1H NMR analysis of the metathesis reaction between 1-hexene and (E)-anethole using grubbs 2nd generation catalyst: Effect of reaction conditions on (E)-1-(4-methoxyphenyl)-1-hexene formation and decomposition

Abstract

The metathesis of 1-hexene and (E)-anethole in the presence of Grubbs 2nd generation catalyst was monitored by in situ1 H NMR spectroscopy at different temperatures (15◦ C, 25◦ C, and 45◦ C) and anethole mol fractions (XAnethole ≈ 0.17, 0.29, 0.5, 0.71, 0.83). Time traces confirmed the instantaneous formation of (E)-1-(4-methoxyphenyl)-1-hexene, the cross-metathesis product. A maximum concentration of (E)-1-(4-methoxyphenyl)-1-hexene is reached fairly fast (the time depending on the reaction conditions), and this is followed by a decrease in the concentration of (E)-1-(4-methoxyphenyl)-1-hexene due to secondary metathesis. The maximum concentration of (E)-1-(4-methoxyphenyl)-1-hexene was more dependent on the XAnethole than the temperature. The highest TOF (3.46 min−1) was obtained for the reaction where XAnethole was 0.16 at 45◦ C. The highest concentration of the cross-metathesis product was however achieved after 6 min with an anethole mol fraction of 0.84 at 25◦ C. A preliminary kinetic study indicated that the secondary metathesis reaction followed first order kinetics.