Role of a Third Liquid Phase in Phase-Transfer Catalysis

The elimination of phenethyl bromide to styrene under phase-transfer catalytic conditions is shown to be sharply accelerated if a three-liquid-phase system can be engineered. Tetrabutylammonium bromide can promote such a system under certain conditions of temperature and concentration, the third phase being rich in catalyst. Excessively concentrated alkali causes a drop in the rate of elimination by nearly 1 order of magnitude, as does a small change in temperature. Such effects are due to destabilization of the third phase and precipitation of the catalyst. None of the observations described apply to either the tetrapropyl or the tetrapentyl salts. The data are explained by reference to anomalous physical and surface chemical properties of the tetrabutyl salt.