Sulphonated fatty acids

This is an unusual and interesting class of surfactants that, although limited to some specialist applications, has properties not found in other surfactant types. 

Chemistry and general properties. The product is prepared by reacting a fatty acid, typically oleic acid (a 08 1 acid), with oleum, or preferably sulphur trioxide. If a saturated fatty acid is used, the product is an a-sulphofatty acid, R(S03H)C00H and the reaction mechanism is thought to be similar to that previously suggested for the sulphonation of methyl esters. With the use of an unsaturated acid, such as oleic, the picture becomes more complex. The reaction chemistry is not fully understood, but the product is a mixture of y-hydroxy sulpho fatty acid and o -sulphonated oleic acid. 

In the former product, the SO3 has added across the unsaturation in the carbon chain, resulting in a saturated alkyl chain, with an internal hydroxyl and sulphonate and a terminal carboxylate. This mechanism probably proceeds via a sultone intermediate, with the final 

The properties of the y -sulphonated product appear to be markedly different, although they have not been studied in as much detail. Sulphonated oleic acid, in which the y-sulphonate is the major component, is fully miscible with water at room temperature as is the di-potassium salt. 

The potassium salt of sulphonated oleic acid is one of very few commercial examples of fatty acid sulphonates and is sold as a 50% solid low viscosity ( 200 cPs) solution. 

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SMEs can also be dried and their powder properties are better than LAS, making SME an attractive ingredient in laundry powders. Products containing high sulphonated fatty acid as the disodium salt also have good solid forms and are used in personal care applications as ingredients in bar products. 

Applications. At present there are very few known applications, although the surfactants have significant potential due to their unique properties. Sulphonated fatty acids are used in some hard-surface cleaning formulations where their low foam is a benefit and in emulsion polymerisation, where they perform similarly to LAS but with greatly reduced tendency to foam. Future applications for these products may include machine dishwash, extended use in detergent products and industrial applications such as pigment dispersants. For these to be realised, further process development will be required to give a more consistent and better defined product. 

Extreme pressure additive in MCCPs, LCCPs, alkyl phosphate ethers, sulphonated fatty acid... 

Thus, if a mole ratio of about 1.2 1 of SO3 to ester is used, the initial reaction gives about 50% conversion of starting material, the products being intermediates I and II. On ageing, these intermediates release SO3, which reacts with the remaining ester, and the final product is a mixture of FAMES acid (FAMES = Fatty Acid Methyl Ester Sulphonate) and SFAS acid (SFAS = Sulphonated Fatty Acid Sodium salt, RCH-COONa). 

Alpha sulphonated fatty acid methylester sulphonic acid neutralisation and bleaching... 

Acid. Conversion to carboxylic acid and alcohol takes place. The sulphonate group may be on either of these. Thus acyl isethionates yield a fatty acid and isethionate ions, mono- and di-alkyl sulphosuccinates yield fatty alcohols and sulphosuccinic acid, and a-sulphonated fatty esters yield the a-sulphonated fatty acid and a low-molecular-weight alcohol. 

In all cases the first action is to determine total activity by titration with benzethonium chloride (BEC), and this is to be taken as mandatory in each of the following cases. After acid hydrolysis a second BEC titration to determine the sulphonated hydrocarbon is probably all that is required in the majority of cases, but the following are alternatives. In the case of a-sulphonated fatty esters, the second BEC titration measures the total a-sulphonated fatty acid plus the sulphonated hydrocarbon (see below). 

With a-sulphonated fatty ester. Acid hydrolysis (section 5.11.4). Then BEC titration in alkaline solution. The increase over the result in acid solution measures the sum of a-sulphonated fatty acid already present and the hydrolysed a-sulphonated fatty ester. 

