Pure N ‐Alkylaminopropionic Acid and N ‐Alkylaminodipropionic Acid Sodium Salts: Synthesis, Characterization, and Physicochemical Properties

Fourteen pure β‐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 [∆ G (–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.