Method for purifying halogenated oligosilanes

Abstract

The invention relates to a method for purifying halogenated oligosilanes in the form of a pure compound or a mixture of compounds with respectively at least one direct SiSi bond, the substituents thereof being exclusively made from halogen or from halogen and hydrogen and in the composition thereof, the atomic ratio of the substituents:silicon is at least 3:2, by the action of at least one purification agent on the halogenated oligosilane and by isolating the halogenated oligosilanes with improved purity. According to prior art, halogenated monosilanes such as HSiCl.sub.3 are purified by treating with organic compounds, preferably polymers, containing amino groups, and are separated from said mixtures. Based on the contained amino groups, said method can not be used for halogenated oligosilanes as the secondary reactions lead to a decomposition of the products. The novel method is used to provide the desired products in a high yield and purity without using the amino groups.

Claims

1. A method for purification of halogenated oligosilanes Si.sub.nX.sub.2n+2 with n=2 through n=6 as compounds or as mixtures of compounds in which the substituents X comprise chlorine or chlorine and hydrogen, the process comprises the steps: (a) adding a complexing agent and a fluoride or fluoride mixture to the halogenated oligosilane, wherein fluoride F.sup. from the fluoride or fluoride mixture is made available for a reaction in an amount of more than 1 ppb calculated as F.sup. in relation to the mass of the halogenated oligosilane, b) carrying out at least one processing step in which at least the fluoride acts upon the halogenated oligosilane, wherein the at least one processing step is selected from the group consisting of stirring, swirling, shaking, heating to reflux, and diffusing, wherein a solvent is added to the halogenated oligosilane and/or fluoride before or during the processing step, the solvent is selected from the group consisting of alkanes, cycloalkanes, ethers, aromatics, and chlorinated silanes, wherein the proportion of the solvent in the mixture with the halogenated oligosilanes is at least 0.01 mass % and wherein a siloxane as a pure compound or mixture of compounds selected from the group consisting of Cl.sub.3SiOSiCl.sub.3, Cl.sub.3SiOSiCl.sub.2SiCl.sub.3, and Cl.sub.3SiOSiCl.sub.2OSiCl.sub.3 is added to the halogenated oligosilane before or during the processing step, wherein the proportion of the siloxane in the mixture with the halogenated oligosilane is at least 0.001 mass %, and (c) carrying out at least one separation method for the isolation of the halogenated oligosilane, wherein the separation method is selected from the group consisting of decanting, filtering, distilling, and subliming.

2. The method according to claim 1, wherein the fluoride is selected from the group consisting of alkali metal fluorides, alkaline earth metal fluorides, silicon fluorides Si.sub.nY.sub.oF.sub.p, with Y=halogen, organyl, siloxanyl and/or hydrogen; o+p=2n+2; n >1, and zinc fluoride.

3. The method according to claim 1, wherein the complexing agent is being selected from the group consisting of polyethers, crown ethers, and cryptands.

4. The method according to claim 1, wherein X in Si.sub.nX.sub.2n+2 is more than 95 atom % chlorine, and/or the hydrogen content in Si.sub.nX.sub.2n+2 is less than 5 atom %.

5. The method according to claim 1, wherein the chlorinated oligosilane contains a diluent selected from the group consisting of SiCl.sub.4, Si.sub.2Cl.sub.6, Si.sub.3Cl.sub.8, and Si.sub.4Cl.sub.10, wherein the proportion of the diluent based on the halogenated oligosilane is least 0.001 mass %.

6. The method according to claim 1, wherein at least one separation method is operated at a pressure of less than 1600 hPa.

7. The method according to claim 1, wherein the at least one processing step and/or one separation method is operated at a temperature of higher than 30 C.

8. A method for the purification of halogenated oligosilanes Si.sub.nX.sub.2n+2 with n=2 through n=6 as compounds or as mixtures of compounds in which the substituents X comprise chlorine or chlorine and hydrogen, the process comprises the steps: (a) adding a complexing agent and a fluoride or fluoride mixture to the halogenated oligosilane, wherein fluoride F.sup. from the fluoride or fluoride mixture is made available for a reaction in an amount of more than 1 ppb calculated as F.sup. in relation to the mass of the halogenated oligosilane, (b) carrying out at least one processing step in which at least the fluoride acts upon the halogenated oligosilane, wherein the at least one processing step is selected from the group consisting of stirring, swirling, shaking, heating to reflux, and diffusing, and (c) carrying out at least one separation method for the isolation of the halogenated oligosilane takes place, wherein the separation method is selected from the group consisting of decanting, filtering, distilling, and subliming.

9. The method according to claim 8, wherein the fluoride is selected from the group consisting of alkali metal fluorides, alkaline earth metal fluorides, silicon fluorides Si.sub.nY.sub.oF.sub.p, with Y=halogen, organyl, siloxanyl and/or hydrogen; o+p=2n+2; n >1.

10. The method according to claim 8, wherein said complexing agent being selected from the group consisting of polyethers, crown ethers, and cryptands.

11. The method according to claim 8, wherein a solvent is added to the halogenated oligosilane and/or the fluoride before or during the processing step, wherein the solvent is selected from the group consisting of alkanes, cycloalkanes, ethers, aromatics, and chlorinated silanes, wherein the proportion of the solvent in the mixture with the halogenated oligosilanes is at least 0.01 mass %.

12. The method of claim 8, wherein X in Si.sub.nX.sub.2n+2 is more than 95 atom % chlorine, and/or the hydrogen content in Si.sub.nX.sub.2n+2 is less than 5 atomic %.

