Method for producing hydridoalkoxysilanes

Abstract

The invention relates to a method for producing a compound of general formula (I), wherein R1 at every occurrence is a substituted or unsubstituted, branched or unbranched alkyl group with 1 to 12 carbon atoms. According to the method, a compound of general formula (II), wherein R1 at every occurrence has the definitions indicated with respect to formula (I) and X is halogen, is reacted with a hydrating agent in acetonitrile as the solvent to form a compound of general formula (I), wherein the hydrating agent is sodium borohydride.

Description

Description Process for the preparation of hydridoalkoxysilanes

[0001] The invention relates to a process for the preparation of hydridoalkoxysilanes.

[0002] The synthesis of hydridoalkoxysilanes from the corresponding haloalkoxysilanes has not been described in the literature to date, with one exception. Jirinec et al. (Jirinec et al., Czechoslov. Chem. Commun., 1961, 26, 1815-1825) tested various lithium aluminum hydrides and sodium trimethoxyborohydride and, using LiHAl('BuO)3 as the best hydrogenating agent, arrived at the result shown in Scheme P1: Scheme Pl In Scheme Pl - the designation “OEt” denotes an ethoxy group, the designation “O^u” denotes a tert-butoxy group.

[0003] Further literature on the hydrogenation of organosilanes can only be found in the area of ​​haloalkylsilanes, where research has been carried out much more extensively. Established hydrogenating agents are hydrogen in combination with typical hydrogenation catalysts such as Pd@C (see EP 0 714 900 A2, 1995), lithium aluminum hydride (see WO 2005 / 051 962 A1), and diisobutylaluminum hydride (see US Pat. No. 5,015,624 A). A simple transfer of these hydrogenating agents to use with haloalkoxysilanes has not been successful to date. This is primarily due to the fact that the alkoxy groups readily react to form alcohols, which in turn react with the haloalkoxysilanes. Ito et al. (Ito et al., Chemistry Letters, 2022, 45, 1434-1436) have reported that various haloalkyl(aryl)silanes could be hydrogenated selectively and in high yields by using sodium borohydride in acetonitrile.

[0004] Haloalkoxysilanes can be prepared from tetraalkoxysilanes, as described in the previously unpublished German patent application No. 10 2023 127 669.7. Tetraalkoxysilanes are economically undesirable compounds, but they are common byproducts of large-scale industrial processes. Furthermore, haloalkoxysilanes themselves are common, undesirable byproducts of large-scale industrial reactions for the catalytic conversion of hydridoalkoxysilanes with halogen-substituted olefins.

[0005] It is therefore desirable to find a process that enables the conversion of haloalkoxysilanes into industrially usable compounds.

[0006] The object of the invention is to eliminate the disadvantages of the prior art. In particular, it is intended to provide a process that enables the preparation of a hydridoalkoxysilane from a haloalkoxysilane.

[0007] This object is achieved by the features of claim 1. Useful embodiments of the inventions emerge from the features of the subclaims.

[0008] According to the invention, a process for preparing a compound of general formula I is provided R 1 i O H-Si-OR 1 i O i R 1 (Formula I), wherein R 1 at each occurrence is a substituted or unsubstituted, branched or unbranched alkyl group having 1 to 12 carbon atoms, wherein a compound of the general formula II R 1 i O X-Si-OR 1 io I R 1 (Formula II), where R 1 has at each occurrence the meanings given in connection with formula I and X is a halogen, is reacted in acetonitrile as solvent with a hydrogenating agent to give a compound of general formula I, wherein the hydrogenating agent is sodium borohydride.

[0009] The process according to the invention makes it possible to produce industrially relevant hydridoalkoxysilanes from haloalkoxysilanes. The compounds of general formula I are hydridoalkoxysilanes. The term "hydridoalkoxysilanes" is used instead of the term "trialkoxysilanes" to clarify that the compounds of general formula I have a hydrogen atom bonded to the silicon atom.

[0010] The process according to the invention is illustrated in Scheme 1. A compound of general formula II is reacted with a hydrogenating agent to form a compound of general formula I. The compound of general formula II corresponds to the compound of general formula I, except that the radical X provided in formula I is replaced by the radical H. Scheme 1 The hydrogenating agent is sodium borohydride. The reaction takes place in acetonitrile.

