Selective Catalytic Oxidation Of Cyclohexene In Room Temperature Ionic Liquids

The Green Chemistry aimed at eliminating pollutions from the beginning has been developed in the late of 1990's. The Green Chemistry provides some measures to solve the pollution of the chemical industries and to keep the development of the economy and society, which is becoming an active area of chemical research in the 21 century. Room temperature ionic liquids (RTILs), which have the advantages of no-toxicity, no-volatility, no-flammability, high thermal stability, wide liquid range (-100²00℃), miscible with most of organic compounds, and have been becoming the latest green solvents to replace the volatile organic solvents. RTILs can reduce or eliminate the environment pollution of the solvents, which have a wide application in all branches of chemistry and important practical values.In this paper, a series of RTILs were synthesized by one-step and two-step method, which were identified by FT-IR,¹H-NMR and ¹³C-NMR spectra. These RTILs are 1-butyl-3-methyl imidazolium tetrafluoborate ([Bmim][BF₄), 1-butyl-3-methyl imidazolium hexflorophosphate ([Bmim][PF₆]), 1-butylpyridinium tetrafluoroborate ([BPy][BF₄]), 1-ethylpyridinium hexflorophosphate ([EPy][PF₆]), 1-butyl-3-methyl imidazolium chloride ([Bmim]CI) and 1-ethyl-3-methylimidazolium bromide ([Emim]Br), repectively.The epoxidation of cyclohexene in ionic liquids catalyzed by Mn(Salen) complex with hydrogen peroxide as oxidant was studied. The effects of the reaction media, various Mn(Salen) complexes, and reaction temperatures on the epoxidation were investigated. It was found that handy hydrogen peroxide could be an alternative to expensive oxidant, such as PhI(OAc)2 and m-CPBA, and that ionic liquid medium gave higher conversion and selectivity to cyclohexene epoxide in comparison with the reaction performed in conventional organic solvent. 100% of the conversion of cyclohexene with 94% of selectivity to cyclohexene epoxide were obtained when the reaction was performed in the solvent of neutral [Bmim][BF4]-CH2Cl2(3:2, v/v) at 273 K using Mn(Salen) complex prepared by salicylaldehyde and o-phenyldiamine as a catalyst. Moreover, the final products could be easily separated from reaction system by simple extraction over hexane. The ionic liquids was reused and found it's the decomposition of Mn(Salen) under the oxidant (H2O2) that leading to the decrease of conversion and selectivity.2-cyclohexene-l-one is synthesized by the oxidation reaction of cyclohexene under V2O5 using H2O2 as oxidant in RTILs. Several factors, such as reaction time, temperature, amount of V2O5 and H2O2, which may have effect on reaction, have been'studied. Comparision reaction between in organic solvents and in RTILs, fine conversion of cyclohexene andhigh productivity of cyclohexene-1-one have obtained in [Bmim][BF4]-acetone. Indeed the conversion of cyclohexene reached 88.7% with 91.1% of selectivity to 2-cyclohexene-l-one when the reaction was performed in the mixed solvent of neutral [Bmim][BF4]-acetone (2:5, v/v) using V2O5 (2%, molar ratio) as a catalyst and H2O2 (cyclohexene/ H2O2=1:3, v/v) as oxidant at 313 K for 10 h, The ionic liquids was reused for six times, and found decrease in the conversion of cyclohexene and slectivity of 2-cyclohexene-l-one.