I
Essentially the same mechanism has been proposed for the bromination of norbornylene.' Quantum mechanically, preference for inversion in the above electrophilic displacement is reasonable. The carbon atom undergoing displacement would be somewhat electron-deficient (resembling a carbonium ion), and p character is preferred to s in an incompletely filled orbital. The essential difference between concerted electrophilic and nucleophilic displacement is the filling of orbitals, the system X-C-Y having only one electron pair in the bonding orbital during electrophilic displacement but having a seccnd pair in a nonbonding orbital, to which the contribution of the central carbon atom is nearly zero, in nucleophilic displacement. Electron repulsion in the non-bonding orbital makes inversion practically mandatory in nucleophilic displacement, while its absence leaves the stereochemistry more flexible in electrophilic displacements. In electrophilic displacements where the carbon atom acquires considerable carbanion character, the central orbital would acquire more s character (sp9 and retention would be favored. Any cyclic three-center bonding resulting from orbital overlap of X and k' would also tend to favor retention. Because of the inherently tentative interpretation of any unprecedented results, we are searching for analogous reactions to support or revise our initial conclusions. Acknowledgment.-\Ye thank Drs. H . N'. Dodgen and S. W. Peterson for helpful discussions and for making available neutron counting equipment a t the m'ashington State University Xuclear Reactor, and the National Science Foundation for financial support (KSF-G 19906).
VI
p-
p.0 OH'
v
IV
R = p-Chlorophenyl
isomer (IV) via hydrolysis of an intermediate 0-alkyl sulfoxide adduct. To complete the cycle, the trans sulfoxide in like manner was converted to the cis as shown in the annexed scheme and described in detail below. Cyclization of 3-(p-chlorophenyl)-l,5-dibromopentanej was effected with sodium sulfide in absolute ethanol to provide 4-(p-chlorophenyl)-thiane (I), m.p. 70-71O. (Anal. Calcd. for CI1H1&YS: C, 62.11; H , 6.16. Found: C, 62.10; H , 6.22.) Oxidation of the sulfide I with aqueous sodium metaperiodate6 and recrystallization of the crude sulfoxide7 from ethyl acetate provided pure cis-4-(p-chlorophenyl)thian-1-oxide, m.p. 172.5-173', ~"mf;': 1058 cm.-', (S = 0). (&And. Calcd. for Cl1HI3ClOS: C, 57.76; H, 5.73; S, 14.04. Found: C, 57.78; H , 5.76; S, 13.81.) The dipole moment of I1 in benzene solution was found to be 3.98 f 0.02 D.8 in fair agreement with 4.30 D. calculated4 from models and model compoundsg for the chair conformation of the cis sulfoxide. ( 7 ) J . I) R o b e r t s , E. R T r u m b u l l , R . W . B e n n e t t a n d R . h r m s t r o n g , J . A m . Chem. Soc., 72, :311ci (1950). Alkylation of I1 with triethyloxonium fluoroborate1° in DEPARTMEST OF CHEMISTRY DONALDS. MATTESON methylene chloride afforded in 76% yield the desired Jt'ASH1SGTO.T STATE USIVERSITV JAMES 0. \vALDBlLLIG kinetically-controlled alkylation product, l 1 cis--l-(PPULLMAN, WASHINGTON chloropheny1)-1-ethoxythioniacyclohexane fluoroborate RECEIVED J A N U A R Y 14, 1963 ( H I ) , m.p. 107-108°. (Anal. Calcd. for C13H18BClFdOS: C, 45.32; K, 3.26; neut. equiv., 344.5. THE INVERSION OF SULFOXIDE CONFIGURATION Found: C, 45.13.43.55; H, j.30, 5.22; neut. equiv., Sir: 347.) a'hen I11 was dissolved in dilute aqueous sodium The configurational stability of sulfoxides was conhydroxide, one equivalent of base was consumed and firmed in 1926 with the resolution of three sulfoxides by shiny platelets of a new sulfoxide, m.p. 119-121°, preHarrison, Kenyon and Phillips.' Soon thereafter cipitated in 93y0 yield. Recrystallization from ethyl examples of geometrical isomerism attributable to the acetate-hexane provided pure trans-4- (p-chloropheny1)sulfoxide grouping were provided.? This communicathian-1-oxide (IV), m.p. 120-120.5', vz;: 1054 cm.-', tion now reports the first examples of the inversion of the configuration of the sulfoxide group.3 (S = O), dipole moment in benzene 2.60 D.8 (calcd. for The recent report" that alkyloxysulfonium salts hychair conformation of trans sulfoxide, 2.24 D . ) . (.And. drolyze in isotopically enriched water to yield the parent ( 5 ) X. L. Allinger a n d S.Greenberg, ibid., 81, 5733 ( 1 9 5 9 ) . (0) iY,J . Leonard and C. R. Johnson. J . Org. Chem., 2 7 , 281 (1962). sulfoxide containing oxygen-18 suggested that such a ( 7 ) I t is noteworthy t h a t oxidation of I with periodate provided a mixture reaction might proceed with inversion of configuration consisting of 707, cis sulfoxide (11) a n d 30% L Y Q ~ S sulfoxide ( I V ) a s ascer1.
