PHOTOLYSIS OF CARBON TETRACHLORIDE
July 20, 1963 [CONTRIBUTION FROM
RADIATIONRESEARCHLABORATORIES, MELLON INSTITUTE
2053
PITTSBI'RGH, P A . ]
The Photolysis of Carbon Tetrachloride in the Presence of Ethane and Ethylene' BY B . C. ROQUITTE AND M. H . J. WIJNEN~ RECEIVED MARCH5, 1963 The photolysis of carbon tetrachloride in the presence of ethane and ethylene has been investigated a t various temperatures and a t various ethane to ethylene ratios. The primary step in the photolysis of CC14 produces CC13 radicals and C1 atoms. Chlorine atoms react with ethylene to produce CZHaCl radicals and with ethane t o form HCl and C Z Hradicals. ~ The recombination and disproportionation reactions 3, 5, 7, 8, 12, 14, 15 and 16 involving these radicals have been investigated. The data indicate: kj/k3 Q 0.05, ks/k? = 0.14 z!= 0.03; k14/ k l ~ 0.22; and kll/klS = 0.22 f 0.03. Data on the cross combinations of the various radicals are also reported.
=
Introduction
Results and Discussion
We have recently investigated the photolysis of carbon tetrachloride in the presence of ethylene. That investigation gave information regarding disproportionation and recombination reactions of CCl, and C2H4Cl radicals. We have now extended this investigation by studying the photolysis of carbon tetrachloride in the presence of ethane and ethylene. Trotman-Dickenson and co-workers4 report that only a small activation energy is required for the abstraction of a hydrogen atom from ethane by a chlorine atom. Thus we should produce ethyl radicals in the presence of CzH4Cland CC13radicals. It should, therefore, be possible to obtain data regarding the various disproportionation and recombination reactions involving cc13, C2H4Cl and C ~ H radiS cals. Until now, information on disproportionation and recombination reactions has been limited mainly to unsubstituted alkyl radicals. Information on the reactions of chlorinated alkyl radicals is, obviously, important for the understanding of the reaction mechanisms in the photolysis and radiolysis of chlorinecontaining compounds. We also hope that this information may contribute to a better understanding of disproportionation and recombination mechanisms in general.
The results of a series of experiments in which carbon tetrachloride was photolyzed in the presence of ethane and ethylene are reported in Table I. The ratio of ethylene to ethane was varied by a factor of 7. Less than 1% of the carbon tetrachloride initially present was decomposed during the photolysis. The following reaction mechanism is suggested to explain the formation and distribution of the reaction products
Experimental The experimental technique and equipment have been described el~ewhere.~A Hanovia type 73 A 10 medium pressure arc was used as the light source. The intensity of the arc was varied by inserting wire gauze screens between the light source and the reaction vessel. Constant temperature a t 58' was maintained by an aluminum block furnace. Temperature control a t 0' was obtained by placing the cell in an ice-water bath and transmitting the light through a 5-mm. layer of water into the cell. The photolysis of carbon tetrachloride in the presence of ethylene and ethane produced the major reaction products: CzHsC1, CaHio, CChH, (CzHaC1)z: CzHsCC13, CHzClCHzCC13 and C2Cle. All the products mentioned above were determined quantitatively by gas chromatography. A 6-ft. column packed with 25% (by weight) of silicone grease on firebrick was used for the analysis. Trace amounts of vinyl chloride were also observed. Since we were not able to obtain pure samples of C2H,CCl3 and of CHzClCHzCC13 we could not measure the sensitivity of these compounds for quantitative determination by gas chromatography. We have attributed sensitivities to these compounds based on their molecular weights and their retention times on the gas chromatograph. This introduces the possibility of a systematic error in reporting the amounts in which these compounds were formed. We do not believe that this error will exceed 10% of the values reported by us. To confirm the identification of the products, individual compounds were collected as they came off the gas chromatograph and analyzed by mass spectrometer. (1) This investigation was supported, in part, b y the U. S . Atomic Energy Commission. (2) Chemistry Department, Hunter College of the City University of New York, 695 Park Ave., New York 21, N. Y . (3) B . C. Roquitte and M. H . J. Wijnen, J . Chem. P h y s . , 3 8 , 4 (1963). (4) G. C . Fettis, J. H . K n o x and A. F. Trotman-Dickenson, Can. J . Chem., 38, 1643 (1960).
