text: TMSCl is prepared on a large scale by the direct process, the reaction of methyl chloride with a silicon-copper alloy.  The principal target of this process is dimethyldichlorosilane, but substantial amounts of the trimethyl and monomethyl products are also obtained. The relevant reactions are (Me = methyl, ):
  Typically about 2–4% of the product stream is the monochloride, which forms an azeotrope with .