Hey guys. In this video, I'm going to teach you about the base catalyzed ester hydrolysis reaction, or better known as the saponification reaction. So guys, saponification is just a base catalyzed hydrolysis of an ester, meaning that if I have an ester, and I expose it to water and base as a catalyst, I'm going to hydrolyze that ester. Okay? Now we would expect to get a carboxylic acid, but if all you have is base present, you're actually going to yield a carboxylate anion. And that makes sense because there would be nothing around to protonate it. Okay? So in the absence of a protonation step, you actually should end up with an O negative carboxylate, or what's also called a carboxylate salt. Okay? Because it has that full negative charge. Okay? So just so you know, that is kind of like, you know, something that you should be aware of that you need the protonation step to get to the carboxylic acid. And now we're just going to go through the mechanism. I'm not sure if you've heard me say this before, but in general guys, in organic chemistry, a base catalyzed mechanism is always easier than an acid catalyzed mechanism. So this is actually going to be a very straightforward mechanism. Okay? Let's go ahead and assume that I'm going to be using, right, I'm using water and base, so I'm just going to use always negative. Okay? That's my base. And in my first step, I'm going to do a nucleophilic attack because, you know, this is already strong enough to attack that partial positive. I don't need to do a protonation and draw a resonance structure to make that carbon active, it's already active because I've got a negatively charged nucleophile. So boom and boom, I'm going to get a tetrahedral intermediate. We've seen this before. So I've got O negative, I've got OR, I've got OH, and I've got my carbon. Okay? Awesome. So then, we're going to go ahead and we're going to reform the double bond. We're not going to protonate because this is nucleophilic acyl substitution. This is a NAS reaction, right? So we're going to kick out a leaving group. Now which one do we kick out? Do we kick out the OH or the OR? Or the R group, and we could kick out the R, but that would be. So anyway, OH or OR? Well, it really depends on the way you want to draw it. Which direction you're trying to go in. Since I'm trying to go towards hydrolysis, I kick out the OR. Okay? So what that's going to give me is a molecule that looks like this. Now it's a carboxylic acid. So if you're thinking, oh, I did get a carboxylic acid. But no, because you're going to have OR negative around now, and that OR negative will deprotonate it. Okay? So then we're just going to get our carboxylate as a product. Okay? Plus alcohol. And that's where it ends. That's the end of the mechanism. Now, if you protonate it afterwards, then fine, you can get a carboxylic acid. But you need that protonation step to get there. Okay? So as you guys can see, super easy mechanism compared to the acid catalyzed version. So let's move on.
22. Carboxylic Acid Derivatives: NAS
Saponification
22. Carboxylic Acid Derivatives: NAS
Saponification - Online Tutor, Practice Problems & Exam Prep
When you hear "saponification"just know that this is a base-catalyzed hydrolysis of an ester. The mechanism and final product are slightly different. Let's take a look.
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PRACTICE PROBLEMS AND ACTIVITIES (15)
- D. N. Kursanov, a Russian chemist, proved that the bond that is broken in the hydroxide-ion-promoted hydrolys...
- The intermediate shown here is formed during the hydroxide-ion-promoted hydrolysis of the ester group. Propo...
- Predict the products and propose mechanisms for the following reactions. (b)
- Suppose we have some optically pure (R)-2-butyl acetate that has been 'labeled' with the heavy O-18 isotope at...
- Propose a mechanism for the base-promoted hydrolysis of γ-butyrolactone:
- (a) Explain why we speak of acidic hydrolysis of an ester as acid-catalyzed, but of basic hydrolysis as base-p...
- (b) Soap manufacturers always use base to hydrolyze fats, and never acid. Suggest two reasons that basic hydro...
- Predict the products of saponification of the following esters.(a) <IMAGE>
- Predict the products of saponification of the following esters.(b) <IMAGE>
- Predict the products of saponification of the following esters.(c) <IMAGE>
- (b) Would you expect methyl p-methoxybenzoate to undergo saponification faster or slower than methyl benzoate?
- What are the products of the following reactions? i. + NH3 excess —> j. + CH3OH excess HCl—>
- Propose a mechanism for the hydrolysis of N,N-dimethylacetamide (a) under basic conditions.
- Propose a mechanism for the hydrolysis of N,N-dimethylacetamide (b) under acidic conditions.
- Propose a mechanism for the basic hydrolysis of benzonitrile to the benzoate ion and ammonia.