Clays as Effective Solid Acid Catalysts for the Preparation of Sugar Esters with Surfactant Properties

Sugar fatty acid esters are a relevant class of surfactants. Base catalyzed transesterification of lower esters may be carried out on an industrial level. Direct esterification of fatty acids with sugars over heterogeneous catalysts should be more environmental friendly, however this approach is quite challenging. The activity of montmorillonites has been investigated in the acylation ofd-glucose with palmitic acid and the number of Lewis acid sites on the catalyst surface measured through FTIR of adsorbed pyridine. The use of a ketone, namely acetylacetone, as solvent allows the formation of an acetal between the sugar and the solvent itself, increasing the solubility of the substrate, with a maximum of conversion when using Fe(III)exchanged montmorillonite K10 as the catalyst. The main reaction product was the dipalmitate ester with an acetal group at the 1,2 position ofd-glucose. This product with a hydrophilic lipophilic balance (HLB) of 4.9 shows interesting properties as surfactant with a CMC value close to 0.036% wt/v measured in sunflower oil.