Process for the preparation of methylchlorosilanes

A process for the preparation of methylchlorosilanes from silicon and methyl chloride in the presence of a copper catalyst and wherein promoter substances may be employed, in which the production rates of the individual methylchlorosilanes, based on the surface area of the silicon employed, are controlled by the structure of the silicon, which comprises selecting the silicon having the desired structure on the basis of its structural parameter QF, the structural parameter QF being determined by

• (a) cutting up silicon test specimens to form a cut surface,
• (b) totaling on the cut surface the areas of precipitates of intermetallic phases having a longitudinal shape to give an area number A,
• (c) totaling on the cut surface the areas of precipitates of intermetallic phases having a circular shape to give an area number B, and
• (d) obtaining the quotient of the area number A and the area number B, called the structural parameter QF.