The intermediates for the Swern oxidation, a reaction introduc...

Question

The intermediates for the Swern oxidation, a reaction introduced in Section 13.9.4, are shown. Provide the arrow-pushing mechanism that rationalizes the formation of each intermediate and the final product(s).

Accepted Answer

All right. Hello everyone. So this question is asking us to draw the mechanism of the given reaction that rationalizes the intermediate and the product formation. So in this diagram that we're given, we are shown basically an example of what's known as the Coy Kim oxidation. And so in the Coy Kim oxidation, we have dimethyl sulfate reacting with cl two. And both of these compounds will react with a secondary alcohol to ultimately produce a ketone, which we do see at the very end of the given scheme here. So let's go ahead and showcase how that happens. Now, the first step is actually going to be a reaction between dimethyl sulfide or dimethyl sulfate and cl two. So one of the lone pairs of electrons on sulfur is going to be used to establish a bond between sulfur and one of our chlorine in co two. And so this is also going to establish the formation of a chloride ion as a by-product. So the first step is complete right in our intermediate up to this point is known as chloro dimethyl sulfo because due to the extra bond that we have to chlorine sulfur now has a positive charge. Now, it's also worth mentioning that because we formed a sium ion that has a positive charge, the chloride ion formed earlier would behave as a counter ion. So just to point that out in any case, though, now, in the second step, we can introduce our secondary alcohol and our secondary alcohol happens to be see here, two copal fn 10. So here's our psychlo penal group. All right. So now we have an interaction between our secondary alcohol and our sium ion. So in this particular case, the oxygen of our alcohol is going to behave as a Nile. So one of its lone pairs of electrons is going to establish a bond between itself and sulfur. Now, at the same time that this is happening, the bond between sulfur and chlorine is going to break to make sure that sulfur doesn't have too many electrons attached to it at once. All right. So here, now we have an established bond between oxygen and sulfur. So here's our hydroxy group where oxygen is now attached to sulfur. And so first still has a positive charge, right? Because we still have those two methyl groups present in the beginning in one loan pair of electrons. But at this point, we have a new issue, right? Because now oxygen also has an additional bond this time to sulfur. So oxygen now has a positive charge as well, which is not favored for oxygen, right? So our next step is going to be dep pronation. Now recall that we have formed chloride ions earlier in this mechanism earlier in the reaction. And so one of our chloride ions is going to go ahead and remove that proton from oxygen, creating HCL and also making oxygen neutral. So here's oxygen, this time neutral connected to sulfur stew and sulfur still has a positive charge. So we have that and also, as mentioned before HCL is a by product. All right. So at this point, our intermediate is starting to look a little bit more like our final ketone product, right? Because now the hydroxy oxygen of our secondary alcohol no longer has a hydrogen attached to it. So at this point, the goal of these sub subsequent steps is to break the bond between oxygen and sulfur or in this case, the Sophon mayo because it has a charge. But in any case, right, for this next step, we're going to introduce an additional reagent, which in particular is triethyl amine. So because triethyl amine is a base, right? It's going to do what bases do and it's going to remove a proton. But the question is from where? Well, in this particular case, trophy amine is actually going to remove a proton from one of the methyl groups that makes up our sulfon ion. So one of the methyl groups attached to sulfur. So here I'll just be showing that and this is actually going to result in a carb anion which will be relevant in the next step. So here's oxygen. I just want to improve my drawing of the ring for a second there. All right. So at this point, as mentioned before, we now have a carbon ion attaching to sulfur and because it's a carbon on carbon has an additional loan pair of electrons. And so now we've arrived at the final step. And so the idea is to ultimately establish or ultimately create a car bal for our ketone product or it's actually an aldehyde. So just to correct myself, very quick, apologies for the confusion, this is actually going to form an aldehyde because our starting material is a primary alcohol. But in any case, at this point, our carbon ion is going to go ahead and remove a proton specifically from the carbon attached to our oxygen. Because once that happens, the lone pair of electrons initially between carbon and hydrogen is going to establish a double bond between itself and oxygen. And so once that happens to make sure that oxygen doesn't have too many bonds at one time, right, the bond between oxygen and sulfur is going to break. And so that's how we ultimately get dimethyl sulfide once more and also our aldehyde product just to correct myself from earlier and there you have it right. So now our mechanism is complete. So with that being said, if you watch this video all the way through, thank you so very much for doing so. And I hope you found this helpful.

The intermediates for the Swern oxidation, a reaction introduced in Section 13.9.4, are shown. Provide the arrow-pushing mechanism that rationalizes the formation of each intermediate and the final product(s).

Key Concepts

Swern Oxidation

Arrow-Pushing Mechanism

Reaction Intermediates

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