Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2003-03-03
2004-08-17
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C556S427000
Reexamination Certificate
active
06777569
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the preparation of a blocked mercaptosilane, from a metal salt of a polysulfane-containing organosilicon compound and an acyl halide or carbonyl dihalide, wherein the metal salt of the polysulfane-containing organosilicon compound is formed by reacting a polysulfane-containing organosilicon and an alkali metal, alkaline earth metal or a strong base derived from an alkali metal or alkaline earth metal. This invention also relates to the use of said blocked mercaptosilane as a coupling agent in rubber mixtures.
2. Description of Related Art
Sulfur-containing organosilicon compounds are useful as essential components in the production of silica-filled tires. A silica-filled tire provides for enhanced performance in automotive applications, specifically, improved abrasion resistance, rolling resistance and wet-skidding properties. There are a broad range of sulfur-containing organosilicon compounds that are used as coupling agents in silica-filled tires. Mercapto-containing organosilicon compounds offer superior coupling at reduced loading, however, their chemical reactivity with organic polymers results in unacceptably high viscosities during processing and premature curing. Blocked mercaptosilanes have been shown to maintain the benefits of mercapto-containing organosilicon compounds without displaying the aforenoted problems. The blocked mercapto-containing organosilicon compounds, in particular, thiocarboxylic-containing silicon compounds, can be prepared by reacting a mercapto-containing silicon compound with an acid halide. The byproduct of this reaction, hydrogen chloride, reacts with the organosilicon compound degrading the desired product, and generating chlorosilanes. These reactions with hydrogen chloride are very fast and cannot be prevented by conventional mechanical means, i.e., temperature or pressure, due to the high solubility of the hydrogen chloride in the product. Neutralization of the above noted chlorosilanes can be done using a base such as sodium alkoxide, or propylene oxide, but degradation of the product and/or an undesirable mixture is obtained making this approach undesirable.
Another process used previously, is to neutralize the hydrogen chloride, in situ, using an acid acceptor, i.e., tertiary amine, see U.S. Provisional Patent Application No. 60/423,577 filed Nov. 4, 2002; but this requires a stoichiometric amount of the amine that reduces batch yield and affords a large amount of an undesirable salt that must subsequently be removed, see U.S. Pat. No. 6,229,036. As is already known, tertiary amine salts are difficult to remove due to their solubility, and conventional filtration methods are mechanically intensive and often lead to poor yields. Furthermore, further processing of the filter cake adds additional costs, such as the disposing of the tertiary amine and the hydrogen chloride salt in itself, which poses significant environmental issues.
As has been shown, the reaction of a metal salt of a mercapto-containing organosilicon compound and an acid halide generates the desired blocked mercaptosilane and a metal halide salt, see U.S. Pat. No. 6,414,061 the contents of which are incorporated herein by reference; but in addition to the previously mentioned difficulties, mercapto-containing organosilicon compounds are expensive making their widespread use prohibitive. Therefore, there is an interest in developing a blocked mercaptosilane using a process that is inexpensive and does not provide for the chemical and environmental concerns noted above. There are a number of known methods to cleave a sulfur-sulfur bond, i.e., the use of bases such as amines, phosphines, metal cyanides, metal hydrides and alkali metals, however, phosphines and metal hydrides are expensive and metal cyanides offer a host of safety concerns.
SUMMARY OF THE INVENTION
Polysulfane-containing silicon compounds are inexpensive and widely available, in addition to their affordability, the metal halide byproduct does not react with the product blocked mercaptosilane nor do polysulfane-containing silicon compounds have the environmental concerns of a tertiary amine halide salt. Alkali metals are both safe and inexpensive. The reaction of an alkali metal with a polysulfane-containing organosilicon compound to generate the metal salt of the polysulfane-containing organosilicon compound, affords the desired acid acceptor, in situ, that can be used to produce the desired blocked mercaptosilane compound and a metal halide salt.
Additionally, the use of an aqueous wash of the product thereby minimizes the aforementioned costs and difficulties of removing the metal salt. Removing the metal halide salt by means of either filtration or by use of a centrifuge requires intensive mechanical unit operations and capital investment, whereas an aqueous wash requires neither but results in a two-phase system where one phase contains the blocked mercaptosilane and the second phase contains an aqueous solution of the metal halide. The primary hazard with this method is the potential for hydrolysis of the blocked mercaptosilane and for organofunctional silanes. However, through the presence of metal halide the ionic character of the aqueous phase is increased and thereby minimizes any hydrolysis reaction, see U.S. Pat. No. 6,294,683.
It is an object of the invention to provide a process for preparing a blocked mercaptosilane for use as a coupling agent, which process minimizes the production of byproducts that react with the blocked mercaptosilane, does not require neutralization or filtering and is commercially affordable.
In keeping with this and other objects of the invention there is provided a process for the manufacture of a blocked mercaptosilane comprising:
(a) reacting at least one polysulfane-containing organosilicon compound of the general formula:
(R
1
3
SiG)
2
S
n
in which each R
1
is independently methoxy, ethoxy or alkyl of from 1 to about 6 carbon atoms, provided, that at least one R
1
group is methoxy or ethoxy, G is an alkylene group of from 1 to about 12 carbon atoms and n is from 2 to about 8, with at least one alkali metal, alkaline earth metal or a basic derivative of an alkali metal or alkaline earth metal to provide the corresponding metal salt of the polysulfane-containing organosilicon compound and;
(b) reacting the metal salt of the polysulfane-containing organosilicon compound with an acyl halide or carbonyl dihalide to provide a blocked mercaptosilane.
In contrast to the process described in aforementioned U.S. Pat. No. 6,414,061 the process of this invention makes it possible to produce a blocked mercaptosilane from readily available polysulfane-containing organosilicon compounds. This results in a high purity blocked mercaptosilane that does not require neutralization or filtering to remove the byproduct metal halide that is formed upon reaction of the metal salt of the polysulfane-containing organosilicon compound with the acyl halide or carbonyl dihalide.
A further object of this invention is to provide a process that involves the use of an aqueous wash of the final product solution, which unlike the distillation step required in aforementioned U.S. Pat. No. 6,414,061, is a more expedient and efficient way to separate the product blocked mercaptosilane from the metal halide byproduct.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the process of this invention, a polysulfane-containing organosilicon compound of the formula (R
1
3
SiG)
2
S
n
in which R
1
, G and n have the aforestated meanings, and an alkali metal, alkaline earth metal or a strong base derived from the alkali metal or alkaline earth metal, can be considered to react to form a metal salt of the polysulfane-containing organosilicon compound in accordance with the reaction (illustrated for an alkali metal such as sodium):
Metal+(R
1
3
SiG)
2
S
n
→(R
1
3
SiG)
2
S-Metal
The metal salt of the polysulfane-containing organosilicon compound and a reactive halide such as an acyl halide or carbonyl dihali
Burton Russell
Simandan Tiberiu L.
Westmeyer Mark D.
Barts Samuel
General Electric Company
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