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 H-1 NMR and ESI-HRMS, respectively. Krafft temperature (T (K)) and surface activities of the surfactants were also examined. It was found that T (K) of all these surfactants is lower than 0 A degrees 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.