Benzene group, surfactant structure

Alkyl ether sulfates are/after alkyl benzene sulfonates(LAS),the group of technically important anionic surfactants with the largest production voluJne and product value. They have in comparison with other anionic surfactants special properties which are based on the particular structure of the molecule. These are expressed,for example,in the general adsorption properties at different interfaces, and in the Krafft-Point. Alkyl ether sulfates may be used under conditions, at which the utilization of other surfactant classes is very limited. They possess particularly favorable interfacial and application properties in mixtures with other surfactants. The paper gives a review of all important mechanisms of action and properties of interest for application. 

Surfactants with very small head group areas such as cholesterol tend to form inverted micelles (Fig. 12.7). Their head groups point into the center of the micelle while the hydrophobic tails form the continuous, hydrophobic outer region. Inverted structures such as inverted liposomes, are also formed in nonpolar solvents such as toluene, benzene, cyclohexane instead of water [534]. 

Sulfonic acids and sulfonate salts contain the -S03H and -SO) groups, respectively, attached to a hydrocarbon moiety. The structural formulas of benzene sulfonic acids and of sodium 1 -(p-sulfophenyl)decane, a biodegradable detergent surfactant, are shown in Figure 1.19. The common sulfonic acids are water-soluble strong acids that lose virtually all ionizable H+ in aqueous solution. They are used commercially to hydrolyze fat and oil esters to produce fatty acids and glycerol used in chemical synthesis. 

Hydrotropes have been known for decades as organic substances that increase the solubility and reduce the viscosity in water of other organic susbstances. They have a structure somewhat similar to those of surfactants in that they have a hydrophilic and a hydrophobic group in the molecule, but are different from surfactants in that the hydrophobic group is generally short, cyclic, and/or branched. Typical hydrotropes include sodium benzene-, toluene-, xylene-, cumene-, and p-cymenesulfonates, 1-hydroxy-2-naphthoate, 2-hydroxy-1-naphthal-enesulfonate, and sodium 2-ethylhexyl sulfate. 

Anionic surfactants with the general structure RpCONH-X-COONa (e.g., X = -(0112)5-) have been reported in the patent literature. These surfactants are synthesized from the corresponding isopropyl ester and 6-amino-hexanoic acid sodium or ammonium salt (H2N(CH2) 5COOM). Another class of anionic surfactants derived from PFCA derivatives are perfluoroacylbenzenesulfo-nates (Scheme 18.11). This group of surfactants is synthesized by Friedel-Crafts acylation of benzene with a PFCA halide (e.g., perfluorooctanoyl chloride) in the presence of at least one equivalent of a Lewis acid (e.g., anhydrous aluminum chloride). This reaction proceeds smoothly and in good yields at subambient or ambient temperatures. The perfluoroacylbenzene is sulfonated with oleum or sulfur trioxide and neutralized with a base (e.g., sodium hydroxide). 

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