13. The method of claim 8, wherein the chlorinated oligosilane contains a diluent selected from the group consisting of SiCl.sub.4, Si.sub.2Cl.sub.6, Si.sub.3Cl.sub.8, and Si.sub.4Cl.sub.10, wherein the proportion of the diluent based on the halogenated oligosilane is least 0.001 mass %.

14. The method of claim 8, wherein at least one separation method is operated at a pressure of less than 1600 hPa.

15. The method according to claim 8, wherein the at least one processing step and/or one separation method is operated at a temperature of higher than 30 C.

16. The method according to claim 8, that wherein a siloxane as a compound or a mixture of compounds selected from the group consisting of Cl.sub.3SiOSiCl.sub.3, Cl.sub.3SiOSiCl.sub.2SiCl.sub.3, and Cl.sub.3SiOSiCl.sub.2OSiCl.sub.3 is added to the halogenated oligosilane before or during the processing step, wherein the proportion of the siloxane in the mixture with the halogenated oligosilane is at least 0.001 mass %.

Description

INDUSTRIAL APPLICABILITY

(1) The method according to the present invention for purifying halogenated oligosilanes provides a significant economic advantage, since both the yield of products as well as the per-time yield can be significantly increased over the prior art by adding the additives according to the present invention.

(2) Furthermore, the purity of the final products is increased by the addition of the purification agent according to the present invention, resulting in an improved market position for the product, thereby achieving a further economic advantage within a method for purifying chlorinated oligosilanes (OCSs).

(3) Various solutions are possible for the technical implementation of the method, from which non-exclusive variants for solving the present problem are listed in the embodiments below.

Embodiment 1

(4) 70 kg hexachlorodisilane was treated with a suspension of 18 g 18-crown-6 and 2.7 g KF in 50 mL cyclohexane. The mixture was stirred for 2 h and then was fractionally distilled. A main run of 62 kg HCDS was obtained after 10 h. In the course of this purification, the original aluminum content of 3.8 ppm and iron content of 1.3 ppm were thus respectively reduced to below 30 ppb.

Embodiment 2

(5) 60 kg hexachlorodisilane was treated with a suspension of 50 g 18-crown-6 and 5 g KF in 150 mL triglyme. The mixture was stirred overnight and then was fractionally distilled. A main run of 45 kg HCDS was obtained after 9 h. In the course of this purification, the original aluminum content of 800 ppb, iron content of 75 ppb, and magnesium content of 180 ppb were thus respectively reduced to below 5 ppb.

Embodiment 3

(6) 8 kg octachlorotrisilane was treated with a suspension of 0.5 g NaF and 4.5 g 15-crown-5 in 30 mL dichloromethane. The mixture was stirred at rt overnight and then was decanted from the undissolved solids. The OCTS was then quickly distilled off under vacuum (approx. 10 hPa) through a short column, and was then fractionally distilled under vacuum (approx. 10 hPa) A main run of 5 kg OCTS was obtained over 8 h. The content values in ppb for the exemplary trace contaminants before and after purification are shown in the following table.

(7) TABLE-US-00002 OCTS Al Cr Mn Cu Fe Mg K Na Ti Ca Crude 920 <30 <30 58 46 110 160 120 <30 750 Purified <30 <30 <30 <30 <30 <30 <50 <50 <30 <50

Embodiment 4

(8) 1.5 kg of a mixture of approx. 90% of a tetrachlorodisilane isomer mixture and 10% pentachlorodisilane was treated with a suspension of 0.1 g NaF and 1 g 12-crown-4 in 20 mL dichloromethane. The mixture was stirred at rt for 2 h and then overnight at 0 C. The liquid phase was decanted from the undissolved solids, filtered through a fritted glass filter (D3), and then rapidly recondensed through a short column under vacuum (approx. 10 hPa). The condensate was then fractionally distilled under vacuum (approx. 10 hPa). A main run of 1.2 kg oligosilane mixture was obtained over 14 h. The content values in ppb for the exemplary trace contaminants before and after purification are shown in the following table.

(9) TABLE-US-00003 TCDS/PCDS Al Cr Mn Cu Fe Mg K Na Ti Ca Purified <30 <30 <30 <30 <30 <30 <50 <50 <30 <50

Embodiment 5

(10) 35 kg hexachlorodisilane was treated with a suspension of 3 g KF, 12 g 15-crown-5 and 15 g 18-crown-6 in 120 mL dichloromethane. The mixture was heated to reflux for approx. 2 h, and then was fractionally distilled. A main run of 28 kg HCDS was obtained over 8 h.

(11) The content values in ppb for the exemplary trace contaminants before and after purification are shown in the following table.

(12) TABLE-US-00004 HCDS Al B Sb Cu Fe Mg K Na Ti Ca Crude 112 420 0.7 5.2 848 11 78 49 734 125 Purified 25 23 0.1 0.8 13 7 6.6 2.2 27 26

Embodiment 6

(13) 40 kg hexachlorodisilane was treated with a suspension of 3.5 g KF, 14 g 15-crown-5 and 17 g 18-crown-6 in 140 mL dichloromethane. The mixture was heated to reflux for approx. 2 h, and then was fractionally distilled. A main run of 32 kg HCDS was obtained over 10 h. From this, 26 kg HCDS was treated with a suspension of 2.2 g KF, 11 g 18-crown-6, and 10 g 12-crown-4 in 100 mL dichloromethane, and then again fractionally distilled. A main run of 20 kg HCDS was obtained after 9 h. The content values in ppb for the exemplary trace contaminants before and after purification are shown in the following table.

(14) TABLE-US-00005 HCDS Al B Sb Cu Fe Mg K Na Ti Ca Crude 55 57 0.9 4.5 21 8.1 39 133 342 77 Purified 3.5 2.4 0.1 0.1 1.6 0.8 0.07 0.9 2.8 6.5