Plasma-assisted organofunctionalization of silicon tetrahalides or organohalosilanes

Abstract

The invention relates to a method for the plasma-assisted synthesis of organohalosilanes in which organohalosilanes of the general empirical formula R.sup.1.sub.mR.sup.2.sub.oSiX.sub.4-p (X=F, Cl, Br or I; p=1-4; p=m+o; m=1-4; o=0-3; R.sup.1, R.sup.2=alkyl, alkenyl, alkinyl, aryl) and/or carbosilanes of the general empirical formula R.sup.3.sub.qSiX.sub.3-qCH.sub.2SiR.sup.4.sub.rX.sub.3-r (X=F, Cl, Br or I; q=0-3; r=0-3; R.sup.3, R.sup.4=alkyl, alkenyl, alkinyl, aryl) are formed by activating a plasma in a mixture of one or more volatile organic compounds from the group of alkanes, alkenes, alkines and aromates with SiX.sub.4 and/or organohalosilanes R.sub.nSiX.sub.4-n (X=F, Cl, Br oder I; n=1-4; R=alkyl, alkenyl, alkinyl, aryl).

Claims

1. A method for the plasma-assisted synthesis of carbosilanes, the method comprising: performing a plasma reaction including: passing a reactant mixture through a plasma reactor comprising a plurality of plasma reaction zones separated by a plurality of rest zones, wherein the reactant mixture comprises one or more volatile organic compounds selected from the group consisting of alkanes, alkenes, alkynes and aromatics and one or more silicon containing compounds selected from SiX.sub.4, Si.sub.2X.sub.6, R.sub.nSiX.sub.4-n, and R.sub.mSi.sub.2X.sub.6-m, wherein X is F, Cl, Br, or I, n is 1 to 4, m is 1 to 6, and R is alkyl, alkenyl, alkynyl, or aryl; igniting nonisothermal plasma in the plurality of plasma reaction zones when the reactant mixture is in the plasma reactor such that the reactant mixture passes through the nonisothermal plasma in each of the plurality of plasma reaction zones and also passes through the plurality of rest zones; and forming carbosilanes of the general empirical formula R.sup.3.sub.qSiX.sub.3-qCH.sub.2SiR.sup.4.sub.rX.sub.3-r, wherein X is F, Cl, Br or I; q=0-3; r=0-3; and R.sup.3and R.sup.4 are independently selected from alkyl, alkenyl, alkynyl, and aryl, wherein the reactant mixture is reacted in the plasma reactor under a pressure of 0.1 to 100 hPa, the ratio of volatile organic compound(s) to silicon containing compound(s) is about 1:1 or less, and the plasma reaction is carried out by coupling-in alternating electromagnetic fields in the 1.0 MHz to 2.45 GHz range.

2. The method of claim 1, wherein the plasma reactor comprises a plurality of reaction zones and rest zones which follow one another alternately and the method includes passing the reactant mixture through the plurality of reaction zones and rest zones.

3. The method claim 1, wherein the reactant mixture is reacted in the plasma reactor at reaction temperatures of 80 C. to +400 C.

4. The method claim 3, wherein the carbosilanes are recovered in a collecting vessel (7) downstream of the plasma reactor by low-temperature condensation at approximately 80 C.

5. The method claim 1, wherein the carbosilanes are obtained in a distillation vessel (10) and the method further comprises: distilling the carbosilanes in a distillation column; and collecting individual carbosilanes in a collecting vessel.

6. The method of claim 5, wherein the plasma reactor and the collecting vessel are washed out with SiX.sub.4.

7. The method of claim 5, further comprising recovering MeSiX.sub.3 from the collecting vessel (15).

8. The method of claim 1, wherein the reactant mixture further comprises methane.

9. The method of claim 8, wherein the reactant mixture further comprises ethane, ethene or ethyne.

10. The method of claim 1, wherein R.sub.3 and R.sub.4 are selected from alkyl and aryl.

11. The method of claim 1, wherein R.sub.3 and R.sub.4 are selected from alkyl and alkenyl.

12. The method of claim 1, wherein R.sub.3 and R.sub.4 are selected from alkyl and alkynyl.

13. The method of claim 1, wherein the reactant mixture comprises halosilanes, SiF.sub.4, SiCl.sub.4 or SiBr.sub.4.

14. The method claim 1 wherein the reactant mixture comprises organohalosilanes or methyltrichlorosilane.

15. The method of claim 1, wherein the reactant mixture further comprises hydrogen.

16. The method of claim 1, wherein the carbosilanes comprise X.sub.3SiCH.sub.2SiX.sub.3.

17. The method of claim 1, wherein the carbosilanes comprise bis(silyl)methane H.sub.3SiCH.sub.2SiH.sub.3, a silyl organylated bis(silyl) methane, or a silyl halogenated derivative of bis(silyl) methane.

