1,1,1,3,3,3-Hexamethyldisilazane

Countertype of Dynasylan HMDS, DowCorning Z-6079, ShinEtsu HMDS3, Silquest A-166

Chemical Structure

Introduction

Silazane is any hydride of silicon and nitrogen having a straight or branched chain of silicon and nitrogen atoms joined by covalent bonds. By extension, the word is also used for any organic derivative of such compounds. They are analogous to siloxanes, with -NH- replacing -O-. Their individual name is dependent on the number of silicon atoms in the chemical structure.

SI-165 is an extremely versatile and strong silylating agent. It is primarily used for the protection of sensitive functional groups during chemical synthesis.

Trimethylsilyl moiety is a versatile blocking agent employed in chemical synthesis. Introduction of silyl protective groups has following advantages:

Masking of reactive functional groups.
Improvement of solubility in polar and or non polar solvent.
Improved product stability.
Easy removal of protective groups .
Additional activation of reactive centres.
Easyelimination of hydrogen bonds.

One of the advantages of SI-165 over chlorosilanes is that no base is needed as a hydrochloric acid acceptor. SI-165 produces ammonia which escapes easily from the reaction mixture during silylation.   

Typical Physical Properties

Applications

SI-165 can be used to introduce trimethylsilyl group into organic molecules containing an active hydrogen atom such as alcohols, carboxylic acids, amines etc. The most common industrial application of SI-165 is in production of semi synthetic beta lactum antibiotics as ampicillin and cephalexin.

The usual procedure is to protect the carboxylic group in the antibiotic with HDMS followed by acylation with the desired acylchloride. Finally, desilylation under mild aqueous conditions gives the desired product.