The invention relates to a process for preparing organosilazane and ammonium chloride.
DE 26 45 703 B2 describes a process for preparing hexamethyldisilazane by reacting trimethylchlorosilane with gaseous ammonia in the presence of hexamethyldisilazane as solvent. The ammonium chloride formed in the reaction is removed from the hexamethyldisilazane by washing with water. The hexamethyldisilazane is then dried with sodium sulfate, and the sodium sulfate is filtered off. The disadvantage of this procedure for salt removal is that partial hydrolysis of the hexamethyldisilazane takes place on washing with water, and thus losses of yield occur, the silazane requires subsequent treatment and filtration, and the ammonium chloride results in a non-reusable form as aqueous solution.
In DE 26 45 792 C2, the ammonium chloride is removed from the hexamethyldisilazane by distillation under reduced pressure at a bottom temperature below 75°C. The chosen distillation conditions avoid substantial quantities of ammonium chloride subliming during the distillation of the hexamethyldisilazane, and thus blocking the conduits. The ammonium chloride remaining in the reactor after the distillation, which still contains hexamethyldisilazane residues, is dissolved by adding dilute hydrochloric acid. The remaining hexamethyldisilazane is thus reacted to hexamethyldisiloxane and is removed as the lighter phase from the aqueous ammonium chloride. This process of salt removal has the disadvantage that the hexamethyldisilazane must be removed from the ammonium chloride by distillation, and thus very expensively. In •addition, it is immediately evident to the skilled worker that this mode of . removal can scarcely be implemented on the industrial scale since solid ammonium chloride, which is no longer stirrable, results as residue in the reactor and consequently still contains hexamethyldisilazane, and thus losses of

yield of hexamethyldisilazane occur. Finally, ammonium chloride is once again obtained as aqueous solution.
Another possibility for salt removal consists of removing the ammonium chloride from the reaction mixture by filtration or centrifugal removal. The ammonium chloride which still contains hexamethyldisilazane is then dissolved in dilute hydrochloric acid, once again producing hexamethyldisiloxane and resulting in ammonium chloride as aqueous solution. Even with this procedure losses of yield of hexamethyldisilazane occur, since considerable amounts of hexamethyldisilazane remain in the ammonium chloride on filtration or centrifugal removal.
Attempts to increase the yield of hexamethyldisilazane by subsequently removing the hexamethyldisilazane present in the ammonium chloride resulting 'from the filtration or centrifugal removal, for example by drying, fail on the industrial scale because, during the drying process with conventional drying equipment, the ammonium chloride sinters to relatively large, very hard agglomerates which are no longer amenable to technical manipulation and, moreover, make complete removal of the hexamethyldisilazane impossible.
All the existing processes have the disadvantage that losses of yield of hexamethyldisilazane occur and the ammonium chloride which is produced results as aqueous solution which is contaminated with organosilicon substances and, consequently, must be subjected to further purification, for example by biological processes, before release to the environment. Recovery of ammonium chloride is impossible or possible only with considerable and thus uneconomic expenditure.
Ammonium chloride is a valuable raw material inter alia for the fertilizer sector, for the explosives sector and for producing zinc/ammonium chloride meits. In addition, ammonium chloride is

employed as nitrogen donor in municipal biological sewage treatment plants.
The object was to overcome the disadvantages of the prior art and, in particular, to provide a simple, economical environment-conscious process for preparing organosilazanes in which no losses of yield of the organosilazanes occur, and the ammonium chloride is obtained in solid, pure form which can be handled, i.e. is free-flowing and nonblocking, in order to make it available for the abovementioned purposes of use.
The invention relates to a process for preparing organosilazane and ammonium chloride, with reaction of an organochlorosilane and ammonia in the presence of organosilazane as solvent, wherein ammonixim chloride is removed from the resulting mixture containing organosilazane and ammonium chloride, by adding an antiblocking agent to the mixture before the removal, or to the ammonium chloride after the removal.
The organosilane is preferably trimethyl-chlorosilane or vinyldimethylchlorosilane or mixtures thereof.
The organosilazane used as solvent is preferably the same organosilazane it is intended to prepare. The process according to the invention is preferably used to prepare hexamethyldisilazane or 1,3-divinyltetramethyldisilazane.
In the removal, the particular organosilazane is separated from the ammonium chloride.
Removal processes are theinnal processes or a combination of mechanical processes and thermal processes, and the combination of mechanical processes and thermal processes is preferred. With a combination of mechanical and thermal processes, the mechanical process is carried out before the thermal process.
The mechanical process preferably comprises filtration or centrifugal removal, with particular preference for centrifugal removal and, in this case, especially ..the use of a skimmer centrifuge.

