One-pot catalytic synthesis of urea derivatives from alkyl ammonium carbamates using low concentrations of CO2

Abstract

To reduce anthropogenic carbon dioxide (CO2) emissions, it is desirable to develop reactions that can efficiently convert low concentrations of CO2, present in exhaust gases and ambient air, into industrially important chemicals, without involving any expensive separation, concentration, compression, and purification processes. Here, we present an efficient method for synthesizing urea derivatives from alkyl ammonium carbamates. The carbamates can be easily obtained from low concentrations of CO2 as present in ambient air or simulated exhaust gas. Reaction of alkyl ammonium carbamates with 1,3-dimethyl-2-imidazolidinone solvent in the presence of a titanium complex catalyst inside a sealed vessel produces urea derivatives in high yields. This reaction is suitable for synthesizing ethylene urea, an industrially important chemical, as well as various cyclic and acyclic urea derivatives. Using this methodology, we also show the synthesis of urea derivatives directly from low concentration of CO2 sources in a one-pot manner.

CeO2-Catalyzed Synthesis of 2-Imidazolidinone from Ethylenediamine Carbamate

“…Koizumi and co-workers reported that CeO 2 (<25 nm) was active for the synthesis of 1 from EDA-CA, but the activity was low (yield 29%, 443 K). 29 In contrast, in our case, by using nano-CeO 2 (84 m 2 /g, 9 nm), the yield reached 83% at a low temperature of 413 K, and such a lower reaction temperature is beneficial for the suppression of EDA-CA decomposition. These results mean that our CeO 2 catalyst is quite active for the reaction.…”

“…The highest yield of 83% was obtained at 413 K with a proper amount of the 2-propanol solvent (15 mL). The formation rate was calculated from the slope of the time course at a low conversion level (<40%, Figure S5 and Table S6) to be 0.60 h –1 at 413 K. The value is a little higher than that with the reported homogeneous catalyst system of Cp 2 Ti­(OTf) 2 (0.47 h –1 ) at 433 K despite the 20 K lower reaction temperature. Koizumi and co-workers reported that CeO 2 (<25 nm) was active for the synthesis of 1 from EDA-CA, but the activity was low (yield 29%, 443 K) .…”

“…Very recently, Choi and co-workers reported an effective homogeneous catalyst of Cp 2 Ti(OTf) 2 for the synthesis of ureas including cyclic ureas from amine carbamates which were prepared from CO 2 and amines, and high yields of the target ureas (70−99%) were obtained. 29 However, these catalyst systems used homogeneous catalysts, and heterogeneous catalysts are preferable to homogeneous ones from the viewpoints of the durability, reusability, and ease of separation of catalysts from reaction mixtures. Hence, the development of effective heterogeneous catalysts for the synthesis of organic ureas from the corresponding carbamates is highly desirable.…”

“…CO 2 chemical absorption with amines is a useful and commercialized method, − and the direct synthesis of ureas from CO 2 captured by amines (namely, amine carbamate) without desorption, purification, and compression is promising. Some researchers reported on the transformation of amine carbamates into organic ureas. − Barzagli and co-workers reported that the CuCl 2 catalyst was effective for the synthesis of urea from ammonium carbamate with a yield of 54% (413 K, 3 days) and 1,3-dialkyl ureas from the corresponding carbamates with a yield of 37–44% (423 K, 5 h) . Recently, Manaka and co-workers found that 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU), an organic strong base, worked as an effective catalyst for the synthesis of urea from ammonium salts including ammonium carbamate, ammonium bicarbonate, and ammonium carbonate, and 35% yield of urea was obtained from the ammonium salts in dimethyl sulfoxide at 373 K for 3 days .…”

Efficient Activation of CO2 over Ce-MOF-derived CeO2 for the Synthesis of Cyclic Urea, Urethane, and Carbamate

“…Several organic bases, including bicyclic guanidine, have been explored for cyclic urea synthesis . The homogeneous titanium complex has also been found effective for synthesizing cyclic urea from alkyl ammonium carbamate . Several heterogeneous catalysts, including Au decorated in the polymer matrix, metal oxides (including CeO 2 ), silica-based catalysts, and MOF, have been reported for this reaction. − Sn and Ni metal complexes have been utilized for carbamate synthesis. − Moreover, CeO 2 has also been explored for carbamate synthesis …”