NOTEB immediately permits calculations of the required kinetic constants kl and kz. Such data, however, as kindly indicated by a referee, might be more completely handled by standard regression analysis, particularly if a computer were available. No doubt there will be many other cases where “concentration-time” integrals, as new experimentially determinable variables, can be applied with advantage in chemical kinetics, since it is now often possible with present-day modes of chemical analysis to obtain decay data for all reactants, and it is also a relatively easy matter with desk calculators to compute areas under experimental curves. Acknowledgment. Mr. G . T. Knight is thanked for supplying data used successfully to check some of these methods. This work was sponsored by the Board of The Natural Rubber Producers’ Research Association.
The Radiolysis of Liquid 1,1,2-Trichlorotrifluoroethane
by A. R. Kazanjian* and D. R. Horrell
The Dow Chemical Company, Rocky Flats Division, Golden, Colorado 80401 (Received January 4, 1971) Publication costs assisted by The Dow Chemical Company
The radiation chemistry of chlorofluorocarbons presents an interesting study because of the three possible types of bond rupture. These are the carbon-carbon, carbon-fluorine, and carbon-chlorine bonds. The relative proportion of each type of bond scission will determine the final radiolysis products. This problem has been investigated using 1,1,Ztrichloro-l,2,P-trifluoroethane. The compound was 7-irradiated and the products were analyzed. A mechanism was deduced from a knowledge of the final products. There are no previous reports on the radiolysis of chlorofluorocarbons and very little work has been done on fluorocarbons. One previous investigation2 has shown that radiolytic scission of the C-C bond is of the same order as the C-F bond break in the 7 radiolysis of liquid hexafluoroethane. This occurred in a compound in which the C-F bond energy (106 kcal/mol) is 20 kcal/mol greater than the C-C bond energy (86 kcal/mol). Other reports of predominant C-F bond rupture have been made by Fallgatter and Hanrahan3 and MacKenzie, et a1.,4 in their work on cyclic and aromatic perfluorocarbons. These conclusions are not in accord with the Obtained in an study Of irradiated liquid CzF6.5 There was no evidence in the
2217 esr work of the production of other than the CF3radical, indicating little or no C-F bond scission. Trichlorotrifluoroethane contains, in addition, C-C1 bonds with an energy of 72-80 kcal/mol. On the basis of bond energy, this latter cleavage appears to be the most likely.
Experimental Section The 1,1,2-trichloro-1,2,2-trifluoroethanewas obtained in a very pure state (99.996%) from Allied Chemical Co. under the trade name of Genesolv-D and used without further treatment. Liquid samples were 7-irradiated in a Gammacell-220, a source containing about 3200 Ci of 6OCo. The dose rate in a Fricke solution was approximately 2.5 X 10’’ eV/ml min. Energy absorption in the irradiated trichlorotrifluoroethane was calculated on the basis of electron density, and exact dose rates were determined for each container and position within the irradiation chamber. Conversion of the parent was usually less than 1%. Samples were irradiated in Pyrex, quartz, stainless steel, Teflon, platinum, and Monel tubes. Results were essentially the same in all the tubes. Sample temperature was 30“. Samples were deaerated, either by He sweeping or by evacuating. Product analyses was made by temperature programmed gas chromatography; see Figure 1. Qualitative analysis was made by comparison of the retention times of the unknown peaks with those of known compounds on two columns. The specific isomers were identified by mass spectrometric (CEC21-11OB) analysis of the compounds isolated by gas chromatography. Quantitative measurements were made by comparison of chromatographic peak areas. Standard solutions of CFCL and C3F4C14 in trichlorotrifluoroethane were made up and shown t o have a relative detector sensitivity of 1 on a weight basis. The other products were also assumed to have the same sensitivity because they are all the same type of compound. Results and Discussion The final radiolysis products and their yields are listed in Table I. The variation in G values may be as much as 25%. There was no difference in yields over the fourfold increase in applied dose. The material balance, C :F : C1, obtained for these products was 2:3:3.2. This discrepancy was not resolved. The only other products observed were smaller amounts of Clz and Fz,spot tested with o-tolidine and starch iodide. Other oxidizing agents interfere in these tests. There (1) This work performed under the auspices of the Atomic Energy Commission Contract AT(29-1)-1106.
