Method for hydrogenating higher halogen-containing silane compounds

Abstract

The present invention relates to a continuous process for hydrogenating halogen-containing silane compounds having at least three silicon atoms, in which at least one halogen-containing silane compound having at least three silicon atoms and at least one hydrogenating agent are converted continuously to form at least one hydridosilane compound having at least 3 silicon atoms and oxidized hydrogenating agent, and wherein oxidized hydrogenating agent is withdrawn and reduced, and the reaction product of this reduction reaction is sent back to the hydrogenation, to the hydridosilane compounds obtainable by this process and to the use thereof.

Claims

1. A continuous process for hydrogenating halogen-containing silane compounds having at least three silicon atoms, comprising: (i) continuously converting at least one halogen-containing silane compound having at least three silicon atoms and at least one hydrogenating agent to form at least one hydridosilane compound having at least 3 silicon atoms and an oxidized hydrogenating agent; (ii) withdrawing and reducing the oxidized hydrogenating agent, and (iii) feeding back the reduced oxidized hydrogenating agent to (i).

2. The process according to claim 1, wherein the halogen-containing silane compound has the generic formula Si.sub.nX.sub.2n+2 where 3n10 and XF, Cl, Br, and/or I.

3. The process according to claim 2, characterized in that wherein the halogen-containing silane compound is Si.sub.5Cl.sub.12.

4. The process according to claim 1, wherein the proportion of the at least one halogen-containing silane compound ranges from 10-30% by weight based on the total mass of the components fed in.

5. The process according to claim 1, wherein the hydrogenating agent is selected from the group of compounds consisting of LiAlH.sub.4, NaBH.sub.4 and i-Bu.sub.2AlH.

6. The process according to claim 1, wherein the hydrogenating agent in the reduced state is metered in H equivalent proportions of 1.0 to 1.5 based on the sum total of halogen atoms to be hydrogenated.

7. The process according to claim 1, wherein at least two series-connected reactors are used for the conversion.

8. The process according to claim 7, wherein the molar ratio in the first reactor of reduced to oxidized hydrogenating agent ranges from 0.4 to 0.75.

9. The process according to claim 7, wherein the first of the two or more series-connected reactors is a stirred tank reactor.

10. The process according to claim 7, wherein at least one of the reactors connected downstream of the first reactor is a flow reactor.

11. The process according to claim 1 characterized in that it that follows on from a process for synthesizing halogenated silane compounds in which i) at least one halosilane of the generic formula Si.sub.nX.sub.2n+2 where n2 and XF, Cl, Br and/or I and ii) at least one catalyst selected from the group of the tertiary phosphines PR.sub.3, the tertiary amines NR.sub.3 and the group of compounds of the generic formula NRR.sub.aR.sub.bY.sub.c where a=0 or 1, b=0 or 1, and c=0 or 1, and ##STR00002## where aa) R, R and/or R is C.sub.1-C.sub.12-alkyl, C.sub.1-C.sub.12-aryl, C.sub.1-C.sub.12-aralkyl, C.sub.1-C.sub.12-aminoalkyl, C.sub.1-C.sub.12-aminoaryl, C.sub.1-C.sub.12-aminoaralkyl, and/or two or three R, R and R radicals, in the case that c=0, together form a cyclic or bicyclic, heteroaliphatic or heteroaromatic system including N, with the proviso that at least one R, R or R radical is not CH.sub.3 and/or bb) R and R and/or R (in the case that c=1) are C.sub.1-C.sub.12-alkylene, C.sub.1-C.sub.12-arylene, C.sub.1-C.sub.12-aralkylene, C.sub.1-C.sub.12-heteroalkylene, C.sub.1-C.sub.12-heteroarylene, C.sub.1-C.sub.12-heteroaralkylene and/or N, or cc) (in the case that a=b=c=0) RCR (where RC.sub.1-C.sub.10-alkyl, C.sub.1-C.sub.10-aryl and/or C.sub.1-C.sub.10-aralkyl), are converted to form a mixture comprising at least one halosilane of the generic formula Si.sub.mX.sub.2m+2 (where m>n and XF, Cl, Br and/or I) and Si.sub.mnX.sub.2(mn)+2 (where XF, Cl, Br and/or I).

