Cope Elimination - Online Tutor, Practice Problems & Exam Prep

The Cope elimination is a concerted mechanism involving the oxidation of amines to form tertiary amine oxides, which can self-eliminate to yield Hofmann products, characterized by less substitution. This process involves a transition state where a dative bond forms between nitrogen and oxygen, facilitating the elimination of a hydrogen atom and the creation of a double bond. The reaction produces hydroxylamines as byproducts, but the focus remains on the Hofmann product, essential for understanding elimination reactions in organic synthesis.

General Reaction

Hey guys. In the next few videos, we're going to discuss a really unique type of elimination reaction called the Cope elimination. So, guys, it turns out that amines are really easily oxidized even by weak oxidizing agents. In fact, if you just leave some amine on your bench at the laboratory and it's exposed to open air, even just the O₂ gas that's in room air is enough to oxidize amines into hydroxylamines and even amine oxides.

It turns out that tertiary amine oxides are capable of doing something called a self-elimination and making an elimination product, specifically a Hofmann product. Now, it might have been a long time since we did elimination but hopefully, you guys can remember there was a Zaitsev product and a Hofmann product. The Hofmann product being the one that was the less substituted. We're going to be forming less substituted elimination products through a covalamine. Now there's a little bit of theory you want to get into beforehand just in case you read it in your textbook. At least I explained it to you one time.

So it turns out that first of all, anything that is a tertiary amine oxide can also be referred to as an N-oxide. That just makes sense. You're saying that there's an oxygen coming off of an N. That would be basically, let me just circle it for you. That would be this kind of structure right there. You got an O directly attached to N. But what we notice is that there's a really weird type of bond there.

Notice that I have an arrow pointing to the O which is something that we won't really talk about a whole lot in organic chemistry at the college level, right? But that contains what's called a dative or a dipolar covalent bond. What does that exactly mean? Let me just define that in case you forgot or in case you've never heard of this before. It's a covalent bond. That means that there is equal sharing of electrons. It's a strong bond. It's covalent just like any other covalent bond you learned about. But we call it dipolar or dative because you've got 2 charges that are separated on that bond. You've got a positive and a negative. Notice that they never go away. You got your positive, you got your negative and it's known as dipolar because one of the species is the one that's giving its electrons away to the other. In this case, we know that the nitrogen has a very nucleophilic basic lone pair, so it's going to go ahead and donate that lone pair to the oxygen forming that dative bond. Now it could very well be denoted just as a straight line because as you guys know, covalent bonds are always just drawn as a stick. You could just draw it as a stick. That would be fine. But in some texts, it's denoted as an arrow. It would be nitrogen arrow oxygen which for the purposes of this class, I just want you to recognize as a bond. This is going to be a covalent bond just like any other bond. Awesome. Now I just cleared that out of the way so we can talk about the reaction and the mechanism.

First of all, before we go into the mechanism, let's just look at the general reaction. What we've gotten is an amine that we're first going to oxidize. This is hydrogen peroxide. So hydrogen peroxide, not the strongest oxidizing agent. But I just told you guys, even O₂ gas, just room air is enough to oxidize an amine. So definitely, hydrogen peroxide can. What you're going to form is that dative tertiary amine oxide or the N-oxide. Now what's special about these guys is that N-oxides can self-eliminate.

So what we're going to wind up getting is in heat, heat is going to wind up separating these and you're going to wind up getting a Hofmann Alkyne. So you can see that basically we had 2 options. We could have either gone in the red direction here or in the blue direction here. We went with the less substitu

Predict the Product

All right. Hopefully, you're able to recognize that this is first of all a cope elimination. Why? Because I've got a tertiary amine. I've got an oxidizing agent which is usually hydrogen peroxide and then I'm adding heat to favor elimination. Now remember, I didn't really get to mention this in the mechanism above. But why does heat favor elimination? You guys remember that? It had to do with entropic effects. It had to do with the fact that when you eliminate, you're creating more particles and you're increasing entropy. As you guys remember from Gibbs free energy, heat is going to favor high entropy. That's why we always go towards an elimination reaction the more you jack up the heat. Just a little bit of theory there. We've got our oxidation. We've got our heat. What does this look like? Well, the first step is going to be to add the O.

Now just so you guys know, I also didn't get to mention this in the prior video that the oxidation step is a mechanism that is not well

Here’s what students ask on this topic:

What is the Cope elimination reaction in organic chemistry?

The Cope elimination is a unique type of elimination reaction where tertiary amine oxides undergo self-elimination to form alkenes, specifically Hofmann products, which are less substituted. This reaction is concerted, meaning it occurs in a single step with a transition state. The process involves the oxidation of an amine to a tertiary amine oxide, which then eliminates a hydrogen atom and forms a double bond. The reaction produces hydroxylamines as byproducts, but the primary focus is on the formation of the Hofmann product.

What is the mechanism of the Cope elimination reaction?

The Cope elimination mechanism is concerted, meaning it occurs in one step. It starts with the oxidation of a tertiary amine to form a tertiary amine oxide. This amine oxide then undergoes a self-elimination process. The oxygen in the amine oxide attacks a hydrogen atom, forming a transition state where a double bond is partially created. This transition state collapses, resulting in the formation of an alkene (Hofmann product) and a hydroxylamine byproduct. The reaction is driven by heat and involves a dative bond between nitrogen and oxygen.

What are Hofmann products in the context of Cope elimination?

In the context of Cope elimination, Hofmann products are the less substituted alkenes formed as the main products. During the elimination process, the reaction favors the formation of the less substituted double bond, which is the Hofmann product. This is in contrast to the Zaitsev product, which is the more substituted alkene. The preference for Hofmann products is due to the steric hindrance and the nature of the transition state in the Cope elimination mechanism.

What role does the dative bond play in the Cope elimination reaction?

In the Cope elimination reaction, the dative bond (also known as a dipolar covalent bond) between nitrogen and oxygen is crucial. This bond forms when the nitrogen donates a lone pair of electrons to the oxygen, creating a strong covalent bond with separated charges. This dative bond facilitates the self-elimination process by stabilizing the transition state and allowing the oxygen to attack a hydrogen atom, leading to the formation of the double bond and the Hofmann product.

What are the byproducts of the Cope elimination reaction?

The primary byproduct of the Cope elimination reaction is hydroxylamine. During the elimination process, the tertiary amine oxide undergoes self-elimination to form an alkene (Hofmann product) and hydroxylamine. The hydroxylamine is formed when the oxygen in the amine oxide attacks a hydrogen atom, resulting in the release of the nitrogen and the formation of a hydroxyl group attached to the nitrogen. While the focus is on the Hofmann product, the hydroxylamine is an important byproduct of the reaction.