Synthesis and Properties of N-Alkyl Amide Sulfates

The critical micelle concentration (CMC), micelle ionization degree (α), Krafft point (KP), and chemical stability in water of sodium and calcium salts of the title surfactants, C m H2 m +1NHCO(CH2) n OSO3Me, abbreviated as m - n -Me (Me = Na, 0.5Ca), have been investigated as a function of the numbers m and n of the hydrocarbon chain length and the spacer methylene chain length, respectively. For the m - n -Na series, the CMC was reduced with increasing both the spacer methylene chain length ( n = 1, 3, 5) and the hydrocarbon chain length ( m = 12, 14, 16). The value of the ratio of reduction in log CMC for m to n was found to be just 4:1, suggesting that the spacer methylene chain is less hydrophobic than in the alkyl chain. Inclusion of an amide linkage near the headgroup in alkyl sulfates leads to a significant increase in the micelle ionization degree and to an increase in Krafft temperature. Furthermore, we found a striking and interesting exception in the Krafft temperature for the sodium and calcium salt pair of m -1-Me homologues. The KP of the 12 - 1 - 0.5Ca surfactant was found to be below 0 °C and was lower than that of the corresponding sodium salt (25.6 °C). This phenomenon is believed to be the first observation that the KP of the divalent salt is lower than that of the monovalent salt having the same surface active ion.