Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing organic compound
Reexamination Certificate
2000-12-14
2002-08-13
Dentz, Bernard (Department: 1625)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing organic compound
C205S444000, C546S173000, C546S339000
Reexamination Certificate
active
06432294
ABSTRACT:
TECHNICAL FIELD
This invention relates to electrochemical oxidation of dihydrocarbyl disulfides in the presence of arenes, and to production of hydrocarbylthioarenes. This invention also relates to certain novel adducts and to the formation of these adducts.
BACKGROUND
Electrophilic thiation is typically accomplished by the use of a sulfenyl chloride, disulfide, or thiosulfonate, with a Lewis or Bronsted acid. Silica gel has been used to catalyze the reactions of sulfenyl chlorides with arenes, while zeolites have been used for catalysis of hydrocarbyl disulfide reactions with phenols.
A method has been reported for thiation using electrochemically generated sulfenium ion in dichloromethane, with low yields; see Do et al.,
Tetrahedron Lett
., 1998, 4657. The sulfur electrophile produced could effect substitution with highly activated phenols in 26-77% yield, but with the less activated anisoles the yields were only 11-35%.
Glass and Jouikov, in commonly-owned, copending application Ser. No. 09/302,908, filed on Apr. 30, 1999, now U.S. Pat. No. 6,207,838, describe electrooxidation of organic disulfides where thiation of arenes is accomplished in liquid SO
2
. Although ahighly effective process, it does involve use of low temperatures and/or elevated pressures to keep the SO
2
in the liquid state during the process.
In both of the foregoing electrochemical methods, an electrophilic thiating agent is prepared electrochemically and then, in a subsequent step, it is added to the arene substrate in order to produce an organothiated arene. Such procedure requires that the electrophilic sulfur species persist until added to the arene. Although the Glass and Jouikov method gives higher yields than the Do, et al. method, the need for using low temperatures or high pressures to keep SO
2
in the liquid state is a shortcoming of that process.
It would be a considerable advantage if a way could be found for electrochemical organothiation to be achieved that avoids the need for low temperature and/or pressurized operation.
BRIEF SUMMARY OF THE INVENTION
This invention provides efficacious technology enabling production of organothiated arenes in good yield without the need for low temperature or high pressure. This invention provides for electrolytic oxidation of an organic disulfide (R
2
S
2
) in the presence of an organothiatable arene substrate in a liquid phase mixture. Organic electrochemical solvents in combination with a supporting electrolyte are used as the medium for the electrolytic oxidation, and thus the low temperature and/or elevated pressure conditions required for liquid SO
2
are avoided. By making the substrate one of the initial reactants during the electrolysis step, the problem of the instability of the electrophilic sulfur species formed by the anodic oxidation of the organic disulfide is averted.
Accordingly one of the embodiments of this invention is a process which comprises subjecting an organic disulfide in which the organic groups are primary or secondary organic groups to anodic oxidation in a solution formed from (i) an organothiatable arene containing only aromatic unsaturation, (ii) an organic electrochemical solvent, (iii) a dissolved supporting electrolyte, such that an organothiated arene is formed.
For some aromatic compounds, even controlled potential electrolysis results in overoxidation of the organothiated arene substrate and this can result in production of excessive amounts of unwanted by-products. Furthermore, the acid produced in the reaction can also result in production of excessive amounts of unwanted by-products. For example, when subjected to controlled anodic oxidation, arenes having a cycloolefinic moiety in the molecule such as acenaphthylene polymerize and form copious amounts of insoluble polymeric precipitates. However, pursuant to this invention, the problem of overoxidation and sensitivity to acid can be minimized, if not eliminated, by conducting the electrochemical reaction in the additional presence of an organic nucleophilic base, such as pyridine, with the resultant formation of novel adducts which are more resistant to oxidation, and which are highly useful as they can be subjected to eliminative aromatization in a subsequent reduction step, resulting in good yields of the desired thiated aromatic compounds. Thus, in the case of acenaphthylene, the inclusion of pyridine in the electrochemical reaction mixture overcame the polymer formation problem and resulted in the formation of an adduct which, upon electrochemical eliminative aromatization, gave 1-methylthioacenaphthylene in a yield of 76%.
Accordingly another of the embodiments of this invention is a process which comprises subjecting a dihydrocarbyl disulfide in which the organic groups are primary or secondary organic groups to anodic oxidation in a solution formed from (i) an organothiatable arene, (ii) an organic electrochemical solvent, (iii) a dissolved supporting electrolyte, and (iv) an organic nucleophilic base such that an adduct is formed in which the aromatic ring of a mononuclear arene or an aromatic ring of a polynuclear arene is dearomatized and is substituted on the dearomatized ring by an organothio group and a cationic organic base.
Such adducts are new compounds having good stability particularly towards oxidation. Thus a further embodiment of this invention is an adduct in which a cycloaliphatic ring is substituted by an organothio group, and by a cationic organic base, and wherein, optionally but preferably, the cycloaliphatic ring is attached, preferably fused, to at least one aromatic ring. The adducts of this invention can be recovered from the reaction mixture by conventional means for use, for example, as chemical intermediates. To illustrate, the adducts can be subjected to eliminative aromatization so as to form an organothiated arene.
Still another embodiment of this invention is a process which comprises:
A) subjecting an organic disulfide in which the organic groups are primary or secondary organic groups to anodic oxidation in a solution formed from (i) an organothiatable arene susceptible to overoxidation, (ii) an organic electrochemical solvent, (iii) a dissolved supporting electrolyte, and (iv) an organic nucleophilic base such that an adduct is formed in which the aromatic ring of a mononuclear arene or an aromatic ring of a polynuclear arene is dearomatized and is substituted on the dearomatized ring by an organothio group and a cationic organic base; and
B) subjecting said adduct to eliminative aromatization such that an organothiated arene is formed.
Yet another embodiment of this invention is a process which comprises subjecting an organic disulfide in which the organic groups are primary or secondary organic groups to anodic oxidation:
A) in a solution formed from (i) an organothiatable arene having an oxidation potential at least about 150 mV higher than that of the organo disulfide, and (ii) a liquid organic dipolar aprotic solvent, such that organothiation occurs and an organothiated arene is produced; or
B) in a solution formed from (i) an organothiatable arene having an oxidation potential that is lower, equal to, or less than 100 mV higher than that of the organo disulfide, (ii) a liquid organic dipolar aprotic solvent, and (iii) a nucleophilic organic base, such that an adduct is formed in which (a) an organothio group and (b) a molecule of the organic base are both bonded to a cycloaliphatic moiety derived from the arene; and
subjecting said adduct to eliminative aromatization such that the organic base is removed from the adduct and the cycloaliphatic ring is aromatized whereby an organothiated arene is formed.
For example, in acetonitrile, dimethyl disulfide shows an irreversible first oxidation peak at 1.05 V vs Ag/O.1M AgNO
3
in acetonitrile reference electrode using the technique of cyclic voltimetry. The oxidation peak of anthracene is about 400 mV more positive than that for dimethyl disulfide. Consequently, pursuant to this invention, dimethyl disulfide can be selectively oxidized electrolytically in the presence
Bojkova Nina V.
Glass Richard S.
Jouikov Viatcheslav V.
Dentz Bernard
Spielman, Jr. E. E.
The University of Arizona
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