Figure 1. Acetophenone conversion (mol%) and 1-phenelethanol yields
(mol%) under 15V of positive external electric field for 24 h with
different organic solvents and stainless-steel electrodes.
One possible reason for the significantly different performance may be
their respective solubilities in water. Compared to the other solvents,
1-butanol has the highest solubility in water, which initially promotes
most of the interaction between the reactants at the interface,
resulting in the highest conversion and reaction rate (more than 2 fold
faster than that with 1-octanol as solvent). On the other hand, these
alcohols are protic solvents, which possess the ability to generate
protons by dissociation. With the largest dielectric constant among the
studied solvents, 1-butanol has the greatest potential to polarize and
generate protons under an external electric field. These protons could
further promote the dissociation of the neutral Ru compound
(RuCl(p-cymene)[(S-S)-Ts-DPEN]) into the cationic Ru complex
(species 2 in Scheme 1) by removing the chloride
ion,31,32 therefore accelerating and promoting the
generation of the catalysts and ultimately increasing the production
rate. While the dipole moment and electrical conductivity might be
important in electrostatically promoted reactions according to our
previous investigation25 and Shaik and
coworkers,2 the differences of these properties
between the five solvents are small. Accordingly, it is difficult to
attribute the differences in reaction performance to dipole moment and
conductivity in the present study.
Table 1. Properties of the studied organic solvents.