Syntheses of sodium 2-(N-alkyl-N-methylamino)ethanephosphates and their physicochemical properties

A series of new amphoteric surfactants, sodium salts of 2-(N-alkyl-N-methylamino)ethanephosphates (alkyl: n-dodecyl, n-tetradecyl and n-hexadecyl) were prepared by reacting alkylbromides with N-methylaminoethanol, followed by addition of phosphoric acid groups and neutralization with sodium hydroxide. The structures of these compounds were confirmed by spectroscopy and elemental analysis. Physical properties such as Krafft point, isoelectric point, critical micelle concentration, occupation area of molecule at surface, foaming power and the effect of pH on surface activity were evaluated. These surfactants were found to exhibit zwitterionic characteristics in the pH range from approximately 5 to 9 and demonstrated good surface-active properties over a wide pH range (pH 4~10). Large occupation areas of the molecule at a surface in comparison with sodium dodecyl sulfate was noted as a characteristic feature of these surfactants.