Alkali Metal Salts of 1,a-Semidiones
The Journal of Physical Chemistry, Vol. 82, No. 70, 1978 1161
Ion Pair Formation in Alkali Metal Salts of 1,2-Semidiones1 Glen A. Russell," G. Wallraff, and J.
L. Gerlock
Department of Chemistry, Iowa State University, Ames, Iowa 500 I 1 (Received September 19, 1977; Revised Manuscript Received January 23, 1978) Publication costs asslsted by the Petroleum Research Fund
The trans/cis ratio of dimethylsemidione is drastically affected by preferrential ion pairing of the cis-semidione with lithium, sodium, or potassium cations even in dimethyl sulfoxide (Me2SO)solution. In the presence of an excess of the proper size cryptand the cis-chelated semidione radical anion is converted into the free radical anion and a trans/& ratio of radical anions >100/1 is observed. The 15-crown-5 or 18-crown-6 ethers have a similar effect in tert-butyl alcohol with potassium as the counterion but in Me2S0 an excess of the ethers fails to bring about a complete conversion to the trans-semidione with either sodium or potassium as the counterion. It is concluded that in Me2S0 the crown complexed cations (Na+ or K+) still can be chelated by the cis-semidione and this chelation is more important when the cation is complexed with the 15-crown-5ether. Sodium cis-dimethylsemidione in Me2S0or tert-butyl alcohol in the presence or absence of crown ether appears to exist in two forms with similar sodium hfsc but which are not readily time averaged. Isomeric ion pairs with sodium cations in and out of the plane of the semidione radical anion are suggested. Perfluorobiacetyl radical anion in MezSO show no chelation between the cis-semidione and alkali metal cations. In etheral solvents the perfluorobiacetyl radical anion shows a spectrum of ionic aggregates in the presence of alkali metal cations. The 1:l ion pairs of lithium or sodium with the cis- or trans-semidiones can be detected by alkali metal splitting (cis) or selective line broadening (trans). Equilibration between the ion pair structures with different cations 6). In the presence of the dianion of perfluorobiacetyl in tetrahydrofuran at 25 "C is slow (lifetimes additional ionic aggregates are detected which are interpreted as quadruple ions.
Introduction We have previously mentioned the effect of alkali metal cations on the cis-trans equilibria of aliphatic 1,2-semidiones by use of ESR spectroscopy.2 A rather dramatic effect is observed in the ESR spectrum in going from lithium (all cis, 1:l complex, uLi+ observed) to cesium (>99% trans, ucs+not observed) for the biacetyl radical anion (I, 11, R = CH3), even in a solvent as polar as diR
\
C=C
I
\
I
,
I
R
R =+
.O, ,O-
\
C=C
I
.O
\
I
0-
,M+
Scheme I R-C-C-R + R-C=C-R + 2R-C=C-R 1I II 00
I1
8
I
4
.O
0 II R-C-C-R + R-C=C-R II
I
1
-0 0-
0-
R-C=&R t R-C=C-R I
0022-3654/78/2082-1161$01.00/0
I
R-C-C-R t R-C=C-R + 2R-C=C-R
0-
methyl ~ulfoxide.~ The translcis ratios were intermediate with Na+, K+, and Rb+ as the cation with the percent of trans isomer increasing smoothly from sodium to potassium to rubidium as the c ~ u n t e r i o n . ~There is no appreciable effect of the nature or concentration of the cation upon the values of uH observed. We have also demonstrated previously that the trans/& ratios observed in a static system are determined by thermodynamic considerations under our reaction conditions (semidione prepared from the base-catalyzed disproportionation of the ahydroxy ketone in Me2S0 a t 25 "C) although the maintenance of a thermodynamic equilibrium need not require a direct interconversion of cis and trans structures. This equilibrium can be maintained by further equilibria (Scheme I) which also causes some complications in studying the semidiones a t low temperatures as well as in nonpolar solvents. The relative thermodynamic stabilities of the dimethylsemidiones are such that in the absence of a specific chelating effect (which would stabilize the cis structure) the trans/& ratio is >100:1 a t 25 "C (Me2S0).3
