The properties of aqueous solutions of sodium 2-sulfoethyl alkanoates and sodium alkyl beta-sulfopropionates

A series of sodium 2-sulfoethyl alkanoates RCOO(CH2)(2)SO3Na was prepared from sodium isethionate and fatty acids containing 9, 11, 13, and 15 carbon atoms. The Krafft point, the critical micelle concentration (CMC), the surface tension, the emulsifying power, the wetting time, the resistance to acid hydrolysis, and the calcium-ion stability of this series of surfactants were examined, and the results were compared with those of the corresponding sodium alkyl beta-sulfopropionates ROCO(CH2)(2)SO3Na, which have another structure of ester-linkage. The CMC values of sodium 2-sulfoethyl alkanoates almost coincide with those value of the sodium alkyl beta-sulfopropionates with the same number of carbon atoms. However, the Krafft point and surface tension at the CMC of sodium 2-sulfoethyl alkanoates were lower than those of the sodium alkyl beta-sulfopropionates with the same number of carbon atoms. Sodium 2-sulfoethyl alkanoates are more stable than sodium alkyl beta-sulfopropionates in their resistance to hydrolysis and to the calcium-ion.