Influence of PVP-PEG mixed aggregates and electrolytes on the rate of alkaline hydrolysis of benzocaine in aqueous and surfactant medium

Abstract

The present work describes the effects of the interactions between the two water-soluble polymers poly(vinyl pyrrolidone) (PVP) and poly(ethylene glycol) (PEG) on the rate of the alkaline hydrolysis of benzocaine. The roles of the surfactants cetyltrimethylammonium bromide (CTABr) and sodium dodecyl sulfate (SDS) in the binding of benzocaine with PVP-PEG mixed systems has also been explored through changes in the reaction rate. Our results revealed that the reaction rate decreases with the increasing [PVP] when [PEG] is fixed. Similarly, the rate of hydrolysis also decreases on increasing [PEG] while [PVP] is fixed. The combined rate constant values for the hydrolysis of benzocaine in the aqueous and mixed PVP-PEG system (kΨ) increases with increasing [CTABr] in the lower concentration range, then decreases with further increase in [CTABr], giving a peaked profile for kΨ vs. [CTABr]. The increase in [SDS] in the mixed PVP-PEG system decreases the rate of hydrolysis. Accordingly, the observed results show that the binding constant values (i.e., the degree of association) of benzocaine with PVP-PEG in the presence of CTABr and SDS are lower. Furthermore, increasing the molecular weight of PEG in the surfactant-PVP-PEG complex decreases the binding constant values of the benzocaine-polymer complex due to the formation of less compact aggregates. The effects of electrolytes (CH3COONa, NaCl, Na2SO4, and NaNO3) were also investigated, and they were found to decrease reaction rate.