COMMUNICATIONS TO THE EDITOR
Nov., 1961
2111
COMMIJNICATIONS TO THE EDITOR ON A POSSIBLE TRACK REACTION IN T H E RADIOLYSIS OF TOLUENE Sir: The dimeric products which are formed on gamma irradiation of liquid toluene may largely be explained by reactions of radiolytically produced benzyl or tolyl radicals. Less important are the methylhexatrienyl biradicals and the phenyl radical. The main reactions yielding dimers are
for the formation of t>hiscompound is obtained i n about an equimolar mixture, A strong linear energy transfer effect’ has bee11 reported for the yields of gases and dimers i n aromatic l i q ~ i d s . ~The . ~ direct demonstration of a dimolecular spur reaction now may give a clue in explaining those facts. Details of the radiation effects in toluene and toluene-benzene mixtures will be published elsclwhere.8 EIDGEX~SSISCHE TECHNISCHE JURG H O I G X ~ HOCHSCHULE TISO G ~ V M A N S ZURICH,SWITZERLAXU RECEIVED JULY 20, 1961 (6) W. G . Burns, “VI Rassegna Internationale Elettronica e Nuc-
C~H~CHS CH3C&C6110CH3
leare,” 3, Rome W. G. Burns, W.Wild and T . F. Willianis + CsH,CH3 CH&sH4CsH0CH3 of Atomic Energy, +R C H ~ C ~ H ~ C ~ H ~ C H Proc. Y Bnd Geneva Conf. on Peaceful + RH ( 2 ) (1958). (7) T. GBumann and R . H . Schuler, J . Chem., 703 (1961). J. Hoign6 and T . Giiurnann, Helu. Chim. Acta, 2141 (1961). + CsH6CH3 +CGHSCH~ + CsH&Hz 99,
--3
(1959) ;
29, 260
u8e8
----.f
65,
Phys.
C&CH;
(8)
44,
( 3)
2 c~H,CH~
+CsHaCHzCHpCsHb
( 4)
Step 2 is formulated in analogy to reactions observed in irradiated benzene2 or when dibenzoyl peroxide is decomposed in this ~ o l v e n t . ~The tolyl radicals are scavenged rapidly by t ~ l u e r i e . ~ It was possible to reproduce steps 2, 3 and 4 by decomposing the toluoyl peroxides in toluene. In this system the benzyl radicals are formed only by the radical transfer reaction (3). The fact that there is formed about half as much bibenzyl as the sum of the isomeric bitolyls shows that this reaction is important. In the radiolytic products we find as the maill additional products the phenyltolylmethaiies, amounting to 20% of all the dimer products. For their formation we suppose the reaction C G H ~ C $. H ~C&CH2
----f
CH3CsHaCH2CsHs (5)
This reaction still takes place in solutions containing iodine, in a system where the benzyl radicals become scavenged (no formation of bibenzyl). Therefore we are forced to assume that this special reaction takes place only in the spur6of the ionizing electrons. A similar disagreement between the reactions induced by the decompositiori of peroxides and those induced by radiation is found in benzenetoluene mixtures. Only the second treatment yields diphenylmethane. Thereby the maximum (1) Work supported b y t h e Swiss Kommission fur Itoniuissenschaft. ( 2 ) T. Gdurnmn, Helv. Chzm. Acta, 44, 1337 (1961). (3) D. F DeTar a n d R A. J. Long, J . A m . Chem. S o c , 80, 4742 (1958). (4) G H. Wilbams, “Homolytic Aromatic Substitution,” Pergamon Press, London, 1960, p. 45. ( 5 ) C J Horhanadel, in ”Comparative Effects of Radiation” by h1 Burton J. S Kirby-Smith a n d J L Msgee, John Wiley and Sons, Inc., New York, N. Y., 1960 p. 159.
