Study Of Structure-Activity Relationship Of Ionic Liquids And Their Application In Organic Synthesis

Recently, the research about ionic liquids as novel media and soft functional materials has become a new field of green chemistry. Ionic liquids have been applied as catalysts and media in many areas, such as organic synthesis, electrochemistry, separation processes, material science etc., due to their favorable properties such as high thermal stability, non-inflammability, good solubility and adjustable physical and chemical properties. One of the distinctive properties of ionic liquids is that their physical and chemical properties could be adjusted by changing the structures and combination of cations and anions. Therefore, the synthesis of functional ionic liquids and the study of their structure-activity relationship and applications are very important. With the development of ionic liquids, more and more functional ionic liquids with special functions are synthesized. However, most of the researches about the selection of suitable ionic liquids are still using the traditional method, which is complex and ineffective. So the study of the structure-activity relationship of ionic liquids is one of the most important jobs in the researches about ionic liquids and very important to the synthesis of functional ionic liquids.In order to keep up with the trend, we studied the structure-activity relationship and essential rule of the structures and melting points of imidazolium ionic liquids; we chosed the suitable ionic liquids and widened the application of them in ring-opening reaction, phase transfer reaction and condensation reaction, and studied the structure-activity relationship of the structures and catalytic activities of ionic liquids; we prepared and characterized four novel Br(?)nsted acidic ionic liquids and used them as catalysts and media in the esterification of acetonitrile with alcohols. The details are given as follows: 1. Structure-Activity Relationship and Essential Rule of the Structures and Melting Points of Imidazolium Ionic LiquidsMelting point is an important parameter of ionic liquid. The data of melting points of 384 imidazolium ionic liquids were collected from Beilstein Gmelin database and about 200 literatures, the anions included I, BF4, (CF3SO2)2N, Cl, Br, PF6 and CF3SO3, and the side chains of cations included aromatic and aliphatic side chain. According to these data, the structure-activity relationship and essential rule of the structures and melting points of imidazolium ionic liquids were studied. The results revealed that the melting point of ionic liquid was decided by the structures of the cation and anion, and the structure of cation was the major factor, which included the symmetry of cation, the induction effect of side chain, the planarity of cation and the effect of H-πbond. The order of these factors was H-πbond> induction effect> symmetry. The structure of anion was the minor factor, which included the bulk of anion, the symmetry of anion, the length of side chain, and the effect of F atom2. Phase Transfer Reaction Catalyzed by Imidazolium Ionic LiquidsIonic liquids based on 1,3-dialkylimidazolium cation were firstly employed as phase transfer catalysts for the phase transfer synthesis of dichlorocarbene and mixed ether. The relationship of the structures and catalytic activities of ionic liquids was also studied. The results revealed that when the dispersion of charge and the lipotropy of cation were high, and the coordinate ability of anion was low, the catalytic activity of ionic liquid was high. Ionic liquids were efficient catalysts for phase transfer reaction, which could overcome the disadvantages of the traditional phase transfer catalysts, such as thermal instable, poisonous and unreusable.3. Br(?)nsted Acidic Ionic Liquids as Efficient Catalysts and Media for the Ring Opening of Phthalic Anhydride to Synthesize Half-Esters and the Quantum Chemical Study of the Sulfonic Acid-Functionalized Ionic LiquidsLewis acid BF3-Et2O was an efficient catalyst for the ring opening of cyclic anhydride to synthesize half-esters. However, it also suffered from some drawbacks, such as unreusable. Bransted acidic ionic liquids were firstly employed as efficient catalysts and media for the ring opening of phthalic anhydride to synthesize half-esters. The results revealed that when using Br(?)nsted acidic ionic liquids as catalysts and media, good yields, short reaction time and mild reaction condition were achieved, the usage of organic solvent was saved greatly, and the ionic liquids could be reused easily without obvious decline in catalytic activities. The catalytic selectivities of ionic liquids were related to their acidities, stronger acidity of ionic liquid resulted in lower catalytic selectivity in the synthesis of half-esters.The minimum-energy geometries and hydrogen bonds of sulfonic acid-functionalized ionic liquids were determined by performing ab initio geometry optimization using the Gaussian 03 program. The results revealed that the acidities and catalytic selectivities of sulfonic acid-functionalized ionic liquids were related to their structures, the sulfonic acid-functionalized ionic liquids with shorter H-0 bond had stronger acidity and lower catalytic selectivity in the synthesis of half-esters.4. Acylation of Alcohols with Acetic Anhydride in Br(?)nsted Acidic Ionic LiquidsBr(?)nsted acidic ionic liquids were employed as a series of efficient catalysts in the acylation of aromatic and aliphatic alcohols with acetic anhydride at room temperature. The structure-activity relationship of the structures and catalytic activities of ionic liquids were also studied. Good yields, mild reaction condition, short reaction time and simple after-treatment were achieved. Ionic liquids could be recycled easily without obvious decline in catalytic activities. The sulfonic acid-functionalized ionic liquids and the ionic liquid with HSO4 had stronger acidities and higher catalytic activities.5. Doebner Condensation in Imidazolium and Pyridinium Ionic LiquidsThe traditional solvents for Doebner condensation were ethanol, pyridine, piperidine and so on, which had many disadvantages. Ionic liquids [bmim]BF4 and [bpy]BF4 were firstly employed as environmentally benign media in Doebner condensation to synthesizeα,β-unsaturated carboxylic acid. The highest yields could reach 93% and 90% in [bmim]BF4 and [bpy]BF4 respectively, which showed that ionic liquids were efficient media for Doebner condensation. Ionic liquids as media for Doebner condensation could simplify the final treatment and reduce the pollution to the environment, and could be recycled easily.6. Directional Design of Novel Brensted Acidic Ionic Liquids and Their Application in the Esterification of Acetonitrile with AlcoholsFour novel Br(?)nsted acidic ionic liquids with two different acid sites on the imidazolium cations 1-(3-sulfopropyl)-3-hydroimidazolium hydrogen sulphate, 1-(3-sulfopropyl)-3-hydroimidazolium tetrafluoroborate, 1-(3-sulfopropyl)-3-hydroimidazolium dihydrogen phosphate and 1-(3-sulfopropyl)-3-hydroimidazolium p-toluenesulfonate were synthesized and characterized by FT-IR,'H NMR,13C NMR and elemental analysis.These novel Br(?)nsted acidic ionic liquids were employed as catalysts and media in the esterification of acetonitrile with alcohols. The results showed that ionic liquid 1-(3-sulfopropyl)-3-hydroimidazolium hydrogen sulphate was the most efficient catalyst and medium which could be recycled easily.