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Exchange and redox reactions of diaryl sulfides with aromatic hydrocarbons
TetraIwdron Letters No.30, pp. 2629-2632,
1970.
MCHAWGE AND REXXJX RFlAClJIONSOFDIABYL
Perganlon Press. Printed in Great Britain.
SULFIDES WITH AROMATICHYDRCXXRBONS
Chung Hwa Han and William E. McSwen Departmentof Chemistry,Universityof Massachusetts,Amherst, Massachusetts 01002 (Receivedin USA 24 April 1970;
receivedin UK for publication 29 May 1970)
When an aromatichydrocarbonis caused to react with a diary1 sulfide in the presence of aluminum chloride,a complex mixture of productsresults. For example,the reactionof diphenyl sulfide with z-xylene has been found to produce phenyl 3,4-dimethylphenyl sulfide (40.3$), phenyl 2,3_dimethylphenyl sulfide (7.3$),2,3-dimethylphenyl 3,4-dimethylphenyl sulfide (3.0%) bis-(2,3_dimethylphenyl) sulfide (5.2$),bis-(j,k-dimethylphenyl) sulfide (ll.l$),benzene (57.5$),a diphenyl-3,4dimethylphenylsulfonium salt (isolatedas the iodide in 5.5% yield), and, after exposure of the reactionmixture to water, hydrolysisproducts of triarylsulfonium salts (0.304 of 3,4-dimethylphenol and
O.@$
of 2,3-dimethylphenol).Cbtiously,the exchange
products (amountingto a total yield of 674) are of greater importancethan the productsof the redox reaction. Similar productsare obtainedwhen m-xylene is used in place of g-xylene,the major ones being phenyl 2,k-dimethylphenyl sulfide (34.e) and diphenyl-2,4-dimethylphenylsulfonlumiodide (13.3%). We suggest that the mechanismof a typical exchange reactionis that shown in Scheme 1. Scheme 1 AlCle
2629
No.30
2630
The proposed intermediate(A) is a tetracovalentsulfur compound,and the existenceof such compoundshas been discussedby other workers (1). Cf course,protonationof the m-xylyl group of (A) would be expectedto occur more rapidly than protonationof a ohenyl group, but such a processwould lead only to regenerationof the reagents;undoubtedly,the reactionis a reversible one. It is significantthat the amount of benzene produced in each reactionis roughly comparableto the total of the molar amounts of substituteddiphenyl sulfidesformed. With regard to the formationof triarylsulfonium salts in these reactions,the oxidizing power of aluminum chloride,especiallyin apparent one electronoxidations,has been observedby variousworkers (2). Cf particularinterestwith respect to this communicationis the report that a thianthrenecation radical is formed when thianthreneis treated with aluminum chloride (3). Furthermore,benzyl phenyl sulfide is known (4) to form a complexwith aluminum chloride, one which undergoesreactionwith water to give thiophenoland benzyl chloride. These facts and analogy with the mechanismwhich has been proposed for the generationof diarylsulfiniumcation radicalsby the action of concentratedsulfuricacid on diary1 sulfides (51,
provide the basis
for the typical mechanism,shown in Scheme 2, which we suggest for the font&ion of triarylsulfoniumsalts in the reactionsof diary1 sulfideswith aromatichydrocarbons. Scheme 2 0 AlCla
(B)
b)
Q-Q
+
Q
_
Q
(c)
do.50
2631
Owing to the positivecharge of the diphenylsulfinium ion radical (C), the substitution reactionhas some of the character (e.g., orientationand activatingeffects of substituents)of an electrophilicsubstitutionreaction,although it is actuallyan aromatic radical substitution reaction. Although the details of the subsequentreactionsare not entirelyclear, it is thought that the conjugateacid of diphenyl sulfideundergoesreactionwith the radical ion (B) (6) to form diphenyl sulfide,benzene and a complex of the conjugatebase of thiophenolwith aluminum chloride. As indicatedbelow for the reaction carried out in chlorobenzeneas solvent,thiophenol has been found to be a product in a situationwhich resulted in the formationof relatively large amounts of triarylsulfonium salts. 0 UCL3
Y
+
2Q4-43
\--/
(B)
+ Al'&
The stoichiometryof a typical redox reaction is thought to be as follows:
When a relativelyunreactivearomatic compound,such as chlorobenzene,is mixed with diphenyl sulfide and treated with aluminumchloride,an exchangeproduct,phenyl E-chlorophenylsulfide, is obtained in only 0.14% yield. The remainingproductsare the result of self-condensation
No.30.
