Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2001-11-15
2002-08-13
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06433206
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of processes for preparing organomercaptans. More particularly, the present invention describes a process for preparing organomercaptan by the catalyzed hydrogenolysis of a disulfide, trisulfide, and/or polysulfide.
U.S. Pat. No. 6,147,242 describes a process for preparing 3-mercaptopropyl-triethoxysilane by the homolytic cleavage of the corresponding bis-disulfide. The method involves reacting a bis-silylalkylsulfide with an alkali metal and a chlorosilane to provide a silylalkylsulfanylsilane intermediate which is recovered and thereafter hydrolyzed in the presence of refluxing aqueous alcohol to the desired mercaptoalkylsilane. The foregoing method is subject to several disadvantages including its use of a chlorosilane which is expensive, the necessity to filter and dispose of hazardous alkali metal salt, and the need to isolate a silylalkylsulfanylsilane intermediate prior to the hydrolysis step.
Itabashi, CA 54, 2153e (1960), CA, 54, 19466c (1960) and CA, 54, 19466g (1960), describes the reaction of various disulfides with hydrogen over molybdenum (VI) sulfide catalyst at 130°-140° C. and 10.7 MPa hydrogen pressure resulting in the hydrogenolysis of the disulfides at the S—S linkage to provide the corresponding organomercaptans in high yields. The high catalyst loading for the reaction (approximately 5 weight percent) and the high cost of the catalyst both add significantly to the expense of this preparative method. A similar process described by Broadbent et al.,
J. Am. Chem. Soc.,
76, 1519 (1954), provides thiophenol quantitatively by hydrogenolysis of diphenyl disulfide over Re
2
S
7
in 2-methoxyethanol at 165° to 195° C. and 15 MPa hydrogen pressure. At these high temperatures, however, subsequent de-sulfurization exclusively results in the saturated hydrocarbon or aromatic substrate.
In general, precious metal and base metal catalysts have found little application in the selective cleavage of the S—S bond due to the known poisoning effect of the resulting sulfides. In the few cases that have been reported, however, palladium catalysts, which are generally known for their resistance to catalyst poisons, have been the most reactive and have achieved the highest yields. The most striking example of this is the hydrogenolysis of methyl cystine to methyl cysteine in the presence of 25 weight percent of palladium catalyst in aqueous acid at room temperature and atmospheric pressure (Bergmann et. al.
Ber. Dtsch. Chem. Ges.
63,987 (1930)). The necessity to use an unusually high loading of expensive palladium catalyst, however, precludes its use in all but a limited number of research applications.
Patent EP 649,837 discloses a process for the preparation of methyl mercaptan from the corresponding dimethyl disulfide using a transition metal catalyst which requires a sulfidation pretreatment with a hydrogen sulfide/hydrogen mixture (containing 15 mole percent hydrogen sulfide) at an hourly flow rate of 2 liters mixture per gram of catalyst at 400° C. for 4 hours. The selectivity and the yield of the process are reported to be improved when the reaction is conducted in the presence of either water or hydrogen sulfide at a concentration of 0.1 to 15 weight percent with respect to the disulfide.
Other catalyst systems have also been reported that are based on transition metal sulfides since the sulfide phases are believed to be more resistant to poisoning by sulfur-containing molecules (Calais et al.
J of Cat.,
144, 160-174 (1993)). The use of platinum sulfides (Dutch Patent Application No. 6,402,424) for the reduction of diphenyl disulfide to phenyl mercaptan as well as the sulfides of Raney Ni and Raney Co (French Patent Application No. 2,008,331) and Ru, Rh, Pt, Ir, and Pd (German Patent Application No. DE 1,903,968) require relatively high hydrogen pressures, typically in excess of 5-10 MPa.
SUMMARY OF THE INVENTION
In accordance with the present invention, a process is provided for preparing an organomercaptan which comprises reacting a sulfide of the general formula (I)
in which each R
1
is the same or different alkyl group of up to about 6 carbon atoms, aryl group of up to about 10 carbon atoms or alkoxy group of up to about 6 carbon atoms, or at least two of R
1
and the silicon atom to which they are bonded form a ring system having up to about 12 members and containing no ethylenic unsaturation, and optionally containing at least one heteroatom selected from the group consisting of oxygen, sulfur and nitrogen, each R
2
is the same or different divalent hydrocarbon group containing no ethylenic unsaturation and having up to about 20 carbon atoms and m is 0 to about 8, with hydrogen under hydrogenolysis conditions in the presence of a catalytically effective amount of Group VIII metal catalyst and in the presence of a catalyst poisoning inhibiting amount of a catalyst poisoning inhibitory agent selected from the group consisting of water, except where the mercaptan product contains at least one hydrolyzable silane group, alkanol of from 1 to about 6 carbon atoms, hydrogen sulfide and mixtures thereof to provide organomercaptan product of the general formula (II)
(R
1
)
3
—Si—R
2
—SH (II)
in which R
1
and R
2
each has one of the aforestated meanings.
Unlike the catalyst sulfidation pretreatment required by the process described in EP 649,837, supra, the process of this invention does not require presulfiding in order to enhance reactivity or inhibit catalyst poisoning.
Under normal conditions, most base metals and precious metal catalysts are poisoned by the formation of sulfides and particularly by alkyl mercaptans. However, it has been discovered that when hydrogenolysis of sulfide is conducted in the presence of a catalyst poisoning inhibitory agent in accordance with this invention, the poisoning effect of the organomercaptan product can be minimized. As a result, both catalytic activity and selectivity increase substantially and high yields of organomercaptan product, e.g., in excess of 98%, can readily be achieved. The hydrogenolysis reaction herein has also been found to occur at more moderate temperatures and pressures. Low catalyst levels can be utilized and still provide completion in less than two hours with high conversion levels and excellent selectivity.
DESCRIPTION OF PREFERRED EMBODIMENTS
The starting sulfide of the present invention can be chosen from among those of the general formula (I):
In sulfide (I), each R
1
is the same or different alkyl group of up to about 6 carbon atoms and preferably of up to 4 carbon atoms, e.g., methyl, ethyl, propyl or butyl; aryl group of up to about 10 carbon atoms such as phenyl or naphthyl; alkoxy group of up to about 6 carbon atoms, and preferably up to 4 carbon atoms, e.g., methoxy, ethoxy, propoxy, isopropoxy, butoxy, or isobutoxy; or at least two of R
1
and the silicon atom to which they are bonded form a ring system having up to about 12 ring members with no ethylenic unsaturation and optionally containing one or more oxygen, sulfur and/or nitrogen heteroatom members, e.g., the ring system having the structure
each R
2
is a divalent hydrocarbon group containing no ethylenic unsaturation and having up to about 20 carbon atoms, and preferably up to about 12 carbon atoms, e.g., a linear or branched alkylene group such as methylene, ethylene, 1,2-propylene, 1,3-propylene, 2-methyl-1,3-propylene, 3 methyl-1,3-propylene, 3,3-dimethyl-1,3-propylene, ethylidene or isopropylidene, a cycloalkylene group such as cyclohexylene or cycloheptylene, an arylene group such as phenylene, tolylene, xylylene or naphthylene, and m is 0 to 8 and preferably 0 to 4.
Reaction of sulfide (1) with hydrogen to provide organomercaptan product (II) in accordance with the invention can be thought of as proceeding in accordance with the reaction:
Many examples of sulfide (1) that can be used for preparing organomercaptans in accordance with the present invention and methods for their manufacture are known in the art and include those disclosed in, e.g., U.
Gedon Steven C.
Hale Melinda
Crompton Corporation
Dilworth Michael P.
Shaver Paul F.
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