NOTES
716
oxide lines were noted. This result confirms the results of BoIz and co-~orkers.~ When the product of the hydrogen atom-ozone reactionwas warmed to about -78" and recooled to -196O, the X-ray pattern rev ed the presence of hydrogen peroxide. The data i ate that: (1) The hydrogen atom-ozone product as formed does not contain hydrogen peroxide. (2) Upon warming to -78' hydrogen peroxide is produced. (3) The product is not crystalline and its presence is most likely manifested by the intense halo at about 3.4 A. The data presented in this report are in general agreement with those reported by Tsentsiper5 and support the contention that a new peroxide species is formed by the reaction of atomic hydrogen with ozone. Hydrogen peroxide forms on warming. This is in agreement with the view of Kobozev12who postulates the reactions
H*
+ 03
- 196"
$204
-115' ----+
HzOz
+ 02
The data of T~entsiper,~ as well as that obtained in the present research, are summarized in Table I.6 The intent of these experiments was to determine if a superoxidic species could be detected in the frozen matrix of the hydrogen atom-ozone reaction product and to ascertain whether hydrogen peroxide is present. Although no proof for $he presence of a new peroxide was obtained, the absence of hydrogen peroxide suggests that a higher unstable peroxide is the progenitor of the hydrogen peroxide which is detected on warming. Acknowledgment.-The authors wish to thank G. P. Tilley of the Central Analytical Laboratories of Olin Mathieson Chemical Corporation for the interpretation of the X-ray diffraction patterns. (5) A. B. Tsentsiper, M. A. Danilova, A. S. Kanisheva, and A. I. Garbanev, Russ. J . Inorg. Chem., 4, 886 (1959)(in English). (6) The conoentration of hydrogen peroxide examined corresponds with ultimate concentrations of residual peroxide reported by Kob0sev.P
+
THE VINYL H SPLIT IN THE MERCURY SENSITIZED PHOTOLYSIS OF ETHYLENE Bu P. KEBARLE Department of Chemistry. University of Alberta, Edmonton, Alberta, Canada Receised September 10, 196.8
The primary reaction in the mercury sensitized decomposition of ethylene has been subject to a number of investigations, For some time there was no agreement whether the decomposition proceeds by a molecular elimination of hydrogen (1)or a split tovinyl radicals and hydrogen atoms (2). It then was shown by Cvetanovic1I2that the decomposition proceeds predominantly and possibly entirely by (1). It is the purpose of the present paper to show that the split to vinyl also owurs but only to about 4% of the total decomposition. The experiments were at 5 5 O , done in a flow system attached to a mass spectrometer.31~The general experimental procedures have been described elsewhere.5 The ethylene was co-decomposed with an (1) R. J. Cvetanovic and A. B. Callear, J. Chem. Phys., 23,1182 (1955). (2) A, B. Callear and R. J. Cvetanovic, ibid. 24, 873 (1956). (3) F.P. Lossing, D. G. H. Marsden, and J. B. Farmer, Can. J. Chem., 34, 701 (1956). (4) P. Kebarle, J. Phys. Chem., 67, 351 (1963). (5) M. Avrahami and P. Kebarle, ibid., 67, 354 (1963).
Vol. 67
excess of mercury dimethyl-d6. Recombination of the methyl radicals, produced by the decomposition of the mercury d i m e t h ~ l ,with ~ vinyl should lead to the formation of propylene-&. This methyl radical technique has been used with success in several ~ases.5'~ Due to the relatively high ratio of radical to substrate concentrations no complicating radical attack on the substrate occurs, but the secondary reactions are predominantly radical-radical interactions. I n a typical run the decomposition of 1 p7 of ethylene with 10 p of mercury dimethyl-& led to the formation of 0.288 p of acetylene and 0.02 p of propylene, in addition to 3 p of ethane (CzD6)and 0.02 p of propane (C3Ds). The latter two products originate from the decomposition of the mercury dimethyl. The hydrogen and methane formed were not determined. The reaction products were analyzed directly with the mass spectrometer and also trapped at liquid nitrogen temperature and separated by gas chromatography. The propylene was collected and readmitted into the mass spectrometer. It was found to consist of 85y0 C3H3D3, 7% C3H2D4,and 8% C3H4D3. The propylene-d3 must be formed by the recombination of CD3 with vinyl radicals. If all the vinyl radicals originate from the primary reaction 2, then the acetylene and propylene measured should give the relative rates of reactions 1 and 2. Accordingly, the primary decomposition should proceed 96% by (1) and 4% by (2). Since some of the methyl-vinyl encounters will lead to disproportionation the above 4y0 are rather a lower limit. In order to show that the vinyl radicals are produced in the primary reaction the following two experiments were made. Ethylene at a constant pressure of 1 p was co-decomposed with variable amounts of mercury dimethyl. The propylene-d3formed and the ethylene decomposed were measured. The results are shown in Fig. 1. Plotted is the propylene-d3 formed, over the ethylene decomposed vs. the square root of ethane formed. The latter quantity should be a measure of the methyl radical concentration. It is seen that the curve levels off at about 5'34, in approximate agreement with the previous result. From the results it is evident that a fixed amount of vinyl radicals is available which is independent of the methyl radical concentration. I n the second experiment a mixture of C2H4 and CZD4 in the ratio 1:1.8 was decomposed (total pressure 1 p ) , together with 10 p of mercury dimethyl-&. The propylene was analyzed as described previously. The following result was obtained: C3H6, 2.4; C3H5D, 1.6; C3H4D2, 3.3; C3H3D3, 33.0; C3HzD4, 4.5; CSHDs, 3.2; C3D6, 52.0%. The presence of all these isotopes is difficult to understand. Nevertheless the two major products are C3H3D3and C3D6, as expected from the proposed mechanism. It is concluded that reaction 2 constitutes about 4% of the total primary decohposition. The results of Cvetanovicl are compatible with the operation of reaction 2. Thus the hydrogen obtained from a mixture of C Z Hand ~ CzD4contained 1.2% HD (the remainder being Hz and Dz). Doubling this figure t o take 'into account the recombination of H and D to Hz and Dz (6) R. F. Pattie, A. G. Harrison, and F. P. Lossing, Can. J. Chem., 39, 102 (1961). ( 7 ) p = microns, partial pressure.
