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Direct synthesis of carbamate from CO2 using a task-specific ionic liquid catalyst

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Abstract

A superbase-derived protic ionic liquid (IL, [DBUH][OAc]) catalyst was used to directly synthesize carbamate from an amine, CO2, and a silicate ester. This IL catalyst was easily prepared using its precursors, DBU, and acetic acid. Using 10 mol% of the catalyst under a CO2 pressure of 5 MPa in acetonitrile at 150 °C, carbamate was isolated in up to 96% yield. Specifically, aliphatic and aromatic amines were activated even though aromatic amines exhibited low activities because of their low pKa values. Other functional groups in amines were barely activated, affording exclusive chemoselectivity for amine activation. Isotope labeling experiments indicated that the proton in the counter cation is crucial in the catalytic cycle to produce water. In addition, a chemical shift corresponding to a mixture of aniline and [DBUH][OAc] was observed in the 1H NMR spectrum, related to the formation of hydrogen bonds between aniline and basic acetate anions. The experimental results indicated that the designed IL catalysts require a protonated cation and a basic anion.

Graphical abstract: Direct synthesis of carbamate from CO2 using a task-specific ionic liquid catalyst

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Publication details

The article was received on 01 Sep 2017, accepted on 24 Oct 2017 and first published on 24 Oct 2017


Article type: Paper
DOI: 10.1039/C7GC02666H
Citation: Green Chem., 2017, Advance Article
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    Direct synthesis of carbamate from CO2 using a task-specific ionic liquid catalyst

    Q. Zhang, H. Yuan, N. Fukaya, H. Yasuda and J. Choi, Green Chem., 2017, Advance Article , DOI: 10.1039/C7GC02666H

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