Interfacial Activity of Quaternary Salts as a Guide to Catalytic Performance in Phase-Transfer Catalysis

The phase transfer catalyzed ethylation of deoxybenzoin has been studied in several solvents, using symmetrical quaternary ammonium bromides as catalysts. In all cases the reactivity passed through a maximum as the size of the catalyst increased. The catalysts were also found to reduce the interfacial tension between the phases. This effect also passing through a maximum as a function of catalyst size. A correlation was observed between the two parameters, such that those catalysts reducing interfacial tension most markedly were also the best catalysts. Therefore, interfacial tension can be a guide to catalytic activity in certain PTC systems.