I
0-
I
or trans I1
I
- 0 0-
0
0
lM+' cis I
A-
fL
0
R
I
-0
I
*o
I
I
*o 0-
R-C-C-R t R-C=C-R /I I/ 00
I
-0
In the present work we examine the effect of macrocyclic (crown) polyethers and cryptands upon this cis-trans equilibria observed, primarily with sodium as the cation in Me2S0 and tert-butyl alcohol solution. Experimental Section Dimethylsemidione was prepared by the reaction of acetoin (CH3COCHOHCH3) with base in Me2S0 or tert-butyl alcohol in the absence of oxygen by use of a H cell in which solutions of acetoin and of base could be deoxygenated by a stream of prepurified nitrogen before mixing of the reagent^.^ Solutions of the crown ethers or cryptands were added to the solutions of the semidiones by hypodermic through the rubber septum caps of the H cell. The disproportionation involved in the formation of a semidione from an a-hydroxy ketone is formulated as shown in Scheme 11. Relative concentrations of the cis and trans semidiones were measured as the ratio of peak 0 1978 American Chemical Society
1162
The Journal of Physical Chemistry, Vol. 82, No. 10, 1978
G. A. Russell, G. Wailraff, and J. L. Gerlock h
Scheme I1 H
H
0 OH
0 0-
0-
I R-CAR t B- + R-C-C-R + R-C-C-R l iI I il i
i
H
H
a
HH
I I R-CAR t R - C - ~ - R +R-C-C-R t R-C-C-R ii Ii i i I iI it I
OOH 0 iI
000-
-0ow
15-C-5,0.6 I1
00
t -
0i SO
I
-0
1
;
TABLE I: Effect of Total Sodium Ion Concentration on the Trans/Cis Ratio for Dimethylsemidione in Me,SO at 25 C O
[Na'B-I, M Ktranslcis LNa'B-1, M Ktranslcis (A) Sodium tert-Butoxide (Acetoin = 0.20 M) 0.10 0.64 0.20 0.54 0.14 0.55 0.27 0.65 0.18 0.81 0.31 0.75 Dimsylate (B-/Acetoin -1.82b 4a 1.15 1.38 0.67 0.46 0.44 0.46
1.61 1.85 2.10
;
;
= 1.21) 0.25 0.29 0.15 0.19 0.15
a Sodium hyperfine splitting detected. peak for cis-semidione from sodium hfsc.
3.2
C.3
18-crown-6
221-cryptand
Na+//Acetoin = 1.2 18.C rown - 6 - 04614 -221-Cryptand
1
w n
-
1.0 1.5 Na* -CH2SOCH3, moie/liter
20
Figure 2. Effect of sodium ion concentration on the trans/& ratios of dimethyisemidione at 25 O C in Me,SO: (A)18-crown-6 macrocyclic ether added; (0)221-cryptand added. All solutions were prepared with 1.2 mol of sodium dimsylatelmol of acetoin.
222-cryptand
Results and Discussion Effect of Na+ Concentration on TransjCis Ratios. According to our previous conclu~ion,~ the transjcis ratio of dimethylsemidiones should go to some large number ( m as measured by ESR spectroscopy) as the sodium ion concentration approaches zero. There is little evidence of this effect as the concentration of sodium tert-butoxide is varied in Me2S0 solution (part A of Table I). The transjcis ratio also is a function of the ratio of sodium tert-butoxide to acetoin. Sodium tert-butoxide is highly associated in Me2S0. This association may partially explain the lack of any significant effect of the total sodium tert-butoxide concentration on the transjcis ratio of part A of Table I. In addition, sodium tert-butoxide exists in MezSO in equilibrium with the sodium dimsylate anion and tert-butyl alcohol (eq 2). tert-Butyl alcohol has a
TABLE 11: Effect of Total Sodium Concentration on the TranslCis Ratio for Dimethylsemidione in Me,SO at 25 Ca 0
0.01 0.021 0.041
N
Na+(CH,),CO- t CH,SOCH, 2 Na+CH,SOCH,- t (CH,),COH
-0.25
I.@
Figure 1. Effect of teff-butyl alcohol concentration on the trans/cis ratio of dimethylsemidione at 25 O C : 0.11 M acetoin, 0.10 M alkali dimsylate. The effect of adding 15-crown-5 and 18-crown-6 ethers in teff-butyl alcohol is shown. With Na' as the counterion ion aHc,, increased from 7.45 (cis), 5.65 (trans) G in Me,SO to 7.65 (cis), 6.50 (trans) G in teff-butyl alcohol. Line widths for the semidione were narrower in teff-butyl alcohol than in Me,SO. With K+ as the counterion aCcO= 1.9 (cis), 1.2 (trans) G could be easily resolved in teff-butyl alcohol but not in Me,SO where amc = 1.4 (cis), 0.7 (trans) G as shown by isotopic substitution.
