Preparation Of Ionic Liquids And Their Applications In The Unit Reactions Of The Fine Synthesis

Ionic liquids are simply liquids that are composed entirely of ions.They have been the subject of considerable interest as environmentally benign alternative to volatile solvents (VOCs)in organic synthesis during the last few years.These solvents possess a number of interesting properties,notably their low melting points,lack of vapor pressure,high thermally stability,ease of reuse,good capacity for solubilizing organic substrates,lack of flammability and large accessible temperature range.To date,some of the important organic reactions have been carried out and investigated in ionic liquids.The vast majority of ionic liquid chemistry based on nitrogen-containing heterocycles focuses on the use of 1-alkyl-3-methylimidazolium and N-alkylpyridinium cations. 1-Alkyl-3-methylimidazolium hexafluorophosphate(AMIMPF₆), 1-alkyl-3-methylimidazolium tetrafluoroborate(AMIMBF₄),N-alkylpyridinium tetrafluoroborate(APyBF₄)and N-alkylpyridinium hexafluorophosphate(APyPF₆)are typically ionic liquids.It has been found that AMIMPF₆,AMIMBF₄,APyBF₄ and APyPF₆ can be prepared with stoichiometric amounts of 1-methylimidazole or pyridine, alkylhalides and potassium,sodium or ammonium salt of hexafluorophosphate or tetrafluoroborate in one-pot solvent-free conditions under 70℃to 100℃to give excellent yields of 88%-95%with shortened time within 3.0-4.0h.The apparent kinetics of the novel procedure has also been investigated.Bronsted acidic task-specific ionic liquids(TSILs)combining the advantageous characteristics of solid acids and mineral acids,are designed to replace traditional mineral liquid acids,such as sulfuric acid and hydrochloric acid in chemical processes.However, the development and exploring of Brφnsted-acidic TSILs are currently in preliminary stage and the number of published Brφnsted-acidic TSILs is limited.Here,some novel SO₃H-functional Brφnsted-acidic TSILs that bear an alkane sulfonic acid group in an imidazolium cation,pyridinium cation,or acyclic tri-alkanyl-ammonium cation have been synthesized via two-step atom economic reactions.The chemical yields for both the zwitterion formation and acidification steps are essentially quantitative,since neither reaction produces byproducts.Their structures were analyzed by ¹HNMR,¹³CNMR,IR and MS spectroscopes.The substituted diphenyl ethers are important intermediate chemicals used in fine chemicals,pesticides and medicines.As a nucleophilic reaction,the substituted diphenyl ether can be prepared in aprotic polar solvent such as DMF,DMSO etc.,in view of economical and environmental points,studying the use of ionic liquids as the green solvents is of great significance.The preparation of some substituted diphenyl ethers in ionic liquids prepared as above has been explored.Some substituted diphenyl ethers were synthesized via Williamson or Ullmann reactions using the ionic liquids as the recyclable green solvents with high yields.Brφnsted acidic ionic liquids(TSILs)synthesized in our work have been used as dual solvent-catalysts for Fischer esterification reactions of acetic acid,metacetonic acid,and benzoic acid with ethanol,butanol,and benzyl alcohol were investigated.The reactions were completed smoothly at room temperature to 110℃for 1.5-3.0h with good yields of 88%-95%.The results indicate that catalytic activity depends on anion acidity and the solubility of the starting material in TSILs.The increasing of the anion's acidity improves the catalytic activity of the TSILs.Furthermore,the produced esters could be separated by decantation after the reaction and the TSILs could be reused without noticeably decreasing the catalytic activity.Then the TSILs have been used as the cheap and recyclable catalysts for one-pot three-component Mannich reaction in water.Sixteenβ-amino carbonyl compounds were obtained in good yields under the mild conditions.The products could simply be separated from the catalyst/water,and the catalyst could be reused at least 7 times without noticeably decreasing the catalytic activity.Subsequently,the TSILs have been found to be effective catalysts for assembling 3,4-dihydropyrimidine-2-(1H)-ones via one-pot three-component Biginelli reaction.The satisfactory results were obtained with good yields,short reaction time and simplicity in the experimental procedure.The catalysts could be recycled and reused for several times without noticeably decreasing the catalytic activity.Electrophilic nitration of aromatics is a fundamental reaction of great industrial importance,whose products are used as organic intermediates or energetic materials.It is also among the most important unit reactions in chemical industry.Brφnsted acidic TSILs have also been used as halogen-free catalysts for regioselective mononitration of aromatic compounds.The reaction conditions including reaction temperature,reaction time,molar ratio of aromatic compounds,nitrating agents and catalyst have also been investigated. Under the optimal reaction conditions,the nitration reactions of aromatic compounds were carried out at r.t.to 80℃with reasonable to good yields;in addition,the TSILs could be recovered and reused without noticeably decreasing the catalytic activity.