COMMUNICATIONS TO THE EDITOR
1960
mental total pressures at 690°K amounted to 25%, while for the total pressure an average value of -9.5 the agreement within 8% is quite satisfactory. Thus, cal/mole deg for ACB was calculated over the temperathe monomer pressure equation (eq l),derived by thirdture range 690-1000°K from the heat capacities of the law considerations from the data at 800"K, is in good monomer and dimer' and their relative amounts in agreement with the original experimental data over the the gas phase. The resulting equations were given whole temperature range. above as eq 3-6. Using the corrected total and transpiration pressures Acknowledgment. This work was made possible by obtained above by combining eq 1 with the data, we calculated revised equations by a least-squares 2-plot the support of the Research Division of the U. S. treatment, for ptot and for the dimer pressure, p ~ . Atomic Energy Commission under Contract No. For the dimer ACp was taken as -11 cal/mole deg,' AT (04-3)-106.
C O M M U N I C A T I O N S TO THE EDITOR
The Elimination of HF from Vibrationally Excited 1,1,2-Trifluoroethane
Sir: We have extended our recent studies' on the elimination of H F from vibrationally excited fluoroethanes to the "hot" molecule CFZHCFHZ*, formed via the cophotolysis of (CFzH)zCO and (CFH2)2CO. Low pressures of the ketones (between 60 and 600 p total pressure, in a roughly 1: 1 mixture) were used in order to eliminate collisional quenching. At 20" the relative rate constants for formation of cis-1,2-, trans-l,Z, and 1,l-difluoroethylene are 6:3.8: 1. The cis and trans isomers were distinguished by their infrared spectra.a We observe the cis:trans ratio to be constant at 1.55 i 0.10 up t o 350", but (ICct8 krrans)kl,l- decreases monotonically from about 10:1 to 5: 1 over this temperature range (see Figure 1). Apparently the critical energies for cis and trans elimination are almost equal. The maximum difference between E,*,* and EtTan8* that could be concealed by our experimental scatter in kc18/klrans is about 1 kcal mole-'. This conclusion is based upon a crude RRK calculation3 with E(298"K) = 85.4, E(650"K) = 96.5, ECt,* = 59 kcal mole-', and 13 effective oscillators. On the other hand the decrease in 1,l- product at lower temperatures may be attributed t o a higher critical energy for this reaction. It is also consistent with previous observations that a halogenation promotes and /3 halogenation decreases the rate of dehydrohal~genation.~If we assume that E,,,* = Etrans*, then a second RRK calculation based on the parameters
+
The Journal of Physical Chemistry
given above and the data in Figure 1 yields a value of El,'-* = 62.4 kcal mole-'. This correlates well with the value of E* for CFHzCFHz*,which is in the range's3 59-62 kcal mole-', and with Maccoll's predi~tion.~ Since kCt8/krranS 'V 1.5 is a ratio of small whole numb e r ~it, ~is tempting to try to rationalize this result on the basis of reaction path degeneracy. However, we have been unable to find any consistent model which reproduces the cis :trans ratio. In examining the various possibilities both the three-center a,a elimination as well as the usual four-center (a,P elimination) transition state were considered. Consideration of the former was prompted by the fact that in separate experimentsa it was found that a,a elimination makes a significant contribution to the total elimination from "hot" CD&F2H*, since dt as well as dz vinyl fluoride was formed. Recently, Hassler and Setser7 observed a cis :trans ratio of about 6 for the elimination of HC1 from "hot" CClzHCC1HZ*; a t 25" the cis:trans:1,l- ratio was 25 :4 :1. These data' also argue against an explanation (1) See G. 0.Pritchard and R. L. Thommarson, J . Phy8. Chem., 71, 1674 (1967),for a summary. (2) H. G. Viehe, Chem. Ber., 93, 1697 (1960). (3) See 9. W. Benson and G. Haugen, J. Phys. Chem., 69, 3898 (1965),and ref 1 for definition and estimation of parameters. (4) A. Maccoll, Advan. Phws. Org. Chem., 3 , 91 (1965). (5) I n fact, in the high-temperature limit where activation energy ditterences are relatively unimportant all three products are formed in the ratio of small whole numbers (about 3 :2:1). (6) G.0.Pritchard and J. T. Bryant, submitted for publication. (7) J. C. Hassler and D. W. Setser, J . Chem. Phys., 45,3237 (1966).
COMMUNICATIONS TO THE EDITOR
1961
10.0
0
300
400
500
600
suggests the worthiness of investigations of the kinetics of reactions in or at the surfaces of micelles and the possible design of micelle catalysts. Though a few noteworthy contributions to the study of reactions in micelles have been made6 the employment of an amphiphile as a nucleophile or general catalyst has yet to be investigated. To this end we have investigated in detail the reactions of esters of type I with micelleforming agents of type 11, 111, and IV and with the nucleophilic agents V.
