DE945982C - Process for the splitting of tetraalkyl orthosilicates - Google Patents

Description

Process for the splitting of Tetraalkylorthosilikaten Siliciumhalogeni, de react with alcohols to form alkoxy derivatives, which are called organic Orthosilicates (tetraalkylorthosilicates) called. Their general formula is Si (0R) 4.

The alkoxysiloxanes known per se, that is, the alkyl esters of pyrosilicic acid (hexaalkylpyrosilicates of the type Si20 (OR) "), of metasilicic acid (dialkylmetasilicates of the type Si O (OR) 2) and the higher esters of podymetosilicic acids (alkylpolymetasilicates of the type Sin0" (OR) 2n), in addition to some alkoxychlorosilanes Si C1, (0 R) s, S, i C12. (0 R) 2 and S 'Cls, (OR) are only formed as by-products in small amounts. Alkoxysiloxanes are also produced according to Friedel-Crafts ("Liebigs Annalen der Chemie", vol. X36 [x865], p. 203, especially p. 2xo, and "Anisales de Chimie et de Physique", 4th series [x866], vol. g, p. 24) when boiling tetraalkyl orthosilicate with a little water in an alcoholic solution through partial hydrolysis and subsequent intermolecular condensation of the silicoles formed. So z. B: from tetramethylorthosilicate by boiling in aqueous methanol II # examethoxydisiloxane. (di hexamethylpyrosilicate) you produce O (OC H3) s. As the hydrolysis progresses, however, esters with ever higher condensation and ever higher molecular weight and finally the hydrolysis end product, pure silica, are obtained. In the same way, S chwarz and Ke ss 1 er prepared kitelic acid polyesters by partial hydrolysis in .aqueous hydrolysis media (Journal of Inorganic and General Chemistry, Vol. 263, pp. 15 to 30). Another way of producing hexaalkyl pyrosilicates, dialkyl metasilicates and alkyl poly metasilicates is to react the chlorides of the corresponding silicas with alcohols. Friede.l and Ladenburg (Liebigs Annalen der Chemie, vol. 147, p. 362) obtained hexaethyl pyrosilicate by reacting the hexadhloride of pyrosilicic acid Sie O C16 with absolute ethyl alcohol and, in an analogous manner, diethyl metasilicate from the dichloride of metasilicic acid Si O C12.

Troost-Hautefeuille. ("Annales de Chimie et de Physique"; 5th row [z876], vol. 7, p. 472) converted the oxychloride Si404C1 $ (octachloride of tetrametosilicic acid) with absolute alcohol to the octaaryl tetrametasilicate Si 4 04 ( O C2 H5) B.

None of these display methods offer any possibility for an economic one Manufacturing-. process of the alkyl esters of pyro-, meta- and polymetosilicic acids. The yield of these esters in the preparation of the tetraalkyl orthosilicates is relatively, low. Treatment of tetraalkyl orthosilicates with water delivers, depending on the progressing hydrolysis, low or high condensation Esters which, however, are very difficult or impossible to isolate in detail and under certain circumstances pass easily and quickly into the end link silicic acid.

The production of the alkoxysiloxanes from the corresponding chlorides but does not require a simple representation of the latter.

It has now been found that tetraalkyl orthosylicates can be obtained in a simple manner Wise and economically more advantageous to convert into other silicon compounds can, including preferably in the alkyl esters of pyro-, meta- and polymetosilicic acids, if the vapors of the tetraorthosilicates are exposed to temperatures above theirs Boiling point, expediently from 500 to 600 °.

The cleavage in the vapor phase is carried out by suitable catalysts favored. Chlorine compounds have been found to be such, which upon treatment split off with steam hydrogen chloride, z. B-. S 'C14 or Sn C14, especially but hydrogen chloride itself. In addition, those with red heat are particularly suitable practically non-volatile chlorides of the metals of the 2nd main group of the periodic Systems, e.g. B. Mg C12 and Ca C12. Basically, fabrics with a large surface are also such as coal, silica gel, pumice stone or unglazed porcelain shards, are suitable; furthermore, the reaction is generally controlled by metal salts; Oxides, hydioxides and volatile and non-volatile acids promoted. It has proven to be beneficial to apply the catalysts to the surface-active substances mentioned.

