The phase transfer catalysis(PTC) reagent, ethyl tri-octyl ammonium bromide(ETABr), strongly catalyzes the reaction of p-nitrophenyl diphenyl phosphinate(p-NPDPIN) with benzimidazole(BI) and its anion(BI⊖). In ETABr solutions, the dephosphorylation reactions exhibit higher first order kinetics with respect to the nucleophile, BI, and ETABr, suggesting that reactions are occuring in small aggregates of the three species including the substrate(p-NPDPIN), whereas the reaction of p-NPDPIN with OH⊖ is not catalyzed by ETABr. This behavior for the drastic rate-enhancement of the dephosphorylation is referred as 'aggregation complex model' for reaction of hydrophobic organic phosphinates with benzimidazole(BI) in hydrophobic quarternary ammonium salt(ETABr) solutions.