18. The method of claim 1, wherein the reactant mixture comprises, R.sub.nSik.sub.4-n, where R is selected from vinyl and ethynyl.

19. The method of claim 1, wherein the carbosilanes comprise RX.sub.2SiCH.sub.2SiX.sub.3or (RX.sub.2Si).sub.2CH.sub.2, where R is selected from vinyl and ethynyl.

Description

(1) The method for plasma-assisted organofunctionalization of SiX.sub.4 or organohalosilanes traverses a plurality of steps and may be described using SiCl.sub.4 as an example, with reference to the drawing, as follows: 1. through the gas inlet (1), CH.sub.4 and SiCl.sub.4 are passed into the reactor (5) and 2. a plasma is ignited by application of alternating electromagnetic fields under reduced pressure (0.1-100 hPa). 3. The reactor may comprise a plurality of plasma zones (2) and rest zones (3) and also cooled surfaces. The reaction gases flow through the reactor (5) toward the vacuum pump, and 4. the volatile constituents (SiCl.sub.4, MeSiCl.sub.3, Me.sub.2SiCl.sub.2, etc.) are retained in a collecting vessel by deep cooling (16) (e.g., at 80 C. with cryostat). 5. After a fixed time, the reaction is ended and the collected silane mixture is run off into a distillation vessel (10), where it 6. can be separated into the individual components by fractional distillation. This produces SiCl.sub.4 (reactant), MeSiCl.sub.3, and Me.sub.2SiCl.sub.2 as colorless liquids. 7. Additionally, in the reactor area, yellow to brownish coatings of methylated oligosilanes and polysilanes are obtained, which 8. by dissolution with SiCl.sub.4 are transferred to the collecting vessel for polysilanes (13).

(2) The method for the methylation of tetrachlorosilane is depicted in the drawing with the following reference numerals: 1. Feed port for silicon tetrachloride and methane 2. Plasma reaction zone 3. Plasma rest zone 4. Plasma electrodes 5. Plasma reaction vessel 6. Port for vacuum pump 7. Low-temperature collecting vessel 8. Condenser 9. Distillation column 10. Distillation vessel 11. Bottom drain port 12. Drain valve 13. Collecting vessel 1 14. Service valve for inert-gas blanketing or vacuum 15. Collecting vessel 2 16. Deep-cooling device

WORKING EXAMPLES

(3) General procedure

(4) SiCl.sub.4 is introduced with the reactant gas (around 10-15 l/min) through nozzles into the reactor (5), and the plasma is ignited. The SiCl.sub.4/reactant gas volume ratio can be varied arbitrarily, and other inert-gas or hydrogen admixtures are possible. Reactant gases employed also include gas mixtures (e.g., methane/ethylene or methane/hydrogen) in different ratios. The SiCl.sub.4/product mixture is collected at the exit from the reactor and worked up by distillation. In this distillation, the products are isolated according to their boiling points, and identified by spectroscopy. In the working examples described here, the products are largely freed from the SiCl.sub.4, the formation of product being between 25% and 60% depending on conditions. The product mixture is analyzed by gas chromatography, and the identity of individual compounds is ascertained by comparison of the fragmentation patterns and the retention times with those of authentic samples.

(5) Product formation may be understood formally, under the prevailing plasma conditions, from a combination of free-radical reactions (e.g., SiCl4.fwdarw.Cl.+Cl.sub.3Si.; CH.sub.4.fwdarw..CH.sub.3+H.; Cl.sub.3Si.+H..fwdarw.Cl.sub.3SiH; Cl.sub.3Si.+.Me.fwdarw.Cl.sub.3SiMe) and carbene insertion reactions into SiC and SiSi bonds (e.g., CH.sub.4.fwdarw.CH.sub.2+H.sub.2; R.sub.3SiCH.sub.3+|CH.sub.2.fwdarw.R.sub.3SiCH.sub.2CH.sub.3; 2Cl.sub.3Si..fwdarw.Cl.sub.3SiSiCl.sub.3|CH.sub.2.fwdarw.Cl.sub.3SiCH.sub.2SiCl.sub.3, etc.