NOTES
March, 1963
717
thanilic acids have been reported previously from this Laboratory. The present paper reports experimental data for the determination of the ionization constant of 4-amino-3-methylbenzenesulfonicacid. All these acids are zwitterions with large charge separations and all show a remarkably small entropy of ionization. Using conductance measurements, Ostwald4 has determined the ionization constant of this acid at 25' and found it to be 7.53 X By analogy with the other aminobenzenesulfonic acids, we assume that this acid is a zwitterion and thus that the ionization reaction is
'!I 20 Fig. I.-Formation of CtH3CD3from CzH3 and CDa radicals in function of CD3 radical concentration.
one obtains 2.4%. Possibly some of the H and D also were lost by addition to the ethylene. Robb and co-workerss in a recent investigation of the mercury sensitized decomposition of ethylene also conclude that the decomposition ( 2 ) participates as a minor reaction. A number of secondary reactions occur in the system studied by these authors and so it cannot be determined accurately to what extend (2) occurs, but an addition of the suitable products leads to a figure of about 3%. LeRoy and Steacie9 in an early investigation in the temperature range 25-390' suggested that at room temperature (2) occurs to a very minor extent if at all but that its importance increases with temperature so that, particularly in the range 200-350°, it begins to contribute significantly as a primary process. Since hydrogen atoms can be produced by the Hg-sensitized decomposition of hydrogen originating from reaction 1, it is not completely certain that the authors could really distinguish between (2) and ethylene disappearance initiated by H atom addition. Thus it would have been of interest to confirm LeRoy and Steacie's high temperature results. Such experiments were not a b tempted, however, since the present apparatus does not lend itself easily to conversion for work at such temperatures. (8) J. R. Mafer, B. Mile, and J. C. Robb, Trans. FaradauSoc.. 67, 1342 (1960). (9) D. J. LeRoy and E. W. R. Steaoie, J . Chem. Phys., 10, 676 (1942).
THE IONIZATION CONSTANT OF $-AMINO3-METHYLBENZENESULFONIC ACID FROM 0 TO 50' BY MEANS OF ELECTROMOTIVE FORCE MEASUREMENTS BY STANLEY D. MORRETT AND D. F. SWINEHART Department of Chemistry, University of Oregon, Eugene. Oregon Received September 119. 1963
The ionization const,ants and related thermodynamic quantities for sulfanilic acid,' metanilic acid,2 and or-
The general method of investigation is that developed by Harned and co-workers.6 The cells were of the type Pt, H2/HAts(m10), Nahts(m2O), NaCl(m30)/ AgC1-Ag where HAts and NaAts are the acid and its sodium salt, respectively, and mlO,mZo, m30 are weight molalities. By elimination of m H + y n + from the cell potential equation
and the thermodynamic ionization constant expression
there results the relation
( E - EO)F 2.30259RT
+ log mI-rAta?nCimAts-log K
- log
YHAts'YCl?'Ab
-
(3)
The ionization constant of HAts is so large (about 7 X that mAts- and mHAt8 are not equal to the stoichiometric values and these values must be corrected for the ionization of the acid mIIAts = moHAts - mH+ mAt8- = moNaAte
+ mH+
where morepresents the stoichiometric molalities. Values of mH+ were calculated by solving eq. 1 for log mH+ and using the Debye-Huckel limiting law for the activity coefficients. This procedure required two successive approximations. The left-hand side of eq. 3 was plotted as a function of ionic strength and extrapolated to zero ionic strength, yielding a first approximation for -log K . Using this value of K , new values of mH+ were computed from eq. 2 and again the lefthand side of eq. 3 was extrapolated to zero ionic strength using the method of least squares. Three complete cycles of these calculations were made (1) R. 0. MacLaren and D. F. Swinehart, J . A m . Chcm. Soc.. 73, 1822 (1951). (2) R. D. McCoy and D. F.
Swinehart, ibt'd., 76, 4708 (1954). (3) R. N. Diebel and D. F. Swinehart, J . Phy8. Chem., 61, 333
(1957). (4) W. Oatwald, 2. phya'k. Chem., 8 , 412 (1889). (5) H. 8. Harned and B. B. Owen, "The Physical Chemistry of Electrolytio Solution*" 2nd Ed., Reinhold Publ. Corp., N e w York, N. Y.,1950.
