (0.2%), methanol (0.1%), and toluene (0.2%) being the most significant impurities. The phosphorus content was determined by elemental analysis and is 130 ppm. Comparative example V2a Carrying out the second process step: Distillation of N-(methyldimethoxysilylmethyl)-O-methylcarbamate not produced according to the invention via a short-path evaporator 400 g of N-(methyldimethoxysilylmethyl)-O-methylcarbamate, prepared according to comparative example Via, are distilled as described in Example 2a. The wall temperature of the short-path evaporator is 125 °C and the applied pressure is 1 mbar. The bottoms are a yellow liquid, from which a small amount of a crystalline solid precipitates upon cooling. The final product is collected in the distillate outlet of the short-path evaporator. It is a colorless liquid. The yield of 343 g is 85.8% and is therefore significantly lower than in the directly comparable example 2a. The purity of the product is 96.2%, with dimethylformamid (2.1%), methyl trimethoxysilane (0.1%), methanol (0.1%) and toluene (0.2%) being the most important impurities. Comparison example V2b Non-inventive implementation of the second process step: Distillation of N-(methyldimethoxysilylmethyl)-O-methylcarbamate using a conventional distillation apparatus. 400 g of N-(methyldimethoxysilylmethyl)-O-methylcarbamate produced according to Example 1a are distilled in a 1 L flask with a Claisen head without a column at a pressure of 1 mbar. The bottom temperature rises slowly from 115 °C to 145 °C and then, after approximately 2 / 3 of the flask contents have been distilled, jumps to 180 °C. The head temperature initially remains largely constant at 100 °C, but after the distillation of approximately 1 / 2 of the flask contents, begins to rise slowly to 103 °C. During the final jump in the bottom temperature, the head temperature initially rises to 110 °C until hardly any more distillate passes over and the head temperature begins to fall. The distillation is then stopped. The distillate yield is approximately 295 g. An analysis of the sump using 1H-NMR shows that the swamp contains hardly any (<1%) N-(methyl-dimethoxysilylmethyl)-O-methylcarbamate. Example 3a Implementation of the 3rd process step according to the invention: Synthesis of α-isocyanatomethyl-methyldimethoxysilane The cleavage of N-(methyldimethoxysilylmethyl)-O-methylcarbamate into isocyanatomethyl-methyldimethoxysilane and methanol takes place in a thin-film evaporator with a length of 25 cm, an inner diameter of 8 cm, and a wall temperature of 300 °C. 300 g of the N-(3-trimethoxysilylpropyl)-O-methylcarbamate distilled in Example 2a are mixed with 0.21 g of dioctyltin dilaurate. The mixture is dispensed at a rate of 165 ml / h at the top of the thin-film evaporator. A nitrogen flow of 65 l / h is directed from bottom to top, i.e., against the direction of flow of the reaction mixture. Under these conditions, the sump discharge is approximately 10% of the dosed amount of silane. The vaporized product mixture, along with the nitrogen stream, is passed through a 10 cm long Vigreux column insulated by an aluminum foil jacket. The liquid reflux from the column is returned to the thin-film evaporator. The top temperature of the Vigreux column is maintained within a constant temperature range of 203–250 °C. The mixture of reactant and product silane is selectively condensed from this gas stream at 54 °C using a conventional glass condenser. In a second condensation step, the methanol is then condensed at 0 °C before the nitrogen stream is directed through a cold trap into the exhaust system of the fume hood, in which the entire system is located. 238 g of condensed silane mixture are obtained. The colorless liquid is processed using 1Analyzed by H-NMR and gas chromatography. It contains 33.5% α-isocyanatomethyl-methyldimeethoxysilane and 63.9% N-(3-trimethoxysilylpropyl)-O-methylcarbamate. Example 3b Implementation of the 3rd process step according to the invention: Synthesis of α-isocyanatomethyl-methyldimethoxysilane 300 g of the N-(3-trimethoxy-silylpropyl)-O-methylcarbamate distilled in Example 2b are reacted using exactly the same procedure described in Example 3a. 234 g of condensed silane mixture are obtained. The colorless liquid is processed using 1 Analyzed by H-NMR and gas chromatography. It contains 34.5% α-isocyanatomethyl-methyldimeethoxysilane and 63.1% N-(3-trimethoxysilylpropyl)-O-methylcarbamate. Example 3c Implementation of the 3rd process step according to the invention: Synthesis of α-isocyanatomethyl-methyldimethoxysilane 300 g of the N-(3-trimethoxy-silylpropyl)-O-methylcarbamate distilled in Example 2c are reacted using exactly the same procedure described in Example 3a. 233 g of condensed silane mixture are obtained. The colorless liquid is processed using 1 Analyzed by H-NMR and gas chromatography. It contains 34.1% α-isocyanatomethyl-methyldimeethoxysilane and 63.3% N-(3-trimethoxysilylpropyl)-O-methylcarbamate. Comparative example V3a Carrying out the 3rd process step: Synthesis of α-isocyanatomethyl-methyldimethoxysilane from N-(methyldimethoxysilylmethyl)-O-methylcarbamate distilled not according to the invention. The same apparatus and reaction conditions were used as in Example 3a, however, an N-(3-trimethoxysilylpropyl)-O-methylcarbamate was used which was prepared according to Example 1a, but was then thin-filmed not according to the invention. 300 g of this material are mixed with 0.21 g of dioctyltin dilaurate. The dosing is carried out at a rate of 165 ml / h at the top of the thin-film evaporator, as in Example 3a. A nitrogen flow of 65 ml / h is introduced from bottom to top, i.e., against the direction of flow of the reaction mixture. After a dosing time of approximately 15 minutes, significantly increased running noise indicates that the thin-film evaporator is beginning to run noticeably less smoothly. After 30 minutes, the wiper basket of the thin-film evaporator finally jams and cannot be turned further, either by the drive mechanism or by hand. The reaction is then stopped. The small amount of product obtained (approximately 50 g) is not analyzed in detail.