If mechanical processes are used, the need for a residual content of organosilazane in the ammonium chloride for carrying out the granulation step described below means that these are carried out in such a way that the organosilazane content in the ammoniiim chloride after the mechanical removal is in the range between, preferably, 10 and 25% by weight.
Thermal processes for removal are preferably processes for drying, with complete recovery of the organosilazane. Examples of devices suitable for drying are thin film dryers, fluidized bed dryers, spray dryers, band dryers and drxim dryers, these dryers preferably being used when the antiblocking agent is added to the mixture before the removal, and the removal takes place by thermal processes. Further devices suitable for drying are dryers with which solid materials 'can be dried. These include, for example, plate dryers, rotary dryers, tumble dryers, double cone dryers and paddle dryers, with plate dryers being preferred. These dryers are preferably used when the removal takes place by a combination of mechanical and thermal processes. If the removal takes place by a combination of mechanical and thermal processes, it is possible, if the granulation step described below is not carried out and the antiblocking agent is added before the removal, for the removal also to take place with only a single device. Examples of devices of this type are heatable filter dryers, suction filter dryers and centrifuge dryers.
The drying is preferably carried out at a temperature from 50 to 150°C under a pressure from 5 to 1000 hPa, particularly preferably at 65 to 13 0°C under 10 to 500 hPa.
The organosilazane content in the ammonixom chloride after the drying is preferably below 500 ppm, particularly preferably below 350 ppm.
The antiblocking agent is added in amounts, based on ajranonium chloride, of preferably 0.05 to 10% by weight, preferably in amounts of 0.05 to 3% by

weight, particularly preferably in amounts of 0.1 to 2% by weight.
It is moreover possible to add only one type of antiblocking agent, but also various types of antiblocking agent or else mixtures thereof.
The antiblocking agents used are preferably inorganic solid substances with average particle sizes of 0.01 to 50 pm. These include, for example, aluminiom silicates, colloidal silica gel, pyrogenic silica, ground clays, perlites, veriiiiculites, gypsiom, talc, cements, chalk powders, mixed calciiim/magnesium carbonates or diatomaceous earth, with pyrogenic silica being preferred.
The reaction of organochlorosilane and ammonia in the presence of organosilazane as solvent can take place, for example, by the process described in DE 26 45 703 B2, which is incorporated herein by reference.
This entails ammonia being passed into the nixture of organochlorosilane and organosilazane until lo more is absorbed.
In the process according to the invention, the unmonium chloride content in the reaction mixture after :he reaction of organochlorosilane and ammonia is jreferably 10 to 40% by weight, particularly preferably .5 to 28% by weight. The ammonium chloride content can )e adjusted in a simple manner through the content of )rganosilazane in the reaction.
An antiblocking agent described above can be .dded to this reaction mixture, and the removal can hen be carried out by one of the processes described bove, or the removal can be carried out first and then n antiblocking agent as described above can be added o the ammonium chloride.
If the antiblocking agent is added before the emoval of the ammonium chloride, the removal referably takes place thermally by one of the rocesses dest:ribed above, or it can also take place echanically by one of the processes described above in