(2) A. Sokolowska and I,. Kevan, J . Phys. Chem., 71, 2220 (1967). (3) M. B. Fallgatter and R . J. Hanrahan, ibid., 69, 2059 (1965). (4) D. R. MacKenzie, F. W. Block, and R . H. W i d , Jr., ibid., 69, 2526 (1965). (5) R. W. Fessenden and R . H. Schuler, J . Chem. Phys., 4 3 , 2704 (1965).
The Journal of Physieal Chemistry, Vol. 76, N o . 14, 1971
2218
I
2
I
4
I
I
6
8
I
I
IO
12
MINUTES 50'
- d
I
14
I
I
I
I
18 90'
16 70'
20
llOo
I
22 130'
I
24 150'
I
26
I
28 BO0
TEMPERATURE
Figure 1. Chromatogram of the radiolysis products from trichlorotrifluoroethane,
Table I : Radiolysis Products from CzFaCla
CFzC1-CFClz -+CFzC1-CFC1 Product
G Jalue
CFnClz C2F4C12( lJ2-dichloro-) CFCls CsFaCla(1,2,3-trichloro-) C2FzC14(1,1J2,2-tetrachloro-) CsF4C14(lJIJ2,3-and 1,2,2,3tetrachloro-) C4FeC14(1,2,3,4-tetrachloro-)
1.4 0.20 1.4 0.20 0.20 0.20
CF2Cl-CFCI2 -+CFzCl
+ C1
+ CFClz
+ CFzCl- CFzClz C1 + CFCl2 +CFCls
C1
CFzC1-CFC1-CFC1-CFzC1 2CFzCl-
CF2Cl-CF2Cl
2CFC12 ---t CFClZ-CFC12
The Journal of Physical Che~nistTy,Vol. 76, No. 14, 1071
14 (1) 10 (2)
7 (3) 7 (4)
BCFZCl-CFCl+
0.70
was no evidence for polymer formation in any of the chromatographic or mass spectrometric work. Considering the products, it appears that only C-C1 and C-C bonds have been broken. The fact that the C-F bond was not broken is not surprising considering its high bond dissociation energy compared with those of the C-Cl and C-C bonds. The following radical mechanism w'rts selected as being most readily accountable for the radiolysis products. The simple combination of the initial free radicals produces exactly those isomers that have been identified. The one exception is the 1,2,2,3-tetrachlorotetrafluoropropanethat is formed along with the 1,1,2,3-tetrachloro isomer. The fraction of each isomer is unknown. The reverse reactions of (1) and (2) and the steps that may precede (1)and (2) (such as ion formation) are not included.
Relative ratio
CFzCl CFCl2
+ CF2Cl-CFCl
3 . 5 (5) 1 (6) 1
(7)
---t
CFzC1-CFC1-CFZC1
1 (8)
CFZCI-CFC1-CFC12
1 (9)
+ CFzCl-CFCl+
The other C-C1 bond could also be broken in reaction 1, even though it was less likely. Apparently this occurrence was very small, as the only four-carbon isomer formed was the one shown in reaction 5. Although it is possible for CFzCl radicals to undergo a disproportionation reaction (lo), it was neglected because the disproportionation : combination ratio was found to be 0.17.6 (6) G. 0. Pritchard and M. J. Perona, J. Phgs. Chem., 7 3 , 2944 (1969).
2219
NOTEB CF2Cl
+ CF2Cl+CFzCl2 + CF2
(10)
Another possible reaction is the combination of chlorine atoms to form Clz ( l l ) , which in turn could scavenge free radicals to form the two predominant products according to (12) and (13). 2c1+
Clz
(11)
+ C F z C l 4 CF2C12 + C1 Cl2 + CFClz --+ CFC1, + C1
Clz
(12) (13)
No attempt has been made to distinguish the above reactions (11-13) from those originally listed (3-9), because they lead t o the same products and the same product ratios. The mechanism can also be used to account for the relative yields. Using whole numbers for simplicity, it can be seen that if reactions 1 and 2 occur in a ratio of 14 to 10, the four radicals formed can subsequently combine to produce the relative yields that were obtained. The yield of the four-carbon compound formed in reaction 5 is somewhat anomalous. According to this scheme, six parts of this compound should have been formed, whereas only 3.5 parts were actually formed. A possible explanation may be that the chromatographic sensitivity is actually less for this compound. This cannot be verified until a standard is obtained. The above mechanism, in which four radicals combine on a 1 to 1 basis to generate the observed products, very conveniently accounts for the products. Acknowledgment. We wish to thank K. J. Grossaint for his support in doing the mass spectrometric analysis.
