Müller-Rochow synthesis

The Müller-Rochow synthesis is a process for the large-scale production of methylchlorosilanes , which was developed almost simultaneously in May 1940 by the US chemist Eugene G. Rochow (1909 to 2002) and the German chemist Richard Müller (1903 to 1999) . Methylchlorosilanes are intermediate products in the manufacture of silicones . There have been various assumptions about the catalytic mechanism of the reaction, but no generally accepted theory.

Reaction equation

Sketch of the Müller-Rochow synthesis
(A) compressor
(B) evaporator
(C) fluidized bed reactor
(D) cooling jacket
(E) cyclone
(F) silicon / copper (cat.)
(G) methyl chloride
(H) condenser
(I) raw silane
( J) for distillation
(K) silicon / copper dust
(L) heat exchanger
(M) residue
(N) reflux methyl chloride

${\displaystyle \mathrm {2\ CH_{3}Cl+Si\longrightarrow (CH_{3})_{2}SiCl_{2}} }$

Technical implementation

The silicon is in powder form with a grain size between 50 and 500 µm. The catalyst used is copper , which is elemental or z. B. is used in the form of copper oxide. As promoters also act nor zinc , tin , phosphorus and other elements. The reaction takes place at 260 ° C to 320 ° C and 0.1 MPa to 0.5 MPa.

In a fluidized bed reactor , chloromethane flows through the powder mixture from below . This type of reactor has the advantage that the heat released by the exothermic reaction can be easily dissipated. After the reactor, the methylchlorosilanes formed can be separated from unused chloromethane in a condenser .

The silane mixture contains the main product dimethyldichlorosilane (in concentrations of 70% to 90%) but also methyltrichlorosilane, trimethylchlorosilane, dimethyltetrachlorodisilane and other silanes . These must be separated from one another by rectification .

Further processing of the silanes

Silanols are formed by hydrolysis of the chloromethylsilanes . These condense into short chains and cycles. In addition, hydrogen chloride is released, which can be used, among other things, for the synthesis of new methyl chloride. A wide variety of silicone compounds can be produced by further polymerization .

Hydrolysis:

${\displaystyle \mathrm {(CH_{3})_{2}SiCl_{2}+2\ H_{2}O\longrightarrow (CH_{3})_{2}Si(OH)_{2}+2\ HCl} }$

Condensation:

${\displaystyle \mathrm {n\ (CH_{3})_{2}Si(OH)_{2}\longrightarrow [-O{-}Si(CH_{3})_{2}-]_{n}+n\ H_{2}O} }$

literature

• Rösch, L .; John, P .; Reitmeier, R .: Organic Silicon Compounds . Ullmann's Encyclopedia of Industrial Chemistry. John Wiley and Sons: San Francisco, 2003. doi : 10.1002 / 14356007.a24_021 .
• Christoph Elschenbroich : Organometallics . VCH, Weinheim, 1992. ISBN 978-3-527-29390-2 .

Web links

• Basic Silicone Chemistry - A Review (PDF; 719 kB)