NOTES
866
Vol. 62
TABLE VI is small compared with AS2 is fortuitous and a conENTHALPY AND ENTROPY CHANQES O N SOLUTION OF NOBLE sequence of effects inherent in these similar solvents. Solubilities of the noble gases are presently GASESIN MOLTENNaF-ZrF4 (53-47 MOLE %) AT 1000’K. Gas
He Ne A Xe
Equilibrium concn. Enthalpy (moles/l.) change Cg X 102 Cd X 105 (kcal./mole)
1.22 1.22 1.22 1.22
33.2 20.0 9.15 4.30
6.2 7.8 8.2 11.1
Entropy change (e.u.) AS1 AS2 ASS
6.2 7.8 8.2 11.1
7.2 8.2 9.7 11.2
-1.0 -0.4 -1.5 -0.1
expansion over the concentration interval defined by a single solubility experiment. In light of the precision of the experiments, no real significance can be attached to the absolute values of A s a . It is possible that the fact that AS3
under examination in molten fluoride mixtures of considerably different chemical composition. Efforts t o attach some fundamental significance to the results will be deferred until additional data are available.
Acknowledgments.-The authors are especially indebted to Mr. W. D. Harmon and his associates who were responsible for mass-spectrometric analysis of the many samples submitted. Many interesting and valuable discussions with Messrs. F. F. Blankenship, M. Blander and R. F. Newton are gratefully acknowledged.
NOTES A REPLY TO LONG ON THE ACTIVATION ENERGY OF CH3 Hz
+
1, at constant acetone pressure. Moreover, the
quantity is also independent of the fractional decomposition a t least up to about 5% decomposition of acetone. This is shown by values obtained by Division of Pure Chemislru, National Research Council,Ottawa, Canada independent investigations for the function RCHJ Received August 9, 1967 Rg;Ha[A]a t 122”; the values are 3.3,43.73 and 3.5’ In a recent notel Long has argued that an in- x lO-lZ (mdecules cm.-2)-1/s sec.-’/z. The correct interpretation has yielded erroneous values fractional decompositions are, respectively, 0.04%, of the rate constants for some hydrogen abstraction 0.3% and 3%; the first fractional decomposition is reactions of methyl radicals. The methods by quoted in reference (3) although it is not given which these constants are obtained from the ex- explicitly in the original work (4). One further perimental data are now sufficiently well known to example taken from unpublished dataa taken in obviate the necessity of repeating them here.2 connection with other work shows that the amounts The crux of Long’s argument is that reaction (4) of CD4 and of CzD6 are linear in the amount of CO (Long’s numbering throughout) is important both formed in the photolysis of acetone-& in the range in the presence or absence of added reactants RH, (CO formed)/(initial acetone) = 0.2 to 1.0%. where CzH6 is the product of methyl radical combi- We therefore conclude that in the absence of added nation. Obviously (4) must be of importance if reactants, (4)is unimportant. (2) We might enquire as to the magnitude of the CH3 CzHe +CH4 CzHs (4) effect t o be expected. Following Long we write photolysis is allowed to proceed to a large fractional (kr/kz)([CzHsl/[Al) decomposition of the radical source and the question (kz[CH31 [A])-l(d[CH4]/dt) = 1 as a most becomes one of the relative rate of reaction (2) and [CZH&‘[A]can be taken as 2 X (4) under conditions normally encountered in this pessimistic estimate; this would imply that a steady type of study. We propose to summarize here some value had been attained by [CzHG] in a time which is short compared t o the time of an experiment. CHI CH3COCH3 +CHa f CHzCOCH, (2) The ratio k4/k2 may be approximated by k4/k2 = of the evidence which indicates that (4) and the (k4’/k2’) (k4/k4’) (k2’/kz) where the primed reactions subsequent reactioiis discussed by Long are not are important under normal conditions. CD3 + CDaCOCD3 +CD4 + CD2COCD3 (2’) (1) The quantity RcH,/R&~[A] is independent CD3 + CzHe +CD3H + CzHs (4‘) of all variables other than temperature if acetone In studying the system acetone-d6-C2H6 Wijnen’ pressure is kept above about 50 mm. and temperature above about 120”. In particular it is “inde- and McNesby and Gordon8 find that CD~H/CDIis pendent of intensity to a very good first approxi- nearly unity when [acetone-ds]/[C2H6] is unity; m a t i ~ n ;” ~actual figures show independence to this is found to be independent of temperature to (4) L. M. Dorfman and W. A. Noyes, Jr., J . Chem. Phys., 16,557 within 15% over a one thousandfold change of BY K. 0. KUTSCHKE AND E. W. R. STEACIE
+
+
+
+
( 1948).
(1) L. H.Long, THIDJOURNAL, 61, 821 (1957). (2) See, for example: (a) E. W. R. Steacie, “Atomic and Free Radical Reactions,” Reinhold Publishing Corp., Inc., New York, N. Y., 2nd Edition, 1954; (b) A. F. Trotmsn-Diokenson, “Gas Kinet.ics,” Academic Press, Inc., New York, N. Y.,1955. (3) A. J. C. Nicholson, J. A m . Chem. Soc., 73, 398 (1951).
(5) A. F. Trotman-Dickenbon and E. W. R. Steacie, zbzd., 18, 1097 (1950). (6) M. Weston, unpubhshed data, N.R.C. (7) M. H.J. Wijnen, J . Chem. Phys., as, 1357 (1955). ( 8 ) J. R. McNesby and A. S. Gordon, J . A m . Chem. Soc., 77. 4719 (1955).
