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Saponification is the reaction of a metallic alkali (base) with a fatty ester to form soap. Saponification is the making of soap.

CH2-OOC-R - CH-OOC-R - CH2-OOC-R (fat)

+ 3 NaOH ( or KOH)

both heated --->>

CH2-OH -CH-OH - CH2-OH (glycerol)

+ 3 R-CO2-Na (soap)

R=(CH2)14CH3 (for example)

Sodium chloride is added to precipitate the soap.

Lye is a form of sodium hydroxide which is a caustic base. If NaOH is used a hard soap is formed, whereas a soft soap is formed when KOH is used.

Animal fat is a fatty ester in the form of triacylglycerol. The alkali breaks the ester bond and releases the fatty acid and glycerol.

The soap is salted out by precipitating it with sodium chloride.

Saponification is often generalized to refer to the breaking of ester bonds using a caustic alkali.

Soap Mummies

Saponification can also refer to the conversion of fat and other soft tissue in a corpse into adipocere. This process is more common where the amount of fatty tissue is high, the agents of decomposition absent or only minutely present, and the burial ground is particularly alkali.

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