Soap formation

It has been found that red lead, litharge and certain grades of metallic lead powder render water alkaline and inhibitive this observation has been confirmed by Pryor . The effect is probably due to a lead compound, e.g. lead hydroxide, in solution. Since, however, atmospheric carbon dioxide converts these lead compounds into insoluble basic lead carbonate, thereby removing the inhibitive materials from solution, these pigments may have only limited inhibitive properties in the absence of soap formation. 

The whole range of carboxylic acids and alcohols can be reacted to form esters. They are found in a large number of natural and synthetic scents and perfumes because of their pleasant odor. Many are used as solvents for paints and resins. Esters are converted back into the original acids and alcohols hy reaction with strong bases in water in a process called saponification (soap formation). 

However, Patton and Carey (42) have suggested that calcium soap formation is a part of usual lipid digestion. Other research indicates that the availability of calcium from calcium soaps infused into rat intestines increases as fatty acid chain length decreases ans as degree of polyunsaturatedness increases (58). 

Esterification. The esterification reaction (Figure 3) involves the reaction of a FFA with an alcohol (usually a low molecular weight alcohol, such as MeOH, EtOH, PrOH, and ButOH) to produce an alkyl ester (biodiesel) and water. Either base or acid catalysts can be used for the reaction. However, base catalysts can only be used at high temperatures (or catalyst deactivation takes place by soap formation). More commonly, acid catalysts such as sulfuric acid are employed to carry out the esterification reaction under mild conditions. 

One association of the above type—viz., acid-soap formation between a fatty acid and its neutral salt or soap—was postulated a century and a half ago by Chevreul (2). However, this concept was not generally accepted until much later, when studies of such workers as McBain (15, 16, 17), Ekwall (6), Malkin (18), Piper (19), and Levi (13) provided convincing evidence of its correctness. The most recently published data on sodium acid-soaps are those of Ryer (20) who, for the stearate system,... 

Verhagen, J.. Vliegenthart, J.F.G.. and Boldingh, J. 1978. Micelle and acid-soap formation of li-noleic acid and 13-L-hydroperoxylinoleic acid being substrates of lipoxygenase-1. Chem. Phys. Lipids 22 255-259. 

Optimal amount of base catalyst is 0.5 to 1.5% w/w. Methoxides are more active than alkali hydroxides. More catalyst than needed favors soap formation and makes phase separation difficult. 

Water may be substituted for the alcohols in the production of CLA by alkali isomerization of soaps (116, 117). When water is used in this reaction, it is necessary to perform the reaction in a pressure vessel, whether in a batch (116) or continuous mode of operation (117). The process for synthesis of CLA from soaps dissolved in water stiU requires a complex series of reaction steps. Bradley and Richardson (118) were able to produce CLA directly from TAGs by mixing sodium hydroxide, water, and oil in a pressure vessel. Their method eliminated the need to synthesize fatty acids followed by soap formation prior to the isomerization reaction. However, the authors reported that they were able to produce an oil with only 40% CLA. Quantitative conversion of the linoleic acid in soybean oil to CLA would have produced a fatty acid mixture with approximately 51% CLA. 

The effect different fatty acids have on cholesterolemia is well known. Whatever the kind of the effect (hyper- or hypocholesterolemic), it seems to be more pronounced when the fatty acids are esterified at the inner than at the outer positions of TAGs. The lower hypercholesterolemic effect of saturated fatty acids at the outer positions (64) can be the result of a combination of different factors such as reduced absorption by unabsorbable soap formation, which in turn interferes with cholesterol absorption in the intestinal lumen, partial desaturation and oxidation in the small intestinal cells, and reduced targeting into the fiver (63). The stronger hypocholesterolemic effect of polyunsamrated fatty acids at the i -2-position (65) could be the result of increased influx in the liver (66). 

The oil and catalyst must be extremely dry because moisture can deactivate the catalyst and cause soap formation. As even trace amounts of water decrease the potency of the catalyst tremendously, the oil should contain <0.01% (w/w) water... 

