Synergetic Effect of Two Kinds of Phase Transfer Catalysts in Third Phase for Dehydrohalogenation of 2-Bromooctane

Dehydrohalogenation of 2-bromooctane in the organic phase with dodecane solvent by using phase transfer catalysts (PTC) was carried out in a batch reactor with potassium hydroxide solvent in the aqueous phase. A synergetic effect of PTC was observed for the combination of tetrahexyl ammonium bromide ((Hex)4NBr) and polyethylene glycols (PEG) in the third phase. The observed reaction rate constant (kobs), which is determined from the first order kinetics, depends on the average molecular weight of PEG, and remarkably increases with the increasing KOH concentration in the aqueous phase. If the optimum combination of (Hex)4NBr and PEG with average molecular weight of 200 (PEG200) is used, the amount of quaternary ammonium salt can be significantly saved (for example, by one-nineteenth).The volume of the third phase and the concentration of water in the third phase (CH2O) were measured and related to the reaction rate constant as well as the distribution coefficient (KA).Catalysts which exist in the third phase can be reused without any loss of catalytic activity.