Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
1999-04-27
2001-02-27
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06194595
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the preparation of organosilicon oligosulfane mixtures containing a high proportion of disulfanes.
BACKGROUND OF THE INVENTION
Processes for the preparation of oligosulfanes have long been known. Various known systems are described below.
DE-PS 2141159 (U.S. Pat. No. 3,842,111) describes a process for the preparation of bis-(alkoxysilylalkyl) oligosulfanes from the corresponding halogen alkylalkoxysilane and alkali metal oligosulfides, preferably in alcoholic solution. However, only mixtures of sulfanes with different chain lengths are produced. These patent documents are entirely incorporated herein by reference.
In a process described in DE-PS 2712866 (U.S. Pat. No. 4,129,585), an alkali metal alcoholate is reacted with a halogen alkylalkoxysilane, metal or ammonium hydrogen sulfide, and sulfur in the presence of an organic solvent. However, the preparation of the alkali metal alcoholate solution is very time-consuming, which makes industrial-scale use of this process problematic. These patent documents also are entirely incorporated herein by reference.
U.S. Pat. No. 5,466,848 discloses a process in which hydrogen sulfide is reacted with an alkoxide, and the reaction product is treated with elemental sulfur, and then with a halogen alkylalkoxysilane, to give the desired organosilicon polysulfane. Likewise, the process according to U.S. Pat. No. 5,489,701 involves working with alkoxides and hydrogen sulfide, a compound which is known to be very unpleasant to handle. JP-OS 7-228588 describes the reaction of anhydrous sodium sulfide and sulfur with halogen alkoxysilanes. This procedure gives a mixture of polysulfanes, as experiments have shown. These three patent documents also are entirely incorporated herein by reference.
Organosilicon polysulfanes, and especially bis(triethoxysilylpropyl)tetrasulfane, are used in combination with highly active silicic acid fillers in the manufacture of vulcanized rubber articles, especially tires.
The advantageous use of high purity disulfanes in terms of both the processing of the material, and of the resulting properties of the vulcanizates, is set out in EP-A 0 732 362 (U.S. Pat. No. 5,580,919) and by Panzer (L. Panzer, American Chem. Soc., Rubber Div. Meeting, 1997). These documents also are entirely incorporated herein by reference.
The Na
2
S
x
required for disulfane preparation can be obtained by reacting sulfur and sodium in molten form, as described in DE-PS 38 03 243, which document is entirely incorporated herein by reference. It should be noted, however, that the melting point of the polysulfide is inversely proportional to its sulfur content. Thus, for example, the Na
2
S
2
required to produce oligosulfane mixtures of high disulfane content has a melting point of 474° C. The only suitable reactor material for such a high temperature is graphite. The difficulties of obtaining reactor components in the necessary dimensions makes industrial application of this process impractical.
DESCRIPTION OF THE INVENTION
The object of the invention is to provide a process for the preparation of organosilicon disulfanes, which process uses a Na
2
S
x
product prepared from elemental sodium and sulfur.
The invention provides a process for the preparation of organosilicon disulfanes of the general formula:
Z-Alk-S
x
-Alk-Z (1)
in which the Z components, which may be the same or different, represent the groupings:
in which each R
1
in the formula, which may be the same as or different from the other R
1
groups in the formula, is a linear or branched alkyl group having 1-6 carbon atoms, a cycloalkyl radical having 5-8 carbon atoms, a benzyl radical, or a phenyl radical optionally substituted by methyl, ethyl or chlorine, and wherein each R
2
in the formula, which may be the same as or different from the other R
2
groups in the fonnula, is an alkoxy group with a linear or branched carbon chain having 1-6 carbon atoms, a cycloalkoxy group having 5-8 carbon atoms, a phenoxy group, or a benzyloxy group, and
wherein Alk, each of which may be the same or different, is preferably a divalent, saturated linear or branched hydrocarbon radical having 1-10 carbon atoms, preferably methylene, as well as preferably ethylene, i-propylene, n-propylene, i-butylene or n-butylene, also n-pentylene, 2-methylbutylene, 3-methylbutylcne, n-pentylene, 1,3-dimethylpropylene and 2,3-dimethylpropylene, with n-propylene being particularly suitable, or the group
where n=1-4 (wherein each “n” may be the same or different), and wherein x=1.5 to 3.0.
The process includes a two-step reaction, in which:
1. suspensions of finely divided sodium are reacted with sulfur in amounts corresponding to the stoichiometry of the Na
2
S
x
product to be produced (e.g., in approximately equimolar amounts for a disulfane product), in an inert organic solvent at temperatures above 98° C., and optionally washed and dried (to thereby form an Na
2
S
x
product), and then
2. the Na
2
S
x
product is partially or completely dissolved or suspended in an inert organic solvent, and this solution or suspension is reacted with an organosilicon compound of general formula (II):
Z-Alk-Hal (II),
in which Z and Alk are as defined above and Hal is a chlorine or bromine atom. After this second reaction step, the desired oligosulfane mixture is isolated.
The proportion of disulfane is preferably 55 to 100 wt. %, and more preferably 55 to 75 wt. %.
The desired oligosulfane mixture may be isolated by any suitable procedure known in the art. For example, the precipitate of inorganic halide can be filtered off, and the solvent can be separated off by distillation or evaporation.
Suitable solvents for step 1 are the known aliphatic hydrocarbons with a carbon chain length of 7 to 12 carbon atoms, and especially 7 to 9 carbon atoms; aromatic hydrocarbons, such as toluene, xylene, ethylbenzene, mesitylene, naphthalene, and tetrahydronaphthalene; or high-boiling ethers, such as ethylene glycol diethyl ether, dibutyl ether, dipentyl ether, and anisole; or mixtures of these solvents. Common features of these solvents are that they preferably boil above 98° C. and at least partially dissolve sulfur.
Advantageously, the sodium is present in the form of small molten beads, so that no passivation of the surfaces occurs due to the reactions with sulfur.
It is possible, however, to use solvents with a lower boiling point if the reaction is carried out under a pressure elevated above atmospheric pressure. The latter variant (i.e., using elevated pressure) is naturally also applicable to use with higher-boiling compounds.
In a preferred embodiment, a suspension of finely divided sodium, in the same solvent as the suspension of sulfur, is added dropwise to the latter.
However, it is also possible to meter finely divided sulfur into a sodium dispersion. In any case, it must be noted that the reaction of these elements is strongly exothermic, although this reaction is readily controllable by those skilled in the art.
The reaction takes place at temperatures of greater than 98° C. to 250° C., and preferably at 100 to 150° C.
Another advantageous embodiment of the invention includes a process wherein sodium and sulfur in the form of suspensions in the same solvents are introduced simultaneously into a cylindrical reactor at spatially separated points, the sulfur being added outside the sodium/sulfur reaction zone and in the agitated flow, as far as possible upstream of the sodium addition point.
The starting substances of formula (II) for the second step of the process can be prepared by the skilled artisan through known processes and are generally available.
Organic solvents which can be used for the second reaction step of the process according to the invention are basically any polar substances in which the Na
2
S
x
is at least partially soluble and which do not react with the organosilicon compound of formula (II). A linear or branched alcohol having 1-5 carbon atoms, e.g., methyl, ethyl, propyl, butyl or pentyl alcohol, is preferably used
Michel Rudolf
Munzenberg Jorg
Degussa-Huls Aktiengesellschaft
Shaver Paul F.
Smith , Gambrell & Russell, LLP
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