T,OK.
Figure 1. The variation with temperature of the rate of formation of l,%difluoroethyleneto 1, l-difluoroethylene.
&3-&CO~H~,,CH3
(n = 0, 416, 8)
e
OaSO[CHz111CH3
based on reaction path degeneracy alone. However, it should be pointed out that there are many more reaction possibilities in the chloro system and that the three isomeric chloroethylenes are also formed by a pathway not involving the “hot” trichloroethane intermediate. A number of experimental and theoretical studies are now being undertaken to characterize the alaand alp transition states and to determine the relative significance of each elimination. In order to explain the proportion of 1,l- product it may very well be necessary to take into account the alaelimination from -CFH2 in CFH&F2H*.
(1)’ (11
8
[CH~]~N[CHZIISCH~ HOCH2CHz [OCHzCHzI 170CeHd[CHz1i&Ha
(IIIY (IVY
The hydrolyses of esters I were followed spectrophotometrically at 410 mp or autotitrjmetrically. In the absence of agents 11, 111, IV, and V the hydrolyses of esters I were found to be first order in [OH-] and first order in ester between pH 8.0 and 10.5 ( p = 0.1 and 0.5). The rate constants for alkaline hydrolysis at 30” and p = 0.1 (kOH in liters per mole per minute) were 2651 (at 5 X to 1.7 X M ) for n = 0; 1165 Acknowledgment. This work was supported by a (at 5 X low5to 1.7 X M ) for n = 4; 953 (at grant from the National Science Foundation. 2.08 X to 8.33 X M ) for n = 6; and 340 (at 5 X t o 1.7 X loe4 M ) for n = 8. All the DEPARTMENT OF CHEMISTRY JAMES T. BRYANT
UNIVERSITY OF CALIFORNIA BERNARD KIRTMAN SANTABARBARA, CALIFORNIA 93106 GLYN0. PRITCHARD (1) A. L. Berger and K. LinderstrZm-Lang, Arch. Biochem. Biophys., 69, 106 (1957). RECEIVED FEBRUARY 10, 1967
Nucleophilic Micelles. I Sir: The study of micelles has provided much of the basis for the understanding of lyophobic bonding, a factor of paramount importance in the stabilization of the tertiary structure of proteins.’l2 The similarity in micelle and protein structure is seen from the X-ray determined tertiary structure of myoglobin3 and lysozyme4 from which it is evident that the nonpolar side chains are, in the main, located in the interior in lyophobic regions while the polar amino acid side chains are generally located a t the periphery of the protein. Much the same information is obtained from chemical and physical studies of other proteins.s This resemblance between the structure of micelles and enzymes
(2) G. NBmethy and H. A. Scheraga, J . Phys. Chem., 66, 1773 (1962). (3) J. C. Kendrew, et al., Nature, 185, 422 (1960). (4) D. C. Phillips, Sci. Am., 215, 78 (1966). (5) G. G. Hammes and H. A. Scheraga, Biochemistry, 5,3690 (1966). ( 6 ) E. F. J. Duynstee and E. Grunwald, J. Am. Chem. SOC.,81, 4540, 4542 (1959); J. L. Kurz, J. Phys. Chem., 66, 2239 (1962); D. G. Herries, W. Bishop, and F. M. Richards, ibid., 68, 1842 (1964); L. J. Winters and E. Grunwald, J . Am. Chem. Soc., 87, 4608 (1965); M. T. A. Behme, J. G. Fullington, R.Noel, and E. H. Cordes, ibid., 87, 266 (1965). (7) For n = 0 , Anal. Calcd for CsHsNO7NaS: C, 33.93; H, 2.14; N, 4.95. Found: C, 33.81; H, 2.28; N , 4.93. For n = 4, Anal. Calcd for C I ~ H ~ ~ N O I SC, N ~42.50; : H, 4.15; N, 4.13. Found: C, 42.11; H, 4.39; N, 4.32. For n = 6, Anal. Calcd for C1dHlsNOrSNa: C, 45.77; H, 4.94; N, 3.81. Found: C, 45.50; H, 5.24; N, 3.74. (8) City Chemical Corp. (9) Courtesy of Professor E. H. Cordes (originally obtained from General Aniline and Film Corp.). (10) For n = 3, Anal. Calcd for ClrHzaNzClz: C, 57.30; H, 8.94; N, 9.55. Found: C, 56.62; H, 9.14; N, 8.89. For n = 9, Anal. Calcd for CioHasNaCla: C, 63.66; H, 10.15; N , 7.43. Found: C, 63.01; H, 10.17; N , 7.42.
Volume 7 1 , Klzimhcr
rj
May 1967
