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Benzene Hexachloride and i t s I
I
1
GEORGE R. CHAMLIN Continental Laboratories, Chicago, Illinois
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NEW insecticide-benzene hexachloride or 1,2,3,4,5,6-hexachlorocyclobexane,called "666" for short from its empirical formula C6H6Clshas been reported in British journals and by the U. S. Department of Agriculture1 as possessing . outstanding . insecticidal properties. Benzene hexachloride was first made in 1825 by Michael Faradav.. who found that benzene reacted with chlorine in sunlight to give a solid body and a dense thick fluid:
.
C1 H
I
C
H-C H-C
/\
C-H
11
+ 3CB
/
C-H
light
H
L
I
H
gamma isomer which was called "Gammexane." It is present to the extent of 10 to 12 per cent in the crude material. COMMERCIAL PREPARATION OF BENZENE HEXACHLORIDE~
Chlorine gas is slowly passed into 660 parts of benzene contained in a lead-lined reaction vessel until 890 parts of the gas have been absorbed. The mixture is then stirred continuously and the temperature maintained a t 15' to 20" C. in the presence of actinic radiations. The supply of chlorine is then interrupted, and the precipitated solid filtered off and dried. The mother liquid is then mixed with 330 parts of benzene and the mixture again treated with 890 parts of chlorine. After filtering the reaction mixture resulting from the second chlorination, the filtrate is again mixed with a smaller quanity of benzene and again chlorinated in a similar manner. In this way, a contiunous process for the preparation of benzene hexachloride results.
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SEPARATION O F THE PURE GAMMA ISOMER
CI
In 1833 ~ i ~ ~ c h ~described ~ l i c hits decomposition by bases to form trichlorobenzene: CI H
H/r
\C v f
H
\c
C/H q
p
C
I
KOH ----t
1
I CI
Cl-C H-C
/C\ C-CI 11 I C-H
+ 3HC1
\/ c.1
--
Peligot and Lauret 'established its composition in 1836, and in 1912 Van der Linden2the existence of four isomers. Pure specimens of alpha and beta isomers of by J. C. smart in 1942, and their "666" were toxocity to insects was investigated by F. J. D. Thomas at Hawthorndale, England. It was found that both isomers were practically nontoxic to insect pests. It was soon shown, however, that the insecticidal action of "666" was due almost entirely to the presence of the 'Report entitled c 6 ~ hN~~ e ~ ~ ~ ~B~~~~~~ ~ t Hexachloride i ~ i d
The crude CsHeCla is treated with a small amount of methanol, in which the alpha and beta isomers are relatively insoluble. Separation of the solid product leaves a solution containing the gamma and delta isomers. On evaporating the solution, a small crop of practically pure gamma isomer is thrown down. This can he recrystallized from CHClaor hot concentrated HN03. According to Dr. Donald Slade (Imperial Chemical Industries, Ltd.), there are probably 16 possibleconfigurations for benzene hexachloride. In view of the strain produced by the close approach of chlorine atoms (this can readily be seen from atomic scale models) he suggests that there are only five probable strainless forms of C6H6Cls,two of which are mirror images. Of the five formed. the structure of beta isomer is the onlv one whose &cture is known with certainty, PROPERTIES
The benzene hexachlorides are stable compounds which are unaffected by continuous exposure to the atmosphere. They are stable to the action of hot water and light for a considerable period. ~h~~ can be recrystallized from hot concentrated HN03. In the ~ presence of alkalies, such as limewater at ordinary tem(666)" by the Bureau of Entomology and Plant Quarantine, peratures, three molecules of HC1 are lost from the
Beltsville. Maryland. V e r . , 45, 236 (1912).
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Wnited States patent 2.218.148.
283
C6H6C16molecule giving a mixture of the isomers of trichlorobenzene. The beta isomer is the most stable, being less reactive to dilute alkalies than the other isomers. In the pure state the isomers of benzene hexachloride are well-defined colorless crystals, relatively insoluble in H20, soluble in organic solvents, practically odorless, and having a bitter taste. The melting points of the alpha, beta, gamma, and delta forms are, respectively, 15g0, 30g0, 112.5', and 138.5"C. A list of solubilities appears in Table 1. The consistently low solubility of the beta isomer and also the higher relative solubilities of the gamma and delta isomers are to be noted.
