Zn–Ca–Al mixed oxide as efficient catalyst for synthesis of propylene carbonate from urea and 1,2-propylene glycol

A series of Zn–Ca–Al oxides with different CaO and ZnO contents have been prepared and evaluated in the synthesis of propylene carbonate(PC) from 1,2-propylene glycol(PG) and urea in a batch reactor. The effect of catalyst composition, basicity and reaction process parameters such as temperature, catalyst dose, molar ratio of PG to urea, purge gas flow and reaction time has been studied to find suitable reaction conditions for the PC synthesis. The PC selectivity and yield under the desired conditions could reach 98.4% and 90.8%, respectively. The best performing catalyst also exhibited a good reusability without appreciable loss in the PC selectivity and yield after five consecutive reaction runs. In addition, a stepwise reaction pathway involving a 2-hydroxypropyl carbamate intermediate was proposed for the urea alcoholysis to PC in the presence of Zn–Ca–Al catalysts, according to the time dependences of reaction intermediates and products.

Chemical fixation of carbon dioxide to cyclic carbonates catalyzed by zinc(Ⅱ) complex bearing 1,2-disubstituted benzimidazole ligand

A new zinc(II)complex of formula[ZnCl2(L1)2](1)[L1=2‐(2‐thienyl)‐1‐(2‐thienylmethyl)‐1Hbenzimidazole]was synthesized and fully characterized by nuclear magnetic resonance and infrared spectroscopy,elemental analysis,electrospray ionization high‐resolution mass spectrometry,and thermogravimetric analysis.The molecular structure was confirmed by single‐crystal X‐ray diffraction.Complex1consists of mononuclear tetrahedral zinc(II)units with a locked geometry resulting from weak intramolecular S···?and?–?interligand interactions.The benzimidazole ligand and its zinc(II)complex were readily obtained through a simple synthetic route.The catalytic activity of1was investigated in the coupling of carbon dioxide with epoxides to produce cyclic carbonates,and a series of parameters were evaluated.The complex efficiently catalyzed the transformation of various epoxides under solvent‐free conditions,with good conversions,turnover numbers,and turnover frequencies.

Lewis base-CO2 adducts as organocatalysts for CO2 transformation

In the recent decade, the development and application of organocatalysis for CO_2 transformation into useful chemicals have attracted much attention. Among these organocatalysts, Lewis base-CO_2 adducts(LB-CO_2) were found to be more efficient.The used Lewis base has great effect on the catalytic activity of its CO_2 adduct. This review reports the recent progress in LB-CO_2 adducts catalyzed the cyclization of CO_2 with epoxides or aziridines to afford cyclic carbonates or oxazolidinones,the carboxylation of CO_2 with propargylic alcohols to α-alkylidene cyclic carbonates, and the reduction of CO_2 to methanol,formamides and methylamines, with the focus on the catalytic mechanism.