Fatty ester a-sulphonates

Fatty ester a-sulphonates normally contain all of the following species. It is assumed here that the sample is the sodium salt, but the sulphonic acid 

Soap (or fatty acid) Unsulphonated fatty ester Low-MW sodium alkyl sulphate (R = methyl to butyl) 

The unsulphonated ester and the fatty acid can be extracted with petroleum ether. The low-molecular-weight alkyl sulphate is alkali-hydrolysable, which affords a method for its determination if required. 

When the sulphonated ester is alkali-hydrolysed, not only does the ester group hydrolyse, as expected, but the sulphonate group is slowly removed as well. Saponification is therefore not a useful way of determining the main active. Acid hydrolysis destroys the ester group but has no effect on the sulphonate group. 

There are several approaches to the complete analysis of raw materials. The following range of methods gives the analyst a degree of choice. There are similar schemes based on the same principles, e.g. that of Battaglini et al. [24]. The analysis of formulated products probably calls for only the determination of the active and the chief impurity, i.e. the sulphonated carboxylate salt. 

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Acyl isethionates Fatty ester a-sulphonates (R = CH3-toC4H9-)... 

The sulphonate group itself is generally very resistant to hydrolysis, but in the case of fatty ester a-sulphonates the sulphonate group is removed by several hours boiling with 1 M alkali. Acid hydrolysis, however, has no effect. 

Alkali. The results are similar, but fatty acids appear as soap. Alkaline hydrolysis is generally to be preferred for esters, but fatty ester a-sulphonates undergo rapid hydrolysis of the ester group accompanied by slower hydrolysis of the sulphonate group, so this is not a practical method for their determination. 

Reproducibility is excellent for most surfactants. The method is particularly good for betaines but is not recommended for fatty ester a-sulphonates, a-olefin sulphonates, soaps or sarcosinates. It is most useful for raw materials and products containing only low concentrations of non-surfactant electrolytes. Users should evaluate for themselves its usefulness for other product types. 

Construction of electrodes and experimental procedure were fully described in section 3.6. It is not recommended for fatty ester a-sulphonates or carboxylates. Whilst a-olefin sulphonates give good curves, it is uncertain which species is titrated. The method is satisfactory for many formulated products, but should be evaluated for individual applications. It is the method of choice when it is applicable. It is most conveniently done by autotitrator. 

Distilled fatty methyl esters with low iodine values are used as the starting raw material for the production of SME. The fatty methyl ester is first reacted with sulfur trioxide at 80-90°C in a falling-film reactor. The dark product obtained from this process is bleached using hydrogen peroxide. After bleaching, the lighter color product is neutralized with alkali to produce an a-sulphonated methyl ester. 

In the first step, an SO3 molecule is implanted in the ester bond to form a mixed anhydride that exists in a very fast equilibrium with its enolic form. Then fast electrophilic addition of a second SO3 molecule occurs to the enolic double bond, and the a-sulphonated anhydride is formed. In the second (slower) step, the intermediate reacts with other fatty acid ester molecules by releasing SO3 that serve in new reaction cycles. The sulphonation goes with air-diluted SO3 at 80-90 C followed by ca. 30 min ageing at 90-95 C. The neutralisation gives rise to sodium salt of the a-sulphocarboxylic acid ester and disodium salt of the a-sulpho-carboxylic acid as a by-product. Before neutralisation, reesterification of the semifinished item has been proposed in consequence of the bad detergency of a-sulphocarboxylates. 

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. 

Battaglini et al. [13] recommended phenol red in alkaline solution for titration of a-sulphonated fatty esters, taking the first appearance of a... 

All sulphate and sulphonate anionics except hydrocarbon sulphonates can be acid-hydrolysed. In every case but one, namely a-sulphonated fatty esters, the hydrolysis destroys their surface activity and renders them incapable of titration with benzethonium chloride. In that exceptional case, the titration per molecule is doubled by the hydrolysis. All esters are decomposed by alkaline hydrolysis or saponification, but in the case of a-sulphonated fatty esters this is not a useful measurement because of the slow hydrolysis of the sulphonate group. Also, alkanolamides, particularly dialkanolamides, are hydrolysed slowly by the normal saponification process, and although this is not a useful method of analysis for them, the possibility of generating measurable amounts of soap and alkanolamine cannot be ignored when alkali-hydrolysing anionic esters. 

