Phase transfer catalysts between polar and non-polar media: a molecular dynamics simulation of tetrabutylammonium iodide at the formamide/hexane interface

Abstract

A molecular dynamics simulation of tetrabutylammonium iodide (TBAI) in the free liquid surface of formamide (FA) and in the interface of formamide and hexane (HX) was performed. TBAI was treated as 18 sites in a flexible model, five sites were employed for formamide and six for hexane. The simulation lasted 425 ps for each system at 300 K. Dynamic and orientational properties of both systems are discussed. The thickness of the polar/non-polar interface amounts to 10–14 Å. Furthermore, the anion moves over large distances in the polar phase whereas the cation remains in the interface. Penetration into the non-polar liquid is not observed for either ionic species. Only a minor influence of the salt on the orientation of formamide, which is preferential at the surface compared with the bulk, is observed and a minor effect on the length distribution of the hexane as a measure of the coiled or elongated arrangement is found.