Epoxide ring-opening reaction promoted by ionic liquid reactivity: interplay of experimental and theoretical studies†
Ionic liquids (ILs) have been widely introduced recently into the epoxide ring-opening reaction as catalysts or solvent without considering the chemical stability of ILs in propylene oxide (PO). Through a combination of electrospray-ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS) investigations and quantum-chemical calculations, we demonstrate that AC- (acetate) and MC-(methylcarbonate) based ILs exhibit modified activity for ring opening of PO compared with the reaction between ILs and epoxide compounds. The chemically unstable ILs and the solvent effect can also dominate the catalytic performance of the coupling reaction of PO with methanol. Based on these findings, we further design the reaction process for highly efficient synthesis of propylene glycol methyl ether, in which the yield of the main product increased more than 40% under the same ILs catalysts. The results explained how the chemical instability and substrate affected the PO coupling reaction and further controlled it.