The Application Of Ionic Liquids In Fine Organic Synthesis

The aim of green chemistry is to eliminate pollutions from the beginning, which is becoming the hotspot and the foreland in chemical research. Traditional chemical reaction and correlated chemical industry are the main source of pollution. Most of the wastes are from the volatile organic compounds (VOC). Finding 'green' solvents to replace the organic solvents, therefore, becomes essential. Room temperature ionic liquids (ILs), which have the advantages of no-toxicity, no-volatility, no-flammability, high thermal stability, wide liquid range (-100℃-200 ℃), miscible with most of organic compounds and inorganic compounds, and facility in recycling etc., should be used to replace for the VOC in chemical processes or extractions .procedures. Furthermore, the polar or ionic character maybe change the reaction pathway, making the catalyst more active and more stable with improvement of the use ratio of atoms, which have attracted much interests in reducing or eliminating environmental pollutions.In this paper, a series of ILs were synthesized by two-step method and identified by FT-IR,¹H-NMR and ¹³C-NMR spectra. These ILs are 1-butyl-3-methyl imidazolium tetra-fluoroborate (BmimBF₄), 1-butyl -3-methyl imidazolium hexafluorophosphate (BmimPF₆), 1-butyl- pyridi-nium tetra-fluoroborate (BPyBF₄), 1-ethylpyridinium tetra- fluoroborate (EtPyBF₄), l-butyl-3-methyl imidazolium tetra-fluoroborate (EmimBF₄), methyl imidazolium tetra-fluoroborate (HmimBF₄), 1-butyl -3-methyl imidazolium bromide (BmimBr),1-butyl-3-methylimidazolium chloride-AlCl₃ (BmimCl-AlCl₃), l-butyl-3-methylimidazolium chloride -FeCl₃ (BmimCl-FeCl₃), l-butyl-3-methylimidazolium chloride-ZnCl₂ (Bmim-Cl-ZnCl₂),1-butyl-3-methylimidazolium chloride-FeCl₂ (BmimCl-FeCl₂), 1-ethyl-3-methylimidazolium chloride-ZnCl₂ (EmimCl-ZnCl₂), 1-ethyl-pyridinium bromide-ZnCl2 (EtPyBr-ZnCl2), 1-butyl-pyridinium bromide-ZnCI2 (BPyBr-ZnCI2), respectively. The acfcfic properties of ILs, such as BmimCl-ZnCl2 were measured by acetonitrile as a probe molecule by FT-IR spectra. The results indicated that the Lewis acidic strength of ILs increased with increasing of the mole fraction of metallic halide.Air and moisture-stable room temperature ILs, such as BmimBF4, BmimPF6, BPyBF4, EtPyBF4, EmimPF6, EmimBF4, HmimBF4 and BmimBr were used as reaction media for olefin epoxidation in the presence of Mn(III) Salen complex. Significant rate-enhancement is observed and high yield of epoxides is obtained in these ionic liquids media. After completion of the reaction, the product and catalyst can be separated by simple extraction. Comparing the performances of various ILs in the styrene epoxidation, it is found that 95% of styrene conversion and 100% of selectivity of styrene oxide could be obtained when using BPyBF4/H2O as reaction medium. This first finding makes a real green process for the epoxidation of alkylene come true.A novel kind of Lewis acidic ionic liquids were synthesized by combining ZnCl2 with dialkylimidazolium halide or alkylpyridinium halide and were used firstly as both Lewis acidic catalyst and green solvent in the Diels-Alder reaction of myrcene with dienophiles. High regioselective synthesis of 'para' myrac aldehyde and other industrial -useful compounds were achieved in all these ionic liquids medium. Comparing with the reaction performed in the conventional organic solvent over ZnCl2 catalyst, excellent yield, rate-enhancement, as well as high regioselectivity of 'para' cycloadduct, were obtained in the Zn-containing ionic liquids. When the reaction was performed at 15 °C for 2 h in the ionic liquids with the molar ratio of ZnCl2 to dialkylimidazolium halide or alkylpyridinium halide being 2:1, myrcene was almost converted into myrac aldehyde quantitatively with 'para'/'meta' regioselectivity of p/m>18. Compared with moist-...