2676
JEAN
+,o-
H . FUTRELL AND AMOS S.NEWTON
VOl. 82
nitrobenzene anion in terms of structures I, I1 and 111. By way of contrast, molecular orbital I I1 II calculations with reasonable values for coulomb and resonance integrals for the nitro group lead to much too little unpaired electron density in I I1 I11 the meta a-orbitals. Several other approaches to electrochemical The hyperfine interaction with the nitrogen generation of radicals are available. A continuous nucleus is presumed to arise by means of u-a flow system from the electrochemical cell into the configurational interaction mainly from the con- microwave cavity could be employed, or a sample tribution of bond eigenfunction I to the ground could be transferred from the cell into a sample state wave function. Brovetto and F e r r ~ n i ~tube ~ for measurement. By comparison, the intra and M ~ C o n n e l lhave ~ ~ shown t h a t not only does muros cell technique offers significant advantages the contribution of bond eigenfunctions I1 and in simplicity and convenience. The present cavity 111 lead to a positive spin density on the ortho design limits the study to reasonably stable anion and para carbon atoms but the cross terms of radicals; eventual development of techniques for these bond eigenfunctions results in a negative observing transient radicals a t a mercury electrode spin density on the meta carbon atoms, the magni- will provide a significant tool in the study of tude of which is usually 1/3 to 1/2 t h a t in ortho or processes. gara position.37 The hyperfine structure does not electrode Preliminary work has been done in this Laboraallow the assignment of the sign of the spin density tory employing a platinum electrode for generation on the carbon atoms, but we feel t h a t the ratio of of radicals by electrooxidation a t controlled the hyperfine coupling constants of the ortho and pctential. para to the meta protons is qualitatively in agreeAcknowledgment.-Financial assistance for this ment with a valence bond description of the project from the National Science Foundation (35) P. Btovetto and S . Ferroni, Nuouo Cimento, 6. 142 (19.57) through grants NSF G-7289 and NSF G-7288 (36) H M McConnell, J . Chcm. Phys., 29, 244 (1958); 30, 328 and from the National Institutes of Health through (19.59). grant M-2728 is gratefully acknowledged. (37) T h e authors a l e indebted to both referees for pointing this out. -0,
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[CONTRIBUTION FROM
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L A W R E N CRADIATION E LABORATORY AND DEPARTMENT OF CHEMISTRY, UNIVERSITY OF CALIFORNIA, BERKELEY, CALIFORNIA]
I The Radiation Chemistry of the Symmetrical Dichloroethylenesl J ‘ 2 6 7 6 - ?G‘c/r F2S
‘
BY JEAN H. FUTRELL AND AMOSS.N J ? y 2
00s
RECEIVED SEPTEMBER 8, 1959
Purified, degassed liquid samples of cis- and Irans-1,2-dichloroethyleneshave been irradiated with helium ions, electrons a i d gamma-rays A comparison of the radiolvsis products has been made with the products formed in the polymerization of these compounds with benzoyl peroxide. Using a combination of gas chromatography and mass spectrometry, several oC the high boiling products (to ~ 3 5 0 ’ )have been characterized as to compound types. T h e yields of volatile products did not change greatly with changes in linear energy transfer but the yields of polymer products were found to increase markedlv with decreasing density of ionization. 4 mechanism has been proposed to explain the formation of the observed p-oducts.
Introduction
As part of a program of investigating the radiation chemistry of organic compounds containing various functional groups, a number of alcohols3 and ethers4 have been investigated; the work has now been extended to the study of a simple olefin. The svmmetrical dichloroethylenes were chosen for this purpose, as they are perhaps the simplest compounds containing the functional groupings RCH= CHR for which the phenomenon of long-chain p d y merization does not dominate and obscure the other reactions taking place. A study of the more complex compound, isgpropenyl acetate, has been reported e l ~ e w h e r e . ~Further, the investigation of ( I ) Much of t h e work presented here is from t h e dissertation s u b mitted by Jean H. Futrell in paxtial fulfillment of the requirements for the P h . D . degree in September, 1958. (2) Author to whom requests for reprints are i o be addressed. (3) W. R . McDonnel and A. S. Newton, THISJ O U R N A L , 76. 4631 (1934). (4) A. S. Newton, J . Phys. Chem., 61. 1485 (1957). (51 A. S. S e w t o n and P. 0. Strom, ibid., 62, 2 1 (1958).
the cis and trans isomers of 1,2-dichloroethylene permits the comparison of the radiation effects on two compounds differing in their physical properties primarily in t h a t the cis isomer has a large dipgle moment (1.8 Debye), while the trans isqmer has no net moment.6 Because a difference in dielectric constant of the substrate might be expected to have an effect on rates of ionic reactioiis, this feature is perhaps pertinent to the issue of the importance of ionic processes in the radiation chemistry of condensed phases.’ Experimental Purification of Compounds.-Eastman White Label chemicals were purified by distillation through a n 85-plate adiabatic column packed with Podbielniak Helipak No. 3013 (6) G. E. K. Branch and M. Calvin, “Theory of Organic Chemistry.” Prentice-Hall, New York, N. Y., 1941, p. 138. (7) M. Burton in “Heat ings on Physical Research Program as i t Relates t o t h e Field of Atomic Energy,” Subcommittee on Researcli a n d Development of the Joint Committee on Atomic Energy, Eighty fifth Congress, Second Session (United States C:overnment Printing Office, Washington 2 3 , L).C., 1958), p . 110.
