Novel Catalytic Process for the Hydroxide Initiated Reaction of the “Weakly Acidic” Substrate in the Third−liquid Phase−transfer Catalytic System

Generation processes of the third phase and the carbanion for Horner-Wadsworth-Emmons (HWE) reaction of the "weakly acidic" substrate in the third-liquid phase-transfer catalysis (TLPTC) system were investigated. The third phase consisted of Et2PO4- (diethyl phosphate anion), Br- and TBA(+) (tetrabutylammonium), and molar content of Et2PO4- was 6.65 times greater than that of TBA(+). The true catalyst was the complex of TBA(+)Et(2)PO(4)(-) and TBAB. Excess Et2PO4- could be associated with TBA(+)Et(2)PO(4)(-), resulting in generation of the third phase. The "true" catalyst showed a higher catalytic activity and the reaction equilibrium constant for the third-phase cycle was 26 times greater than that for the organic-phase cycle. Results from background reaction, interfacial tension, and hydrogen-deuterium exchange reaction experiments suggested that the phosphonate were deprotonated by "naked" OH-, without help of the catalyst. These novel generation processes of the third phase and the carbanion were key factors for this efficient TLPTC system.