0. 5
21 1-cryptand
;
3.4
Broadened
height X (line width)2 which follows for a Lorentzian line shape. The macrocyclic ethers employed have the following structures and were purchased from PCR Research Chemicals, Inc.
15-crown-5
I
I
C,? C.6 C,7 0.6 0,s M O L E F R A C T I O N t-BUTYL ALCOHOL IN DMSO C.1
(B) Sodium 0.05 0.069 0.231 0.461 0.692 0.923
15 C 5 I34211
Q , 15-C-5:S)SM
R-C-C-R t R-C= &-R + 2R-C=b-R
CI
1X-5,O.OBI.I
0.082
0.103 0.124 0.145 0.207 0.311 0.549 a
0.212 0.222 0.233 0.253 0.294 0.315 0.336 0.357 0.419 0.523 0.761
0.98 0.66 0.42 0.29 0.31 0.26 0.24 0.17 0.13 0.10 0.10
Acetoin = 0.190 M, sodium dimsylate = 0.212 M.
pronounced solvent effect on the transjcis ratio as shown in Figure 1. Under the experimental conditions of Figure 1 (ratio of acetoin to base held constant) the trans/cis ratio with sodium as the cation varied from slightly more than 1 in pure MezSO to something less than 0.05 in pure
Alkali Metal Salts of 1,2-Semidiones
The Journal of Physical Chemistry, Vol. 82,
No. 10, 1978 1163
TABLE 111: Ratio of TranslCis Dimethvlsemidiones in a Variety of Solvents (0.1M Potassium Gegenion, 25 C) % solvent separated Translcis ions for 80% SE , value E Donor fluoreny 1 Solvent (S) 100% s 20% Me,SO for Sa (pure S) no. of Sb sodiumC 45.0 45 30 100 Me,SO 17.5 17.5 43.8 37 27 DMF 7.8 8.7 40.9 30 39 100 HMPA 3.0 5.2 38.9 7.5 Trig1yme 0.25 1.7 40.2 12 33 100 Pyridine 100b
Only one isomer detected.
caused the trans/& ratio to increase with potassium as the gegenion but an excess of the crown ethers failed to convert all of the cis- to the trans-semidione. With lithium as the counterion in MezSO only the cis-semidione could be observed in the presence or absence of 15-crown-5 ether. In going from Me2S0 to tert-butyl alcohol as solvent two of the major effects which might influence the cis-trans equilibrium of dimethylsemidione are the dielectric constant and hydrogen bonding. The lower dielectric constant of tert-butyl alcohol would favor ion pairing of the cis-semidione and thus cause a decrease in the trans/cis ratio. Hydrogen bonding should be more important for the trans-semidione because both oxygen atoms are available and this effect alone would lead to an increase in the trans/& ratio. The results seem to be qualitatively in agreement with this interpretation (see Table V). For the tight ion pairs observed in absence of complexing agents the trans/& ratio decreases when Me2S0 is replaced by tert-butyl alcohol as solvents, e.g., with 0.1 M K+, trans/& = 13 in Me2S0, 0.25 in tert-butyl alcohol. Here apparently the dielectric constant is the important consideration. For looser ion pairs, such as observed with Na+ or K+ complexed with 18-crown-6 the trans/cis ratio increases when MezSO is replaced by tert-butyl alcohol, e.g., with K+(18-crown-6) the trans/& ratio is 42 in Me2S0, but increases to >lo0 in tert-butyl alcohol. Apparently the increased hydrogen bonding for the trans species overcomes the effect of the change in dielectric constant. In the case of the 15-crown-5 complexes for which the trans/& ratios observed in Me2S0 suggest an intermediate stage of looseness; the Na+(l5-crown-5) system seems to follow the dielectric constant prediction (trans/cis decreases from Me2S0to tert-butyl alcohol), but K'(15-crown4 shows the opposite effect since it forms a looser ion pair with the cis-semidione radical anion. There may be some other specific hydrogen bonding effect which can explain these observations, but it seems certain that the ability of tert-butyl alcohol to affect the relative thermodynamic stabilities of the trans and cis species depends on the tightness of the cis ion pair observed in MezSO.