[0011] Preferred is R 1 in the compound of general formula I, at each occurrence, a substituted or unsubstituted, branched or unbranched alkyl group having 1 to 6 carbon atoms. R is particularly preferably 1in the compound of general formula I, at each occurrence, an unsubstituted, branched or unbranched alkyl group having 1 to 6 carbon atoms. Preferred compounds of general formula I are trimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane, and tripentoxysilane. Particularly preferred compounds of general formula I are triethoxysilane and trimethoxysilane.

[0012] The rest R 1 the compound of general formula II corresponds at each occurrence to the radical R 1 in the compound of general formula I. Preferably, R 1 in the compound of general formula II, at each occurrence, a substituted or unsubstituted, branched or unbranched alkyl group having 1 to 6 carbon atoms. R is particularly preferably 1in the compound of general formula II, at each occurrence, an unsubstituted, branched or unbranched alkyl group having 1 to 6 carbon atoms. Preferred compounds of general formula II are halotrimethoxysilane, halotriethoxysilane, halotripropoxysilane, halotributoxysilane, and halotripentoxysilane. Particularly preferred compounds of general formula II are halotriethoxysilane and halotrimethoxysilane.

[0013] The radical X of the compound of general formula II is preferably fluorine, chlorine, bromine or iodine. The radical X is preferably chlorine. Preferred compounds of general formula II are chloro-trimethoxysilane, chloro-triethoxysilane, chlorotripropoxysilane, chlorotributoxysilane and chlorotripentoxysilane. Particularly preferred compounds of general formula II are chloro-triethoxysilane and chloro-trimethoxysilane. Chlorotriethoxysilane can be used to prepare triethoxysilane by means of the process according to the invention. Chlorotrimethoxysilane can be used to prepare trimethoxysilane by means of the process according to the invention.

[0014] The molar ratio of the compound of general formula II to the hydrogenating agent is preferably in a range from 5:1 to 1:5, more preferably in a range from 1:1 to 1:5. Even more preferably, the hydrogenating agent is used in excess, based on the compound of general formula II. However, the excess should not be too large. It is therefore preferred that the molar ratio of the compound of general formula II to the hydrogenating agent is in a range from 1:1 < UHM < 4, where UHM denotes the molar amount of the hydrogenating agent. It is preferred that the molar ratio of the compound of general formula II to the hydrogenating agent is in a range from 1:1.1 to 1:3.5, more preferably in a range from 1:1.1 to 1:3, even more preferably in a range from 1:1.5 to 1:2.5 and particularly preferably 1:2.

[0015] The reaction time for reacting the compound of general formula II with the hydrogenating agent can be in a range from 12 to 96 hours. Preferably, the reaction time is in a range from 20 to 80 hours, more preferably from 24 to 72 hours, and particularly preferably the reaction time is 24, 48, or 72 hours.

[0016] In a preferred embodiment of the invention, the molar ratio of the compound of general formula II to the hydrogenating agent is in a range of 1:1 < UHM < 4, where UHM denotes the molar amount of the hydrogenating agent, and the reaction time is in a range of 12 to 96 h, preferably 24 to 72 h. In a more preferred embodiment of the invention, the molar ratio of the compound of general formula II to the hydrogenating agent is in a range of 1:2 and the reaction time is in a range of 24 to 72 h. In a particularly preferred embodiment of the invention, the molar ratio of the compound of general formula II to the hydrogenating agent is in a range of 1:2 and the reaction time is 24, 48 or 72 h.

[0017] It can be provided that the concentration of the compound of general formula II in the solvent is in a range of 20 wt.% to 80 wt.%, more preferably 30 to 70 wt.%, even more preferably 40 to 60 wt.% and particularly preferably 50 wt.%, in each case based on the total weight of the solution.

[0018] The maximum concentration of the hydrogenating agent in the solvent can correspond to the saturation limit. Preferably, a suspension of the hydrogenating agent in the solvent is used. Thus, the amount of hydrogenating agent used in the suspension is above the saturation concentration. This ensures that the concentration of the hydrogenating agent in the solvent corresponds to the saturation concentration.

