Alkali Metal Salt as Catalyst for Direct Synthesis of Carbamate from Carbon Dioxide

Abstract

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.

Methyl N-phenyl carbamate synthesis over Zn/Al/Ce mixed oxide derived from hydrotalcite-like precursors

“…MPC could be synthesized via the reactions of phenylurea and dimethyl carbonate (DMC) 4 and/or methanol, 5 aniline and DMC 2,6-10 and/or methyl carbamate (MC), 3,11 and even aniline and C 1 source (e.g. CH 3 OH and CO 2 ), [12][13][14] etc. And some new synthetic paths have also been developed recently.…”

The Reaction of o‐Aminoacetophenone N‐Tosylhydrazone and CO2 toward 1,4‐Dihydro‐2H‐3,1‐benzoxazin‐2‐ones

“…A proposed mechanism was outlined in Scheme . First, Cs 2 CO 3 binds with aniline and extracts a proton from it . Then the carboxylation of amine by CO 2 takes place to produce intermediate C .…”

“…First, Cs 2 CO 3 binds with aniline and extracts a proton from it. [19] Then the carboxylation of amine by CO 2 takes place to produce intermediate C. Afterward, intermediate C sequentially releases Ts À and N 2 under the assistance of base, leading to carbene intermediate D. Finally, intramolecular insertion of carboxylic to carbene delivers 1,4-dihydro-2H-3,1-benzoxazin-2ones (3 a).…”

Transition Metal‐Free Synthesis of Carbamates Using CO2 as the Carbon Source

“…In 2017 and 2018, Choi and co‐workers developed a more environmentally friendly carbamate synthesis by replacing a zinc catalyst with an ionic liquid [30a–c] . Having first reported an efficient synthesis by using Zn(OAc) 2 , [30a] they later found that ionic liquids could replace the transition metal catalyst.…”