Selectivity Engineering of Phase Transfer Catalyzed Alkylation of 2 -Hydroxyacetophenone: Enhancement in Rates and Selectivity by Creation of a Third Liquid Phase

摘要

Enhancements in rate of reaction and selectivity of the desired product in biphasic reactions are achieved by creating a third liquid phase,under appropriate conditions,where the third liquid phase is the locale of the main reaction,having a dramatic effect on product distribution in complex chemical reactions.Thus,in the case of phase transfer catalysis (PTC),conversion of liquid-liquid (L-L) PTC into liquid-liquid-liquid (L-L-L) PTC is of considerable techno-commercial interest resulting in waste minimization which is a major theme of green chemistry.Etherification of 2'-hydroxyacetophenone with 1-bro-mopentane,under traditional liquid-liquid phase transfer catalysis,results in loss of catalyst.However,the transformation of two liquid phases into three liquid phases (L-L-L) PTC leads enhancement in rates by orders of magnitude,with 100% conversion of the limiting reactant 1-bromopentane and 100% selectivity to 2'-pentyloxyacetophenone.This strategy eliminates separation problems and results in high reaction rates reducing the total reaction time.Moreover,the catalyst-rich third phase is recycled more than 7 times without loss in activity.The kinetics of the reaction are studied in great detail.There is a substantial reduction in activation energy under L-L-L PTC vis-a-vis L-L PTC,where the locale of the reaction is shifted from the organic phase to the third phase.