June 5 , 19BO
IIAUIATION CHEMISTRY OF SYMMETRICAL DICI-ILOROETIIYLEKES
2677
Benzoyl Peroxide Experiments .-Comparisons were made with the products observed when benzoyl peroxide was decomposed in the presence of excess of each of the respective 1,2-dichloroethylenes. One mmole of benzoyl peroxide (Monomer-Polymer Corporation, analysis, 96'% active), was weighed into a flask fitted with a break seal. This was evacuated and 50 ml. of the purified and degassed compound added by vacuum transfer. The flask was sealed and heated TABLE I a t 70" for 100 hr.,'4 after which the products were analyzed PHYSICALPROPERTIESOF THE SYMMETRICAL CICHLORO- as described below except the KOH treatment of the gas was ETHYLENES eliminated. It was established that only traces of HCI were formed in the reaction. Washing the gas with water and ----Cts-isomer----. --7'~oiz.~-isomer-----. l'ruyerty Measured Lit.a lleasured Lit." testing with silver nitrate yielded only a faint turbidity. Volatile Products.-After irradiation the target vessel 7L?;D 1.4426 1,4428 1.4395 1,4397 dZ54 1.2698 1.2736 1.2420 1.2489 was sealed into a vacuum system and opened under vacuum in such a manner t h a t its contents drained into a flask for B.p. (760 refluxing under vacuum. Gaseous and low-boiling products tnm.j 60 36" 60 36" 47.66' 1 7 67" evolved from the liquid in this process were pumped through refrigerated traps with an automatic Toepler pump.9 F.p. -81.52' -80.0" -49.36" -49.8' Fractions volatile a t - 196, - 125 and -80' were separated J . A. IZeddick and E. E. Toops, "Organic Solvents," and were analyzed with a Ccnsolidated Engineering Corpora\ ' i i l . VI1 o f "Technique o f Organic Chemistry," h.Weisstion model 21-103 mass spectrometer. Because analyses berger, Ed., 2nd E d . , Interscience Publishing Co., New for HC1 are erratic with this mass spectrometer, the constitVork, N. Y . , 1955, p . 204-206. uents in the gas fraction volatile a t - 125' were contacted with KOH pellets prior to analysis in order to remove this Preparation of Targets.-Pyrex glass cells of the type de- component. The HC1 yield was determined by both the described by Garrison, Haymond and Weeks8 were used for crease in gas volume and by gravimetric determination of the helium-ion irradiations and for some of the electron irchloride in the KOH scrubbing pellets. The two methods radiations. I n other electron irradiations the cell design agreed quite satisfactorily. No HC1 was observed in the was modified to consist of a spherical body rather than a n residual gas and no trend was observed in the HCl yields Erlenmeyer shape (so t h a t all electrons would be stopped with total dose indicating HC1 absorption effects on the colwithin the vessel), and a platinum lead was sealed into the lection apparatus to be negligible for the dose range studied. glass wall for more effective beam monitoring. These cells Polymer Products.-Various techniques involving conaccommodated from 115 to 140 ml. of liquid, depending on centration of the polymer products, separation of the high the construction. Gamma-irradiation cells were cylindrical boiling constituents by gas chromatography, and identificaglass ampoules 1 inch in diameter and 3 inches tall, fitted tion of the individual components by mass spectrometry with break-tip and seal-off tubes. These contained 15 ml. of were used to study the polymer products. I n some cases liquid and a n equal volume of gas space. the residual liquid after separation of the low boiling products The purified dichloroethylene isomers were degassed by was concentrated in a small Vigreux column. I n others refluxing under vacuums and were distilled and sealed in the the bulk dichloroethylenes were removed by vacuum evapappropriate target vessels under vacuum. oration. The density and weight of the residual material Irradiation Procedures.-The helium-ion irradiations was used to calculate the volume where complete recovery were made with the external beam of the 60-inch Crocker was impossible. I n some cases a semi-micro molecular Laboratory cyclotron with 40 to 43 mev. ions incident on the distillation was run on the high boiling products. liquids at beam currents of the order of 0.1 to 0.2 pamp. The All fractions were analyzed by gas chromatography using irradiations were conducted a t room temperature (approxi5 mm. i.d. glass columns 2 m. in length with stationary mately 25") and the temperature was roughly controlled by phases of General Electric Silicone Fluid 96-40 or Fluorolube an air blast against the target. The target was shaken vigHG-1200 (Hooker Electrochemical