sorbed et liylerie or rcact with the conventionally bound cthylcnt~i n the sanic’ coniplcx, t he latter mcchaniam t)eing analogous to the schcmc proposcvj by (’ossec”
for polymerization by %icglci,-K a t t a catalysts. At no time was thr prcsencc oi hcxenes or octcnes cd, which is cvnsistrJiit Lvith nwchanisrn 2 or 3 . ‘I’crmiiiatioli of polpmrrization at t h r dinirr is explained by the ready rcplawmtnt of hutcne as a ligand by cthylctird proreeding at a rate far greater than the coupling. .1 cXnowledymcxt. lye arc grateful to I’rofessor It. I,. Martin (1-iiivrrdy of ~Iclbouriie)for helpful discuhsion of‘thr results.
The Ratfiation-lnduced Chlorination of Toluene by Stannic Chloride1
Thc extent to which radiation-induced reactions in organic. systenis h a v ~ionic mechanisms is in dispute. That some reactions go mu ionic intermediates was proved ~ v h r n\*rrmcil and co-authors2 showed that polymerization of isot)utene, essentially similar to that induced by high-energy radiation, was induced by vacuum ultraviolet radiation with a threshold frrqueiiry corresponding to the ionization potcntial. The radiationinduced reaction has been shown3 to have a (;-value (molrcules 100 e.v.) for initiation of about 0.2. It is clear that even if recapture of clcctrons hy their parcnt positive ions is the general rule, as suggested by Samuel and SIager,* there w i l l hr some electrons which escape recapture. These will bc the more rnergetic secondaries (“delta rays”) whosc track is longer than the distance over which Coulomb fields are dominant. IIagec’ has suggested that the (2 of such clectrons will hr about 0.2 (varying with the energy criterion for prrmaiient separation), arid has tried to shou that this rirld is also characteristic for the formation of charge carriers in polymers under irradiation. On the other hand, much larger yields of ionic intermediates have been proposed by Chang, Yang,
and Jl’agncrfi and by U~illiams.7 Chang, Yang, and n’agncr suggrst that olefins capture the primary clectrons bef‘orc part*nt-ion recapture can take place, whilc Ll’illiarns proposrs the rearrangement of the radicalions formed in the initial ionization process before the rlcctron can return. I n either case, a G of about 3 for ionic rrartions would be expected. Wir naturc and yield of ionic processes in radiation chrmistry is therefore a promising subject of investigation. I’articular interest attaches to the question whether standard ionic reactions, such as thc carbonium and carbanion reactions of orgaiifc chemistry, can be induced by radiation. Thrse considerations led 11s to attempt irradiations of systems coritaiiiing an aromatic hydrocarbon as the major constituent, an olefin, and a 1:ricdd-Crafts catalyst. If carbonium ions are formed, as suggested by LVilliam~,~ thc alkylation reaction should be obtained with good yicld. Our first rxperiinrnts were carried out a t room temperaturt. with solutions of aluminum chloride and ethylene in benzene, which were irradiated by CoG0 y-rays. Analysis of irradiated arid unirradiated tubes showed that the thermal reaction obscured any radiation-induced reaction. I t \vas therefore decided to carry out irradiations at Dry-Ice temperature. Because no means existed for obtaining a reasonable ydose rate for chilled samples, irradiations wcre performed using elrctrons from a I-SIev. resonant transformer. In order to keep the system liquid (z’.e., iuiiform), we switched from benzrne (m.p. +So) to toluene (m.p. - Y Y , O ) . I t was then found that alumiTable I
Peak
T y p i r ~ retentton I time, inin
Identity
A
72
m- and p-Ethyltoluene
H
11
n-Propyl benzene 0-C hlorotoluene m- and p-Chlorotoluene o-Ethyltolurnr
-“
c
85
1)
90 94
E
648
XOTES
Table I1 : Results of Toluene Irradiations Dose rate, Tube
18 28" 23 18 12 14
8 4 17 20 I9
1 26 29 9 22 30 34 59 61 64 65 66
73 74
75 77
78 79 82 83 31
33 35 37 38
3!) 41 46 85
87 88 89 9 I' 02r
93"
Jrradiation conditions (deviation fronr standard)
e . v . /g./spr.
