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How and Why a Protic Ionic Liquid Efficiently Catalyzes Chemical Fixation of CO2 to Quinazoline-2,4-(1H,3H)‑diones: Electrostatically Controlled Reactivity
journal contribution
posted on 2019-10-17, 13:41 authored by Xueli Mu, Lingli Han, Tao LiuA density
functional theory study has been conducted to gain insight
into the intriguing experimental observations on the synthesis of
quinazoline-2,4-(1H,3H)-diones from
2-aminobenzonitriles reacting with CO2 catalyzed by protic
ionic liquids (ILs). We explored the molecular mechanism of the titled
reaction, as well as the origin and catalytic nature of different
ILs toward the reaction in detail. The calculated energetically viable
mechanism involves CO2 attack, intramolecular rearrangement,
and intramolecular cyclization stages. This mechanism features the
initial polarization of the CN triple bond with the assistance
of the real catalytic species, [HDBU+][TFECOO–], where the cation [HDBU+] acts as Brønsted acid
and the anion [TFECOO–], the adduct of anion [TFE–] and CO2, acts as a nucleophile. The calculated
results present the electrostatically controlled character of the
reaction, where the reactivity relies on the electrostatic interaction
of the IL cation with the anion. The reactivity can be controlled
and regulated by the basicity of the deprotonated counterpart of the
IL cation as well as the CO2 adsorption ability of the
IL anion. The best catalytic performance of [HDBU+][TFE–] is attributed to its strongest basicity of the deprotonated
counterpart of [HDBU+] and its most efficient CO2 adsorption property of [TFE–]. These theoretical
results are expected to provide guidance for designing efficient IL-based
catalysts in preparing quinazoline-2,4-(1H,3H)-diones by reacting 2-aminobenzonitriles with CO2.