Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2001-06-29
2002-05-07
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06384256
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for the production of sulfur containing organosilicon compounds by phase transfer catalysis techniques. The process involves first reacting an alkali metal hydroxide compound with a sulfide compound and sulfur in water to form a polysulfide mixture. The polysulfide mixture is then reacted with a silane compound in the presence of a phase transfer catalyst.
BACKGROUND OF THE INVENTION
Sulfur containing organosilicon compounds are useful as reactive coupling agents in a variety of commercial applications. In particular, sulfur containing organosilicon compounds have become essential components in the production of tires based on rubber vulcanates containing silica. The sulfur containing organosilicon compounds improve the physical properties of the rubber vulcanates containing silica resulting in automotive tires with improved abrasion resistance, rolling resistance, and wet skidding performance. The sulfur containing organosilicon compounds can be added directly to the rubber vulcanates containing silica, or alternately, can be used to pre-treat the silica prior to addition to the rubber vulcanate composition.
Numerous methods have been described in the art for the preparation of sulfur containing organosilicon compounds. For example, U.S. Pat. No. 5,399,739 by French et al. describes a method for making sulfur-containing organosilanes by reacting an alkali metal alcoholate with hydrogen sulfide to form an alkali metal hydrosulfide, which is subsequently reacted with an alkali metal to provide an alkali metal sulfide. The resulting alkali metal sulfide is then reacted with sulfur to provide an alkali metal polysulfide which is then finally reacted with a silane compound of the formula X—R
2
—Si(R
1
)
3
, where X is either chlorine or bromine to produce the sulfur-containing organosilane.
U.S. Pat. Nos. 5,466,848, 5,596,116, and 5,489,701 describe processes for the preparation of silane polysulfides. The '848 patent process is based on first producing sodium sulfide by the reaction of hydrogen sulfide with sodium ethoxylate. The sodium sulfide is then reacted with sulfur to form the tetrasulfide, which is subsequently reacted with chloropropyltriethoxysilane to form 3,3′-bis (triethoxysilylpropyl) tetrasulfide. The '116 patent teaches a process for the preparation of polysulfides, without the use of hydrogen sulfide, by reacting a metal alkoxide in alcohol with elemental sulfur, or by reacting sodium metal with elemental sulfur and an alcohol, with a halohydrocarbylalkoxysilane such as chloropropyltriethoxysilane. The '701 patent claims a process for the preparation of silane polysulfides by contacting hydrogen sulfide gas with an active metal alkoxide solution and subsequently reacting the reaction product with a halohydrocarbylalkoxysilane such as chloropropyltriethoxysilane.
U.S. Pat. No. 5,892,085 describes a process for the preparation of high purity organosilicon disulphanes. U.S. Pat. No. 5,859,275 describes a process for the production of bis (silylorganyl) polysulphanes. Both the '085 and '275 patents describe anhydrous techniques involving the direct reaction of a haloalkoxysilane with a polysulphide.
U.S. Pat. No. 6,066,752 teaches a process for producing sulfur-containing organosilicon compounds by reacting sulfur, an alkali metal, and a halogenalkoyxsilane in the absence of a solvent or in the presence of an aprotic solvent.
Most recently, U.S. Pat. No. 6,140,524 describes a method for preparing short chain polysulfide silane mixtures of the formula (RO)
3
SiC
3
H
6
S
n
C
3
H
6
Si(RO)
3
having a distribution where n falls in the range of 2.2≦n≦2.8. The '524 method reacts metal polysulfides, typically Na
2
S
n
with a halogenopropyltrialkoxysilane having the formula (RO)
3
SiC
3
H
6
X wherein X is a halogen, in alcohol solvent.
Alternative processes for the preparation of sulfur-containing organosilanes have been taught in the art based on the use of phase transfer catalysis techniques. Phase transfer catalysis techniques overcome many of the practical problems associated with the aforementioned prior art processes for producing sulfur-containing organosilicon compounds. Many of these problems are related to the use of solvents. In particular, the use of ethyl alcohol can be problematic because of its low flash point. Additionally, it is difficult to obtain and maintain anhydrous conditions necessary in many of the aforementioned prior art processes on an industrial scale.
Phase transfer catalysis techniques for producing sulfur-containing organosilicon compounds are taught for example in U.S. Pat. Nos. 5,405,985, 5,663,396, 5,468,893, and 5,583,245. While these patents teach new processes for the preparation of sulfur containing organosilicon compounds using phase transfer catalysis, there still exist many practical problems with the use of phase transfer techniques at an industrial scale. For example, there is a need to control the reactivity of the phase transfer catalyst in the preparation of sulfur-containing organosilanes so as to provide efficient, yet safe reactions that can be performed on an industrial scale. Furthermore, there is a need to improve the final product stability, appearance and purity. In particular, the phase transfer catalysis process of the prior art results in final product compositions containing high quantities of un-reacted sulfur species. These un-reacted sulfur species can precipitate in stored products with time causing changes in product sulfide distribution.
The need to improve product quality is of particular importance when an alkali metal or ammonium hydrogen sulfide is used as a starting material in phase transfer catalysis techniques. In these reactions, dangerous and odorous hydrogen sulfide is produced in side reactions. Product compositions containing even minor amounts of hydrogen sulfide deter their use in large-scale industrial processes.
It is therefore an object of the present invention to provide an improved process for the production of sulfur containing organosilicon compounds based on phase transfer catalysis techniques.
It is a further object of the present invention to provide a process for producing sulfur containing organosilicon compounds based on phase transfer catalysis techniques that result in a final product composition of greater stability, purity, and appearance.
It is yet a further object of the present invention to provide a process for producing sulfur containing organosilicon compounds based on phase transfer techniques using a sulfide compound that minimizes or eliminates hydrogen sulfide as a side product.
It is still a further object of the present invention that provides a process for producing sulfur containing organosilicon compounds based on phase transfer techniques using starting materials that are less costly that conventional prior art methods and minimizes un-reacted side products.
SUMMARY OF THE INVENTION
The present invention provides a process for the production of sulfur containing organosilicon compounds by phase transfer catalysis techniques. The improvement of the present invention is characterized by reacting an alkali metal hydroxide compound with a sulfide compound and sulfur in water to form a polysulfide mixture, which is then reacted with a silane compound in the presence of a phase transfer catalyst.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a process for the production of organosilicon compounds of the formula:
(RO)
3−m
R
m
Si-Alk-S
n
-Alk-SiR
m
(OR)
3−m
where R is independently a monovalent hydrocarbon of 1 to 12 carbon atoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms; m is an integer of 0 to 2, n is a number from 1 to 10;
comprising:
(A) reacting an alkali metal hydroxide compound, a sulfide compound having the formula M
2
S
n
or MHS,
where H is hydrogen, M is ammonium or an alkali metal,
n is as defined above,
and sulfur in water to form a polysulfide mixture,
(B) reacting said polysulfide mixture with a silane compound of
Backer Michael Wolfgang
Bank Howard Marvin
Gohndrone John Michael
Maki William Charles
Skinner Charles Edmund
Dow Corning Corporation
Shaver Paul F.
Warren Jennifer S.
Zombeck Alan
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