100% transb 100% trans Mainly trans" In Me,SO
TABLE VII: Trans/Cis Ratio of Dimethylsemidione at 25 'C in the Presence of 222-Cryptand in Me,SO
>50
Me,SO
100% trans 100% trans 100% trans
a No effect of cryptand on trans/cis ratio. or tert-butyl alcohol.
3.1 18.8
>loo
100% cisa Mainly cis 100% trans
a
Mx
lo2.
l-Na+t o tal 1[222y 11.2 10.2 9.5 8.7 7.9 6.2 4.6 2.9 0 0
oNa' detected.
ktranslcis
0.44 0.66 0.80 0.99 1.20 1.50 3.5gb 3.16b 9.84b >l 0 O C Cis not detected.
TABLE VIII: Values of log Ks for Complex Formation between Cryptands and Cations in WaterP
a
Crypt and
Lit
Na'
K'
211 221 222
4.3 2.5 0
2.8 5.4 3.9
< 2.0 3.9 5.4
Reference 16.
Effects of Cryptands. The cryptands had a more dramatic effect on the trans/cis ratio than did the crown ethers. Table VI summarizes the effects observed in MezSO with lithium, sodium, and potassium cations. With sodium cations all three cryptands were more effective than either of the crown ethers in shifting the trans/& equilibria. For potassium cations the 222 and 221 cryptands were more effective than the 211 cryptand or the crown ethers while for lithium the 211 cryptand was more effective than the 221 or 222 cryptands or the crown ethers. Table VI1 shows the essentially stoichiometric effect of 222 cryptand on the trans/& ratio with sodium gegenion MezSO solution. These results are in agreement with stability constants for complex formation measured in water (or alcohol) solution, Table VIII. The cryptands when effective with sodium or potassium counterion increased the overall strength of the ESR signal, increased the trans/& ratio, and a t low sodium ion concentration allowed an asymmetric sodium hyperfine splitting to be partially observed. Potassium hfsc was never detected. Semidione Ion Pairing in Etheral Solvents. Dimethylsemidione cannot be studied in etheral solvents. Treatment of the a-hydroxy ketone with base, even in the presence of crown ethers, gives very low intensity signals with poor resolutions, presumably because of the equilibria in Scheme I. Attempts to reduce biacetyl with alkali metals or electrolytically yields condensation products, notably I11 (reaction 5).
(5) 0-
111
1166
The Journal of Physical Chemistry, Vol. 82, No.
IO, 1978
G. A. Russell, G.Wallraff, and J. L. Gerlock 20
Trans-"
c 15
G
1
G
15
20
1
trans Figure 5. Mixture of the four 1:l ion pairs identified in the reduction of perfluorobiacetyl by a mixture of sodium and lithium iodides.
Perfluorobiacetyl does not undergo this condensation and gives fairly strong ESR signals in a variety of etheral solvents upon reduction (eq 6) with alkali metals17 or upon 3LiI t 2CF3COCOCF, 2[CF3COCOCF,]-.Li+ t LiI, ( 6 ) -t
reaction with lithium or sodium iodides (aFtrms= 8.5, aFcis = 11.8 G, Me2S0).18 Ion pairing is less pronounced for perfluorobiacetyl radical anion than for biacetyl radical anion. Thus, in MezSO the same trans/& ratio (>loo) is observed with Li+, Na+, K+, Rb+, and Cs+. Hyperfine splitting by lithium in MezSO is not observed.18 With lithium as the cation in THF the cis ion pair shows a strong lithium splitting, aF = 11.20, aLi = 0.56, aC?FS= 5.3 G. Alkali metal splitting is also observed in the cm-semidione with sodium as the cation (aNa= 0.54 G) but not with potassium.ls Now the trans-semidione shows nonequivalent trifluoromethyl groups (aF = 11.35, 5.20) with a coalescence temperature >80 "C. The coalescence temperature decreases as the gegenion is changed to sodium or potassium so that the spectrum with potassium counterion at 25 "C is in the fast-exchange mode but selective line broadening is still observed. The nonequivalence of the trifluoromethyl groups must be connected with the following equilibrium: CF 3
0\
I .O
M'
I
CF3\
c=c
e
\
I
CF 3
-0
c=c \
I
0.
