MICELLAR EFFECTS ON ACIDITY FUNCTIONS

An anionic detergent, sodium lauryl sulfate (NaLS), increases -HR, based on the ionization of tri-p-anisylmethanol, by up to 2.5 units, and -H0′, based on the protonation of p-nitroaniline or 1-amino-4-nitronaphthalene, by up to 1.0 unit. Salts decrease the micellar effect on these acidity functions in the sequence : no salt > LiCl ≈ NaBr ≈ NaCl ≫ (CH3)4NCl. Added cetyltrimethylammonium bromide (CTABr) decreases both -HR and -H0′, with 103 M CTABr decreasing -HR by 1.4 units and 10-2 M CTABr decreasing -H0′ by 0.3 unit in 0.1 M HCl. These results show that anionic micelles stabilize and cationic micelles destabilize a triaryl cation much more than an ammonium ion.