Fatty acid ester sulfonates

Sodium fatty acid ester sulfonates are known to be highly attractive as surfactants. These have good wetting abiHty and exceUent calcium ion stabiHty as weU as high detergency without phosphates, and are used in powders or Hquids. They can also be used in the textile industry, emulsion polymerization, cosmetics, and metal surface fields. Moreover, they are attractive because they are produced from renewable natural resources and their biodegradabiHty is almost as good as alkyl sulfates (134—137). 

Fatty JicidFster Sulfonates. Fatty acid ester sulfonates (FAES) are generally produced from methyl esters, ie, methyl ester sulfonate (MES) and prepared via sulfonation, followed by bleaching and neutralization, in a relatively difficult and complex process ... 

Fatty acid esters, 9 142 Fatty acid ester sulfonates, 23 528-529 Fatty acid ethoxylates, 24 149-150 Fatty acid methyl esters (FAME), 12 429 13 26t... 

Sulfonates include alkylbenzenesufonates (ABS), the most widely used of the non-soap surfactants short-chain alkylarenesuifonates lig-nosulfoliates napllialenesulfoliates cz-olefinsulfonales petroleum sulfonates sulfonates with ester, amide, and ether linkages and fatty acid ester sulfonates. 

Nissan Sunbase. [Nipptm Oils Fats] Sodium fatty acid ester sulfonate lime soap dispersant nonphosphate detergent base builds for honsehtdd detergents omilsifier, dispersmit... 

To overcome these difficulties, drilling fluids are treated with a variety of mud lubricants available from various suppHers. They are mostly general-purpose, low toxicity, nonfluorescent types that are blends of several anionic or nonionic surfactants and products such as glycols and glycerols, fatty acid esters, synthetic hydrocarbons, and vegetable oil derivatives. Extreme pressure lubricants containing sulfurized or sulfonated derivatives of natural fatty acid products or petroleum-base hydrocarbons can be quite toxic to marine life and are rarely used for environmental reasons. Diesel and mineral oils were once used as lubricants at levels of 3 to 10 vol % but this practice has been curtailed significantly for environmental reasons. 

Results described in the literature have resulted in several patents, such as one for the improvement of the transport of viscous crude oil by microemulsions based on ether carboxylates [195], or combination with ether sulfate and nonionics [196], or several anionics, amphoterics, and nonionics [197] increased oil recovery with ether carboxylates and ethersulfonates [198] increased inversion temperature of the emulsion above the reservoir temperature by ether carboxylates [199], or systems based on ether carboxylate and sulfonate [200] or polyglucosylsorbitol fatty acid ester [201] and eventually cosolvents which are not susceptible for temperature changes. Ether carboxylates also show an improvement when used in a C02 drive process [202] or at recovery by steam flooding [203]. 

From both economic and ecological points of view, substances derived from esters of monocarboxylic acids sulfonated in the a position form an interesting class of surfactants [1]. The general formula of these a-sulfomonocarboxylic esters, also called a-sulfo fatty acid esters or, in short, a-ester sulfonates, is Rj-CH(S03Me)-C00-R2 (with Rj and R2 = alkyl groups, Me = alkali metal). 

Ester sulfonates will become more and more interesting in the future because the raw materials for their preparation are fatty acid esters which can be prepared from oils and fats, and thus from renewable resources. They can be used as possible substitutes for surfactants based on petrochemicals. 

Also the a-ester sulfonates are less important today. In the Federal Republic of Germany, for example, the total production of surfactants was about 700,000 t/a in 1993. For a more detailed analysis of different types of surfactants, use must be made of data collected before the unification of Germany. In 1988 the consumption of surfactants in detergents was about 227,500 t/a, the consumption of anionic surfactants was about 116,000 t/a and less than 1000 t/a of a-sulfo fatty acid esters [5] (the values refer to German Detergent Law). 

Compared with the fatty alcohol sulfates, which are also oleochemically produced anionic surfactants, the ester sulfonates have the advantage that their raw materials are on a low and therefore cost-effective level of fat refinement. The ester sulfonates are produced directly from the fatty acid esters by sulfona-tion, whereas the fatty alcohols, which are the source materials of the fatty alcohol sulfates, have to be formed by the catalytic high-pressure hydrogenation of fatty acids esters [9]. The fatty acid esters are obtained directly from the fats and oils by transesterification of the triglycerides with alcohols [10]. 

