INTRODUCTION OF ALKYL POLYGLUCOSIDES
Alkyl glucosides consist of a hydrophobic alkyl residue derived from a fatty alcohol and a hydrophilic saccharide structure derived from D-glucose, which are linked through a glycosidic bond. Alkyl glucosides show alkyl residues with about C6-C18 atoms, as do most surfactants from other categories of substances, for example the well-known alkyl polyglycol ethers. The prominent characteristic is the hydrophilic headgroup, constituted by saccharide structures with one or several glycosidically inter-linked D-glucose units. Within organic chemistry, D-glucose units are derived from carbohydrates, which are widely found throughout nature in the form of sugars or oligo and polysaccharides. This is why D-glucose units are an obvious choice for the hydrophilic headgroup of surfactants, since carbohydrates are practically inexhaustible, renewable raw materials. Alkyl glucosides can be represented in a simplified and generalized manner by their empirical formula.
The structure of D-glucose units shows 6 carbon atoms. The number of D-glucose units in alkyl polyglucosides is n=1 in alkyl monoglucosides, n=2 in alkyl diglucosides, n=3 in alkyl triglucosides, and so on. In the literature, mixtures of alkyl glucosides with different numbers of D-glucose units are often called alkyl oligoglucosides or alkyl polyglucosides. While the designation“alkyl oligoglucoside” is perfectly accurate in this context, the term “alkyl polyglucoside” is usually misleading, since surfactant alkyl polyglucosides rarely contain more than five D-glucose units and are therefore not polymers. In the formulas of alkyl polyglucosides, n denotes the average number of D-glucose units,i.e., the degree of polymerization n which is usually between 1 and 5. The Chain length of the hydrophobic alkyl residues is typically between X=6 and X=8 carbon atoms.
The way in which surfactant alkyl glucosides are manufactured, in particular the choice of raw materials, enables wide variation of the end products, which may be chemically pure alkyl glucosides or alkyl glucoside mixtures. For the former, the conventional rules of nomenclature used in carbohydrate chemistry are applied in this text. The alkyl glucoside mixtures frequently employed as technical surfactants are commonly given trivial names such as “alkyl polyglucosides,” or “APGs.” Explanations are provided in the text where necessary.
The empirical formula does not reveal the complex stereochemistry and polyfunctionality of alkyl glucosides. The long-chain alkyl residues may possess linear or branched carbon skeletons, although linear alkyl residues are often given preference. Chemically speaking, all D-glucose units are polyhydroxyacetals, which usually differ in their ring structures(derivable from five-member furan or six-member pyran rings) as well as in the anomeric configuration of the acetal structure. Moreover, there are various options for the type of glycosidic bonds between the D-glucose units of alkyl oligosaccharides. Particularly in the saccharide residue of alkyl polyglucosides, these possible variations lead to manifold, complex chemical structures, making designation of these substances increasingly difficult.
Post time: May-27-2021