Soap formation, from fatty acids

Nitrile Process. Fatty nitriles are readily prepared via batch, Hquid-phase, or continuous gas-phase processes from fatty acids and ammonia. Nitrile formation is carried out at an elevated temperature (usually >250° C) with catalyst. An ammonia soap which initially forms, readily dehydrates at temperatures above 150°C to form an amide. In the presence of catalyst, zinc (ZnO) for batch and bauxite for continuous processes, and temperatures >250° C, dehydration of the amide occurs to produce nitrile. Removal of water drives the reaction to completion. 

In the production of soap from fatty acids the distillation process normally associated with fat splitting is usually a sufficient pretreatment for the raw materials (Von Barren and Klimmek, 1977). Methods are available, however, to treat the fatty acids prior to distillation to prevent undesirable by-product formation, e.g. acid washing to remove trace metals. It is good practice to store fatty acids for the manufacture of high-quality soaps for as short a time as possible to prevent deterioration. 

Neutralization Step The formation of soap from fatty acids is achieved through the reaction of the fatty acid with the appropriate caustic. This reaction is extremely rapid for... 

Caustic soda by reaction of sodium amalgam and water Nitration of organic compounds with aqueous nitric acid Formation of soaps by action of aqueous alkahes on fats or fatty acids Sulfur removal from petroleum fractious by aqueous ethauolamiues Treating of petroleum products with sulfuric acid... 

Further addition of fatty acid eventually results in the formation of micelles. Micelles formed from an amphipathic lipid in water position the hydrophobic tails in the center of the lipid aggregation with the polar head groups facing outward. Amphipathic molecules that form micelles are characterized by a unique critical micelle concentration, or CMC. Below the CMC, individual lipid molecules predominate. Nearly all the lipid added above the CMC, however, spontaneously forms micelles. Micelles are the preferred form of aggregation in water for detergents and soaps. Some typical CMC values are listed in Figure 9.3. 

The formation of an ester from an alcohol and an acid is an equilibrium reaction. The reverse reaction can be promoted by removing the acid from the reaction mixture, for example by treating it with NaOH. Animal fats are converted to soaps (fatty acid salts) and glycerine (a trialcohol) in this manner. 

In steatorrhea, the formation and precipitation of insoluble calcium soaps formed from calcium and fatty acid has been generally credited as the cause of reduced calcium and fat absorption. 

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). 

Long-chain fatty acids are insoluble in water, and their titration curves are concentration-dependent because of the formation of organized aggregates (acid soaps, soap micelles, fatty acid precipitates) which concentrate protons at the surface. At concentrations above the critical micellar concentration, solutions of long-chain fatty acid soaps manifest a diprotic curve when they are titrated from pH 10 to 4 (23). The first... 

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 process was best adapted to fresh fat. Stocks in which hydrolysis occurred were difficult to process because of the formation of soap in the aqueous phase. The soap was derived only from already liberated free fatty acids. Under the mild conditions of this digestion process, there was no appreciable saponification of neutral fat. The fat was also alkali refined to produce a final product free of acidity. A typical final product had a free fatty acid content of 0.01% and a Fovibond color of 2 yellow and 0.3 red. This process gave improved yields over conventional wet rendering (59, 60). 

Chelants and Antioxidants Soaps, fatty acids, and fragrances are susceptible to oxidation during aging (25). The oxidation process is quite complex but typically results from the reaction of the unsaturated bonds in these components with oxygen in the air, resulting in the formation of shorter chain-length acids. 

---