Synthesis and surface properties of N-alkyl-N-methylgluconamides and N-alkyl-N-methyllactobionamides

Three series of nonionic N-alkylaldonamides, N-alkyl-N-methylgluconamides (Cn-MGA, Cn: n-C10H21, n-C12H25, n-C14H29, n-C16H33, and n-C18H37), N-alkyl-N-methyllactobionamides (Cn-MLA, alkyl as above-mentioned), and N-oleyl-N-methylglucon/lactobionamide, were synthesized in the reaction of an appropriate N-alkyl-N-methylamine with delta -D-glacolactone and lactobionic acid, respectively. Krafft temperatures of aqueous solutions and surface properties of these surfactants at 20 degreesC, i.e., surface excess concentration, Gamma (cmc), surface area demand per molecule, A(min), efficiency in surface tension reduction, pC(20), effectiveness in surface tension reduction, Pi (cmc), critical micelle concentration, CMC, and CMC/C-20 parameter as well as standard free energies of adsorption, DeltaG(ads)degrees, and of micellization, DeltaG(mic)degrees, were determined. It was shown that introduction of the methyl group to the amide nitrogen increased the solubility of the surfactants, which was confirmed by their Krafft temperatures. Lactobionamides are more water soluble than gluconamides. On the other hand, the Cn-MGA surfactants are more surface active than the respective Cn-MLA ones. This observation is based on the determined adsorption and micellization parameters. The presence of one double bond in a hydrocarbon chain as in oleyl-amides increases their hydrophilic character compared with that of saturated C18 derivatives. No distinct differences were, observed between the A(min) values obtained for both series studied, although they differ markedly in the size of the hydrophilic groups. (C) 2001 Academic Press.