• Home
  • Search Results
  • Proton Transfer and Ionicity: An 15N NMR Study of Pyridine Base Protonation.

Proton Transfer and Ionicity: An 15N NMR Study of Pyridine Base Protonation.

The journal of physical chemistry. B (2019-02-20)
Mohammad Hasani, Samrat A Amin, Jeffery L Yarger, Stephen K Davidowski, C Austen Angell
ABSTRACT

Protic ionic liquids (PILs) are made by proton transfer from a Brønsted acid to a base and are of interest for their solvent and electrolyte properties such as high ionic conductivity. Unfortunately, many PILs have been misnamed, because their ionic content is minimal due to an insufficient driving force for the proton transfer. Here we review this problem and introduce a new method, using 15N NMR spectroscopy, of characterizing the relation between the extent of proton transfer to a given base and the strength of the proton-donating acid. The experimental data reveal a sigmoid "titration type" curve that indicates clearly the acid strength, at which molecule bases, of substituted pyridine type, are fully protonated. We compare results for two bases of similar shape but different basicity, protonated by equimolar amounts of the different acids. The extent of protonation is also reflected in the ionic conductivity, and we show that the important part of the protonation sigmoid is quantitatively reproduced by data for conductivity and viscosity displayed in the form of a Walden plot (log equivalent conductivity vs log fluidity). The acid strength, for this study, is based on gas phase proton affinities, but we note that a similar sigmoid is obtained if we use the condensed phase Hammett acidity functions instead. Our findings allow us to rank the AlCl4- anion as the weakest proton acceptor in use in IL studies, consistent with its role in the most conductive ILs.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Methanesulfonic anhydride, 97%
Sigma-Aldrich
2-Fluoropyridine, 98%

Social Media

LinkedIn icon
Twitter icon
Facebook Icon
Instagram Icon

MilliporeSigma

Research. Development. Production.

We are a leading supplier to the global Life Science industry with solutions and services for research, biotechnology development and production, and pharmaceutical drug therapy development and production.

© 2021 Merck KGaA, Darmstadt, Germany and/or its affiliates. All Rights Reserved.

Reproduction of any materials from the site is strictly forbidden without permission.