Cleavage of Phenyl Ethers - Online Tutor, Practice Problems & Exam Prep

Acidic cleavage of phenyl ethers involves treating them with strong acids like HBr or HI, resulting in the formation of phenol and an alkyl halide. The ether's oxygen becomes protonated, making it susceptible to nucleophilic attack, leading to the cleavage of the ether bond. Unlike regular ethers, phenyl ethers do not yield further alkyl halides due to the stability of phenol. This reaction highlights the unique properties of phenols and their resistance to further reactions under acidic conditions.

Cleavage of Phenyl Ethers Concept 1

Hey, everyone. So in this video, let's talk about the acidic cleavage of phenyl ethers. Now recall when an ether is treated with HBr or HI, it will undergo acidic cleavage. Here, the difference now is we're dealing with a Phenyl ether. We're going to say the products of acidic cleavage of phenyl ether will always produce phenol as a product plus an alkyl halide.

Up to this point, we knew that excess acidic cleavage could change an ether into 2 alkyl halides at the end. Because of the special properties of phenol, once we get to phenol, it would not undergo further reaction to make an alkyl halide. It would stay in its phenyl state. If we take a look here, we have our phenyl ether. We're using HX, so that could be HBr or HI.

We know that this oxygen would grab an H⁺ from our acid becoming protonated. Because it's protonated now, it's susceptible to nucleophilic attack. This alkyl halide would come in and it would have to hit the carbon, the ether carbon tha

Cleavage of Phenyl Ethers Example 1

Hey, everyone. So here it says, provide a mechanism for the acidic cleavage of propoxybenzene. Alright. So benzene is our conjugated ring. Propoxy, so that's oxygen connected to a propyl group, so 3 carbons.

Here we're doing acidic cleavage, let's say we're using HBr as our strong acid of choice. Now, remember what's going to happen here is oxygen is going to grab an H⁺ from our acid, and what we're going to get here is our protonated oxygen. It's making 3 bonds, so it's positively charged. At this point, normally, we would look and see what kind of ether, oxygens, and carbons I'm dealing with to decide which one gets attacked by the incoming halogen.

But because this is a phenyl ether, we don't have to worry about that. The incoming nucleophile will always, always attack the ether carbon that is not part of the benzene ring. So, here, this bromine is going to come in, it's going to hit the ether carbon, this carbon because it's not part of the benzene ring. Because remember, you can either hit this carbon or this carbon. They're the ether carbons.

So we hit that carbon there which causes this bond to break and go to oxygen. This ensures that we're going to make phenol as a product, plus we're going to make our alkyl halide. Okay. So then here goes our alkyl halide. These will be our 2 final products for this particular acid or acidic cleavage of propoxybenzene.

Alright. So just remember, when it's phenyl ethers, it's pretty straightforward. Acidic cleavage will always make a phenol product plus an alkyl halide product.

Predict the product formed from the following acidic cleavage reaction. 

Alright, everyone. So here in this practice question, it says, predict the product formed from the following acidic cleavage reaction. So here we're dealing with a Phenyl ether and we're reacting it with excess strong acid in the form of hydroiodic acid. Now remember, when it comes to a Phenyl ether, our products will always be a Phenol plus an Alkyl halide. So here, this is our ether carbon that's part of Benzene. It has to be what's produced at the end in the form of phenol, so it's an OH group attached to it, plus, and then this ether carbon, it's going to gain the halogen. The halogen in this case would be the iodine. So here, the iodine would attach to it. And here's the thing. The iodine when it attaches, it could attach in one of two ways. Right? It could have come from the top, or it could come from the bottom. And because of that, there's a possibility of two answers. So maybe iodine attaches this way or iodine attaches this way where this bond is wedged and this becomes dashed. Both are possibilities. You have to show both. So you'd have a like a racemic mixture of these two alkyl halides involved because you're attaching a halogen to a chiral center. Right? It becomes chiral when it attaches. Right? So these will be our products. We have our phenol that has to be created plus our two alkyl halides. Alright. So these would be our final answers.

Determine which of the following choices represents the major product from the following reaction. 

• A.
• B.
• C.
• D.

Choose the correct chemical sequence necessary for the following synthesis. 

• A. 1. HBr (xs)/ heat2. KOH3. Benzyl bromide
• B. 1. HI (xs)/ heat2. KOH3. Bromobenzene
• C. 1. H₃O⁺2. Br₂ / FeBr₃3. NaOEt
• D. 1. HI (xs)/ heat2. Benzyl bromide3. KOH

Here’s what students ask on this topic:

What is the mechanism of acidic cleavage of phenyl ethers?

The mechanism of acidic cleavage of phenyl ethers involves several steps. First, the ether oxygen is protonated by a strong acid like HBr or HI, making it more susceptible to nucleophilic attack. The protonated ether then undergoes nucleophilic attack by the halide ion (Br^- or I^-), targeting the carbon atom bonded to the oxygen that is not part of the benzene ring. This attack leads to the cleavage of the C-O bond, resulting in the formation of phenol and an alkyl halide. The phenol remains stable and does not undergo further reaction under these conditions.

Why does phenol not undergo further reaction in the acidic cleavage of phenyl ethers?

Phenol does not undergo further reaction in the acidic cleavage of phenyl ethers due to its stability. The aromatic ring in phenol provides resonance stabilization, making the phenol less reactive towards further nucleophilic attack. Additionally, the hydroxyl group in phenol is less likely to be protonated under the reaction conditions, preventing further cleavage. This stability ensures that phenol remains as one of the final products in the reaction.

What are the products of the acidic cleavage of phenyl ethers?

The products of the acidic cleavage of phenyl ethers are phenol and an alkyl halide. When a phenyl ether is treated with a strong acid like HBr or HI, the ether bond is cleaved, resulting in the formation of phenol (C₆H₅OH) and an alkyl halide (R-X, where R is the alkyl group and X is the halide, either Br or I). The phenol remains stable and does not undergo further reaction.

How does the presence of a benzene ring affect the cleavage of phenyl ethers?

The presence of a benzene ring in phenyl ethers significantly affects the cleavage process. The aromatic ring provides resonance stabilization to the phenol product, making it less reactive towards further nucleophilic attack. This stabilization ensures that once phenol is formed, it does not undergo further reaction to form additional alkyl halides. The benzene ring's stability is a key factor in the unique behavior of phenyl ethers during acidic cleavage.

What role does the protonation of the ether oxygen play in the cleavage of phenyl ethers?

The protonation of the ether oxygen is a crucial step in the cleavage of phenyl ethers. When the ether oxygen is protonated by a strong acid like HBr or HI, it becomes more electrophilic and susceptible to nucleophilic attack. This protonation increases the positive charge on the oxygen, weakening the C-O bond and facilitating its cleavage. The nucleophilic halide ion (Br^- or I^-) then attacks the carbon atom bonded to the oxygen, leading to the formation of phenol and an alkyl halide.