[0019] The process according to the invention can be carried out at ambient pressure and / or ambient temperature. For example, the process according to the invention can be carried out at room temperature. Room temperature can be understood as a temperature in a range of 10 to 30°C. For example, the process can be carried out at atmospheric pressure. The atmospheric pressure can be, for example, 101,325 Pa (1.01325 bar).

[0020] The process according to the invention is preferably carried out under a protective gas. A preferred protective gas is argon.

[0021] It may be provided that the process according to the invention is carried out without a catalyst. The process according to the invention can thus be carried out in the absence of a catalyst.

[0022] The process according to the invention enables the reaction of haloalkoxysilanes with sodium borohydride in acetonitrile to give the corresponding hydridoalkoxysilanes. Acceptable yields are achieved, particularly compared to the prior art. To increase the yield, it can be provided that unreacted haloalkoxysilane is recirculated to the process according to the invention. For this purpose, the process according to the invention can be repeated once or several times.

[0023] If the reaction mixture obtained in the embodiment of the process according to the invention contains, in addition to the hydridoalkoxysilane, one or more by-products and / or unreacted haloalkoxysilane, it can be provided that the hydridoalkoxysilane is separated from the by-product(s) and / or the unreacted haloalkoxysilane. For this purpose, it can be provided that the hydridoalkoxysilane is separated from the reaction mixture. The by-products can be Si(OR 1 )4 and / or O(Si(OR 1 )3)2, where R 1 which has the meanings given in connection with the compound of general formula I. Separation of hydridoalkoxysilane from the by-product(s) and / or remaining haloalkoxysilane is very easy due to the differences in boiling points and / or volatility of the compounds.

[0024] It may be provided that the by-product(s) are used again as starting material(s) for the production of a haloalkoxysilane, for example ClSiCOR, according to the process described in the previously unpublished German patent application No. 10 2023 127 669.7 1 ^, can be used.

[0025] The previously unpublished German patent application No. 10 2023 127 669.7 describes a process that enables the conversion of tetraalkoxysilanes to haloalkoxysilanes. Tetraalkoxysilanes are economically undesirable compounds. The process according to the invention now enables the conversion of the haloalkoxysilanes obtained from the tetraalkoxysilanes to hydridoalkoxysilanes. This enables the conversion of tetraalkoxysilanes to the corresponding hydridoalkoxysilanes, whereby in a first step, tetraalkoxysilanes are converted to the corresponding haloalkoxysilanes, and in a second step, the haloalkoxysilanes thus obtained are converted to the corresponding hydridoalkoxysilanes. The second step is the hydrogenation reaction provided for by the invention. The second step can thus be the final step following the first step. The resulting hydridoalkoxysilanes are of high economic relevance.

[0026] Thus, a process for preparing a hydridoalkoxysilane from a tetraalkoxysilane can be provided, comprising a first step (1) and a second step (2), the second step being described above. The process is shown in Scheme 2. Scheme 2 In the compound of general formula III, R 1 at each occurrence, the meanings given in connection with the general formula I. The compound of the general formula III is a tetraalkoxysilane.

[0027] Step (1) is based on the process described in the unpublished German patent application No. DE 10 2023 127 669.7. As shown in Scheme 3, a compound of general formula III can be reacted in the presence of an organophosphane catalyst with a halogenating agent of general formula Formula IV is implemented. Scheme 3 The halogenating agent of general formula IV is intended to R 3 is selected at each occurrence from the group consisting of hydrogen, halogen and a radical R 4 consists; R 4 is selected at each occurrence from the group consisting of a substituted or unsubstituted, branched or unbranched alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted aryl group, and a substituted or unsubstituted alkylaryl group; x is 0 or 1; and y is at each occurrence 0 or 1; with the proviso that at least one of the radicals R 3 Halogen is.

[0028] The halogenating agent of general formula IV necessarily contains a halogen atom. The halogenating agent of general formula IV can be a compound of general formula IV-A or a compound of general formula IV-B Formula IV-A Formula IV-B. In the halogenating agent of the general formula IV-A, R 3 the meanings given in connection with the general formula IV, x is 0 or 1. The halogenating agent of the general formula IV-A is a compound of the general formula IV in which y is 0 at each occurrence. In the halogenating agent of the general formula IV-B, R 3 the meanings given in connection with the general formula IV, x is 1. The compound of the general formula IV-B is a compound of the general formula IV in which y is 1 at each occurrence.