(6) Explanations/def.:

(7) Me=methyl=CH.sub.3 Vi=vinyl=CHCH.sub.2 Et=ethyl=CH.sub.2CH.sub.3 1. SiCl.sub.4 in the presence of methane, CH.sub.4: Me(H)SiCl.sub.2 (3%), MeSiCl.sub.3 (8%), Me.sub.2SiCl.sub.2 (5%) By admixing hydrogen (H.sub.2), the fraction of Me(H)SiCl.sub.2 is particularly increased: Me(H)SiCl.sub.2 (18%), MeSiCl.sub.3 (17%), Me.sub.2SiCl.sub.2 (12%) If the fraction of methane is significantly reduced, Cl.sub.3SiCH.sub.2SiCl.sub.3 is formed in a fraction of more than 40%, and the fractions of Me(H)SiCl.sub.2>>MeSiCl.sub.3>Me.sub.2SiCl.sub.2 are now significantly lower. If, instead of methane, ethane, C.sub.2H.sub.6, is used, there is an increase in the relative proportion of methyl radicals and carbenes (.CH.sub.3 and .|CH.sub.2) in the reaction mixture, thereby increasing the fraction of methylated products and carbosilanes: Cl.sub.3SiCH.sub.2CH.sub.3 (2.8%), ViSiCl.sub.3 (25.49%), MeViSiCl.sub.2 (1.6%), Cl.sub.3SiCH.sub.2SiCl.sub.3 (53%), ViCl.sub.2SiCH.sub.2SiCl.sub.2Me (17.6%), with, additionally, small amounts of Cl.sub.3SiH, Me(H)SiCl.sub.2, Cl.sub.6Si.sub.2 formed. 2. SiCl.sub.4 in the presence of ethane, C.sub.2H.sub.4 HSiCl.sub.3 (3%), ViSiCl.sub.3 (29%), Cl.sub.3SiCCH (10.6%), Vi.sub.2SiCl.sub.2 (2.4%), ViEtSiCl.sub.2 (12.7%), Cl.sub.3SiCH.sub.2CH.sub.2CH.sub.3 (4.7%), Cl.sub.3SiCH.sub.2SiCl.sub.3 (38%), Cl.sub.3SiCH.sub.2SiCl.sub.2Vi (2.6%). If only a little ethene is fed in, the primary products are chlorinated hydrocarbons, benzene, and, in terms of silanes, almost exclusively Cl.sub.3SiCH.sub.2SiCl.sub.3 in addition to a little ViSiCl.sub.3. If further methane, CH.sub.4, is added to the ethene, the following products are formed: HSiCl.sub.3 (2%), MeSiCl.sub.3 (1%), Me.sub.2SiCl.sub.2 (<1%), Cl.sub.3SiCCH (3.4%), Cl.sub.3SiCH.sub.2CH.sub.3 (5.2%), Cl.sub.3SiCHCH.sub.2 (26%), MeViSiCl.sub.2 (0.6%), EtSiCl.sub.3 in traces, Cl.sub.3SiCH.sub.2CHCH.sub.2 (26%), Cl.sub.3SiCH.sub.2CH.sub.2CH.sub.3 (1.5%), Cl.sub.2ViSi (CCCHCH.sub.2) (18%), Cl.sub.3SiCH.sub.2SiCl.sub.3 (18%). 3. By using methyltrichlorosilane, MeSiCl.sub.3, instead of SiCl.sub.4, the fraction of Me.sub.2SiCl.sub.2 is significantly increased in the presence of methane. Where the combination MeSiCl.sub.3/ethene is used, the following products are isolated: SiCl.sub.4 (6.9%), Me.sub.2ViSiH (1.2%), ViSiCl.sub.3 (32.2%), EtSiCl.sub.3 (6.4%), MeViSiCl.sub.2 (31%), Cl.sub.3SiCH.sub.2SiCl.sub.3 (17.2%), MeCl.sub.2SiCH.sub.2SiCl.sub.3 (5.1%). The combination MeSiCl.sub.3/CHCH (4-5 l/min) yields the following products: SiCl.sub.4 (43.4%), ViSiCl.sub.3 (3.6%), MeViSiCl.sub.2 (6.8%), Cl.sub.3SiCH.sub.2SiCl.sub.3 (46.4%). 4. Alternative procedure with reduced gas flow rates (0.2 l/min each): a mixture of CH.sub.4 and SiCl.sub.4 (1:1) is passed into the plasma reaction vessel 5 via the port 1 under a pressure of 1-2 hPa, and a plasma is generated in the region of the plasma electrodes (4). Then methylated chloropolysilanes deposit in the plasma reaction vessel 5 and in the collecting vessel 13. The volatile chloro- and methylchlorosilanes are condensed in the vessel 7 and collected in vessel 10, while the gaseous reaction products are taken off via the port 6. Over the course of 2.5 h, 181 g of product mixture are collected in the vessel 10, and are separated via the distillation column 9 into the individual products. In this case, from the product mixture, 21.6 g of MeSiCl.sub.3 and 1.8 g of Me.sub.2SiCl.sub.2 are obtained as colorless liquids. By dissolution in SiCl.sub.4, the methylated chloropolysilanes are transferred from the plasma reaction vessel 5 to the collecting vessel 13, and are taken off via the bottom drain port (11).