I
IRVING ROSEN and JOHN
P. STALLINGS
Central Research Laboratory, Diarnbnd Alkali Co., Painesville, Ohio
Radiation-Induced Chlorination of Toluene anld Butyric Acid This discussion sh uld interest chemists and chemical companies engaged in the chlorinati of organic materials. It places in proper perspective some previously reported promising uses of gamma radiation-induced chlorinations and adds to the knowledge of two chlorination reactions
IN
RECENT YEARS, gamma radiation as an initiator of chemical reactions has received considerable attention. Several authors have referred to the unusual effect obtained when toluene, chlorinated at about 20' C. in the presence of gamma radiation, formed addition-chlorinated material containing no side-chain substitution (7, 5-10). O n the other hand, ultraviolet light leads only to products with such sidechain substitution, and it was thought that this difference arises from ionization by gamma radiation instead of radical formation. Because of the potential application of gamma radiaFion to chlorination reactions, some gamma and ultraviolet radiation-induced chlorinations of toluene and butyric acid were compared experimentally and with data available in the literature.
Procedure and Discussion
Chlorination of Toluene. Dry toluene was chlorinated in the absence of a solventin a 7 x 39 cm. borosilicate glass reaction vessel. The chlorine was introduced through a fritted-glass tube placed a t the bottom of the reaction vessel. The reaction mixture was cooled by a glass cold finger, 3.0 cm. in outside diameter, in the center of the reaction vessel. Salt water from an ice-salt mixture was circulated through the cold finger by means of a Sigma pump. A 15-watt General Electric Co. black light fluorescent lamp (Catalog No. F15T8-BL) was placed adjacent to the reaction tube. The toluene was saturated with chlorine and the light was turned on while the chlorine continued to pass into the toluene. In a typical reaction, 2.35 moles of dry chlorine was passed into 5.56 moles of toluene, over a period of 200 minutes, while the temperature of the reactants
was maintained a t 13' to 15' C. The amount of chlorine taken up by the toluene was 1.08 moles. The reaction mixture was distilled at reduced pressure. After unreacted toluene and some benzyl chloride had been recovered, the addition-chlorinated material was collected. The data and analyses of a typical experiment are given in Table I. The elemental analyses of the last three fractions were close to the calculated values, for 1,2,3,4,5,6-hexachloromethylcyclohexane : 27.6% carbon, 2.64% hydrogen, and 69.9% chlorine. The other possible addition product, 1,1',2,3,4,5,6-lieptachloromethylcyclohexane, contains 24.7% car2.08% hydrogen, and 73.2% chlorine. A sample of the penultimate fraction reported in Table I was refluxed in 1 N alcoholic sodium hydroxide and was found to contain 34.6% hydrolyzable chlorine. The theoretical amount of hydrolyzable chlorine in 1,2,3,4,5,6-hexachloromethylcyclohexane is 34.9%; the theoretical in 1,1',2,3,4,5,6heptachloromethylcyclohexane is 41 .S%. This result is evidence of the absence of a-chlorination in the addition product. To obtain some confirmatory evidence for the absence of chlorination of the methyl group, the infrared spectra of the products were compared with that of methyl-
Table 1.
cyclohexane. Both the products and the reference compound exhibited strong absorption bands a t 7.3 microns indicating the presence of a methyl group in the products. This absorption band was not present in the spectrum of a-
chloromethylcyclohexane. Most of the published work on the addition-chlorination of toluene describes products which also contain side-chain substitution. A characteristic of these reactions appears to be the elevated temperature a t which they were carried out (75). van der Linden (74) tried to addition-chlorinate toluene by saturating the toluene with chlorine and irradiating in sunlight. Vigorous reactions took place, the identified products of which were the hexachloro addition products of benzyl and benzal chlorides. The only reported instances in which unsubstituted addition products were isolated occurred when the chlorination reaction temperatures were kept low. Qvist (76) obtained the 1,2,3,4,5,6hexachlorome thylcyclohexane by passing chlorine into toluene in the dark a t 0' C. over long periods of time, but did not report yields. By the use of ultraviolet light initiation at 0 ' C., Kharasch and Berkman (72) believed they obtained the 1,1',2,3,4,5,6 - heptachlorornethylcyclohexane as the principal addition product
Addition-Chlorinated Products of Toluene
low Temperature Ultraviolet Chlorination of Toluene Gave Addition-Chlorinated Products Containing Six Chlorine Atoms per Molecule
B.P.,
C.