combination with a thermal process, in which case the mechanical removal preferably always precedes the thermal removal. Removal by a combination of mechanical and thermal processes is preferred.
If the removal takes place by the combination of mechanical and thermal processes, a granulation step can then be carried out after the mechanical removal.
The granulation of the ammonium chloride containing organosilazane or organosilazane and antiblocking agent is carried out using conventional wet granulation devices.
The maximum dimensions of the resulting granule particles are in this case determined by the size of the holes in the granulation cylinder used. Holes with sizes of from 1 to 10 mm are preferably employed, particularly preferably from 2"to 8 mm.
If the antiblocking agent is added after the removal, the ammonium chloride is removed by a combination of mechanical and thermal processes, in which case a granulation step as described above is necessary after the mechanical removal and before the thermal removal.
The dried ammonivim chloride is preferably ground, the grinding preferably being to an average particle size (weight average) of from 10 to 600 ^m, particularly preferably from 20 to 200 ^m.
It is possible to use for the grinding all Icnown grinding devices which can be used for such purposes. These include, for example, pinned disk nills, centrifugal flow mills, vibrating mills, pneiomatic mills, drum mills, cone mills, toothed disk nills, roll mills, ball mills and pendulum mills.
The process according to the invention has the idvantage that it is easy to carry out on the >roduction scale, affords a high yield of )rganosilazane and is environmentally conscious because :he resulting ammonium chloride can be reused.
Another advantage is that the resulting .mmonium chloride has a high resistance to blocking and

is very free-flowing, and thus no difficulties with handling, for example in emptying from containers, occur even after prolonged storage.
As a consequence of the low organosilazane content still present, the ammonium chloride prepared by the process according to the invention represents a non-hazardous material according to current regulations and can thus be reused universally in a more straightforward manner.
The ammonium chloride prepared by the process according to the invention has a purity, in terms of the content of environmentally relevant impurities such as, for example, the heavy metals lead, cadmium, chromium, nickel, zinc, copper and mercury, which is comparable with that of conventional ammonium chloride marketed in the specialist chemicals trade.
A ' preferred process A according to the invention for preparing organosilazanes, in particular hexamethyldisilazane and 1,3-divinyltetramethyldi-silazane, takes place by reacting organochlorosilazane and ammonia in the presence of organosilazane as solvent, with
in a 1st stage most of the organosilazane being removed from the ammonium chloride formed,
in a 2nd stage the ammonium chloride still containing organosilazane being granulated,
in a 3rd stage the organosilazane still present in the granules being removed and recovered,
in a 4th stage an antiblocking agent being added,
with grinding of the granules being carried out where appropriate before the 4th or after the 4th stage.
Another process B according to the invention for preparing organosilazanes, in particular

hexamethyldisilazane and I,S-divinyltetramethyldi-silazane, takes place by reacting organochlorosilane and ammonia in the presence of organosilazane as solvent, with
in a 1st stage antiblocking agent being added to the reaction mixture containing ammonium chloride,
in a 2nd stage most of the organosilazane being removed from the ammonium chloride,
where appropriate in a 3rd stage the ammonium chloride still containing organosilazane being granulated,
in a 4th stage the organosilazane still present being removed and recovered,
the resulting ammonium chloride being ground where appropriate in a 5th stage and
where appropriate further antiblocking agent being added in a 6th stage.
The removal of the organosilazane from the ammonium chloride in the 2nd stage of process B and in the 1st stage of process A preferably takes place by the mechanical processes described above.
In the case where the 3rd stage is not carried out in process B, it is possible to combine the 2nd stage and the 4th stage together in such a way that the removal of the ammonium chloride and the removal therefrom of the remaining organosilazane take place using a single device. Examples of devices suitable for this purpose are filter dryers, suction filter dryers and centrifuge dryers.
In the following examples, all data in parts and percentages are based on weight unless otherwise indicated. . liriless otherwise indicated, the following examples are carried out under the pressure of the

surrounding atmosphere, that is to say about 1000 hPa, and at room temperature, that is to say about 20°C.
The resulting ammonium chloride has been assessed for its resistance to blocking.
To determine the resistance to blocking, the material to be investigated was packed into an iron pipe (height: 100 mm; diameter: 50 mm) with screw thread, then loaded with a metal plunger weighing 3 kg (diameter: 49 mm) and subsequently stored in a drying Dven at 50°C for 16 hours. After cooling to room temperature, the metal plunger was cautiously removed, ::he screw closure was opened and the material was removed from the pipe. If the material was extensively blocked, it was cautiously pushed out of the iron pipe ising the metal plunger. The resistance to blocking .was ietermined qualitatively by crushing the material and /as assessed using the following scoring scheme:
. = Free-flowing and pourable
: = Powder flows with assistance out of the iron pipe, with some lumps. Some lumps remain and disintegrate on shaking.
= Cylinder of powder which has been pushed out partly disintegrates. Remaining Ixomps disintegrate to floury material under gentle pressure.
= Cylinder of powder which has been pushed out can be broken up very easily. Resulting lumps can very easily be crushed to a powder almost without residue.
= Cylinder of powder which has been pushed out can be broken up very easily. Very few lumps which can very easily be broken up are produced.
= Cylinder'-of powder which has been pushed out can be broken up easily. Many small and relatively