[0029] It can be provided that all residues R 3 are independently hydrogen or halogen, with the proviso that at least one of the radicals R 3 halogen. Preferably, the halogen is chlorine. It can be provided that at least one of the residues R 3in the halogenating agent of the general formula IV R 4 Preferably, R 4 independently of one another, each represents a substituted or unsubstituted, branched or unbranched alkyl group having 1 to 12 carbon atoms. More preferably, R 4 independently of one another, each represents a substituted or unsubstituted, branched or unbranched alkyl group having 1 to 6 carbon atoms. R is particularly preferably 4 Methyl.

[0030] The halogenating agent of general formula IV is preferably selected from the group consisting of dichlorosilane (HiSiCh), trichlorosilane (HSiCh), tetrachlorosilane (SiCU), hexachlorodisiloxane (O(SiCh)2), methyltrichlorosilane (CHsSiCh), methyldichlorosilane (HSiCHsCh), and dimethyldichlorosilane (CHsSiCh). Tetrachlorosilane is particularly preferred. Tetrachlorosilane is produced in very large quantities and with high purity as a by-product of the Siemens process for producing high-purity silicon.

[0031] The organophosphane can be a compound P(R 5 )3, where R 5 at each occurrence is selected from the group consisting of halogen, a substituted or unsubstituted, branched or unbranched alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted alkylaryl group. Preferably, the catalyst is selected from the group consisting of triphenylphosphane, tri(>-tolyl)phosphane, tri(o-tolyl)phosphane, tricyclohexylphosphane, tri(ω-butyl)phosphane, and trichlorophosphane. A particularly preferred catalyst is triphenylphosphane.

[0032] Step (1) can be carried out at ambient pressure and / or ambient temperature. For example, the process according to the invention can be carried out at room temperature. Room temperature can be understood as a temperature in a range of 10 to 30°C. For example, the process can be carried out at atmospheric pressure. The atmospheric pressure can be, for example, 101 325 Pa (1.01325 bar).

[0033] Step (1) is preferably carried out under a protective gas. A preferred protective gas is argon.

[0034] No solvent is required in step (1). Step (1 can therefore be a solvent-free process. However, it can be provided that the halogenating agent of the general formula IV is provided in an aprotic organic solvent. The aprotic organic solvent can be, for example, toluene. The maximum concentration of the halogenating agent of the general formula IV in the solvent can correspond to the saturation limit, but the concentration is preferably below this limit. In one embodiment, the halogenating agent of the general formula IV can be present in the solvent in a concentration ranging from 1% by weight, based on the total weight of the solution, up to the saturation concentration. The halogenating agent of the general formula IV can be present in the solvent, for example, in a concentration ranging from 1% by weight to 50% by weight.-%, each based on the total weight of the solution.

[0035] The compound of general formula III and the halogenating agent of general formula IV can, in one embodiment, be provided in a molar ratio of 4:1 to 1:4, more preferably of 3:1 to 1:3, even more preferably of 3:2 to 2:3 and particularly preferably of 2:1 to 1:2. By choosing the molar ratio, the number of radicals R 1 which are replaced by halogen atoms, whereby in the present invention, only one halogen atom is introduced. Thus, the molar ratio can be selected depending on the desired target product. In one embodiment, the compound of formula III and the halogenating agent of formula IV are provided in a stoichiometric ratio.

[0036] In the compound of general formula III, the halogen at each occurrence is selected from the group consisting of bromine, chlorine, fluorine and iodine. In the halogenating agent of general formula IV, the halogen at each occurrence is Occurrence each selected from the group consisting of bromine, chlorine, fluorine and iodine.

[0037] After completing step (1), the compound of general formula II can be separated from the reaction mixture. The separated compound of general formula II can then be used in step (2).

[0038] The term "alkyl," unless otherwise stated, refers in particular to a saturated aliphatic hydrocarbon group having a branched or unbranched carbon chain of 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms. The alkyl group may optionally be substituted with one or more substituents, each substituent independently being alkyl, alkoxy, halogen, haloalkyl, cyano, nitro, or dialkylamino, unless specifically stated otherwise.

