Acid-base equilibrium dynamics in methanol and dimethyl sulfoxide probed by two-dimensional infrared spectroscopy

Chiho Lee, Hyewon Son, Sungnam Park

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2 Citations (Scopus)

Abstract

Two-dimensional infrared (2DIR) spectroscopy, which has been proven to be an excellent experimental method for studying thermally-driven chemical processes, was successfully used to investigate the acid dissociation equilibrium of HN<inf>3</inf> in methanol (CH<inf>3</inf>OH) and dimethyl sulfoxide (DMSO) for the first time. Our 2DIR experimental results indicate that the acid-base equilibrium occurs on picosecond timescales in CH<inf>3</inf>OH but that it occurs on much longer timescales in DMSO. Our results imply that the different timescales of the acid-base equilibrium originate from different proton transfer mechanisms between the acidic (HN<inf>3</inf>) and basic (N<inf>3</inf><sup>-</sup>) species in CH<inf>3</inf>OH and DMSO. In CH<inf>3</inf>OH, the acid-base equilibrium is assisted by the surrounding CH<inf>3</inf>OH molecules which can directly donate H<sup>+</sup> to N<inf>3</inf><sup>-</sup> and accept H<sup>+</sup> from HN<inf>3</inf> and the proton migrates through the hydrogen-bonded chain of CH<inf>3</inf>OH. On the other hand, the acid-base equilibrium in DMSO occurs through the mutual diffusion of HN<inf>3</inf> and N<inf>3</inf><sup>-</sup> or direct proton transfer. Our 2DIR experimental results corroborate different proton transfer mechanisms in the acid-base equilibrium in protic (CH<inf>3</inf>OH) and aprotic (DMSO) solvents.

Original languageEnglish
Pages (from-to)17557-17561
Number of pages5
JournalPhysical Chemistry Chemical Physics
Volume17
Issue number27
DOIs
Publication statusPublished - 2015 Jul 21

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Physics and Astronomy(all)

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