Nov. 5, 1962
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4155
a series of appropriately substituted compounds stabilizes a radical more than a carbanion. The have been compared in a common solvent under following relative rates of oxidation have been conditions such that the extent of ionization observed in dimethyl sulfoxide-t-butyl alcohol was considerable. For instance, in t-butyl alcohol (80-20) containing excess potassium t-butoxide solution containing excess potassium t-butoxide the (C6Hs)zCHCN > CeHsCHzCN > CHiCN rates of oxidation are: p-nitrotoluene > 2,4-di> P-NOzGHsCHzCeHs ? P-NOZCBHSCHB @-NOzCeHsCH(COHS)Z (all in t-butyl alcohol) nitrotoluene > 2,4,6-trinitrotoluene; p-nitrodi( csH~)?cHCozCzHs> CeHsCHzCOzCzHs >> phenylmethane > p,p’-dinitrodiphenylmethane>> C H ~ C O Z C Z(stable) H~ 2,2’,4,4’-tetranitrodiphenylmethane (stable) ; pCaH CHgCOCH, nitrotriphenylmethane > tris - (9- nitropheny1)methane; phenylacetonitrile > p-nitrophenylace>> p-nitrothiophenol tonitrile; thiophenol (stable) ; while in dimethyl sulfoxide-f-butyl al(7) Alfred P. Sloan Foundation Fellow. cohol mixtures (80-20), aniline >> p-nitroaniline ( 8 ) Eastman Kodak Co. Predoctoral Fellow, 1959-1960.. (stable), and p-nitrocumene > 2,4-&nitrocumene. GLENA. RUSSELL’ OF CHEMISTRY Under conditions wherein ketones are oxidized DEPARTMENT ANTHONY J. M O Y E ~ STATE UNIVERSITY readily in basic solution, many p-dicarbonyl com- IOWA AMES,IOWA K. NACPAL pounds are table,^ presumably due to the fact that RECEIVED JULY25, 1962 the second carbonyl group stabilizes the enolate anion more than the radical and thereby decreases THE FORMATION OF RADICAL-ANIONS BY the ease with which reaction 1 will occur. In a ELECTRON TRANSFER BETWEEN ANIONS AND similar manner we have observed that in dimethyl THEIR UNSATURATED ANALOGS IN sulfoxide-t-butyl alcohol solutions (S0-20%) in DIMETHYL SULFOXIDE SOLUTION1~z the presence of a two-fold excess of potassium t- Sir: butoxide, the relative rates of oxygen absorption are We have shown in a previous publication3 that CH3CeHiNOz-5 > CHz(CsH4NOz-P)a _ . > CH(CeHJVOz-5)3 electron transfer between carbanions and organic (all in t-butyl alcohbl) electron acceptors (r),such as the nitroaromatics, CHaCOCHa > CHz( COCHs)?, CHz( cH3co)COzCzH~ often occurs readily. CHXOC~HS > CHdCOCaHrb Istable) R:- + T + + R.-+ products Experimentally this irreversible process is not as conveniently studied as the reversible electron transfer reaction between a dianion and its unI n aliphatic series one usu-tlly expects radical saturated analog. stabilities of tert. > sec. > prim. whereas carbanion T- + K Z ~ T . - O ~ T H T - + Z 2 ~ +- H + stabilities are usually prim. > sec. > tert. Thus, It is known that in basic solution electron transother factors being equal, the conversion of a tert.-carbanion to a tert.-radical should always fer occurs between hydroquinones and quinones4 pre~ occur more readily than the conversion of a prim.- and between benzoin and b e n ~ i l . Dianions carbanion to a prim.-radical. I n every appropriate pared from alkali metals and an olefin will in certain case we know of this relationship holds. Thus, cases react with more of the olefin to produce in t-butyl alcohol solution 2,4-dinitrocumene is radical-ions. Such reactions have been observed oxidized more readily than 2,4-dinitrotoluene. for stilbene,6a tetraphenylethyleneEb and cycloIn dimethyl sulfoxide-t-butyl alcohol mixtures 0ctatetraene.m Calculations indicate that in the alkali metal adducts of aromatic hydrocarbons? (SO-20) these relative rates are observed the radical-anion is favored over a mixture of di(CH3)2CHCOCH(CHj)z > CHaCHzCOCHzCH3 > CH3COCH3 anion and unreacted hydrocarbon.? I t is also (CH3)zCHSO?CH(CH3)2 > CHaCHzSO?CH?CH8>> recognized that dianions, obtained by the addition 7
CH3SO2CH3(stable) (CH3)zCHCK > CHaCHzCN > CH3CN ( C H ~ ) ? C H C O L C .> & ,CH3CHzCOzCzHs>> C H ~ C O J C Z(stable) H~ (CHa)zCHCOCsIIs > C I I J C H ~ C O C G> H ~CH3COCsHbfi (CH3)zCHNOz > CHaCH2N02 > CHaNOz‘
Substitution of a phenyl group for a hydrogen atom does not have a consistent effect on the ease of oxidation of the resulting carbanion. The phenyl group is recognized to be important in stabilizing both radicds and carbanions and one might expect these effects to cancel in regard to the ease of occurrence of reaction 1. However, in most cases the phenyl-substituted compound oxidizes more readily than the unsubstituted compound, indicating that in general the phenyl group (5) W. E. Doering and R. M. Haines, J . A m . Chem. Soc., 7 6 , 482 (1954). ( 6 ) These series were oxidized in the presence of deficient base The oxidations are more rapid in deficient base than in the presence of excess potassium &butoxide (see ref. 3c).