Description

(1) FIG. 1 shows an illustrative experimental setup.

LIST OF REFERENCE NUMERALS

(2) (1) Si.sub.5Cl.sub.12 feed

(3) (2) feed of fresh Dibal-H (i-Bu.sub.2AlH)

(4) (3) feed of recycled Dibal-H (i-Bu.sub.2AlH)

(5) (4) CSTR

(6) (5) circulation pump

(7) (6) flow tube reactor

(8) (7) short-path evaporator

(9) (8) feed of Dibal-Cl to recycling

(10) (9) feed of crude product to distillation

(11) (10) distillation column 1

(12) (11) low boiler fraction

(13) (12) feed of crude product to 2nd distillation

(14) (13) distillation column 2

(15) (14) product of value

(16) Example:

Preparation of dodecachioroneopentasilane Si5Cl12

(17) The preparation of Si.sub.5Cl.sub.12 is effected in batchwise operation in a cone mixer dryer. In the first step, at 20 C. and 1 bar under a protective gas atmosphere, 20 kg of a liquid mixture of perchlorosilanes having predominantly 3 silicon atoms are admixed with 3 kg of hexane and 60 g of diazabicyclo[2.2.2]octane dissolved in 450 g of diethyl ether. The mixture reacts within 40 h to give solid Si.sub.5Cl.sub.12 and the by-product SiCl.sub.4. After the reaction step, the low boilers (hexane and diethyl ether) and the SiCl.sub.4 by-product are removed from the reaction mixture at 50 C. under reduced pressure (200 to 1 mbar) to obtain 16 kg of Si.sub.5Cl.sub.12.

Preparation of neopentasilane (NPS) and the Thermal Workup Thereof

(18) (H Equivalent Content of the Hydrogenating Agent: 1.1)

(19) The hydrogenation of Si.sub.5Cl.sub.12 with diisobutylaluminium hydride is performed in two reaction stages. The first reactor (4, cf. FIG. 1), a continuous stirred tank reactor (CSTR) with forced external circulation (pump, 5), is initially charged with diisobutylaluminium hydride and the recycled diisobutylaluminium hydride (3) is metered in continuously. Thus, the hydrogenating agent (diisobutylaluminium hydride) is metered in constantly in appropriate H equivalent contents (2). The Si.sub.5Cl.sub.12 (1) is metered continuously into the reactor (4) in solid form while keeping the reaction temperature constant at 10 C. The Si.sub.5Cl.sub.12 conversion in this reaction step is about 65%. By means of a fill level regulator in the CSTR (4), a defined volume flow rate is conveyed through a valve into the downstream flow tube reactor (6), where a reaction temperature of 10 C. is likewise set. In the flow tube reactor, a final conversion of 100% Si.sub.5Cl.sub.12 is attained.

(20) In the short-path evaporator (7), the output from the reaction stage is worked up thermally. A large portion of the unconsumed diisobutylaluminium hydride hydrogenating agent and of the depleted diisobutylaluminium hydride hydrogenating agent is removed in the short-path evaporator (7). The top product of the short-path evaporator is purified in the downstream distillation columns. 0.20 kg of pure NPS is obtained per hour.

(21) The hydridosilanes in the distillate are determined qualitatively by GC-MS analysis. The distillate contains hydridosilanes in a proportion of >99.0 area %.

(22) Yield based on weight (kg/h of hydridosilanes as distillate per kg/h of perchlorosilane mixture used): 16.5%.

(23) The unconsumed or depleted hydrogenating agent (8) from the short-path evaporator (7) is treated with NaH (15) and the recycled hydrogenating agent (3) is subsequently returned to the CSTR (4).