126-30 131-34 132-37 137-42
Pressure, Mm. H g 0.7-0.8 0.7 0.5 0.5
Found, %
Wt., Grams 8.2 14.3 14.4 6.6
C
...
28.9 27.5 26.8
VOL. 50, NO. 10
H
... 3.10 2.85 2.58
OCTOBER 1958
c1
...
68.0 69.7 69.6
151 1
in yields of 45 to 55% based on chlorine input. This result is ambiguous, however, as the reported percentage of hydrolyzable chlorine in the compound corresponds to that for the 1,2,3,4,5,6hexachloromethylcyclohexane. Harmer and others (7-9) obtained the 1,2,3,4.5,6hexachloromethylcyclohexane by chlorinating toluene at -5’, 20°, and 35’ C. with gamma radiation. Their yields were 4.5 to 18% based on the toluene. These latter results were attributed to a different primary action and reaction mechanism induced by gamma radiation than is postulated for conventional initiators. Because similar results have been obtained with ultraviolet radiation, it appears that the effect of temperature is more important than the source of initiation of the chlorination. Gamma-Ray Source. The source of gamma radiation was 620 curies of cobalt-60 in the form of a 2 X 13 inch tube, protected by 2 tons of lead shielding. Materials to be irradiated were placed in a borosilicate glass tube 3.5 cm. in diameter and lowered into the radiation source, which delivered 0.24 megarep per hour, as determined by chemical dosimetry (77). Chlorination of Butyric Acid. Butyric acid was chlorinated in a 22 X 3.5 cm. borosilicate glass tube fitted with a fritted glass gas-inlet tube and exhaust line. This reaction tube was placed inside the 620 curie cobalt-60 gamma-ray source, and a measured amount of chlorine was passed through the acid. After removal from the cobalt-60 gamma-ray source, the dissolved unreacted chlorine was removed by passing air through the mixture. The gain in weight represented the amount of chlorine utilized. The experimental results, along with pertinent previously reported results, are given in Table 11. The relative concentrations of the monochlorobutyric acids were determined from the infrared spectrum, of the reaction mixture. Pure samples of butyric acid and of the a , p; and ymonochlorinated isomers exhibited prominent absorption bands at 12.90, 8.34, 9.82, arid 8.71 microns, respectively. The infrared analyses are estimated to be accurate to within 3%. T o determine the effect of gamma radiation on substitution chlorination reactions, butyric acid was selected as the
Table II.
1 51 2
literature Cited
Conclusions
(16‘) -Qvist, W., Finska Kemistsamfundets Medd. 37, 45 (1928). (17) Weiss, J., Nucleonics 10, No. 7 , 28 (1952).
... 0.42
The products obtained from the ultraviolet and gamma radiation-initiated chlorinations of toluene were about the same. Similar results were obtained with butyric acid. Previous workers have attributed the unusual addition product of the gamma radiationinduced chlorination of toluene to the possibility of a different primary action and reaction mechanism. I t is conceivable that the ionization produced by gamma radiation in the primary step may result in a chlorine radical. Once the chain-initiating radical is formed, however, the chain reaction producing chlorine radicals should be propagated independently of the means of initiation. O n this basis, different products from different means of initiation of a chain reaction are not to be expected. The formation of addition chlorinated toluene, without side-chain substitution, apparently depends to some extent upon the temperature of the reactants. It is suggested that gamma radiation has about the same effect as ultraviolet radiation on the course of aliphatic substitution and addition chain chlorination reactions, and acts merely as a free radical initiator.
