Green synthesis of 1-phenyl-1-ortho-xylene ethane in IL and reaction mechanism

Abstract

1-Phenyl-1-ortho-xylene ethane (PXE) in IL was synthesized, and the catalysts used were AlCl₃ in 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) or 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), and H₂SO₄. When the concentrations of AlCl₃ in IL, ortho-xylene and styrene were 0.35, 0.03 and 0.005 mol, respectively, it could be discovered that ([BMIM][Br]) was the best catalyst. When the mole fraction concentration of AlCl₃/[BMIM][Br] was more than 0.40%, the reaction was able to achieve 100% conversion. When the reaction time was longer than 60 minutes, the percentage conversion of ortho-xylene attained was 100%. The mechanisms of the reaction were investigated by the DFT method at the B3LYP/6-311++G(d, p) level. The potential energy surface (PES) profile indicated that the energy of transition state was 22.59 kcal mol⁻¹. This indicated that the activation energy of reaction was 28.24 kcal mol⁻¹, which illustrated that the reaction occurred easily. Vibrational frequencies were observed in FT-IR spectra, the corresponding vibrational modes ν_s(H4–C3Al–H5) and ν_as(H4–C3Al–H5) indicated that an Al³⁺ ion was combined with a C3 atom. In addition, the repeated use of the catalysts was studied; the ionic liquids could still catalyze the reaction and the percentage yield of PXE was larger than 91% after 6 runs.