The Kinetics of the Thermal Isomerization of Ethylcyclopropane^1a

Abstract

Ethylcyclopropane simultaneously undergoes an isomerization to 1-pentene, cis-and trans-2-pentene, and 2-methyl-1-butene and a decomposition to butadiene and methane. The reaction has been studied in the gas phase by static methods from 454 to 484" and over a pressure range of 84 to 5 X mni.; under these conditions, the isomerization to the pentenes was found to be a homogeneous unimolecular process. The decomposition to butadiene may be taking place via a free-radical process or by a unimolecular disproportionation reaction. The lifetime of the activated niolecule is about a factor of 10 longer than that of the methylcyclopropane decomposition reaction as evidenced by a shift of the log k / k us. log P curve to lower pressures for ethylcyclopropane. All degrees of freedom appear to participate in increasing the lifetime of the activated niolecule. The Marcus extension of the Rice-Ramsperger-Kassel theory is applied to this reaction. The high pressure rate constant for isomerization to pentenes niay be expres'sed as ICi, = 1014.40 exp[(-61.6 f 1.4) kcsl./RT] sec.-'.(1) (a) This paper is abstracted, in part, from the dissertation submitted by M. L. H. to the Graduate School of Tale University, 1963, in partial fulfillment of the requirements for the Ph.D. degree; (b) to whom requests for reprints should

Recoil Tritium Reaction: Ring Opening and Alkyl Replacement in Substituted Cyclopropanes1

“…However, the isomerization rates of DMC and EC are much slower than those for cyclopropane molecules with equal excitation energies. [26][27][28][29] The fastest observed isomerization reactions of both cisand fnras-DMC are the geometric isomerizations to the opposite isomer; structural isomerizations to pentenes occur with rate constants one-tenth to one-twentieth times as fast,27 as shown in the "thermal isomerization" columns of Table III.…”

Syntheses of three stable isotope‐labeled ethylcyclopropanes

“…Methylcyclopropane gave rise to 1‐butene, cis ‐ and trans ‐2‐butene, and isobutylene (2‐methyl‐1‐propene) 3. Ethylcyclopropane ( 1 ) in the gas phase at 454–484°C formed 1‐pentene, cis ‐ and trans ‐2‐pentene, and 2‐methyl‐1‐butene 4. 1,1‐Diethylcyclopropane ( 3 ) was isomerized at 425–475°C to 3‐ethyl‐1‐pentene and 3‐ethyl‐2‐pentene 5.…”

“…What was not at all anticipated in 1965 was the independent and nearly simultaneous discoveries of the thermal conversions of ethylcyclopropane ( 1 ) to methane and butadiene ( 2 ) 4 and 1,1‐diethylcyclopropane ( 3 ) to 2‐ethylbutadiene ( 4 ) 5. These reactions appeared to be homogeneous unimolecular parallel processes and constituted fair proportions, about 20%, of the overall conversions of starting materials to products.…”

“…These reactions were clearly ‘of a type previously not reported’. Mechanistic possibilities were cautiously formulated by the authors, 4, 5 and other contrasting perspectives were shared soon thereafter 6. But no mechanistic clarifications were sought soon thereafter or have been pursued through experimental or theoretical approaches over recent decades.…”

“…But no mechanistic clarifications were sought soon thereafter or have been pursued through experimental or theoretical approaches over recent decades. Halberstadt and Chesick noted in 1965 that pyrolysis of a mixture of 1 and 1 ‐ d 10 followed by analysis of the methane produced through MS could unambiguously test between a molecular mechanism versus one involving free‐radical intermediates such as CH 3 and CH 2 =CH–CH 2 CH 2 4 (Scheme ).…”