9
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( 1 ) Reactions of Resonance Stabilized Anions. V. (2) This work was supported by a grant from the Nalional Science Foundation and the Petroleum Research Fund, administered by the American Chemical Society. Grateful acknowledgment is hereby made to the donors of the Petroleum Research Fund as well as to the National Science Foundation. (3) G. A. Russell and E. G . Janzen, J. A m , Citein. Soc., 84, 4143 (1962). ( 4 ) T. H . James and A. Weissberger, ibid., 60, 08 (1038); I,. Michaelis, M . P. Schubert, R . K. Reber, J. A. Ruck and S. Granick, ibid., 60, 1678 (1938); J. H. Baxendale and H. R. Hardy, Trans. F a r a d a y Soc., 49, 1433 (1953); H. Diebler, M. Eigen and P . Matthies, 2. Nalurforsch., 16B, 629 (1961). (5) A. Weissberger, H. Mainz and E. Strasser, Ber., 62, 1942 (1929); A. Weissberger, i b i d . , 65, 1815 (1932); L. Michaelis and E. S. Fletcher, J . A m . Chem. Soc., 69, 1246 (1936); J . L. Ihrig and R. G. Caldwell, ibid., 78, 2097 (1956). ( 6 ) (a) D . E. Paul, D . Lipkin and S. I. Weissman, ibid., 78, 116 (1956); (b) J. F . Garst and R . S. Cole, Abstracts of Papers, 142nd Meeting of the Am. Chem. SOC.,Atlantic City, 1962, p. 5-Q; (c) T. J. Katz and H . L. Strauss, J . Chem. P h y s . , 32, 1873 (1960). (7) N. S. Hush and J. Rlackledge, i b i d . , Z3, 514 (1955); C. J. Hoijtink, E. DeBoer, P. €I. van der Heij and W. P. Weijland, Rcc. lrav. chim., 75, 487 (1956).
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1'01. 84
Fig. 1.-Iiadical-anion produced by electroii traiisfer between azobenzene (0.01 111) and hydrazobenzene (0.01 -11)in dimethyl sulfoxide (80)-t-butyl alcohol (20) containing 0.02 JJ potassium t-butoxide.