Claims

Patent claims 1. Method for the preparation of isocyanatoalkyl alkoxysilanes (SI) of general formula (6), OCN-R 2 -Si(R 3 ) 3-x (OR 4 ) x (6) by a multi-stage process, comprising a first process step in which a haloalkyl alkoxysilane (SH) of general formula (7), XR 2 -Si(R 3 ) 3-x (OR 4 ) x (7) with a metal cyanate (MOCN) and an alcohol (A) of general formula (8), R 1 OH (8) to a carbamatoalkyl alkoxysilane (SC) of general formula (9) R 1 O-CO-NH-R 2 -Si(R 3 ) 3-x (OR 4 ) x(9) is carried out, provided that this reaction is carried out partly or completely in the presence of a component (K) which increases the solubility of anions in the organic reaction mixture and which is present in the reaction mixture in an amount of 0.05 to 5 wt% based on the mass of the total reaction mixture, a 2nd process step in which the carbamatoalkyl alkoxysilanes (SC) are purified by distillation, wherein distillation is carried out in an evaporation unit (VD) in which the silane (SC) is evaporated in a layer thickness of maximum 5 cm, a pressure of maximum 80 mbar and temperatures of maximum 200°C, and a 3rd process step in which the isocyanatoalkyl-alkoxysilanes (SI) are produced by thermolytic alcohol elimination from the silane (SC), wherein R 1 , R 3 and R 4independently of each other, an unsubstituted or halogen-substituted hydrocarbon residue with 1-10 C atoms, R 2 a divalent unsubstituted or halogen-substituted hydrocarbon residue with 1-10 C atoms, which may be interrupted by non-adjacent oxygen atoms, X represents a halogen atom, and x represents a value of 0, 1, 2 or 3.

2. Method according to claim 1, characterized in that the first method step is carried out in the presence of at least one aprotic solvent (L).

3. A process according to claim 1 or 2, characterized in that in the first process step all solids including the metal cyanate (MOCN) and component (K) are placed in the solvent (L) and the haloalkyl alkoxysilane (SH) and the alcohol (A) are added wholly or partially during the reaction.

4. A method according to any one of claims 1 to 3, characterized in that in the first process step the haloalkyl alkoxysilane (SH) is added at least 80 wt.% only during the reaction.

5. A method according to any one of claims 1 to 4, characterized in that in the first process step the total amount of alcohol (A) to be used is divided such that at least 5% of the total amount of alcohol is already placed in the reaction mixture before the start of the reaction and preferably at least 50% of the total amount of alcohol is added to the reaction mixture only during the reaction.

6. Method according to any one of claims 1 to 5, characterized in that in the first process step the amount of alcohol (A) in the feedstock and the dosing rate of the remaining amount of alcohol (A) is controlled via the boiling point of the reaction mixture such that enough alcohol is supplied that the reaction mixture has a boiling point >110 °C before the start of the alcohol dosing.

7. Method according to claim 6, characterized in that in the first process step the upper limit of the boiling point remains at least 5 °C below the boiling point of the solvent (L).

8. Method according to claim 6, characterized in that this is controlled in the 1st method step during the entire reaction duration.

9. Method according to claim 7, characterized in that this is controlled in the 1st method step during the entire reaction duration.

10. Method according to any one of claims 1 to 9, characterized in that in the first method step at least 0.01 to at most 5 parts by weight of a metal iodide is used per 100 parts by weight of metal cyanate (MOCN).

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