Iodination of alkanes : ethane, propane and isobutane

Abstract

The rate constants for the reaction [graphic omitted] have been determined by thermal iodination of the title alkanes between 230 and 345°C, and obey the Arrhenius equations: [graphic omitted] where k₂ is in mole^–1 cm³ sec^–1 and energies are in cal mole^–1. As the iodinations proceed, inhibition reactions occur which lead to final equilibria. Using a computer, the “best values” of the equilibrium constants K₅ and K₆ [graphic omitted] [graphic omitted] have been determined from the product development curves for ethane, propane (K₅) and isobutane (K₆). For propane and isobutane there is reasonable agreement between these values and those computed from thermodynamic data, but for ethane there is a major discrepancy.

During the reactions with ethane and propane the initially formed iodides decomposed to olefins and hydrogen iodide. These reactions occurred 5–10 times more rapidly than would be expected from published data on the homogeneous pyrolysis of iodides, and were probably heterogeneous in our system.