Figure 4. Current flow at different reaction time under various negative external electric fields.
On the other hand, with the increase of the inhibiting electric potential, decreased (S)-1-phenylethanol enantioselectivities were observed. However, these changes in the enantioselectivity are probably not due to the ability of OEEF to control reaction selectivity but are more likely attributed to the catalyst decomposition. Figure 5 showed the NMR analysis for the identification of the structures of the catalysts before and after reactions. Samples 1 (spectrum A) and 2 (spectrum B) were obtained by dissolving the Ru catalysts in CD3OD and reaction mixture (1-butanol and acetophenone mixture) respectively, and peaks from the Ru catalyst are clearly present at approximately 6.57 and 6.79 ppm. For sample 3 (spectra C), collected from the reaction run at positive 15 V for 24 h, small signals (due to the low initial concentration and difficulty of detection in 1H NMR spectra) for the Ru catalyst can be seen. However, the NMR spectra for sample 4, from the reaction run at negative 15 V for 24 h, showed no signals for the Ru catalyst. It remains unknown if the decomposition of the Ru catalyst was caused by the negative external electric field, and further investigation is required.