WO2001012636A1

WO2001012636A1 - Method of producing hexamethyldisilazane

Info

Publication number: WO2001012636A1
Application number: PCT/EP2000/007437
Authority: WO
Inventors: Helmut Kraus; Lutz Heuer
Original assignee: Bayer Aktiengesellschaft
Priority date: 1999-08-13
Filing date: 2000-07-31
Publication date: 2001-02-22
Also published as: AU6279000A; DE19938475A1

Abstract

The invention relates to a method of producing hexamethyldisilazane from chlorotrimethylsilane and ammonia by contacting ammonia and chloromethylsilane in a pressure-proof vessel at 60 to 150 °C and processing the reaction mixture once it has cooled down to -10 °C to +45 °C.

Description

Process for the preparation of hexamethyldisilazane

The present invention relates to an improved process for the preparation of hexamethyldisilazane of the formula (CH ₃ ) ₃ Si-NH-Si (CH ₃ ) 3 from chlorotrimethylsilane and ammonia.

Hexamethyldisilazane is a chemical that can be used industrially in many different ways. It is used, for example, as a silylation reagent in the manufacture of penicillins, cephalosporins and vitamins, for the hydrophobization of surfaces and polymers which have OH groups and as an aid in phosgenation.

A number of processes for the preparation of hexamethyldisilazane have already become known. In these, chlorotrimethylsilane is generally reacted with ammonia in the presence of organic solvents. According to DE-PS 938 845 and DE-OS 24 26 109 aliphatic and aromatic hydrocarbons, organopolysiloxanes or already prepared hexamethyldisilazane are used as solvents.

Common organic solvents, e.g. n-Hexane must be used in amounts of at least 4 parts by weight, better at least 6 parts by weight (based on 1 part by weight of chlorotrimethylsilane), because otherwise reaction mixtures which are difficult or impossible to stir are obtained. If hexamethyldisilazane which has already been prepared is used as the solvent, it can be used in small amounts. That as

By-product resulting ammonium chloride then contains part of the hexamethyldisilazane and cannot be separated from it by normal distillation. You either have to use a thin-film evaporator or convert the hexamethyldisilazane contained in the ammonium chloride to hexamethyldisiloxane with dilute hydrochloric acid. It is also possible that the reaction mixture despite the Use of excess ammonia still contains unreacted chlorotrimethylsilane (see DE-OS 26 45 792).

DE-OS 26 45 703 describes the preparation of hexamethyldisilazane from chlorotrimethylsilane and ammonia in hexamethyldisilazane as solvent (at least 1 part by weight of solvent per part by weight of chlorotrimethylsilane), with large amounts of water being added to work up the reaction mixture and the ammonium chloride as aqueous Solution is separated.

In a continuous process according to US Pat. No. 4,644,076 in particular

Reaction vessels with special stirrers carried out a so-called high-shear agitation, so that the ammonium chloride is obtained in a more manageable form. In addition, extremely difficult to handle sodium amide is added to the hexamethyldisilazane prepared before the distillation in order to remove the ammonium chloride contained therein.

In the process described in J. Am. Chem. Soc. 68, 241 (1946), is carried out without a solvent, a large excess of liquid ammonia is introduced and chlorotrimethylsilane is metered in over the course of almost 4 hours. No temperature and pressure details are given. In any case, however, it was carried out in a different way than the process according to the invention, because in the process according to this reference, hexamethyldisilazane is only obtained in a 45% yield. In addition, considerable amounts of trimethyldisilanol and hexamethylsiloxane are obtained. According to this reference, a Dewar vessel is used which is provided with a cork stopper. Since Dewar vessels are used to handle liquefied gases at low temperatures and cork stoppers can only be used at normal pressure or reduced pressure, it is obvious that work was carried out at temperatures below -33 ° C and under normal pressure. There is therefore still a need for a process for the preparation of hexamethyldisilazane which does not require solvents or special apparatus, which gives the desired product in high yields and which can be used with shorter metering and reaction times.

A process has now been found for the preparation of hexamethyldisilazane from chlorotrimethylsilane and ammonia, which is characterized in that ammonia and chlorotrimethylsilane are brought together in a pressure-resistant vessel at 60 to 150 ° C. and the reaction mixture is cooled to -10 to + 45 ° C. - is working.

In the process according to the invention, ammonia e.g. Use in 1.5 to 6 times, preferably in 2 to 4 times the amount that is theoretically required.

Ammonia and chlorotrimethylsilane are preferably brought together at 70 to 120 ° C. You can e.g. proceed in such a way that the ammonia is placed in the pressure-resistant reaction vessel, heated to the desired temperature and then the chlorotrimethylsilane is pumped in, for example, over the course of 5-60 minutes. Ammonia and chlorotrimethylsilane can also be pumped simultaneously into the pressure-resistant reaction vessel at the desired temperature. Continuous operation is also possible, in which the starting materials are introduced simultaneously or alternately in succession into a pressure-resistant reaction tube kept at the desired temperature.

It must always be ensured that there is an excess of ammonia while the starting materials are being combined.

During the reaction, the pressure can be, for example, 30 to 100 bar. It is preferably in the range from 35 to 80 bar. If necessary, the chlorotrimethylsilane inlet tube can be flushed or cleared with nitrogen immediately before the start of the inlet, for example by pressing 1 to 5 bar of nitrogen through the inlet tube into the pressure-resistant reaction vessel.

