Vanadium-catalyzed epoxidation reaction of cinnamyl alcohol in ionic liquids

Abstract

Chirally pure 3-phenylglycidol is a key intermediate in the manufacture of a range of drugs. In order to scale up the reaction in an ionic liquid (IL)/supercritical carbon dioxide (scCO 2 ) miscibility switch system, a study was started to select the optimum IL in this case. The vanadium-catalyzed epoxidation reaction of cinnamyl alcohol to 3-phenylglycidol in the presence of imidazolium- type liquids and tert-butyl hydroperoxide (TBHP) as the oxidant was studied experimentally. Three ILs, i.e., (i) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([bmim][Tf2 N]), (ii) 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([bmim][TfO]), and (iii) 1-butyl- 3-methylimidazolium nitrate ([bmim][NO3 ]), ranging from hydrophobic to hydrophilic, were selected as suitable candidates in terms of viscosity and stability, and were studied as solvents in the epoxidation reaction. In accordance with previously studied catalytic oxidations in ILs, the most hydrophobic ionic liquid [bmim][Tf2 N] results in the best yield and selectivity. Activities and product profiles are similar to those obtained in toluene, the benchmark solvent for these reactions. The maximum selectivity towards 3-phenylglycidol is 65%, with cinnamaldehyde and benzaldehyde as side products. The optimum reaction conditions require 1.5 equivalent of TBHP as the oxidant and 3 mol% of vanadyl acetylacetonate as the catalyst at 25 °C. Therefore, [bmim][Tf2 N], is a potential solvent for epoxidation reactions under miscibility switch conditions.