Solvent and Temperature Effects on the Hydrogen Bond
by E. A. Robinson, H. D. Schreiber, and J. N. Spencer* Lebanon Valley College, Anneille, Pennsylvania (Receieed January 89,1971)
1700$
Pvhlhatinn costs assisted by Lebanon Valley College
The temperature dependence of the molar absorptivity of the fundamental hydroxyl stretch of various phenols has been determined in the solvents tetrahydrofuran, benzene, and chlorobenzene in which the hydrogen bonding capability of the solvent is well established, in carbon tetrachloride in which hydrogen bonding to the solvent seems likely, and in perfluoromethylcyclohexane. All spectra were recorded on the Beckman DK-2A spectrophotometer equipped with the Beckman tem-
perature regulated cell holder controlled to f1". Teflon stoppered cells (1-cm) were used for all spectra. The reference cell contained the pure solvent for each system. The cells had previously been shown to be adequately sealed against loss of the solute or solvent by evaporation.' The solute concentrations were about 0.002 M for phenol, catechol, guaiacol, and sym-trichlorophenol, 0.001 M for resorcinol, and 0.008 M for o-nitrophenol for all solutions studied. The molar absorptivities reported are the average molar absorptivities of a t least three separate solutions a t each-temperature. The samples were prepared by adding weighed amounts of each solute t o the solvent. All reagents were stored in a dry nitrogen atmosphere and transfers were done quickly in order to avoid water contamination. Standard purification techniques were used for all reagents. The molar absorptivity of the fundamental hydroxyl stretching frequency of various phenols as a function of temperature is given in Table I. The frequency shifts relative to the gas phase hydroxyl frequency of phenol, 3654 cm-1,2 and the negative fractional change of the molar absorptivity with temperature, (- 1 / 6 0 ) (deldt), are also given in Table I. The fractional change of molar absorptivity with temperature is reported because for some solutes the absorption is due t o two hydroxyl groups and for other solutes only one hydroxyl group is responsible for the absorption. Thus a common basis is used for comparison. Selecked spectra are given in Figures 1,2, and 3. The spectra of catechol and guaiacol in benzene, chlorobenzene, and tetrahydrofuran bear a resemblance to the spectra of phenol in these solvents. This similarity of spectra is interpreted as being due to disruption of the intramolecular hydrogen bond in catechol and guaiacol by these solvents. It is seen that the molar absorptivity of catechol in tetrahydrofuran and chlorobenzene is about twice that of guaiacol as would be expected if disruption of the intrabond occurred. However, if the intramolecular bond in catechol should be disrupted by association with the solvent the molar absorptivity would be expected to show nearly the same relation t o phenol as does the molar absorptivity of resorcinol in these solvents. Likewise, the molar absorptivity of guaiacol should be nearly that of phenol should the intrabond be disrupted by the solvent. It is seen that in all cases for which data are reported the molar absorptivity of resorcinol is nearly twice that of phenol. The data of Table I show that the molar absorptivity of catechol is less than that of resorcinol and the molar absorptivity of guaiacol is less than that of phenol in benzene, chlorobenzene, and tetrahydrofuran. The fractional change of molar ab(1) G. P. Hoover, E. A. Robinson, R. S. McQuate, H. D. Schreiber, and J. N. Spencer, J . Phys. Chem., 73, 4027 (1969). (2) L. J. Bellamy, R. L. Williams, and H. E. Hallam, Trans. Faraday SOC., 54, 1120 (1968).
The Journal of Physical Chemistry, Vol. 76, No. 14, 1971
