A thermodynamic and kinetic study of the ionic association of N-methylpyridinium iodide in mixed solvents

Paul Hemmes, James N. Costanzo, Frank Jordan

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The thermodynamics of ionic association of N-methylpyridinium iodide were investigated by UV and conductance, while the kinetics of the process were studied by ultrasonic relaxation spectroscopy. The UV data were treated taking explicit account of the variable ionic strength existing in the solutions studied and this treatment led to essentially wavelength independent association constants in the 290-310-nm range. The high linear correlation obtained in the log K association vs. 1/dielectric constant plot in aqueous ethanol for all UV and conductance data combined is suggestive of a classical ionic association process being monitored in the entire range of solvent compositions employed. Ultrasonic absorption measurements demonstrated the existence of two relaxation processes in 95, 90, and 88% acetone-water (v/v). The high-frequency relaxation was concentration dependent (at fixed solvent composition) and was due to the formation of ion pairs from free ions. The low frequency relaxation is due to a desolvation process which converts a solvent-separated ion pair to a contact pair. The relaxation frequency of the slower process is linearly dependent upon the water concentration in the solvent mixtures. This is shown to be evidence for the removal of a single water molecule in the process of interconverting the two ion pair species.

Original languageEnglish (US)
Pages (from-to)387-391
Number of pages5
JournalJournal of physical chemistry
Issue number4
StatePublished - Jan 1 1978

All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Physical and Theoretical Chemistry

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