0.77 0 . 4 SO2C12
Isomer Distribution,
P
Initiator Ultraviolet 0 . 6 0 megarep 0.72 megarep Bz202
INDUSTRIAL AND ENGINEERING.CHEMISTRY
5 6 9
10
64 61 56 45
(1) Anderson, L. C., Bray, B. G., Martin, J. J., Univ. of hlich., Eng. Research Inst., Project 1943-4 (1955). (2) Brown, H. C., Ash, A. B., J . Am. Chem. Soc. 77, 4019 (1955). (3) Bruylants, A., Tits, M., Dauby, R., Bull. SOC. chim. belg. 58, 310 (1949). (4) Bruylants, A., Tits, M., Dieu, C., Gauthier, R., Zbid., 61, 366 (1952). (5) Chem. Week 78, No. 4, 54 (1956). (6) , , Collinson. E.. Swallow. A . J.. Ouart. Revs. 9, 311 (1955); Chem. Rkos: 56, 471 (1956). (7) Harmer, D. E., U. S. Atomic Energy Comm., AECU-3077 (1955). (8) Harmer, D. E., Anderson, L. C., Martin, J. J., Chem. Eng. Progr. Symp. Ser. 11, 50, 253 (1954). (9) Harmer, D. E., Martin, J. J., Anderson L. C., J . chim.phys. 52, 667 (1955). (IO) Heiks, R. E., Chem. Week 78, No. 7, 45 (1956). (11) den Hertog, H. J., devries, B., van Bragt, J., Rec. trav. chim. 74, 1561 (1955). (12) Kharasch, M. S., Berkman, M. G.. J. Org. Chem. 6, 810 (1941). (13) Kharasch, M. S., Brown, H. C., J. Am. Chem. SOC.62, 925 (1940). (14) van der Linden, T., Rec. trav. chim. 57, 1075 11938). (15) Pieper, ’ O . , Ann. Chem. 142, 304 11867).
Gamma Radiation Has No Unusual Influence on Chlorination of Butyric Acid
Reactants. Mole Butyric acid Chlorine 0.5 0.50 0.50 0.8
experimental material because of the previous work done on it, and the nature of the molecule. Neglecting the steric and inductive influence of the -COOH group, the statistical probability of freeradical chlorination in the a , ,B, and y positions is 28.5,28.5, and 43.0%: respectively. In the work reported in the literature, however, the amount of alpha isomer produced is low, less than lo%, and the amount of beta isomers is usually equal to or greater than the amount of gamma isomer formed ( 2 . 3, 7 1 , 13). As can be seen in Table 11, the results of the gamma-ray induced chlorination are of the same order as those reported in the literature with ultraviolet initiation. While only a little work was done on the gamma-ray induced chlorination of butyric acid with sulfuryl chloride, the results were about the same as those reported by Kharasch and Brown. These results show that gamma radiation does not have any unusual influence on the course of the reaction, compared with ultraviolet radiation.
Yield of Monochlorobutyric Acids, %
45
CORRECTION Determination of Free convection Heat Transfer Properties of Fluids In the article “Determination of Free Convection Heat Transfer Properties of Fluids” [J. E. Boberg and P. S. Starrett. IND.ENG.CHEW 50, 807 (May 1958)]. the thermal conductivity term was omitted from Equation 3 and the subsequent carry-over of this error has occurred in the illustrative problem. The data apply only for the laminar case and the erroneous equation was used in the illustrative problem. It is apparent from the correct statement of Equation 3
that for the turbulent case a knowledge of the thermal conductivity is requisite. If data are taken in the turbulent region, the grouping a413
~
31 33 35
RECEIVED for review February 12, 1958 Accepted May 16, 1958
95 (4) 79 75 70-90 (13)
__
k113
may be obtained directly as a function of mean film temperature.
