Abstract
Large quantities (>3 g) of a new series of alkyl uronates were synthesized in two steps from commercial methyl hexopyranosides. Firstly, several tens of grams of free methyl α-d-glucopyranoside were selectively and quantitatively oxidized into corresponding sodium uronate using 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO)-catalyzed oxidation. Hydrophobic chains of different length were then introduced by acid-mediated esterification with fatty alcohols (ethyl to lauryl alcohol) leading to the desired alkyl glucuronates with moderate to good yields (49%–72%). The methodology was successfully applied to methyl α-d-mannopyranoside and methyl β-d-galactopyranoside. Physicochemical properties, such as critical micelle concentration (CMC), equilibrium surface tension at CMC (γcmc), solubility, and Krafft temperature were measured, and the effect of structural modifications on surface active properties and micelle formation was discussed.
Highlights
Carbohydrate-based surfactants, including sugar esters, have recently become more and more attractive because of their renewable origin, biodegradability, non-toxicity, and physicochemical behaviors [1,2,3]
Best way obtain thethe desired alkyl to obtain desired alkyluronates uronatesrespecting respectingthe theatom-energy atom-energyprinciple, principle,and andwithout without the the use use of hazardous reactants/solvents, was to use a two-step protocol starting from commercial methyl glycoside: an oxidation step followed by an esterification reaction
Except for octyl (1-α-methyl)glucuronate 3d and octyl (1-β-methyl)galacturonate 5, these results suggest a moderate ability of these alkyl sugar esters to form micelles, due to an area of limpid solution restricted and close to the critical micelle concentration (CMC)
Summary
Carbohydrate-based surfactants, including sugar esters, have recently become more and more attractive because of their renewable origin, biodegradability, non-toxicity, and physicochemical behaviors [1,2,3]. Among others properties, they are able to reduce the surface tension and to penetrate into lipid bilayers, are highly dispersible, and possess a high emulsifying power [4]. Sugar fatty esters are formed by one or several hydrophilic sugar headgroups and one or several hydrophobic alkyl chains Due to their biodegradability, they constitute viable eco-friendly alternatives to petroleum-based surfactants [7]. The configuration α or β of the sugar headgroup influences the micellar
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