HEBT OF DISSOCIATlON OF BOROS PHOSPHIDE, BP(s)
Sir: Williams and Ruehrweinl have made semiquantitative studies of the vaporization of BP by a gas saturation method. Their phosphorus dissociation pressure data are given in the first two lines of Table I and are expressed by the equation log
P p , (inm.)dles =
( - 1 3 . 7 X 103)/T
+ 10.1
whirh corresponds to a heat of dissociation of 62.6 kcal. mole-l at 1523’11. and an entropy of dissociation of 46.2 cal. deg.-l per mole of E’&). Since the entropy2 of P,(g) is 65.92 cal. deg.-l at 1523OK., this entropy change would require the contribution of phosphoruq atoms to the entropy of BP at 298°K. t o be near zero, assuming reasonable values for the entropy contribution of boron and the heat capacity of BE’. Tnasmuch as such a low entropy contribution on the part, of phosphorus is unlikely, it was believed that a “third law” calculation would providc a more reliable heat of dissociation. For the purposes of this calculation, the contribution of boron to the free energy function of a boron phosphide \vas assumed to be the same ab for elemental boron. The change in the flee energy function upoii dissociation is then the difierence hetween the free energy function for P&) and that for two gram atoms of phosphorus in BP(s) The values of the free energy function for hound phosphorus n-ere estimated b y taking the atomir (1) F. V. STilliams and R. A. Ruehruein, J . -4m. Chem Soc., 82 1332 (1960). ( 2 ) D. R Stull and G. C Sinke “Thermodynamic Properties of t h e Elements,” American Chemical Society, Washington, D C., 1936, p. 148.
COMMUNICATIONS TO THE EDITOR
2112
ON THE MORRIS MECHAKISM O F HYDROLYSIS OF CHLORINE
TARLEI HEATOF DISSOCIATION OF B P
T,"E(. PP,mm.
1473 6.3 9.52
AF/T, cal. mole-' deg.-l -A( F -- H 2 y ~ . I ~ )cal. /T, mole-' deg.-l 40.3 AHzgs,le/T, pal. mole-' deg.-l 49.8 AHII)RJG,kral. mole-' 73.4 Average AHPI~.IB = 73.2 ircnl. mole-'
1523 12.6 8.15
1573 24.2 6 85
39.9 48.0 73.1
39 6 46 4 73 0
heat of phosphorus in a phosphide to be 6 cal. per degree3 and the contribution of phosphorus to the entropy of a phosphide to be 5 cal. deg.-l per gram atom. The value.: of the free energy function for P&) were taken from the tabulation of Stull and Sinke.2 The results of the calculation are presented in Table I. I n view of the findings of h l a t k w ~ i c h the , ~ dissociation reaction is presumed to be
+
(26/11) BP(s) = (2/11) RIIP~(s) Pz(g) STATEUNIVERSITY OF XEWYORE COLLEGE OF CERAMICS AT ALFREDUNIVERSITY ALFRED,N. Y.
Vol. 65
Sir : In a recent paper Lifshitz and Perlmutter-Hayman1 discuss the mechanism of the hydrolysis of chlorine and demonstrate the inadequacy of Morris's scheme2 suggesting hydroxyl ion is the active agent of chlorine hydrolysis even in acid solutions. This demonstration is entirely correct, but we wish to mention that we criticized Morris's reaction scheme already in 1947,3 since it does not fit the kinetic results obtained by us in 1945. Apparently our paper of 1947 was overlooked by Lifshitz and Perlmutter-Hayman. The value of k of the rate of the hydrolysis of chlorine given in the article of Lifshitz and Perlmutter-Hayman is 5.60 see.-' at 9.3". R7e determined k = 1.75 sec.-l a t 0" and 8.97 at 17.6O.' The Arrhenius plot gives the value 1; = 4.3 at 9.5". The comparison of the two results, not made by Lifshitz and Perlmutter-Hayman, means good agreement of the old and new data on the rate of chlorine hydrolysis.
EUGENE SHILOV ACADEMY OF SCIENCIES OF THE UKRAINIAN SSR S. SOLODUSHEKKOV KIEV30, U.S.S.R. CLIFFORD E. MYEES RECEIVED AUGUST 21, 1961
RECEIVED SEPTEMBER 23, 1961 (3) 0.Kubaschewski and J. A. Caterall. "Thermochemical D a t a of Alloys," F'ergamon Preas, New York, N. Y.,1956, p. 135. (4) V. I. Matkovich, Acta Cryat., 14,93 (1961).
IXSTITUTE OF ORGANIC CHEMISTRY
(1) A. Lifshitz and B. Perlmutter-Hayman, J . Phys. Chem., 64,1663 (1960). (2) J. C. Morris, J . A m . Chem. Soc., 68, 1692 (1946). (3) E. A. Shilov and S. Solodushenkov, J . Phys. Chem. (Russ.). 21, 1159 (1947); Chem. Abstr., 42, 2945 (1948). (4) E . Shilov and S. Solodushenkov, Acta Physicochimico U.R.S.S. 20, 667 (1945).
