Enhanced extraction of phenol from model oils using ionic liquids elucidated with neutron diffraction

Phys Chem Chem Phys. 2020 May 13;22(18):10219-10226. doi: 10.1039/d0cp01013h.

Abstract

Aromatic cation ionic liquids (ILs) based on alkylpyridiniums are shown to be good phenol extractants from model oils (hexane/toluene). ILs with hard basic anions are found to have best extraction efficiency consistent with tetraalkylammonium salts ([NR4]X). Key extraction interactions were analysed using small angle neutron diffraction. Trifluoromethanesulphonate ([OTf]- or triflate) anions provide the synergistic effects of reduced cation-phenol centre of mass (COM) distances and increased hydrogen bonding that are linked to the improved extraction efficiency. Increases in cation electron density (methylpyridinium ([Me-Py]+) vs. methylpicolinium ([Me-3-Pic]+)) also reduce cation-phenol COM interaction lengths consistent with small increases in extraction efficiency for the same ionic liquids.