Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2001-03-29
2002-06-18
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C252S183130
Reexamination Certificate
active
06407276
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention provides a method for improving selectivity for dialkyldichlorosilane product resulting from reacting silicon with an alkyl chloride.
Dialkyldichlorosilanes such as dimethyldichlorosilane are used commercially in the manufacture of methylsilicone polymers that are starting materials for methylsilicone sealants and heat cured rubber. Rochow, U.S. Pat. No. 2,380,995, disclosed a method of preparing dimethyldichlorosilane (Me
2
SiCl
2
) using a direct reaction between methyl chloride (MeCl) and elemental silicon (Si) in the presence of a copper (Cu) catalyst in 1945. It is now a common practice to generate dimethyldichlorosilane by reacting silicon with methyl chloride using copper as a catalyst together with the promoters zinc (Zn) and tin (Sn). With concentrations by weight, based on silicon, of Cu (1-5%), Zn (0.04-20%), and Sn (5-30) ppm, the following reaction product mixture and associated weight percents is typically obtained with reaction temperatures below about 290-300° C.
Me
2
SiCl
2
(“Di”) (80-93%);
MeSiCl
3
(“Tri”) (5-10%);
Me
3
SiCl (1-5%);
MeHSiCl
2
(0.5-3%);
Me
2
HSiCl (0.1-1%);
Other low boilers (0.1-0.5%);
Residue (0.5-5%).
From the preceding table, the selectivity for dimethyldichlorosilane (Me
2
SiCl
2
) relative to methyltrichlorosilane (MeSiCl
3
) in the product mixture is high. A high selectivity for dimethyldichlorosilane results when copper (Cu), zinc (Zn), and tin (Sn) have the following generally used concentrations by weight, based on silicon: Cu (0.5% to 5%), Zn (0.01% to 0.5%), and Sn (5 ppm to 100 ppm).
Unfortunately, the selectivity for dimethyldichlorosilane is reduced if the Cu, Zn, or Sn concentrations exceed the generally used concentrations or if the reaction temperature exceeds 300° C. In particular, the selectivity for dimethyldichlorosilane is substantially reduced if the copper concentration by weight exceeds 5%. However, if waste products of the reaction are recycled back into the reaction, the copper level will exceed 5% and may rise to as high as 25-30%. Additionally, it may be desirable to have the reaction occur at a temperature higher than 300° C. in order to increase the reaction rate.
Thus, there is a need to improve selectivity for dimethyldichlorosilane when the copper weight percent exceeds 5% based on silicon or the reactor temperature is higher than 300° C.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a method for forming a dialkyldichlorosilane, comprising reacting at a reaction temperature elemental silicon with an alkyl chloride using copper as a catalyst together with promoters zinc, tin, and a special promoter comprising silver, a silver compound, gold, a gold compound, or combinations thereof.
The present invention provides a chemical mixture used in a chemical reaction that generates a dialkyldichlorosilane, said chemical mixture comprising reactants, a catalyst, and promoters, wherein the reactants include elemental silicon and an alkyl chloride, wherein the catalyst includes copper, wherein the promoters include zinc, tin, and a special promoter comprising silver, a silver compound, gold, a gold compound, or combinations thereof, and wherein the chemical reaction is executed at a reaction temperature.
The present invention improves selectivity for dimethyldichlorosilane when the copper weight percent exceeds 5% based on silicon or the reactor temperature is higher than 300° C.
REFERENCES:
patent: 2380995 (1945-08-01), Rochow
patent: 2380996 (1945-08-01), Rochow et al.
patent: 2380997 (1945-08-01), Patnode
patent: 2389931 (1945-11-01), Reed et al.
patent: 2427605 (1947-09-01), Hurd
patent: 2464033 (1949-03-01), Gilliam
patent: 2473260 (1949-06-01), Rochow et al.
patent: 3446829 (1969-05-01), Zock
patent: 4824984 (1989-04-01), Klar et al.
patent: 4864044 (1989-09-01), Lewis et al.
patent: RE33452 (1990-11-01), Ward, III et al.
patent: 4973725 (1990-11-01), Lewis et al.
patent: 5117030 (1992-05-01), Cattoz et al.
patent: 5338876 (1994-08-01), Jung et al.
patent: 5714131 (1998-02-01), Margaria et al.
patent: 0 348 902 (1995-03-01), None
Lewis et al., Catalyzed Direct Reactions of Silicon, 1993, Elsevier Science Publishers, B.V., pp. 1-66.
Eugene G. Rochow, The Direct Synthesis of Organosilicon Compounds, 1945, pp. 963-965, vol. 67.
Bablin John Matthew
Colborn Robert Edgar
Lewis Larry Neil
Bennett Bernadette M.
Shaver Paul F.
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