Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-01-05
2003-02-11
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C556S429000, C556S479000, C556S427000, C524S084000, C524S188000, C524S262000
Reexamination Certificate
active
06518335
ABSTRACT:
BACKGROUND OF THE INVENTION
Sulfur-containing silane coupling agents are useful in providing rubber, including automotive tires, with improved properties, generally by coupling inorganic fillers or fibers with the rubber matrix in a fashion which leads to the improved properties. The sulfur-containing silane coupling agents which have achieved commercial success to date have been produced by disadvantageous processes which involve the handling of large quantities of chlorine-containing by-products. Thus, there is an ongoing need in the art to prepare sulfur-containing silane coupling agents safely in high yields and efficiencies by processes which do not involve chlorine-containing intermediates or by-products.
Current large-scale commercial production of such sulfur-containing silane coupling agents is based on the raw material trichlorosilane. Trichlorosilane is reacted with either allyl chloride or vinyltoluene to provide the respective intermediates, 3-chloropropyltrichlorosilane or (trichlorosilylethyl)-toluene. The former is reacted with alcohol to produce a 3-chloropropyltrialkoxysilane, which is reacted with sodium hydrosulfide or sodium tetrasulfide to produce the desired products, plus four equivalents of chlorine. The latter is reacted with sulfur monochloride, and the sulfurated trichlorosilane intermediate is reacted with alcohol to produce the desired product, plus five equivalents of chlorine.
Both of the above embodiments suffer from additional disadvantages in that yields from the reaction of trichlorosilane with allyl chloride are well below quantitative, based on the limiting reactant, with concurrent generation of undesired by-products. The reaction of trichlorosilane with vinyltoluene is susceptible to polymerization of the vinyltoluene, with subsequent reduced efficiency to (trichlorosilylethyl)toluene and formation of a polymeric by-product.
There is a need for a process that can simply and efficiently prepare certain known and novel silane coupling agents by a direct reaction, not producing chlorine-containing by-products. More specifically, there is a need for a process to produce sulfur-containing coupling agents that does not begin with trichlorosilane and does not involve chlorine-containing intermediates or by-products.
SUMMARY OF THE INVENTION
The present invention provides a process for preparing sulfur-containing silane coupling agents, some of which are novel compositions, by the reactions of alkoxysilane acetals with nonionic, chlorine-free sulfurating agents including, but not limited to, thiols, di- and higher thiols, hydrogen sulfide, and sulfur, in the presence of an acid catalyst, and optionally in the presence of hydrogen and a reduction catalyst. The process is depicted by the general reaction:
DETAILED DESCRIPTION OF THE INVENTION
It is an object of the invention to provide an improved process for the synthesis of sulfur-containing silane compounds, useful as coupling agents, by reactions involving chlorine-free intermediates and sulfurating agents. It is another object of the invention to provide novel sulfur-containing silane compounds, useful as coupling agents. It is another object of the invention to provide a process for preparing intermediates for sulfur-containing silane compounds in high yields. It is yet another specific object of the invention to provide a process for preparing sulfur-containing silane compounds by a chlorine-free reaction that produces silanes without the production of undesired chlorine or polymeric intermediates or by-products.
It has been discovered that the acetal groups of alkoxysilane acetals can be reacted with sulfurating agents without causing significantly adverse reactions at the alkoxysilane groups. More particularly, the process of the invention is based on the following reaction:
where R is a saturated or unsaturated linear, branched, or cyclic divalent hydrocarbon group of 2 to 12 carbon atoms optionally containing divalent —O— or —S— linkages; R
1
is an alkyl group of 1 to 4 carbon atoms, an aryl group of 6 to 12 carbon atoms, or an aralkyl or alkaryl group of 7 to 13 carbon atoms; each R
2
can be R
1
or the 2 R
2
groups taken together form an R group so as to form a ring; R
3
is a hydrogen atom or R
1
; R
4
is R
3
, —RSH, or —RSiR
1
x
(OR
2
)
3−x
; x is an integer having a value of 0, 1, or 2, j=0 or 1, n is an integer having a value of 1 to 4; when n=1, j=1, when n>1, j=0, X is R
4
and Y is —SR
4
or —OR
2
, or alternatively X and Y taken together are —SR— which forms a 1,3-dithiacycloalkane ring with the carbon bearing R
3
, when n=1, or X and Y are both hydrogen atoms when n=1 and R
4
is a hydrogen atom. The sulfur-containing silane coupling agents provided by the process of the present invention may thus be monomers or oligomers and may contain more than one molecular species. Where more than one group of R, R
1
, R
2
, R
3
, or R
4
is present in a molecule, said groups R, R
1
, R
2
, R
3
, and R
4
may be the same or different.
