Properties of aqueous solutions of disodium di‐3‐sulfopropyl α,θ‐alkane dicarboxylate

A series of disodium di‐3‐sulfopropyl α,θ‐alkane dicarboxylates NaO3S(CH2)3OOC(CH2)nCOO(CH2)3SO3Na (n=10, 12, 14, and 16) were prepared by the reaction of propane sultone with decane, dodecane, tetradecane or hexadecane dicarboxylic acids, and were estimated as to Krafft point and critical micelle concentration (cmc). The Krafft points of these α,θ‐type surfactants were determined from the temperature at which the abrupt changes in the conductivities of the aqueous solutions in the presence of the solid surfactant were below 0 C for n=10, 23.5 C for n=12, 31.0 C for n=14 and 38.5 C for n = 16. The α,θ‐type surfactant solution showed two break points in each plot of electroconductivity as a function of surfactant concentration. These results were considered to be due to the existence of the second cmc characteristic of these surfactants. A plot of the values obtained from the 1st cmc and the 2nd cmc of the α,θ‐type surfactants decreases logarithmically according to the increasing total number of methylene groups (N). Their relationship is given as follows: log cmc =−0.142N+3.77 (1st cmc); log cmc =−0.143N+4.20 (2nd cmc).