Overview of Anionic Surfactants

1. Soaps
It is a salt of higher fatty acid, general formula: (RCOO)nM. Fatty acid hydrocarbons R are generally long chains of 11 to 17 carbons, and common ones include stearic acid, oleic acid, and lauric acid. According to the different substances represented by M, they can be divided into alkali metal soaps, alkaline earth metal soaps and organic amine soaps. They all have good emulsifying properties and the ability to disperse oil. But it is easy to be destroyed. Alkali metal soap can also be destroyed by calcium and magnesium salts, and electrolytes can also cause it to salt out.
Alkali metal soap: O/W
Alkaline earth metal soap: W/O
Organic amine soap: triethanolamine soap
2. Sulfate RO-SO3-M
Mainly sulfated oils and higher fatty alcohol sulfate esters. The aliphatic hydrocarbon chain R has between 12 and 18 carbons. The representative of sulfated oil is sulfated castor oil, commonly known as Turkish red oil. Higher fatty alcohol sulfates include sodium dodecyl sulfate (SDS, sodium lauryl sulfate) and fatty alcohol polyoxyethylene sodium sulfate (AES). SDS has strong emulsifying properties, is relatively stable, and is resistant to acids and calcium and magnesium salts. In pharmacy, it can precipitate with some high-molecular cationic drugs, causing certain irritation to mucous membranes. It is used as an emulsifier for external ointments, and is also used for wetting or solubilizing solid preparations such as tablets. Fatty alcohol polyoxyethylene ether sulfate (AES) has the ability to resist hard water, has good oil removal performance, and has a certain thickening effect.
3. Sulfonate R-SO3-M
Belonging to this category are aliphatic sulfonates, alkylaryl sulfonates and alkylnaphthalene sulfonates. Their water solubility and resistance to acid and calcium and magnesium salts are slightly worse than those of sulfates, but they are not easily hydrolyzed in acidic solutions. Aliphatic sulfonates include: sodium secondary alkyl sulfonate (SAS-60), sodium fatty acid methyl ester ethoxylate sulfonate (FMES), sodium fatty acid methyl ester sulfonate (MES), dioctyl succinic acid sulfonate Sodium (Aloso-OT) and other drug absorption enhancers can be used for non-oral routes; sodium dodecylbenzene sulfonate, which is an alkyl aryl sulfonate, is currently a widely used detergent. Cholelithiates such as sodium glycocholate, sodium taurocholate, etc. are often used as solubilizers for monoglycerides of fatty acids and emulsifiers for fats in the gastrointestinal tract.