Catanionic reverse micelles as an optimal microenvironment to alter the water electron donor capacity in a SN2 reaction
Villa, Cristian C.; Correa, Nestor Mariano; Silber, Juana J.; Falcone, Ruben Dario; Catanionic reverse micelles as an optimal microenvironment to alter the water electron donor capacity in a SN2 reaction; American Chemical Society; Journal of Organic Chemistry; 84; 3; 2-2019; 1185-1191
Villa, Cristian C.
Correa, Nestor Mariano
Silber, Juana J.
Falcone, Ruben Dario
The effect of interfacial water entrapped in two types of catanionic reverse micelles (RMs) on the kinetic parameters of the SN2 reaction between dimethyl-4-nitrophenylsulfonium trifluoromethanesulfonate (S+) and n-butylamine (BuNH2) was explored. Two catanionic surfactants, composed of a mixture of oppositely charged ionic surfactants without their original counterions, were used to create the RMs. Thus, benzyl-n-hexadecyldimethylammonium 1,4-bis(2-ethylhexyl) sulfosuccinate (BHD-AOT) and cetyltrimethylammonium 1,4-bis(2-ethylhexyl) sulfosuccinate (CTA-AOT) were formed. Also, the well-known anionic surfactant sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (Na-AOT) was employed as a comparison. Our results showed an important catalytic-like effect of all RMs investigated in comparison with a water-benzene mixture, and the rate constant values depend on the type of surfactant used. Faster reaction in BHD-AOT RMs than in CTA-AOT and Na-AOT RMs was observed. This behavior was attributed to the strong interaction (by hydrogen bonding with AOT anion and ion-dipole interaction with BHD+) between the entrapped water and the BHD-AOT interface, which reduces the solvation capacity of water on S+. In CTA-AOT (and Na-AOT) RMs, the water-interface interaction is weaker and the electron pairs of water can solvate S+ ions. In summary, the chemical structure of the counterion on the catanionic surfactant alters the interfacial region, allowing the progress of a reaction inside the RMs to be controlled. ©