The process in the vapor phase is basically carried out in such a way that that tetraalkylorthosilicate vapor - through a reaction tube resistant to hydrogen chloride or a differently shaped reactor at the appropriate reaction temperature through the contact or through the empty apparatus together with the appropriate amount anhydrous hydrogen chloride is passed. As a splitting device, pipes or other containers made of ceramic material, also made of acid-resistant stainless steel (e.g. nickel-chromium alloyed or silicon-chromium-aluminum steels) or even from Serve iron. Chloride catalysts are slurried in a known manner Carriers, such as pumice stone, used after thorough drying. When using of H Cl gas as a catalyst, it has proven to be advantageous, optimal Adhere to the addition of about 0.5 moles of HCh per mole of tetraalkyl orthosilicate. Lower amounts HCl does not appear as effective under the same conditions, while higher additions to undesired side reactions, mainly to the extensive splitting with separation of silica, as well as increasing attack on the metal equipment that may be used leads. The cleavage product condensed in the cooler contains the split off alcohol and unreacted tetraalkyl orthosilicate the distillable esters of pyrosilicic acid, Metasilicic and polymetasilicic acids. In addition, forms as a result of secondary reactions an exhaust gas that contains some carbon monoxide and saturated and unsaturated hydrocarbons mainly from hydrogen and the corresponding olefin (ethylene, butylene, etc.) consists. On distillable "high songs" (as such, the alkyl esters of the Pyro, meta = and polymetosilicic acids are called) arise in the spa: oil process mainly hexaalkylpyrosilicate you O (O R) g, dialkyl metasilicate Si O (O R) 2, octaalkyl tetrametasilicate at Si4 04 (O R) 8, polymeric dialkyl metasilicate (SiO (OR) ß) ,.

On non-volatile, non-writing, powdery gravel by-products have been proven: Dialkylmetapolysilicates approximately with the general formula Sin02n_1 (0R) 2, e.g. B. Dialkyl metadisilicate Sie 03 (O R) 2, dialkyl metadisilicate Si3 05 (O R) 2 etc., also metasilicic acid H2 Si 03, Si 02 or their polymers and in small amount of silica itself.

The proportion of volatile and non-volatile fission products fluctuates depending1 on the level of the reaction temperature. Generally up to one predominates Cleavage temperature of about 600 ° almost always results in the formation of the hexaalkylpyrosilicate, while under more extreme conditions, from around 700 °, the formation of the higher-edged, non-volatile compounds increases and under certain circumstances to a total decomposition of the tetraalkyl ester to be cleaved leads. Below 60 ° the yield of distillables falls "High songs" from strongly. It has been found to be useful to maintain a degree of cleavage of the tetraalkyl orthosilicate of not more than 8o%, A good yield of "high songs" with the least amount of by-products to achieve. If you are satisfied with a lower turnover, e.g. B. about 5o%, so can even at a lower gap temperature, e.g. B. 5oo °, or increased, z. B. double throughput to be worked. It has been found to be particularly beneficial for the reaction when one is based on dry raw materials.

The isolation of the "high boilers" from the cleavage product can take place as long as the boiling points of the individual alkyl derivatives allow it, largely through simple Fractionation can be carried out at normal pressure, otherwise in a vacuum. The one in the splitting process The alcohol that is split off is practically anhydrous. The unreacted in the reaction apparatus, retraalkylorthosilicate distilled over before the "high boilers" can easily be used again for further divisions.

For the following examples, a tetraethyl orthosilicate came with the Boiling point 162 to 163 ° / 722 torr for use, the free from moisture, ethyl alcohol and high-boiling components. In principle, raw esters can also be used directly can be assumed. In the examples, as already mentioned, "high songs" the volatile, d. H. distillable esters such as hexaalkyl pyrosilicate, dialkyl metasilicate (monomeric and polymeric) as well as octaalkyltetrarnetasilicate, as residue the non-volatile, non-melting dialkyl metapolysilicates and metapolysilicic acids.

The superiority of the new process is that it is over the previous method a higher yield of high songs and one accordingly provides less accumulation of pebbly, less valuable by-products. The practical execution is very simple and at the same time particularly economical, too a continuous way of working is made possible.

EXAMPLE i 100 g of tetraethyl orthosilicate, about 30 g per hour, were added dropwise into an empty, difficult-to-melt glass tube, about 40 mm long and about 25 mm in diameter (effective tube volume about 150 ccm), heated to 600 °. The cleavage products condensed in the attached Liebig condenser and collected in an ice-cold receiver weighed 97.7 g. 2.7 g of residue were deposited in the reaction tube. When the cleavage products were worked up by distillation in a fractionating column at normal pressure or in vacuo, the following were obtained: 9 g of ethyl alcohol, KP. 78 ° / 72o Torr, 16 g "HoChsieder", b.p. 125 to 220 ° / 12 Torr (mainly hexaethylpyrosilicate Si20 (OC2H5) s, b.p. 150 to 160 ° / 12 Torr), also about carbonaceous-pebbly residue . About 60 g of unchanged tetraethyl orthosilicate distilled over at 60 ° / 12 Torr, corresponding to a conversion of 40%. The space-time yield of high boilers (g per hour per liter of catalyst space) was 30.5. If the same amount of tetraethyl orthosilicate is heated without a catalyst for 6 hours on a 30 cm long column filled with saddles with dephlegmation, only 0.75 g of high boilers (including any i?, Excess) are obtained, corresponding to a conversion of only 0.75% .