2632
reactionsof diphenyl sulfide and includethianthrene(1.7$),
diphenyl-p-thiophenoxyphenyl-
sulfoniumiodide (22.4$),his-(p-diphenylsulfoniophenyl) sulfidediiodide (10.3$),thiophenol (1.3$),
benzene (3.5%) and diphenyldisulfide (0.63s).
The structuresof the triarylsulfonium salts were proved by pyrolysisand subsequentvpc analysesof the pyrolysates(7). The diary1 sulfide8were isolatedby use of preparativescale vpc and both their ir and nmr spectra comparedwith authenticsamples. Reference8and Footnotes K. Mislow, T. Sinrmons, J. T. Melillo and A. L. Ternay, Jr. have suggestedthat a tetracovalentsulfur compoundis formed 8s an intermediatein the hydrochloricacid-catalyzed racemizationof opticallyactive sulfoxides: J. Amer. Chem. Sot., g, 1432 (1964). V. Franzen and C. Mertz providedevidence for the formationof a tetracovalentsulfur intermediatein the exchangereactionsof triarylsulfonium selts with organolithium resgents: Ann., 62, 24 (1961). Thi.8 li8t iS not intendedt0 be exhaustive.
(2) J. J. Rooney and R. C. Pink, for example,hare reportedthe occurrenceof one electron oxidationsof aromatichydrocarbons,such as anthracene,chryseneand perylene,to the correspondingcation radicalsby the action of aluminum chloride: Proc. Chem. Sot., 142 (1961). See al80 Ii.M. Buck, W. Bloemhoffand L. J. Costerhoff,TetrahedronLetters,5 (1960); R. E. Banks, L. F. Farnell,R. 1. Haszeldine,P. N. Preston and L. H. Sutcliffe, Proc. Chem. Sot., 3% (1964). (3)
H. J. Shine and J. L. Piette, J. Amer. Chem. Sot., 82, 47%
(4)
D. P. Harnish and D. S. Tarbell,J. Amer. Chem. Sot., &
(5)
H. J. Shine, "The FormationOf CatiOnS and Cation Radical8 from Aromatic Sulfide8and Sulfoxides,"ch. 6 in M. J. Janssen,ed., GrganosulfurChemistry,IntersciencePublishers, New York, 1. Y., 1967. See also U. Schmidt, K. H. Kabitze,K. Markan and A. Miller, Angew. Chem., 3 708 (1960); Ann. Chem., 672, 78 (1%4); Angew. Chem. Internat.Ed., 5 602 (1964). The thianthreneradical ion producedby the action of concentratedsulfuricacid on thianthreneis the same as that producedby the action of aluminum chloride (3) on the same substrate,as shown by the epr spectra of the two samples.
(6)
Evidence for the formationof a radical intermediateanalogousto (B), one in which the sulfur atom accossnodates nine electronsin its valence shell, has been reported.byR. J. Gritter and D. J. Carey, J. Org. Chem., a ll.60(1964). Also, evidence for the formation of triarylsulfurintermediatesin Various reactionshas been reportedby M. Finkelstein, R. C. Petersonand S. D. Ross, J. Electrochem.Sot., 110, 422 (l%?) and by 3. W. Knapczyk and W. E. McEwen, J. Amer. Chem. Sot., & 145 0969) -
(7)
G. H. Wiegand and W. E. McEwen, J. Org. Chem., 2, 2671 (1968).
(1962).
