A DFT study on the reaction mechanism for dimethyl carbonate synthesis from methyl carbamate and methanol

Using density functional theory, the reaction mechanism for dimethyl carbonate (DMC) synthesis from methyl carbamate (MC) and methanol (CH3OH) with and without catalysts is investigated. And to investigate solvent effects, the reactions are simulated in CH3OH solvent by using the conductor like solvent model (COSMO). In our calculation, the uncatalyzed MC methanolysis reaction is kinetically and thermodynamically unfavorable. However, it is obviously catalyzed by acid and base catalysts. By orbital energy calculation, MC methanolysis reaction is considered as the charge-controlled reaction. Thus, electrostatic potential fitted charges as reaction indicator is used to infer the activity of species after catalyst Zn(NH3)2(NCO)2 initiation. And it is confirmed to be successful in reactivity prediction. The catalytic cycles involved the selected active species are proposed. By calculating activation energies, the catalytically active species is considered to be Zn(NH3)2(NCO)(NHCOOCH3), which derives from the reaction of Zn(NH3)2(NCO)2 with CH3OH. The DMC synthesis from the catalytically active species and CH3OH is favored, of which the reaction activation energy is effectively decreased.

. ESP fitted charges as reaction indicator is successful in prediction reactivity of the active species.Figure optionsDownload high-quality image (77 K)Download as PowerPoint slideHighlights
► The mechanism for MC methanolysis reaction is clearly presented.
► The base catalyst is in favor of MC methanolysis via facilitating CH3O− formation.
► The catalytically active specie is Zn(NH3)2(NCO)(NHCOOCH3).
► The ESP fitted charges is confirmed be to appropriate as the reactivity indicator.