Example e As in Example i, 100 g of tetraethylo.rtnosilicate were added at 60 ° in a hard-to-melt glass tube, which is filled with 150 ccm of pumice: sstein-Mg C12 Catalyst was filled, split. The pumice stone was 10% of its weight on impregnated with crystallized MgC12 and in the reaction tube at 6oo ° in vacuo for so long dried hard until no trace of moisture was lost. At fission products 89.2 g were obtained, of which 18 g ethyl alcohol, 35.5 g "high songs", boiling point 130 bis 270 ° / 14 Torr, mainly again hexaethyl pyrosilicate, bp. 13o to 16o ° / 14 Torr, in addition to some octahyl tetrametasilicate Si404 (OC2H5) s, bp. 16o to 19o ° / 14 Torr, and monomeric diethyl metasilicate Si O (O C2 H5) 2, KP-24o to 27o ° / 14 Törr, furthermore 3.5 g non-distillable residue. Unchanged tetraethyl orthosilicate were 24.5 g, b.p. 60 to 70 ° / 14 Torr, recovered, corresponding to a conversion of 75.5 0/0. 6 g of residue had separated out in the reaction tube itself. The space-time yield on "Hochsie, dern" was 67.5 Example 3 100 g of tetraethyl orthosilicate were like in example i split in an empty, difficult-to-melt glass tube at 600 °, but with the simultaneous introduction of dry hydrogen chloride as a catalyst. The amount of H Cl gas fed in was 0.5 mol of H Cl per 1 mol of tetraethylorthosilicate feed. The work-up of the cleavage products by fractionation in a water jet vacuum gave with a conversion of 78; 5% in addition to 13.5 g of ethyl alcohol 43.5 g of "high boiling", bp. i2o up to 270 ° / 14 Torr, and 4 g of resinous carbonaceous residue. Of the "Hoclhsiedern" are 20 g of hexaethyl pyrosilicate with a boiling point of 129 to 16o ° / 14 Torr, about 17.5 g of octaethyl tetrametasilicate with a bp. 16o to 24o ° / 14 Torr and about 6 g of manomeric and polymeric diethyl metasili: cat with bp. 240 to 27o ° / 14 Torr. 2.7 g of residue were formed in the reaction tube. The space-time yield of "high songs" was 82. Example 4 100 g of tetraethyl orthosilicate were added at 500 ° into an empty iron pipe with the same dimensions as those of the sdh-nver fusible Glass tube in Examples i to 3 under otherwise identical conditions as in the example i entered drop by drop. There were next to 0.6 g of residue in the reaction tube 98.7 g cleavage products obtained, namely 2.5 g ethyl alcohol, 85.5 g unchanged tetraethyl orthosilicate, 7.6 g "high boilers", b.p. 125 to 220 ° / r2 Torr (mainly hexaethylpyrosilicate), and 0.9 g of nondistillable carbonaceous residue. The conversion of tetraethyl orthosilicate was 14.5%. The space-time yield of "high boilers" was 14.5-example 100 g of tetraethyl orthosilicate were in an empty iron pipe as in Example 4, but at a reaction temperature split at 60o °. The conversion was 46%. 94.3 g of liquid cleavage products fell at. There were 4 g of residue in the reaction tube. The processing of the liquid fission products in vacuo gave 10 g of ethyl alcohol, 54 g of unchanged tetraethyl orthosilicate, 24.3 g "high boilers" with a boiling point of 12o to 27o ° / 12 Torr and 2 g of distillation residue. from the high boilers were about 10.3 g of hexaethyl pyrosilicate with a boiling point of 12o to 140 ° / 12 torr, about 8.5 g of octahydrate tetrarnetasilicate with a boiling point of 15o to 21o ° / 12 Torr and about 5.5 g monomeric and polymeric diethyl metasilicate with a boiling point of 22o to 27o ° / 12 Torr. The space-time yield in "high boilers" was 46.2.

EXAMPLE 6 100 g of tetraethyl orthosilicate were subjected to cleavage at 60 ° in an iron pipe over a pumice-Caldumchlori @ d = catalyst. As in all previous examples, the feed rate of the tetraester was about 30 g per hour. The conversion was 72%. 36 g of "high boilers" (mainly hexaethyl pyrosilicate) were obtained. 5.5 g of residues were obtained, of which 2.5 g were in the reaction tube itself and 3 g as distillation residue during the fractionation of the liquid cleavage products in vacuo. The space-time yield of "high boilers" with a contact space of about 150 ccm is calculated to be 68.5.