Standard
Standard 1)ose = 1.56 X IO2l e.v./g. 1)ose = 1.56 X IO2' c.v./g.
nose = 0 . m x 1 0 2 1 c.v./g. 1)ose = 0.624 x 1021 c.v./g. 5%; ( v . / v . ) SnClr 5(;{)( v . / v . ) SnClr 5%%(v./v.) SllCl4 5yh ( v . / v . ) SnC14 5y0SnCI4; dose = 6.24 X loz1 e.v./g. 107; ( v . / v . ) SnCl4 10% ( v . / v . ) SnCI, 10% (v./v.) SnCll 107%SnC14; dose = 1.25 X loz1e.v./g. 10y6SnC14; dose = 1.25 X lo2' e.v./g. S O SIlClr N o SnCI, 0.495 (v./v.) 8nCI4; reduced dose rate 0.4Y0 (v./v.) SnCl,; reduced dose rate 0.78% ( v , / v . )SnCl,; reduced dose rate 0.78(%( v . / v . ) SnCI,; reduced dose rate 0 . 7 8 7 , (v./v.) SnC14; reduced dose rate lteduced tlosc rate 'Iteduced dose rate Iledriced dose rat,c Iteduced dose rate R.cduved dose rate Iteduced dose rate Ilcduced dose rate Itedured dose rate K O et,hylene So et>hylene So ethylene KO ethylene So et,hylene 0.1 ?/( ethylene 0 . 1 df ethylene 0 , I X f N O instead ( i f ethylene Iloom tcrnpCrvt>ureirradiation Iloo;n t,cmpcr:i.t.iircirradiat>ion Itoom tcinpcratrirc irrsdiiition Ilooin temperatiire irraditition 2(%, (v./v.) CCI, insteitd of SnCl, 2cVc ( v . / v . ) (XI,instead of SnCln 2% (v./..) CCl, instead of SnCl4
x
10-19
Peak .2. m- a n d pethrltolriene t'.p.m
Peak B. n-propylhenrrno G X 10s P.p.m. G X 103
8 20 3 32 2 97 3 10 3 (Kl 3 18 3 80
12 17 9 12
4 41 2 79 3 52
12 28 18
4 4 3 4
37 62 81 16
13 .. I1 15
3 63
..
...
..
...
2 3 3 4
4 3
22 26 11 6 Trace Trace 10 40 52 41
1
17
..
...
.. 13
...
2 2
... 2 2
.. 33 7
..
I'eak C , o-chlorotoluene P.p.111 G X 108
Peak D, m- a n d Peak 15, o-ethylv-r-chlorotoluene toluene P.P. 111. C X 10' I'.p.ni. G X lo*
41 60 225 217 506 406
32 34 45 47 39 57 43 41 96 77
22 7 296 167 158 50 54 269 283 676 572
5 1
306 27'2 462 363
29 51 87 69
356 301 553 438
..
169
80
169
..
4 4 4 2 ..
..
2
6 9 6 1
..
168 182 120 125
43 56
...
..
63 80 47 52
.. ..
51
..
...
, .
, . .
..
... ... ... ...
..
... ...
..
...
34
..
...
57 105 83
..
...
..
...
..
...
80
..
...
54 128 108
.
I
171
81
181
85
..
...
..
... ...
..
... ...
27
38.5
11 6
15
4 2
3
77
12
62
11
63
12
48
8
22
4
52
8
18
3
37
7
27
4
0 304
12
2
38
6
55
10
111
21
..
...
0 212
7
1
30
5
68
13
112
21
..
...
0 217 0 868 0 711
8 6.3
1 1 1 2
38 16.5
6
11 7 8 13 11 17 18 16 15 20 24 19 33 22 29 32 34 14 33 21 27
115 8'2 92 108 117 149 143 127 112 111 181 164 170 133 2w 268 5 20 7 95 211 165 138
21 15 17 20 22 28 26 23 21 21 33 30 31 25 48 50 38 18 40 31 26
..
...
3
3 41 2 83
50
4 21
.. 68
25
8 4
1 09
16
0 68
... 4 3
65.5 38.5
...
..
10 6 ..
...
..
..
.. .. ..
.. ..
..
... ... ...
..
55 36 8 44 72 61 92 100 88 82 106 126 102 176 119 158 172 5 182 76 174 112 143
..
...
..
..
782
149
28 1
54
4 09
...
..
..
886
169
39 1
75
3 96
...
..
..
