A Reinvestigation of the Ionic Liquid Diisopropylethylammonium Formate by NMR and DFT Methods

Poul Erik Hansen; Torben Lund; Jacob Krake; Jens Spanget-Larsen; Søren Hvidt

doi:10.1021/acs.jpcb.6b08561

A Reinvestigation of the Ionic Liquid Diisopropylethylammonium Formate by NMR and DFT Methods

J Phys Chem B. 2016 Nov 3;120(43):11279-11286. doi: 10.1021/acs.jpcb.6b08561. Epub 2016 Oct 21.

Authors

Poul Erik Hansen¹, Torben Lund¹, Jacob Krake¹, Jens Spanget-Larsen¹, Søren Hvidt¹

Affiliation

¹ Department of Science and Environment, Roskilde University , DK-4000 Roskilde, Denmark.

PMID: 27731642
DOI: 10.1021/acs.jpcb.6b08561

Abstract

The complex between diisopropylethylamine (DIPEA) and formic acid has been reinvestigated. Mixing the compounds in the ratio 1:1 leads to a phase separation in which the upper phase is DIPEA and the lower phase is the "ionic liquid" named DIPEF. A combined NMR and DFT study shows that the lower phase primarily is formic acid:formate and diisopropylammonium ions in the ratio 2:1 (acid:base) plus the formic acid dimer. Addition of more acid leads to more and more of the acid dimer. The proton transfer in the system is 65-80%. The structural picture presented in this paper is very different from that presented elsewhere. However, the present picture should be considered using acids and bases with a pK_a difference less than 8. The formic acid content in the DIPEF ionic liquid causes desorption of the dye-sensitized solar cell (DSC) dye N719 from the photo anode, and DIPEF is therefore not a suitable electrolyte for DSCs.