The key difference between hydration and hydrogenation is that hydration refers to the addition of water molecules to an organic compound, whereas hydrogenation refers to the addition of a hydrogen molecule to an organic compound.
Hydration and hydrogenation are important in chemical synthesis reactions. Both these reactions involve the opening up of a double bond in an organic compound by addition of a substituent to the carbon atoms in the double bond. The substituents that are added in these processes are different from each other.
CONTENTS
1. Overview and Key Difference
2. What is Hydration
3. What is Hydrogenation
4. Side by Side Comparison – Hydration vs Hydrogenation in Tabular Form
5. Summary
What is Hydration?
Hydration is the addition of a water molecule to an organic compound. The organic compound is usually an alkene, which has a double bond between two carbon atoms. The water molecule is added to this double bond in the form of a hydroxyl group (OH–) and a proton (H+). Therefore, the water molecule dissociates into its ions before this addition. The hydroxyl group is attached to one carbon atom of the double bond while the proton is attached to the other carbon atom.
Figure 01: A Simple Hydration Reaction
Since it involves bond breaking and bond forming, the reaction is highly exothermic. That means; the reaction releases energy in the form of heat. It is a stepwise reaction; in the first step, the alkene acts as a nucleophile and attacks the proton of the water molecule and bind with it through the less substituted carbon atom. Here, the reaction follows the Markonikov rule.
The second step includes the attachment of the oxygen atom of the water molecule to the other carbon atom (highly substituted carbon atom) of the double bond. At this point, the oxygen atom of the water molecule carries a positive charge because it bears three single bonds. Then comes another water molecule which takes up the extra proton of the attached water molecule, leaving the hydroxyl group at the less substituted carbon atom. Thus, this reaction leads to the formation of an alcohol. However, alkynes (triple bond containing hydrocarbons) can also undergo hydration reaction.
What is Hydrogenation?
Hydrogenation is the process of addition of a hydrogen molecule to an organic compound. Further, this reaction involves the treatment of an organic compound with hydrogen gas. Usually, the reaction occurs in the presence of a catalyst such as nickel, palladium or platinum. Non-catalytic hydrogenations are possible only at very high temperatures. Also, this process is important in the reduction of unsaturated organic compounds. That means; the hydrogenation can open up double bonds or triple bonds in organic compounds and turn them into compounds containing single bonds.
The process of hydrogenation has three components: unsaturated substrate, hydrogen source and catalyst. The reaction conditions such as temperature and pressure vary depending on the type of unsaturated compound and the catalyst. The substrate can be either an alkene or an alkyne. The hydrogenation can take place in two ways: homogeneous catalysis and heterogeneous catalysis.
In homogeneous catalysis, the catalyst metal binds with both alkene and hydrogen to give an intermediate product (alkene-catalyst-hydrogen intermediate complex). Then the transfer of one hydrogen atom from metal to carbon in the double bond (or triple bond) occurs. What happens next is the transfer of the other hydrogen atom from the hydrogen source to the alkyl group with simultaneous dissociation of the alkane.
Figure 02: Three Steps of Hydrogenation
In heterogeneous catalysis, the unsaturated bond binds with the catalyst while hydrogen source undergoes dissociation into two hydrogen atoms. Then a reversible step occurs where one hydrogen atom binds to the unsaturated bond. Finally, an irreversible reaction occurs where the other hydrogen atom attaches to the alkyl group.
What is the Difference Between Hydration and Hydrogenation?
Hydration and hydrogenation are important processes in chemical synthesis. The key difference between hydration and hydrogenation is that hydration refers to the addition of water molecules to an organic compound, whereas hydrogenation refers to the addition of a hydrogen molecule to an organic compound.
Below infographic summarizes the difference between hydration and hydrogenation.
Summary – Hydration vs Hydrogenation
Hydration and hydrogenation are important processes in chemical synthesis. The key difference between hydration and hydrogenation is that hydration refers to the addition of water molecules to an organic compound, whereas hydrogenation refers to the addition of a hydrogen molecule to an organic compound.
Reference:
1. “Specification for Ion-Selective Electrodes, Reference Electrodes, Combination Electrodes and Ion-Selective Electrode Meters for Determination of Ions in Solution.” doi:10.3403/00222406u.
Image Courtesy:
1. “Hydrationreaction” By Ccroberts – Own work (Public Domain) via Commons Wikimedia
2. “Hydrogenation on catalyst” By Michael Schmid – Drawing created myself (CC BY-SA 4.0) via Commons Wikimedia