Surfactant ether sulfates

Shampoos based on lauryl sulfates can range from 6—17% of the active surfactant. However, though they are effective cleansers, the alkyl sulfates tend to be defatting. In an effort to make these shampoos more mild, many shampoos are now based on blends of amphoterics and alkyl sulfates or the less irritating alkyl ether sulfates. 

A.lkylSulfoacetates. These surfactants are prepared by esterification of sulfoacetic acid or by sulfonation of the alkyl chloroester. They are considered to produce good foaming and are less irritating to the eyes than the alkyl and alkyl ether sulfates (10). 

Cosurfactant requirements can be minimized usiag a surfactant having a short-branched hydrophobe or a branched-alkyl substituent on an aromatic group (232,234) and a long ethoxy group chain (234). Blends of surfactants optimized for seawater or reservoir brine salinity include linear alkyl xylene sulfonate—alcohol ether sulfate mixtures (235). 

Anionic surfactants are the most commonly used class of surfactant. Anionic surfactants include sulfates such as sodium alkylsulfate and the homologous ethoxylated versions and sulfonates, eg, sodium alkylglycerol ether sulfonate and sodium cocoyl isethionate. Nonionic surfactants are commonly used at low levels ( 1 2%) to reduce soap scum formation of the product, especially in hard water. These nonionic surfactants are usually ethoxylated fatty materials, such as H0CH2CH20(CH2CH20) R. These are commonly based on triglycerides or fatty alcohols. Amphoteric surfactants, such as cocamidopropyl betaine and cocoamphoacetate, are more recent surfactants in the bar soap area and are typically used at low levels (<2%) as secondary surfactants. These materials can have a dramatic impact on both the lathering and mildness of products (26). 

Modification of the top electrode may also be achieved. This was done by adding a small amount of surfactant, such as an ether phosphate or an ether sulfate, to the spin-coal solution of the luminescent polymer [89[. The lipophobic ether chains segregate at the surface of the (predominantly) hydrocarbon polymer, becoming available for complexation with the aluminum cathode which is deposited on top. Thus, the dipole in the surfactant points away from the electrode and lowers its work function to improve the injection of electrons. 

When ammonium lauryl sulfate is reacted with ethylene oxide, the result is the larger molecule ammonium laureth sulfate. This molecule has the same detergent and surfactant qualities, but it is larger consequently it does not penetrate the skin and hair as easily. The term laureth is actually a contraction of lauryl ether. The full name is ammonium lauryl ether sulfate. 

The most common ingredient in shampoos is also the most common detergent in use in other products a class of surfactants known as straight-chain alkyl benzene sulfonates. Examples are ammonium lauryl sulfate, its sodium relative, and the slightly larger but related molecule ammonium lauryl ether sulfate (sometimes abbreviated as ammonium laureth sulfate). 

Higher molecular primary unbranched or low-branched alcohols are used not only for the synthesis of nonionic but also of anionic surfactants, like fatty alcohol sulfates or ether sulfates. These alcohols are produced by catalytic high-pressure hydrogenation of the methyl esters of fatty acids, obtained by a transesterification reaction of fats or fatty oils with methanol or by different procedures, like hydroformylation or the Alfol process, starting from petroleum chemical raw materials. 

Ethylene oxide is an important intermediate chemical not only for the production of nonionic surfactants like fatty alcohol ethoxylates, alkylphenol ethoxy lates, or propylene oxide/ethylene oxide block copolymers, but also for manufacturing of anionic surfactants like alcohol ether sulfates. 

Table 6 shows a comparison of commercially produced C, 4 LAS samples in a current North American light-duty liquid (LDL) formulation containing more than 20% LAS together with alcohol ether sulfate (AES), amide, and hydrotrope. The highest viscosity is observed with the high 2-phenyl/low DATS sample, whereas the high 2-phenyl/high DATS sample had the lowest viscosity. The DATS provides the dual function of surfactant and hydrotrope. 

FIG. 36 Synergistic mixture of alkane- (paraffin) sulfonates (PS) and fatty alcohol ether sulfates (FAES). Cleaning effect in miniplate test at 50°C, tap water (12° German hardness), 0.075 g of active surfactant mixture per liter. 

