Interfacial Generation of a Carbanion: The Key Step of PTC Reaction Directly Observed by Second Harmonic Generation
Chem. Eur.J. 2018 | 24,3975 –3979
Michal Hamkalo, Dr. Piotr Fita, Prof. Michal Fedorynski, Prof. Mieczyslaw Makosza
Abstract:
We present the first unambiguous evidence of the interfacial mechanism of phase‐transfer catalysis (PTC) by direct observation of the formation of carbanions in the interfacial region between the aqueous and the organic phase by using a surface‐sensitive spectroscopic method known as second harmonic generation (SHG). Ion exchange of carbanions adsorbed at the surface after addition of lipophilic tetraalkylammonium salts (TAA) to organic phase and transport of the lipophilic ion‐pairs to the organic phase is observed. Results allow for the formulation of a more detailed mechanism of PTC.
Figure Legend: a) Simplified top view of the experimental setup for SHG measurements: F1, long pass filter; L1‐L3, lenses; FA, adjustable neutral density filter; P1, P2, polarizers; C, sample cell; M1‐M6, mirrors; F2, short pass filter; PM, photomultiplier; b) side view of the same setup.