1.9 0.3 0.3 12.1 0.3 7.8 1.8 1.1 6.9 0.1
Benzene Carbon tetrachloride Chloroform Cycloheranone Diesel oil Dioran Ether Ethyl alcohol Ethyl acetate Ethylene glycol Glycerin Methyl acetate Methyl alcohol Naphtha (heavy) 1s-propyl alcohol
Nil
6.7 1.6 1.5 0.4 2.1
Toluene Distilled water (parts per million) Xylene
(5)
and to the lower half of the cages a t the rate of 20 mg. per sq. ft. of surface. Fresh bedbugs were introduced weekly. Mortality in these cages was complete after 90 days. In several small tests in rooming houses and on a large scale in a nearby prison, a 0.5 per cent solution of "gammexane" in CClagave complete freedom from bedbugs for a period of over six months. Musca domestica and Culicidae: "Gammexane" reacts surely against the housefly and mosquito by spraying 5 cc. of an alcoholic solution (two per cent) per cubic meter of room. The flies were killed within one hour, and after ten minutes nearly all flies were so paralyzed that they could no longer fly. When sprayed on surfaces in suitable solvents, "gammexane" remained as a nearly invisible deposit and acted as a contact insecticide for several months. Since "gammexane:' is stable a t high temperatures, we were able to apply i t as a vapor by heating on hot plates. Preliminary tests showed "gammexane" to be five to ten times more effective than any other insecticide to date against many other household insects, such as carpet beetles, clothes moths, fleas, lice, silverfish, and ants. These insects were killed on contact with a residue left by spraying 50 mg. per sq. ft. of surface. Its agricultural and veterinary uses have given highly promising results. INSECTICIDAL PREPARATIONS
"Gammexane" may be formulated into various preparations similar to dichloro-diphenyl-trichloroethane. A powder form may be prepared by grinding Tests, still in progress conducted in our laboratories 10 per cent of crude "666" with fine talc. This can be and in the field, indicate that "gammexane" is highly further diluted for use on crops. For some uses the material is mixed in an organic solvent. The solvents toxic to many insects. Periplaneta americana (the American cockroach): nsed in practice include xylene, carbon tetrachloride, "Gammexane" mixed with bait ( 1 to 500) was fed for and perchloroethylene. Solutions containing 5 per 10 days to 100 cockroaches (10 in each of 10 jars), all cent "gammexane" or more may be diluted for use but 3 of which died. In other tests one per cent of with kerosene or other suitable oil. By the addition "garnmexane" in talc was applied on a band one inch of an emulsifying agent concentrated solutions can be wide across the center of a pen 20 inches square; all prepared which on addition of water give stable emulthe adult roaches exposed were killed within 20 hours. sions. Unlike many insecticides "gammexane" has proved Concentrations as low as 0.002 per cent were completely to be exceptionally stable to high temperatures. This effective in 104 hours. When 10 per cent DDT (dienables i t to be volatilized from hot plates, producing chloro-diphenyl-trichloroethane) and 97 per cent sodium fluoride were compared with "gammexane," only 60 an insecticidal smoke. By these means the insecticide per cent of those roaches treated with DDT and 50 may be nsed directly against insects or to give a toxic per cent of those with sodium fluoride were dead a t the invisible film on surfaces. This method is being studied further. end of 48 hours. In a practical test in a restaurant a spray containing T. O. X--I C. ITY one per cent "gammexane" was applied to the surronndinvestigations conducted by Dr. H. ing surfaces. ~ ~ ~hours~later t624 dead ~ and . f Pharmacological ~ ~ ~ dying c o c ~ r o a c ~ ewere s counted, and twoweeks later Taylor in England indicate that "gammexane" is relatively nontoxic to animals and man. The effect of the remises were comoletelv free of insect^.^ abso'ption through the skin was investigated in our Cimex lectularius (the bed&): In order to simulate laboratories by painting the bodies of rats with an emulnatural conditions, cages miniature mattresses were used, spray was applied to the mattresses sion containing 10 per cent of the insecticide. No ill effects were observed. "Gammexane" powder was also ' I am indebted to Mr. Harold I. Stern, without whose help to come in 'Ontact with the laboratory workers' and knowledge the practical tests outlined in this paper could not skin for 30 days without any apparent effects. have been made. ~
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