Synthesis and Surface Activities of Amidobetaine Surfactants with Ultra‐long Unsaturated Hydrophobic Chains

Recent studies have shown that the surfactants bearing an ultra‐long hydrophobic chain (>C18) exhibit unique self‐assembly properties. However, their synthesis and surface activities have been less documented. In this work, monounsaturated alkyl dimethyl amidopropyl betaines, UCnDAB (n = 18, 22, and 24), were prepared by the reaction of the corresponding fatty acids with N,N‐dimethyl‐1,3‐propanediamine, followed by quaternization with sodium choloroacetate of the obtained intermediates. The intermediates and final surfactants were characterized by 1H NMR and ESI‐HRMS, respectively. Krafft temperature (TK) and surface activities of the surfactants were also examined. It was found that TK of all these surfactants is lower than 0 °C, and their critical micellar concentration (CMC) is within the range of 10−3 mmol/L. In addition, the linear relationship between lg CMC and n is still in evidence.