large lumps which can easily be broken up are produced.
7 = Cylinder of powder which has been pushed out can
be broken up easily. Many small and relatively large lumps which can be broken up are produced.
8 = Powder cylinder which has been pushed out can be
broken up only by very heavy pressure. Many small and relatively large hard lumps remain.
9 = Cylinder of powder which has been pushed out
cannot be broken up by pressure. Coarse, hard and lumpy material remains.
L-3 = No risk of blocking
1-5 = Scarcely any risk of blocking
5-7 = Critical range
3-9 = Material blocks
?he organosilazane content in the ammonium chloride was letermined by ^H-NMR.
The average particle size was determined using .n LS particle size analyzer (Coulter LS 130).
omparatlve Example 1
950 parts by weight of trimethylchlorosilane nd 1161 parts by weight of hexamethyldisilazane were laced in a reaction vessel. Gaseous ammonia was passed nto this mixture. The reaction was started at 20°C, nd the temperature rose to 45°C while ammonia was eing passed in. The reaction mixture was then kept at tils temperature by cooling the reaction vessel. After assing in ammonia for 90 minutes, absorption of nmonia had ceased. Nevertheless, the ammonia supply as continued at 45°C for a further 45 minutes. The taction mixture was then cooled to room temperature. le reaction-With ammonia had produced a mixture of 80%

by weight hexamethyldisilazane and 20% by weight ammoniiom chloride {dispersion A) .
The hexamethyldisilazane was removed from this mixture by centrifugation using a skimmer centrifuge. The resulting ammonium chloride (ammonixim chloride A) had a hexamethyldisilazane content of 15.8% by weight after the centrifugal removal.
300 g of the ammonium chloride A were then dried in a rotary evaporator at a temperature of 110°C under a vacuum of 50 hPa for 2 hours. During the drying, the ammonium chloride agglomerated to very hard particles of stable shape and various sizes.
After powdering, the dried ammonium chloride had an average residual hexamethyldisilazane content of 3000 ppm and a blocking resistance of 8.
Drying attempts starting from dispersion A and ammonium chloride A were carried out on the industrial scale using the following dryer systems at 110°C and 50 hPa:
Vacuum plate dryer (VTT system) from Krauss Maffei, Munich, Germany (ammonixim chloride A)
Vacuum filter dryer from Rosemund, Liesthal, Switzerland (dispersion A)
Suction filter dryer from Seitz FilterTverke, Bad Kreuznach, Germany (dispersion A)
Vertical/horizontal thin film dryer from KUnzi, Bubendorf, Switzerland (dispersion A)
Titus centrifuge dryer from Fima, Obersontheim, Germany (dispersion A)
With all types of dryer, the ammonium chloride caked after a short time to hard particles of cherry to snowball size-; and in the case of the thin film dryer hard deposits which gradually became glassy formed

between the rotor and the walls, so that the drying process had to be stopped in all cases.
After powdering, the resulting ammonium chloride had a blocking resistance of 8.
Example 1
Ammonium chloride A was granulated using a granulator from Alexanderwerke (Remscheid, Germany) with holes 3-5 mm in size. The resulting ammonium chloride granules had a stable shape. Using the vacuum plate dryer from Krauss Maffei used in Comparative Example 1, the granules were then dried without technical difficulties at 110°C and 50 hPa to recover the hexamethyldisilazane present in ammonium chloride A. There was no caking of the granules during the drying.
After powdering, the resulting ammonium chloride had a hexamethyldisilazane content of 250 ppm and a blocking resistance of 8.
Example 2
The dried ammonium chloride obtained in Example 1 was ground with a double pinned disk mill (Alpine Labor Condux) at 34,000 revolutions per minute to an average particle size of 66 |Lim (weight average) and then mixed with 0.5% pyrogenic silica with the name Wacker HDK® H 30 (can be purchased from Wacker-Chemie 3mbH, Munich, Germany) with a BET surface area of 250 mVg and a carbon content of 1.9%.
The silica-containing ammonium chloride showed a blocking resistance of 2.
Sxample 3
1%, based on the ammonium chloride present in iispersion A, of pyrogenic silica with the name Jacker HDK® N 20 (can be purchased from Wacker-Chemie ;mbH, Munich, Germany) with a BET surface area of !00 mVg was--mlxed in. The hexamethyldisilazane was then ■emoved by centrifugation using a skimmer centrifuge.

