Thermal Isomerizations of 1,1-Dimethyl-2,2-d₂-cyclopropane

Abstract

The gas-phase thermal isomerization of 1,1-dimethylcyclopropane at 420 °C gives 3-methyl-1-butene and 2-methyl-2-butene. The mixture of products formed from 1,1-dimethyl-2,2-d 2-cyclopropane is consistent with conventional rationales; neither tert-butylcarbene nor isobutylcarbene is involved as a mechanistically significant intermediate. Both kinetic and deuterium labeling evidence suggests that heterogeneous wall-catalyzed processes afford secondary products, including 2-methyl-1-butene.

Kinetics of the thermal isomerization of 1,1‐dimethylcyclopropane

“…These observations suggest that 3M1B is the dominant precursor of 2M1B. Baldwin and Shukla [3] provided extensive evidence that the 2M1B they observed was produced by surface-catalyzed reactions, and they offered possible mechanisms. That would explain the 2M1B produced in our static reactor, but not that observed in the products of the highest temperature shock-tube run, in which the homogeneity of the process precluded production of products on the reactor surface.…”

“…Baldwin at Syracuse University, who has described the method of preparation previously [3]. CP grade 3M1B was obtained from Matheson Gas Products, and 2M2B (>99%) and 2M1B (>98%) were purchased from Aldrich.…”

“…The static reactor used for runs at lower temperatures consisted of a wellaged 100 cm 3 Pyrex cell surrounded by an aluminum furnace, equipped with an Omega 650-J-D digital thermometer.…”

“…Citing the isomerization of DMCP as "a veritable fixed point in related hydrocarbon thermal rearrangement chemistry shown by other alkyl-and dialkyl-substituted cyclopropanes" as the need for a re-examination, Baldwin and Shukla [3] heated DMCP and 1,1-dimethyl-2,2-d 2 -cyclopropane in a Pyrex bulb at 693 K for various lengths of time and found the same products as those observed by Flowers and Frey, and a value for the rate constant comparable to the one expected from the Arrhenius parameters reported by the latter. They also showed that 3M1B and 2M2B are the primary isomerization products of DMCP, and that 2M1B is formed on reactor surfaces from the primary products.…”

Kinetics of the thermal isomerization of 1,1,2‐trimethylcyclopropane

“…Toluene did not significantly change the extent of isomerization of the alkenes in the static reactor experiments, but it did appear to slightly increase the isomerization rates in the shock tube experiments. Baldwin and Shukla [13], studying 1,1-dimethylcyclopropane isomerization in a static reactor, noted isomerization of product alkenes and attributed this to surface-triggered formation of cationic species, followed by hydrogen or methyl shifts. They cited additional evidence for such processes from earlier isotope-labeling experiments and NMR-spectroscopic studies.…”