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Acid Hydrolysis of Triglycerides Chemistry Tutorial

Key Concepts

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Acid Hydrolysis of Triglycerides

Acid hydrolysis of a triglyceride (triacylglycerol) produces glycerol and 3 fatty acids as shown in the general chemical equation given below:

triglyceride
(triacylglycerol)		 + 3 water acidic conditions
→ 		glycerol
(propane-1,2,3-triol) 		+ 3 fatty acids
  H
|		   O
||		  
H- C -O- C -R
  |   O
||		  
H- C -O- C -R′
  |   O
||		  
H- C -O- C -R′′
  |
H		      
+ 3H2O H+(aq)
→
  H
|		  
H- C -OH
  |  
H- C -OH
  |  
H- C -OH
  |
H		  
+ R-COOH +

R'-COOH +

R"-COOH

If R, R' and R" are all the same, then the fatty acids produced will also all be the same fatty acid.

For example, in the triglyceride known as tristearin or glyceryl tristearate, which is found in animal fat, R, R' and R" are all -(CH2)16CH3.
The product of the acid hydrolysis of 1 tristearin molecule will be 1 molecule of glycerol and 3 molecules of CH3(CH2)16COOH (stearic acid).
This acid hydrolysis reaction is shown below:

tristearin
(glyceryl tristearate)		 + 3 water acidic conditions
→ 		glycerol
(propane-1,2,3-triol) 		+ 3 stearic acid
  H
|		   O
||		  
H- C -O- C -(CH2)16CH3
  |   O
||		  
H- C -O- C -(CH2)16CH3
  |   O
||		  
H- C -O- C -(CH2)16CH3
  |
H		      
+ 3H2O H+(aq)
→
  H
|		  
H- C -OH
  |  
H- C -OH
  |  
H- C -OH
  |
H		  
+ 3CH3(CH2)16COOH

Similarly, tripalmitin (glyceryl tripalmitate) which is extracted from palm oil, is a triglyceride in which R, R' and R" are all -(CH2)14CH3.
The acid hydrolysis of 1 molecule of tripalmitin produces 1 molecule of glycerol and 3 molecules of palmitic acid, CH3(CH2)14COOH as shown in the chemical equation below:

tripalmitin
(glyceryl tripalmitate)		 + 3 water acidic conditions
→ 		glycerol
(propane-1,2,3-triol) 		+ 3 palmitic acid
  H
|		   O
||		  
H- C -O- C -(CH2)14CH3
  |   O
||		  
H- C -O- C -(CH2)14CH3
  |   O
||		  
H- C -O- C -(CH2)14CH3
  |
H		      
+ 3H2O H+(aq)
→
  H
|		  
H- C -OH
  |  
H- C -OH
  |  
H- C -OH
  |
H		  
+ 3CH3(CH2)14COOH

The triglyceride known as glyceryl trioleate is found in olive oil, and R, R' and R" are all derived from oleic acid (CH3(CH2)7CH=CH(CH2)7COOH) so the acid hydrolysis of 1 molecule of glyceryl trioleate produces a glycerol molecule and 3 molecules of oleic acid, as shown in the chemical equation below:

glyceryl trioleate
(triglyceride)		 + 3 water acidic conditions
→ 		glycerol + 3 oleic acid
  H
|		   O
||		  
H- C -O- C -(CH2)7CH=CH(CH2)7CH3
  |   O
||		  
H- C -O- C -(CH2)7CH=CH(CH2)7CH3
  |   O
||		  
H- C -O- C -(CH2)7CH=CH(CH2)7CH3
  |
H		      
+ 3H2O H+(aq)
→
  H
|		  
H- C -OH
  |  
H- C -OH
  |  
H- C -OH
  |
H		  
+ 3CH3(CH2)7CH=CH(CH2)7COOH

However, most naturally occuring fats and oils are mixed triglycerides, that is, R, R' and R" are not the same.
When a mixed triglyceride is hydrolysed then more than 1 type of fatty acid will be produced.

Cocoa butter, a principal ingredient in the making of tasty chocolate, is made up of triglycerides in which R and R" can be derived from stearic acid (CH3(CH2)16COOH) while R' is derived from oleic acid (CH3(CH2)7CH=CH(CH2)7COOH).
When this triglyceride undergoes acid hydrolysis, each molecule of triglyceride produces 2 molecules of stearic acid and 1 molecule of oleic acid as shown below:

cocoa butter
(triglyceride)		 + 3 water acidic conditions
→ 		glycerol + 2 stearic acid + 1 oleic acid
  H
|		   O
||		  
H- C -O- C -(CH2)16CH3
  |   O
||		  
H- C -O- C -(CH2)7CH=CH(CH2)7CH3
  |   O
||		  
H- C -O- C -(CH2)16CH3
  |
H		      
+ 3H2O H+(aq)
→
  H
|		  
H- C -OH
  |  
H- C -OH
  |  
H- C -OH
  |
H		  
+ 2CH3(CH2)16COOH +

CH3(CH2)7CH=CH(CH2)7COOH

Beef tallow, once used to make horribly smelly, smokey candles, is also made up of triglycerides.
In a beef tallow triglyceride, R and R" can be derived from oleic acid while R' is derived from stearic acid.
When 1 molecule of this triglyceride undergoes acid hydrolysis, 2 molecules of oleic acid are produced and only 1 molecule of stearic acid, as shown in the chemical equation below:

beef tallow
(triglyceride)		 + 3 water acidic conditions
→ 		glycerol + 2 oleic acid + 1 stearic acid
  H
|		   O
||		  
H- C -O- C -(CH2)7CH=CH(CH2)7CH3
  |   O
||		  
H- C -O- C -(CH2)16CH3
  |   O
||		  
H- C -O- C -(CH2)7CH=CH(CH2)7CH3
  |
H		      
+ 3H2O H+(aq)
→
  H
|		  
H- C -OH
  |  
H- C -OH
  |  
H- C -OH
  |
H		  
+ 2CH3(CH2)7CH=CH(CH2)7COOH +

CH3(CH2)16COOH

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Digestion of Triglycerides

Chewing food in your mouth breaks it down into smaller pieces, and, small pieces of food have a larger surface area on which chemical reactions can occur than large pieces of food. So, the rate of chemical reactions is increased by creating these smaller food particles.

The act of breaking triglycerides up into fatty acids happens in the small intestine.
In the small intestine, bile salts secreted in bile from the liver cause fats to form small globules which can either be absorbed directly, or, can be acted upon by the enzyme lipase which is a component of the pancreatic and intestinal juice found in the small intestine.
The products of the enzyme catalysed hydrolysis of triglycerides can include glycerol and one or more of the following:

An example of an unbalanced, general chemical reaction in which all the products are formed is shown below:

triglyceride H2O
→ enzymes 		glycerol + diglyceride + monoglyceride + fatty acid
  H
|		   O
||		  
H- C -O- C -R
  |   O
||		  
H- C -O- C -R
  |   O
||		  
H- C -O- C -R
  |
H		      
H2O
→
enzymes
  H
|		  
H- C -OH
  |  
H- C -OH
  |  
H- C -OH
  |
H		  
+
  H
|		   O
||		  
H- C -O- C -R
  |   O
||		  
H- C -O- C -R
  |      
H- C -OH    
  |
H		      
+
  H
|		   O
||		  
H- C -O- C -R
  |      
H- C -OH    
  |      
H- C -OH    
  |
H		      
+ R-COOH

All the products of this hydrolysis reaction can be absorbed through the intestinal wall.
These are then used

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