Fourteen pure b-aminopropionic acid amphoteric surfactants were synthesized from methyl acrylate using primary amines. The synthesis was done in two steps. First, Michael addition of a primary amine to methyl acrylate gave two separable addition products. Second, because the resulting esters gave, by the classical saponification procedure, undesired retro-Michael products, they were treated with sodium trimethylsilanolate to give the corresponding pure anhydrous acid salt under mild non-aqueous reaction conditions. Two types of amphoteric surfactants were obtained: the monocarboxylate and the dicarboxylate series. The pure surfactants were characterized by IR, 1 H NMR, and 13 C NMR spectroscopy. The surfactant critical micelle concentrations were evaluated. From these the Gibbs free energy of micellizations [DG(-CH 2 -) mic ] were calculated. These are related to the methylene units that contribute an average of -1.0 (±0.3) kJ mol -1 for both the monocarboxylate and the dicarboxylate series.
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