Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfur containing
Reexamination Certificate
2002-08-28
2003-12-23
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfur containing
C549S466000, C548S243000, C568S067000
Reexamination Certificate
active
06667421
ABSTRACT:
BACKGROUND OF THE INVENTION
Aryl thiols are useful products and intermediates for the preparation of chemical derivatives useful in agricultural, pharmaceutical, photographic, coloration, rubber, plastics, metal finishing, corrosion protection, and other fields. One of the most important methods for the production of aryl thiols is by the reduction of the more readily produced aryl sulfonyl chlorides.
Many reduction processes have been employed, such as the use of zinc and acetic or sulfuric acid, or zinc plus red phosphorus and iodine. These processes lead to the generation of large amounts of harmful metal salts to be disposed of. Sulfonyl chlorides can also be reduced directly with pressurized hydrogen using certain metal sulfide catalysts such as cobalt, nickel, tungsten, molybdenum or iron sulfides. In these processes large amounts of catalysts, as much as 5% to 15% by weight relative to the reactant, are required.
Processes have also been proposed for the reduction of aryl sulfonyl chlorides to the corresponding thiols using pressurized hydrogen where the catalyst is a noble metal such as platinum or palladium. For example, U.S. Pat. No. 4,209,469 discloses a process for the production of an aryl thiol by hydrogenating the aryl sulfonyl chloride in a protic or aprotic solvent in the presence of a platinum catalyst at a temperature of 100 to 180° C. and a pressure of 2 to 140 bar (200-14000 kPa). A highly acidic byproduct, hydrogen chloride, is formed during the reaction. After the hydrogenation is complete, 2.5 moles of sodium hydroxide are added per mole of sulfonyl chloride to neutralize the HCl and convert the thiol to the sodium salt. However, carrying out the reduction step under strongly acidic conditions and high temperatures causes unacceptable corrosion of even expensive nickel-based alloys.
A process intended to overcome this corrosion problem is disclosed in “Reduction of Sulfonyl Chlorides to Thiols”, V. L. Mylroie and J. K. Doles,
Catalysis of Organic Reactions,
Blackburn ed., Marcel Dekker, Inc., NY, 1990. They used a palladium on carbon catalyst for the hydrogen reduction step in the presence of a solvent such as tetrahydrofuran, along with one of several alkaline materials to simultaneously neutralize the hydrogen chloride byproduct as it forms and minimize corrosion. A strong base tested, N,N-dimethylbenzeneamine, was reported to perform poorly and little thiol was produced. A strongly basic Amberlite® resin tested was reported to produce disulfides as well. This lowered the yield of thiol and/or required that a second process using Raney® cobalt catalyst be used to convert disulfides to the thiols. Nevertheless, they obtained relatively good yields of thiol when using N,N-dimethylacetamide as the base. They concluded from these experiments that it was necessary to use a mild base such as N,N-dimethylacetamide rather than a strong base for the neutralization of hydrogen chloride during the hydrogenation step.
However, a mild base such as N,N-dimethylacetamide does not adequately prevent corrosion from a very strong acid such as hydrogen chloride. In tests of the above process, significant corrosion was observed using N,N-dimethylacetamide for neutralization of the hydrogen chloride, even when an expensive nickel-based alloy such as Hastelloy® C was employed. Another disadvantage of the above process is that a large amount of N,N-dimethylacetamide is required for neutralization, and the recovery of the N,N-dimethylacetamide from the product solution is difficult. There is a need for a process to convert aryl sulfonyl chlorides to aryl thiols using a hydrogen reduction process with a noble metal catalyst, but without these disadvantages.
SUMMARY OF THE INVENTION
This invention relates to a process for the production of an aryl thiol, which comprises hydrogenating an aryl sulfonyl chloride with hydrogen in a solvent in the presence of (i) a catalyst comprising palladium and (ii) an effective amount of a base whose conjugate acid has a pK
a
of about 2 or greater, wherein the base is selected from the group consisting of ionic bases soluble in water and tertiary amines soluble in the solvent, the tertiary amines not having a methyl group attached to the amine nitrogen. Preferably the palladium catalyst further comprises from about 5% to about 20% by weight of tin relative to the palladium, more preferably about 8% to about 12%.