[0039] The term "aryl", unless otherwise stated, refers in particular to a monovalent cyclic aromatic hydrocarbon group which may comprise a mono-, bi-, or tricyclic aromatic ring. Examples of aryl groups are - optionally substituted - phenyl, naphthyl, phenanthryl, fluorenyl, indenyl, azulenyl, oxydiphenyl, biphenyl, methylenediphenyl, aminodiphenyl, diphenyl sulfidyl, diphenyl sulfonyl, diphenylisopropylidenyl, benzodioxanyl, benzodioxylyl, benzoxazinyl, benzoxazinonyl, benzopiperadinyl, benzopiperazinyl, benzopyrrolidinyl, benzomorpholinyl, methylenedioxyphenyl, ethylenedioxyphenyl, and the like, although the list is not exhaustive. Preferably, aryl includes optionally substituted phenyl and optionally substituted naphthyl, with phenyl being particularly preferred.The aryl group may optionally be substituted with one or more substituents, each substituent independently being alkyl, alkoxy, halogen, haloalkyl, cyano, nitro or dialkylamino, unless specifically stated otherwise.

[0040] The term “alkylaryl”, unless otherwise stated, refers in particular to a monovalent aryl group bearing one or more alkyl groups. group, wherein the aryl group and the alkyl group are as defined above. Preferably, the aryl group is a phenyl group, where the alkyl group may be, for example, methyl, ethyl, n-propyl, n-propyl, n-butyl, n-butyl, n-butyl, or n-butyl. Preferably, the aryl group carries only one alkyl group. The alkylaryl group may optionally be substituted with one or more substituents, each substituent independently being alkyl, alkoxy, halogen, haloalkyl, cyano, nitro, or dialkylamino, unless specifically stated otherwise.

[0041] The term "cycloalkyl," unless otherwise specified, refers particularly to saturated carbocyclic groups consisting of mono- or bicyclic rings. The cycloalkyl group may optionally be substituted with one or more substituents, each substituent independently being alkyl, alkoxy, halogen, haloalkyl, cyano, nitro, or dialkylamino, unless specifically stated otherwise. Examples of cycloalkyl moieties include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and the like, including partially unsaturated derivatives thereof, such as cyclohexenyl, cyclopentenyl, and the like.

[0042] The term “halogen” refers, unless otherwise stated, to fluorine, chlorine, bromine or iodine.

[0043] The invention is explained in more detail below using exemplary embodiments which are not intended to limit the invention. Reagents used

[0044] The following reagents were used in the examples: Chlorotriethoxysilane: Sigma-Aldrich; 98%; CAS 4667-99-6 Chlorotrimethoxysilane: TCI, 90%, CAS 4668-00-2 Acetonitrile: Sigma-Aldrich, 99.8%, anhydrous (< 0.001% H2O), CAS 75-05-8 Toluene: VWR Chemicals; 99.8%; anhydrous (< 0.002% H2O), CAS 108-88-3 Sodium borohydride: but; 98%; CAS 16940-66-2 Lithium borohydride: Sigma-Aldrich; >90%; CAS 16949-15-8 Tri-w-butyltin hydride: Sigma-Aldrich; 97%, CAS 688-73-3 Hydrogen: Linde; 3.0 Gas; CAS 1333-74-0 DIBAL-H: diisobutylaluminum hydride, Sigma-Aldrich; analytically pure; CAS 1191-15-7 Red-Al: Sodium bis(2-methoxy-ethoxy) aluminum dihydride, Sigma- Aldrich, 60 wt% in toluene; CAS 22722-98-1 1 -Methylimidazole: NMI, Sigma-Aldrich; 99%; CAS 616-47-7 Platinum(IV) oxide hydrate: but; 80-82% Pt; 99.95% metal purity; CAS 52785-06-5 Palladium: but; 10% on activated carbon; CAS 7440-05-3 Measurement method

