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17%
experiment in which phenylmercuric bromide was treated with potassium chloride in a solvent mixture consisting of tert-butyl alcohol, chloroform and benzene for 4 hr. with high speed stirring, no halide exchange producing phenylmercuric chloride was observed. I n addition, phenyl-(bromodichloromethyl)-~iiercury,~ prepared by the above reaction in which bromodichloromethane was used in place of chloroform, was shown to be inert toward chloride ion under similar conditions. These results speak strongly against a dihalocarbene insertion mechanism for the reaction of phenylmercuric chloride with haloforms and potassium tert-butoxide. LVere such a mechanism to phenyl-(bromodichloromethy1)-mercury obtain, would be the product expected in the phenylmercuric bromide-chloroform-potassium tcrt-butoxide reaction in view of the demonstration t h a t neither phenylmercuric bromide nor phenyl-(bromodichloromethyl)-mercury undergo exchange with chloride ion under the conditions used. Our results indicate t h a t the formation of the phenyl(trichloromethy1)-mercurial isolated proceeded by simple nucleophilic displacement of bromide ion by the trichloromethyl anion. Hinej demonC6H6HgBr
+ CCla- --+-CGHjHgCCli - Br-
VO!.
h4
yields iii the case of the former mercurial. Phenyl(dibromochloromethyl)-mercurybserves excellently as starting material for the synthesis of l-bronio1-chlorocyclopropaiies by the same procedure. The mechanism of the phenyl-(trihalomethy1)mercury-olefin reaction is under investigation. Details concerning these and related experiments will be reported a t a later date. Acknowledgment.-'I he authors are grateful to the L.S.Xriny Research Office (Durham) for generous support of this work. (8) 1 l . p 110-111' ldec,), A n a l . Calcd. for C7HjCIDr,IIg: H A , 41 ; 3 0 ; CI, 7 :10, Br, ,12,U3, I'ound: HA. 4 L j f i ; C1, 7 . 0 7 ; Br, : 3 2 . i l L : E P A R T X E ~ T OF CHEMISIRY UIETMARS E T F ~ K T H
~ I A S A C I I U S EISSTITCTE ITS
TECHSOLOGY ~ A M E S51. UCKLITCH L I A R C H 24, 1962 OF
C A M B R I D G E , hIASSACHUSET'I'S KECEIVED
LARGE SECONDARY INTERMOLECULAR KINETIC ISOTOPE EFFECTS IN N ON-EQUILIBRIUM SYSTEMS. ENERGIZATION BY CHEMICAL ACTIVATION Sir :
strated the intermediacy of this anion in the formation of dichlorocarbene by the basic hydrolj-sis of chloroform, and the lifetime of such carbanion intermediates (relative to their decomposition to dihalocarbenes) is sufficiently long to allow other reactions besides dihalocarbene formation to be observed. Also pertinent is the fact t h a t nucleophilic displacement of chloride ion from mercury in organomercuric chlorides (e.g., by iodide ion6) is known to occur readily. It therefore is not surprising to encounter a displacement reaction such as the one demonstrated b y us. \Then bromine-containing halofornis were used in this reaction] the products were those expected,
The existence of very large, normal, secondary intermolecular kinetic isotope effects was pointed out recently by liabinovitch and Current, and the quantum statistical basis of the phenomenon described.l These eiiects may arise quite widely in uiiimolecular systems in which the energized species are produced in some non-eyuilibriulii distribution j ' ( c ) , i.c., one in which the poptlations of the various energy levels of interest are not governed by the ambient temperature si;d statistical thermodynamic equilibriurn considerations. The experimental techniques may in suitable cases include excitation by electrbil impact, light absorption, radiation, c$r. 111 Fact, thermal collisional C.P. ;activation may alsu be employed arid, under contlitions where noli-equilibrium populations I)re\,ail (the lower pressure region of thermal uiiiniolecular but the interpretation of these reactions is compli- reacticns), has been shown to give rise to very large cated b y the fact t h a t exchange between bromide iizversc intermolecular secondary isotope e5ects.' ion (from the haloform-base reagent mixture, The above mentioned authors perforlned experiwhich is used in twofold excess) and phenylmercuric ments involving excitation of vibrational and active chloride does occur. rotational degrees of freedom by chemical activaThe use of phenyl-(trichloromethy1)-mercury tion,3 in which the rates of C-H rupture of enerand phenyl-(tribromomethy1)-mercury in the syn- gized ethyl-d, and ethyl-d:
