Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfur containing
Reexamination Certificate
2000-03-03
2001-06-05
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfur containing
C568S021000
Reexamination Certificate
active
06242652
ABSTRACT:
The present invention relates to a process for selectively producing organic trisulfides.
BACKGROUND OF THE INVENTION
Organic polysulfides, especially organic trisulfides, are useful for many purposes such as additives for elastomers, antioxidants for lubricating oils, intermediates for the production of organic chemicals, insecticides, and germicides, and additives for diesel fuels to improve cetane number and ignition qualities. Organic polysulfides are also useful in the compounding of high pressure lubricants and in the acceleration of rubber treating processes.
Organic polysulfides can be produced by reacting mercaptans with elemental sulfur in the presence of a catalyst. The reaction can generally be depicted as follows:
where R, R
1
and R
2
are alkyl radicals, generally containing 1 to 20 carbon atoms, which can be the same or different, x is an integer from 2 to 1 0, and x is the average number of sulfur atoms per polysulfide molecule in the product.
The product of the above reaction typically comprises a distribution of individual organic polysulfide compositions, each containing a different number of sulfur atoms. In many commercial applications, especially for use in high pressure lubricants, organic trisulfides exhibit more desirable properties than other organic polysulfides. For example, organic polysulfides containing more than three sulfur atoms exhibit high copper-strip corrosivity (ASTM Copper Strip Corrosion Test D-130-56), rendering them unsatisfactory for many commercial applications. In addition, organic disulfides can be undesirable because they have a high flash point and exhibit poor lubrication properties.
If an organic polysulfide product contains a high quantity of organic polysulfides having more or less than three sulfur atoms, costly separation processes and equipment are necessary to remove undesirable polysulfides and recover a more pure organic trisulfide product that is suitable for commercial purposes. Therefore, a reaction product having a distribution of organic polysulfides which maximizes the amount of organic trisulfides while minimizing the amount of other organic polysulfides is desired.
Several processes exist for the preparation of high purity organic trisulfides; however, most existing processes require materials, conditions, and/or steps which make commercial implementation uneconomical. For example, the trisulfide selective process taught in U.S. Pat. No. 5,442,123 requires expensive process equipment, an expensive catalyst, and low reaction temperatures, which increase the required reaction time. Thus, it is desirable to develop a process for selectively producing organic trisulfides which minimizes equipment, labor, and time and employs a relatively inexpensive catalyst.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for selectively producing organic trisulfides.
Another object of the inventive process is to provide a reaction product having a higher concentration of organic trisulfides than products from conventional processes for making organic polysulfides.
A further object of the inventive process is to provide a reaction product having a lower concentration of organic disulfides than products from conventional processes for making organic polysulfides.
A still further object of the inventive process is to provide a reaction product having a lower concentration of organic polysulfides containing more than three sulfur atoms than products from conventional processes for making organic polysulfides.
An even further object of the present invention is to eliminate the need for expensive processes and equipment necessary to separate organic trisulfides from other organic polysulfides.
A still further object of the inventive process is to eliminate costly materials, conditions, and/or steps which are required by conventional methods of selectively producing organic trisulfides.
Other objects and advantages of the present invention will become more apparent as the invention is more fully disclosed hereinbelow.
According to an embodiment of the present invention, a process for the selective production of organic trisulfides is provided. The process comprises contacting, in a reaction vessel, a mercaptan, a sulfur compound, and a catalyst under reaction conditions sufficient to produce an organic polysulfide product and hydrogen sulfide. During the reaction, the concentration of hydrogen sulfide in the liquid phase within the reaction vessel is increased to a desired concentration. After the desired hydrogen sulfide concentration is reached, the hydrogen sulfide produced by the reaction is trapped in the reaction vessel until the organic polysulfide product within the reaction vessel has a desired distribution of organic polysulfides.
DETAILED DESCRIPTION OF THE INVENTION
It has been discovered that the weight ratio of organic trisulfides to organic disulfides in a reaction product produced by reacting a mercaptan and a sulfur compound in the presence of a catalyst can be increased by controlling the concentration of hydrogen sulfide in the liquid reaction solution during specific reaction time periods.
As used herein, the term “liquid reaction solution” means a mixture of liquid phase compounds present in a reaction vessel. The composition of the liquid reaction solution of the present invention changes as the reaction progresses, but during at least a portion of the reaction period the liquid reaction solution can comprise unreacted mercaptan, unreacted sulfur compound, the catalyst, organic polysulfides, and hydrogen sulfide.
The mercaptan suitable for use as a reactant in the process of the present invention can be any mercaptan having the formula of RSH, wherein R is a hydrocarbyl radical having 1 to about 30, preferably about 1 to about 20, and most preferably 2 to 15 carbon atoms. The hydrocarbyl radical can be linear or branched and can be alkyl, aryl, cycloalkyl, alkylaryl, aralkyl, alkenyl radicals, or combinations of two or more thereof. Preferably the hydrocarbyl radical is an alkyl radical. Presently preferred mercaptans are tertiary mercaptans. The presently most preferred mercaptan is t-butyl mercaptan.
The sulfur compound suitable for use as a reactant in the process of the present invention can be any sulfur containing compound capable of reacting with a mercaptan to produce an organic trisulfide and hydrogen sulfide. Preferably the sulfur compound is elemental sulfur.
The amount of sulfur compound contacted with the mercaptan depends on the desired sulfur content of the organic polysulfide product. For an average sulfur content of q sulfurs per polysulfide molecule, (q-1) moles of sulfur must be added per 2 moles of mercaptan and 1 mole of hydrogen sulfide will be produced per 2 moles of mercaptans reacted. It is, however, preferred that about 0.5 to about 10, preferably about 1.0 to about 5, and most preferably 1.0 to 2.0 moles of mercaptan per mole of sulfur is used.
The catalyst suitable for use in the process of the present invention can be any catalyst capable of catalyzing the reaction of a mercaptan and a sulfur compound to form hydrogen sulfide and an organic trisulfide. The presently preferred catalyst comprises a basic catalyst which can be an inorganic base, an organic base, or combinations of two or more thereof. Suitable organic bases include, but are not limited to tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetramethylammonium bisulfide, tetraethylammonium bisulfide, trimethylamine, triethylamine, n-butylamine and combinations of two or more thereof. Suitable inorganic bases include, but are not limited to, lithium hydroxide, sodium hydroxide, sodium bisulfide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium bicarbonate, sodium carbonate, sodium oxide, sodium sulfide, magnesium oxide, calcium oxide, calcium carbonate, sodium phenoxide, barium phenoxide, calcium phenoxide, R
1
ONa, R
1
SNa, and combinations of any two or more thereof; where R
1
is a C
1
-C
18
alkyl radical, or combinations of
Kelly Kameron D.
Phillips Petroleum Company
Stewart Charles W.
Vollano Jean F.
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