The resulting silica-containing ammonium chloride (ammonium chloride B) had a hexamethyl-disilazane content of 16.5% by weight after the centrifugal removal.
300 g of ammoniiom chloride B were then dried in a rotary evaporator at a temperature of 110°C under a vacuum of 50 hPa for 2 hours. The ammonium chloride did not form lumps during the drying. The resulting product was a powder which had an average residual hexamethyl¬disilazane content of 120 ppm, a blocking resistance of 2 and an average particle size of 309 pm (weight average).
Example 4
Ammonium chloride B was dried on the industrial scale using the vacuum plate dryer from Krauss Maffei used in Comparative Example 1 without technical difficulties at 110°C and 50 hPa to recover the hexamethyldisilazane present in ammonium chloride B. The ammoniiom chloride did not cake during the drying.
The resulting product was a powder with an average residual hexamethyldisilazane content of 140 ppm, a blocking resistance of 2 and an average particle size of 280 \m. (weight average).
Example 5
0.5%, based on the ammonium chloride present in dispersion A, of the pyrogenic silica used in Example 2 was mixed in. The hexamethyldisilazane was then removed by centrifugation using a skimmer centrifuge. The resulting silica-containing ammonium chloride (ammonium chloride C) had a hexamethyldisilazane content of 14.3% ■ by weight after the centrifugal removal.
Ammonium chloride C was granulated in analogy to Example 1. Despite the silica addition, ammonium chloride granules of stable shape were obtained. The granules were then dried using the vacuum plate dryer from Krauss-- Maffei used in Comparative Example 1 at 110°C and 50 hPa to recover the hexamethyldisilazane

present. The granules did not cake during the drying but partly disintegrated into smaller particles. The dried granules were then ground in analogy to Example 2 to an average particle size of 64 lim (weight average) .
Determination of the residual hexamethyldi-silazane content showed a value of 210 ppm, and determination of the blocking resistance showed a value of 3. After further addition of 0.5% of the pyrogenic silica used in Example 2, the resulting powder was free-flowing with a blocking resistance of 1.
Example 6
The silica-containing dried ammonium chloride from Example 2 was investigated by AES (atomic emission spectroscopy) for its content of lead, cadmium, chromium, nickel, zinc, copper" and mercury. The content of all the elements was below 5 ppm.

claims
1. A process for preparing organosilazane and
ammonium chloride, with reaction of an
organochlorosilane and ammonia in the presence of
i organosilazane as solvent wherein ammonitom chloride is removed from the resulting mixture containing organosilazane and ammonium chloride, by adding an antiblocking agent to the mixture before the removal, or to the ammonixim chloride after the removal.
2. A process for preparing organosilazane and ammonium chloride as claimed in claim 1, wherein the antiblocking agent is added before the removal, and the complete removal of the ammonium chloride takes place thermally or by a combination of mechanical and thermal processes.
3. A process for preparing organosilazane and ammonium chloride as claimed in claim 2, wherein the removal takes place by a combination of mechanical and thermal processes, and a granulation step is carried out after the mechanical removal.
4. A process for preparing organosilazane and ammonium chloride as claimed in claim 2 or 3, wherein additionally antiblocking agent is added to the ammonium chloride after the removal.
5. A process for preparing organosilazane and ammonium chloride as claimed in claim 1, wherein the antiblocking agent is added to the ammonium chloride after the removal, and the removal of the ammonium chloride takes place by a combination of mechanical and thermal processes, and a granulation step is carried out after the mechanical removal and before the thermal removal.

6. A process for preparing organosi1azane and ammonium chloride substantially as herein described and exemplified.