In spite of all their merits, ester sulfonates have not been used to a great extent as yet [12]. The reason is that a practicable process for producing a-sulfo fatty acid esters with good qualities is difficult because of the formation of byproducts with worse properties (e.g., the disalts of the a-sulfo fatty acids). 

The a-sulfo fatty acid esters are obtained by a-sulfonation of the fatty acid esters, and in basic mediums they form the corresponding salts. 

For technical applications, the production of ester sulfonates from the (purified) sulfo fatty acids involves too much effort, especially because the relevant fatty acid esters can be produced directly from the triglycerides of fats and oils by transesterification. The only possible way to produce ester sulfonates is the sulfonation of fatty acid esters. 

Smith and Stirton applied this mechanism to the sulfonation of long-chain fatty acid esters [31]. Instead of forming the well-defined mixed anhydride during the reaction of fatty acids with S03, the acid esters form a complex less defined in structure and composition. In this complex the a-hydrogen is activated, so that a second molecule of S03 can react. These two addition steps are fast. The final step is again a slow rearrangement of the intermediate with a loss of one molecule of S03. 

Nagayama et al. [36] studied a-sulfonation using nuclear magnetic resonance (NMR). They reported the presence of two intermediates. The first intermediate is the adduct of S03 to the carbonyl oxygen formed at low temperatures. In contrast to the mechanism of Stein et al., they did not propose a rearrangement of this intermediate but a second addition of S03 to the activated a-hydrogen to give the second intermediate. The reaction of the intermediate with sodium hydroxide can lead to the disodium salt if the neutralization is immediate or to the sodium a-sulfo fatty acid ester if the neutralization is delayed. 

In the first step an S03 molecule is inserted into the ester binding and a mixed anhydride of the sulfuric acid (I) is formed. The anhydride is in a very fast equilibrium with its cyclic enol form (II), whose double bonding is attacked by a second molecule of sulfur trioxide in a fast electrophilic addition (III and IV). In the second slower step, the a-sulfonated anhydride is rearranged into the ester sulfonate and releases one molecule of S03, which in turn sulfonates a new molecule of the fatty acid ester. The real sulfonation agent of the acid ester is not the sulfur trioxide but the initially formed sulfonated anhydride. In their detailed analysis of the different steps and intermediates of the sulfonation reaction, Schmid et al. showed that the mechanism presented by Smith and Stirton [31] is the correct one. 

Neutralization leads to the salt of the a-sulfo fatty acid ester, but only if the neutralization step is delayed. If the neutralization is immediate the a-sulfonated anhydride forms a disalt of the a-sulfo fatty acid as a byproduct [38]. The production of the disalt is also effected by the ratio between S03 and the ester. A high surplus of S03 would shorten the reaction time, but the amount of disalt in the end product would increase. For 90°C and 30 min an optimal S03/es-ter ratio is 1.2 1 [37]. 

Most of the technically produced a-sulfo fatty esters are prepared from unbranched saturated fatty acid esters that are derived from 8 22 carboxylic acids and Cj-C3 alcohols. In particular the C12 (lauric), C14 (myristic), C16 (palmitic), and C18 (stearic) acids are interesting because the ester sulfonates... 

In the literature a number of different techniques for the preparation of a-sulfo fatty acid esters can be found. There is equipment for small-scale and commercial scale sulfonation. Stirton et al. added liquid sulfur trioxide dropwise to the fatty acids dispersed or dissolved in chloroform, carbon tetrachloride, or tetrachoroethylene [44]. The molar ratio of S03/fatty acid was 1.5-1.7 and the reaction temperature was increased to 65 °C in the Final stage of sulfonation. The yield was 75-85% of the dark colored a-sulfonated acid. The esterification of the acid was carried out with either the a-sulfonic acid alone, in which case the free sulfonic acid served as its own catalyst, or with the monosodium salt and a mineral catalyst. 

