This thesis describes a collection work concerning the exploration of various novel homogeneous and heterogeneous ionic liquid (IL) catalysts for the efficient synthesis of cyclic carbonates from a variety of epoxides and CO2. In terms of economy and reusability of catalysts, we have firstly developed a series of commercial silica grafted imidazolium-based ILs (IMISs) heterogeneous catalysts towards the cycloaddition reaction of allyl glycidyl ether and CO2. Interestingly, the catalytic performances of those supported ILs are heavily dependent of their molecular composition. ILs with longer alkyl chain length and more nucleophilic anion show significantly enhanced catalytic activity. In addition, the texture properties of silica supports (specific surface area and pore size) play an important role to determine catalytic activity of the immobilized ILs owing to the reactant-confined diffusion effects. In particular, we also have found that the combination of zinc halide with IMIS enables to significantly increase the catalytic activity of those bare IMISs. On the basis of this interesting finding, the effects of various transition metal ions (CoCl2, NiCl2, CuCl2, and MnCl2) on the catalytic performance of bare IMIS catalysts have been systematically investigated. Catalytic reaction tests demonstrated that the incorporation of such metal ions can significantly enhance the catalytic reactivity of IMISs towards cycloaddition reaction of CO2 and epoxide in solvent-free conditions. This work has demonstrated a facile, low-cost and efficient strategy to improve the reactivity of heterogeneous IL catalysts.To develop more versatile efficient catalytic systems for the cycloaddition reaction of CO2 and epoxides, various homogeneous and heterogeneous ILs with functional groups (?COOH and ?OH) have also been investigated in this thesis. Surprisingly, both ?COOH and ?OH group functionalized ILs show dramatically promoted activity in the cycloadditon reactions compared with the conventional ILs without any functional moieties. Moreover, the introduction of ?COOH group is more effective to enhance the catalytic reactivity of bare ILs than that of ?OH groups, as ?COOH is a stronger Br?nsted acid and hydrogen bond donor. We also performed detailed investigations on a variety of factors that affected the reactivity, such as the molecular composition of IL molecules, and catalytic reaction parameters (temperature, CO2 pressure, reaction time, and the using amount of catalysts). In addition, upon the simple addition of a small amount of acetate acid into the non-functional IL catalytic system, we have found that the resulting IL catalyst exhibited a competitive catalytic activity compared with ?COOH functionalized ILs. Moreover, in comparison with the traditionally used small molecular co-catalysts such as alcohol and water, the use of acetic acid is more efficient for the promotion of IL catalyzed cycloaddition reactions.In this thesis, we have also synthesized various highly cross-linked porous poly(N-vinylimidazole-co-divinylbenzene) (PVIm) beads with tunable pore size and specific surface areas by means of suspension polymerization technique. Followed by the further surface modification of the PVIm beads with various alkyl halides, a variety of IL-grafted porous polymer beads (PVIm-RX) were achieved and used as heterogeneous catalysts for the synthesis of cyclic carbonates from CO2 and epoxides. All catalytic reactions are carried out under mild conditions (90?130 ?C, 0.86?2.17 MPa) in the absence of organic solvents. The effects of texture properties of the PVIm matrix, molecular compositions of the ionic liquid moieties, and catalytic reaction parameters on the catalytic reactivity of cycloaddition reactions were also systematically investigated. The results demonstrate that grafted ILs with more nucleophilic anions, bulkier alkyl chains, and hydroxyl groups enable to effectively improve their reactivity. Additionally, the incorporation of small amount of ethanol or water into the reaction system enables to significantly promote the corresponding cycloaddition reactions. Note that those obtained PVIm-RX heterogeneous catalysts exhibited higher turnover number than that of IL-grafted porous silica catalysts.
본 논문은 지구온난화 현상의 중요 원인 물질 중의 하나인 이산화탄소를 에폭시화합물과 반응시켜 유용한 물질인 카보네이트 화합물로 전환시키는 촉매 공정의 개발에 관한 것이다. 이 공정은 이온성 액체를 촉매로 사용하고 추가적인 용매를 사용하지 않고 비교적 수월한 반응 조건에서 효율적으로 카보네이트 화합물을 제조할 수 있는 특징을 지니고 있다. 다양한 촉매에 대한 연구 결과에서 얻은 결론은 다음과 같다.(1) 상업용 실리카를 담체로 선정하여 이미다졸염계의 이온성 액체를 그래프팅시켜 불균일계 촉매 IMIS를 제조하였다. 이온성 액체의 알킬기의 길이가 길고, 음이온의 친핵성이 클수록 높은 활성을 나타내었다. 그리고 이 불균일계 촉매는 여러 번 반복하여 사용하여도 촉매의 활성이 잘 유지되었다. 또한 zinc halide(할로겐화 아연)을 이 촉매와 반응시켜 제조한 IMIS-Zn 촉매가 원래의 촉매 IMIS보다 훨씬 우수한 성능을 나타내어 zinc halide가 좋은 조촉매임을 알 수 있었다.(2) 카르복실기(-COOH)나 하이드록시기(-OH)를 관능기로 갖는 균일계와 불균일계 이온성 액체를 촉매로 제조하였으며, 이들은 각각 관능기를 갖지 않은 촉매에 비해 훨씬 뛰어난 촉매 활성을 나타내었다. 또한 카르복실기가 치환된 촉매가 하이드록시기가 치환된 촉매보다 더 우수한 촉매활성을 나타내었다. 이 두가지 관능기의 역할은 에폭시화합물과의 수소 결합에 의하여 에폭시화합물을 활성화시키는 것으로 판단된다. 한편 -OH기나 -COOH기를 갖는 H2O, C2H5OH, CH3COOH를 별도로 이온성 액체 촉매에 첨가하여 실험한 결과에서도 이들이 원래 촉매의 활성을 증가시키는 것으로 나타났다.(3) 기공크기와 표면적을 조절할 수 있도록 가교된 poly(N-vinylimidazole-co-divinylbenzene) (PVIm)를 제조한 후 alkyl halide와 표면 반응시켜 PVIm-RX 촉매를 제조하였다. 음이온의 친핵성이 크고, 알킬기의 길이가 길고, 하이드록시기를 갖는 촉매가 CO2와 에폭시화합물의 부가반응에 좋은 촉매 활성을 나타내었다.