(7) CF,
M' The rate of the process which time averages the trifluoromethyl group is independent of the concentration of the alkali metal cation in solution.18 The rates of alkali metal ion exchange in these ion pairs is remarkably slow. Thus with mixtures of lithium and sodium, potassium, or rubidium cations four distinct species can be detected with no indication of time averaging at 25 "C. For example, in THF with a mixture of lithium and sodium iodide, perfluorobiacetyl yields the following ion pairs: (a) lithium ion pairs with cis-perfluorobiacetyl radical anions, aF = 11.14, aLi= 0.56 G; (b) sodium ion pair with cis-perfluorobiacetyl radical ion, aF = 11.36 aNa= 0.49 G (aNabest seen in the presence of dibenzo-18-crown-6 ether); (c) lithium ion pair with trans-perfluorobiacetyl radical anion, aF = 5.25, 11.35 with line broadening in the slow exchange mode; (d) sodium ion pair with trans-perfluorobiacetyl radical ion, aF = 8.26 with selective line broadening in the fast exchange mode. The observed spectrum (Figure 5) is simply the composite of the spectra observed with lithium and sodium as the sole cations. In isopropyl or ethyl ether again lithium metal
Figure 6. Mixture of cis- and trans-perfluorodimethylsemidione observed by lithium powder reduction of the dione in isopropyl ether at 25 OC.
reduction of perfluorobiacetyl forms a cis and a trans species, Figure 6. The cis spectra is similar to the one observed in T H F (aF = 10.72, aLi= 0.70 G) but the trans species has a hfsc by two lithium cations (aF = 7.9, aLi= 0.24(2)). The simplest interpretation is that a triple ion similar to IV is involved. Ll+
o\c&c CF3'
7
3
\O
t LI
IV Extensive reduction of perfluorobiacetyl by the alkali metals in etheral solution produces additional ion aggregated species which can be observed in solutions containing the four previously described ion pairs (a-d). High degrees of reduction in 2-methyltetrahydrofuran with lithium metal produces a new cis species without lithium hfsc (aF= 10.75 G) and an additional trans species (aF = 7.85 G) without line width alternation or lithium hfsc. The concentrations of these species increase with the extent of reduction and are not particularly decreased by dilution. Triplet spectra are not observed in frozen solutions. These species are the only species observed immediately after reduction at a lithium surface (at 0 "C a mixture of the cis and trans species is observed initially, but a -80 "C only the trans species is observed). With time and/or upon warming to 25 "C the four previously described 1:l ion pairs are formed provided the extent of reduction is not too extensive. The formation of these paramagnetic ions seems definitely connected with the presence of appreciable concentrations of the dianion of perfluorobiacetyl. Quadruple ions such as V and VI may well be involved. The fact that the electron does not exchange between the two biacetyl units in V and VI is surprising. This would lead to hfsc by 12 equivalent fluorine atoms with aF l / z that observed for the monomeric radical anions. In structure Va the two r systems are orthogonal which
-
)c=d
c F3
Va
'CF3
CF3 /
'CF3
Vb
might explain the absence of exchange. In the trans quadruple ion VIa the two R systems give overlap in a
The Journal of Physical Chemistry, Vol. 82, No. 10, 1978
Alkali Metal Salts of 1,2-Semidiones
1107
9
A
I
!
Flgure 8. Lithium salts of psrfluorobiacetyl in tetrahydrofuran at 25
"C. (A) Low field half of the spectrum obtained by reduction of the dione with lithium iodide at 25 "C. The spectrum shows the 1:1 cis ion pair with aL' = 0.56 G, A F = 11.20 G; the trans 1:l ion pair with the second, fourth and sixth lines not detected, AF = 8.26 G a second cis species (V) marked by X with A F = 10.90 G. At lower degrees of reduction the spectrum from V is not detected. (6)The effect of an excess of dibenzo-18-crown4 upon spectrum A. The wing peaks are expanded in the inserts. V is no longer seen and the trans-semidione is now obviously in the slow exchange mode with ACF: = 5.25, 11.35 G. The broadened lines are marked by 0 . (C) The effect of adding an excess of lithium iodide to spectrum 6. Species V is again seen and the rate of averaging the CF, groups in the trans-semidione has increased.
