Interpreting ion-specific effects on the reduction of an arenediazonium ion by t-butylhydroquinone (TBHQ) using the pseudophase kinetic model in emulsions prepared with a zwitterionic sulfobetaine surfactant.

Specific salt effects on the reduction of an amphiphilic arenediazonium ion, 16-ArN2(+), by TBHQ in opaque, stirred, and kinetically stable emulsions prepared with a zwitterionic sulfobetaine surfactant are consistent with the chameleon effect: selective anion binding/induced cation binding in the interfacial region of the emulsions. Added NaX salts with different anions decrease the observed first-order rate constant, k(obs), for the reduction in the order X(-) = ClO4(-) > Br(-) ≈ CCl3CO2(-) > Cl(-) > MeSO3(-). Added MCln salts of increasing cation valence at constant total Cl(-) concentration increase kobs in the order M(n+) = Cs(+) < Ca(2+) < Al(3+) in the same emulsions. These results, combined with recent results for nonionic and ionic emulsions, demonstrate that pseudophase kinetic models provide general, coherent explanations of chemical reactivity in homogeneous micelles, microemulsions, vesicles, and now biphasic emulsions and with all types of basic surfactant structures: nonionic, cationic, anionic, and now zwitterionic.