The saponification of ester is the process of producing glycerol and soap. Saponification involves a reaction of a base, normally sodium hydroxide, with an ester group on a compound. Triglyxcerides, which are an ester of a fatty acid, hydrolyze to form the sodium salt of a caboxylate. As well as soap, such saponifiation processes can also produce glycerol.
Substances that can be converted to soap are known as saponifiable substances. Vegetable oils and animal fats are the most common to be saponified. Triglycerides are mixtures that come from diverse fatty acids and can be converted to soap in a one- or two-step process. In the one-step process, the triglyceride is treated with a strong base like lye, which accelerates separation of the ester bond and releases the fatty acid salt and glycerol. This one-step process is the main method used to produce glycerol. When making soap, the triglycerides are purified. Triglycerides can also be saponified in a two-step process that starts with steam hydrolysis of the triglycerides. This process produces the carboxylic acid and glycerol after which the fatty acid is neutralized with alkali to produce soap. The advantage of the two-step process is the fatty acids can be purified, which produces a higher quality soap.