Making Azo Compunds

Hey

I'm having some trouble answering the following part of a question

Write the structures of the products you would expect to be formed at each stage when:

a) phenylamine is dissolved in sulfuric acid

The problem I'm having is that I thought that it would be the Sulphuric acid together with nitric acid but without this I have no idea as I would have expected to get the N=-(triple bond)N+ here but I can't as there is no N.

Would it instead be simply: The phenlyamine structure with an SO2O- group on it plus H2O?

Reply 1

shengoc

SirMasterKey

Hey

I'm having some trouble answering the following part of a question

The problem I'm having is that I thought that it would be the Sulphuric acid together with nitric acid but without this I have no idea as I would have expected to get the N=-(triple bond)N+ here but I can't as there is no N.

Would it instead be simply: The phenlyamine structure with an SO2O- group on it plus H2O?

Well, phenylamine is an amine, the lone pair on the nitrogen is free to protonate, especially since you have a strong acid(sulphuric acid), and after this protonation, the NH2 is no longer activating the aromatic ring, but deactivating it since it is now positively charged.

You must be thinking of nitration, but nitration of phenylamine is best done with a nitrating agent that doesn't involve acid, ie [NO2+][BF4-]

Reply 2

SirMasterKey

shengoc

Well, phenylamine is an amine, the lone pair on the nitrogen is free to protonate, especially since you have a strong acid(sulphuric acid), and after this protonation, the NH2 is no longer activating the aromatic ring, but deactivating it since it is now positively charged.You must be thinking of nitration, but nitration of phenylamine is best done with a nitrating agent that doesn't involve acid, ie [NO2+][BF4-]

I'm not too sure what you mean by that, is it that it has become an NH3+ and as such this NH3+ is now free to react as the delocalised system is no longer in balance keeping the molecule stable?

Reply 3

shengoc

SirMasterKey

I'm not too sure what you mean by that, is it that it has become an NH3+ and as such this NH3+ is now free to react as the delocalised system is no longer in balance keeping the molecule stable?

no, no you know how reactivity of aromatic compounds are controlled by the substituents, ie NH2 is activating as the lone pair on the N can delocalize into the aromatic system and therefore make it more electrophilic.

NO2 is however electron donating(both mesomerically and inductively) and so is deactivating the aromatic compounds. Let say from benzene to nitrobenzene, you are unlikely to get a second nitro substitution at the same temperature as it is already deactivated, and the aromatic compound is already less electrophilic than benzene.

phenylamine in presence of an acid acts as a base and becomes deactivated. but there is no other nucleophile for it to react, even if there is, you won't get electrophilic substitution(easily)

Making Azo Compunds

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