How and Why a Protic Ionic Liquid Efficiently Catalyzes Chemical Fixation of CO₂ to Quinazoline-2,4-(1H,3H)-diones: Electrostatically Controlled Reactivity

Abstract

A 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 CO 2 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 CO 2 attack, intramolecular rearrangement, and intramolecular cyclization stages. This mechanism features the initial polarization of the CN 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 CO 2 , 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 CO 2 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 CO 2 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 2aminobenzonitriles with CO 2 .

Catalytic Conversion of CO2 from Simulated Flue Gases with Aminophenol-Based Protic Ionic Liquids to Produce Quinazoline-2,4(1H,3H)-diones under Mild Conditions

“…As shown in Figure a, upon addition of 2-aminobenzonitrile to the [HTMG]­[ m -AP] catalyst, an additional proton signal was observed at δ = 8.29 ppm in the 1 H NMR spectra, which could be attributable to the active proton transfer of the 2-aminobenzonitrile NH 2 proton to the [ m -AP] − anion (hydrogen bond acceptor); this phenomenon indicated the existence of strong intermolecular hydrogen bonding interactions between [HTMG]­[ m -AP] and 2-aminobenzonitrile. Similar results of the activation of 2-aminobenzonitrile through hydrogen bonding have been previously proposed in the literature. ,, …”

“…aminobenzonitrile through hydrogen bonding have been previously proposed in the literature. 18,39,40 The interactions between [HTMG][m-AP] and CO 2 were also confirmed by using FT-IR and 13 C NMR techniques. After [HTMG][m-AP] was interacted with CO 2 , it was observed that a new peak appeared at 1787 cm −1 , which could be assigned to the asymmetric CO vibration of carbamate salt (NH−COO − ), 41 and the peak at 1470 cm −1 belonging to the C−O stretching vibration shifted to 1498 cm −1 due to the formation of new carbonate ions (O−COO − ) as depicted in Figure 3b.…”

Ionic-Liquid-Catalyzed Approaches under Metal-Free Conditions

“…On the basis of our experimental results, Liu and co-workers performed a density functional theory (DFT) study to gain insight into the mechanism of the above reaction as well as the origin and catalytic nature of different ILs toward the reaction. The calculated energetically viable mechanism involves CO 2 attack, intramolecular rearrangement, and intramolecular cyclization stages, as shown in Scheme C.…”

Tuning Ionic Liquid-Based Catalysts for CO2 Conversion into Quinazoline-2,4(1H,3H)-diones

“…After the nucleophilic attack, intramolecular nucleophilic cyclization, rearrangement, and hydrogen transfer, quinazoline-2,4( 1H , 3H )-diones are obtained and [HDBU][TFE] is regenerated. However, Mu and Liu et al [ 66 ] investigate using systematic DFT calculations that one o -aminobenzonitrile molecule requires two CO 2 molecules to yield one quinazoline-2,4-(1 H ,3 H )-dione. One CO 2 acts as a reactant, while another transferred to [TFE–CO 2 ] acts as the catalyst.…”