It is advantageous to continue stirring for a while after the starting materials have been combined, for example 30 minutes to 3 hours. The temperature can e.g. deviate from the reaction temperature by up to + 20 ° C or fall during stirring, e.g. up to room temperature or up to 10 ° C above room temperature.

When the starting materials have been combined and any subsequent stirring time has elapsed, the reaction mixture present is then cooled to -10 to + 45 ° C., preferably -5 to + 15 ° C.

The workup can then be carried out in various ways. For example, the pressure can now be released and the ammonium chloride formed can be separated from the present suspension by filtration and, if appropriate, the filtrate distilled.

It is preferred to add the cooled reaction mixture, which is still under pressure, e.g. 1 to 2 equivalents, preferably 1.1 to 1.5 equivalents of aqueous alkali lye, the temperature being kept in the range from -10 to + 50 ° C, preferably -5 to + 20 ° C, e.g. by pre-cooling the alkali and / or cooling the reaction mixture. Then you can relax and separate the aqueous phase from the product phase. The product phase can e.g. by

Distillation to be worked up further. The ammonium chloride present in the aqueous phase can optionally be worked up separately to form ammonia and a saline solution.

The aqueous alkali can also be added only after partial or complete pressure release. Other processing methods are also possible.

The inventive method allows the production of hexamethyldisilazane in a simple manner, without the use of solvents, without the use of

Special apparatus, in yields of over 85% and using short dosing and reaction times. These effects are extremely surprising, since in the previously known solvent-free process, the desired product was only obtained in a yield of 45%, so that it was a considerable inventive step to find the process according to the invention and the associated technical advantages.

Examples

example 1

408 g of ammonia were introduced into a 3 1 stainless steel autoclave and heated to 80.degree. The pressure was then 42 bar. Subsequently, 3 bar of nitrogen were pressed in through the inlet pipe for flushing and 505 ml of trimethylchlorosilane were pumped in immediately after 25 minutes. The temperature rose to 90 ° C. The pressure to 49 bar. After stirring for 2 hours, the temperature had dropped to 41 ° C. 680 ml of 6.3 N aqueous sodium hydroxide solution were then pumped in over the course of 8 minutes. The temperature rose to 45 ° C. The autoclave was then slowly released and the contents removed. After phase separation, 314.5 g of product phase were obtained. According to Η-NMR it contained 90.3% hexamethyldisilazane, corresponding to a yield of 88.2% of theory.

Example 2

230 g of ammonia were introduced into a 2 1 stainless steel autoclave and heated to 80 ° C., a pressure of 41 bar being established. After nitrogen had been injected analogously to Example 1, 338 ml of trimethylchlorosilane were pumped in over the course of 12 minutes. The temperature rose to 107 ° C, the pressure to 57 bar. The mixture was stirred at 90 to 100 ° C for 1 hour and then cooled to + 7 ° C within 2 hours. 453 ml of 6.3 N aqueous sodium hydroxide solution (precooled to -5 ° C.) were then pumped in with cooling within 8 minutes. The temperature was then + 6 ° C. The mixture was allowed to warm to room temperature, relaxed slowly and and separated

Phases. According to the Η-NMR, the product phase contained 97.6% hexamethyldisilazane. The TOC value of the water phase was 340 mg / 1. Example 3

275.4 g of ammonia were placed in a 2 1 stainless steel autoclave and 338 ml of trimethylchlorosilane were pumped in at 80 ° C. in the course of 23 minutes. After stirring for 1 hour at 90 to 95 ° C., the mixture was allowed to cool to 80 ° C. and the pressure was released to 5 bar via a cold trap. After cooling to + 4 ° C., 453 ml of 6.3 N aqueous sodium hydroxide solution (precooled to 0 ° C.) were pumped in over the course of 20 minutes. Then the pressure was released completely and the phases were separated. The product phase combined with the cold trap content contained 96.8% hexamethyldisilazane. The TOC value of the aqueous phase was 140 mg / 1.

Example 4

Example 2 was repeated, but only 153 g of ammonia were used. A product phase was obtained which contained 95.5% hexamethyldisilazane.

Claims

claims

1. A process for the preparation of hexamethyldisilazane from chlorotrimethylsilane and ammonia, characterized in that ammonia and chlorotrimethylsilane are brought together in a pressure-resistant vessel at 60 to 150 ° C and the reaction mixture is worked up after cooling to -10 ° C to +45 ° C.

2. The method according to claim 1, characterized in that ammonia is used in the 1.5 to 6 times the amount that is theoretically required.

3. Process according to claims 1 and 2, characterized in that the ammonia is placed in the pressure-resistant reaction vessel, heated to the desired temperature and then the chlorotrimethylsilane is pumped in.

4. The method according to claims 1 to 2, characterized in that

Ammonia and chlorotrimethylsilane are simultaneously pumped into the pressure-resistant reaction vessel at the desired temperature.

5. The method according to claims 1 to 4, characterized in that the pressure during the reaction is 30 to 100 bar.

6. Process according to Claims 1 to 5, characterized in that aqueous alkali metal hydroxide solution is added to the cooled, still pressurized reaction mixture, the temperature being kept in the range from -10 to + 50 ° C, then relaxed and the aqueous phase now present from the

Separates product phase.