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 any ester except a-sulphonated fatty ester. Either acid or alkaline hydrolysis. Then any of the following. 

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. 

Any sulphate with a-sulphonated fatty ester. BEC titration in alkaline solution after acid hydrolysis gives twice the a-sulphonated ester (approximately—see above) plus any sulphonated hydrocarbon, less the sulphate. Determine the sulphate separately by measuring any one of its decomposition products. 

The results then give total active (yl), other ester or amide (B) and twice the a-sulphonated fatty ester plus any sulphonated hydrocarbon (C). (C — A- -B) then gives (twice) the a-sulphonated ester, and any sulphon-ate hydrocarbon is found by difference. 

BEC titration in alkaline solution gives the sulphonated hydrocarbon plus twice the a-sulphonated fatty ester plus soap from the isethionate and acyl methyltaurate. 

A detailed classification of the chemical compounds usually employed was given by (Dubief et al., 2005). The most important of these are organic acids (carboxylic acids and aromatic sulphonic acids), fatty compounds and their derivatives (fatty acids, fatty alcohols, natural triglycerides, natural waxes, fatty esters, oxyethylenated and oxypropy-lenated waxes, partially sulphated fatty alcohols, lanolin and its derivatives, ceramides), vitamins (A, B and E) (see Section 8.6), protein derivatives (extracts or hydrolysates of keratin, collagen and vegetable proteins), silicones (dimethicone and others), cationic surfactants, cationic polymers, amphoteric and betainic polymers. 

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... 

Most recently, development testwork was performed on a large perovskite deposit (Powderhom) located in the USA. An effective beneficiation process was developed, where a concentrate assaying >50% Ti02 was achieved in the pilot plant confirmation tests [7]. During this development testwork, a number of different collectors were examined at different pH values. Figure 25.5 shows the effect of the different collectors on perovsikte flotation. The most effective collector was phosphoric acid ester modified with either fatty alcohol sulphate or petroleum sulphonate. 

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. 

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. 

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. 

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). 

Another class of sulphonates is the a-olefin sulphonates which are prepared by reacting linear a-olefin with sulphur trioxide, typically yielding a mixture of alkene sulphonates (60-70%), 3- and 4-hydroxyalkane sulphonates ( 30%), and some disulphonates and other species. The two main a-olefin fractions used as starting material are C 2 ie Fatty acid and ester sulphonates are produced... 

Sulphonated natural oils, sulphonated oleic acid esters and a-ester sulphonates were investigated as polymerization emulsifiers and have been successfully used as special emulsifiers for establishing certain product properties [49]. Fatty alcohol sulphates have been used as emulsifiers since the very begirming of emulsimi polymerization, and are distinguished by particularly good polymerizatiOTi behaviour and by formation of... 

The sulphonates derived from fatty acid alkyl esters (mainly, as sodium salts of a-sulphomonocarboxylic esters or, in other words, methyl ester sulphonates) become more and more attractive in view of their renewable raw material sources, such as triglycerides of animal and vegetable origin. Fatty acid alkyl esters are produced via a direct transesterification of triglycerides with alcohol, typically methanol, or via direct esterification of fatty acids. The same thin-film sulphonation techniques (see Table 1.5) with gaseous SO3 are used today to manufacture these surfactants [62, 70]. The two-step sulphonation can be represented by the sequential reactions [70, 71] shown in Fig. 1.4. 

Water content is adjusted to the total surfactant concentration of 30-42 % wt. The residual sulphite in the product may be oxidised to sulphate. The sulphonation proceeds also well when using partially hydrated crystalline sodium sulphite in a jacketed shear-stress reactor. This process modification is especially appropriate for manufacturing concentrated sulphosuccinate monoesters as flakes or vermicelli (often with plasticisers and fillers added in situ) suitable in mild synthetic soap bars [78]. The Cn-ig alcohols (I), ethoxylated (x2-4 mole EO) alcohols (II), and fatty monoethanolamides (III) esters of sulphosuccinic acid, mainly as sodium and alkanolamine salts, are of most practical importance as very mild high-foaming surfactants useful for personal care products and in wool, fur, and leather treatment. Very mild disodium PEG-5 laurylcitrate sulphosuccinate (in combination with sodium lauryl ethersulphate) serve for cosmetics produced by Witco as "Rewopol SB CS 50". 

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