Structure and Dynamics of Neat and CO₂-Reacted Ionic Liquid Tetrabutylphosphonium 2-Cyanopyrrolide

Results of molecular dynamics simulations are reported in which the structure and dynamics of the reacted and unreacted forms of the task-specific ionic liquid (TSIL) tetrabutylphosphonium 2-cyanopyrrolide were computed. This particular ionic liquid is one of several newly discovered TSILs containing aprotic heterocyclic anions designed specifically for CO 2 capture. The physical properties, liquid structure, and dynamics of the ionic liquid were computed as a function of extent of reaction with CO 2 . Translational and rotational dynamics showed little change upon reaction with CO 2, in sharp contrast to traditional TSILs and consistent with experimental viscosity measurements. It is shown that this is due to the failure of a hydrogen-bond network to form upon reaction with CO 2 . The Henry’s law constants for the physical solubility of CO 2, N 2, O 2, and H 2 O were computed for the unreacted TSIL and found to be comparable to values observed with other ionic liquids. In the reacted state, the solubility of CO 2, N 2, and O 2 remained essentially unchanged, whereas the solubility of H 2 O increased by over a factor of 10 because of favorable hydrogen-bonding interactions with the carbamate.