+
CClr f h V ----f cc13 c1 C1 CzHa +CzHiCl 2CzHaCl(CzH4Cl)z 2C*HaCl+ CZH4 CzH4Clz 2CzHaCl+ CzHsCl CzHaCl 2CC13 +CzCla CzH4Cl cc13 +CClaCzHaCl CzHaC1 CCl3 +CCl3H CzHaC1 C1 -I- CZHB +CzHs HCl 2CzHs +CaHio 2CzH5 +CzHs CzH4 CzHs CzHaCl+ C4HgCl CzHs CzHaCl +CZHB CzH3Cl CzHs CzHaCl+ CzH4 CzHsCl CzHs cc18 +CzHsCC13 eel, +CZH4 CC13H CzHs
+
+
+ +
+ + +
+ +
(1) (2) (3)
+ +
(4) (5) (6) (7) (8) (9) (10) (11) (12) (13)
+
(15) (16)
+
+ + +
(14)
Reactions 1 to 8 describe the primary process and the resulting reactions if CC14is photolyzed in the presence of C2H4. These reactions have been discussed in detail previously.3 The formation of butane and of 1,1,1-trichloropropane clearly suggests that ethyl radicals are produced if CCl, is photolyzed in the presence of ethylene and ethane. The formation of ethyl radicals is explained by reaction 9. Reaction 9 has an activation energy of about 1 kcal./mole4 and is thus quite probable even a t the relatively low temperatures of this investigation. Reactions 10 to 16 represent possible recombination and disproportionation reactions of ethyl radicals with each other and with C*H,Cl and CCl, radicals. We have not observed any evidence in this and in our previous study to suggest that reaction 17 is of any importance under the experimental conditions of this investigation. C1
+ CzHa +CzH3 + HC1
(17)
Although reaction 17 is analogous t o reaction 9, several reasons may be advanced to exclude reaction 17. First, the C-H bond in C2H4is considerably stronger than the C-H bond in C2H6. Thus El? will be considerably larger than Es. Second, the addition of chlorine atoms to ethylene requires only a small6 or no6 activation energy. Thus reaction 17 is not expected to compete with reaction 2 except a t high (5) T . D. Stewart and B . Weidenbaum, J . A m . Chem. SOC.,S7, 2036 (1935). (6) H.Smitz, H. J. Schumacher and A . Jager, 2 . physik. Chem., BS1,281 (1952).
2054
B. C. ROQUITTE AND M. H. J. WIJNEN
Vol. 85
TABLE I PHOTOLYSIS OF CARBON TETRACHLORIDE I N THE PRESENCE OF ETHANE AND ETHYLENE‘ kis/ E W . Pc,E,~
PCzE,b
PCCl:
1 2 3 4 5 6* 7 8 9 10 11 12*
14.5 9.0 23.0 10.5 15.0 10.5 12.0 15.5 11.0 25.0 4.5 11.0
7.5 21.0 16.0 4.5 5.5 7.5 11.0 7.5 21.5 11.0 15.0 57.0
33.5 31.0 34.5 29.0 33.5 18.0 21.0 22.0 20.5 22.0 20.0 20.0
1,84 8.13 2.40 3.61 1.81 3.01 3.01 1.18 6.62 0.60 7.83 7.16
13 14 15 16 17 18 19 20 21 22* 23’
6.54 40.0 36.0 34.0 18.0 11.6 16.0 24.0 18.6 20.0 20.0
42.0 14.5 36.0 5.0 5.0 4.5 4.5 5.6 28.5 38.0
3.39 0.73 1.39 0.29 .65
54.0
46.5 41.0 44.5 31.5 31.5 33.0 30.0 32.0 31.0 31.0 30.0
10.5 17.0 33.0 5.5 11.5 20.0
29.0 29.5 32.0 29.5 26.5 31.5
1.91 2.06 2.64 0.88 1.17 1.76
R C ~ H ~ O ‘ RC&CI
k61‘2k101/l
ki/
ks
Temperature, 0”
24 11.0 25 11.0 26 10.8 27 19.0 28 19.6 29* 20.5
.88
.88
.90 2.06 1.76 1.76
.. , .
1.19 1.41 1.20
.. , .
..
