Organic Chemistry

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12. Alcohols, Ethers, Epoxides and Thiols

Making Ethers - Alcohol Condensation

Condensation reactions join two smaller molecules together to form a single, larger molecule.

  • Only forms symmetrical ethers


The Mechanism of Alcohol Condensation.

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so another way to make ethers is through a reaction called acid catalyzed alcohol condensation. So I know this sounds really complicated, but it's not that bad, as you guys will learn later in or go to. Ah, condensation. Reaction is simply a reaction that takes two molecules and makes them into a one bigger molecule. So I'm just gonna say it's a reaction that takes two smaller molecules, and then it turns them into one bigger molecule. Okay, that's the definition of condensation. So what we're gonna be doing here is we're gonna be taking to alcohol's. It's an alcohol condensation. Right? So we're gonna take to alcohol's we're gonna put them together, we're gonna condense them, and they're gonna turn into a one, either. Okay, so how does this work? Well, let me just go ahead and just draw the mechanism for you. So the way this works is you have alcohol in the presence of acid and heat, okay? And what's gonna wind up happening is that the acids gonna protein 81 of the alcohol. So let's go ahead and just draw this part really quick. I've got my h 30 plus that I'm gonna write like this because it's easier to the protein it that way. Same thing is H 30 Plus, I'm just writing it a little bit different. So my o h is going to grab an h from the acid and what I'm gonna wind up getting. If something looks like this, I have a protein needed alcohol now. Okay, now, what's gonna happen is that that protein ated alcohol just turned into a good leaving group. Water is a good leaving group, right? So my other equivalent of alcohol, the one that did not get protein ated, is gonna do a backside attack on this good leaving group. So we're basically going to get an s and two reaction where I get this attacking that carbon and kicking out the good leaving. So now we're gonna wind up getting is let me just draw in the same colors that I used the black alcohol that still has an H on it. Okay, but now that's gonna be attached to the two carbon Jane from the red alcohol. Okay, On top of that, there's gonna be a water that just left by itself. Does that make sense? So far, so we've got the black one attacking the red one. This looks like an ether, but we've got a problem. There's a formal charge. So what can we do about that formal charge? Remember, this is called acid catalyzed for a reason. That means that you always have to end up with the same amount of acid that you start off with because it's a catalyst that can't be consumed or destroyed in the reaction. So what that means is that I use the water to pick up the proton and what I'm gonna wind up getting at the end, is it gonna get ether? Plus the same age through, Plus that I started off with And there you have it. We just made it. We just condensed and ether out of alcohol. Now, there is gonna be a significant limitation for this synthesis. Okay, Can anyone tell me it's only in the yields a certain type of either. Okay. And actually, there's a typo here that I will correct in your notes. Things should not say alcohol's. It should say ethers. Okay, but it's going to form on Lee symmetrical ethers, Okay? And the reason is because we're always gonna be reacting acid in alcohol and you're gonna have an abundance of alcohol. So what that means is that one molecule is going to react with another molecule of the same alcohol, and you're gonna wind up getting the same are groups on both sides. So that's why I'm saying that it's symmetrical because you're always gonna get the same are groups on both sides. Sometimes you want that. But for example, if you wanted an asymmetrical ether, it has to be asymmetrical. Maybe Williamson ether synthesis would better be a better choice because that when it doesn't matter, you could just add our groups as you want. Okay, so let's move on and keep talking about ethers.