hexamethyldisilazane

Hexamethyldisilazane, abbreviated HMDS, is an organosilicon compound with the formula (CH3)3Si–NH–Si(CH3)3. It is a colorless, volatile liquid at room temperature and has a strong, ammonia-like odor. The molecule consists of two trimethylsilyl groups connected by a single NH bridge, giving a disilazane framework. HMDS is moisture-sensitive and is typically stored under inert atmosphere to minimize hydrolysis.

Production and handling

HMDS is commonly prepared by the ammonolysis of chlorotrimethylsilane: 2 Me3SiCl + NH3 → (Me3Si)2NH + NH4Cl. It can also be formed or used in situ in reactions that require a silylating agent. Upon contact with water, HMDS hydrolyzes to yield ammonia and siloxane byproducts, illustrating its sensitivity to moisture. Because of its volatility and reactivity with moisture, HMDS is usually handled under dry, inert conditions and in a well-ventilated space.

Uses

The primary use of HMDS is as a silylating reagent in organic synthesis. It transfers the trimethylsilyl (TMS) group to alcohols, phenols, and amines to form their corresponding trimethylsilyl ethers or amines, enabling protection and later deprotection steps in multi-step syntheses. It is also employed in surface treatments of glass, silica, and semiconductor substrates to render surfaces hydrophobic and to modify surface reactivity.

Safety and handling

HMDS is flammable and irritating to skin, eyes, and the respiratory tract. It evolves ammonia on hydrolysis and reacts with moisture; therefore, it should be stored and used under inert atmosphere, with appropriate protective equipment and good ventilation. It should be kept away from water, oxidizers, and incompatible materials.