Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2000-06-28
2002-07-16
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C548S101000, C546S002000, C544S064000, C544S225000
Reexamination Certificate
active
06420581
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention involves the preparation of zinc hexasulfide amine complexes.
2. Prior Art
Complexes of zinc hexasulfide with an amine are described in an article in the publication, “Direct Approaches to Zinc Polychalcogenide Chemistry: ZnS
6
(N-MeIm)
2
and ZnSe
4
(N-MeIm)
2
” by Dev, Ramli, Rauchfuss and Stern, JACS 112, 6385 (1990). The article describes the preparation and properties of the complexes, and suggests that they are “relevant to the action of zinc catalysts for the addition of polysulfur radicals to polyolefins in the rubber vulcanization process.”
It is known to make zinc hexasulfide amine complexes (as shown in JACS 112, 6385) by reacting zinc powder, sulfur and a molar excess of the appropriate amine at an elevated temperature; then cooling the reaction product to room temperature and diluting with ethanol. The product appears, on cooling, as a yellow powder which is recovered by filtration. While the zinc hexasulfide amine complexes can be made by this general process, it is also known to produce one complex from another by amine substitution, whereby the desired amine is reacted with a completed complex, displacing the amine from the complex and substituting the desired amine thereon.
In the article “Donor Solvent Mediated Reactions of Elemental Zinc and Sulfur, sans Explosion”, Verma et al, Inorganic Chemistry, 1995, pages 3072-3078, there is a teaching of a reaction of zinc dust, sulfur and N-methylimidazole (Melm) at 90° C. for a few hours. The reaction mixture is diluted with a nonpolar solvent which leads to precipitation of yellow microcrystals of ZnS
6
-(Melm)
2
. In the experimental section of the article it is mentioned that the zinc used was −325 mesh, which would be less than 45 microns.
It has been found that zinc hexasulfide amine complexes, as made by the process of the present invention and included in effective amounts in vulcanizable rubber, give compositions which vulcanize much faster, more quickly than the formulations previously in use. Specifically, the presence of zinc hexasulfide amine complexes in an amount of from 0.1 to 10 parts by weight per 100 parts by weight of vulcanizable rubber, proves to be effective in producing vulcanizates with fast cure rates and superior physical properties.
SUMMARY OF THE INVENTION
In one embodiment the present invention is a process for the manufacture of zinc hexasulfide amine complexes comprising reacting zinc, sulfur and a molar excess of amine at an elevated temperature to obtain a reaction mixture comprising zinc hexasulfide amine complexes and excess amine. Most of the excess amine may be separated from solid zinc hexasulfide amine complexes in the reaction mixture by techniques such as decantation, filtering and/or siphoning. A first solvent is added to the reactants or to the reaction mixture in which the zinc hexasulfide amine complexes are largely not soluble in an amount sufficient to obtain a slurry of the reaction mixture in the first solvent suitable for a subsequent separation process in which zinc hexasulfide amine complexes are to be recovered. The zinc hexasulfide amine complexes product is recovered as a solid in the subsequent separation process.
In a second embodiment the present invention is a process for the manufacture of zinc hexasulfide amine complexes comprising reacting zinc, which is at least about 99.5% pure with a particle size −100 mesh, with sulfur and a molar excess of amine at an elevated temperature. A reaction mixture is obtained comprising zinc hexasulfide amine complexes and excess amine. Most of the excess amine may be separated from solid zinc hexasulfide amine complexes in the reaction mixture by techniques such as decantation, filtering and/or siphoning. A solvent is added to the remaining reaction mixture in which the zinc hexasulfide amine complexes are not soluble. The zinc hexasulfide amine complexes product is recovered by filtering zinc hexasulfide amine complexes as solids from the reaction mixture and drying the solids to obtain the product.
Other embodiments of the present invention are based on details including reaction conditions, reactant and solvent compositions and process details, all of which are hereinafter disclosed in the following discussion of each of these facets of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The reaction of the process of the invention is most effectively conducted at a temperature of from about 50° C. to about 125° C. for about 0.5 hours to about 10 hours.
Complexes of zinc hexasulfide and an amine that are effective in the compositions of the invention include zinc hexasulfide which has been complexed with an amine of from 3 to 24 carbon atoms. Preferred amines include tertiary amines and tertiary diamines, or mixtures thereof. Among these preferred amines are N,N,N′,N′-tetramethylethylenediamine (TMEDA), 1,1,3,3-tetramethylguanidine, 1-Butylimidazole, 1,2-Dipiperidinoethane, 1,2-Dimorpholinoethane, 1,2-Di-(N-Methylpiperazino) ethane, N-Methylimidazole, 1-Benzyl-2-methylimidazole, 1,2-Dimethylimidazole, N-3-Aminopropylimidazole, 1-Vinylimidazole, 1-Allylimidazole, N-Cyclohexyl-N′,N′,N″,N″-tetramethylguanidine and 4-Dimethylaminopyridine, or mixtures thereof.
The preferred amine is N,N,N′, N′-tetramethylethylenediamine, and particularly preferred to be at least about 85% N,N,N′,N′-tetramethylethylenediamine and less than about 2 wt. % water.
There should be a sufficient amount of first solvent added to the reactants or reaction mixture to reduce the amount of amine required in the process to be a little or moderately in excess of the stoichiometric requirement for an effective reaction as opposed to a large excess. A preferred amount of added first solvent will reduce the amount of amine required from about 2 to about 6 times the stochiometric amount.
It would be advantageous for most of the excess amine to be separated as a supernatant from solid zinc hexasulfide amine complexes in the reaction mixture prior to addition of the first solvent by a technique such as decantation, filtering and/or siphoning. When most of the excess amine is separated from solid zinc hexasulfide amine complexes in the reaction mixture the product may be washed with the first solvent to remove excess amine and impurities.
The zinc hexasulfide amine complexes may be separated from the reaction mixture as a cake of solids, and the cake washed to minimize color and/or odor from zinc hexasulfide amine complexes product. The cake may be washed with an aqueous solution of a caustic or hypochlorite.
The amine may not be miscible with the first solvent. In that case, the reaction mixture may be filtered and the product washed with the first solvent. The filtrate would form two liquid phases comprising a first solvent phase and an amine phase, the first solvent and amine being recycled and reused in the process.
The first solvent may comprise saturated hydrocarbons, aromatic hydrocarbons or alcohols, preferably included in the group of hexanes, heptanes, toluenes, xylenes, methanol, ethanol and propanol.
The solid zinc hexasulfide amine complexes may be purified by being dissolved in a second solvent in which they are soluble, followed by separating the resulting solution from insolubles and precipitating the complexes by adding first solvent to the solution. The second solvent could comprise chloroform, methylene chloride or N-methyl-2-pyrrolidone (NMP).
It was surprisingly discovered that when at least about 99.5% pure zinc was used in the reaction of the invention, preferably with a particle size of −100 mesh (all particles that are less than 150 microns will fall through a 100 mesh screen), the amount of amine (TMEDA) that can be removed by decantation, filtering and/or siphoning following the reaction is significantly more than with a less pure zinc of a particle size of less than 10 microns. Even more surprising was the finding that the product had properties similar to the recrystallized product prod
Lodaya Jayant S.
Maender Otto W.
Mitchem Paul M.
Flexsys America L.P.
Morris Louis A.
Nazario-Gonzalez Porfirio
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