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Abstract
Application studies of novel saccharide-type nonionic surfactants were performed. The homolog series of N-alkyl-N-(2-hydroxyethyl)gluconamides and N-alkyl-N-(2-hydroxyethyl)glucoheptonamides (alkyl: n-C^sub 10^H^sub 21^, n-C^sub 12^H^sub 25^, and n-C^sub 14^H^sub 29^) were synthesized and their structures were confirmed by means of elemental analysis and ^sup 1^H-NMR spectroscopy. The investigations showed that the application of N-alkyl-N-(2-hydroxyethyl)aldonamides as surfactants in an aqueous media can be limited. This is because of their relatively high Krafft point temperature. However, some variants can be successfully applied in mixtures with an anionic surfactant: sodium salt of n-dodecyl sulfate (SDS). The addition of SDS causes significant improvement of the Krafft point temperatures. In some cases a synergistic effect was observed, i.e., the Krafft point temperature of the binary mixture was lower that the corresponding values for the solutions containing individual compounds. It is also remarkable, that the aqueous solutions of binary surfactant mixtures were characterized by improved foaming properties, as compared to that of pure SDS.
Keywords Saccharide-derived surfactants * N-alkyl-N-(2-hydroxyethyl)gluconamide * N-alkyl-N-(2-hydroxyethyl)glucoheptonamide * Synthesis * Surface activity * Krafft point temperature * Foaming ability
Introduction
Aldo(bio)namides are carbohydrate-based molecules and as such represent renewable raw materials that are synthetically versatile and environmentally friendly. Aldonamides, derivatives of monosaccharides, have useful physical properties (e.g., surfactancy) which make them suitable for many applications in personal care, dental, detergent, and cosmetic areas. Many papers on the synthesis of surface active aldo(bio)namides are present in the literature [1-4]. Most of these compounds are prepared from appropriate amines and aldo(bio)nic acids or their lactones. Aldonamides derived from primary alkylamines and derivatives of monosaccharides (free aldonic acids or their lactones) have very low solubility in water. The amphiphilic N-octyl-D-gluconamide is practically insoluble in water at room temperature, dissolves readily in hot water (gives of critical micelle concentration of 27.7 mmol), and forms long-lived, ultrathin micellar fibers on cooling [5]. The formation of suprastructures in water is explained by very dense packing of the molecules in the crystal's unit cell because of the strong hydrogen-bond network between the hydrophilic headgroups. The solubility of ordinary alkylaldonamides can be improved either by methyl group incorporation into the amide linkage (as in N-aLkyl-Nmethylaldonamides [6, 7], preparation of derivatives with two gluconic acid moieties (dicephalic [8-10] or bolaform [11] structures) or preparation of derivatives of...