Soap

Abstract

SOAPSoap is one of the oldest known manufactured chemical substances and was first produced thousands of years ago through the reaction of animal fats with the ashes from plants (1). Early soaps were used primarily for the cleansing of clothing, not for personal hygiene, because of cultural as well as practical reasons. For instance, these animal fat soaps possessed almost unbearable odors and probably contained excessive amounts of unreacted caustics. In the 1990s, soaps are produced using a variety of processes, including kettle boiling, continuous saponification, and hydrolysis/neutralization, as well as different fats and oils feedstocks, yielding finished materials that possess specifically desired properties for application as personal cleansing products.Soap is one example of a broader class of materials known as surface-active agents, or surfactants (qv). Surfactant molecules contain both a hydrophilic or water-liking portion and a separate hydrophobic or waterrepelling portion. The hydrophilic portion of a soap molecule is the carboxylate head group and the hydrophobic portion is the aliphatic chain. This class of materials is simultaneously soluble in both aqueous and organic phases or preferential aggregate at air-water interfaces. It is this special chemical structure that leads to the ability of surfactants to clean dirt and oil from surfaces and produce lather.Although soaps have many physical properties in common with the broader class of surfactants, they also have several distinguishing factors. First, soaps are most often derived directly from natural sources of fats and oils (see Fats and fatty oils). Fats and oils are triglycerides, ie, molecules comprised of a glycerol backbone and three ester-linked fatty oils. Other synthetic surfactants may use fats and oils or petrochemicals as initial building blocks, but generally require additional chemical manipulations such as sulfonation, esterification, sulfation, and amidation.Second, soaps form insoluble complexes, commonly referred to as curd, in the presence of calcium and magnesium ions in solution. Calcium and magnesium ions are the principal metal ions found in water and their level is commonly referred to as the hardness of the water; hard water has high levels of both of these ions, soft water has very low levels. This curd reduces the effectiveness of soap as a surfactant and gives rise to other undesirable properties during use, eg, precipitation on surfaces. Many synthetic surfactants are considerably less susceptible to water hardness. This water hardness insensitivity has led to the replacement of soap by synthetic surfactants in a variety of applications, such as dish and laundry detergents and shampoos. Although soap is still the predominant material used in personal cleansing products, eg, facial, body, and hand cleansing, soap-based personal cleansing products are being rapidly replaced by products that contain increasing amounts of synthetic surfactants to meet changing consumer needs, such as rinsing and lather in hard water and...

Ionic-Liquid-Induced Changes in the Properties of Aqueous Zwitterionic Surfactant Solution: Solvent and Rotational Relaxation Studies

“…In recent years, zwitterionic micellar systems have emerged as another common and widely studied example of restricted environment. − The zwitterionic surfactants, such as sulfobetaines and carboxybetaines, are formally neutral, but their micelles incorporate anions owing to the higher charge density of the cationic ammonium inner surface, compared with that of the anionic sulfonate or carboxylate surface. − Due to these unique properties they are quite useful in separation processes. By using packed zwitterionic columns for liquid chromatography, one can separate inorganic anions or cations, , and acidic or basic proteins, both independently and simultaneously in a single run using optimum conditions.…”

Heterogeneously Catalyzed Esterification of FFAs in Vegetable Oils

“…When a basic homogeneous catalyst is used for the transesterification of feeds with FFAs, soaps are produced as by-products through the unwanted saponification reaction [7] of carboxylic acids, with the base (e.g., KOH, NaOH, and CH 3 ONa) as shown below (see reaction (a)):…”

Solubility of sodium soaps in aqueous salt solutions

“…Chemically, soaps are metallic salts of aliphatic carboxylic acids, which include a hydrophilic carboxylate head group and a hydrophobic hydrocarbon tail [3]. Depending on the nature of the cation, the physical properties of metal carboxylates may vary considerably.…”