ethyl ether showing hfsc by two lithium atoms is actually the quadruple ion VI. In diethyl ether with cesium as the
I
I
Figure 7. Sodium hyperfine splitting observed for cis-perfluorodimethylsemidione at 25 OC in tetrahydrofuran solution: (A) spectrum observed after brief exposure of the dione to sodium iodide; (B) spectrum after additional exposure; (C) spectrum B after addition of dibenzo18-crown-6 ether; (D) effect of further addition of sodium iodide to C.
spiroconjugative manner, and this may not be particularly condusive to electron transfer. Moreover, in either V or VI the cations will be much more closely associated with the dianion than with the radical anion. This alone may explain the absence of metal hfsc and also the lack of electron exchange. This asymmetry coupled with the overlap considerations mentioned previously would preclude a completely delocalized structure where the electron is equally distributed over the two biacetyl units. For an electron to exchange between the two biacetyl units would require a movement of both cations, a process which apparently has a sufficiently high Ea&that exchange is not observed. In T H F or 2-methyltetrahydrofuran alkali metal splittings are not observed for these species. There is a possibility that the trans species observed in isopropyl or
VIa
VIb
cation the cis species (V) at -40 "C also shows hfsc by two cations (aF N 11,ucs = 0.7(2) G) and possibly in this case the size of cesium is such that the chelate structure I cannot be found and instead ionic aggregation occurs to yield V. The absence of hfsc by M+ in V and VI with M+ = Li+ or Na+ may be connected with the possibility of equilibria such as Va Vb, VIa it VIb. In any event it should be emphasized that these higher ionic aggregates are formed not when the concentration of the radical anion is increased but when the reduction has proceeded to form an appreciable amount of the dianion. Figure 7 shows the sodium hfsc observed in T H F for the cis-perfluorobiacetyl radical anion. The spectra also illustrate the line width alternations observed for the
1168
The Journal of Physical Chemistry, Vol. 82, No. 10, 1978
trans-semidione. Spectrum A of Figure 7 is observed after brief exposure of the biacetyl to sodium iodide. The sodium hfsc for the cis-semidione is symmetric. The trans-semidione is a 1:9:9:1 quartet with the second, fourth, and sixth lines of 1:5:15:20:15:6:1 heptet (expected for six equivalent fluorine atoms with aF = 8.35 G) unobserved. In spectrum B additional exposure to sodium iodide has increased the sodium ion concentration and the sodium hfsc is nearly lost. The second and sixth lines of the trans-semidione are detected as shown by the arrows. Spectrum C results when an excess of dibenzo-18-crown-6 ether is added to the solution giving spectrum B. There is very little effect of the crown ether on the cis/trans ratio, but the symmetrical sodium hyperfine has been restored. Upon dissolving additional sodium iodide spectrum D results with again loss of the sodium hfsc. Saturating the solution yielding spectrum D with the crown ether gave a spectrum essentially identical with C with aNa= 0.54 G. Addition of dibenzo-18-crown-6ether to the lithium salts of perfluorobiacetyl in the T H F also had an effect on the observed species although the cis/trans ratio was not changed appreciably. In the absence of the crown ether, lithium iodide reduces the dione to the cis 1:l ion pair with lithium hfsc, the trans 1:l ion pair with alternative line width broadening, and a cis ion pair without lithium hfsc attributed to V (Figure 8A). Addition of a large excess of crown ether removes V from the spectrum and slows down the rate of the process which time averages the CF, groups in the trans-semidione (Figure 8B). Further addition of lithium cations so that the cation is present in excess of the crown ether restores V and increases the rate of the process time averaging the trifluormethyl groups (Figure 8C). The crown ether by chelation of the lithium cation prevents the formation of V and also VI. We have shown previously that one of the important processes for time averaging the CF3 groups in the trans-semidione involves the participation of VI (Le., the rate of time averaging increases with the degree of reduction).18
B.
K. Bandlish, W. R. Porter, and H. J. Shine
Acknowledgment. This work was supported by a grant from the donors of the Petroleum Research Fund, administered by the American Chemical Society.
