4356
VOI. a4
COMMUNICATIONS TO THE EDITOR
Examples are known where the molecule-ion derived from olefinic hydrocarbons reacts with the neutral olefin to form the even-electron carbonium ion,K ;.e., the protonated olefin. Elementary considerations suggest that any reaction characteristic of firotonated intermediates should be subject to inhibition or modification in the presence of a strong Bronsted base. We wish to report an unambiguous example of this effect which proves, ipso facto, that the radiation-induced polymerization of cyclopentadiene is an ionic reaction. Cyclopentadiene has been found to polymerize reproducibly when irradiated a t - 78' with cobalt60 gamma-rays. The preparative technique follows the description given for other monomers,6 except for double distillation in vacuo below -40', and subsequent storage' a t - 78'. By this procedure, the spontaneous formation of dimer was reduced to insignificant proportions. Irradiation beyond a dose of 6.0 X lo" e.V.g.-', corresponding to 2.0% conversion, results in gel formation. The yield of polymer is linear with irradiation dose up to about 20y0 conversion (G(-CsH6) = 25,000). At doses exceeding 5.0 X 1019 e.V.g.-', the pure monomer is converted to a firm rubber, impervious to solvents. The extreme potency of ammonia in reducing the polymerization yield is shown by the representative data of Table I. TABLE I EFFECTOF AMMONIAON THE RADIATION-INDUCED POLYMERIZATION OF CYCLOPENTADIENE AT - 78' Ammonia concentration, mole fraction X 10'
None None Xone 1.8 0.20 ,012 .0054
Dose X 10-18, e.V.g. -1
1.0 5.0 10.0 50.0 50.0 50.0 50.0
Conversion to polymer, %
3.4 15.2 25.5 0.29 0.64 1.30 2.7
radical with ammonia by hydrogen atom abstraction is precluded in this system by the fact that = 3 kcal./mole,12 which must surely exceed the 1-kH-H bond dissociation energy in -/ cyclopentadiene. I n any event, hydrogen atom transfer reactions with ammonia would lead to chain transfer rather than the termination which must apply here. The preceding facts and arguments, taken together with the knowledge that cyclopentadiene polymerization is effected readily by a variety of Friedel-Crafts ionic catalysts, l 3 compel the conclusion that ammonia interferes a t such low concentrations by virtue of its possession of an unshared pair of electrons. I n other words, the basicity of ammonia renders i t an excellent ion scavenger. Apart from simple proton transfer to ammonia, we do not rule out the possible ammonolysis of a carbonium-ion intermediate, viz., R + 2"3 +R-NHz $- NH4+. These results suggest the possible utility of ammonia as an ion scavenger in the radiation chemistry of hydrocarbon gases and liquids, especially where chain reactions of unknown mechanism are prevalent. Further work is in hand, and will be reported in due course.
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(12) Calculated from F. D. Rossini, e: a!., "Selected Values of Chemical Thermodynamic Properties," N.B.S. Circular 500, 1952. (13) P. J. Wilson, Jr., a n d J. H. Wells, Chem. Rcws., 34, 1 (1944). (14) Undergraduate research participant (summer 1962) supported by National Science Foundation under grant G-21638.