[0045] The mole fractions of the target compounds given in Tables 2B, 3B, 4B, 5B and 6 were calculated using 29 Si NMR spectra were determined in the resulting reaction solution. The amounts in “mol%” refer to the sum of all integrals, which reflect the molar amounts, of the silicon species in the 29Si NMR spectra. The molar percentages were determined from the integral area relative to the internal standard HMDSO. In addition to the reaction solution, SiLL was obtained in Comparative Examples 8 and 10. SiLL is a gaseous compound that did not remain in the reaction mixture and thus could not be detected in the NMR of the reaction solution. The presence of SiU was determined based on its pyrophoric behavior upon opening the apparatus. Examples 1 to 4, 6 and 7 and Comparative Examples 5 and 8 to 11

[0046] Examples 1 to 4, 6 and 7 as well as Comparative Examples 5 and 8 to 11 illustrate the reaction of a compound of the general kormel II with a hydride to a compound of general formula I. All reactions were carried out under argon atmosphere using the SCHLENK technique.

[0047] The reaction was carried out in 50 ml Schlenk flasks. The hydrogenating agent and, if applicable, the catalyst were initially added to the solvent in the flask. The haloalkoxysilane was slowly added dropwise. The reaction mixture was stirred at room temperature for the time specified in the tables. The stirring speed was 700 revolutions per minute (rpm). Examples 1 to 4

[0048] Examples 1 to 4 demonstrate the reaction of chlorotriethoxysilane 1 with NaBH4 in acetonitrile to triethoxysilane 2 without the use of a catalyst. The reaction is shown in Scheme B1. (Scheme Bl) Chlorotriethoxysilane 1 is a compound of the general formula II, in which all radicals R 1 ethoxy and X is chlorine. Triethoxysilane 2 is a compound of the general formula I, in which all radicals R 1Ethoxy. Triethoxysilane 2 is a hydridotrialkylsilane. Dry acetonitrile was used in each case.

[0049] Table 1A shows the molar ratios of chlorotriethoxysilane 1 to NaBH4 in the starting mixture and the reaction times for each example. Table 1B shows the molar percentages of the target compound 2, the starting compound 1, and potential byproducts in the reaction mixture. Potential byproducts are tetraethoxysilane 4 (O(Si(OCH2CH3)4)) and 1,1,1,3,3,3-hexaethoxydisiloxane 5 (O(Si(OCH2CH3)3)2). Comparison example 5

[0050] The procedure was the same as in Examples 1 to 4, except that the molar ratio of chlorotriethoxysilane 1 to NaBEU in the starting mixture was 1:4 (see Table 1A). The results of the reaction are shown in Table 1B. Table 1A The term “VB” indicates a comparative example. Table 1B The term “VB” indicates a comparative example. Examples 6 and 7

[0051] Examples 6 and 7 demonstrate the reaction of chlorotrimethoxysilane 11 with NaBEU in acetonitrile to triethoxysilane 12 without the use of a catalyst. The reaction is shown in Scheme B2. CISi(OCH 3 ) 3 - ► HSi(OCH 3 ) 3 . acetonitrile 11 12 (Scheme B2) Chlorotrimethoxysilane 11 is a compound of the general formula II, in which all radicals R 1 methoxy and X is chlorine. Trimethoxysilane 12 is a compound of the general formula I, in which all radicals R 1 Methoxy. Trimethoxysilane 12 is a hydridotrialkylsilane. Dry acetonitrile was used in each case.

[0052] Table 2A shows the molar ratios of chlorotrimethoxysilane 11 to NaBH4 and the reaction times for each example. Table 2B shows the molar percentages of the target compound 12, the starting compound 11, and potential byproducts in the reaction mixture. Potential byproducts are tetramethoxysilane 14 (O(Si(OCH3)4)) and 1,1,1,3,3,3-hexamethoxydisiloxane 15 (O(Si(OCH3)3)2). Table 2 A Table 2B Comparative example 8

[0053] The procedure was the same as in Examples 1 to 4, except that the hydrogenating agent LiBHi was used instead of the hydrogenating agent NaBHi.