Example ? 100 g of tetraethylorohosilicate were cleaved at a rate of 30 g per hour together with 0.5 moles of HCl gas per 1 mole of ester feed as a catalyst in an empty iron pipe at 60 °. Revenue 79.5 0/0. The "high boilers" amounted to 46.5 g, KP-125 to 270 ° / 14 Torr, mainly again hexa-methylpyrosilicate, bp 125 to 140 ° / 14 Torr. The residue in the reaction tube was 3.8 g, 2.5 g during the distillation. The space-time yield of "high boilers" was 88.5.

Example 8 Are you satisfied with a lower conversion by If the feed rate of the ester to be cleaved increases, a significant one can be achieved achieve greater space-time yield of "high boilers".

100 g of tetraethylorthosilicate were together with 0.25 mol of H CL gas per 1 mol of ester feed in the alloyed iron pipe with 15o ccm effective reaction space split at 60o °. The hourly feed of tetraethyl orthosilicate was this time 60 g per hour. The conversion was 50.50 / 0. On "high boilers" (mainly hexaethyl pyrosilicate, Bp 125 to 140 ° / z2 Torr) were 32 g, corresponding to a space-time yield of z25. The total residue was 4.5 g, of which 2 g in the reactor and 2.5 g at the distillation of the cleavage product.

Example 9 100 g of tetraethyl orphosilicate vapor were obtained as in Example at the same speed, namely 6o g per hour, at 60o ° together with 0.25 times H Cl gas per 1 mol of ester feed through a stainless steel pipe (e.g. V 4A) from 25 mm diameter headed. At a conversion of 65% were ho g ethyl alcohol and recovered 35 g of unreacted tetraethyl orthosilicate. "Boilers" were 38 g formed, corresponding to a space-time yield of 72.5. Non-distillable Residues were a total of 6 g, of which 4 g in the reaction tube and 2 g during the distillation of the fission products.

Example 1o There were 100 g of tetraethyl orthosilicate containing 10.5 g freshly distilled silicon tetrachloride (stoichiometric 0.5 mol HCl per 1 mol incoming tetraester), under otherwise the same conditions as in the example 7 at 60o ° - passed through an empty iron pipe. On unchanged tetraethyl orthosilicate 27 g were obtained back, corresponding to a conversion of 730/0. In addition to 17 g split off 37.5 g of "high boilers" were formed in ethyl alcohol. The non-volatile residue was 8 g.

Example ii When passing 100 g of crude tetraethyl orthosilicate through which, in addition to 7 g of free hydrogen chloride, about 93 g of chloroester-containing tetraethyl ortho, silicate contained, through an iron pipe heated to 60o ° were 51.5 g of unreacted Crude TetraäthylorNhosilikat, bp 47 to 55 ° / 13 Torr, recovered, that is a Sales of 41.40 / 0. 20.9 g of "high boilers", bp. 12o to 26o ° / 15 Torr, corresponding to a space-time yield of 4o. The non-distillable residue was 5 g.

Example 1.2 In the cleavage of 100 g of tetrabutyl orthosilicate 60o ° in an iron pipe with 0.5 moles of HCl gas per 1 mole of tetrabutylorthosilicate feed the degree of cleavage was 50%. The hourly feed of the ester into the reaction tube was 3o g. In addition to 19 g of split-off n-butyl alkali, 50 g of unreacted, recycled tetrabutyl orthosilicate recovered. At "high boilers" were obtained in the distillation in a water jet vacuum 28 g with a boiling point of 20o to 31o ° / 14 Torr, mainly hexabutylpyrasilicate with a boiling point of 200 to 23o ° / 14 torr, accordingly a space-time yield from 53.5. The non-volatile residues were a total of 5 g.

Claims (2)

PATENT CLAIMS: i. Process for splitting tetraalkyl orthosilicates, characterized in that they are exposed in the vapor phase in the presence or absence of catalysts to temperatures which are above their boiling point, preferably between 500. and 6oo °. 2. The method according to claim i, characterized in that the catalysts used are hydrogen chloride or chlorine compounds which split off hydrogen chloride on treatment with steam, or the chlorides of the metals of main group 2 of the Periodic Table are used. 3. The method according to claim 1 and 2, characterized in that dry starting products are used. Considered publications: "Chemie der Silicones" by Andreas Hungar, 1952, p. 54, para. 2, Verlag Technik, Berlin; Journal of Inorganic and General Chemie, Vol. 263 (195o), pp. 15-30.