Triacylglycerol Reactions: Hydrogenation - Online Tutor, Practice Problems & Exam Prep

Hydrogenation of triacylglycerols involves adding hydrogen (H₂) to carbon double bonds, converting them to single bonds. This process can be complete, removing all double bonds, or partial, where some remain. Complete hydrogenation increases melting points, while partial hydrogenation is used commercially to create various margarines, affecting their hardness based on remaining pi bonds. A nickel catalyst is commonly employed, requiring one mole of H₂ for each pi bond reduced. Understanding these reactions is crucial for applications in food science and lipid chemistry.

Triacylglycerol Reactions: Hydrogenation Concept 1

In this video on Triacylglycerol reactions, we take a look at hydrogenation. Now, recall that under this type of reaction, we're going to have 2 hydrogens being added to 1 pi bond. And we say here that the conversion from double bonds to single bonds will help to decrease unsaturation as we lose our pi bonds, and this will cause an increase in melting point.

When we take a look at hydrogenation reactions, realize that there was complete hydrogenation where all of our carbon-carbon double bonds are reduced to single bonds. And then we also have partial hydrogenation when some, but not all carbon-carbon double bonds are reduced to single bonds. Now, if we take a look here at the complete one, we have here our triglyceride molecule or our Triacylglycerol molecule, and we're going to say here, triolein is its name. And here, if we look at our products, we can see that all 3 double bonds have been removed. And now we have just single bonded fatty acid chains.

Here remember when it comes to hydrogenation we use H 2 with some type of metal catalyst. Here, nickel is a common type of metal catalyst that is used. Also remember that when it comes to hydrogenation, 1 mole of H 2 is required for every single pi bond that we have. Because there are 3 Pi Bonds that were erased and are no longer part of my product, that means I used 3 moles of H 2 to do this complete hydrogenation.

Now, again with partial hydrogenation, some but not all carbon double bonded carbon bonds are reduced to single bonds. Here, we start out with 3, and at the end, we only have one left. 2 of them were removed and reduced. So, since 2 pi bonds were removed, that would mean that we needed 2 moles of H 2 and we still use our Nickel catalyst.

Now, what's the whole point of doing partial hydrogenation? Why not go all the way and reduce all the pi bonds to single bonds? Well, we're going to say that this is commercially manufactured. We're going to say here that partial hydrogenation converts oils to different types of margarines. And ultimate consistency is based on the number of pi bonds. So companies will make these partially hydrogenated oils in order to make different types of margarines; we can actually affect the hardness of these margarines because there are soft margarines versus hard margarines based on the number of pi bonds remaining in our product.

Alright. So normally we do complete hydrogenation, but some companies are able to only do partial hydrogenation where they want to create margarines from oils. Alright. So just keep this in mind, hydrogenation, that it can be complete or it can be partial.

Determine a possible triacylglycerol molecule formed when linoleic acid undergoes partial hydrogenation and consumes 1 mole of hydrogen gas.

• A. Palmitoleic acid
• B. Stearic acid
• C. Linolenic acid
• D. Oleic acid

Assuming a complete reaction with hydrogen gas, which of the following molecules would have the greatest increase in melting point?

• A.
• B.
• C.
• D.

Here’s what students ask on this topic:

What is the process of hydrogenation in triacylglycerols?

Hydrogenation of triacylglycerols involves adding hydrogen (H₂) to carbon-carbon double bonds (C=C), converting them to single bonds (C-C). This can be complete, where all double bonds are reduced, or partial, where some double bonds remain. Complete hydrogenation increases the melting point of the fat, making it more solid at room temperature. Partial hydrogenation is often used in the food industry to create margarines with varying consistencies. A nickel catalyst is commonly used, and one mole of H₂ is required for each pi bond reduced.

Why is nickel used as a catalyst in the hydrogenation of triacylglycerols?

Nickel is used as a catalyst in the hydrogenation of triacylglycerols because it facilitates the addition of hydrogen (H₂) to the carbon-carbon double bonds (C=C) efficiently. Nickel provides a surface for the hydrogen molecules to adsorb and dissociate into atoms, which then react with the double bonds in the triacylglycerol molecules. This process speeds up the reaction without being consumed, making it an effective and reusable catalyst for industrial applications.

What is the difference between complete and partial hydrogenation of triacylglycerols?

Complete hydrogenation of triacylglycerols involves converting all carbon-carbon double bonds (C=C) to single bonds (C-C), resulting in fully saturated fatty acids. This increases the melting point, making the fat more solid at room temperature. Partial hydrogenation, on the other hand, only reduces some of the double bonds, leaving others intact. This process is used commercially to produce margarines with varying consistencies, as the remaining double bonds affect the hardness of the final product.

How does partial hydrogenation affect the properties of margarine?

Partial hydrogenation affects the properties of margarine by altering its consistency and hardness. By reducing only some of the carbon-carbon double bonds (C=C) to single bonds (C-C), the process leaves a certain number of double bonds intact. The number of remaining double bonds determines the hardness of the margarine. More double bonds result in a softer margarine, while fewer double bonds make it harder. This allows manufacturers to produce margarines with specific textures and melting points to meet consumer preferences.

How many moles of H₂ are required for the complete hydrogenation of a triacylglycerol with three double bonds?

For the complete hydrogenation of a triacylglycerol with three double bonds, three moles of hydrogen (H₂) are required. Each mole of H₂ reacts with one pi bond (double bond) to convert it into a single bond. Therefore, if a triacylglycerol molecule has three double bonds, it will need three moles of H₂ to fully saturate all the double bonds.