Concept: Concept: General Reaction3m
On this page, we’re going to discuss a reaction called transesterification.
Base-catalyzed transesterification occurs when an ester is exposed to an alkoxide base with a dissimilar alkyl group. If I’m using an alkoxide base, let’s say that I was in a basic environment because it’s base-catalyzed. Imagine that my alcohol instead of having an R group, the R group that I have on my alkyl group, I have R prime. R prime just means different. It's something different, maybe one is a methyl and one is an ethyl. What’s going to wind up happening is after it reacts, we're going to wind up getting another ester. It seems like nothing changed but wait, the R group is going to be different. I’m going to get one R group transferring with another or substituting with another. This happens because in equilibrium, all these OR groups are going to be constantly substituting back and forth and back and forth.
If you have different alkyl groups in different positions, they’re going to wind up blending together and you’re going to wind up getting OR groups of both types on your ester. That’s very problematic because when you have an ester, you want to make sure that it has all the same alkyl group. You don't want a bunch of different random alkyl groups. There is one way this can be avoided. The way this can be avoided is simply to only expose esters to alkoxides with the same R group. Imagine that now I have let's say R1 and I’m exposing it to an alkoxide that is OR1 negative. What's going to happen? In equilibrium, it's going to switch and it’s going to do this whole mechanism that I’m going to show you. But are we going to be able to actually tell that it's happening? The answer is no reaction in terms of ‘Does it have any effect on my product?’ No, because I am going to get substitutions taking place. But since my R groups are identical, I won't be able to notice this difference. I won’t be able to notice that a reaction is actually taking place because it's not really mattering for my reaction. The only time it would matter is if I have a different R group. Let’s say it was R1 and R2, now I’m going to get a mixture of R groups transesterifying. In this next video, I’m going to show you guys the mechanism and heads up, it’s easy.
Concept: Concept: General Mechanism3m