GO6
116
242
46
1 0 0 0 0 0 3 2 2
074 980 336 310 217 274 41 61 89
300 2 4 4 4 5
I 2 1
75 89 91 92 87 77 94 77
2 36
3 4 10 2 .. 2
...
16.5 22 61 12 .. 11 16
...
..
..
.
..
4.2 10 19 5
3 1
..
...
4 ..
1
.. .. .. .. .. 23.5 18.5 .. ..
.. ..
... ... , . .
I
.~ .. , .
3
.. , .
..
..
...
.. , .
... ... ..
..
, . .
..
...
..
, . .
..
.. .. .. ..
,..
..
... ...
.. ..
..
, . .
.. ,..
... ...
..
...
..
..
..
... ... ...
..
...
..
... ...
..
KOTES
649
Table I1 (Continued)
Tube
Irradiation conditions (deviation from standard)
Dose rate, e.v./g./seo. X 10-19
Peak-A, m- and Peak B , n-propylp-ethyltoluene bensene P.p.m. G X 103 P.p.m. G X 103
04c 2% ( v . / v . )CCl, instead of SnClc 95" 297, (v./v.) CC1, inRtead of SnCla 102 cu. 0.1 M NO instead of ethylene
Peak C , o-chlorotoluene P.p.m. G X 103
Peak D, m- and Peak E , o-ethylp-ohlorotoluene toluene P.p.m. G X 108 P.p.m. G X 103
1.68
..
..
..
,
.
928
177
441
84
. .
2.76
..
, . .
..
..
1058
202
316
60
.,
, .
..
227
43
164.5
31
4.37
Three unidentified small peaks before peak A. were observed.
.
I
...
One unidentified small peak before peak A.
,
.
Several large unidentified peaks
--
num chloride was virtually insoluble in cold toluene, and stannic chloride (SnC14) was substituted. Thus the system eventually investigated was a solution of stannic chloride and ethylene in toluene.
Experimental Materials. Toluene (A.C.S. analyzed) was passed through an Aerograph A-90-P gas chromatograph. The column used was 3 m. long, 3/6,-in.0.d. aluminum, and filled with 20% polymetaphenyl ether (5-ring), on 45/60 mesh Chromosorb P. The column temperature was 80". Samples of 2 ml. were injected, and about 1.5 ml. was collected from each sample. Chromatographic analysis using hydrogen flame detection of the purified toluene showed less than 10 p.p.m. of impurities. Stannic chloride (Mallinckrodt) was used as received. Ethylene (Matheson, C.P.) was introduced into the vacuum system from a lecture bottle and condensed a t 77°K. It then was purified by redistilling three times under vacuum. Carbon tetrachloride (C.P.) was used as received. Nitric oxide (NO) (Matheson) was condensed a t 77°K. by the same method used for the ethylene. A blue color (K20,) showed that S O z was an important impurity. Redistillation under vacuum gave a colorless material. Sample Pyeparation. The sample tubes were thin disk-shaped glass vessels of ca. 20-mm. diameter, 3.5mm. internal thickness, and 4.5-mm. external thickness. Their internal volume was just over 1 ml. The diskshaped voluine was connected by a glass capillary to a ground-glass joint. Solutions of stannic chloride in toluene were prepared and a volume of 1 ml. was introduced into the tube by means of a long-needle syringe. The tube was then chilled to 195'K., connected to a vacuum system, and degassed with occasional warming. Ethylene was admitted into a bulb of known volume, purified by dis-
tillation, and then brought to the desired pressure and temperature. The sample tube was chilled to 77°K. and the ethylene distilled in, whereupon the sample tube was sealed a t the capillary. The gas volume was low enough to justify the assumption that practically all the ethylene was in solution at 195°K. When the material was kept a t 77°K. during sealing, a clean seal with no evidence of decomposition products was obtained. Samples were then kept a t 195°K. before and after irradiation. Irradiations. Sample tubes were placed, in reproducible geometry, flat on a bed of Dry Ice snow and irradiated with l-Mev. '(nominal) electrons from a resonant transformer. When dose rates above 1019 e.v./ sec. were used, electrons were delivered in 5-sec. bursts. (This was judged the lowest time reproducible without undue error.) Total dose per burst was thus kept below 3 X lozoe.v./g. and heating (assuming no heat transfer to the Dry Ice) to less than 30" per burst. A small fraction of the liquid was observed to rise into the capillary stem of the irradiation tube on some occasions; when