Most of the inhibitors in use are organic nitrogen compounds and these have been classified by Bregman as (a) aliphatic fatty acid derivatives, b) imidazolines, (c) quaternaries, (d) rosin derivatives (complex amine mixtures based on abietic acid) all of these will tend to have long-chain hydrocarbons, e.g. CigH, as part of the structure, (e) petroleum sulphonic acid salts of long-chain diamines (preferred to the diamines), (/) other salts of diamines and (g) fatty amides of aliphatic diamines. Actual compounds in use in classes (a) to d) include oleic and naphthenic acid salts of n-tallowpropylenediamine diamines RNH(CH2) NH2 in which R is a carbon chain of 8-22 atoms and x = 2-10 and reaction products of diamines with acids from the partial oxidation of liquid hydrocarbons. Attention has also been drawn to polyethoxylated compounds in which the water solubility can be controlled by the amount of ethylene oxide added to the molecule. 

The apatite barite bulk flotation was accomplished with a mixture of tall oil fatty acid and sulphonate (Aero 827) at an alkaline pH. Sodium silicate and caustic tapioca starch were used for pyrochlore depression during the bulk apatite barite flotation stage. 

Floatability of bastnaesite found in barite-fluorite ores is extremely poor using either fatty acid flotation or sodium oleate. Research work conducted on an ore from Central Asia showed that the floatability of bastnaesite improved significantly after barite preflotation [5]. The flotation of bastnaesite from a carbonatite ore improved with the use of oleic acid modified with phosphate ester. The flotation of bastnaesite from deposits ofpegmatitic origin can be successfully accomplished with several types of collectors, including tall oil modified with secondary amine, and tall oil modified with petroleum sulphonate-encompassing group. 

During fluorite flotation, Quebracho and lignin sulphonate mixture (MESB) was used with collector composed of a mixture of oleic acid and phosphoric ester. Collectors used for bastnaesite flotation included tall oil fatty acid modified with three ethylene tetra... 

Among the precipitants employed were tannic acid, tartar emetic, rosin soaps, fatty acid (stearic, oleic) soaps, sulphonated oils (Turkey red oil), earth lakes (mixed natural silicates), phosphates, casein and arsenious acid. The fastness properties of these pigments... 

N-Benzylamides are recommended when the corresponding acid is liquid and/or water-soluble so that it cannot itself serve as a derivative. The benzyl-amides derived from the simple fatty acids or their esters are not altogether satisfactory since they are often low melting those derived from most hydroxy acids and from polybasic acids or their esters are formed in good yield and are easily purified. The esters of aromatic acids yield satisfactory derivatives but the method must compete with the equally simple process of hydrolysis and precipitation of the free acid, an obvious derivative when the acid is a solid. The procedure fails with esters of keto acids, sulphonic acids and inorganic acids and some halogenated aliphatic esters. 

The effects of a range of sodium n-alkyl sulphates and sodium n-alkyl sulphonates upon the mechanical stability of natural rubber latex are summarised in Figures 4 and 5 respectively. As in the case of added potassium fatty-acid soaps, small additions of... 

Pickling and plating bath Phosphate esters Fatty acid sulphonates Alkanolamides Complex amphoterics Wetting agents... 

Raw materials. It is possible to use any fatty acid as a feed material for sulphonation but economic considerations dictate that oleochemical material be preferred. Fatty acids are readily obtained from vegetable and animal oils and fats which are fatty acid triglycerides. These are transesterified to generate glycerol and three moles of a fatty acid ester, normally a methyl ester. The methyl ester can be distilled to give a specific cut and the fatty acid finally isolated by hydrolysis or hydrogenation of the ester. It is common to use animal fats (tallow) in which case the dominant C chains are 16 and 18. 

Composition vs. performance. With this product group, little work has been done in this area. As already seen, the a-sulpho fatty acids show poor solubility, even at higher temperatures and they do not foam like a usual anionic surfactant. It is well known that many sulphonates do not foam well in the presence of soaps and it may be that, since these surfactants contain both the sulphonate and soap function, they effectively have internal foam control. 

Chemistry and general properties. Sodium isethionate is 2-hydroxyethane sulphonate, sodium salt and will form an ester with a fatty acid halide, normally an acyl chloride (Figure 4.26). 

Prevents oxidation of sulphonated oils and fatty acids. 

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