Phenol oxidation can be coupled with other reactions to form n...

Question

Phenol oxidation can be coupled with other reactions to form new C―C bonds using reactions studied previously. Predict the product of the following series of reactions.

(a) Chemical reaction diagram showing phenol oxidation with H2CrO4 and heat to predict product formation.

Accepted Answer

Alright, hello everyone. So this question is asking us what is the product of the reaction given below? So our starting material is hydroquinone reacting first with chromic acid that's H two cro four followed by 23 dimethyl cyclopentolate, two equivalents of it. So because we have multiple steps in this particular reaction, it's important to take it step by step, right? Understand what product is being formed in between before talking about the second reaction. So a short material as mentioned before, it is hydro quinone and hydroquinone is specifically a phenol, right? Because we have a hydroxy group attached to a benzene ring, there are two of them in this case. And so our first step is going to be the oxidation of this phenol using chromic acid. Again, that's H two cro four. So how does that happen? Or rather what happens in the oxidation of a phenol? So recall that the reason why the oxidation of a phenol requires such a powerful oxidizing agent such as chromic acid is because the reaction itself inherently breaks the aromatic of the pol. So here we have a para hydro quino and the reason I say that is because the two hydroxy groups are on opposite sides of the benzene ring, hence, they are per to each other. And so if the starting material is an Ortho hydroquinone or a pera hydroquinone, like this one, both hydroxy groups will be turned into carbos. So here I would redraw the ring. But the difference is that now the ring is no longer aromatic. This time around, we have two car bles on opposite sides of the ring. And the ring itself is turned into cyclohexane, 14, if you take out the oxygens. So we have two double bonds in between the two carbons that are not part of the car bottles themselves. So our intermediate now is benzoquinone and it's benzoquinone that we have to consider when talking about the second part of the reaction. So here we have Benzo Quinon this time reacting with two equivalents of a conjugated diet because notice how our second starting material, our second reagent that is 23 dimethyl cyclopia, 139 has two double bonds inside of the ring separated by one single bond in between them. And it's in the S sis configuration because the double bonds are on the same side relative to the single bond in between them. Now, we have that and benzoquinone itself is an all keen, not only is it an all keen, it's an all keen with electron withdrawing groups attached to it. That is the car bals themselves. This means that benzoquinone itself is a dying or file. And our reagent force step two of this overall reaction is a diet. All this is to say, right, that step two is it deals all the reaction. Now, benzoquinone is symmetrical, right, which means that we have two double bonds to consider two keen groups. So we have two walks and two equivalents of our diet. And so what that means is that dies, alder is going to take place on both sides of benzoquinone itself because it has two diets. So for the purposes of illustration, I'm going to draw how the first deals all the reaction takes place and then I'm just going to draw the second equivalent in. So recall that deal's older is a heat catalyzed concerted cycle edition. So to illustrate how this happens, I'm going to go ahead and draw in one equivalent of the dying. Now, it's also worth mentioning that the dying itself is part of a five member ring. And so because the fifth carbon of the ring is not going to participate in the reaction, it's going to be a bridge. So I'm going to draw that one additional carbon above the dying itself because it's not participating in the reaction. So how exactly does this happen? Right. Recall that deals alder is the concerted movement of six electrons to establish a new six member ring. So for the purposes of this discussion, let's label the two carbons of the dying itself that is the akin one and two. And so the four carbons of the dying, the four carbons of the dying, I'm going to label 345 and six. So just to be clear in case I misspoke by accident, the two carbons of the dienno that is the akin of benzoquinone are labeled one and two and the four carbons of the dying itself are labeled 345 and six and I'm numbering them in a circular pattern just so we're clear. All right. So now, basically what's going to happen is that the pi electrons involved in our system are going to move to establish connections in between these atoms. So at the same time that the pi bond between carbons one and two attack carbon number three, the pi bond between carbons three and four moves in between carbons four and five. And then that means that the pi bond between carbons five and six moves in between or rather moves to connect carbon six to carbon one. So as a result, right, we end up with a new six membered ring in addition to the ring from benzoquinone staying the same. So this time, there should be a double bond in between the carbon that I labeled four and five. And I also forgot the methyl groups. So let me just go ahead and add those. And we also have to consider our bridge which is still going to be present. All right. So this was the first deals alder reaction, right? The same thing is going to happen on the other side, which means that our product is actually going to be a structure with three fused rings in the center, we have the ring from benzoquinone. And then on either side, we have one more ring again, one on each side, from both deals all the reactions and both of the outer rings have one bridged carbon. And so there you have it, here is the structure of our final product. And so with that being said, thank you so very much for watching. And I hope you found this helpful.

Phenol oxidation can be coupled with other reactions to form new C―C bonds using reactions studied previously. Predict the product of the following series of reactions.
(a)

Key Concepts

Phenol Structure and Reactivity

Oxidation Reactions

C―C Bond Formation

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