Betapol , a human milkfat substitute produced by Loders Croklaan (Wormerveer, the Netherlands), is produced by interesterification of vegetable oils in which the component TAGs have been modified to more closely resemble those found in breast milk. This product closely mimics the specific structure and fatty acid composition of human milkfat and resembles breast milk in terms of its nutritional value and high content of palmitic acid at the sn-2 position than other milkfat substitutes. In addition, the use of Betapol in infant formula can lead to improved mineral and fat absorption and less calcium soap formation within the intestinal lumen resulting in softer stools. 

The sodium or potassium salt of palmitic acid, or of stearic acid or the mixed salts of several acids obtained from ordinary fats, is the common substance known as soap. This particular reaction of hydrolysis, is, therefore, known, also, as a reaction of saponification (soap formation). Strictly speaking the reaction of saponification applies only to the alkaline hydrolysis of fats, i,e., of glycerol esters, but, as the hydrolysis of other esters is a reaction of exactly the same character, the term is used to apply equally to the hydrolysis of any ester in presence of an alkali. In the case of the lower alcohol and lower acid esters, e.g., ethyl acetate, the salt formed is not a soap but is a crystalline salt, sodium acetate. 

Gradual soap formation occurs with strong acids or bases sorbitan esters are stable in weak acids or bases. 

A combination of 2 parts of caustic soda and 1 part of sodium carbonate is often used in single stage boiling. Soda-ash softens the water while interacting with Ca and Mg salts (if such are present) it creates an active reaction of the medium which is most favourable for the formation of stable emulsions and suspensions increases fibre swelling, thus contributing to the release of impurities from the fibre neutralises fatty acids contained in the fabric by soap formation obviates soap hydrolysis in the presence of wool reduces the adherence of detergents to wool in the alkaline medium conditions. 

When these numbers are used, for 1% NaOH, [A ] is only 5% of [HAq]. Alternatively, a very high pH (close to 14, which is not practical) is required for the surface-active agent to be totally soluble in the aqueous phase. However, more [A ] is accumulated at the oil/water interface, which instantaneously reduces IFT. Sharma et al. (1989) took into account crude-oil/caustic interface (surface phase). They formulated the acid species dissociation and soap formation in the surface phase. 

The precursor steps of soap formation, shown below with Fe as the metallic surface, arise from the attack of the metal surface by alkylperoxy radicals and alkylhydroperoxide. This process may be called corrosive wear . Reactions (4.28) and (4.29) [18, 19], where the FeO reacts further with organic acids and forms the iron soaps. Reaction (4.30) ... 

Modified acid-degumming is a physical refining pretreatment that incorporates the benefits of caustic soda neutralization. This physical refining preparatory process treats the oil with a degumming acid and then partially neutralizes it with NaOH in solution. The amount of NaOH used is limited to prevent soap formation. The metal-phospholipid complexes are dissociated by the acid into insoluble metal salts and phospholipids in their acid form, which are still soluble in oil. The NaOH addition raises the pH and converts the phospholipids into sodium salts that are hydratable. The hydrated salts can be centrifuged for separation or dried to form agglomerates for adsorption on silica for removal with filtration. 

The primary soybean oil quality issues for biodiesel production are free fatty acids, moisture, and phosphorus. These correspond well to the requirements for edible oil but bleaching and deodorization are generally not required for biodiesel. It is desirable to have levels of free fatty acid and moisture as low as possible. If both contaminants are <0.1%, there will be no effect on the biodiesel process (Van Gerpen, 2005). In fact, levels of free fatty acids and moisture of 0.5%, as is common for crude as-pressed oil, can be used directly for biodiesel production. However, there will be some additional soap formation during processing that will need to be removed. 

Scheme 6.34 Soap formation from triglyceride over NaOH catalyst.

It is considered that the combination of FFA esterification over an add catalyst and transesterification of triglycerides over a base catalyst offers a useful pathway to utilize poor-quahty oils that are high in FFAs [220, 221]. Pre-esterification is therefore an attractive process to decrease the FFA level in waste oils (Scheme 6.35), limiting their potential for soap formation (Scheme 6.32). 

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