Jump to main content
Jump to site search

Issue 12, 2017
Previous Article Next Article

Effect of protonation on the solvation structure of solute N-butylamine in an aprotic ionic liquid

Author affiliations

Abstract

We report on the acid–base reaction of an amine solute in an aprotic ionic liquid from a structural point of view. Thus, the solvation structures of n-butylamine and n-butylammonium (BuNH2 and BuNH3+, respectively, acid–base reaction: BuNH2 + H+ ⇄ BuNH3+) in 1-methyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)amide ([C2mIm][TFSA]) were investigated by high-energy X-ray total scattering combined with molecular dynamics simulations. We found that the solvation structure drastically changed as a result of the protonation reaction in [C2mIm][TFSA]. The NH3+ group was preferentially solvated by TFSA anions in the protonated BuNH3+ system, whereas the neutral NH2 group was surrounded by both TFSA and C2mIm+ ions in the BuNH2 system. With regard to the nearest neighbor solute–TFSA interaction, the solvation number for TFSA anions (nTFSA) increased upon protonation (i.e. BuNH2:nTFSA = 2 and BuNH3+:nTFSA = 3). Both BuNH2 and BuNH3+ interacted with O atoms within TFSA through hydrogen bonding (i.e. N–H⋯O) interactions, and the N–H⋯O distance was appreciably shorter for positively charged BuNH3+ as compared to neutral BuNH2. These results revealed that the solvation is more stable in energy for the protonated BuNH3+ group because of its stronger hydrogen bonding as compared to neutral BuNH2. This is the origin of the large Gibbs energy for the protonation reaction (ΔG = −94.7 kJ mol−1) and the high acid dissociation constant (pKa = 16.6) of BuNH2 in [C2mIm][TFSA] solution.

Graphical abstract: Effect of protonation on the solvation structure of solute N-butylamine in an aprotic ionic liquid

Back to tab navigation
Please wait while Download options loads

Supplementary files

Publication details

The article was received on 02 Dec 2016, accepted on 01 Feb 2017 and first published on 01 Feb 2017


Article type: Paper
DOI: 10.1039/C6CP08247E
Citation: Phys. Chem. Chem. Phys., 2017,19, 8194-8200
  •   Request permissions

    Effect of protonation on the solvation structure of solute N-butylamine in an aprotic ionic liquid

    K. Hashimoto, K. Fujii, K. Ohara and M. Shibayama, Phys. Chem. Chem. Phys., 2017, 19, 8194
    DOI: 10.1039/C6CP08247E

Search articles by author