3RD-PHASE CATALYTIC ACTIVITY OF HALOGEN EXCHANGE-REACTIONS IN PHASE-TRANSFER CATALYTIC-SYSTEM

The purpose of this study was to clarify the cause of high catalytic a ctivity of a third phase in a phase transfer catalysis system. The hal ogen substitution reaction between benzyl chloride in an organic phase and potassium bromide (KBr) in an aqueous phase was carried out. The conditions of formation of the third phase were searched by changing t he kinds of phase transfer catalysts, organic solvents and the concent ration of KBr in an aqueous phase. When tetrabutylammonium bromide was used as a phase transfer catalyst, a third phase was formed with both dodecane and toluene as organic solvents. On the other hand, when tet rapentylammonium bromide was used as a catalyst, a third phase was for med with dodecane but not with toluene. The distributions of catalysts , benzyl bromide and Br-among phases were measured. Based on the resul ts, the place where the reaction occurred could be classified into thr ee types, that is, in an organic phase (type I), at the interface betw een an organic phase and an aqueous phase (type II) and in a third pha se (type III). The reaction rate of type III was the largest because o f high concentration of both reactants in a third phase. The reaction rate varied with the kinds of third phase significantly. This variatio n could be explained by a difference in the concentration of benzyl ch loride in the third phase. The rate constant of the first-order kineti cs was, however, independent of the kinds of third phase. This value a greed with that of an organic phase of type I. Repeated use of a third phase was also studied to apply phase transfer catalysts to industria l purpose. After the reaction was completed, an organic phase containi ng a product was removed and a new organic phase containing a reactant was charged. By repeating this operation, the third phase could be re used without any loss of its catalytic activity. (C) 1997 Elsevier Sci ence Ltd.