..
.. ..
0.98
.. 0.68 .38 .34 .. ..
.. .. .. ..
.. 0.28 .24 .39 .29 .34 .38
5.98 6.80 5.89 5.30 5.89 4.71 5.30 3.48 4.71 3.42 4.71 4.68
5.41 5.41 5.95 7.03 5.92 4.19 4.19 3.38 5.09 2.86 5.32 4.82
10.20 20.07 12.54 12.93 10.03 12.04 12.04 7.87 16.55 5.06 18.56 16.91 Temperature, 30’ 2.58 1.85 7.62 1.44 2.63 3.20 1.84 1.83 4.37 1.44 1.62 1.97 1.44 2.08 2.81 1.72 1.95 3.69 1.46 1.87 3.45 1.46 2.72 3.71 1.76 1.60 5.54 1.72 2.39 5,14 1.58 2.39 5.14 Temperature, 58” 1.59 1.38 4.65 1.45 1.14 4.90 2.05 1.94 5.92 1,l5 1.32 2.95 1.43 1.51 3.92 1.38 1.60 4.41
3.99 0.92 3.68 3.44 4.91 1.47 1.47 2.41 0.98 3.41 0.90 0.81
19.33 8.64 17.44 17.44 24,OO 10.16 11.16 14.17 8.47 15.73 8.00 7.30
16.09 14.64 16.23 13.06 17.41 11.87 13.06 12.46 11.87 12.17 13.06 11.01
2.42 2.46 2.26 2.60 2.61 2.44 2.55 2.50 2.43 2.33 2.45
1.87 1.84 2.00 1.87 1.79 2.01 1.93 2.04 1.86 1.87 1.83 3.90
0.25 2.39 0.61 2.27 1.68 1.08 0.99 2.04 0.31 .81 .81
2.57 7.37 2.97 6.96 5.93 4.66 4.86 6.71 2.68 3.62 3,s
4.45 3.67 3.46 3.48 3.28 3.28 3.58 3.48 3.86 2.70 3.09
2.44 2.47 2.48 2.45 2.52 2.48 2.58 2.52 2.46 2.42 2.43
1.96 1.96 1.99 1.97 1.94 2.17 1.94 2.03 1.98 2.36 2.20
0.25 .16 .36 .84 .49 .36
2.20 1.83 2.81 3.35 2.80 2.29
3.28 3.48 3.67 2.70 2.90 2.70
2.44 2.47 2.44 2.91 2.35 2.34
1.86 1.86 1.90 1.90 2.13 2.02
0.85 .46 .68
2.43
0.67 .62 .41
0.38 0.48 1.19 0.28 .59 .46
a Open spaces indicate that under the given conditions this compound was formed in too small amounts to allow its determination; experiment numbers marked * were carried out a t 9% intensity, all others a t 1007,. Pressures in mm. a t temperature of investigation. R = rate of product formed in molecules/(sec. cc.) X 10-12.
temperatures as indeed observed by Rust and Vaughan.’ Accepting the reaction mechanism we may derive the following equations for the cross combinations of the various radicals produced during the photolysis
Thus the data given in Table I for R c ~ Hare ~ cnot ~ experimentally observed values but calculated values subject to a systematic error if k12/(k101’2k31’2)deviates from 2.0. Schindlers obtained k12/k101/2k31i2= 1.92from of the radiolysis of C2H6C1in the gas phase. ~CCI,C,H,CI/R~’~C = ~ ki/ksi’2k31’2 C I ~ ~ ~ ’ ~ ~ C(1) ~ ~ ~ ~ aI ~study ~ According to the reaction mechanism, chloroform Rc~H,ccI,/R~‘~c,c~,R~’~c~H,~ = k 1 5 / k d ’ 2 k l ~ 1 ’ 2 (11) is produced by reactions 8 and 16 only. The following R C , H ~ C I / ~ “ ~ C , H , ~ R ‘ ’ ’k~i ~C/ k~i~o ”~~Ck 3I “~~~ (111) may be derived under this condition. The data obtained for ~ C C ~ ~ C ~ H ~ C ~ / ~ ’ ~ ~ equation C ~ C I ~ ~ ~ ~ ~ ~ C ~ H ~ C I ~ ~ and R c ~ H ~ c c I ~ / R ‘ / ~ c ~ are c Igiven ~ R ~in ’ ~Table c ~ HI~and ~ indicate k 7 / ( k 6 1 i Z k 3 1 / 2= ) 2.5 f 0.15 and k16/(k6”2k10”2) = 2.0 f 0.15. An identical value for k i / ( k 6 1 ’ 2 k 3 1 i 2 ) Equation IV is plotted in Fig. 1. In spite of some has been obtained by us p r e v i ~ u s l y . ~No other data are available in the literature for the ratio k 1 6 / ( k 6 1 / 2 k 1 0 1 i 2 ) . scatter, the data show clearly a general agreement with eq. IV and thus with the proposed reaction mechanism. In deriving eq. I and I1 we have accepted that 1,4Figure 1 also shows that