Synthesize the dye shown starting with aniline and naphthol us...

Question

Synthesize the dye shown starting with aniline and naphthol using reactions from Chapters 23 and 24. [Hint. Start by identifying how each substituent might be installed and then plan the order of their introduction.]

Accepted Answer

All right. Hi, everyone. So this question says to synthesize the following compound using toluene and nap as the starting reagents hint identify the substituents and the order in which they can be added to each reactant. So recall here that our starting material to the left is tallow and the one to the right side here is nathal. So when we consider the structure of our final product, we can see that the one ring structure that's to the left side comes from Tween, whereas the two ring structure on the right side must come from napfa. And so when we consider what is linking the two together, the nitrogen double bound to another nitrogen indicates that this is going to be an example of diazo coupling. And in addition to diazo coupling, there are a few different substituents on the benzene ring or the Aromatic ring of Toleen as well as a carboxylate group on one of the rings here in NAL. Now, the substituent on our toy ween, if you recall can be added via electrophysics substitution or eas for short and the carboxylate group, a Nepal here can be added via the Kobe reaction. However, one thing that's worth noting about the Kobe reaction is the most stable location in which the carboxylate group can attach itself to. And if we consider the structure of nap thal, right, the most important resonance structure of the carbon ion involves the one where the aromatic ring is not actually compromised. So when we consider this oops after I fix this ring for a moment here, if we consider the most important resonance structure or Nal in a Kobe reaction, the carbon ion should be on the Ortho position relative to the car bono here. That is actually closer to the second ring structure because that way the aromatic ring is never destroyed. However, that's actually where Diazo coupling is taking place, right? Because notice how our Diazo group is attached to that same Ortho position here. So therefore, Diazo coupling has to occur first so that the Colby reaction product does not take the Ortho position where our Diazo group is, right. So Diazo coupling is going to happen first. So what we can do first right is we can take our tolly Ween and proceed with our electro pilic aromatic substitution. So that we end up with all of our substituents here plus a nitro group because we call that a nitro group can be converted into an amino group which can then be converted into our Diazo group. So first, let's go ahead and get started with our substituents here and where they happen to be located because what I want to draw your attention to is the fact that the methyl group of Toleen is an O group and therefore, electron donating and Ortho para directing. So because of this, right, the first substituent that we're going to install are going to occupy either the Ortho or the pair of positions. However, what I want to draw your attention to is the fact that this detonated sulfonic acid group is what's attached to the pairs position relative to the metal group. And the reason why I bring this up if you recall is because the per product is generally the most favored when the pers position is unoccupied. Right? So if I were to proceed with sulfur nation first, in which my sulfonic acid group is attached, I would get a mixture of two products. Really, one of them would have my sulfonic acid group in the Ortho position relative to the methyl group. Where is the other one would have the sulfonic acid group in the paras position relative to the methyl group. However, even though both products are going to be found, they can't be separated because recall that the preposition is the most favored when available. So our pair of product is going to be our major product at about 70% abundance. Whereas our Ortho product will appear at about 30% abundance. So we can separate the nature product, which is what we need here by using steam distillation and then once we've obtained our para product in which the sulfonic acid group is on the opposite side relative to the methyl group, we can go ahead and proceed with the addition of the nitro group on our Ortho position. So that's going to be my next step. Right. I'm going to take my paras suation product and proceed with nitration using HN three and to us O fort because that we'll install a nitro group on the ort opposition relative to the sulfonic acid group. And it's at this point that we can go ahead and proceed with the addition of chlorine because notice that the sulfonic acid group and nitro groups are actually both meta directing. So by proceeding with chlorination after nitration, right, chlorine is going to add itself onto the Ortho position relative to the methyl group, but to a metal position relative to both the sulfonic acid group and the nitro group. So here is how we get our substituted toying. So it's at this point that we can proceed with the formation of our diazo group by reacting our nitro group with tin in the presence of HCL. So that's going to replace her Toleen here were substituted Tole me to include a diazo. So now we're ready to combine our two starting materials via diazo coupling. But before I do that, I want to make sure that I have enough space. So let me just move these previous steps over. So now that we have a diazo right, we can go ahead and react it with Nepal in the present of sodium hydroxide and cold temperature. So now these two are going to combine and so we're going to have oops our new coupling product, right. So here I've essentially combined these two ring structures via the diazo group in between them. So for our last step is when we can introduce our carboxylate using the Kobe reaction. However, recall that in order for the Kobe reaction to take place, we have to have a reactant that looks like an Enola eight. So the phenolic hydroxy group of nap here must be dep proton it first. So this last step is actually kind of a two step sequence in one because first, we have to deproteinate our Bino hydroxy group to form an EOL late using hydroxide. And then we can introduce the addition of co two to get the carboxylate. And one thing I actually want to go back and note now that I'm considering the intermediate I do previously is that after our Diazo coupling reaction recall that we are in fact using sodium hydroxide, which is a base. So previously, I drew a proton sulfonic acid group. But after diazo coupling, it would actually be dep proton instead. So I just wanted to go back and correct that before I go ahead and draw the reaction or the product of the Kobe reaction. So when I scroll down here, I get the following Kobe reaction product in which the carboxylate is on the other Ortho position relative to or EOL. And there you have it, here is your completed synthetic procedure. So with all this being said, if you stuck around until the end of this video, I thank you so very much for watching and I realized I cut off some of my product. But regardless, once again, thank you so very much for watching. And I hope you found this helpful.

Synthesize the dye shown starting with aniline and naphthol using reactions from Chapters 23 and 24. [Hint. Start by identifying how each substituent might be installed and then plan the order of their introduction.]

Key Concepts

Amino Group Reactivity

Naphthol Chemistry

Dye Formation Mechanism

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