A pH Scale for the Protic Ionic Liquid Ethylammonium Nitrate

Ryo Kanzaki; Hitoshi Kodamatani; Takashi Tomiyasu; Hikari Watanabe; Yasuhiro Umebayashi

doi:10.1002/anie.201511328

A pH Scale for the Protic Ionic Liquid Ethylammonium Nitrate

Angew Chem Int Ed Engl. 2016 May 17;55(21):6266-9. doi: 10.1002/anie.201511328. Epub 2016 Apr 13.

Authors

Ryo Kanzaki¹, Hitoshi Kodamatani², Takashi Tomiyasu², Hikari Watanabe³, Yasuhiro Umebayashi⁴

Affiliations

¹ Graduate School of Science and Engineering, Kagoshima University, 1-21-35, Korimoto, Kagoshima, 890-0065, Japan. kanzaki@sci.kagoshima-u.ac.jp.
² Graduate School of Science and Engineering, Kagoshima University, 1-21-35, Korimoto, Kagoshima, 890-0065, Japan.
³ Graduate School of Science and Technology, Niigata University, 8050, Ikarashi 2-no-cho, Nishi-ku, Niigata, 950-2181, Japan.
⁴ Graduate School of Science and Technology, Niigata University, 8050, Ikarashi 2-no-cho, Nishi-ku, Niigata, 950-2181, Japan. yumescc@chem.sc.niigata-u.ac.jp.

PMID: 27071502
DOI: 10.1002/anie.201511328

Abstract

To quantify the properties of protic ionic liquids (PILs) as acid-base reaction media, potentiometric titrations were carried out in a neat PIL, ethylammonium nitrate (EAN). A linear relationship was found between the 14 pKa values of 12 compounds in EAN and in water. In other words, the pKa value in EAN was found to be roughly one unit greater than that in water regardless of the charge and hydrophobicity of the compounds. It is possible that this could be explained by the stronger acidity of HNO3 in EAN than that of H3 O(+) in water and not by the difference in the solvation state of the ions. The pH value in EAN ranges from -1 to 9 on the pH scale based on the pH value in water.

Keywords: acid-base catalysis; acidity; ionic liquids; pH scale; potentiometric titrations.

Publication types

Research Support, Non-U.S. Gov't