there is no noticeable temperadichlorobutane is formed by recombination of two ture effect indicating that &, - E l 6 and E8 - (’/& CZH4CI radicals and that C4H10 is formed by recombina’/2&) are zero or close to zero. This is in agreement tion of two ethyl radicals. It is obvious that in that with general observations regarding activation energy case we must also accept recombination of Cz& differences between recombination and disproportionaand CZH~CIradicals to form 1-chlorobutane. Untion reactions. From Fig. l we obtain k16/k16 = fortunately, we have not been able to measure the 0.22 f 0.03 and kg/k61’2k31’2 = 0.36 f 0.04. Recently, amounts of 1-chlorobutane formed since the retention Gregory and Wijneng studied the photolysis of mixtures time of this compound coincided with the appearance of diethyl ketone and carbon tetrachloride. They obof the excess undecomposed cc14 on the gas chromatained k16/k16 = 0.24 =t0.04 in excellent agreement tograph. For reasons to be discussed later it was imwith the value obtained in this investigation. From portant to us to obtain an estimate of the amounts & / k 6 1 1 2 k 3 1 1 2and k7/k6112k31i2 (eq. I) we calculate ks/k-, = of 1-chlorobutane formed. We have calculated there0.14 f 0.03. This value is in good agreement with fore the amounts of 1-chlorobutane formed according to eq. I11 from the amounts of C4H10 and ( C Z H ~ C I ) ~previous data yielding k8/k7 = 0.11 j = 0.02.3 Equation V is derived from the reaction mechanism observed assuming k12/(k101”%319 to be equal to 2.0.
+
(7) F F R u s t and W E Vaughan, J Ovg C h e m , 6 , 472 (1940); 7 , 491 (1942).
(8) R. N. Schindler, to be published. (9) J. E. Gregory and M. H. J. Wijnen, to be published.
ANTHRACENE-IODINE INTERACTION
July 20, 1963
2055
and relates R c ~ H ~toc R ~ ( c ~ Hand ~ c Rli2c4~,, ~)~
Equation V is plotted in Fig. 2 for the data obtained a t 0, 30 and 58'. Again no temperature effect is visible. From Fig. 2 we obtain kz/k3 0.05 and k14/ k31'2k10112= 0.42 i 0.03. Previous estimates indicated k5/k3 6 0 . 1 . 3 No data are available in the literature for k14/k31'2klo1'2.Accepting k 1 2 / k 3 1 / z k l o 1 = / z 1.928 we calculate kI2/k14 = 0.22. I t is interesting to compare the various ratios of rate constants for disproportionation over recombination ( D / R ) obtained in this investigation
I .o
0.5 1/2
I .5
1/2
RcZcig R(c~H,cI)~/R C ~ H ~ is. CC
of R C C I ~ H / R C Z H ~ Cv sC. ~ k%c16R%c~mci)z/ ~ RCZHSCCIJ a t 0" ( O ) , 30" ( 0 ) and a t 58' ( A ) .
Fig. 1.-Plot
D/R = 0.12
The ratio of disproportionation over recombination for two ethyl radicals is 0.14 f. 0.02.10-12 The results clearly indicate that the substitution of one or more ethyl radicals by chlorinated alkyl radicals has a considerable effect on the ratio of disproportionation over recombination. The number of hydrogen atoms available for disproportionation seems to have little or no relation to the observed ratios. Finally, we have attempted to measure the activation energy difference between reactions 2 and 9
I .o
2.0
3.0
Rl/2
C4HIO/~'tzH4Ci~P*
Fig. 2.-Plot
of R C Z H S C I / R ( C Zus. H R~ C%~ c) Z~ H ~ ~ / R a~t 0" c~H~c~~~ ( O ) , 30' ( 0 )and 58" ( A ) .
