THEORY OF SAPONIFICATION

Saponification is the chemical reaction responsible for the protocell behavior we have observed under the microscope with Martin, and also produces soap when done at larger scales. In definition, saponification is the reaction between lye (HO-) and an ester (which is our case is animal or vegetal fat/oil). The reaction produces alcohol and soap (carboxylate ions mixture).

Note: the R in organic chemistry states for a hydrocarbon chain. This is a general formula that works for any kind of R and R’ chain.

This is the general definition of the reaction. As you can see in the formula what is happening is basically that the hydrocarbon chain R’ of the ester detaches and binds to the HO-, forming an alcohol.

In this experiment we prepare soap from animal fat (lard) or vegetable oil. Animal fats and vegetable oils are esters of carboxylic acids; they have a high molecular weight and contain the alcohol, glycerol. Chemically, these fats and oils are called triglycerides. The principal acids in animal fats and vegetable oils can be prepared from the natural triglycerides by alkaline hydrolysis (saponification). We also can choose to add a scent to your soap by adding an essential oil.

SUMMARY

Vegetable oil and animal fats are the main materials that are saponified. These greasy materials, triesters called triglycerides, are mixtures derived from diverse fatty acids. Triglycerides can be converted to soap in either a one- or a two-step process. In the traditional one-step process, the triglyceride is treated with a strong base, which accelerates cleavage of the ester bond and releases the fatty acid salt and glycerol. This process is the main industrial method for producing glycerol. If necessary, soaps may be precipitated by salting it out with saturated sodium chloride. The saponification value is the amount of base required to saponify a fat sample. For soap making, the triglycerides are highly purified, but saponification includes other base hydrolysis of unpurified triglycerides.