Green Microwave-Assisted Synthesis of Cyclic/Acyclic Ureas from Propylene Carbonate

摘要

Herein, an organocatalyzed synthetic pathway for the preparation of (a)cyclic ureas from their parent primary aliphatic or aromatic mono-/diamines with propylene carbonate (PC) as a carbonylating agent (CAT) obtaining reasonable to very good yields with high selectivity. Our method is considered green as nine out of twelve green chemistry principles (GCPs) are fulfilled. Most importantly, the absence of solvent, energy-efficient pathway, in addition to the ease of synthesis and separation, under fast reaction times down to a few minutes together with the straightforward workup with minimum use of organic solvents. Our method was successful in preparing 1,3-diphenylurea from aniline giving 8% yield in 10 minutes, to our knowledge, this was not previously reported using aromatic amines with carbonate esters. The prepared compounds were fully characterized by spectroscopic and thermal techniques. The method is applicable for primary rather than secondary amines, which implies high chemoselectivity of the former for the synthesis of urea compounds.