Microwave-Assisted Synthesis Of Cucurbit[n] Uril And Self-Assembled Structures In Ionic Liquids

Supramolecular chemistry is the research of studying particular structures and functions of supramolecular system based upon two or more chemical species linked through intermolecular interactions. Emerging as one important type of supramolecular host structure, the research on CB[n] (Cucurbit[n]uril), including the synthetic method and self-assemble structures, plays an important role in supramolecular chemistry. Room temperature ionic liquids (RTILs) are designable at molecular level with specific combination of organic cations and anions around room temperature, which have special advantages, such as non-volatility, low melting point, etc. With the development of task-specific ionic liquids, such as SO3H-functionalized ionic liquids (SFILs), they have been applied in various research fields as new media of green chemistry. In this work, we firstly introduce both SFILs and microwave irradiation in the synthesis of CB[n], which is proved convenient and expeditious.A new microwave-assisted (MW-assisted) synthesis method of cucurbit[n]uril in SFILs is provided. The results show that, under the reaction conditions of 800 W (microwave power), 160℃(reaction temperature) and 30 min (reaction time), and also with the composition of Behrend's polymer (0.250 g), [C3SO3Hmim]HSO4 (1.000 g) and water (2.000 g), Behrend's polymer could be transformed to CB homologues (0.159 g) comprising CB[5], CB[6] and CB[7]. Furthermore, the effects of reaction conditions and SFILs structures on product distribution and yield are investigated. The experimental results show that cationic groups of SFILs barely influence product distribution, while the anionic groups are crucial factor to determine the total yield. The SFILs could be reused at least three times without noticeable change of either product distribution or yield. After the reaction, a novel self-assembled structure based upon CB[6] molecules is able to crystallize from the reaction system spontaneously. The separation process is highly reproducible with good yield. This new method not only realizes the application of SFILs in CB[n] synthesis, but highlights the economical and environmental benign features.The structures and properties of the novel 3D supramolecular self-assembled system separated spontaneously are also investigated. The results show that the self-assembled structures have porosity and ideal thermostability, which are also the first 3D frameworks that are directly linked based upon CB[6] molecules and anionic groups via weak interactions. The formation of this novel self-assembled structures markedly improves the solubility of CB[6] in water and even organic solvent DMSO. In water, the self-assembled structure maintains highly assembled, while in DMSO and alkali metal solutions, the structure is partially damaged.