Understanding the mechanism, thermodynamic and kinetic features of the Kukhtin–Ramirez reaction in carbamate synthesis from carbon dioxide

Abstract

In this article, thermodynamic and kinetic aspects of the Kukhtin–Ramirez reaction of the carbamate formation from carbon dioxide have been investigated in the presence of various phosphorous reagents (PRs), in the gas and solvent phases, theoretically. The obtained carbamate is a precursor for the synthesis of oxazolidine-2,4-dione as a biologically important compound. Two kinds of phosphorous reagents have been considered: type 1 is the PRs which have variable numbers of nitrogen atoms while, type 2 is composed of PRs without nitrogen atoms. By investigation of the local nucleophilicity indices (N_k) and steric exchange energy (dE), the reaction kinetics was studied in the presence of these kinds of PRs. It was illustrated that the steric repulsion between the lone pair electrons of the phosphorus atom and its bonded groups and the nucleophilicity character of this atom are impressive factors in the reaction kinetics. On the other hand, the analysis of stabilization energies associated with the donor–acceptor orbitals of the oxide forms of PRs (PORs) shows that the number of nitrogen atoms of the studied PRs have remarkable effects on the thermodynamics of the overall reaction. Finally, it has been shown that the obtained ΔE_Reaction by MPWB95 and B3LYP functionals, are in an acceptable correlation with the Mulliken atomic spin density (P_k⁻) of the phosphorous atom.