Crystal structure and density functional theory investigations on carbon dioxide capture reactivity of primary amine and secondary amine, the case of diethylenetriamine

The primary objective of this study is to compare the reactivity of primary amine and secondary amine groups in diethylenetriamine (DETA) during the process of CO₂ capture. To achieve this goal, the reaction energies, optimal structures, the frontier molecular orbitals and electrostatic potentials for [2-[(2-aminoethyl)amino]ethyl]carbamic acid (CO₂NH₂) and bis(2-aminoethyl)carbamic acid (CO₂N) were computed within density functional theory (DFT). Subsequently, DFT calculations were performed on 6-[[2-[(2-aminoethyl)amino]ethyl]amino]-2-(prop-2-yn-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NH₂BQL), 6-[bis(2-aminoethyl)amino]-2-(prop-2-yn-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NBQL), [2-[[2-[[1,3-dioxo-2-(prop-2-yn-1-yl)-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl]amino]ethyl]amino]ethyl]carbamic acid (CO₂NH₂BQL), and (2-aminoethyl)[2-[[1,3-dioxo-2-(prop-2-yn-1-yl)-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl]amino]-ethyl]carbamic acid (CO₂NBQL) by introducing a third molecule, 6-bromo-2-(prop-2-yn-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Br-BQL). The results were studied from such various perspectives as ΔH (enthalpies), ΔG (free energies), bond lengths, bond angles, highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) energies, as well as dipole moment. The results indicated that the primary amine group in DETA is more reactive in CO₂ capture, as confirmed by the crystal structure of CO₂NH₂BQL. These findings contribute valuable insights into the design of CO₂ capture material with an emphasis on reactivity by offering an ingenious strategy.