Making Ethers - Alcohol Condensation: Videos & Practice Problems

Ethers can be synthesized through acid-catalyzed alcohol condensation, a process where two alcohols combine to form one ether. The mechanism involves protonation of one alcohol, creating a good leaving group (water), followed by a backside attack from the other alcohol, resulting in an ether and regenerating the acid catalyst. This method primarily yields symmetrical ethers due to the use of identical alcohols. For asymmetrical ethers, the Williamson ether synthesis is preferred, allowing for varied R groups. Understanding these reactions is crucial for mastering organic synthesis techniques.

The Mechanism of Alcohol Condensation.

So another way to make ethers is through a reaction called acid-catalyzed alcohol condensation. I know this sounds really complicated, but it's not that bad. As you guys will learn later in organic chemistry 2, a condensation reaction is simply a reaction that takes 2 molecules and makes them into 1 bigger molecule. That's the definition of condensation. What we're going to be doing here is taking 2 alcohols in an alcohol condensation, putting them together, condensing them, and turning them into 1 ether. How does this work? Let me just draw the mechanism for you involving the presence of acid and heat.

The acid will protonate one of the alcohols. Here's how it looks: I've got my H3O+ that I'm going to write it this way because it's easier to deprotonate. So, the alcohol (OH) is going to grab an H from the acid, and what I'm going to get is a protonated alcohol now. This protonated alcohol just turned into a good leaving group. Water is a good leaving group, right? My other equivalent of alcohol, the one that did not get protonated, is going to do a backside attack on this good leaving group. So, we're basically going to get an SN2 reaction where the unprotonated alcohol attacks the carbon and kicks out the good leaving group. Here's what we end up with: the black alcohol that still has an H on it but is now attached to the 2-carbon chain from the red alcohol. On top of that, there's going to be water that just left by itself. Does that make sense so far?

We've got the black one attacking the red one. This looks like an ether, but there's a problem with a formal charge. What can we do about that formal charge? Well, remember, this reaction is called acid-catalyzed for a reason. That means you always have to end up with the same amount of acid you started off with because it's a catalyst. It can't be consumed or destroyed in the reaction. So, I use the water to pick up the proton. What we end up getting at the end is an ether plus the same H3O+ that we started off with. There you have it, we just condensed an ether out of alcohol. However, there is a significant limitation to this synthesis method. It's only going to yield a certain type of ether, specifically symmetrical ethers. The reason is that we're always going to be reacting with acid in alcohol and you'll have an abundance of alcohol, resulting in one molecule reacting with another molecule of the same alcohol, generating the same R groups on both sides. Sometimes you want that, but if you wanted an asymmetrical ether, the Williamson ether synthesis might be a better choice because it allows you to add R groups as you want. So let's continue discussing ethers.

Here’s what students ask on this topic:

What is acid-catalyzed alcohol condensation in organic chemistry?

Acid-catalyzed alcohol condensation is a reaction where two alcohol molecules combine to form one ether molecule. This process involves the presence of an acid catalyst and heat. The mechanism starts with the protonation of one alcohol, creating a good leaving group (water). The other alcohol then performs a backside attack, resulting in the formation of an ether and the regeneration of the acid catalyst. This method primarily yields symmetrical ethers because it typically involves identical alcohols.

How does the mechanism of acid-catalyzed alcohol condensation work?

The mechanism of acid-catalyzed alcohol condensation involves several steps. First, an acid protonates one of the alcohols, turning it into a good leaving group (water). The other alcohol then performs a backside attack on the carbon attached to the leaving group, resulting in an SN2 reaction. This forms an ether and releases water. The acid catalyst is regenerated at the end of the reaction, ensuring it is not consumed. This process typically yields symmetrical ethers due to the use of identical alcohols.

Why does acid-catalyzed alcohol condensation primarily yield symmetrical ethers?

Acid-catalyzed alcohol condensation primarily yields symmetrical ethers because it usually involves the reaction of identical alcohol molecules. When two molecules of the same alcohol react, the resulting ether has the same R groups on both sides, making it symmetrical. This is due to the abundance of the same alcohol in the reaction mixture. For asymmetrical ethers, the Williamson ether synthesis is preferred, as it allows for the use of different R groups.

What are the limitations of acid-catalyzed alcohol condensation?

The main limitation of acid-catalyzed alcohol condensation is that it primarily produces symmetrical ethers. This is because the reaction typically involves identical alcohol molecules, leading to ethers with the same R groups on both sides. If an asymmetrical ether is desired, the Williamson ether synthesis is a better choice, as it allows for the use of different alcohols or alkyl halides, resulting in varied R groups in the final ether product.

What is the difference between acid-catalyzed alcohol condensation and Williamson ether synthesis?

Acid-catalyzed alcohol condensation and Williamson ether synthesis are both methods for producing ethers, but they have key differences. Acid-catalyzed alcohol condensation involves the reaction of two alcohols in the presence of an acid catalyst, primarily yielding symmetrical ethers. In contrast, Williamson ether synthesis involves the reaction of an alkoxide ion with a primary alkyl halide, allowing for the formation of asymmetrical ethers with varied R groups. Williamson ether synthesis is more versatile for creating a wider range of ether structures.