Soap is a common cleaning product globally used for personal hygiene, cleaning and various other applications. From centuries, soaps is playing an essential role in human life. Additionally, ranging from basic formulations to a wide variety of products soap fulfill particular needs, like skin care, household cleaning, and industrial uses. The chemistry of soap comprises of sodium or potassium salts of fatty acids, having both hydrophilic (water-attracting) and hydrophobic (water-repelling) ends. This dual behavior of soaps help in removing dirt, grease and other stains by formation of micelles.
The History
People use Soap over the thousands of the years. From the process of saponification of oils and fats by alkali, we get soap. Consequently, just like most of the other human discoveries, the first saponification is one of them by chance. According to the Roman history, first soap was discovered fortuitously near mount Sapo which was an ancient location for animal sacrifices. Accidentally, the animal fat got mixed with wood ashes (source of alkali) and rain water, led to the formation of soap mixture. Later, Roman homemakers realized that a unknown yellow mixture of Tiber river water made their clothes cleaner and brighter compared to other water.1
However, the real development in soap making was made by French chemist and doctor, Nicolas Leblanc, who created a soap making process obtaining soda from common salt. The process was known as Leblanc process, reported in 1780.
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The Leblanc process involved the reaction of table salt with sulphuric acid generating sodium sulphate. Further, sodium sulphate was heated at high temperature with coal and lime stone to form sodium carbonate. Leblanc’s process make the soap making process more reachable at reasonable cost, and soap, once a luxury good only royalty and the wealthy could afford, has evolved into the primary product for daily personal hygiene.
The Chemistry of Soap Molecules
It is astonishing that modern soap making process still uses the same chemistry as old-fashioned soaps despite advancements in science and technology. Particularly. the process of saponification involves the hydrolysis of a triglyceride (fat or oil) using an alkaline solution, typically lye ( NaOH or KOH). Triglycerides are usually triesters consists of three long aliphatic carboxylic acid chains joined to a single glycerol molecule (eqn 1). The standard process is to heat vegetable or animal fat in sodium hydroxide (lye), therefore hydrolyzing it into carboxylate salts (Soap) and glycerol. The salts got their metal partners from the cations of hydroxide used (eqn 2).
Cleansing Action of a Soap
The basis for cleansing action of soap is its capacity to emulsify fats and oils so that water may wash them away. Soap molecules have both hydrophilic and hydrophobic properties. Particularly, the chemistry of soap consists of two distinct parts (Fig.1). The hydrophilic head that attracts water and the hydrophobic tail that repels it . When soap dissolves in water, the hydrophilic heads stay in. Further, the water and the hydrophobic tails stick to the oil or grease. This traps the grease inside micelles, which are tiny spherical structures. The micelles are removed along with the trapped oil and grime when the surface is rinsed with water, leaving it clean (Fig. 2). Therefore, soap works well as a cleaning agent to remove the contaminants that are both oil-loving and water-soluble.2
Closing Remarks for the Chemistry of Soap
Over the past few years, there has been steady expansion in the worldwide soap market. Earlier, the market estimates to be worth USD 43.31 billion in 2022. In 2030 it will rise at a compound annual growth rate (CAGR) of 5.70% to reach USD 67.18 billion by 2030. The soap is still the most important base for cleaning bars today. Additionally, soap manufacturers must identify and control some factors such as alkali concentration, temperature, agitation and mixing etc. Also, these factors are important in order to produce high-quality soaps. The soaps that give consumers the proper cleaning, skin moisturizing, and feel. Therefore, modifying these elements will facilitate soap composition technology to satisfy consumer preferences and market expectations.
References
1. Marcel Friedman, Ronni Wolf, Chemistry of soaps and detergents: Various types of commercial products and their ingredients, Clinics in Dermatology, 14, 1, 1996, 7-13.
https://doi.org/10.1016/0738-081X(95)00102-L.
2. Benedict Nnachi Alum (2024). Saponification Process and Soap Chemistry. INOSR APPLIED SCIENCES 12(2):51-56. https://doi.org/10.59298/INOSRAS/2024/12.2.515600
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