Malonic Ester Synthesis: Videos & Practice Problems

Malonic ester synthesis is similar to acetoacetic ester synthesis, with the key difference being the presence of an additional OET group. Both reactions yield carboxylic acids upon hydrolysis. The reagents and mechanisms remain unchanged, allowing students to apply their knowledge from acetoacetic ester synthesis directly to malonic ester synthesis. Understanding this relationship simplifies the learning process and reinforces the concept of beta dicarbonyl compounds in organic synthesis.

General Reactions

Now we're going to take a look at the other form of beta dicarbonyl ester reactions, which is malonic ester synthesis. You see this chart, and you're thinking, "Oh my gosh, another set of reagents that I need to memorize," and you're probably getting depressed. But don't. This is the same exact thing as acetoacetic ester. Notice that every single reagent here hasn't changed. Nothing has changed. The only difference is that because I'm starting off with malonic ester, I have an extra OET group over here. What that means is that after I hydrolyze, not just this one turns into carboxylic acid. They both do. That means that the only difference between acetoacetic ester and malonic ester synthesis is that my products have carboxylic acids at the end. That's it. Everything else stays the same. You could literally take everything you learned from acetoacetic acid and, when you see malonic, just draw the same thing as acetoacetic acid and add the carboxylic acid at the end. I'm not even going to go over every reaction here because this is the same as acetoacetic ester. Let's go through this practice problem. Go ahead and try to solve it yourself, and then I'll step in and help.

Predict the Products

One word of caution here. If you feel like you couldn't get this question right because you're having a hard time interpreting this condensed structure, you probably need to go back and review condensed structures. Just saying because we're pretty late in Orgo 2 and they could show up anywhere. Condensed structures, I do have videos about them. If you need extra help, I got you. But anyway, the way you interpret this was it's a carbon with these 2 esters coming off of it. It would be COOET. That would be like that and like that. And then obviously it's CH₂, so I'm just going to put HH. Again, this is just another way to write malonic ester. The first step was my base. Do you think that this base was a good choice for this ester? Sure. The R group is the same. I don't have to worry about transesterification. The negative is going to grab one of the H's and make an enolate. I'm going to make something that looks like this. Now that enolate is going to be exposed to the following alkyl halide, something like this. Cl carbon carbon Just make sure I'm getting this right. CH₃₂ then CH₂. Yep, that's right. Then we're going to do a backside attack. What that's going to give us is now a malonic ester that is substituted And what's attached now is I have my new bond. Well, I want to use a different color. I have my new bond and then I have the thing that I attached. So 1, 2. I believe that's right. Wait. Making sure I think I'm actually off. Yes. It should actually be that is that and then that is that. Perfect. Just making sure it's not a bad idea to slow it down and make sure that What's important about hydrolysis here is that you're going to hydrolyze What's important about hydrolysis here is that you're going to hydrolyze both of your esters. That means that you're going to get carboxylic acid on one side and carboxylic acid on the other. You can't stop it. Plus your R group. Then finally, we have decarboxylation. You might be wondering how do I know which one to decarboxylate because we said that carboxylic acid can decarboxylate. It doesn't matter which one. You could either take off the green one or you could take off the red one, but you can't take off both. Pick 1, make it go away, the other one stays. Let's just say the red one leaves. That's going to give me a final compound that looks like this. O H carbon. What's that attached to? Carbon, carbon. 1, 2, 3, 1, 2, 3, something like that, plus my CO₂ gas. Notice that once again, I just did an alpha alkylation, but I used malonic ester to do it and notice that I have a carboxylic acid as the end product because I started off with malonic ester. I hope that made sense. It's not as scary as it looks. It's actually really fun. This is actually one of my favorite reactions students like it. That being said, let's move on to the next videos.

Provide the major product for the following reaction

• A.
• B.
• C.
• D.

Answer: (D)

Provide the major product for the following reaction

• A.
• B.
• C.
• D.

Answer: (A)

Here’s what students ask on this topic:

What is the malonic ester synthesis?

Malonic ester synthesis is an organic reaction used to synthesize substituted carboxylic acids. It involves the alkylation of malonic ester (diethyl malonate) followed by hydrolysis and decarboxylation. The key feature is the presence of an additional OET group, which results in the formation of two carboxylic acids upon hydrolysis. This reaction is similar to acetoacetic ester synthesis, with the main difference being the final product containing carboxylic acids.

How does malonic ester synthesis differ from acetoacetic ester synthesis?

Malonic ester synthesis differs from acetoacetic ester synthesis primarily in the starting material and the final product. In malonic ester synthesis, the starting material is malonic ester (diethyl malonate), which has an additional OET group. Upon hydrolysis, both ester groups are converted to carboxylic acids. In contrast, acetoacetic ester synthesis starts with acetoacetic ester and results in a product with one carboxylic acid and one ketone group. The reagents and mechanisms for both reactions are otherwise similar.

What are the steps involved in malonic ester synthesis?

The steps involved in malonic ester synthesis are: (1) Deprotonation of malonic ester using a strong base to form an enolate ion. (2) Alkylation of the enolate ion with an alkyl halide to introduce the desired alkyl group. (3) Hydrolysis of the ester groups to form carboxylic acids. (4) Decarboxylation of one of the carboxylic acids to yield the final substituted carboxylic acid product.

What reagents are used in malonic ester synthesis?

The reagents used in malonic ester synthesis include: (1) A strong base such as sodium ethoxide (NaOEt) or sodium hydride (NaH) for deprotonation. (2) An alkyl halide (R-X) for the alkylation step. (3) Aqueous acid (H₃O⁺) or base (NaOH) for hydrolysis of the ester groups. (4) Heat for the decarboxylation step to remove one of the carboxylic acid groups.

Can you provide an example of malonic ester synthesis?

Sure! Let's synthesize 2-methylbutanoic acid using malonic ester synthesis. (1) Deprotonate diethyl malonate with sodium ethoxide to form the enolate ion. (2) Alkylate the enolate with 1-bromopropane to introduce the propyl group. (3) Hydrolyze the ester groups with aqueous acid to form malonic acid. (4) Heat the malonic acid to decarboxylate one of the carboxylic acids, yielding 2-methylbutanoic acid.