Preparation and application of hexamethyldisilazane

Background and overview[1][2]
Hexamethyldisilazane (HMDS) is an important organosilicon compound, which has a wide range of applications in the fields of organosilicon chemistry and organic synthesis. Hexamethyldisilazane is not only a key raw material for the synthesis of hexamethyldisilazide (BSU), but also a commonly used silylation reagent in organic synthesis, which has important industrial application value. In organosilazane chemistry, it can be used for chlorine exchange with chlorosilane monomers to obtain polysilazane. This method has a huge advantage in synthesis over the direct ammonia method. Used as a bonding aid for photoresist in the semiconductor industry. In the pharmaceutical industry, hexamethyldisilazane is used in the synthesis of amikacin, penicillin, and cephalosporin.

Preparation [1-2]
Industrially, HMDS is mostly made by using trimethylchlorosilane as raw material and reacting with ammonia gas in an inert organic solvent. Since the ammonium chloride particles generated in the process of the amination reaction can easily enclose the product, it is necessary to wash and separate the reaction mixed product after the reaction is completed to obtain the product. However, HMDS is prone to hydrolysis reaction to generate hexamethyldisiloxane and trimethylsilanol during the water washing process, resulting in a decrease in the yield of the target product. Both Chinese patents CN101613363A and CN101704835A use this method to produce hexamethyldisilazane, and the reported product purity and yield are both low. Therefore, the hydrolysis reaction of hexamethyldisilazane during the washing operation is one of the key factors affecting the yield in the current industrial production.


1. CN201210252719.5 provides a method for synthesizing hexamethyldisilazane.
The mixed solvent method of hexamethyldisiloxane is used to produce hexamethyldisilazane. The addition of hexamethyldisiloxane in the reaction system will inhibit the occurrence of side reactions of hexamethyldisilazane hydrolysis and improve the reaction. Yield. The technical scheme adopted by the present invention is:


1) Add reaction raw material trimethylchlorosilane and reaction solvent to the reaction kettle, and stir evenly. The reaction solvent is a mixed solvent of hexamethyldisiloxane and a benzene solvent. The benzene solvent is one or more of benzene, toluene or xylene. The mixed solvent includes a mixture of hexamethyldisiloxane and a benzene-based solvent in any volume ratio. Preferably, the mixed solvent is hexamethyldisiloxane: benzene solvent=1-25:1. The reaction solvent may also include only hexamethyldisiloxane.


2) Feed ammonia gas into the reaction system, strictly control the ammonia gas speed, control the reaction temperature ≤ 80°C, and the reaction pressure ≤ 0.2Mpa. In the late stage of the reaction, the exothermic heat becomes smaller, the temperature of the reaction system drops, and the pressure rises. After the ammonia gas is stopped, the pressure and temperature do not change significantly, which proves the end of the reaction, and the ammoniating reaction is stopped at this time.


3) Add water to the reaction system successively for the first water washing. After washing, let it stand for 5 minutes to remove the lower NH4Cl aqueous solution by phase separation; add lye to wash the organic phase, and then stand for 5 minutes after washing to remove the lower water phase by phase separation; Add water to the phase for the second water wash, and the upper material after phase separation is the crude product hexamethyldisilazane. The lye is sodium hydroxide or potassium hydroxide solution, and the washing water used for the second washing after the alkaline washing is used for the first washing in the washing process.


4) The crude product hexamethyldisilazane is rectified and separated in the rectification tower, and the finished product hexamethyldisilazane can be extracted at the top temperature of 124～127℃. The invention adopts the mixed solvent method to synthesize hexamethyldisilazane by one-step amination reaction. The addition of hexamethyldisiloxane in the reaction system can inhibit the occurrence of the side reaction of hexamethyldisilazane hydrolysis and increase the reaction yield. . The method has short reaction time, high yield, low energy consumption for rectification, reduces the production cost of hexamethyldisilazane, and has greater industrial advantages.


2. A column-type continuous synthesis method of hexamethyldisilazane
Aiming at the shortcomings of the prior art, a technical solution for the continuous synthesis method of hexamethyldisilazane in a column type is provided. Through two reaction columns and two plate and frame filter presses, the chlorine produced in the reaction is effectively removed. The ammonium solid is separated to avoid clogging, so that the reaction can proceed smoothly to the end, and avoid diluting the concentration of the raw material due to the solvent, which affects the reaction speed and reduces energy consumption.


Application [3]
Trimethylsilyl imidazole is an important basic silanization protection reagent, and also a key raw material for the synthesis of an important neutral silanization reagent bis(trimethylsilyl)acetamide. It is used in amino acids, carboxylic acids, alcohols and amides. It is widely used in the silanization protection of cephalosporins, especially in the synthesis of cephalosporin antibiotics.


CN200810120761.5 provides a new method for preparing high-purity trimethylsilylimidazole, using hexamethyldisilazane and imidazole as raw materials, in the presence of stabilizers, synthesizing high-purity trimethyl by reactive distillation technology Silimidazole. The method for synthesizing high-purity trimethylsilylimidazole by reactive distillation method provided by the present invention uses hexamethyldisilazane and imidazole as raw materials, and reacts in the presence of stearate or phosphite stabilizer The temperature is 100°C to 200°C, and the reaction time is 1 to 16 hours to generate high-purity trimethylsilyl imidazole. Compared with the traditional method, the method adopted by the present invention is very novel and has the following characteristics:


1) Using stearate and phosphite as stabilizers to avoid product decomposition and reduce the by-products of imidazole and silicon ether;


2) Due to the use of reactive distillation technology for synthesis, the process flow is simplified, and the conversion rate and selectivity of the reaction are improved;


3) Because the by-products with low boiling points are removed in the reaction, the reaction temperature is increased, the reaction time is shortened, and the energy consumption is reduced;


4) The product has high purity, good quality, and does not contain halogen ions.