Types of Cleansing Agents

Commercially, cleansing agents fall into two types based on their chemical composition: soaps and synthetic detergents. Soaps are sodium or potassium salts of long-chain fatty acids, made by the alkaline hydrolysis of natural oils and fats with NaOH or KOH -- a reaction specifically called saponification. Because oils/fats are chemically triesters of long-chain fatty acids and glycerol (propan-1,2,3-triol), saponification converts an oil/fat plus 3 NaOH into glycerin (glycerol) plus three molecules of the sodium salt of the fatty acid, R-COONa (soap). The particular oil and alkali used affects the finished soap's quality: potassium soaps are gentler ('soft') on the skin, so toilet soaps are made using better grades of oil together with KOH, with care taken to remove any excess alkali left over from the reaction; laundry soaps, in contrast, are made using NaOH and typically include added fillers such as sodium rosinate (which acts as a lathering agent), sodium silicate, borax, and sodium and trisodium phosphate. Synthetic detergents are man-made cleansing agents designed to work effectively even in hard water, and the chapter distinguishes three chemical types among them: anionic detergents are sodium salts of long-chain alkyl sulfonic acids or of long-chain alkyl-substituted benzene sulfonic acids (for example, sodium lauryl sulphate, used as a household detergent and as an additive in toothpaste); cationic detergents are quaternary ammonium salts carrying one long alkyl chain (for example, cetyltrimethyl ammonium b …