The process of making soap from cooking oil (which is primarily composed of triglycerides) involves a reaction called saponification. This is a hydrolysis reaction where triglycerides react with an alkali, such as sodium hydroxide (NaOH), in the presence of water to form glycerol and soap (which are fatty acid salts). Below, I'll outline the step-by-step mechanism of saponification.
Step 1: Triglyceride Structure
Triglycerides are esters made from glycerol and three fatty acids. The general structure can be represented as follows:
O
||
CH2-O-C-R1
|
CH-O-C-R2
|
CH2-O-C-R3
Where R1, R2, and R3 are the hydrocarbon chains of the fatty acids.
Step 2: Nucleophilic Attack
-
A hydroxide ion (OH⁻) from the sodium hydroxide (NaOH) acts as a nucleophile and attacks the carbonyl carbon of the ester bond in the triglyceride.
Diagram:
O O || ||
CH2-O-C-R1 --> CH2-O-C-R1 | | OH⁻ attack OH O CH-O-C-R2 → CH-O-C-R2 | | CH2-O-C-R3 CH2-O-C-R3
### Step 3: Tetrahedral Intermediate Formation
2. This attack forms a tetrahedral intermediate where the carbon is attached to four substituents.
**Diagram:**
OH
|
O O || / CH2-O-C-R1 | / CH-O-C-R2 | | CH2-O-C-R3
### Step 4: Collapse of Intermediate
3. The tetrahedral intermediate collapses, yielding a carboxylate ion and releasing glycerol. This occurs with the breaking of the bond to the original fatty acid chain (R1, R2, or R3), resulting in soap formation.
**Diagram:**
O- OH
| |
CH2-O-C-R1 --> CH2-OH (Glycerol) | CH-O-C-R2 | CH2-O-C-R3
### Step 5: Final Products
4. Repeat the above steps for all three ester bonds in the triglyceride, leading to the formation of three fatty acid carboxylate ions (soaps) and one molecule of glycerol.
The final products represented as:
3 RCOO⁻ Na⁺ (soap) + Glycerol
### Step 6: Overall Reaction
The overall reaction can be summarized as follows:
\\[ \text{Triglyceride} + 3 \text{NaOH} + 3 \text{H}_2\text{O} \rightarrow 3 \text{RCOONa (soap)} + \text{Glycerol} \\]
### Conclusion
This step-by-step mechanism illustrates how triglycerides in cooking oil are saponified to produce soap and glycerol. The curve arrows would indicate the movement of electron pairs in the mechanisms as described. In a drawn diagram, the arrows would start from the nucleophile (OH⁻) to the carbonyl carbon and also show the electron movement in bond breaking and forming during the reaction sequence.