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-m ethylglucon/lactobionamide, were synthesized in the reaction of an appropri ate N-alkyl-N-methylamine with delta -D-glacolactone and lactobionic acid, respectively. Krafft temperatures of aqueous solutions and surface properti es of these surfactants at 20 degreesC, i.e., surface excess concentration, Gamma (cmc), surface area demand per molecule, A(min), efficiency in surfa ce tension reduction, pC(20), effectiveness in surface tension reduction, P i (cmc), critical micelle concentration, CMC, and CMC/C-20 parameter as wel l as standard free energies of adsorption, DeltaG(ads)degrees, and of micel lization, DeltaG(mic)degrees, were determined. It was shown that introducti on of the methyl group to the amide nitrogen increased the solubility of th e surfactants, which was confirmed by their Krafft temperatures. Lactobiona mides are more water soluble than gluconamides. On the other hand, the Cn-M GA surfactants are more surface active than the respective Cn-MLA ones. Thi s observation is based on the determined adsorption and micellization param eters. The presence of one double bond in a hydrocarbon chain as in oleyl-a mides 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.