Synthesis of symmetrical or asymmetrical urea compounds from CO₂via base catalysis

Base Catalysis by Mono- and Polyoxometalates

“…However, CO2 is much less reactive than CO and phosgene, and a large energy input (e.g., highly reactive reagents, high CO2 pressures, and stoichiometric amounts of strong acids or bases) is usually required to transform CO2 into various chemicals. Therefore, the low-energy catalytic fixation of CO2 is highly desirable, and several effective catalytic systems have been reported [110][111][112][113][114][115][116]. Mizuno and co-workers reported that a simple monomeric tungstate TBA2[WO4] could act as a highly efficient homogeneous catalyst for the chemical fixation of CO2 with amines, 2-aminobenzonitriles, and propargylic alcohols to urea derivatives, quinazoline-2,4(1H,3H)-diones, and cyclic carbonates, respectively (Schemes 1-3) [38,42,45].…”

Carbon dioxide uptake as ammonia and amine carbamates and their efficient conversion into urea and 1,3-disubstituted ureas

“…Their traditional synthesis required unsafe chemicals such as phosgene or carbon oxide and Au or Pt catalysts [35][36][37][38]. In recent years the direct synthesis of substituted ureas has been accomplished with the non toxic and cheap carbon dioxide in the presence of different catalysts and dehydrating agents to increase the yield of reaction [39][40][41][42]. Ionic liquids in conjunction with a base (CsOH) or transition metal (Fe, Co, Ni, Cu, Zn) acetates were also employed as reaction medium and catalysts to obtain 1,3-disubstituted ureas in good yield [43][44][45][46].…”

Chemical Technologies for Exploiting and Recycling Carbon Dioxideinto the Value Chain

“…[145] Furthermore, dimethylcarbonate as well as diphenylcarbonate can be utilized to convert amines to carbamates, [146] which can then be transformed to the isocyanates by elimination of water. [147] The carbamates can also be synthesized directly from CO 2 and amines [148,149] or by transesterification of urea with alcohols. [150] In these ways, fixed CO 2 may be introduced into polyurethane chemistry (vide infra).…”