this happened, it was shaken down between bursts. Intervals between bursts were a t least 2 min. Frost was removed from the upper surface of the tubes immediately before each burst. A considerable number of tubes broke during irradiation: in particular, all those containing more than 0.1 M NO. Analysis. Tubes surviving irradiation were brought to room temperature immediately before analysis and opened by breaking the sealed tip. Samples of 0.5 to 5 ~ 1 were . removed by microsyringe and analyzed on an Aerograph Hy-FI (hydrogen flame ionization) gas chromatograph using a 3 m. long, l/s-in. o.d., stainless steel column filled with 2074 polymetaphenyl ether (&ring) on 80/100 Chromosorb W. The column temperature was 85". Products emerging after toluene were determined by planimetric measurement of the Volume 68, Sumber 8 March, 1964
NOTES
650
peak areas. Five peaks were identified by comparison with authentic samples. Peak areas were compared to those obtained by running standard solutions a t the beginning and end of each day. Several unsuccessful attempts were made to resolve the meta and para peaks by using columns filled with phenothioxin, dipropyl tetrachlorophthalate,* and bentone.g The formation of insoluble polymer was observed in some irradiated samples, but no attempt was made to analyze it. Dosimetry. It was necessary to perform individual dosimetry on each irradiation tube before it was used. The same geometry was used as in the actual irradiations, except that a wooden underlay was substituted for the Dry Ice bed. Ceric dosimetry was performed according t o the procedure of Taimuty, Towle, and Peterson.lo
Table 111
______-__
Tube number----------. 93
Peak
91
92
F G H I
0 21 0 13 0 42
0 29 0 24
J K C D L
1 04
2 15
0 40
1 93
7 23
8 20 3 58 0 55
5 72
2 93
6 07 3 71 1 19
94
95
0 17 0 26
0 25 0 11
1 84
2 51
100
I
0 2 0 6
36 93 34 91 2 67
I
m-ANDD-CHLOROTOLUENE
80
Results Results of the irradiations are presented in Table 11. The experimental conditions (column 2 ) are presented in terms of their deviation from a set of conditions which were adopted as standard. These were: toluene, 0.98 ml.; SnC14, 0.02 ml.; ethylene, 7 ml. STP (about 0.3 M ) ; dose, 3.12 X loz1 e.v./g. (50 Mrads); dose rate, approximately 3 X I O l 9 e.v./g./ sec. (0.5 PIIrad/sec.) ; temperature, 195OK. Unirradiated samples showed no product peaks a t any composition, after storage times similar to the irradiated samples, or in the standard composition after 40 hr. at room temperature or 23 days a t 195'K. Yields of products are given in parts per million by volume (p.p.m.) and molecules per 100 e.v. (G). All values are averages of two or more gas chromatographic analyses. The unidentified peaks obtained in the carbon tetrachloride irradiations weie different for each sample and also varied widely in area. Their areas (in in.2/pl. of sample) are shown in Table 111 together with the corresponding values for peaks C and D (in order of increasing retention time). All peaks except J are absent in one or more samples and are much smaller than the chlorotoluene peaks (C and D).
Discussion of Results In view of the very considerable scatter of the results, caution in their interpretation is required. The most striking regularity in the results 5s the dependence on stannic chloride concentration, which is shown in Fig. 1. Here results of all runs a t each concentration The Journal of Physical ChemiRtry
60
G x 1000
XO-CHLOROTOLUE
40
2c
C
2
5 SnCI, (v/v)-
percent
Figure 1. Yield of chlorotoluenes as a function of SnC14 concentration.
have been averaged. It appears that combined naand p-chlorotoluene yields are about 30% higher than the o-chlorotoluene yield, and that yields approach an asymptotic level. This level appears to be near ( 8 ) S. H. Langer, C. Zahm, and G. Pantaaoplos, J . Chromatog., 3 , 154 (1960). (9) J. V. Mortimer and P. L. Gent, Nature, 197, 789 (1963). (10) S . I. Taimutg, L. H. Towle, and D. L. Peterson, Nucleonics, 17, No. 8, 103 (1959).
