Anionic surfactants carboxylate salts

ANIONIC SURFACTANTS Carboxylic acid salts Sulfonic acid salts Sulfuric acid ester salts Phosphoric and polyphosphoric acid esters Perfluorinated anionics... 

A selection of important anionic surfactants is displayed in table C2.3.1. Carboxylic acid salts or tire soaps are tire best known anionic surfactants. These materials were originally derived from animal fats by saponification. The ionized carboxyl group provides tire anionic charge. Examples witlr hydrocarbon chains of fewer tlran ten carbon atoms are too soluble and tliose witlr chains longer tlran 20 carbon atoms are too insoluble to be useful in aqueous applications. They may be prepared witlr cations otlrer tlran sodium. 

Carboxylate, sulfonate, sulfate, and phosphate ate the polar, solubilizing groups found in most anionic surfactants. In dilute solutions of soft water, these groups ate combined with a 12—15 carbon chain hydrophobe for best surfactant properties. In neutral or acidic media, or in the presence of heavy-metal salts, eg, Ca, the carboxylate group loses most of its solubilizing power. 

Ether carboxylates are used not only in powdered detergents but in liquid laundry detergents for their hard water stability, lime soap dispersibility, and electrolyte stability they improve the suspension stability and rheology of the electrolyte builder [130,131]. Formulations based particularly on lauryl ether carboxylate + 4.5 EO combined with fatty acid salt and other anionic surfactants are described [132], sometimes in combination with quaternary compounds as softeners [133,163]. Ether carboxylates show improved cleaning properties as suds-controlling agents in formulations with ethoxylated alkylphenol or fatty alcohol, alkyl phosphate esters or alkoxylate phosphate esters, and water-soluble builders [134]. 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

In recent studies, Friberg and co-workers (J, 2) showed that the 21 carbon dicarboxylic acid 5(6)-carboxyl-4-hexyl-2-cyclohexene-1-yl octanoic acid (C21-DA, see Figure 1) exhibited hydrotropic or solubilizing properties in the multicomponent system(s) sodium octanoate (decanoate)/n-octanol/C2i-DA aqueous disodium salt solutions. Hydrotropic action was observed in dilute solutions even at concentrations below the critical micelle concentration (CMC) of the alkanoate. Such action was also observed in concentrates containing pure nonionic and anionic surfactants and C21-DA salt. The function of the hydrotrope was to retard formation of a more ordered structure or mesophase (liquid crystalline phase). 

Observations of large contact angles in emulsions were first reported by Aronson and Princen [105,106]. The authors have studied oil-in-water droplets stabilized by anionic surfactant in the presence of various salts. Similar systems were studied by Poulin [110]. Anionic surfactants such as sulfate, sulfonate, or carboxylate surfactants [106,110] exhibit a good stability and a strong adhesion in the presence... 

The head groups of these surfactant molecules are negatively charged. The most widely used anionic surfactants are those containing carboxylate groups, such as soaps, sulfonate, and sulfate ions Soaps, which are salts of weak carboxylic acids, are formed by the hydrolysis of fats (triglycerides) by sodium hydroxide. Sulfonates, such as sodium docusate and decane sulfonate, have been widel used in pharmaceutical systems. The most popular alkyl sulfate is sodium lauryl sulfate, which is... 

Some carboxylate surfactants, such as long-chain fatty acids or their anionic esters with Coenzyme A, are precipitated in the presence ( fCSmd M + (Constantinides and Steim, 1986). Measurements of CMC in the presence of divalent ions should be avoided since the insoluble surfactant could introduce serious artifacts. Traces of transition-metal ions can catalyze autooxidation of some polyoxyethylene surfactants. In a recent article by Xiao (Xiao, 2006), interactions between anionic surfactant (SDS) micellar solutions and several familiar metal salt solutio b. 

The major subgroups of anionic surfactants include the alkali carboxylates (soaps), sulfates, sulfonates, and to a smaller degree, phosphates. The esterification of alcohol with sulfuric acid yields probably the best-studied surfactant, sodium dodecylsulfate or SDS. SDS, a sulfate ester, is an extremely effective emulsifier because of its high-electrostatic repulsion. Other sulfates are, for example, sulfated esters from fatty acids, sulfated ethers, and sulfated fats and oils. Sulfonates stem from the reaction of sulfonic acid with suitable substrates. Members of the class of sulfonates are, for example, sulfonic acid salts or aliphatic sulfonates. Other anionic surfactants include substances such as carboxylated soaps and esters of phosphoric acid. 

The effect of divalent cations is not amenable to empirical expression, probably because these cations influence the degree of dissociation of the salt, and thus the hydrophilicity of the polar group, in a complex way. It is found that the calcium and magnesium salts of most anionic surfactants are (much) less hydrophilic than their sodium counterparts as a general trend. Sulfonates are less sensitive than sulfates, which are less sensitive than carboxylates [47-49]. 

Soaps also belong to the group of anionic surfactants. These are alkali salts (mainly Na and K) from medium- to long-chain saturated and unsaturated fatty acids (C12-C22). Based on their chemical structure and their electrochemical behaviour, they belong to anionic surfactants of the carboxylate type. The consumption of soaps is 105 000 t/a in Germany, which corresponds to a raw waste-water concentration of around 24 mg/1. 

Anionic surfactants are typically alkali metal salts of long-chain carboxylic or sulfonic acids, for example sodium di-2-ethylhexyl sulfosuccinate (Aerosol OT). 

The free-radical addition of TFE to pentafluoroethyl iodide yields a mixture of perfluoroalkyl iodides with even-numbered fluorinated carbon chains. This is the process used to commercially manufacture the initial raw material for the fluorotelomer -based family of fluorinated substances (Fig. 3) [2, 17]. Telomeri-zation may also be used to make terminal iso- or methyl branched and/or odd number fluorinated carbon perfluoroalkyl iodides as well [2]. The process of TFE telomerization can be manipulated by controlling the process variables, reactant ratios, catalysts, etc. to obtain the desired mixture of perfluoroalkyl iodides, which can be further purified by distillation. While perfluoroalkyl iodides can be directly hydrolyzed to perfluoroalkyl carboxylate salts [29, 30], the addition of ethylene gives a more versatile synthesis intermediate, fluorotelomer iodides. These primary alkyl iodides can be transformed to alcohols, sulfonyl chlorides, olefins, thiols, (meth)acrylates, and from these into many types of fluorinated surfactants [3] (Fig. 3). The fluorotelomer-based fluorinated surfactants range includes noiuonics, anionics, cationics, amphoterics, and polymeric amphophiles. 

In order to experimentally verify linkages between surfactant action and process performance one needs appropriate analytical techniques. A number of books and reviews [73-83] discuss methods for the determination of anionic surfactants. Most are applicable only to the determination of sulfate- and sulfonate-functional surfactants. Difficulties associated with their application to carboxylate-functional surfactants include lack of stoichiometry in the formation of anionic-cationic surfactant pairs, interferences due to inorganic species, and the need to control the solution pH so that the surfactant remains in the salt form. 

Two-dimensional LC to determine anionic surfactants (types of carboxylates, sulfates and sulfonates), cationic surfactants (quaternary ammonium and alkyl pyridinium salts) and amphoteric surfactants (amidobetaines) was proposed by Noguchi et al. (1998). First column (anion exchange column for anionics and cation exchange column for cationic and amphoteric surfactants) separated according to functional group and a second column (octadecylsilica) allowed the separation of alkyl homologues. The method was applied to shampoo. 

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