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Kinetics and mechanism of counterionic salt-catalysed piperidinolysis of anionic phenyl salicylate in the presence of cationic–nonionic mixed micelles

Posted on 9. April, 2018.

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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 (= KXBr or RXBr ) 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 KXBr or RXBr. These observations were also recorded upon addition of a nonionic surfactant, C16E20, in an aqueous solution of HDAB. The mean value of KXBr or RXBr obtained in the presence of pure HDAB (KXBr or RXBr = 50.3) is 2.3 times larger than that in the presence of mixed HDAB–C16E20 (mKXBr or mRXBr = 21.7). From rheometric measurements of aqueous HDA+/4-ClC6H4CO2 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 HDA+/C16E20/4-ClC6H4CO2- with 0.015 M HDAB and 0.006 M C16E20 at various [4-ClC6H4CO2Na] revealed the existence of spherical micelles.

Published in Progress in Reaction Kinetics and Mechanism, Volume 43, Number 1, 2018, pp. 41-52.

Authors: Ibrahim I. Faggea,b*, W. Hamdah W. Ahmada, Sharifuddin Md Zaina and M. Niyaz Khana
aDepartment of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
bCurrent address: Department of Chemistry, Faculty of Science, Kano University of Science and Technology, Wudil, Nigeria

Keywords: piperidine, phenyl salicylate, micellar structural growth, semi-empirical kinetics, spherical micelles, wormlike micelles

Image: Graph of shear viscosity (ŋ) against shear rate (ƴ) for the piperidinolysis of PheS- containing 0.015 M HDAB and [4-ClC6H4CO2Na] (M) = (a) 0.008 (•) 0.015 (♦) 0.030 (▲) 0.050 (Օ) 0.080 (Δ) and 0.150 (□) at 25 °C and (b) 0.008 (•) 0.015 (♦) 0.030 (▲) 0.050 (Օ) 0.080 (Δ) and 0.150 (□) at 35 °C.