Si,Si'diorganyl-N-alkyl-tetrachloro-disilazanes and a process for their preparation

Abstract

The invention relates to a process for the preparation of Si,Si'-diorganyl-N-alkyl-tetrachloro-disilazanes of the formula RSiCl.sub.2 --NR'--SiCl.sub.2 R, in which R is C.sub.1 -C.sub.4 -alkyl, vinyl or phenyl and R' is C.sub.1 -C.sub.4 -alkyl, and to these compounds themselves, with the exception of those where R=R'=CH.sub.3. To prepare the compounds mentioned, organyltrichlorosilanes RSiCl.sub.3 and monoalkylamines R'NH.sub.2 are reacted with one another in an aprotic solvent at -10.degree. C. to +70.degree. C., the molar ratio of RSiCl.sub.3 :R'NH.sub.2 being at least 0.3:1.

Description

DESCRIPTION

The present invention relates to a process for the preparation of Si,Si'-diorganyl-N-alkyl-tetrachloro-disilazanes of the formula RSiCl.sub.2 --NR'--SiCl.sub.2 R, in which R is C.sub.1 -C.sub.4 -alkyl, vinyl or phenyl and R' is C.sub.1 -C.sub.4 -alkyl, and to these compounds themselves, with the exception of that where R=R'=CH.sub.3. The compound mentioned last is already known and has hitherto been obtained by transsilylation of the completely methylated disilazane (CH.sub.3).sub.3 Si--N(CH.sub.3)--Si(CH.sub.3).sub.3 (J. P. Mooser et al., Z. Naturforsch. 29 b (1974) 166-173):

(CH.sub.3).sub.3 Si--N(CH.sub.3)--Si(CH.sub.3).sub.3 +2(CH.sub.3)SiCl.sub.3 .fwdarw.Cl.sub.2 (CH.sub.3)Si--N(CH.sub.3)--Si(CH.sub.3)Cl.sub.2 +2(CH.sub.3).sub.3 SiCl This process has the disadvantage that drastic reaction conditions (reflux, reaction time of 40 days) are necessary and aluminum chloride must additionally be added so that a complete reaction is achieved. Trimethylchlorosilane additionally arises as a by-product.

The present invention achieves the object of preparing this compound and a series of its higher homologs in a simple manner.

The present invention relates to a process for the preparation of Si,Si'-diorganyl-N-alkyl-tetrachloro-disilazanes of the formula RSiCl.sub.2 --NR'--SiCl.sub.2 R, in which R is C.sub.1 -C.sub.4 -alkyl, vinyl or phenyl and R' is C.sub.1 -C.sub.4 -alkyl, which comprises reacting organyltrichlorosilanes RSiCl.sub.3 and monoalkylamines R'NH.sub.2, in which R and R' have the meaning given, with one another in an aprotic solvent at a temperature of -10.degree. C. to +70.degree. C., the molar ratio of RSiCl.sub.3 :R'NH.sub.2 being at least 0.3:1.

Preferably, R is methyl, ethyl, vinyl or phenyl and R' is methyl. In particular, R is ethyl and R' is methyl. The molar ratio of RSiCl.sub.3 :R'NH.sub.2 is preferably 0.3:1 to 1:1, in particular 0.5:1 to 0.7:1. A molar ratio of RSiCl.sub.3 :R'NH.sub.2 of more than 1:1, for example 2:1, of course is also successful, but such as excess of RSiCl.sub.3 is superfluous and the unreacted portion must be separated off from the dichlorosilazane desired.

The reaction temperature is preferably 0.degree. C. to +20.degree. C. Polar aprotic solvents, in particular ethers, are preferably used.

The reaction equation is:

2RSiCl.sub.3 +3H.sub.2 NR'.fwdarw.RSiCl.sub.2 --NR'--SiCl.sub.2 R+2H.sub.2 NR'.HCl

Mixtures of the organyltrichlorosilanes give a mixture of the possible disilazanes, for example reaction of the binary mixture of CH.sub.3 SiCl.sub.2 and (C.sub.2 H.sub.3)SiCl.sub.3 with CH.sub.3 NH.sub.2 gives the ternary mixture of CH.sub.3 SiCl.sub.2 --N(CH.sub.3)--SiCl.sub.2 CH.sub.3, (C.sub.2 H.sub.3)SiCl.sub.2 --N(CH.sub.3)--SiCl.sub.2 (C.sub.2 H.sub.3) and (C.sub.2 H.sub.3)SiCl.sub.2 --N(CH.sub.3)--SiCl.sub.2 CH.sub.3.

The Si,Si'-diorganyl-N-alkyl-tetrachloro-disilazanes according to the invention can be converted into polymeric silazanes by reaction with at least 6.7 moles of ammonia per mole of chlorodisilazane in aprotic solvents, preferably tetrahydrofuran, at -80.degree. C. to +70.degree. C., preferably at -10.degree. C. to 0.degree. C. These silazanes can then be converted into ceramic materials containing silicon nitride by pyrolysis in a nitrogen or argon atmosphere at 800.degree. to 1400.degree. C. The polymeric silazanes dissolve in all the customary aprotic solvents. They can be shaped into three-dimensional shaped articles before the pyrolysis, for example by monoaxial or isostatic pressing, slip casting or extrusion.

