Synthesis And Properties Of Alkyl-di(Ethoxy) And Alkyl-Tri(Ethoxy) α-D-glucopyranosides

Surfactants are special compounds with amphiphilic properties that exhibit important physical and chemical properties both at the interface and in bulk solution.Usually,they consist of two distinct parts,one polar and the other non-polar.In recent years,with increasing environmental awareness,more and more researchers are turning to sustainable surfactants.Alkyl glycosides（APG）,whose raw materials are renewable resources,are low-cost and biodegradable,and they are the most commonly used non-ionic surfactants.APG had good environmental friendliness and biocompatibility,and were considered as a world-class surfactant in the 1990s.Because of their excellent properties,such as wetting,foaming,and salt tolerance,APG have great potential in household detergents,cosmetics,agricultural products,drug delivery systems,and enhanced oil recovery.The increase of the hydrophobic chain would make long-chain alkyl glycosides insoluble in water.In order to improve their application value,seven alkyl-di（ethoxy）α-D-glucopyranosides（n=6-14）were synthesized by introducing a hydrophilic group segment（（-OCH₂CH₂-）₂）,and some important properties were investigated,such as dissolution,foam,emulsification,moisture absorption,surface and liquid crystal properties,etc.The hydrophilic-lipophilic balance（HLB）,water solubility,hygroscopicity,critical micelle concentration(C_cmc)and surface tension value(γ_cmc)decreased as the alkyl chain length increased.Decyl glycoside（n=10）had the best foaming performance,and its emulsifying effect was the best in the n-octane/water system.Lauryl glucoside had the best foam stability and had the best emulsifying performance in the rapeseed oil/water system.The thermotropic liquid crystal properties of this series of glycosides were studied by polarized light microscope,and it was found that the glycosides with carbon atoms of 7 to 14 in the hydrophobic chain had liquid crystallinity,and the fan-shaped focal cone texture could be observed during the cooling process.In addition,glycosides would form lyotropic liquid crystal phases after adding the solvent,and glycosides with different water content would show different types of liquid crystal phases,including hexagonal phase,bicontinuous cubic phase and lamellar phase.In the second part of this paper,a series of alkyl-tri（ethoxy）α-D-glucopyranosides（n=6-16）were synthesized and their properties were also studied.In addition,the thermal stability test of tetradecyl glycoside with long alkyl chain was carried out.The results showed that it would decompose at 221.3°C,and the temperature should reach 457.4°C when it was completely weightless,indicating that the glycoside had good thermal stability.In conclusion,the relationship between their structure and physicochemical properties was revealed through the study of the properties of the above glycosides,thereby providing a theoretical basis for their application.