SOLVENT EFFECT ON IODIDE EXCHANGE

Abstract

The exchange of iodine between hydrogen iodide and n-butyl iodide has been studied in several organic solvents. In solvents of high dielectric constant (methanol, ethanol, n-butanol), exchange occurred by reaction of iodide ions with butyl iodide. In solvents of low dielectric constant (n-hexanol, n-dodecanol, acetic acid), it appeared that exchange also occurred between butyl iodide and the associated IHI− triple ion. Orders of magnitude of the individual specific rate constants have been calculated, using approximate values for the dissociation constants of hydrogen iodide. The rate constant – dielectric constant relation developed by Laidler and Eyring for ion – neutral molecule reactions appears to hold for exchange in homologous solvents, but does not seem to represent the effect of nonhomologous solvents. This discrepancy and the small differences observed in activation energies for the various exchanges may be due to solvation effects.