of alkali metals to olefins or aromatics, will undergo electron-transfer with ketones to give ketyl radical anions.8 The electrolytically produced dianion Fig. 8.-1+ddical-anioii produced by electrim transfcr of dinitrodurene undergoes electron transfer with between %,3-dipheiiylquiiiosalirle (0.01 -11) and 1,2-dihydrudinitrodurenega while possibly the dianion formed 2,3-diphetiylquinosaline (0.01 X) in dimethyl sulfoxide by alkali metal reduction of phenanthradene (8O)-t-butyl alcohol (20) containiiig 9.02 JI potassium undergoes electron transfer with phenanthradine. Yb t-butoxide. We have investigated the formation of radicalanions by use of a 1 : 1 mixture of an unsaturated 1,1,2,2 - tetraphenylethane - tetraphenylethylene, compound and its dihydro derivative in the pres- hydrazo - bis - isobutyronitrile - azo - bis - iso1,2-bis-(4pyridyl) -ethane-lJ2-bisence of potassium t-butoxide in dimethyl sulfoxide butyronitrile, solution.'O The observation of the formation of (4-pyridyl)-ethylene, N, 1,l-triphenylmethylamineradical-ions must depend on the ability of the N -diphenylmethyleneaniline, and N -phenylbenzyl base and solvent system to ionize the dihydro com- amine-N-benzylideneaniline. Many of the radical-ions produced have not been pound ( T H J as well as the ease of electron transfer. By virtue of the unique properties of dimethyl reported by more conventional synthesesGa,: sulfoxide we have been able to observe many elec- Figures 1 and 2 give the spectra of the radical-iuns tron transfer reactions in the presence of potassium produced by electron transfer between hydrazot-butoxide which cannot be observed in conven- benzene and azobenzene and between 1,2-dihydrotional solvents. Experiments were performed using 2,3-diphenylquinoxaline and 2,3-diphenylquinoxaa Varian V-4500 100 kc. e.p.r. spectrometer line. The e.s.r. spectra of some of the new radicalequipped with a flow system. Solutions (0.02 M) anions are summarized in Table I. We have estimated the concentrations of radicalwere saturated with thoroughly deoxygenated nitrogen before mixing. The solvent was di- anions by comparison with diphenylpicr ylhydrazyl methyl sulfoxide (80%)-t-butyl alcohol (20%) in three of the cases and found over 500; of the containing potassium t-butoxide equivalent to the starting compounds in the form of the radicalanions in the fluoren-!I-01-fluorcii-!)-one, xanthenpotentially ionizable hydrogen atoms. Electron transfer was observed in these systems : 9-ol-xanthen-9-onej and hydrazobetizene-azobenacridan-acridine, 1,2-dihydro-2,3-diphenylquinoxa-zene systems. Many of the radical-anions have been detected line - 2,3 - diphenylquinoxaline, 9,9' - bifluorenein the base-catalyzed autoxidation of the dihydroA - 9,9'- bifluorene, 9,10 - dihydroanthraceneanthracene, hydrazobenzene - azobenzene, furoin- compounds. Significant concentrations of the radifuril, fluoren - 9 - 01 - fluoren - 0 - one, xanthen - 9- cal-anions were found in the reaction of traces of 01 - xanthen - 9 - one, benzhydrol - benzophenone, oxygen with hydrazobenzene, dihydrociniiamoin, 1,1,4.4 - tetraphenyl - 2 - butene - 1,1,4.4 - tetra- fluoren-9-01, xanthen-9-01, 9, IO-dihydroanthracene, phenyl - 2,3 - butadiene and acridan - azobenzene. acridan, lI1,2,2-tetraphenylethane, 1 ,2-dihydro-?, 3Electron transfer was not observed in these systems, diphenylquinoxaline, 9,9'-bifluorene, N-phenylbeneven in pure dimethyl sulfoxide : 1,3-~yclohexadiene zylamine, 1,4-dihydronaphthalene and I , 1,4,4-benzene, 1,4- dihydronaphthalene - naphthalene, tetraphenyl-2-butene in dimethyl sulfoxide (SO)-t-butyl alcohol (20) solution containing excess ( 8 ) \V. Schlenk and R. Ochs, B e l . , 49, 608 (1016); G. Wittig and D' potassium t-butoxide. In these cases a radicalW i t t e n h e r g , Aiin., 606, 1 (1937). anion may be the primary reaction product (9) (a) D. H. Ceske, J. L. Ragel, M . Bambenck a n d A . 1,. Balch, Abstracts of Papers, 142nd Meeting of the Am. Chem. SOC., Atlantic City, 1962, p. 10-T. ( b ) J. J. Eisch and R. M. Thompson, Abstracts of Papers, 140th Meeting of the Am. Chem. SOC.,Chicago, 1961, p. 33-Q.
TH-
+
0 2
+
7 . -
+ H+ +
.02-;
7 -
+
7r.-
0 2
--+
+ .or-
(a)
or a result of dehydrogenation followed by electron transfer
(IO) NOTE ADDED 111 PROOF.-The dipotassium salt of a , a , a ' , o ' base base tetrakis-(ethyIsulfony1)-p-xylene (which can be made from t h e parent compound by potassium t-butoxide in t-butyl alcohol solution) underTH? 0 2 T ; T TH, %T.(b) goes electron transfer with 7,7,8,8-tetrakis-(ethylsulfonyl)-p-quinodimethan i n acetonitrile solution (W. R. Hertler and R. E. Bensun, (11) D. H. Geske and A. H. M a k i , J . A m . Chenz. SOL.,82, 2671 .I. A m C'ht;m. Soc., 84, 3-174 (1062)). ( I M O ) ; I