[0054] Table 3A shows the molar ratio of chlorotriethoxysilane 1 to LiBEU and the reaction time. Table 3B shows the molar percentages of the target compound 2, the starting compound 1, and potential byproducts in the reaction mixture. The byproducts are tetraethoxysilane 4 (O(Si(OCH3)4)), 1,1,1,3,3,3-hexaethoxydisiloxane 5 (O(Si(OCH3)3)2), and gaseous SiEU 6. Table 3A The term “VB” indicates a comparative example. Table 3B The term “VB” indicates a comparative example. Comparison example 9

[0055] Comparative Example 9 shows the reaction of chlorotriethoxysilane 1 with tributyltin hydride (BusSnH, where "Bu" stands for a butyl group) in toluene to produce triethoxysilane 2 using the catalyst NMI. The catalyst was used in an amount of 1 mol%, based on the sum of the amounts of chlorotriethoxysilane 1 and BusSnH. The reaction is shown in Scheme B3. Bu 3 SnH CISi(OCH 2 CH 3 ) 3 ► HSi(OCH 2 CH 3 ) 3 Toluene, NMI (Scheme B3) Dry toluene was used.

[0056] Table 4A shows the molar ratio of chlorotriethoxysilane 1 to BuaSnH in the starting mixture and the reaction time for the example. Table 4B shows the molar percentages of the target compound 2, the starting compound 1, and potential by-products in the reaction mixture. Potential by-products are tetraethoxysilane 4 (O(Si(OCH2CH3)4)) and 1,1,1,3,3,3-hexaethoxydisiloxane 5 (O(Si(OCH2CH3)3)2). Table 4 A The term “VB” indicates a comparative example. Table 4B The term “VB” indicates a comparative example. Comparative examples 10 and 11

[0057] The procedure was the same as in Examples 1 to 4, except that toluene was used instead of acetonitrile in both comparative examples, and the hydrogenating agent DIBAL-H was used instead of the hydrogenating agent NaBHi in Comparative Example 10, and the hydrogenating agent Red-Al was used in Comparative Example 11. Dry toluene was used. The experiments were each carried out twice.

[0058] Table 5A shows the molar ratios of chlorotriethoxysilane 1 to the respective hydrogenating agent and the reaction times. Table 5B shows the molar percentages of the target compound 2, the starting compound 1, and potential by-products in the mixture obtained during the reaction. The by-products are tetraethoxysilane 4 (O(Si(OCH3)4)), 1,1,1,3,3,3-hexaethoxydisiloxane 5 (O(Si(OCH3)3)2), and gaseous SiHi 6. Table 5 A The term “VB” indicates a comparative example. Table 5B The term “VB” indicates a comparative example. Comparative examples 12 and 13

[0059] For comparison purposes, experiments were conducted on the hydrogenation of chlorotriethoxysilane 1 with hydrogen in the presence of a catalyst. Hydrogen was used in excess. The catalyst was used in an amount of 1 mol%, based on the sum of the molar amounts of the starting materials. The experiments were carried out in 50 ml Schlenk flasks. The respective catalyst was initially dissolved in dried toluene as a solvent. Hydrogen was then passed through the reaction mixture for a period of 2 h at room temperature. 5 min after the start of the flow, the chlorotriethoxysilane 1 was slowly added dropwise.

[0060] Table 6 shows the mole percentages of the target compound 2, the starting compound 1, and potential by-products in the mixture obtained during the reaction. In Example 12, the by-product is tetraethoxysilane 4 (O(Si(OCH3)4)). In Example 13, the by-products are tetraethoxysilane 4 (O(Si(OCH3)4)) and 1,1,1,3,3,3-hexaethoxydisiloxane 5 (O(Si(OCH3)3)2). Table 6 Results

[0061] Examples 1 to 4, 6, and 7 confirm that the process according to the invention, when using sodium borohydride as the hydrogenating agent, enables the preparation of hydridoalkoxy compounds under the specified conditions. Comparative Examples 8, 10, and 11 show that DIBAL-H (see Comparative Example 10), lithium borohydride (see Comparative Example 8), and Red-Al (see Comparative Example 11), which are very commonly used for haloalkylsilanes, are not suitable hydrogenating agents. When DIBAL-H and lithium borohydride were used, even monosilane was formed. Sodium borohydride proved to be a better hydrogenating agent than tri-ω-butyltin hydride (see Comparative Example 9). The examples further show that, depending on the particular haloalkoxysilane, a reaction time in the range of 24 to 72 hours is optimal.