4123 (1948).
1970.
MCHAWGE AND REXXJX RFlAClJIONSOFDIABYL
Perganlon Press. Printed in Great Britain.
SULFIDES WITH AROMATICHYDRCXXRBONS
Chung Hwa Han and William E. McSwen Departmentof Chemistry,Universityof Massachusetts,Amherst, Massachusetts 01002 (Receivedin USA 24 April 1970;
receivedin UK for publication 29 May 1970)
When an aromatichydrocarbonis caused to react with a diary1 sulfide in the presence of aluminum chloride,a complex mixture of productsresults. For example,the reactionof diphenyl sulfide with z-xylene has been found to produce phenyl 3,4-dimethylphenyl sulfide (40.3$), phenyl 2,3_dimethylphenyl sulfide (7.3$),2,3-dimethylphenyl 3,4-dimethylphenyl sulfide (3.0%) bis-(2,3_dimethylphenyl) sulfide (5.2$),bis-(j,k-dimethylphenyl) sulfide (ll.l$),benzene (57.5$),a diphenyl-3,4dimethylphenylsulfonium salt (isolatedas the iodide in 5.5% yield), and, after exposure of the reactionmixture to water, hydrolysisproducts of triarylsulfonium salts (0.304 of 3,4-dimethylphenol and
O.@$
of 2,3-dimethylphenol).Cbtiously,the exchange
products (amountingto a total yield of 674) are of greater importancethan the productsof the redox reaction. Similar productsare obtainedwhen m-xylene is used in place of g-xylene,the major ones being phenyl 2,k-dimethylphenyl sulfide (34.e) and diphenyl-2,4-dimethylphenylsulfonlumiodide (13.3%). We suggest that the mechanismof a typical exchange reactionis that shown in Scheme 1. Scheme 1 AlCle
2629
No.30
2630
The proposed intermediate(A) is a tetracovalentsulfur compound,and the existenceof such compoundshas been discussedby other workers (1). Cf course,protonationof the m-xylyl group of (A) would be expectedto occur more rapidly than protonationof a ohenyl group, but such a processwould lead only to regenerationof the reagents;undoubtedly,the reactionis a reversible one. It is significantthat the amount of benzene produced in each reactionis roughly comparableto the total of the molar amounts of substituteddiphenyl sulfidesformed. With regard to the formationof triarylsulfonium salts in these reactions,the oxidizing power of aluminum chloride,especiallyin apparent one electronoxidations,has been observedby variousworkers (2). Cf particularinterestwith respect to this communicationis the report that a thianthrenecation radical is formed when thianthreneis treated with aluminum chloride (3). Furthermore,benzyl phenyl sulfide is known (4) to form a complexwith aluminum chloride, one which undergoesreactionwith water to give thiophenoland benzyl chloride. These facts and analogy with the mechanismwhich has been proposed for the generationof diarylsulfiniumcation radicalsby the action of concentratedsulfuricacid on diary1 sulfides (51,
provide the basis
for the typical mechanism,shown in Scheme 2, which we suggest for the font&ion of triarylsulfoniumsalts in the reactionsof diary1 sulfideswith aromatichydrocarbons. Scheme 2 0 AlCla
(B)
b)
Q-Q
+
Q
_
Q
(c)
do.50
2631
Owing to the positivecharge of the diphenylsulfinium ion radical (C), the substitution reactionhas some of the character (e.g., orientationand activatingeffects of substituents)of an electrophilicsubstitutionreaction,although it is actuallyan aromatic radical substitution reaction. Although the details of the subsequentreactionsare not entirelyclear, it is thought that the conjugateacid of diphenyl sulfideundergoesreactionwith the radical ion (B) (6) to form diphenyl sulfide,benzene and a complex of the conjugatebase of thiophenolwith aluminum chloride. As indicatedbelow for the reaction carried out in chlorobenzeneas solvent,thiophenol has been found to be a product in a situationwhich resulted in the formationof relatively large amounts of triarylsulfonium salts. 0 UCL3
Y
+
2Q4-43
\--/
(B)
+ Al'&
The stoichiometryof a typical redox reaction is thought to be as follows:
When a relativelyunreactivearomatic compound,such as chlorobenzene,is mixed with diphenyl sulfide and treated with aluminumchloride,an exchangeproduct,phenyl E-chlorophenylsulfide, is obtained in only 0.14% yield. The remainingproductsare the result of self-condensation
No.30.
