Kinetics and Mechanism of Counterionic Salt-Catalysed Piperidinolysis of Anionic Phenyl Salicylate in the Presence of Cationic–Nonionic Mixed Micelles

The quantitative correlation of counterion-Affinity to aqueous hexadecyltrimethylammonium bromide (HDAB, cationic micelles/nanoparticles) and the counterion-induced HDAB micellar growth, in the presence of different amounts of poly(ethylene glycol hexadecyl ether) (C16E20, nonionic surfactant), was achieved by the use of a semi-empirical kinetic (SEK) method. The values of the ratio of cationic HDAB, as well as mixed HDAB-C16E20, micellar binding constants of X and Br, KX/KBr (= KX Br or RX Br ) for X = 4-ClC6H4CO2, were obtained by the SEK method. The concentration range (0.006-0.015 M) of pure HDAB was found to have no influence on the values of KX Br or RX Br These observations were also recorded upon addition of a nonionic surfactant, C16E20, in an aqueous solution of HDAB. The mean value of KX Br or RX Br obtained in the presence of pure HDAB (KX Bror RX Br = 50.3) is 2.3 times larger than that in the presence of mixed HDAB-C16E20(mKX Br or mRX Br = 21.7). From rheometric measurements of aqueous HDAClC6H4CO2-with 0.015 M HDAB, single symmetric maxima (at both 25 and 35 °C) were obtained at [4-ClC6H4CO2Na] = 0.03 M. This is evidence for the existence of wormlike micelles/nanoparticles. However, the absence of a maximum in rheometric data for aqueous HDA16E20/4-ClC6H4CO2 with 0.015 M HDAB and 0.006 M C16E20 at various [4-ClC6H4CO2Na] revealed the existence of spherical micelles