J. A. KRYNITSKY AND R.
191s [CONTRIBUTION FROM
THE
w.BOST
Vol. 69
VENABLE CHEMICAL LABORATORY OF THE UNIVERSITY OF NORTH CAROLINA]
The Preparation of Hexachlorocyclopentadiene and Certain Derivatives1 BY J. A. KRYNITSKY~ AND R. W. BOST In connection with a study of the stabilities toward hydrolysis of certain highly chlorinated and fluorochlot inated hydrocarbons, i t was of interest to prepare some highly chlorinated derivatives of the cyclopentadiene type. Straus, et al.,3 report the replacement of "positive" hydrogen with chlorine through the action of potassium hypochlorite. In this manner, they first succeeded in obtaining hexachlorocyclopentadiene from the parent hydrocarbon. In the present investigation, such a preparation was tried but soon discarded in favor of the method described below which gave superior yields and could be readily carried out with materials on hand. During a n unsuccessful attempt to prepare decachlorocyclopentane through the vapor phase chlorination of octachlorocyclopentene (I),i t was found that a t temperatures above 325' the compound does not add chlorine but rather begins to pyrolyze slowly to yield chiefly hexachlorocyclopentadiene (11) and chlorine. Further investigation showed that as the temperature is increased, the rate of pyrolysis is increased and that other products such as hexachlorobenzene are also formed. Thus a t 400430°, 1.05 moles of I yielded in addition to recovered I, 0.47 mole of I1 and only a trace of hexachlorobenzene. However, a t 4703SOo, 14.5 moles of I yielded besides the starting material, 10.8 moles of 11, and approximately 0.8 mole of hexachlorobenzene. In these pyrolyses, carbon tetrachloride was used as a diluent. To check whether this diluent took part in the reaction, an experiment was carried out using only pure carbon tetrachloride. I t was found that a t temperatures up to 500', no appreciable pyrolysis took place and no hexachlorobenzene was found. This is in agreement with data which have been previously r e p ~ r t e d . A ~ further experiment was run in which (I) was pyrolyzed at 470-480' in the absence of carbon tetrachloride. In this case hexachlorobenzene was obtained in addition to (I) and (11). It has been shown by several investigator^^^^^^ that halogens attached vicinal to a double bond possess a n enhanced activity whereas those at(1) From s thesis presented by John A. Krynitsky to the Graduate School of the University of North Carolina, June, 1943, in partial fulfillment of the requirements for the degree of Doctor of Philosophy, and based on work done in connection with a research project sponsored by the Naval Research Laboratory. Publication delayed for security reasons. ( 2 ) Present address: Naval Research Lsboratory, Washington, D. C. (3) Straus, Kollek and Heyn. Ber., 68B,1884 (1930). (4) C. D. Hurd, "The Pyrolysis of Carbon Compounds," 1st ed. 132 (1929). .~ ( 5 ) H. J. Prins, J . p r a k l . Ckem., 89, 414-424 (1914). (6) H. J. Prins, RCC.trou. chim., 61, 1065-1080 (1932). (7) Conant, Kirner and Hussey, THIS JOURNAL, 47, 488 (1925).
tached to a double bond are repressed. Advantage of this difference in reactivities was taken in treating sodium ethoxide with I1 to produce the diethyl acetal of tetrachlorocyclopentadiene-one (111). Prins5~6~8,9,10 found that certain aliphatic chlorinated hydrocarbons could be made to condense, in the presence of aluminum chloride, with chlorinated olefins to yield higher members of the chlorinated aliphatic series. He further showed that many highly chlorinated compounds (containing a t least one hydrogen) could be dehydrohalogenated very readily by the action of alcoholic alkali to create a new double bond in the molecule. In the present work, these reactions were extended to include a member of the alicyclic series. Thus, I1 was condensed with trichloroethylene to give 1-(a, P, p, P-tetrachloroethyl) -pentachlorocyclopentadiene-2,4 (IV). The product thus formed was then dehydrohalogenated by the action of alcoholic potassium hydroxide to produce perchloromethylfulvene (V) . The physical properties obtained for these compounds and some of their intermediates are given in Table I.
-
cc1- cc12 'I I cct CClZ
\ CCll ,/'
CCl
11
CCl-CCl
11
CCl
\/
CHCt=CCln AlCli
I1
CCl
I/
ACI
CCI
\C
