Comparison of the alkalinity of hydroxypyridine anion-based protic ionic liquids and their catalytic performance for Knoevenagel reaction: The effect of the type of cation and the position of nitrogen atom of anion

Cholinium Pyridinolate Ionic Pair-Catalyzed Fixation of CO2 into Cyclic Carbonates

A halide-free ionic pair organocatalyst was proposed for the cycloaddition of CO2 into epoxide reactions. Cholinium pyridinolate ionic pairs with three different substitution positions were designed. Under conditions of temperature of 120 °C, pressure of 1 MPa CO2, and catalyst loading of 5 mol %, the optimal catalyst cholinium 4-pyridinolate ([Ch]+[4-OP]-) was employed. After a reaction time of 12 h, styrene oxide was successfully converted into the corresponding cyclic carbonate, and its selectivity was improved to 90%. A series of terminal epoxides were converted into cyclic carbonates within 12 h, with yields ranging from 80 to 99%. The proposed mechanism was verified by 1H NMR and 13C NMR titrations. Cholinium cations act as a hydrogen bond donor to activate epoxides, and pyridinolate anions combine with carbon dioxide to form intermediate carbonate anions that attack epoxides as nucleophiles and lead to ring opening. In summary, a halide-free ionic pair organocatalyst was designed and the catalytic mechanism in the cycloaddition of CO2 into epoxides reactions was proposed.

Polyphosphazene-Functionalized Microspheres as Efficient Catalysts for the Knoevenagel Reaction under Mild Conditions

Inspired by the formation of microspheres by hexachlorocyclotriphosphazene and 4, 4'-sulfonyldiphenol, polyphosphazene-functionalized microspheres were developed. Benefits from the supported supper basic phosphazene, the yield exceeded 99 % at room temperature in the manner of second-order reaction kinetics toward Knoevenagel reaction and was still maintained at 99 % after 16 runs. In the experimental temperature from 0 °C to 90 °C, the yield increased from 92 % to 99 %, reflecting that the catalyst had strong applicability under mild conditions. This behavior was conducive to energy conservation. Meanwhile, simple separation and recovery further enhanced this advantage. In addition, the catalyst was also found to be insensitive to aqueous solution or organic solvents such as toluene, THF, EtOH and CH₃ CN. This property gave the Knoevenagel reaction a vast choice. All these features exhibit that this novel catalyst is an attractive and applicable alternative in organic synthesis.

Physicochemical Properties of Various 2-Hydroxyethylammonium Sulfonate -Based Protic Ionic Liquids and Their Potential Application in Hydrodeoxygenation

In order to obtain the regularities of physicochemical properties of hydroxy protic ionic liquids (PILs) and broaden their potential application, a series of 2-hydroxyethylammonium sulfonate-based PILs were synthesized through proton transfer reaction and characterized by NMR and FT-IR and elemental analysis. Their phase transfer behavior (T _m) and initial decomposition point (T _d) were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. Meanwhile, the regularities of density (ρ), viscosity (η) and electrical conductivity (σ) of synthesized PILs at different temperatures were measured. The results indicated that their physicochemical properties were tightly related with their structures and the interactions between cations and anions. In addition, the dissociation constants (pKa) of synthesized PILs were obtained by acid-base titration, which revealed that all synthesized PILs had pKa exceeding 7 and their cations were the crux of determining the pKa value. Moreover, several synthesized PILs with a low melting temperature also showed potential application in the deoxidation reaction of cyclohexanol, as they had conversion rates approximating 100% and the selectivity of cyclohexane or cyclohexene was about 80%.