As esters of sulfuric acid, the hydrophilic group of alcohol sulfates and alcohol ether sulfates is the sulfate ion, which is linked to the hydrophobic tail through a C-O-S bond. This bond gives the molecule a relative instability as this linkage is prone to hydrolysis in acidic media. This establishes a basic difference from other key anionic surfactants such as alkyl and alkylbenzene-sulfonates, which have a C-S bond, completely stable in all normal conditions of use. The chemical structure of these sulfate molecules partially limits their conditions of use and their application areas but nevertheless they are found undoubtedly in the widest range of application types among anionic surfactants. 

As the concentration is increased, the viscosity of the solution generally increases, although not linearly, and may eventually undergo a sudden decrease. This is due to changes in the internal geometry of the surfactant molecules. At relatively low concentrations the alcohol ether sulfate solution consists of spheri-... 

Alcohol ether sulfate solutions are easily thickened by the addition of electrolytes and other surfactants, particularly alkanolamides, and even highly di-... 

The foam volume and stability of alcohol sulfates is relatively increased in hard water compared to soft water. The amount and quality of foam is dependent on the alkyl length. Sulfates with C12-C,4 alkyl chains produce the richest creamy foam with small bubbles. C8-C10 alcohol sulfates are foam depressants and C16-C18 alcohol sulfates are poor foaming surfactants. Foams produced by alcohol sulfates are also relatively stable in the presence of sebum. Sodium and ammonium alcohol sulfates foam better than triethanolamine alcohol sulfates. Alcohol ether sulfates produce lighter foams than those of alcohol... 

Glasl [149] reported the foaming properties of several alcohol sulfates and alcohol ether sulfates using the perforated disk method as described in the DIN standard 53902. All values were obtained at 0.28 g/L surfactant concentration, both in distilled water and in water of 16°dH hardness at 20, 40, and 60°C. The results are shown in Figs. 15-17. 

Sodium dodecylbenzenesulfonate is undoubtedly the anionic surfactant used in the greatest amount because it is the basic component in almost all laundry and dishwashing detergents in powder and liquid forms. However, alcohol and alcohol ether sulfates are the more versatile anionic surfactants because their properties vary, with the alkyl chain, with the number of moles of ethylene oxide added to the base alcohol and with the cation. Consequently, alcohol and alcohol ether sulfates are used in almost all scientific, consumer, and industrial applications. 

The applications of alcohol sulfates in consumer products depend on the alkyl chain and in some cases on the cation. Alcohol sulfates with alkyl chains 8 C1() are seldom used in consumer products except occasionally as hydrotropes in liquid detergent formulations. However, alcohol sulfates in the range C10-C18 are used in many commonly used formulations although other surfactants are generally added to enhance their properties. In some of these applications, particularly in shampoos, they compete with alcohol ether sulfates of the same alkyl chain distribution. The pattern of use of alcohol sulfates or alcohol ether sulfates in formulations varies with consumer personal care and laundry washing preferences in different cultural areas of the world. 

Alcohol ether sulfates are used in mixture with sulfonates, either alkyl-benzenesulfonates or a-olefinsulfonates, and other surfactants, such as fatty alkanolamides, in manual liquid dishwashing detergents and light-duty detergents. These combinations show the excellent emulsifying and foaming properties required in dishwashing. 

It is difficult to find an industrial sector that does not use alcohol sulfates or alcohol ether sulfates. These surfactants are rendered so versatile in their chemical structure through varying their alkyl chain distribution, the number of moles of ethylene oxide, or the cation that it is possible to find the adequate sulfate achieving the highest mark in nearly every surfactant property. This and the relative low cost are the two main reasons for their vast industrial use. 

Alcohol ether sulfates with different number of moles of ethylene oxide are also used in emulsion polymerization and in the paint industry as dispersing agents. A particular use of alcohol ether sulfates is as foamers in low- and medium pressure drilling for water, oil, and gas. The foam produced by the surfactant reduces the pressure of the water column as water is replaced by air. 

Solutions with low content of alcohol and alcohol ether sulfates cannot be analyzed by the two-phase method and specialized procedures have been developed. ISO method 7875/1 [267] is the standard method for analyzing sulfates and other anionic surfactants at very low concentrations, such as in waste-waters. The absorbance of the chloroform layer containing the surfactant-dye complex is spectrometrically measured at 650 nm and quantified using a calibration curve. Different improvements of this method have been developed [268,269]. 

Thin-layer chromatography (TLC) is used both for characterization of alcohol sulfates and alcohol ether sulfates and for their analysis in mixtures. This technique, combined with the use of scanning densitometers, is a quantitative analytical method. TLC is preferred to HPLC in this case as anionic surfactants do not contain strong chromophores and the refractive index detector is of low sensitivity and not suitable for gradient elution. A recent development in HPLC detector technology, the evaporative light-scattering detector, will probably overcome these sensitivity problems. 

