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Difficulty: MediumAlkanoic Acids, Esterification, Saponification, Fats, and Oils

A vegetable oil containing glyceryl tristearate is boiled with aqueous sodium hydroxide during soap manufacturing. Which of the following sets of products is formed from this saponification reaction?

  1. Propane-1,2,3-triol and sodium stearateAnswer
  2. B
    Stearic acid and sodium hydroxide
  3. C
    Propane-1,2,3-triol and octadecan-1-ol
  4. D
    Octadecane and sodium trioxocarbonate(IV)

Answer

Propane-1,2,3-triol and sodium stearate
Saponification is the alkaline hydrolysis of fats and oils (triesters of glycerol). When glyceryl tristearate is heated with aqueous sodium hydroxide, the ester bonds are irreversibly broken to yield propane-1,2,3-triol (glycerol) and sodium stearate, which is a soap.

Step-by-Step Solution

1
Identify the functional group and reactants
Glyceryl tristearate is a triacylglycerol (fat/ester) reacting with a strong alkali (NaOH\text{NaOH}).
Understanding the nature of the reactants helps determine the type of chemical process taking place.
2
Determine the reaction mechanism (saponification)
Alkaline hydrolysis cleaves the three ester ester bonds in the triglyceride.
Base-catalyzed hydrolysis of esters is irreversible and yields the alcohol component and the carboxylate salt.
3
Identify the resulting products
The alcohol component formed is propane-1,2,3-triol (glycerol) and the salt formed is sodium stearate (soap).
The glycerol backbone is released as propane-1,2,3-triol while the long-chain fatty acid chains form sodium carboxylate salts.

Key Concept

Saponification of Fats and Oils
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Topics

Alkanoic Acids, Esterification, Saponification, Fats, and Oils

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