The Synthesis Of Functional Ionic Liquids Contain Urea And The Application As Receptors In The Anion Recognition

Due to the fundamental roles that anions play in a wide range of biological, environmental, chemical and medicinal processes, numerous efforts have been devoted to the design of receptors capable of selectively binding and sensing anions. Room temperature ionic liquids (ILs) are composed of organic cation and inorganic anion or organic anion, with a melting temperature of less than25℃. Because of their designable, ionic liquids are "task-specific" or "tailor-making" materials by tuning the combination between anions and cations or grafting proper functional groups. In the dissertation, a series of novel functional ionic liquids have been synthesized by grafting urea moiety to imidazolium/pyridinium. These functional ionic liquids have multiple bonding sites. We use these ionic liquids as anion receptors and find they can selectively bind anions by cooperating with conventional hydrogen bonds (N-H…X), ionic hydrogen bonds [(C-H)+…X] and charge-charge interactions. The ionic liquid receptors also have high sensitivity in optics and signal transduction of recognition events.The dissertation consists of five chapters summarized as the following.Chapter1. General introduction of ionic liquids, anion recognition chemistry, and a min-review of the researches in anion receptors based on imidazolium and pyridinium.Chapter2. Design, synthesis and recognition properties for anions of a series of mono-benzimidazolium-urea based ILs receptors1-6. The ILs receptors1-6were synthesized by grafting urea moiety to benzimidazolium via quaternization and anion exchange reaction. All of these compounds were characterized by1H NMR,13C NMR, and mass spectrometry, and compound1·Cl·2H2O was further confirmed by X-ray diffraction. The recognition properties of these ILs receptors with various anions (fluoride, chloride, bromide, iodide, acetate, hydrogen sulfate, and dihydrogen phosphate) were monitored by UV-Vis, fluorescence emission spectra and NMR titrations. The UV-Vis studies show that the mono-benzimidazolium-urea based ILs receptors could selectively recognize fluoride at low concentration. The fluorescence emission spectra show that the receptors displayed good affinities for more basic anions, such as fluoride, acetate and dihydrogen phosphate, and the binding constants are all about105M-1. The results also reveal that ILs receptors have higher sensitivity in optics and signal transduction of recognition events, and charged (C-H)+benzimidazolium moiety and urea group play a synergistic effect in anion recognition. The NMR titrations show that the mono-benzimidazolium-urea based ILs receptors bind anions by cooperating with conventional hydrogen bonds (N-H…X), ionic hydrogen bonds [(C-H)+…X] and charge-charge interactions. While the anion with strong base such as fluoride and dihydrogen phosphate, they will cause deprotonation of the mono-benzimidazolium-urea based ILs receptors at high concentration.Chapter3. Design and synthesis of a series of bi-benzimidazolium-urea based ILs receptors7～10for the recognition of a,co-dicarboxylate (-OOC-(CH2)m-COO-, m=1～6). The ILs receptors7～10were synthesized by grafting urea moiety to benzimidazolium via quaternization and anion exchange reaction. All of these compounds were characterized by1H NMR,13C NMR, and mass spectrometry. The compound8·(BF4)2·H2O was further confirmed by X-ray diffraction. The recognition properties of these ILs receptors were monitored by UV-Vis, fluorescence emission spectra and NMR titrations. The UV-Vis and fluorescence emission spectra studies show that bi-benzimidazolium based ILs receptors7～9exhibit higher affinities than urea-based neutral receptor10, which due to benzimdazolium have good sensitivity in optics and signal transduction of recognition events. The affinities between receptors7～9and a,co-dicarboxylate show the match in chain length, and they all formed1:1complexes with α,ω-dicarboxylate, exhibit higher binding constants (105～106M-1). It also reveals that charged (C-H)+benzimidazolium moiety and urea group as bonding sites play a synergistic effect in anion recognition. The NMR titrations show the bi-benzimidazolium-urea based ILs receptors bind α,ω-dicarboxylate by cooperating with conventional hydrogen bonds (N-H…X), ionic hydrogen bonds [(C-H)+…X] and charge-charge interactions. In addition, the aryl proton signals of ILs receptors appear splitting during titration process, it was probably due to the binding of ILs receptors and a,co-dicarboxylate is a slow anion exchange process. Chapter4. Design and synthesis of a series of di-(imidazolium-urea) based ILs receptors11-15for the recognition of α,ω-dicarboxylates (-OOC-(CH2)m-COO-, m=1～6), maleate and fumareate. The ILs receptors11～15were synthesized by grafting urea moiety to imidazolium/benzimidazolium via quaternization and anion exchange reaction. All of these compounds were characterized by1H NMR,13C NMR, and mass spectrometry. The recognition properties of these receptors were monitored by UV-Vis, fluorescence emission spectra and NMR titrations. The results show that the ILs receptor11binds dicarboxylates by cooperating with conventional hydrogen bonds (N-H…X), ionic hydrogen bonds [(C-H)+…X] and charge-charge interactions. The ILs receptors exhibit higher affinities for a,co-dicarboxylates which have shorter chain length such as malonate, succinate, maleate and fumareate, and they all formed1:1complexes. This may be relevant to the conformation of the receptors. The pincer di-(imidazolium-urea) based receptors have cis-and trans-forms, and the cis-form show higher affinities for a,co-dicarboxylate of shorter chain lengths, the trans-form show higher affinities for α,ω-dicarboxylate of longer chain lengths.Chapter5. Design and synthesis of pyridinium-urea based ILs receptors16and17for the recognition of fluoride, chloride, bromide, iodide, acetate, hydrogen sulfate, dihydrogen phosphate and a,co-dicarboxylate (-OOC-(CH2)m-COO-, m=1-6). The ILs receptors16and17were synthesized by grafting urea moiety to pyridinium via quaternization and anion exchange reaction. All of these compounds were characterized by1H NMR,13C NMR, and mass spectrometry. Upon addition of the various anions to the solution of receptor16, the solution shows a unique color change for fluoride, acetate and a,co-dicarboxylate ("OOC-(CH2)m-COO-, m=1～6) respectively, thus pyridinium-urea based ILs receptors16can act as optical chemosensors for fluoride, acetate and a,co-dicarboxylate (-OOC-(CH2)m-COO-, m=1～6). In addition, these anions may induce receptors16forms the radical cation16+·, these results were further confirmed by UV-vis spectra, NMR titrations and EPR.