NOTES
July, 1958
867
about 500". The most likely explanation of these MECHANISM OF REACTION OF DIISOdata is that k4'/k2' N 1. Similarly, work with PROPYL FLUOROPHOSPHONATE WITH mixtures of deuterated and normal methyl radiCUPRIC a,a'-DIPYRIDYL CHELATE' 1 and c a l ~ led ~ ~to' ~the conclusion that k&~' BY F. M. FOWHES, G. S. RONAYAND L. B. RYLAND that k2'/k2 exp (-1600/RT). The correction term thus becomes about 0.003 in the middle of the Shell DeVdOpment Company, Emeryville, California temperature range at 400°K. Such an effect is Received December 8 S 3 1067 negligible. T. Wagner-Jauregg and associates recently have (3) A careful recalculation of the published and unpublished results of Whittlelo on the acetone-d2 published2 rate measurements for the hydrolysis of D F P in solutions of cupric sulfate and a,a'-dipysystem shows that, in the absence of DZ ridyl. As we have recently determined the type and distribution of species in solution of cupric ni13 log RcH,/R&[A] = 5.986 - (2119)/T trate and a,a'-dipyridyl, a these equilibrium data while in the presence of 5 or 20 cm. DZbut with the have been correlated with the rate data of WagnerJauregg and associates to determine the catalytic same 10 cm. of acetone one finds activity of the various species and to obtain a bet13 log RcH,/R&,[A] = 5.829 - (2048)/T ter understanding of the mechanism of the reaction. Equilibria of Species.-In the above-mentioned This leads to an equation for the difference (A) publication3 it was shown from potentiometric tibetween RCR,/R&,[A] in the presence and absence tration curves that in solutions of the l : l chelate of a,a'-dipyridyl and cupric salts the following speof deuterium of cies exist: the acidic ion, DipyCu(H20)z++, (speA = 0.16 - 71/T cies A); the soluble non-ionized base, DipyCuindicating that all values in the presence of Dz are (OH)z, (species B2) and the weakly basic dimer, H too high below -170" and too low above this 0 temperature. I n the temperature range usually DipyCu( o)CuDipy, (species (BI)2). Presumably studied this difference may be as high as 15%. It H must be realized that over 40% of the methyl radicals which normally produce methane or an intermediate species B1, DipyCu(HzO)OH+, ethane may produce CHID in the presence of D2. also exists but was not detected in these studies. With so large a perturbation in the system, the The distribution of species a t various pH values degree of agreement achieved (to within 0.4 kcal. and concentrations may be calculated from the mole-') is considered adequate. The residual equilibrium constants for 30" uncertainty probably reflects the difficulty of A C,Bz + 2H+ K A = 10-18.20 (1) analyses in the presence of large excesses of non2A (BJ, + 2H+ Kaz -- 10-10.8' (2) condensable gases. It is t o be noted that these Experimental Data and Discussion uncertainties are in the region of several tenths of The rate data shown in Table I for the hydrolysis a kcal. mole-' rather than the several kcal. mole-' required by Long's hypothesis. Similar results may of D F P in the presence of copper dipyridyl sulfate be calculated from the data of other workers using were obtained by Wagner-Jauregg and associates of other methyl radical sources. We conclude, there- the Army Chemical Center Medical Laboratory.z fore, that reaction (4) is of minor importance in the The solutions contained 1150 pmoles/liter of both presence of D2, and, by inference, in the presence of ala'-dipyridyl and cupric sulfate and 2300 pmoles/ HZ as well. This is also in agreement with the liter of DFP in 0.05 M KN03. The data of Table I show how change of pH in observations of Davison and Burton," who noted that the ratio CH~D/CHIwas independent of de- solutions of 1: 1 cupric dipyridyl salts alters the procomposition provided [CO]/[A] < 0.02; this cor- portions of species A, B2 and (B1)2as calculated from K A and K,z. With increase of pH from 6 to responded to [CO]/[A] = 0.04. I n conclusion it might be pointed out that should 8, where only species A and (Bl)2 are present in apLong's hypothesis be correct, the value of the acti- preciable quantities, the rate is found to be proporH2 remains unsettled. tional to the product of [A] X [OH-] and is not afvation energy for CH, Davison and Burton'' determined only E2 - El fected by the concentration of (Bl)2. It may be and used EZ= 9.7 kcal. mole-'; the latter was shown that at pH 9 to 11, the rate is also dependent measured by TrotmawDickenson and Steacie6by the on [Bz]and on [OH-] as shown in the following very method to which Long objects. We feel, equation, which shows the contribution of each however, that on the basis af the evidence as a catalytic species to the observed rate whole, reaction (4) and subsequent steps may be kl(0bS.) = ~A[AI[OH-] k ~ z [ B s I ~oE-[OH-I ignored in the normal iiivestigations, and that E, By the calculated values of [A], and the obas given in reference 2(a> rests on as firm an ex- servedusing first-order rate constants (IC1) at p H 6 to 8, perimental foundation as most values of activation the third-order rate constant ICA may be calculated energy. from kl/[A][OH-] to be 1.4, 1.05, 1.13, 1.16 or
+
+
__
+
+
(9) J. R. McNesby and A. S. Gordon, %bid.,76, 1416 (1954). (10) E. Whittle and E. W. R. Steacie, J . Chem. Phys., Zl, 993
(1953).
(11) S. Davison and M. Burton, J . A m . Chem. Soc., 74, 2307
(1952).
+
(1) This paper reports work done under contract with the Chemical COTPI. U. S. Army, Washington 25, D. C. (2) T. Wagner-Jauregg, e t al., J . A m . Chem. Soc., 77, 922 (1955). (3) L. B. Ryland, G. 8. Ronay and F. M. Fowkes, THIRJOURNAL, 62, 788 (1958).