References and Notes Aliphatic Semidiones. 33. This work was supported by a grant from the Petroleum Research Fund. G. A. Russell and D. F. Lamson, J. Am. Chem. Soc., 94, 1699 (1972). G. A. Russell, D. F. Lamson, H. L. Malkus, R. D. Stephens, G. R. Underwood, T. Takano, and V. Malatesta, J . Am. Chem. SOC.,96, 5830 (1974). E. R. Talaty and G. A. Russell, J. Am. Chem. SOC.,87, 4867 (1965). S. H. Exner and E. C. Steiner. J . Am. Chem. SOC..96. 1782 11974). M. S. Greenberg, R. L. Bodner, and A. I.Popov, 'J. bhys. Chem:, 77, 2449 (1973). C. Reichardt and K. Dimroth, Fortsch. Chem. Porsch., 11, 1 (1968). V. Gutmann and V. Maver, Struct. Bondino(i3erlin). 12, 113 (1972); V. Gutmann, Chimia, 31, 1 (1977). T.E. Hogen-Esch and J. Smid, J. Am. Chem. Soc., 88, 307 (1966). V. Gutmann, Chemtech, 255 (1977), has defined solvent acceptor numbers which show similar variations of the Reichardt and Dimroth E, values. R. M. Izatt, R. E. Terry, 8. L. Haymore, L. D. Hansen, N. K. Dalley, A. G. Avondet, and J. J. Christensen, J . Am. Chem. SOC.,98, 7620 (1976). J. Smid, "Ions and Ion Pairs in Organic Reactions", M. Szwarc, Ed., Wiley-Interscience,New York, N.Y., 1972, Chapter 3; J. Sniid, Angew Chem., Int. Ed. Engl., 11, 112 (1972). M. A. Bush and M. R. Truter, J. Chem. SOC.,Perkin Trans. 2 , 341 (1972). The equilibrium of Scheme Ishifts toward the radical anion when the dielectric constant of the solvent is increased, when the temperature is increased, or when the counterion is changed from Lit to Na'. Ion pairing will stabilize both the dianions and the radical anions and there are comproportionation reactions known where the reverse effects are observed, e.g., tetraphenylethylenein THF (T2T @ 2T-e) where a higher radical anion concentrationis observed with lithium as cation than with sodium." I n the semidione system the additions of the crown ethers to the lithium salts actually resulted in a decrease in total radical anions concentration,exactly opposite to the effect observed with sodium or potassium as the counterion. B. Lundgren, G. Levin, S. Claesson, and M. Szwarc, J. Am. Chem. SOC.,97, 262 (1975). J. J. Christensen D. J. Eatough, and R. M. Izatt, Chem. Rev., 74, 351 (1974). G. A. Russell, J. L. Gerlock, and G. R. Underwood, J. Am. Chem. SOC.,94, 5209 (1972). G. A. Russell and J. L. Gerlock, J. Am. Chem. Soc., 96, 5838 (1974).
+
I o n Radicals. 41. S-Alkylation and S-Arylation of Organosulfur Cation Radicals with Organometallics'12 Baldev K. B a n d l l ~ hWilliam ,~ R. Porter, Jr.,4 and Henry J. Shine" Department of Chemistry, Texas Tech University, Lubbock, Texas 79409 (Received July 29, 1977) Publication costs asslsted by the National Science Foundation
Thianthrene and phenoxathiin cation radical perchlorates were allowed to react with dialkyl- and diarylmercurials (R2Hg,R = Me, Et, C6H5,o-MeC6H4,p-MeCsH4,rn-C1CsH4,p-C1C6H4,p-MeOC6H4)to give the corresponding S-alkyl-and S-arylsulfoniumsalt. Analogous reactions with N-methyl- and N-phenylphenothiazine cation radical perchlorates did not occur. However, reaction of these cation radicals, and the former two, occurred with diethyland diphenylzinc.
Alkyldiarylsulfonium salts are commonly prepared by reaction of the diary1 sulfide with an alkyl halide and a silver salt.5 The method has been used extensively also for S-alkylating heterocyclic sulfides."8 It is not, however, useful for S-arylation. Triarylsulfonium salts may be made by the reaction of an ethoxydiarylsulfonium salt with an arylmagnesium halide,5 or by reaction of a diarylsulfoxide
with an aromatic hydrocarbon in either concentrated sulfuric a ~ i d ,or~ in , ~the presence of aluminum chloride,1° or phosphorus p e n t ~ x i d e . ~ Each of these methods of arylation has seen limited use, and the method using the sulfoxide suffers particularly from the effects of the acids on the aromatic itself. Alkylation of some alkyl p-tolyl sulfides has also been achieved by reaction of the eth-
0022-3654/78/2082-1168$01.00/00 1978 American Chemical Society
