Vaporization of protic ionic liquids derived from organic superbases and short carboxylic acids

• Type: Article in International Scientific Journal
• Date: 2017

Authors

Ribeiro, FMS (Author) Other; Lima, CFRAC (Author) FCUP; Vaz, ICM (Author) Other; Rodrigues, ASMC (Author) Other; Sapei, E (Author) Other; Andre Melo (Author) FCUP; Silva, AMS (Author) Other; Luis M N B F Santos (Author) FCUP

Journal

Title: Physical Chemistry Chemical Physics

Vol. 19 No. 2

Pages: 16693-16701

ISSN: 1463-9076

Publisher: Royal Society of Chemistry

Indexing

ISI Web of Knowledge - 12 Citations

Scopus - 13 Citations

Other information

Authenticus ID: P-00N-539

DOI: 10.1039/c7cp02023f

Abstract (EN): This work presents a comprehensive evaluation of the phase behaviour and cohesive enthalpy of protic ionic liquids (PILs) composed of 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) or 1,8-diazabicyclo[5.4.0] undec-7- ene (DBU) organic superbases with short-chain length (acetic, propionic and butyric) carboxylic acids. Glass transition temperatures, T-g, and enthalpies of vaporization, Delta H-vap, were measured for six [BH][A] (1 : 1) PILs (B = DBN, DBU; A = MeCOO, EtCOO, nPrCOO), revealing more significant changes upon increasing the number of -CH2- groups in the base than in the acid. The magnitude of Delta H-vap evidences that liquid PILs have a high proportion of ions, although the results also indicate that in DBN PILs the concentration of neutral species is not negligible. In the gas phase, these PILs exist as a distribution of ion pairs and isolated neutral species, with speciation being dependent on the temperature and pressure conditions at high temperatures and low pressures the separated neutral species dominate. The higher T-g and Delta H-vap of the DBU PILs are explained by the stronger basicity of DBU (as supported by NMR and computational calculations), which increases the extent of proton exchange and the ionic character of the corresponding PILs, resulting in stronger intermolecular interactions in condensed phases.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 9