Saponification
Saponification is a process of cleaving
- C2H5O2CCH3 + NaOH → C2H5OH + NaO2CCH3
Saponification of fats
Vegetable oils and animal fats are the traditional materials that are saponified. These greasy materials, triesters called triglycerides, are usually mixtures derived from diverse fatty acids. In the traditional saponification, the triglyceride is treated with lye, which cleaves the ester bonds, releasing fatty acid salts (soaps) and glycerol. In one simplified version, the saponification of stearin gives sodium stearate.
- C3H5(O2C(CH2)16CH3)3 + 3 NaOH → C3H5(OH)3 + 3 NaO2C(CH2)16CH3
This process is the main industrial method for producing glycerol (C3H5(OH)3).
Some soap-makers leave the glycerol in the soap. Others precipitate the soap by salting it out with sodium chloride.
Fat in a
Saponification value
The saponification value is the amount of base required to saponify a fat sample.[3] Soap makers formulate their recipes with a small deficit of lye to account for the unknown deviation of saponification value between their oil batch and laboratory averages.
Mechanism of basic hydrolysis
The hydroxide anion adds to the carbonyl group of the ester. The immediate product is called an
Expulsion of the alkoxide generates a carboxylic acid:
The alkoxide ion is a strong base so the proton is transferred from the carboxylic acid to the alkoxide ion, creating an alcohol:
In a classic laboratory procedure, the triglyceride trimyristin is obtained by extracting it from nutmeg with diethyl ether. Saponification to the soap sodium myristate takes place using NaOH in water. Treating the soap with hydrochloric acid gives myristic acid.[4]
Saponification of fatty acids
The reaction of fatty acids with base is the other main method of saponification. In this case, the reaction involves neutralization of the carboxylic acid. The neutralization method is used to produce industrial soaps such as those derived from magnesium, the transition metals, and aluminium. This method is ideal for producing soaps that are derived from a single fatty acid, which leads to soaps with predictable physical properties, as required by many engineering applications.
Applications
Hard and soft soaps
Depending on the nature of the alkali used in their production, soaps have distinct properties.
Lithium soaps
Fire extinguishers
Fires involving
Oil paints
Saponification can occur in
Saponification in oil paintings was described as early as 1912.[10]: 151 It is believed to be widespread, having been observed in many works dating from the fifteenth through the twentieth centuries; works of different geographic origin; and works painted on various supports, such as canvas, paper, wood, and copper. Chemical analysis may reveal saponification occurring in a painting's deeper layers before any signs are visible on the surface, even in paintings centuries old.[9]: 16
The saponified regions may deform the painting's surface through the formation of visible lumps or protrusions that can scatter light. These soap lumps may be prominent only on certain regions of the painting rather than throughout. In John Singer Sargent's famous Portrait of Madame X, for example, the lumps only appear on the blackest areas, which may be because of the artist's use of more medium in those areas to compensate for the tendency of black pigments to soak it up.[9]: 12–13, 15 The process can also form chalky white deposits on a painting's surface, a deformation often described as "blooming" or "efflorescence", and may also contribute to the increased transparency of certain paint layers within an oil painting over time.[9]: 16, 19
Saponification does not occur in all oil paintings and many details are unresolved.[9]: 19 At present, retouching is the only known restoration method.
See also
References
- ^ "Saponification | chemical reaction". Encyclopedia Britannica. Retrieved 2021-05-23.
- ISBN 978-0-471-72091-1
- ^ "Quality Laboratory Oil Examination Procedures and Practices". American Oil Chemists' Society. Archived from the original on 25 December 2012. Retrieved 17 December 2012.
- .
- ^ "How Saponification Makes Soap". ThoughtCo. Retrieved 2023-07-05.
- ^ "Double bonds and hydrogenation". GCSE Bitesize. BBC. Archived from the original on 2018-08-18. Retrieved 2017-03-10.
- ISBN 3-527-30673-0.
- ISBN 978-1-884446-05-4. Retrieved January 16, 2018.
- ^ JSTOR 40588562. PDF of full issue.
- ^ Fleury, Paul (1912). "Manufacture and Different Treatments of White Zinc, its Modifications and Improvements". The Preparation and Uses of White Zinc Paints (1st ed.). London: Scott, Greenwood & Son. pp. 122–154.
... and although Petit declares this theory false, it is none the less on it and on its data that he bases his system of manufacture of hydrated white zinc, of which he is the inventor that is to say, the saponification of the oil, or the formation of metallic salts, dissolved therein.