DETAILS OF THE INVENTION
The process of the present invention can be illustrated by the following equation, wherein Ar represents an unsubstituted or substituted aryl derivative and —SO
2
Cl is bonded directly to a carbon atom in an aromatic ring system moiety of the aryl group:
The aryl group of the aryl sulfonyl chlorides useful in the present invention includes unsubstituted and substituted, mononuclear and polynuclear, aromatic, carbocyclic and heterocyclic, ring systems. As used herein, the term “aryl”, used either alone or in compound words such as “aryl sulfonyl”, “alkylaryl” or “aryloxy” denotes a radical derived from an aromatic ring system. The term “aromatic ring system” denotes fully unsaturated carbocycles and heterocycles in which the polycyclic ring system is aromatic (where aromatic indicates that the Hückel rule is satisfied for the ring system). The term “aromatic carbocyclic ring system” includes fully aromatic carbocycles and carbocycles in which at least one ring of a polycyclic ring system is aromatic (where aromatic indicates that the Hückel rule is satisfied). The term “aromatic heterocyclic ring system” include fully aromatic heterocycles and heterocycles in which at least one ring of a polycyclic ring system is aromatic (where aromatic indicates that the Hückel rule is satisfied). Examples of suitable aryl groups are groups containing aromatic and heteroaromatic five and six-membered rings such as benzene, thiophene, pyridine, pyridazine, pyrazine, pyrimidine, triazine, triazole, pyrrole, imidazole, pyrazole, furan, oxazole, isoxazole, thiazole, thiadiazole, oxathiazole and polycyclic rings comprising combinations of the mononuclear aromatic structures, such as naphthalene, benzo[b]thiophene, benzofuran, quinoline, isoquinoline, quinoxaline, indole, isoindole, naphthyridine, indazole, benzopyrrole, benzotriazole, benzimidazole, benzoxazole, benzothiadiazole, and benzisothiazole. Additionally, polynuclear structures may be included, where one of the rings is aromatic and the other saturated. Examples include such compounds as 1,2,3,4-tetrahydronapthalene, dihydroindole, dihydroisoindole and dihydrobenzopyran. An enormous variety of aryl ring systems suitable for the process of the present invention and methods for preparation of these aryl ring systems are well known in the art. For extensive reviews see:
Comprehensive Organic Chemistry,
D. Barton and W. D. Ollis eds., Pergamon Press, NY, 1979, Volumes 1-6;
Comprehensive Heterocyclic Chemistry,
A. R. Katritzky and C. W. Rees eds., Pergamon Press, NY, 1984, Volumes 1-8;
Comprehensive Heterocyclic Chemistry II,
A. R. Katritzky, C. W. Rees and E. F. V. Scriven eds., Pergamon Press, NY, 1996, Volumes 1A-11; and the references cited therein.
Suitable substituents on the aryl group are those moieties that are not reducible under the palladium-catalyzed hydrogenation reaction conditions, which are understood by one skilled in the art. For a review of the susceptibility of organic groups to hydrogenation, see P. N. Rylander,
Catalytic Hydrogenation in Organic Syntheses,
Academic Press, NY, 1979 and M. Freifelder,
Catalytic Hydrogenation in Organic Synthesis Procedures and Commentary,
John Wiley & Sons, NY, 1978. For example, substituent groups resistant to these hydrogenation reaction conditions include such halogens as fluorine and chlorine; straight chain, branched and cyclicalkyl groups; straight chain and branched alkoxy groups; aryloxy groups such as phenoxy; carboxylic acid groups; cyano groups; and aryl groups and alkylaryl groups such as 4-methylbenzyl or 4-ethylpyridinyl.
The term “alkyl”, used either alone or in compound words such as
E. I. du Pont de Nemours and Company
Vollano Jean F.
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