21. Enolate Chemistry:Reactions at the Alpha-Carbon
Haloform Reaction
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Haloform Reaction
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Alright, guys. So the Hala form reaction is simply a base catalyzed Alfa halogen nation of metal key tones. Okay, so it's the same thing as based catalyzed alcoholic nation, except that you specifically have ah, metal ketone. Let me show you the mechanism. So, guys, the re agents are just the same as we were dealing with before. The only difference being that I'm starting with a t least one metal group on one side. Okay, what's gonna happen is after the formation of your in late and attacking the exes, you're gonna get a poly halogen ated Alfa Carbon, Okay, makes sense so far. But here's the deal. If you have a metal key tone, you've now made an awesome leaving group because you have C X three. So the next equivalent of base that reacts instead of just sitting around and be like, Hey, I've got nothing else to holiday me. I'm done. The next equivalent can actually go through an n a s mechanism and they conform a tetra hydro intermediate. So what you would get is a tetra Hydro intermediate that looks like this o negative O h r c x x x and guys carbon is usually not a good leaving group, but a carbon with three ha Logins is an extremely good leaving group. So then I would kick out the c X three. Okay. And what that's gonna give me is let me just draw over here that's gonna give me carb oxalic acid crazy. Right? So it's gonna give me carb oxalic acid. Plus it's gonna give me see x three Negative. Okay, Now I know my head's in the way a little bit, but then toe end this reaction. The c X three negative is gonna deep protein, eighth e acid because it's an acid, right, And you're gonna wind up getting a car Boxley and the molecules that the reaction is named for Hala form Hala form is just basically a metal group with three hydrogen replaced with Callejon's. Okay, So the entire idea behind Hala form is that the Alfa Carbon of this reaction is transformed into a good leaving group through successive hallucinations and eventually the O. H negative just kicks it out entirely, which is something that would not happen in a base catalyzed mechanism. Without it, because of a base were toe attack here, it would have nowhere to go because there's nothing to kick out. It doesn't have a good leaving group, But on this reaction, it does have elite good leaving group. Which is why you get the final products. Okay. No guys, just extra fax. How form? It depends on what you're using. If it was chlorine Centobie chloroform, right. If it's iodine, that would be iota form. And some of these end up being test that you actually use in your chemistry lab Thio test for methyl ketone. So ah, lot of times iota form will precipitate out of the solution and it will be a It's like a yellow precipitate. And it's a test to see if you had a metal key tone. Because if you have that precipitate, that means that you formed iota form, which means that you had a metal group on your ketone. Interesting, right? Cool guys. So let's move on to the next reaction
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Problem
ProblemProvide the major product for the following reaction.
A
B
C
D
Additional resources for Haloform Reaction
PRACTICE PROBLEMS AND ACTIVITIES (3)
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