+
duced by reaction 8) and R c ~ H =~~ R C ~ H 0.28,~ R c ~ H(to , ~account for C2H6 and CzH4 production by C1 CzHa +CzHdC1 (2) reaction 11) R C ~ H ~ C I0 . 2 2 R ~ ~ ~( ~= c iR c ~ H ~ C1 + CzH8 +CzH6 HC1 produced by reaction 14) R C ~ H ~ C C~I ~. ~ ~ R c ~ H ~ c c (9) ( = R c ~ H produced ~ by reaction 16). Data thus obAccording to these reactions R c ~ H ~ c I / [CzHal/ Rc~H~ tained for kz/kg are given in Table for all runs where [ C Z H ~= ] kz/kg. In the above equation R c ~ Hde~ c ~ we were able to measure CzH5C1I production. I t is notes the rate of production of CzH4C1radicals, R c ~ H ~ obvious that this method was not expected to give the rate of production of ethyl radicals. Approxiand does not give accurate values for k z / k g . In spite ~CR I c~H may ~ be calculated mate values for R C ~ Hand from R c ~ H = ~ c~~R ( C ~ H -t~RCCI~)H~C IR C C I ~ C-k~ H ~of C Ithe scatter, the data, nevertheless, indicate that kz/kg does not vary considerably between 0 and 58'. R c ~ H ~ c~~. ~ ~ R c c ~ ~(toc ~account H ~ c Ifor C2H3C1 proThis indicates that E9 is approximately equal to E?. (10) R. K. Brinton a n d E. w. R Steacie, Can. J. Chem., 33, 1840 (1955). If we accept E2 = 0 kcal.,6our data thus substantiate (11) D.G.L. James a n d E. W. R . Steacie, Proc. Roy. SOL.(London), 8 1 4 4 , the relatively low value of E9 = 1 kcal. reported by 289 (19,iS). Trotman-Dickenson and co-workers. (12) P. Ausloos and E. W. R. Steacie, C a n . J . Chem., 3S, 1062 (1955).
+
+
+
++
+
+
+
[CONTRIBUTION FROM THE CHEMISTRY DIVISION,
THEFRANKLIN INSTITUTE LABORATORIES, PHILADELPHIA 3, PENNA.]
Effect of Gases on the Conductivity of Organic Solids. I. The Anthracene-Iodine Interaction1 BY IM. iM. LABESAND 0. N. RUDYJ RECEIVED MARCH7, 1963 Although gases are generally thought to affect the surface conductivity of organic crystals alone, evidence is presented that the bulk dark conductivity of anthracene is increased in a sensitive, specific and reversible manner upon exposure to iodine.
Introduction ln several investigations o f the
of gases on the
dark and photoconductivity of organic crystals,?it has (1) Supported by the
U. S. Army Chemical Center under Subcontract
SCE-17250-60with Melpar, Inc. (2) (a) A. T . Vartanyan, Doklady A k a d . Nnuk S.S.S.R., 71, 647 (1950); (b) A. G.Chynoweth, J Chem.Phys., 23, 1029 (1954); (c) A. Bree and L. E. Lyons, i b i d . , as, 384, 1284 (1956); (d) A. Bree and L. E. Lyons, J . Chem. S O L . , 5179 (1960), (e) W. G. Schneider and T. C. Waddington, J . Chem. P k y s . , 96, 358 (1956); (f) D. M .J. Compton a n d T . C. Waddington, ibid., 16, 1075 (1956); (9)T. C . Waddington a n d W. G. Schneider, Can. J . Chem., 36, 789 (1858).
generally been accepted that these phenomena are restricted t o the surface. Thus in a sandwich cell provided with a guard ring, Waddington and Schneider2g report no effect of oxygen on the photocurrent of anthracene, whereas in a surface cell a pronounced increase is observed. These same types of surface effects on the conductivity have been observed for a large number of dye films exposed to gases.3 A particularly unusual example is the 'Iaim Of the sensitivity Of photoconduction in a (3) A. Terenin, Proc. Chem. Soc., 321 (1961).