NOTES
G(C7H&l) = 0.2. There appears to be no dependence of chlorotoluene yields on dose (with the doubtful exception of the single run 19), temperature, or ethylene concentration. There seems to be a direct dependence of yield on dose rate, but lhis is not considered reliable. The CgH1,yields are so small that few conclusions can be drawn. They disappear a t room temperature and when CCL is present. It may be possible to distinguish two processes : one which yields o-ethyltoluene and n-propylbenzene and which is suppressed by 0.78% SnC14, and another which yields m- and/or p-ethyltoluene and n-propylbenzene and which is only partially suppressed by 10% SnCle. iZ very marked contrast is seen between the SnC14 and CCl, results. The latter show considerably larger yields and many rnore products. This contrast is reminiscent of that cited by Chang, Yang, and Wagner6 between the radiolysis of olefins (which they consider to go by an ionic mechanism) and that of paraffins. While there is no conclusive evidence that the products determined in these experiments result from ionic intermediates, a number of considerations lead us i o such an opinion. They are: the apparent lack of a temperature coefficient: the small number of products; and the fact that the reaction is not suppressed by the radical scavengers C,H4 and NO. A G-value of approximately 0.2 for the formation of intermediates is indicated; apparent1.y they react with SnCl4with a rate constanl only slightly larger (at most one power of ten) then that of competing reactioos. If these intermediates are ionic, it seems plausible to identify them with delta-ray ion pairs. An alternative hypothesis would be that the observed reactions result from energy dissipated directly in the solute, but the trend toward a maximum yield a t high solute concentrations tends to negate this hypothesis. A striking feature of the results is the very low yield of alkylation products. This leads to the conclusion that the formation of conventional carbonium ion intermediates is probably very rare. After completing this work, we have learned of two papers in which confirmatory results are reported. Allen and Hummell’ have estimated the yield of separated ion pairs produced by 1.5-Nev. X-rays in liquid hexane as 0.09 to 0.13 ion pair per 100 e.v. Busler, Martin, and Williams12 have studied the ionic radia.tion-induced polymerization of cyclopentadiene and tentatively estimate a yield of 0.26 initiator per 100 e.v. (11) A. 0. Allen and A. Hummel, Discussions Faraday Soc., in press. (12) W R Busler, D H Martin, and Ff. Wllhams, i b i d , in press.
651
Solvent Effects in the Racemization of 1,l’-Binaphthyl. A Note on the Influence of Internal Pressure on Reaction Rates1
by Allan K. Colter and Lawence 11. Clemens Department of Chemistry, Carnegie Institute of Technology, Pittsburgh 15, Pennsylvania (Received September 27, 1969)
In the course of an investigation of the effects of charge-transfer complexing on the rates of racemization of optically active 1,l’-binaphthy12 we were surprised to observe substantial kinetic solvent effects, even among a series of relatively nonpolar solvents. Since the racemization process has a rather well defined activated complex3 and involves little redistribution of charge, it seemed ideally suited for an investigation of solvent effects not inrolving strong specific reactansolvent interactions. d number of authors have *developed a common approach to the problem of kinetic solvent effects in nonpolar reactions, using transition state theory and the theory of regular solutions.* For a reaction A B -+ products, the specific rate in a dilute nonideal solution, ICl, is related to that in some standard state, ko, by the expression
+
where EA, EB,El, and E , are molar energies of vaporization of A, B, the solvent, and the activated complex, respectively, and VA, VB, VI, and I;-+ are the corresponding molar volumes. The quantities ( E I V )are called ~
~
~
~~~
Abstracted in part from a thesis submitted by L. M.Clemens in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Carnegie I n d t u t e of Technology, June, 1963. (2) L. M. Clemens, unpublished work. (3) F. H. Westheimer in M.S. Newman, “Steric Effects in Organic Chemistry,” John Wiley and Sons, Inc., S e w York, K. Y . . 1956, Chapter 12. (4) (a) K . J. Laidler and H. Eg-ring, Ann. S . Y . Acad. Sci., 39, 303 (1940); (b) S. Glasstone, K. J. Laidler, and H . Eyring:. “The Theory of Rate Processes.” McGraw-Hill Book Co., Inc., New York, N. Y., 1940, p. 413; (c) K . J. Laidler. “Chemical Kinetics,” McGraw-Hill Book Co., Inc., Xew York, N. Y., 1950, p. 121; (d) A. A . Frost and R. G. Pearaon, “Kinetics and Mechanism,” Second Ed., John Wiley and Sons, Inc., Sew York. Iu.Y., 1961, p. 131. (1)
V o l u m e 68, S u m b e r 3 M a r c h , 1064
