(560db) Electrostatically Enhanced Catalytic Phase Transfer Hydrogenation of Acetophenone Under Low External Electric Field | AIChE

(560db) Electrostatically Enhanced Catalytic Phase Transfer Hydrogenation of Acetophenone Under Low External Electric Field

Authors 

WANG, N. - Presenter, The University of Kansas
Weatherley, L., The University of Kansas
Phase transfer catalysis (PTC) has been extensively studied as a practical method for organic synthesis, as it not only achieves high reactivity and selectivity but also features operational simplicity, and economic and environmentally benign reaction systems. While having various advantages, PTC processes are not as efficient as homogeneous catalysis due to the mass transfer limitation between the two essentially immiscible liquid phases. Additionally, the novel design of phase transfer catalysts is a significant challenge. Recently, the use of external electric fields to establish electrostatic dispersion has been proved as an energy-efficient method for eliminating mass transfer resistance in liquid/liquid systems theoretically and experimentally in different processes. With the presence of an oriented-external electric field (OEEF), the charged components/species can be selectively transferred from the feed liquid phase to a second liquid phase at an accelerated rate due to the electrostatic forces which enhance the dispersion and droplet mechanics. While phase-transfer catalysts and external electric fields each enhance mass transfer across phase boundaries, the latter is much easier to apply, avoiding lengthy rational design of phase transfer catalysts for targeted reactions.

In the present work, the OEEF promoted phase transfer catalysis reaction was reported for the first time. The reaction of choice for this study was the transfer hydrogenation of acetophenone, with sodium formate as the hydrogen source. The two phase system was established with acetophenone/organic solvent as the less dense organic phase and sodium formate solution as the more dense aqueous phase. An external electric field was applied across the two phases without any agitation. It was demonstrated experimentally that an OEEF can act as promoter or inhibitor for the phase transfer hydrogenation of acetophenone depending on its direction, showing a potential on controlling rate of chemical reactions. With 1-butanol as organic solvent, the conversion can be achieved as high as 86% with an enantioselectivity of 94% under room temperature and pressure. This work presents a methodology for promoting PTC reactions in the absence of a chemical phase transfer agent and shows promise for significantly improving the performance of organic reactions with OEEF in biphasic liquid systems.