Regarding hexamethyldisilazane
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In the laboratory, using dimethyldisiloxane as a solvent, hexamethyldisilazane is obtained by passing ammonia over trimethylchlorosilane. The crude product resulting from this reaction is washed with water, followed by alkaline treatment with a 15% sodium hydroxide solution; after separation of the layers, a crude product free of ammonia is obtained. Through distillation, hexamethyldisilazane with a purity of over 99.5% is achieved. After the experiment, the crude product becomes cloudy after being left standing for 2–3 days. It is speculated that ammonium chloride may have been carried into the product along with water, causing turbidity. Could anyone explain what might be the reason for this? How to solve it?
Hexamethyldisilazane is unstable at room temperature, prone to hydrolysis and decomposition, and is sensitive to both water and acids. Therefore, it is possible that impurities such as residual trimethylchlorosilane and sodium hydroxide were not completely removed during preparation and distillation, which led to the introduction of water and other impurities. This affected the purity and stability of the product, causing turbidity. Whether ammonium chloride is present still requires further testing to confirm. To address this issue, the following aspects can be considered: 1. Thoroughly dehumidify before preparation and distillation to ensure that the reaction system is dry ； 2. Try to remove residual impurities such as trimethylchlorosilane and sodium hydroxide by carrying out additional washes with water and alkali, as well as more rigorous distillation processes ； 3. When storing, care should be taken to prevent hexamethyldisilazane from coming into contact with humid air; it is best to use nitrogen for protection and store it in a dry and well-ventilated area. .