NOTES
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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 T. Wagner-Jauregg and associates recently have (3) A careful recalculation of the published and unpublished results of Whittlelo on the acetone-d2 published2 rate measurements for the hydrolysis of DFP in solutions of cupric sulfate and a,a'-dipysystem shows that, in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. In 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 at 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 to 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 DFP 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. In 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).
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Vol. 62
TABLEI HYDROLYSIS OF DFP IN SOLUTIONS OF COPPER DIPYRIDYL SULFATE [A 1 .mol&.
PH
Downloaded by CENTRAL MICHIGAN UNIV on September 15, 2015 | http://pubs.acs.org Publication Date: July 1, 1958 | doi: 10.1021/j150565a026
6.0 6.0 6.5 7.0 8.0 8.0 9.0 9.0 10.0 10.5 10.9
1100 1100 830 390 47 47 4.2 4.2 0.16 0.018 0.0029
[Bzl pmoldl.
....
....
0.6 2.5 30 30 270 270 950 1130 1150
(Bib
~A[A][OH-] per rmn.
kBz[Ba)
25 25 160 429 536 536 438 438 200 20
