Oct. 5, 1960
COMMUNICATIONS TO THE EDITOR
5253
creased, since the molar volume of the group -C(OH)=CHis smaller than that of the group -COCH2by about 4.0 ml./mole (estimated from the densities of unsaturated alcohols and isomeric carbonyl compounds) ; if the internnl Hbond is taken into account, this difference would undoubtedly be somewhat greater. If the ring formation has the positive volume requirement RESEARCH INSTITUTE FOR M. M . PECHET described above, the molar volume of the enol MEDICINEAND CHEMISTRY R . H. HESSE form should be larger than that of the keto form H . KOHLER by about 5 ml./mole. The effect of pressure on CAMBRIDGE 42, MASS., A N D MASSACHUSETTS GENERALHOSPITAL this equilibrium was studied by Kabachnik, BOSTON,MASS. Yakushkima and Kislyakova,’ who reported no RECEIVEDAUGUST4, 1960 significant change in K for the pure substance. Since the rate of interconversion is extremely T H E KETO-ENOL EQUILIBRIUM OF ETHYL variable (depending on traces of impurities”) ACETOACETATE UNDER H I G H PRESSURE i t appeared desirable to repeat this work. The Sir : new data (Table I) show that K in the pure liquid It has been demonstrated in recent years that increases with pressure; the molar volume of the studies of the effect of pressure on reaction rates enol form exceeds that of the keto form by 1.0in the liquid phase often permit certain conclusions 1.5 ml./mole. This would suggest that it may be possible to recognize reactions involving a cyclic to be drawn regarding the mechanism involved. For instance, reactions are accelerated if they transition state by a retarding effect of pressure. proceed through a transition state that has a An experimental program to test this statement greater separation of charge than the reactant(s) is about to start in this laboratory. and vice versa, since the intense electric field of an TABLE I ion causes local compression of solvent molecules.2 K AV I n the expression d In kldp = -AV*/RT, the fi(atm ) voenolb keto/enol (ml /mole) c volume of activation is negative in such cases. 1 7.7 12.0 -1.5 On the other hand, a reaction is decelerated 1350 7.2 13.0 -1.0 ( A V* is positive) if the formation of the transition 2500 7.0 13.2 -1.3 state depends on homopolar bond breaking and 3700 6.4 14.6 vice versa,3 since the sum of the van der Waals The apparatus will be described a t a later date. At radii of the fragments exceeds that of the re- 25’. Samples of the ester were withdrawn without releasing the pressure, collected in a quartz vessel and analyzed actant. a t once in the usual way ( R . H.Meyer and P. KappelIt appeared that another feature often of interest meyer, Ber., 44, 2718 (1911)) Care was taken t o insure in mechanistic studies, i e . , formation of a cyclic the system was a t equilibrium and that interconversion transition state, could be subject to a pressure during analysis was negligible. Calculated from (In K, e f f e ~ t .A ~ comparison of the densities of straight In K 1 ) = - A V / R T . chain hydrocarbons shows that the molar volume of Acknowledgment.-This work was done a t the n-CmHPm+2 exceeds that of n-Cm--6H2,,-10 by 96 Rohm and Haas Research Laboratories. The f 1 ml./mole (m ranging from 11 to 17). This author had the benefit of many helpful discussions difference is a measure of the volume of hexa- with Mr. 0. H. Loeffler and Drs. C. Huggett and methylene, -(CH2)6-. This value is 12 ml./ R . Iwanciow. mole smaller than the molar volume of cyclohexane ( 7 ) br. I. Kahachnik, S. E. Yakushkima and N. V . Kislyakova, (108 ml./mole). Parachor data5 on ring structures Doklady A k a d . X a u k . , S.S.S.R., 96, 1169 (1954); rf. C . A . , 49, 8815 similarly suggest that ring structures have greater (1955). The authors stated t h a t the system was allowed 4 hours to volume requirements than straight chains. Pre- reach equilibrium; in this work i t was found t h a t a t least 20 hours sumably the core of such doughnut-like molecules was necessary. is too small to be accessible to other molecules. STATE UNIVERSITYOF NEW YORK CENTER %-ILLIAMJ. LE NOBLE I n this work, the keto-enol equilibrium was LONGISLAKD studied as an example. If the process of forming OYSTERBAY,NEW YORK RECEIVEDAUGUST23, 1960 a cyclic structure such as the enol form of ethyl acetoacetateB does not contribute to the change in molar volume, the equilibrium constant ( K T H E STEREOCHEMISTRY OF JACOBINE keto/enol) should decrease as the pressure is in- Sir. (1) For an excellent review, see S. D. Hamann, “Physico-Chemical Recent investigations‘ have shown all previous Effects of Pressure,” Academic Press, Inc., New York, N. Y., 1957. structures proposed for jacobine, jaconecic acid (2) H . C . David and S. D. Hamann, Trans. Fav. SOC.,SO, 1188 and isojaconecic acid to be incorrect. The struc(1952!. (3) A. E . Nicholson and R. G. W. Norrish, Disc. Far SOC.,97 tures of these compounds are correctly represented (1956). by I, I1 and 111, respectively. We wish now to (4) C . Walling aod J. Peisach have considered this possibility present evidence which permits assignment of recently in the dimerization of isoprene to cyclic products ( T m s J O U R N A L 80, 5819 (1958)). stereochemistry to the above compounds, as ( 5 ) S. Sugden, “The Parachor and Valency,” Geo. Rutledge & shown in l a , IIa and IIIa.
SO0 cm.-l, w-hich was identical with VIb, the 3hydroxyetiolactone prepared from the synthetic etiolactone (V). The isolation and characterization of 5a-(4,5)dihydroaldosterone (Ia) and 3$0H,Sa-(4,5)tetrahydroaldosterone (Ira) indicates that the ring A reduced products with A/B trans ( 5 a ) in configuration are favored.
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Sons, Ltd., London, 1929. (6) G. W. Wheland, Ch. XIV, “Advanced Organic Chemistry,” 2nd Edition. John Wiley &Sons, Inc., h-ew York, N. Y.,1949.
(1) R. E. Bradbury and S. Masamune, T i m J O U R N A L 81, , 5201 (19591, andalso see T. A. Geissman. Ausl. J. Chcm., 18, 247 (1959).
