| Betaine type zwitterionic surfactants have the unique properties such as desirable synergism effect with a wide variety of ionic and nonionic surfactants, good degradability, rather low irritation, and high foam stability. However, their wider application in industry is limited by their high production cost. In this paper, the long-chain alkylbetaine surfactants were prepared by simple and effective two-step route using cheap natural long fatty acids as raw material, and thus the cost of the alkylbetaine surfactants was greatly reduced in comparison with conventional synthesis route. In view of the green preparation method, the long-chain alkylbetaine surfactants are biologically safe, be environmentally friendly and easy to be biologically degraded.The synthesis of a-monochlorocarboxylic acids with short carbon chain has been developed successfully. Nevertheless, it is reported that the yield of long-chain a-chlorocarboxylic acids was yet low and there existed many byproducts due to the relative low reaction activity. In the present work, the selectivity and reaction rate were grately improved by using chlorosulfuric acid as catalyst and molecular oxygen as the radical scavenger, resulting the yield of above 96% under the optimized conditions. The structure of a-chloro-fatty acid was characterized by chlorine element analysis, infrared spectrum and nuclear magnetic resonance.The synthesis of a-long-chain alkylbetaine via aminolysis of a-monochloro-fatty acid with trimethylamine was investigated. The effects of molar ratio of reactants, reaction temperature and the type of reactor on the yield of a-long-chain alkylbetaine have been studied. Experimental results showed that the reaction can give a good yield (ca.92.5%). The crude product is purified by the electrodialysis desalination with the efficiency of 99%. The structure of the a-long-chain alkylbetaines was characterized by chemical analysis, element analysis, infrared spectrum, nuclear magnetic resonance and mass spectrometry.Kinetics and mechanism of the reaction of a-monochloro-fatty acid with trimethylamine were investigated. The experimental results suggested that the reaction proceeded through the SN2 mechanism. The rate equations were derived empirically. The experimental results also showed that the solvent effect on the reactivity was significant. In the case of protic polar solvents, the increase in solvent polarity favored the dispersal of charges at the transition state, therefore the reactivity was increased. The dipolar aprotic solvents can promote the SN2 reaction rate greatly because hydrogen-bonding interactions with anions did not take place in dipolar aprotic solvents. The solvation degree of nucleophiles was lower by dipolar aprotic solvents than by protic solvent, which benefited the generation of transition state.The surface tension and physicochemical properties of a-long-chain alkylbetaine revealed that its surface activity was higher than that of the other surfactants with the same chain length. The system presented the lowest surface tension, critical micelle concentration(cmc) and standard Gibbs energy of micellization when the pH of a-long-chain alkylbetaine solution approached isoelectric point. The mixed solutions ofα-decylbetaine and sodium dodecyl sulfate behaved synergistically in both surface tension reduction and mixed micelle formation.Some applied performances of a-long-chain alkylbetaines were examined and compared with that of BS-12. The results suggested that a-long-chain alkylbetaines exhibited better foaming performance, wettability and decontamination ability than BS-12. Moreover, the application performance of soap with addition of a-long-chain alkylbetaine was investigated. The results showed that the the foam performance, wettability, hard water-resistance and decreasing skin irritation of the soap were improved significantly by adding a-long-chain alkylbetaines. This indicates that a-long-chain alkylbetaine is a kind of high performance and low-cost zwitterionic surfactant.
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