KX',
\
/
S=O
--+
S-OK /'
H:O
+
X-
-+
/
O=S \
+ KOH + H X
(1)
In the present study cis-4-(p-chlorophenyl)-thian1oxide (11) was transformed to the corresponding trans (1) P . W. B Harrison, J. Kenyon a n d H. Phillips, J . Chem. Soc., 207Y (1926). ( 2 ) E. V . Bell a n d G . &I. B e n n e t t , i b i d . , 1798 (1927). ('3) Walden inversion has been shown t o occur during trans-esterification of sulfinic esters which have related molecular dissymmetry a t t h e sulfur a t o m : H Phillips, i b i d . , 127, 2352 (1925) ( 4 ) S J . I.eonard a n d C . R. J o h n s o n , J A m Chein Soc., 84, 3701 ( I Y G Z ) .
tained b y infrared analysis On t h e o t h e r h a n d , oxidation of I with hydrogen peroxide in acetone or with perbenzoic acid in chloroform yi-lded approximately 307, I1 a n d 7 0 R I Y , T h e implications of these a n d similar d a t a bearing on t h e mechanism of oxidation of sulfides will he discussed in t h e full paper. At t h e same time detailed infrared studies of these compounds will be presented. 1,. (8) T h e dielectric a n d density measurements were made by M r . N e u m a n n of these 1.aboratories. (9) Thian-1-oxide, 4 19 I ) . [A 1. Vogel a n d C. W.N. C u m p e r , J . Chem. SOL..:1321 (1959)l a n d p-chlorotoluene, 1 9.j I). [ S . I.. Allinger, S. P Jindal a n d M. A . UaRooge, J Ovx. C h e m . , 27, 4290 1 1 Y i i 2 ) ) f 10) H. Meerwein, E. Battenberg. H. Gold, E Pfeil a n d G. Willang, J . Praki. C h e n i . , 164, 83 11939). (11) S G . Smith a n d S . Winstein, l'etvahedvo?i, 3 , 3 1 7 i l Y a S ) .
c.
COMMUNICATIONS TO THE EDITOR
.Ipril 5, 1963
Calcd. for CllHl&lOS: C, 57.76; H , 5.73. Found: C, 5i.55; H , 5.76.) Material identical (m.p., m.m.p. and infrared spectrum) with IV was obtained by chromatography of the residue from the mother liquors from the recrystallization of 11. In agreement with the structural assignments, I1 was eluted from alumina prior to IV. Reaction of IV with triethyloxonium fluoroborate gave in 5370 yield trans-4-(p-chlorophenyl)-l-ethoxythioniacyclohexane fluoroborate (V), m.p. 166-167'. (Anal. Calcd. for Cl3HlsBC1F4OS: C, 45.32; H, 5.26; neut. equiv., 344.3. Found: C, 45.33; H , 5.06; neut. equiv., 343.) Hydrolysis of V with dilute alkali provided in 9270 crude yield the cis sulfoxide I1 identical (m.p., m.ni.p. and infrared spectrum) after a single recrystallization with that obtained above by the oxidation of the sulfide with periodate. Infrared spectra indicated that the crude sulfoxides IV and I1 isolated from solvolysis of I11 and V, respectively, contained less than 5% of contaminating isomeric sulfoxide. In these examples a hydrolytic pathway involving inversion a t the sulfur atom significantly predominates over alternates, e . g . , carbon-oxygen cleavage. Oxidation of the sulfide I with potassium permanganate in glacial acetic acid gave 4-(p-chlorophenyl)thian-1,l-dioxide (VI), m.p. 208-209', v::;~" 1300, 1120 cm.-', (SOs). (Anal. Calcd. for CllHl3C1O2S: C, 54.07; H, 5.35. Found: C, 53.90; H, 5.58.) The same sulfone was obtained by oxidation of I1 and IV with permanganate. Work now in progress in this Laboratory will provide additional examples of sulfoxide inversion, including the interconversion of optical isomers. ~ ~ A Y NSTATE E CNIVERSITY DEPARTMEST OF CHEMISTRY DETROIT2, hfICHIGAS
CARL R.
