Substituent dependence of imidazoline derivatives on the capture and release system of carbon dioxide

Abstract

The reversible capture–release behaviors of CO₂ by imidazoline derivatives bearing several 2-substituents were investigated under dry conditions containing a very small amount of water. The imidazoline having a cyclic guanidine moiety only captured CO₂ quantitatively, and then the cyclic guanidine derivative gave the guanidinium bicarbonate by CO₂ fixation together with a slight amount of water. In contrast, the imidazolines bearing n-butylthiol and n-pentyl groups never captured CO₂ even with the addition of an equimolar amount of water. Furthermore, the binding structure between CO₂ and the cyclic guanidine derivative was studied in detail by elemental analysis, FTIR-ATR, solid-state NMR, TGA, and DFT calculations in order to predict the CO₂ capture–release mechanisms depending on the imidazoline structure.