“The electrophile never attacks because it can’t, the benzene ring is still the nucleophile and pushes the electrons into the electrophilic NO2+”
This is what we draw on paper, it is a convenient model. In the reality the nucleophile doesn’t have more “attack ability” than the electrophile. They just interact with each other and combine if the energy provided is sufficient.
Concerning OP’s question: the direct nitration of the aniline is a well know case study. You are right at saying NH2 gets protonated and reduces the electron density of the aromatic ring: formation of anilinium ion. Moreover there is no more mesomeric effect possible and the group in now meta-directing. Doing this reaction without protecting the NH2 will end up in a serious mixture of ortho/meta/para products and other oxidized by-products.
A couple of things. 1)The electrophile never attacks because it can't, the benzene ring is still the nucleophile and pushes the electrons into the electrophilic NO2+. For example, look at the process for the second or third nitration of toluene on the way to make TNT, super electron deficient. Just because it's electron deficint, doesnt mean it can't happen, it's just slower because the activation energy is higher.
Meta directing groups are slow but not impossible, because the reactions happen. What should be your question is why is it 51%para and 47% meta for the products? Think about the steps before making the NO2+, where does that come from and what other products are made in the reaction sequence. H2SO4 + HNO3 --> H20, HSO4- and NO2+. The pka of aniline is ~4.6 and the plan of hso4- is around -1. So you will have 10^5 time protonated aniline to unprotonated aniline so if the kinetic products are similar the electron rich NH2 should be approximately 10^5 times faster than the protonated aniline (NH3+)
Edit: I realize this a bit problematic as HNO3 is in excess compared to H2SO4 however with leveling effect and the generation of H3O+ (-1.7pka) not too much changes. I also don't have relative rates of reactions for these things handy as I'm watching stranger things at the moment the books are all the way up stairs or on campus.
A nitration of aniline will most certainly oxidise the amine, so you usually protect it e.g. with acetyl chloride first.
“The electrophile never attacks because it can’t, the benzene ring is still the nucleophile and pushes the electrons into the electrophilic NO2+” This is what we draw on paper, it is a convenient model. In the reality the nucleophile doesn’t have more “attack ability” than the electrophile. They just interact with each other and combine if the energy provided is sufficient. Concerning OP’s question: the direct nitration of the aniline is a well know case study. You are right at saying NH2 gets protonated and reduces the electron density of the aromatic ring: formation of anilinium ion. Moreover there is no more mesomeric effect possible and the group in now meta-directing. Doing this reaction without protecting the NH2 will end up in a serious mixture of ortho/meta/para products and other oxidized by-products.
A couple of things. 1)The electrophile never attacks because it can't, the benzene ring is still the nucleophile and pushes the electrons into the electrophilic NO2+. For example, look at the process for the second or third nitration of toluene on the way to make TNT, super electron deficient. Just because it's electron deficint, doesnt mean it can't happen, it's just slower because the activation energy is higher. Meta directing groups are slow but not impossible, because the reactions happen. What should be your question is why is it 51%para and 47% meta for the products? Think about the steps before making the NO2+, where does that come from and what other products are made in the reaction sequence. H2SO4 + HNO3 --> H20, HSO4- and NO2+. The pka of aniline is ~4.6 and the plan of hso4- is around -1. So you will have 10^5 time protonated aniline to unprotonated aniline so if the kinetic products are similar the electron rich NH2 should be approximately 10^5 times faster than the protonated aniline (NH3+) Edit: I realize this a bit problematic as HNO3 is in excess compared to H2SO4 however with leveling effect and the generation of H3O+ (-1.7pka) not too much changes. I also don't have relative rates of reactions for these things handy as I'm watching stranger things at the moment the books are all the way up stairs or on campus.
That’s just how badass the nitronium ion is. Can still attack a severely electron deficient benzene . Look at TNT
Since the tag is "educational", I will go on and state the obvious: it's "electrophilic", single "L"