Co.) adsorbed on 40 to 60 orously during the irradiation. One sample of cis-1,Z-dimesh Sil-0-Cell Firebrick. Temperatures up to 153" were chloroethylene was irradiated at approximately 80" while used without bleeding. At higher column temperatures, lieated remotely by a n infrared lamp in a manner described cimtinunus elution of the stationary phase interfered w i t h previously.10 The local dose rate in the area of helium ion the mass spectrometer identification of the components. absorption was about 2 X 1022 ev./g./min. Samples were injected into the column to determine the Electron irradiations were conducted with the microwave emergence times of the principal constituents. This w a i linear electron accelerator which has been described by followed by a second injection in which each respective comLemmon and Mosier.ll I n other experiments the 2-mev. ponent was collected from the column effluent as a discrete Van de Graaff accelerator a t the California Research Corsample in refrigerated traps attached at the proper emergence poration was employed. The lowest practicable rates of ir- time. These separated components were then characterized radiation were used, with air-blast cooling, t o keep the tarby their mass spectrometer fragmentation patterns. Mass gets a t or near room temperature. I n the Van de Graaff Spectrometer fragmentation patterns of available chlorinated experiments the local dose rate was very approximately 3 X hydrocarbons were used to obtain correlations between 1020 ev./g ./min . molecular structure and fragmentation patterns for polvGamma radiolyses were conducted in a 2000-curie CoS0 chloro compounds. These same commercial compounds source12 and were monitored by means of oxygen saturated mere used in the gas chromatography runs to establish the Fricke dosimeters [G(Fe+++)= 15.51. The dose rate to response per pl. liquid injected and the correlation between the dosimeter was 2.19 X 10l8 ev./g./min. Use of a cychi- boiling point and emergence times. In this way the volume hexane dosimeter, assuming G ( H y ) = 5.413 gave the same fraction of various components was determined from the gas value of the radiation intensity as the Fricke dosimeters. chromatographic peak areas and calibrations. The unacCorrections were made for differences in electron density counted peak area in a given fraction was ascribed to conibetween the calibrating material and the samples, yielding a pounds boiling too high t o be detected a t the column tem1018 ev./g./min. for the dichloroethydose rate of 1.96 perature used, the highest useful limit being a boiling point lenes. of 350' using the Fluorolube HG-1200 column. Details on these procedures are available elsewhere .I6 (8) W. M. Garrison, H. R. Haymond a n d B. M. Weeks R a d i a t i o n The residual material from molecular distillation of the Research, 1, 97 (1954). "polymer" consisted of material having a vapor pressure too (9) A. S. Newton, A n a l . Chewb., 28, 1214 (1958). low for these techniques t o yield useful information. Where (10) A. S. Newton, J . Phys. Chew&.,61, 1490 (1957). possible, this was characterized by average mol. wt. (f.p. (11) R . M. Lemmon and D. F. Mosier, R a d i a t i o n Research, 4, 373 depression in benzene) and composition, One or more (1956). staiiiless steel helices. Gas chromatography and mass spectrometric analysis were used to monitor the distillation, and the purified product was distilled with a boiling range of less than 0.01" and with a purity of 99.98 =I=0.02y0 as determined by cryoscopic methods. The properties of the purified isomers are listed in Table I .
-
7--
x
(12) B. M. l'olbert, G. Nielsen, G. Edwards, I. hI. \Vhitli.mure and N. B. Garden, "A High-Intensity Cobalt-60 Source," in Chemistry Division Quarterly Report, UCRL-3710, Feb. 1957, y. 72. (13) R . H. Schuler, J. Pizys. C h e i x , 61. 1472 (1037), hl. Burton and S. Lipsky, ibzd., 1481 (1957), fiives G(Hd as 3.9.
( 1 4 ) C. 1;. Frank and A. U. Lllnckman, ']'HIS J O U H N A I , 72, 328.i ( I 950). (15) Jean II. Futrell, University of Califurnia Radiation Lshuratory Report U C R L 8 3 6 2 , July, 1938.
"78
JEAN
H.FUTKELL A N D ~ I R IS. ONEWTON S
VOl. s2
TABLE IT YIELDS' O F VOLATILE PRODUC1.S FROM Cis- A F D t r U n S - l , 2 - D I C H L O K O E T € ~ Y L E N E IRRADIATED WITH He ++,e - AND ?-RAYS c Cis-l,2 DCE----t,'ap,s-l,2 DCE--------.Product Het+ e-b Y He++ e -b 7 H e + + (80')
0.027 1.83 1.02
0,018 0,040 0 040 0.085 0.049 1.9 1.59 1 .50 1.6 2.0 1.05 0.83 0.82 0.8 1. 0 0.006 0,009 ,004 ,002 ,003 ... 0.34 0.3G ,2d .26 .25 0 24 1.35 1. 0 1 21 1.2 1.4
