Nov. 20, 1964
COMMUNICATIONS TO THE EDITOR
Reaction of excess 1,l-dimethylallene (TIb), 3-chloro3-methylbutyne, and potassium t-butoxide a t - 40' resulted in formation of l-isopropylidene-2-(2-methylpropeny1idene)cyclopropane (Vb), b.p. 39-41 (2 m m . ) , of fair purity in 19% yield. Considerable polymerization occurs during addition, and 1,l-dimethyl-2-methylene-3 - ( 2 - methylpropeny1idene)-cyclopropane (Vc), the product anticipated by capture of dimethylvinylidene carbene (IV) by the internal double bond of IIb, has as yet not been isolated. The structure of Vb was assigned on the basis of its analysis, its infrared absorption a t 5.03 and 5.72 p for allenic and exo unsaturation, and its n.m.r. peaks for cyclopropyl hydrogens (multiplet) a t 7 8.63, olefinic methyls (multiplet) a t S.26, and allenic methyls (multiplet) a t 8.15.5 Adducts Va and Vb are affected rapidly by heat, acids, and oxygen; studies of their transformation products are in (9) T h e distillation product does not exhibit n.m.r. absorption for vinyl protons as anticipated if Vc were present. (10) Product \'a rearranges almost quantitatively t o an isomeric hydrocarbon when heated under nitrogen a t 90-150° or when gas chromatographed a t 150' on Carbowax 2 O M or SE-30. Vb rearranges into other products under such conditions. (11) This research has been supported by the Petroleum Research F u n d , Grant 454-A.
DEPARTMENT OF CHEMISTRY ROLAND F. BLEIHOLDER OHIO STATE CSIVERSITY HAROLD SHECHTER COLUXBVS, OHIO RECEIVED ACGVST4, 1964
of carriers, separations were made by gas chromatography using a 3-m. silicone grease column with temperature programming. Fractions were trapped a t the end of the column, and after dissolving in ethanol, they were counted in a liquid-sheath Geiger counter. Two measurements were made: the first, 4 hr. after collection, to establish transient equilibrium between 80mBrand its daughter, and the second after 20 h r . , so that 80mBr(4.5 hr.) and 82Br (36 hr.) were both determined in the same experiment. The total activity obtained from the column was normalized to the over-all organic yield determined independently from a small portion of the irradiated material taken before analysis. Table I shows values for the isotope ratios, established on the basis of several experiments, of the seven major products from neutronirradiated bromoethane. Variation of the time of irradiation from 1 to 24 hr. did not alter the observed ratios, so that the effects cannot be ascribed to thermal exchange or slow reactions of the inorganic bromine with small amounts of impurities in the irradiated mixtures. TABLE I
RATIOS OF I S O T O P l C YlELDS O F P R O D U C T S FROM NEUTROS-IRRADIATED BROMOETHANE
Sir :
Yield for 80mBr/yield for a*Brhlolar fraction oi B n present during irradiation 01 0 2 0 .5 0 75 10 - 3
7 -
Product
Differences in the Behavior of Bromine Isotopes Activated by Neutron Capture in Bromoethane
5033
C2HSBr CH3Br CHZBr2 CHBra CHzBr.CH2Br CH,. CHBrz CH2BrCHBr, Total organic
0 2 1 1 0 0 0 0
96 40 82 06 74 77 45 96
1 03 2 15 1.76 1 08 0 72 0 80 0 46 0 98
1 2 2 1 0 0 0 1
47 40 02 30 74 86 52 08
1 2 2 1 0 0 0 1
47 50 15 47 70 93 53 13
1 58 3 05 2 28 1 53 0 61 0 89 0 61 1 09
have reported differences in Several recent the isotopic yields of organic radiobromine formed by neutron capture in organic bromides. Some of these effects, for example, in bromoform,' were shown to be The root-mean-square deviation of yields from redue to thermal exchange reactions. Longer lived peated runs was + 5%, except in the case of the methyl isotopes may then show a greater degree of exchange, bromide fractions, where larger errors ( f20%) were and yields are dependent upon the time of i r r a d i a t i ~ n . ~ obtained; apart from this fraction, the errors only The other isotope effects reported for liquid s y s t e r n ~ ~ ~ ~ slightly exceeded those expected from the statistics of are found in chloro- or fluorobromomethanes, and are counting ( f3%). discussed extensively by Filatov. Wexler and Davies have shown5 that the percentage The effects reported in the bromopropanes6j7 have of charged atoms formed by neutron capture is different been in dispute for some years, and Willard has refor each bromine isotope, and Nesmeyanov and others ported* several unsuccessful attempts to reproduce the (see ref. 5) have attempted to explain isotopic differences results of Capron and his co-workers, who claimed to on the basis of ion-molecule reactions. The recent have found