Alcohol Synthesis - Video Tutorials & Practice Problems
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Up to this point in the course, we’ve learned 4 methods to make alcohols. This will be a brief review of those methods.
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concept
Forming alcohols through Oxymercuration-Reduction.
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in this section, we're gonna talk a lot about alcohols. So it's important for us to take a minute to remember all the different ways that we can make alcohol's from prior chapters. So let's go ahead and get started. It turns out that there are four different ways that we've already learned to make alcohols. And I'm gonna go ahead and remind you of what those are now. So let's say that I have a double bond and I'm trying to add ah hydroxyl group to it, okay? And I want to add it specifically in this position. Okay, What addition? Reaction could I use to put a hydroxyl right on that secondary position? The answer is that there's only one reaction that could yield this kind of alcohol. And that would be oxy, Mercury ation or what? We just called Oxy Mark. Okay. Why is that? Because if you remember, Oxy, Mercure ation is in addition reaction that adds Markov nick off alcohol, which is good because you could tell that that is the Markov Nick off Orme or substituted location. Okay, but there's another thing of that special vault oxy Merck, which is that there's no carbon cat ion in the intermediate. Okay? And remember that Carvell Catalans have a tendency to do what they shift. Okay, so in this case, this is an example of where I can admire Kalashnikov alcohol without worrying about a rearrangement. Okay, so now all I have to do is fill in the re agents for Oxy Merck. Does anyone remember them? Well, basically, we would have is some kind of mercury molecule, so B h g Oh, a C two. Okay. And then what we would put with that is water. Why is that? Because we want to show specifically that we're using water to add the alcohol. Okay, on the bottom of the arrow. Then we did the reduction step. Remember that the full name of this reaction is oxi mercury ation reduction. The reduction is, um, is completed by N A B H four, which later on we will learn is a reducing agent and a base. So any wage. Okay, those are the re agents. I know it looks like a lot, but we you know, we have been over this before, and this is one of the ways that you can add alcohol toe a double bond. Alright, so we've been over one of the four ways. But let's keep going because it turns out that there's a lot more that we could do to a double bond.
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concept
Forming alcohols through Hydroboration-Oxidation.
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So what if we take that same double bond? But we want to add the alcohol here instead. Okay, notice that in this molecule I have the alcohol on the least substituted position. Doesn't remember what kind of reaction that would be. Well, it's gonna be another edition reaction, but has a completely different name. This is hydro operation. Okay, remember, hydro operation is really unique because it's gonna be the Onley anti more cognitive way we have toe add alcohol or going to the least substituted position. Okay, so let's just go ahead and remember what the re agents were. Does anyone remember? It was really hydro beret. Shin means that you need boron in there. And it was really gonna be any boron source, most commonly bh three. But your professor, your textbook may use a different source of boron. There's all kinds of different sources that we can use and B h three and many times I'll be complex to th f. Okay, but sometimes you won't see that step. But sometimes th s th f is a solvent, so it's not absolutely required that you write that. Okay, but sometimes you'll see it. And that's the That's it for the top. The top is just adding boron. OK, the bottom is the oxidation step because remember that it's hydro gration oxidation. What's for those regents in that was hydrogen peroxide and once again, a base. Okay, so those are the re agents that could generate an ante Markov Nankov alcohol from a double bond.
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Forming alcohols through Acid-Catalyzed Hydration.
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cool. So we've gone over two ways. Now, let's go on to the next one. The next one noticed that. Let's say that I start off with that double bond, but now what I wind up getting is an alcohol not in the secondary position, but in the tertiary position. Okay, that's kind of odd and notice that the Taliban used to be here. But now my alcohol isn't even attached where the double bond was before. Okay, any clue what this might be? This is also gonna be a Markov Nick off edition, but it's a Mark Kafelnikov addition that also has a carbon Karen in the intermediate. So what, this in the reaction. So what this means is that this is gonna have to be an acid catalyzed hydration. Sorry. Acid dash catalyzed hydration. There we go. And the re agents for this one were much easier. It was really just any strong acid. So I'm just gonna put here h a over water. But most commonly, the asset that we would use a sulfuric acid. So most commonly, what you're gonna see is, um, like h 20 over h two s or the other way around to both are fine. Okay, so that's that's usually what you would see on. Remember, what that's going to do is it's gonna add a water, but it's gonna add it to the most stable location, which is the one that is created tertiary position that's created after it shifts. Okay, so those are the three different ways that we have to make alcohol from. In addition, reaction. And this is just meant to be an overview of the reactions that we've already learned. Okay, if you need to brush up on your edition reactions, I would recommend to go to the addition Reactions chapter And I always teach all these three in a row as well, so you'll be ableto really learn the full mechanisms and catch up on some of the stuff that you might be rusty on.
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concept
Forming alcohols through SN2 reactions.
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So now let's go to this last way to generate alcohol that we've learned in the past. And this one's actually really easy. Okay, notice that what I have here is an alcohol. Hey, lied. And at the end, I haven't alcohol. There is a dead giveaway as to what this reaction might be because I have stereo chemistry given. And what I'm showing is that the halogen used to be on a wedge towards me. And after reaction, the alcohol is going to be on a dash away from me. So does anyone know what kind of reaction might invert the stereo chemistry? That would be s N two. Okay, so it turns out that we can generate alcohol's through s and two reactions, but it's Onley in some specific situations. Basically, it's when you haven't, uh, alcohol. Hey, light that is open to backside attack. That would be basically, um, a a metal, A primary or secondary. Al Kyohei lied because remember that tertiary These are just two backed up. They can't do a backside attack. And I need my nuclear file to be anyway. H okay. And if I can use anyway h what? I'm gonna wind up. Getting is a backside attack where I kick out the X and I wind up getting my alcohol. All right, so these are the four commonly used methods to make alcohol. This is all intended to be somewhat of a review for you guys of reactions that hopefully you've already talked about. But if not, I would just encourage you to reference those chapters. You can get a little bit more of a feel of what's going on, all right?