Calcium carbide was used as a sustainable dehydrating agent for the synthesis of carbamates, glycerol carbonate, and cyclic carbonates directly from CO₂.

An easily synthesized ionic liquid was used as an organocatalyst to synthesize carbamates directly from amine, CO2, and silicate esters.

Several zinc salts were employed as catalysts for the synthesis of carbamates directly from aromatic amines, CO , and silicate esters. Zn(OAc) offered the best performance among the salts tested. The addition of an N-donor ligand such as 1,10-phenanthroline increased the yield. The best catalytic performance of Zn(OAc) can be explained by carboxylate-assisted proton activation. The interaction between the substrate and the catalyst can be observed by chemical shifts in H and N NMR spectra. Isocyanate was a key intermediate, which was generated from amine and CO . Silicate ester was finally converted to siloxane, which was determined by Si NMR. The commercially available catalyst system could be reused. The yield of isolated carbamate could reach up to 96 % with various substrates, and the catalytic reaction was amine-selective in the presence of other functional groups.

Carbamates are an important motif in agricultural chemistry, medicinal chemistry, and polyurethane preparation. Potassium carbonate (K2CO3) is a common, nontoxic, and inexpensive chemical and is widely used in organic synthesis. Herein we report the use of K2CO3 as a catalyst for direct synthesis of carbamate from amine, silicate ester, and carbon dioxide. Especially, both alkyl amines and aromatic amines could be activated, largely expanding the substrate scope compared with the use of alcohol as the coupling reagent. Anion-assisted deprotonation of amine was the key step in the catalytic process, and the alkali metal served as a Lewis acid. Isolated yield of the corresponding carbamate was up to 97%. The use of K2CO3 as the catalyst decreased 49 kJ mol–1 activation energy of the reaction compared with our previously reported ionic liquid catalyst from Arrhenius analyses.

A facile one-pot, phosgene-free method for the synthesis of N-phenylcarbamates is developed. Using this method, various aromatic carbamates could be prepared from aromatic amines, CO2 and metal alkoxides. Aniline reacted with titanium methoxide (Ti(OMe)4) in the presence of CO2 (5 MPa) to give methyl N-phenylcarbamate in 85% yield, in 20 min. Titanium residue could be regenerated by reaction with dimethyl carbonate at 220 °C for 16 h.