Two-dimensional TLC on silica gel G has been used to identify alcohol ether sulfates in liquid laundry detergents. The spots of the chromatograms were examined by UV, IR, and NMR spectroscopy and the spectra compared with those of standard surfactants [283]. 

Alcohol sulfates and alcohol ether sulfates separated by HPLC on a styrene-divinylbenzene copolymer column with 4 1 (v/v) methanol and 0.05 M ammonium acetate aqueous solution as the mobile phase were analyzed by simultaneous inductively coupled argon plasma vacuum emission spectroscopy (IPC), monitoring the 180.7-nm sulfur line as a sulfur-specific detector [294]. This method was applied to the analysis of these surfactants in untreated wastewaters. 

Subacute and chronic toxicity of alcohol and alcohol ether sulfates has been extensively tested in several animals and sometimes humans. The duration of the tests was in some cases as long as 2 years. When administered below the toxic amount no specific damages were observed in any of the species tested [333]. No severe side effects were observed in the study by Swisher, carried out with volunteers who ingested considerable amounts of anionic and nonionic surfactants over long periods [348]. Similarly, the effects produced by the intake of daily doses of 1 g of alcohol sulfate per person over 8 weeks [349],... 

Alcohol and alcohol ether sulfates have also been studied to determine their toxicity by percutaneous absorption in rats and guinea pigs [354-356]. Alcohol ether sulfates penetrate in the order of 1 ng/cm2/day and alcohol sulfates are less penetrant by a factor of 10. The surfactant absorbed was metabolized. Since it is known that human skin is less permeable than animal skin, only very small amounts of alcohol or alcohol ether sulfates can be absorbed even in the case of complete body exposure. 

Contact of surfactants with the skin and mucus membranes occurs either accidentally or as a consequence of normal use. Examples of this normal and everyday use are cleaning formulations, shampoos, foam baths, and toothpastes. Again this contact is seldom made with individual surfactants, in this case alcohol sulfates and alcohol ether sulfates, but through formulated products. It is known that surfactants present significant interactions, so that mixed systems are generally less aggressive than their individual components. However, the effect of pure surfactants merits attention, particularly sodium dodecyl sulfate, which is commonly used as a reference for many studies because of its high purity and availability. 

The biodegradation of surfactants is studied by means of many different tests and sometimes under different conditions. Some factors with significant influence on the results are uncontrollable factors and in other cases are not controllable. This causes a dispersion in biodegradability data that makes comparisons difficult. For this reason only general conclusions can be obtained from the data available. Swisher carried out an exhaustive collection of available data in his complete study on surfactant biodegradation [385]. Some basic and significant features of biodegradation of alcohol and alcohol ether sulfates are discussed below. 

Alcohol and alcohol ether sulfates are commonly considered as extremely rapid in primary biodegradation. The ester linkage in the molecule of these substances, prone to chemical hydrolysis in acid media, was considered the main reason for the rapid degradation. The hydrolysis of linear primary alcohol sulfates by bacterial enzymes is very easy and has been demonstrated in vitro. Since the direct consequence of this hydrolysis is the loss of surfactant properties, the primary biodegradation, determined by the methylene blue active substance analysis (MBAS), appears to be very rapid. However, the biodegradation of alcohol sulfates cannot be explained by this theory alone as it was proven by Hammerton in 1955 that other alcohol sulfates were highly resistant [386,387]. 

Schoberl et al. reported the data compiled in Germany for the most important industrial surfactants [383]. Natural and oxoalcohol sulfates have primary biodegradation results of 99% and 98-99%, respectively, by the confirmatory test. Natural and oxoalcohol ether sulfates biodegrade 98-99% and 96%, respectively, in the confirmatory test. Reported values of total biodegradation are shown in Table 35A and Table 35B. 

Until the 1950s ether carboxylates were almost in very limited amounts in the textile industry. It was only in 1957 [9] that the first ethercarobxylates were mentioned, in combination with other surfactants such as alkyl sulfates and ether sulfates, for use in shampoos. In spite of the special properties of ether carboxylates, their use was low in the industry as well as in cosmetics at that time. This was also due to the fact that at that time properties such as toxicity, biodegradability, and mildness to the skin did not have the high priority they do now. 

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