2632
reactionsof diphenyl sulfide and includethianthrene(1.7$),
diphenyl-p-thiophenoxyphenyl-
sulfoniumiodide (22.4$),his-(p-diphenylsulfoniophenyl) sulfidediiodide (10.3$),thiophenol (1.3$),
benzene (3.5%) and diphenyldisulfide (0.63s).
The structuresof the triarylsulfonium salts were proved by pyrolysisand subsequentvpc analysesof the pyrolysates(7). The diary1 sulfide8were isolatedby use of preparativescale vpc and both their ir and nmr spectra comparedwith authenticsamples. Reference8and Footnotes K. Mislow, T. Sinrmons, J. T. Melillo and A. L. Ternay, Jr. have suggestedthat a tetracovalentsulfur compoundis formed 8s an intermediatein the hydrochloricacid-catalyzed racemizationof opticallyactive sulfoxides: J. Amer. Chem. Sot., g, 1432 (1964). V. Franzen and C. Mertz providedevidence for the formationof a tetracovalentsulfur intermediatein the exchangereactionsof triarylsulfonium selts with organolithium resgents: Ann., 62, 24 (1961). Thi.8 li8t iS not intendedt0 be exhaustive.
(2) J. J. Rooney and R. C. Pink, for example,hare reportedthe occurrenceof one electron oxidationsof aromatichydrocarbons,such as anthracene,chryseneand perylene,to the correspondingcation radicalsby the action of aluminum chloride: Proc. Chem. Sot., 142 (1961). See al80 Ii.M. Buck, W. Bloemhoffand L. J. Costerhoff,TetrahedronLetters,5 (1960); R. E. Banks, L. F. Farnell,R. 1. Haszeldine,P. N. Preston and L. H. Sutcliffe, Proc. Chem. Sot., 3% (1964). (3)
H. J. Shine and J. L. Piette, J. Amer. Chem. Sot., 82, 47%
(4)
D. P. Harnish and D. S. Tarbell,J. Amer. Chem. Sot., &
(5)
H. J. Shine, "The FormationOf CatiOnS and Cation Radical8 from Aromatic Sulfide8and Sulfoxides,"ch. 6 in M. J. Janssen,ed., GrganosulfurChemistry,IntersciencePublishers, New York, 1. Y., 1967. See also U. Schmidt, K. H. Kabitze,K. Markan and A. Miller, Angew. Chem., 3 708 (1960); Ann. Chem., 672, 78 (1%4); Angew. Chem. Internat.Ed., 5 602 (1964). The thianthreneradical ion producedby the action of concentratedsulfuricacid on thianthreneis the same as that producedby the action of aluminum chloride (3) on the same substrate,as shown by the epr spectra of the two samples.
(6)
Evidence for the formationof a radical intermediateanalogousto (B), one in which the sulfur atom accossnodates nine electronsin its valence shell, has been reported.byR. J. Gritter and D. J. Carey, J. Org. Chem., a ll.60(1964). Also, evidence for the formation of triarylsulfurintermediatesin Various reactionshas been reportedby M. Finkelstein, R. C. Petersonand S. D. Ross, J. Electrochem.Sot., 110, 422 (l%?) and by 3. W. Knapczyk and W. E. McEwen, J. Amer. Chem. Sot., & 145 0969) -
(7)
G. H. Wiegand and W. E. McEwen, J. Org. Chem., 2, 2671 (1968).
(1962).
4123 (1948).