Computational comparison of the reactions of substituted amines with CO(2).

Substituted amines are a popular choice as molecules to selectively react with and separate CO(2) from gas mixtures. Such separations are of particular interest, for example, for CO(2) separations for carbon capture and sequestration. It is desirable to tune amine-CO(2) reaction energies to suit a particular separation. Herein, we use DFT-B3LYP simulations to characterize the products and energetics of reactions of CO(2) with a range of substituted amines, considering both 1:1 and 2:1 amine/CO(2) reaction stoichiometries. The results show that by adjusting both the nature and the placement of functional groups, it is possible to tune reaction energies over a substantial range. Decomposition of the 2:1 reaction into separate carbamate and ammonium formation steps shows that the Brønsted basicity and Lewis basicity towards CO(2) are largely uncorrelated and provide an independent means of tuning the overall reaction energies.