Preparation And Performance Of Catalysts For Reactions Of Carbon Dioxide With Epoxides

Chemical fixation of CO2 is a very attractive subject not only from the viewpoint of carbon resource utilization, but also from increasing environmental concerns. As potential pathways, alternating copolymerization and cycloaddition between CO2 and epoxides such as propylene oxide (PO) and cyclohexene oxide (CHO) to produce aliphatic polycarbonates and cyclic carbonate have been extensively investigated. However, the thermodynamic stability of carbon dioxide has hampered its utilization as a reagent for chemical synthesis, and the preparation of high efficiency catalysts become the focus of research in this field. A wide variety of promising catalysts have been developed to promote this copolymerization process. It is of interest to investigate novel catalysts to facilitate the reactions of CO2 with epoxides. This dissertation presents our efforts in finding some novel catalysts for the reactions.Three heterocyclic carboxylic acid zinc complexes were prepared from diethyl zinc with 2-furancarboxylic acid,2-thiophenecarboxylic acid and 2-pyridinecarboxylic acid, respectively. Their catalytic behaviours were evaluated for the copolymerization of carbon dioxide with epoxides. All these three complexes are highly effective catalysts for the copolymerization of carbon dioxide with CHO. The best results were found in the case of 2-thiophenecarboxylic acid zinc complex, which gave a turnover number of 560.1. The thermal properties of PCHC were measured by TG and DSC, and the Tg lies in the range 115-119?and the Tp is up to 266.5?. Terpolymerizations of carbon dioxide with CHO in the presence of a third monomer including y-butyrolactone, maleic anhydride and propylene oxide were conducted, and the related terpolymerization mechanism is discussed.Six Schiff base ligands were prepared through reactions of 2-furaldehyde,2-thiophenecarboxaldehy with different diamines, their corresponding zinc complexes were prepared by their reaction with ZnCl2. The cycloaddition reaction of CO2 with epichlorohydrin was effectively catalyzed by these complexes yielding cyclic carbonate. The best result was obtained by N,N'-bis(2-furaldehyde)?-phenylenediamine-ZnCl2 (BFPD-Zn) with a TON up to 413.4. The cycloaddition reaction was presumed as a polymerization/depolymerization mechanism.Several ligand compounds were prepared by the reaction 2-carboxybenzaldehyde with different diamines, and the copolymerization of CO2 with CHO was efficiently when these ligands coordinated with ZnEt2, and the highest TON was achieved up to 516.6.Five monoimine Schiff base Zinc complexes were synthesized, and [N-(2-furaldehyde)-anthranilate]Zn and [N-(2-carboxybenzaldehyde)-anthranilate]Zn complexes were found to have catalytic activity for the copolymerization of CO2 with CHO yielding PCHC with TONs of 269.1 and 194.6, respectively.