JOHNSON
RECEIVED J A N U A R Y 31, 1963 ISOTOPE EFFECTS IN RECOIL TRITIUM REACTIONS WITH HYDROCARBONS'
Sir:
The two highest yield reactions of recoil tritium atoms in scavenged alkane systems are almost invariably those involving abstraction of a hydrogen atom or substitution for it by the tritium atom. Several recent publications have concerned themselves with the mechanistic significance of the relative yields of these two reactions, both from individual molecules alone*-j and from two parent alkane molecules in competition with one another in the same system.6 One suggested interpretation of these measured yield^^.^ is consistent with most of the data, but appears to be in direct conflict with previously reported isotope effects observed in hydrogen abstraction from methane by recoil tritiu~n.~ I n the context of the simple model for the reactions of a very energetic atom slowing down into an energy range for which chemical bond formation is possible, v-lnseveral effects could possibly exist that might
1021
lead t o differences in results measured for isotopicallysubstituted molecules. If the average energy loss per non-reacting collision is affected by isotopic substitution, different numbers of "hot" collisions would be expected in traversing a given energy range, and thereby could lead t o different fractions reacting in that energy range for isotopic molecules. Isotope effects arising from differences in average energy loss are designated here as moderator isotope effects, and have been invoked in explanation of experiments involving CH4vs. CD,, and CH3Fvs. CD3F.jm9 If either the energy range over which the substitution reaction occurs or the probability of reaction per collision varies with isotopic substitution, then isotopic differences could appear. The over-all effect of these two possible differences will be defined here as probability integral isotope effects. I n any particular real system, any or all of these sources of isotopic variation could be present. In general, moderator and probability integral isotope effects can be distinguished through experiments involving measurements of reactions occurring simultaneously in the same system.6,10 In such direct competitions possible variations from moderator differences are essentially eliminated since all the molecules are exposed to the same spectrum of tritium energies. The abstraction reaction has been reinvestigated with higher precision measurements on CH2D2as shown in Table I. The substitution of T for H has been tested for isotope effects through competitions between protonated and deuterated methanes and n-butanes, as summarized in Table 11. The samples were analyzed by radio-gas chromatography; the nuclear reaction He3 (n,p) H 3 served as the tritium source. TABLE I RELATIVEYIELD OF TRITIATED MOLECULES FROM TYPICAI RECOILTRITIUM EXPERIMENTS IVITH CHzDz Sample Scavengera (HT 4- Yields (relative units)n number
(cm.)
HT/DT
DT)/RT
HT
D T ,Methane-l
438 Sone 2.34 1.11 94 39 119 1.51 0.86 41 27 79 440 0 . 0 2 12 392 1.02 0 2 1.34 0.79 34 26 75 143 3.27 0 2 1.34 0.79 36 27 79 1.32 0.79 35 27 78 445 4 . 9 0 Oz a Total pressure 100 cm., including 1.0-1.6 cm. of He3; irradiated for 60 min. in a neutron flux of 5 x 10'O neutrons/cm.2/sec. A yield of 7 5 represents 25';; of the total tritium activity stopped in the gas phase. TABLE I1 DISTRIBUTION OF RADIOACTIVITY B E T ~ V E E S PARESTCOMPOUNDS F O R COMPETITIVE RECOIL T R I T I U M r < E A C T I O S S IS THE GASP H A S E
Experiment number
ii-Butane
Xethane
Pressure ratio butane methane
Specific acti\-ity ratio Obsd. Cor."
418 CIHIO CDI 0.109 2.91 2 98 2 89 2.96 119 CDI ,109 CrHio 422 CIHii) CHI ,113 2 19 2 23D 2 .%G 2.30 123 CHa ,113 CIHIO 112 CHI ,112 1 81 1.88 C4Dio ( 1 ) This research wa- supported by A.E.C. C o n t r a c t S o . A'~-(11-1)-~07, a Corrected for production of methane4 by reaction of T with a n d b y a Xational Science Foundation Pre-doctoral Fellowship ( J . W . R . ) . n-butane. The original measurements of substitution into ( 2 ) 1). Urch a n d R . Wolfgang, J . A m . C h e m . S o c . , 83, 2982 (1961). fully-protonated methane and butane6 gave values for the specific (.3) R . a'olfgang. e l a i . , "Chemical Effects of Nuclear Transformations," activity ratio ranging from 2.29 t o 2.60. This scatter has now \-