The thin film reactor for the continuous sulfonation of fatty acid esters was introduced by the Witco Technical Center in Oakland, New Jersey [46]. Hurl-bert et al. designed this type of reactor for small-scale sulfonation with S03 [47,48]. The reaction partners could be filled into the reactor through three inlets. One was for the carrier gas (air or nitrogen), one for the liquefied ester that is picked up from the carrier gas, and the last one was for the vaporized S03. The ester and the S03 reacted in a turbulent liquid film. Details of this reactor are given by Kapur et al. [46]. 

Even if the fatty acid esters have been sulfonated under optimal conditions the ester sulfonates are dark-colored [12,33] so the sulfonated product has to be bleached. The second pretreatment is the neutralization of the acid product to obtain the salt of the a-sulfo fatty acid ester. Different techniques have been published in the literature. Kapur et al. suggested bleaching with 3-4 wt % NaOCl (15 wt % solution) after neutralization with a 30% aqueous solution of sodium hydroxide. This technique is for small-scale sulfonation [46]. 

Sodium a-sulfonated fatty acid esters of long-chain alcohols have a structural effect on the Krafft point different from that of amphiphiles with short alkyl chains [60]. In a series of homologs with the same total carbon number the Krafft points are highest when the hydrophilic alkyl chain lengths in the a-sulfonated fatty acid and the alcohol are fairly long and equal. In this case the packing of the molecules becomes close and tight. 

For long-chain alcohol esters it is interesting to see that the interfacial tension between a 0.01 wt % aqueous solution and octane or xylene has a minimum for ester sulfonates with a total 22 carbon atoms in the fatty acid chain and the ester chain [60]. The balance in length between the two chains has only a poor effect. Thus, a-sulfonated fatty acid esters with a total number of 22-26 carbon atoms in the molecule have excellent interfacial activities. To attain the same magnitude in the interfacial tension between linear alkylbenzenesulfonate (LAS) solution and octane, the required concentration of LAS is 0.1 wt %. This is 10 times the concentration needed for a-sulfonated fatty acid esters [60]. 

In mixtures of ester sulfonates and disalts the remission decreases as the content of disalts increases (Fig. 10). But small amounts of disalts do not have a strong negative effect on the detergency of the ct-sulfo fatty acid esters [581. 

When a-sulfo fatty acid esters are used as the major active component in detergents they can cause problems because of their foaming properties. In European horizontal drum-type automatic washers they produce too much foam, and in the rinse cycle of the American and Japanese pulsator-type washers the foam cannot be completely rinsed out [38]. The problem of inefficient rinsing can be solved by the addition of soap [63] or sulfonated unsaturated fatty acid esters [64]. For European applications special foam inhibitors are needed. 

A special application of a-sulfo fatty acid esters is for highly concentrated hard surface cleaners which are used after dilution in a pail of water. Normally hydrotropes are needed to increase the solubility of the surfactants in water and assure clear, homogeneous, and storage-stable products. If the LAS, which are typical surfactants in hard surface cleaners, are replaced by ester sulfonates the hydrotrope can be deleted from the formula [62]. 

A great number of detergent compositions using a-sulfo fatty acid esters are given in the patent literature. The a-ester sulfonates are major or minor components, besides other surfactants and builders [68-76]. Some examples of laundry and dishwashing detergents are given below. 

Generally speaking, up to now the importance of a-sulfo fatty acid esters in cosmetic products has been low [1 p. 367], In the future they may become more interesting because of their mildness. a-Sulfomethyl laurate and most other ester sulfonates are mild to the skin also, they are not human skin sensitizers or primary skin irritants. Tests have shown that a-sulfomethyl laurate is mild enough to be in bath products, such as bubble bath [62]. Three patents for different applications are given to show how ester sulfonates can be used in cosmetics. 

Amine salts of a-sulfonated fatty acids and esters are also used as antistatic agents. Mixtures of alkyl a-sulfo fatty acid ester diethanolamine salts and hexa-decyl stearate or butyl stearate are coated onto nylon yarn after fiber formation and before stretching [97]. Polypropylene can be made antistatic with an amine salt of a-sulfolauric acid [C10H21CH(SO3Na)COO +NH(CH2CH(OH) CH3)3] [98]. 

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