Process for the preparation of hexachlorodisilane by cleavage of higher polychlorosilanes such as octachlorotrisilane

Abstract

The invention relates to a process for converting polychlorosilanes into hexachlorodisilane, by one or more trimeric polychlorosilanes or a trimeric polychlorosilane in a mixture with higher molecular weight polychlorosilanes being exposed to a gas discharge and hexachlorodisilane being formed and isolated.

Claims

1. A process for converting polychlorosilanes into hexachlorodisilane, comprising: mixing one or more trimeric polychlorosilanes or a trimeric polychlorosilane in a mixture with higher molecular weight polychlorosilanes with hydrogen chloride; and then, exposing the mixture of the hydrogen chloride and the one or more trimeric polychlorosilanes or the trimeric polychlorosilane in a mixture with higher molecular weight polychlorosilanes to a gas discharge to obtain a product comprising the hexachlorodisilane, wherein the trimeric polychlorosilane is octachlorotrisilane, and wherein octachlorotrisilane or octachlorotrisilane in a mixture with higher molecular weight polychlorosilanes and the hydrogen chloride are mixed such that a molar ratio of octachlorotrisilane/hydrogen chloride is from 3:1 to 2:1.

2. The process according to claim 1, wherein the gas discharge is a nonthermal plasma.

3. The process according to claim 1, wherein the polychlorosilanes are converted into the hexachlorodisilane in a vacuum.

4. The process according to claim 1, having a specific energy input of between 0.1 Ws/cm.sup.2 and 10 Ws/cm.sup.2.

5. The process according to claim 1, having a specific energy input that is effected using a phase-accurate measurement of instantaneous power at a band width of at least 250 kHz, wherein the measurement of instantaneous power is carried out in a coaxial reactor having a 50 cm.sup.2 discharge area.

6. The process according to claim 1, further comprising: distilling the product after the exposing.

7. The process according to claim 6, wherein the product has a hexachlorodisilane content of not less than 99.999 wt %.

8. The process according to claim 1, wherein the one or more trimeric polychlorosilanes or the trimeric polychlorosilane in a mixture with higher molecular weight polychlorosilanes mixed with the hydrogen chloride and exposed to the gas discharge has less than 100 weight ppm of impurities.

9. The process according to claim 1, wherein the one or more trimeric polychlorosilanes or the trimeric polychlorosilane in a mixture with higher molecular weight polychlorosilanes mixed with the hydrogen chloride and exposed to the gas discharge is a polyperchlorosilane having less than 100 weight ppm of impurities.

10. The process according to claim 1, being carried out in a reactor that is equipped with one or more glass tubes.

Description

EXAMPLE 1

(1) Octachlorotrisilane was continuously transferred into the gas phase, mixed with hydrogen chloride gas in a molar ratio of 2:1 and passed at a pressure of 50 mbar.sub.abs. through a quartz glass reactor having a gas discharge sector. The gas discharge was operated using a substantially sinusoidal voltage curve and had on average a specific energy input of about 3 Ws/cm.sup.2. The power was measured by the method, familiar to one skilled in the art, of multiplicative phase-accurate combining of instantaneous current I (x=t.sub.0) with instantaneous voltage U(x=t.sub.0) into the instantaneous power value in the exemplary coaxial reactor with 50 cm.sup.2 discharging area.

(2) The values thus obtained vary appreciably, for example in response to transient discharges. In such cases, the 1 sigma value for the stochastic deviation of the energy input in Ws/cm.sup.2 is in the range from 1 mWs/cm.sup.2 to 10 Ws/cm.sup.2.

(3) The measuring instrument used had a 3 dB cut-off frequency of about 250 kHz. Instruments having a higher cut-off frequency can give rise to stochastic deviations other than those referred to above.

(4) The gaseous reaction/conversion products obtained after passage through the gas discharge sector were condensed at 20° C. and subjected to a final distillation. The distillation was carried out batchwise in a distillation apparatus equipped with a 50 cm column pack with Sulzer metal packing.

(5) Trichlorosilane was distilled off first. The pressure was then reduced to about 650 mbar.sub.abs. and pure hexachlorodisilane was distilled off at a base of column temperature of about 80° C. and a top of column temperature of around 70° C.

(6) The .sup.29Si NMR depicted in FIG. 1 only had a signal at δ=−7.4 ppm (in DMSO, 99.34 MHz 29Si NMR spectrum of hexachlorodisilane obtained by the process according to the present invention).