M. A. BONIN" W. R. BUSLER FFRANCON WILLIAMS KNOXVILLE, TENNESSEE RECEIVED SEPTEMBER 17, 1962
DEPARTMENT OF CHEMISTRY UNIVERSITY OF TENNESSEE
TRANSFORMATIONS OF EBURICOIC ACID. 111.' A-NOR-3,I I-DIKETO-14-METHYLPREGNANE DERIVATIVES S i r:
In a previous communication from this laboratory2 we reported the degradation of eburicoic The interpretation of the action of ammonia is acid to A8-14-methylpregnene derivatives via the clarified by several points: (a) ammonia has a high a-pyrone I. We now wish to describe the conproton affinity, P N H 3 = 202 kcal./mole,6 this being version of this key intermediate to 14-methyl-Athe reason why ammonia acts as a very efficient nor-3-ketopregnanes and A5-pregnenes. Related base for ion-molecule reactions involving proton compounds such as A3(S)-A-norpregnene-2,20-&one3 transfer from hydrocarbon ions. (b) Ammonia have been shown to possess anti-androgenic activity has a large dipole moment (p = 1.46 debye) which of a high order.4 allows for strong ion-dipole interaction. (c) The Oxidation of the pyrone I with KMn04 in aceionization potential of ammonia = 234 kcal./ tone5furnished in 40% yield the A8-diketo acid IIa, rnole)'O exceeds that of cyclopentadiene (Ic~H~ = Xg;.., 268 nip ( 6 = m.p. 252-255'; [ a ] ~ %'E; 198 kcal./mole) I1; hence charge transfer from cyclo- 0,100). Its methyl ester, m.p. 178-179'; [ a ] ~ pentadiene to ammonia is inapplicable. (d) An 88'; cZx268 mp ( E = 9,400); on reduction efficient reaction of a neutral hydrocarbon free with zinc and acetic acid gave the saturated diketo ester IIb, m.p. 282'; [.ID 4- 70"; which was con(5) D. 0. Schissler and D. P . Stevenson, J . Chem. Phys., 24, 926 (1956). verted with ethanedithiol in BFa-etherate t o the (6) J. V. F. Best, T. H. Bates and Ff. Williams, Trans. Favoday 7-thioethylene ketal IIc, m.p. 211-212'; [ a ] f~ SOL..53, 192 (19132); J . Chem. SOL.,1531 (1962). 19'; and thence with sponge nickel in ethanol to (7) Irradiations were carried out a t the Oak Ridge National Labora-
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tory a t a dose rate of 3.2 X 101' e.V.g. --I min. --I; we are indebted t o Dr. C. J. Hochanadel for his very helpful cooperation. (8) A. P. Altshuller, J . A m . Chem. SOC.,77, 3480 (1955). (9) V. I.. Tal'roze and E. L. Frankevich, Doklady A k a d . . Y a k S S S R , 111, 376 (1956); see compilation b y D. P. Stevenson and D. 0. Schissler i n "The Chemical and Biological Action of Radiations," Vol. V, Academic Press, London, 1961, pp. 257-259. (10) K. Watanabe and J. R. hlottl, J . Chem. Phys., 26, 1773 (1957). (11) W. C. Price and A. D. Walsh, P r o c . Roy. SOC.(London). 8179, 201 (1911).
( 1 ) Paper I1 of this series, G. W. Krakower, J. W. Brown and J. Fried, J. Org. Chem., 27, in press (1962). (2) D. Rosenthal, J. Fried, P . Grabowich and E. F. Sabo, J . A m . Chem. SOL.,84, 877 (1962).
(3) F . L. Weisenborn and H. E. Applegate, ibid.,81, 1960 (1959). (4) L. J. Lerner, A. Bianchi and A. Borman, Pmc. SOC.E x p t l . B i d . M e d . , 103, 172 (1960). (5) P. Hofer, H. Linde and K . Meyer, Hclw. Chirn. A d a , 43, 1955 (1960). a n d earlier papers. (6) Rotations in chloroform a t 2Y0, unless indicated otherwise.
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COMMUNICATIONS TO THE EDITOR
Nov. 20, 1962
X
.
AcO O & =,
' ,
, I
AcO'
+
RP
= 0; X = OH; A* +4-RRzRz = 0 ; X = OCHa 2 = H; X OCH,
IIb, RI IId, RI
x
COOCH3
C-0
=
CHI C k2 or ka. If kobs.e is the observed rate constant for isotopic exchange and kobsa for rxciiiizatioii, then equations (2) and ( 3 ) can be \vritten, which provide isotop effects associated o n l ~ with . an equilibrium 11, ..J C J . C r a m . C. A. K i n g s b u r y and B. Rickborn. J. AIII Chew. 5m..83, 3688 :l981); i b ) 1). J ( ' r a m , I) .4. Scott and \V D. S i e l s e n . cbid., 83, 3696 (1961).
k,. CsHa I
CH?*CI CH=CHz
(+)-IN-2-d
Optically active ( +)-IV-2-h2 was dissolved in tert-butyl alcohol-0-D (0.386 M) which was 0.409 M in potassium tert-butoxide, and the solution was heated a t 75' for 257 min. The olefin was recovered (75%) through pentane extraction, olefins IV and cts-V2 were separated from one another by preparative vapor phase chromatography, and analyzed for deuterium and optical activity. Compound IV was completely free of deuterium," and exhibited the same rotation as the starting material, a Z 5 ~3.25' (1 1 dm., neat). Compound V contained only 0.46 of one atom of deuterium per molecule. The nuclear magnetic resonance spectrum of cis-V indicated that most of this deuterium was a t C-4. Clearly a minimum of 54% of the re-
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(2) D. J. Cram, i b i d . , 74, 2141 (1952). (3) Comhustion and falling drop method.