EXAMPLE 1

50 ml (63.5 g; 0.42 mole) of methyltrichlorosilane were dissolved in 300 ml of dry tetrahydrofuran in a 500 ml three-necked flask with a cold finger and stirring device. The cold finger was cooled to -78.degree. C. (dry ice) and the solution was cooled to -10.degree. C. 25.7 ml (19.8 g; 0.64 mole) of methylamine were now passed in so that the internal temperature did not rise above -5.degree. C. The methyl ammonium chloride formed was filtered off, after warming to 20.degree. C. The filtrate was subjected to fine distillation. 22.5 g of the Si,Si'-dimethyl-N-methyl-tetrachlorosilazane distilled over at 96.degree. C. under 81 mbar (yield 42%).

.sup.1 H-NMR data: N(CH.sub.3) .delta.=2.8 ppm, intensity: 1 singlet. Si(CH.sub.3) .delta.=0.95 ppm, intensity: 2 singlet.

EXAMPLE 2

0.6 mole (96.9 g; 76.3 ml) of vinyltrichlorosilane was dissolved in 700 ml of dry tetrahydrofuran in a 1 l three-necked flask with a cold finger and stirring device. The cold finger was cooled to -78.degree. C. (dry ice) and the solution was cooled to 0.degree. C. 27.9 g (0.9 mole) of methylamine were now passed in.

The methylamine hydrochloride formed was filtered off with suction and the filtrate was subjected to distillation. 50.6 g (0.18 mole; yield 60%) distilled over at 142.degree. C. under 81 mbar.

.sup.1 H-NMR data in CDCl.sub.3 : N(CH.sub.3) .delta.=2.85 ppm singlet. Si(C.sub.2 H.sub.3) .delta.=6.2 ppm multiplet.

EXAMPLE 3

0.6 mole (98.1 g; 79.1 ml) of ethyltrichlorosilane was dissolved in 700 ml of tetrahydrofuran in a 1 l three-necked flask with a cold finger and stirring device. The cold finger was cooled to -78.degree. C. and the solution was cooled to 0.degree. C. 27.9 g (0.9 mole) of methylamine were now passed in.

The methylamine hydrochloric formed was filtered off with suction and the filtrate was subjected to distillation. 107.8 g (0.28 mole; yield 93%) distilled over a 64.degree. C. under 14 mbar.

.sup.1 H-NMR data in CDCl.sub.3 : N(CH.sub.3) .delta.=2.87 ppm singlet. Si(CH.sub.2 H.sub.5) .delta.=1.15 ppm multiplet.

EXAMPLE 4

0.3 mole (48.4 g; 38.1 ml) of vinyltrichlorosilane and 0.3 mole (49 g; 39.6 ml) of ethyltrichlorosilane were dissolved in 700 ml of tetrahydrofuran in a 1 l three-necked flask with a cold finger and stirring device. The cold finger was cooled to -78.degree. C. and the solution was cooled to 0.degree. C. 27.9 g (0.9 mole) of methylamine were now passed in. The methylamine hydrochloride formed was filtered off with suction and the filtrate was subjected to distillation.

43.2 g of a mixture of all three possible isomers distilled over at 70.degree. to 80.degree. C. under 14 mbar.

.sup.1 H-NMR data of Cl.sub.2 (C.sub.2 H.sub.3)Si--N(CH.sub.3)--Si(C.sub.2 H.sub.5)Cl.sub.2 in CDCl.sub.3 : N(CH.sub.3) .delta.=2.37 ppm singlet. Si(C.sub.2 H.sub.3) .delta.=6.2 ppm multiplet. Si(C.sub.2 H.sub.5) .delta.=1.15 ppm multiplet.

Claims

1. A process for the preparation of an Si,Si'-diorganyl-N-alkyl-tetrachloro-disilazane of the formula RSiCl.sub.2 --NR'--SiCl.sub.2 R, in which R is C.sub.1 -C.sub.4 -alkyl, vinyl or phenyl and R' is C.sub.1 -C.sub.4 -alkyl, which comprises reacting an organyltrichlorosilane RSiCl.sub.3 and a monoalkylamine R'NH.sub.2, in which R and R' have the meaning given, with one another in an aprotic solvent at a temperature of -10.degree. C. to +70.degree. C., the molar ratio of RSiCl.sub.3 :R'NH.sub.2 being at least 0.3:1.

2. The process as claimed in claim 1, wherein the molar ratio of RSiCl.sub.3 :R'NH.sub.2 is 0.3:1 to 1:1.

3. The process as claimed in claim 1, wherein the molar ratio of RSiCl.sub.3 :R'NH.sub.2 is 0.5:1 to 0.7:1.

4. The process as claimed in claim 1, wherein R is methyl, ethyl, vinyl or phenyl and R' is methyl.

5. The process as claimed in claim 1, wherein R is ethyl and R' is methyl.

6. The process as claimed in claim 1, wherein an ether is used as the aprotic solvent.

7. An Si,Si'-diorganyl-N-alkyl-tetrachlorodisilazane of the formula RSiCl.sub.2 --NR'--SiCl.sub.2 R, in which R is C.sub.1 -C.sub.4 -alkyl, vinyl or phenyl and R' is C.sub.1 -C.sub.4 -alkyl, excluding R=R'=CH.sub.3.

8. An Si,Si'-diorganyl-N-alkyl-tetrachloro-disilazane as claimed in claim 7, wherein R is ethyl, vinyl or phenyl and R' is methyl.

9. An Si,Si'-diorganyl-N-alkyl-tetrachloro-disilazane as claimed in claim 7, wherein R is ethyl and R' is methyl.