The alkoxysilane acetal raw materials are well-known in the art. The normal preparation is by hydrosilation of an unsaturated acetal, CH
2
═CR
3
R
5
CR
3
(OR
2
)
2
, with a hydroalkoxysilane, R
1
x
(R
2
O)
3−x
SiH, in the presence of a catalyst,
where j, R, R
1
, R
2
, and R
3
are as defined above; R
5
is a divalent saturated or unsaturated linear, branched, or cyclic hydrocarbon group of 1 to 10 carbon atoms, optionally containing —O— or —S— linkages; the divalent group R being formed from the group CH
2
═CR
3
R
5
— upon hydrosilation.
The unsaturated acetals are articles of commerce, as are the hydroalkoxysilanes, and the catalysts used for hydrosilation. A particularly preferred hydroalkoxysilane is trimethoxysilane, as prepared by the direct reaction between silicon metal and methanol.
Preferred alkoxysilane acetal raw materials include compounds wherein R is a linear or branched divalent hydrocarbon group of 2 to 4 carbon atoms, R
1
is an alkyl group of 1 to 2 carbon atoms, R
2
is an alkyl group of 1 to 2 carbon atoms or 2 R
2
groups taken together form an R group, and R
3
is a hydrogen atom or an alkyl group of 1 to 2 carbon atoms. Most preferred versions of the alkoxysilane acetal include compounds wherein R is a linear divalent hydrocarbon group of 2 carbon atoms or a branched divalent hydrocarbon group of 3 carbon atoms, R
1
is a methyl group, R
2
is a methyl group or an ethyl group, and R
3
is a hydrogen or a methyl group. Thus, compounds in the most preferred group include the following:
Preferred sulfurating agents will depend on the product desired and may be selected singly or in combination from the group of thiols, di- and higher thiols, hydrogen sulfide, and sulfur, optionally in the presence of hydrogen and an effective reduction catalyst. Sulfur serves as a source of hydrogen sulfide in the presence of hydrogen and an effective reduction catalyst. Dithiols, including 1,2-dimercaptoethane, 1,2-dimercaptopropane, and 1,3-dimercaptopropane are particularly preferred for preparing certain sulfur-containing silane coupling agents which are novel compositions. The ratio between silane and sulfurating agent is not narrowly critical, but preferably is between a slight excess of sulfurating agent to near stoichiometric equivalent.
A suitable reduction catalyst is selected from the group of metal-containing catalysts which are effective for reduction in the presence of sulfur and its compounds. Cobalt polysulfide is a preferred reduction catalyst for the process of the present invention, with a use level of 0.5 to 5 wt-% being preferred, and 1 to 3 wt-% being most preferred.
The process of the invention is preferably conducted in the presence of an acid catalyst, selected from the classes of protic (Bronsted) acids or nonprotic (Lewis) acids. The former is exemplified by para-toluenesulfonic acid and a wide variety of carboxylic and inorganic acids. The latter is exemplified by boron trifluoride, zinc salts, e.g., zinc chloride, and a number of other covalent metall
Hartman Kenneth W.
Reedy James D.
Crompton Corporation
Dawson Robert
Dilworth Michael P.
Zimmer Marc S.
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