Did you know the process of making starch in our bodies uses a dehydration synthesis reaction? Explore this lesson to learn about dehydration synthesis reactions and see examples of how they are used, both biologically and chemically.
What Is Dehydration Synthesis?
Dehydration reactions are quite useful both biologically and chemically, from forming disaccharides, like sucrose, to converting alcohols to ethers. Let’s take a look at this fascinating reaction and discover its use in science.Dehydration synthesis is the process of joining two molecules, or compounds, together following the removal of water. When you see the word dehydration, the first thing that may come to mind is ‘losing water’ or ‘lacking water.
‘ This is a perfect way to remember what occurs during a dehydration reaction. Essentially, water is lacking, because the water was lost, following the joining of two molecules to make a large molecule.Dehydration synthesis is classified as a type of chemical reaction.
A chemical reaction is the process where chemical substances called reactants transform into new substances called products. But a dehydration synthesis also has a different alias it can go by; this is a condensation reaction.How is the term condensation reaction related to dehydration synthesis? Great question! During a condensation reaction, two molecules are condensed and water is lost to form a large molecule. This is the same exact process that occurs during a dehydration synthesis. Thus, when you see both terms, remember that they are often used interchangeably.Switching gears, let’s dig deeper into this lesson and explore what actually happens during this reaction.
We will use two different dehydration synthesis examples to illustrate what happens in the presence, or absence, of an acid catalyst.
A catalyst is a substance that speeds up the rate of a reaction without being consumed. For the first example we will discuss a chemical process involving the dehydration of two alcohols to make an ether product. The second example, a biological process, will involve the dehydration synthesis of glucose, a monosaccharide, to form a disaccharide, sucrose. Monosaccharides are classified as simple sugars. They are used as the building blocks for complex sugars. Disaccharides are sugars made from two monosaccharides.Always keep in mind the two events that must happen during this reaction:
- The formation of a new product from two reacting molecules
- The loss of water confirmed by its placement on the product side of this reaction
Example #1: Alcohol Condensation to Make an Ether Product
The electron pair on oxygen is attracted to the charge on the acid proton. These electrons move to form a bond with the acid proton. The result is the addition of hydrogen to the ethanol molecule. Note that the double arrows indicate that this step is reversible and moves quite fast.
Step 2: The second alcohol comes in and acts like a nucleophile. A nucleophile is a species that is willing to donate its electrons to form a bond with another molecule or atom.
The oxygen on the second alcohol attacks the carbon atom, forcing a water molecule to leave. The end result is the formation of an ether called the oxonium ion intermediate and loss of water.Step 3: Although water has been lost and two molecules have joined to form an ether product, the ether is an ion.
An ion is a molecule or atom that carries a net positive or negative charge.
To remove this charge, the electron pair from the water molecule moves to form a bond with the proton. The result is an ether product and leftover hydronium ion.
Example #2: Sucrose Formation via Dehydration Synthesis
Step 1: One glucose molecule takes its hydroxyl group (OH) and uses that as a nucleophile to form a bond with the hydrogen atom on the other glucose molecule.
Let’s review. Dehydration synthesis is a type of chemical reaction that involves the combining of reacting molecules to make a large molecule, following the loss of water. This type of reaction is also classified as a condensation reaction.
Many different biological or chemical processes utilize the dehydration synthesis reaction. Examples include the formation of disaccharides, like sucrose, from monosaccharides, like glucose, and alcohol condensation to make an ether product. An acid catalyst can be used during a dehydration synthesis reaction.