a greater total organic yield for R2Brthan discoverylO that most 82Br is produced through an for 80mBr. isomer 82mBr(6.2-min. half-life) suggests that the prodWe wish to report isotopic effects in mixtures of broucts from this isotope may arise predominantly from moethane and bromine irradiated in the thermal column processes associated with internal conversion, for of British Experimental Pile O . , a t A.E.R.E., Harwell example, the formation of highly charged atoms'] by (slow neutron flux 4 X lo5 sec. - I ; y-ray flux less emission of Auger electrons. Reactions could then than l o 4r./hr.). Inorganic bromine, as Brz or HBr, was proceed by charge transfer from neighboring molecules, first removed with an aqueous wash, and after addition or through interaction with localized radiolysis products formed by the Auger electrons.12 Differences in t h e (1) A. N . Nesmeyanov, A. E. Borisov, and I. Zvara, Radiokhimiya, 1, 323 (1959). isotopic yields would then be expected if the activation (2) A. N. h'esmeyanov, A. E. Borisov, E . S. Filatov, V . I. Kondratenko, of 80mBrwas predominantly through recoil. C.-H Chang, K . Panek, and B. M . Shukla, i b i d , 1, 712 (1959). (3) A . N. Nesmeyanov and E S. Filatov, i b i d . , 3, 501 (1961). (4) M . Milman and P. F 1). Shaw, J . Chem Soc., 2101 (1956). ( 5 ) E . S. Filatov, U s p . K h i m . , 3 , 752 (1962). (6) P. C . Capron and E Crevecoeur, J . C h e m P h y s . , 21, 1843 (1953). (7) D. J. Apers, P . C. Capron, and L. Gilly, J chim. p h y s , 64, 314 (1957). (8) J. E Willard, "Chemical Effects of Nuclear Transformations,"
International Atomic Energy Agency, Vienna, 1961, p. 215.
(9) S. Wexler and T H. Ilavies, J . C h r m . P h y s . , 2 0 , 1688 (19.52). (10) (a) J . F Emery, 148th Sational Meeting of the Amei-ican Chemical Society, Chicago, Ill., Sept., 1964, Abstract R26; ( b ) 0 U . Anders, % b i d Abstract R 2 5 . (11) (a) S. Wexler and T. H. Davies, J . C h r m P h y s , 18,376 (19.70). (b) S. Wexler, P h y s . R e a , 93, 182 (1954) 112) P. R Gei-sler and J. E Willard, J . P h y s . Chepn., 67. 1 f i i . i ( I O ( i 3 )
COMMUNICATIONS TO THE EDITOR
5034
Vol. 813
The NOs- effect is attributed to a decrease in GH? with a concomitant increase in GH2O2. Quantitatively, these results are consistent with the assumption that an intermediate in the spur disappears by a firstorder process in competition with reaction with Nos-. This is a pseudo-unimolecular process since the NO3effect is temperature independent and not proportionali to Ti/v. Plausible arguments have been presented8 for the ea,-, instead of the H atom, as the main precursor of molecular Hz. Assume the eaq- to be the intermediate which reacts with X03-. Then, eq. I would yield a lifetime for the ea,- in the spur of 5 X lo-'" sec., based on a rate constantg for reaction of NOa- with ea,,- of 8.15 X 10g -\I-' set.-'. This is much longer than the lifetime of 6 X IO-" sec. to be expected for the eaClin 0.8 1V sulfuric acid owing to reaction with Ha,+ (13) W. E Harris, C a n . J C h e m . , 39, 121 (1961): alone, based on a rate constantg of 2.06 X 101" .ZIP' T. E. GILROY set.-'. This, together with absence of any marked NJC'CLBAR PHYSICS LABORATORY GEORGE MILLER influence of pH, forces the conclusion t h a t the NOaOXFORD,ESGLAND P. F. D. SHAW effect is not attributable to reaction of NOa- with RECEIVEDSEPTEMBER 16, 1964 ea,-, This is consistent with the observation of Slahlman'o that there is no effect of Haqf on the dependence of GH?on NOS- concentration. XIageeL1proposed that three consecutive elementary Kinetic Evidence for H 3 0a s the Precursor of Molecular processes yield OH and H 3 0 as the primary chemical Hydrogen in the Radiolysis of Water' intermediates in the radiolysis of water. LVith these assumptions, the results in Table I indicate that di- and tribromoethanes are more often formed with s2Br than with somBrand suggest that hydrogen atom substitution proceeds more readily through a mechanism involving Auger electron emission. Conversely the scission of carbon-carbon bonds, and the substitution of bromine atoms in heavily scavenged systems, may be caused predominantly by atoms having recoil energy. Besides the compounds listed, and carbon tetrabromide and tetrabromoethane, small yields of compounds containing more than two carbon atoms have been found in this system. Since such products may be important in determining reaction mechanisms, a fuller discussion is withheld until complete analyses can be reported.
