New amphoteric surfactants derived from lysine. I. Preparation and properties of Nε‐acyllysine derivatives‐acyllysine derivatives

New amphoteric surfactants were prepared from Nε‐acyllysine which was obtained by the thermal dehydration of a higher fatty acid salt of lysine and was not soluble in water. Nα,Nα‐dimethyl‐Nε‐acyllysine was prepared by the catalytic reductive condensation of Nε‐acyllysine ester with formaldehyde in good yield. Nα,Nα,Nα‐trimethyl‐Nε‐acyllysine was obtained from the reaction of Nα,Nα‐dimethyl‐Nε‐acyllysine ester with methyl iodide. Confirmation of the structure of these derivatives was obtained by spectrometric and spectroscopic analyses. The solubility of Nε‐acyllysine was improved significantly by the introduction of Nα‐methyl groups. Physicochemical and surface active properties of the derivatives were investigated in terms of isoelectric points, dissolution temperatures, surface tensions, critical micelle concentrations (cmc), foaming properties and wetting powers. Nα,Nα,Nα‐trimethyl‐Nε‐acyllysine had lower dissolution temperatures than Nα,Nα‐dimethyl‐Nε‐acyllysine. The latter showed lower surface tensions than the former at cmc. Nα,Nα‐dimethyl‐Nε‐lauroyllysine was best in wetting power and foaming property.