[0062] Several reactions were carried out between haloalkoxysilanes and sodium borohydride with varying reaction times and stoichiometry ratios (see Examples 1 to 4, 6, and 7). For the reaction of chlorotriethoxysilane 1 with sodium borohydride, the optimum for the synthesis of triethoxysilane was obtained in Example 3, based on these examples, with a reaction time of 48 h and a molar ratio of chlorotriethoxysilane 1 to sodium borohydride of 1:2. In Example 6, an optimum was obtained for the reaction of chlorotrimethoxysilane 11 with sodium borohydride with the same molar ratio but a significantly shorter reaction time of 24 h. Comparative Example 5, however, shows that too large an excess of hydrogenating agent can be detrimental.

[0063] The side reactions that occur to the corresponding tetraalkoxysilanes and hexaalkoxydisiloxanes do not pose a serious problem. Byproducts can be separated from the product mixture. For example, the hexaalkoxydisiloxane can be converted back to the tetraalkoxysilane using a base and the corresponding alcohol (see PS Wahyu et al., ACS Omega, 2021, 6, 51, 35186-35195). The tetraalkoxysilane can be converted back to the haloalkoxysilane (see the previously unpublished German patent application No. 10 2023 127 669.7 and step (1), above).

[0064] Comparative Examples 12 and 13 demonstrate that, under the chosen conditions, catalytic hydrogenation is not a suitable method for producing hydridoalkoxysilanes from haloalkoxysilanes. Only condensation products are obtained.

Claims

Patent claims 1. Process for the preparation of a compound of general formula I R 1 i O H-Si-OR 1 i O i R 1 (Formula I), wherein R 1 at each occurrence is a substituted or unsubstituted, branched or unbranched alkyl group having 1 to 12 carbon atoms, wherein a compound of the general formula II R 1 i O X-Si-OR 1 io IR 1 (Formula II), where R 1 has at each occurrence the meanings given in connection with formula I and X is a halogen, is reacted in acetonitrile as solvent with a hydrogenating agent to give a compound of general formula I, wherein the hydrogenating agent is sodium borohydride.

2. Method according to claim 1, characterized in that R 1in the compound of general formula I at each occurrence is a substituted or unsubstituted, branched or unbranched alkyl group having 1 to 6 carbon atoms.

3. A method according to claim 1 or claim 2, characterized in that R 1 in the compound of general formula I is at each occurrence an unsubstituted, branched or unbranched alkyl group having 1 to 6 carbon atoms.

4. A process according to any one of the preceding claims, characterized in that X is fluorine, chlorine, bromine or iodine.

5. A process according to any one of the preceding claims, characterized in that X is chlorine.

6. Process according to one of the preceding claims, characterized in that the molar ratio of the compound of general formula II to the hydrogenating agent is in a range from 5:1 to 1:

5.

7. Process according to one of the preceding claims, characterized in that the molar ratio of the compound of general formula II to the hydrogenating agent is in a range from 1:1 to 1:

5.

8. Process according to one of the preceding claims, characterized in that the molar ratio of the compound of general formula II to the hydrogenating agent is in a range of 1 : 1 < UHM < 4, where HHM denotes the molar amount of the hydrogenating agent.

9. Process according to one of the preceding claims, characterized in that the concentration of the compound of general formula II in the solvent is in a range from 20% by weight to 80% by weight, based on the total weight of the solution.

10. Process according to one of the preceding claims, characterized in that the maximum concentration of the hydrogenating agent in the solvent corresponds to the saturation limit.

11. The process according to any one of the preceding claims, characterized in that it is carried out at ambient pressure and / or ambient temperature.

12. The process according to any one of the preceding claims, characterized in that it is carried out without a catalyst.

13. Process according to one of the preceding claims, characterized in that the reaction time for the reaction of the compound of general formula II with the hydrogenating agent is in a range of 12 to 96 hours.

14. Process according to one of the preceding claims, characterized in that the reaction time for the reaction of the compound of general formula II with the hydrogenating agent is in a range of 20 to 80 hours.

15. Process according to one of the preceding claims, characterized in that the reaction time for the reaction of the compound of general formula II with the hydrogenating agent is in a range of 24 to 72 hours.

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