Sir: GH20:a and GH;?bfor the decomposition of water by 6oCo y-radiation and G H for ~ ~ the decomposition of water by fission recoils are markedly dependent on solute concentration. This is attributed to reaction of solute with free-radical precursors, e.g., reaction with OH radicals before they combine to form Hz02.2a Attempts to derive the observed dependence from the "diffusion-kinetic" model have resulted4 in a quantitative inconsistency. We have found that the precursor of molecular H 2 disappears by a first-order process. Therefore, homogeneous kinetics can be substituted for diffusion kinetics to express the dependence of GH2on solute concentration. Evidence to support this suggestion resulted from further examination of the striking effect6 of NOaon Ce4+ reduction in sulfuric acid solutions. Tl+ increases G(Ce3+) from 2 G ~ ~ 0 G ~H - GOH to %GH?o? GH GOH. NOa- a t concentrations greater than 0.01 III markedly enhances G(Ceat) both in the presence and in the absence of T1+, the effect being equal in both cases. The NO3- effect is not p H dependent; no significant difference was observed between 0.08 and 0.8 A'sulfuric acid. The enhancement,6 AG(Ce3+),for NOa- concentrations from 0.1 to 5.0 -If is quantitatively expressed by eq. I.
+ +
1, SG(Ce3+) = 0.185
+
+ o.O804/[NO3-]
(I)
(1) This research was sponsored b y t h e U. S . A t o m i c Energy Commission u n d e r contract w i t h t h e Union Carbide Corporation. ( 2 ) ( a ) T. J. S w o r s k i , J . A m . Chem. SOL., 7 6 . 4687 (1951); Radiation R e s . , 2 , 227 (195.5, ( b ) J . A . Ghormley a n d C. J. Hochanadel. ibrd., a , 227 (1955). ( 3 J . \V. Boyle, W. F. Kiefer, C. J . Hochanadel, T. J. Sworski, and J. A. Ghormley, Proc. I n t r r n . Conj. Peacefnl L-ses A t . E n e v g y , 7 , 576 (1957) (4) A . K u p p e r m a n in " T h e Chemical a n d Biological Action of Radiations," Vol. .5. h f . Haissinsky, Ed., Academic Press. N e w York. N . Y., 1 9 6 1 , Chapter 111. (.5) T. J . S w o r s k i , J . A m . Chem. S o c . , 7 7 , 4689 (1955). (6) H. A . Mahlman, J . P h y s . Chem.. 64, 1598 (1960).
H20---t HpOi
HtO+
+ e+ OH
+ H10 --+ H30i + e- +H30
(1)
(2) (3)
We suggest t h a t H 3 0 is the main precursor of molecular H z and disappears by three processes
+ H2O -+- Ha,+ + e Ha0 f H30 --+ Hz + 2H20 Ha0 + OH +2H20
Ha0
aq
(4)
(5) (6)
Assume that H 3 0 disappears by a first-order process, k7[H30], in competition with reaction with NOa-, ks[H30][N03-]. Then, eq. I yields a lifetime for H 3 0 in the spur of 2.30,'k8 or about 4 X 10-lo sec., assuming reaction with NOa- to be diffusion controlled. The pseudo-unimolecular rate constant, k i , in this model is taken to be k.,[H20] ks[H30] kg[OH]. In the decomposition of water by fission recoils,3 GH2 is independent of UOISOl concentration up to about 0.01 M , and then i t decreases approximately linearly with the square root of the 1;02S04 concentration. GH2,previously approximated3 as a square-root dependency, is quantitatively expressed by eq. 11.
+
1/GH2 = 0.571
+
+ 0.645[UOzS04]
(11)
This dependency is consistent with the assumptions that H 3 0 is the sole precursor of Hz and that it disappears by a first-order process in competition with reaction with uranyl sulfate, k g[ H 3 0 ][U02S04]. Equa(7) 3t. V. Smoluchowski, 2. Physik. Chem. (Leipzig), 91, 129 (1918). (8) H. A . S c h w a r z , Radialion Res. S u p p l . , 4 , 89 (1964). (9) J . H. Baxendale, el al., .Valuve, 201, 468 (1964). (10) H. A . Mahlman, Chemistry Division Annual Progress Report. Oak R i d g e Sational Laboratory. Oak Ridge, T e n n . , 1963, ORSL-3488. (11) J . L. hlagee, Radialion Res. Suppl., 4 , 20 (1964).
