172
ROSS VAN VOLKENBURGH,
K. M'.
GREENLEE,
J. M. DERFERAND
[CONTRIBUTION FROM THE I)EPARTMENT O F CHEMISTRY OF
THEOHIO
c. E. BOORD
VOl. 71
STATE UNIVERSITY]
The Synthesis of Some Cyclopropane Hydrocarbons from Methyl Cyclopropyl Ketone' BY Ross VAN VOLKENBURGH, K. W.GREENLEE, J. M. DERFERAND C. E. Boom gave the highest yield of isopropenylcyclopropane. The formation of this hydrocarbon is best explained by a Whitmore-type* mechanism involving a carbonium ion, this ion (cyclopropyldimethylcarbonium) apparently being most easily stabilized without rearrangement by expulsion of a proton from one of the methyl groups, rather than by ring rupture or expansion. It is noteworthy that the tertiary hydrogen atom on the cyclopropane ring is not expelled to produce isopropylidenecyclopropane. An explanation of this behavior is possible if i t is recalled that the cyclopropane group sometimes appears to have inany of the attributes of a double bond and the structure of isopropenylcyclopropane may thus he considered as somewhat analogous to that of isoprene. 'This would account for the failure in the present case of hydrogen to be expelled according to Saytzeff's rule (since its nature would be somewhat vinylic) and for the consequent expulsion of a hydrogen atom from a methyl group normally low in reactivity, to form the pseudoconjugate isopropenylcyclopropane, stabilized to some extent by resonance. Further, the strain of a double bond attached to a three membered ring may also be a factor. Since more than one mechanism is apparently involved in methods (A) and (El, i t appears that as the acid strength of the catalyst is increased, the reaction proceeds through the carbonium ion to a greater extent. Inasmuch as nothing except isopropeiiylcyclopropane was found when method C W ~ uqed, S the dehydration over sulfuric acid must h a r e proceeded almost exclusively through the csrbuniurn ion mechanism. 'The structure of isopropenylcyclopropane was proved by an ozonolysis experiment (on a sample prepared b j method C) from which methyl cycloprop! 1 ketone was isolated and identified through its setriicarbazone; a mixed melting point with hlr~tbo5 t!ie corresponding derivative of an authentic , Ii i >ample of the ketone showed no depression. The lsopropenylcy-clopropane, ' (, :I 57 80 21 physical properties of a sample of isopropenylMethylpentndiene, % 20 c y h p r o p a n e of 99.4 mole per cent. purity are 2,2-DimetliyItetrahydrofuran, 71 10 IS given in Table 11. I n order to verify the identity I t wil! be notcd that of the first three iiiethods, of the isopropenylcyclopropane prepared by the the one employing the stronqcst acid (sulfuric) other three methods, a series of mixed melting points were tletermined with a portion of the (1) T h i s paper forms pdrt of R thests which A i l 1 b t siilitn~ttedby hydrocarbon whose structure had been proved by Kow Van Volkenburgh t o the Gradnate School o f 7 he Ohio S t a t e University in partial fulfillment of the requirrments for t h e degree ozonolysis; no significant depression occurred of Iloctor of Philosophy T h t iii\citigdtion was sponsored by the with any of the samples. American k'etroleum I n s t i t u t e (Rescarch Projcct 45) in cooperation The preparation of isopropylcyclopropane by with T h e Ohio S t a t e Gniterbitg Research Foundation. (2) 1; S Indu
