Unlike most other electrophilic aromatic substitutions, sulfon...

Question

Unlike most other electrophilic aromatic substitutions, sulfonation is often reversible (see Section 17-4). When one sample of toluene is sulfonated at 0 °C and another sample is sulfonated at 100 °C, the following ratios of substitution products result:

c. Because the SO₃H group can be added to a benzene ring and removed later, it is sometimes called a blocking group. Show how 2,6-dibromotoluene can be made from toluene using sulfonation and desulfonation as intermediate steps in the synthesis.

Accepted Answer

Hey everyone and welcome back to another video and states less than we are going to solve the following problem. Unlike other electra Philip aromatic substitution, Benzene, sulfur nation is reversible symphonic asset can be added to the benzene ring and removed later. This makes the symphonic acid group, alternatively known as the blocking group. Show how to synthesize one comma two comma three tribal more benzene starting from benzene using cell phone nation and desalination as intermediate steps. Now, let's think about benzene ring because that's our starting material. So we are just going to draw a six member ring with three double bonds as our benzene. And to perform cell phone nation, we have to recall that the region's required for that are fuming sulfuric acid, meaning those would be sulfur trioxide in the presence of So fairy cast that Okay. And what we're doing here, we're just replacing one of the hydrogen atoms with the cell phonic acid group. And we are farming S. 03 H. That's our cell phonic acid group. What we want to remember here is that symphonic acid group is a matter director. Now, can we identify our made up positions? They are over here and then here, right, Because those are Ortho meta and then power position over here. So if we immediately start by adding our symphonic acid group, we will be able to add two bromine atoms, but we will have no way to add the final one. And similarly let's think about the bromo substitution. If in order to perform halogen ation, we want to make sure that we use the following set of regions. So we're using booming in the presence of iron three bromide. That's our lewis asset required for the given reaction. And we are simply performing that aromatic substitution where one of the hydrogen atoms is now replaced with grooming. And I was similarly to what we did before. We may recall that bromo substitution as an Ortho para director meaning if we first of all add our bromo substitution that will be directing towards these two Ortho positions and the power position. So that's how it's done. We can think about our sequence whether if we first of all instead add one bromine atom, it would then be directing towards or so and power positions. So power works for us. If we add our cellphone group over here and then the symphonic acid group would be pointing to major positions and we will be adding two bromo substations adjacent to that broom in and that really works for us. Right, Because the major product four, the cell phone nation of bromo Benzene would be formed at the power position. So let's see how that works. We may start by drawing our benzene ring because we pretty much understand the strategy we get our benzene ring and we understand that the first step that we want to perform would be. My apologies, we are missing a subscript of two here, right blooming is the atomic. So the first step would be adding blooming in the presence of iron three bromine. So if we do that we're performing our hydrogenation reaction and we are getting our mono substituted product that would be Bmo benzene. Now we understand that as directing to Ortho and para positions and power will be the major product. As you recall whenever we have a competition between Ortho and para positions. Now if we perform cell phone nation, we're essentially saying that this is a reversible reaction. We are adding fuming sulfuric asset and as we said before is directing to Ortho empower positions. And one of the products which is actually the major product would be formed at the power position and this is how we get it. We may someplace say that the resulting product over here would be bro more substitution at position number one. And that we are adding our symphonic asset. S. 03 age at the power position and now well done. We pretty much understand what we have to do now because it's made a director and grooming is or so. Power Director. We notice that both of them are directing to these two positions meaning what if we repeat the broom in ation stuff? We can essentially add two equivalents of blooming in the presence of iron three bromide and we would be done. So let's see that first of all we state that there must be two equivalence. So we're saying two equivalents Of Blooming in the Presence of Iron three Bromide. And as we said these two hydrogen atoms will be substituted with roaming we are getting our intermediate product. So there will be three bromo substitute prints adjacent to each other And then our cell phonic asset group as 03 age. Now you may simply think about it this way we were asked to form one comma two comma three tribe promo benzene. But this is not really the structure that we wanted to get. We still have that symphonic acid group. But I have good news for you. Just as a problem suggests we have an easy way to remove it because it's a blocking group that can be easily removed. So if we perform an additional reaction where we are using water in the presence of heat where water is a source of protons, right to essentially restore the benzene ring. We are going to lose our cell phone in casting group and we are going to bring that hydrogen back. We will get our found product just as required by the problem. So if we draw our found product, we noticed that indeed we get our final product one, comma two, comma three tribal More benzene. This is our final product. And we can just label this as our final answer. And this is our complete outline of the procedure. So let's review the steps step number one is the addition of blooming in the presence of iron three bromide using electro filic aromatic substitution elimination mechanism. Then when we have formed our bruma benzene, we're treating it with fuming sulfuric acid to form our symphonic acid group. The major product is formed at the power position and when the two groups are directing at the same position made up with respect to symphonic acid and or so with respect to bromine, we understand that we may just add two more equivalents of romaine using the previous pathway and form our intermediate, which is then diesel fascinated. In other words, we're removing this S. 03 age group by using water in the presence of heat and we are getting our final product. Now the correct answer choice to this multiple choice question is B However, if you have any questions, don't have States, leave your comment down below in the comment section and thank you for watching.

Key Concepts

Electrophilic Aromatic Substitution (EAS)

Reversibility of Sulfonation

Isomer Distribution and Temperature Effects

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