Fast equilibrium of zwitterionic adduct formation in reversible fixation–release system of CO2 by amidines under dry conditions

We investigated the fixation of CO2 by several amidines in solution and found that simple monocyclic amidines fixed CO2 under dry conditions to quantitatively afford the corresponding bicarbonates through hydrolysis of the zwitterionic adducts by adventitious water. In contrast, linear amidines did not form the bicarbonates under the same conditions, while 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) could not effectively trap CO2. The CO2 fixed by the monocyclic amidines was quantitatively released by argon bubbling at a temperature as low as 60 °C. The CO2 fixation–release process could be repeated several times without loss of the high efficiency.