K₃PO₄-catalyzed carboxylation of amines to 1,3-disubstituted ureas: A mechanistic consideration

K₃PO₄ was found to effectively catalyze the carboxylation of amines by CO₂, producing corresponding 1,3-disubstituted ureas in high yields and selectivities. X-ray diffraction and FT-IR spectroscopic analysis of the solid mixture, recovered from the carboxylation of n-butylamine, revealed that K₃PO₄ was completely transformed into KH₂PO₄ and KHCO₃. Mechanistic and computational studies suggested that the high activity of K₃PO₄ could be attributed to the synergy effect exerted by the co-presence of KHCO₃ and KH₂PO₄, generated from the interaction of K₃PO₄ with CO₂ and water.