What is Hydrogenation? - Process & Reaction

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  • 0:01 Definition of Hydrogenation
  • 1:19 Saturated Versus…
  • 1:59 Relationship Between…
  • 3:21 The Mechanism of Hydrogenation
  • 5:21 Lesson Summary
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Lesson Transcript
Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

Organic compounds can become saturated using a chemical reaction called hydrogenation. Complete this lesson to learn about the process of hydrogenation and how this reaction works.

Definition of Hydrogenation

Hydrogenated fats and oils are common terms you may have encountered at your local grocery store. On food labels, you can likely find at least one container that reads 'does not contain hydrogenated fats.' Although there are several nutritional warnings against these types of fats, have you ever wondered how these are generated in the first place? Well, the answer lies in a chemical reaction called hydrogenation.

The process of hydrogenation involves the use of hydrogen molecules to saturate organic compounds, in the presence of a catalyst. Catalysts are species that are used to speed up the rate of a reaction without being consumed during the process. Keep in mind that catalysts are essential to running this reaction. Common catalysts used during hydrogenation are metals such as nickel and platinum.

An important requirement in the hydrogenation process, besides a catalyst, is the presence of a hydrogen atom. As we will see shortly, the purpose of the hydrogen atom is to come in and remove the double or triple bond between atoms. In other words, hydrogen atoms turn an unsaturated hydrocarbon into a saturated one. What does unsaturated and saturated mean?

Saturated Versus Unsaturated Hydrocarbons

Saturated hydrocarbons are compounds that only contain single bonds in their structure. The perfect example of a saturated hydrocarbon is the alkane functional group. Alkanes are organic compounds that contain single bonds between their carbon and hydrogen atoms.

Unsaturated hydrocarbons are compounds that contain double bonds in their structure. The alkene functional group is a great example of an unsaturated hydrocarbon. Alkenes contain at least one double bond between the carbon atoms in their structure. Examples of both saturated and unsaturated hydrocarbons are shown here:

Relationship Between Nutrition and the Hydrogenation Reaction

Hydrogenated fats and oils are common ingredients found in some of the foods we purchase. They are used to extend the shelf life of a food item or keep the intended food flavor stable. Did you know that certain margarine products used in making your favorite cookies are manufactured using hydrogenation? Most certainly so! When making certain margarine products, the double bond in its structure is hydrogenated. Hence, it is converted from an unsaturated to a saturated hydrocarbon.

But, how does hydrogenation relate to our health risks regarding the consumption of hydrogenated fats and/or oils? Unfortunately, these risks have a lot to do with the hydrogenation mechanism of these ingredients. As we will see shortly, when the hydrogen molecule attaches itself to an unsaturated hydrocarbon, its double bond will convert to a single bond.

At high temperatures, during hydrogenation, the double bond can rearrange (or change positions) in unsaturated hydrocarbons. If they rearrange, the end result may be a product that still contains double bonds. In nutrition we call these products, following hydrogenation, trans fats. Trans fats are not good for our health as they increase our cholesterol and put us at risk for problems such as heart disease. Now that we know what hydrogenation is as well as its role in how our food is processed, let's look at the mechanism of hydrogenation.

The Mechanism of Hydrogenation

Recall that saturated organic compounds (i.e., hydrogenated fats and oils) are formed from hydrogenation. But what is the mechanism for this chemical reaction? Let's use the hydrogenated fat oleic acid as an example. This fat is commonly found in our food products such as vegetable oil. As we use this example, take note of what is your saturated and unsaturated compound. Also, pay close attention to the role of the hydrogen atom and catalyst in this reaction.

Step 1: A hydrogen molecule comes in and reacts with the metal atom on the surface of a catalyst (a).

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