[thephoenician88]

i know there are limitations to this reaction and i know that a nitrobenzene ring will not react in an acylation, however, why doesn't this reaction work....


is it because there's a nitrile? it's strong activating through, not deactivating

[spirochete]

Remember that AlBr3 has an incomplete octet so it's a strong lewis acid. . .

[omegasynthesis999]

Think about possible side reactions...

[thephoenician88]

Think about possible side reactions...

what...

no, actually i found out why. Friedel crafts don't react with electron withdrawing groups, meaning, amines in general.

[sjb]

Think about possible side reactions...

what...

no, actually i found out why. Friedel crafts don't react with electron withdrawing groups, meaning, amines in general.

Amines are typically electron donating, not withdrawing. Perhaps one reason your alkylation won't go as planned is the nucleophilic attack of the amine on the haloalkane, or perhaps more importantly here the nucleophilic attack of the nitrogen into the empty p-orbital of aluminum (though it's possible AlBr₃ is really Al₂Br₆) a la spirochete's suggestion.

S

[spirochete]

Of course SJB is correct, that's the reason this reaction doesn't go.  An amine is activating because it donates electrons through resonance to certain cationic intermediates produced by an electrophilic attack.  Nitrogen also withdraws electron density inductively through sigma bonds because it's more electronegative than carbon, but in this case resonance is the more important contributer to stability.

Now draw the structure after the nitrogen attacks the AlBr3.  What's different?  How might this affect the stability of the intermediates produced by electrophilic attack? 

[shelanachium]

To nitrate an aromatic amine it is best to N-acetylate it first. Aromatic amines are easily oxidised resulting in total degradation - and a nitration mixture is a strong oxidant indeed. Also in acidic media the aromatic amine is largely converted to a cation such as [C6H5NH3]+ and this is inert to attack by electrophiles such as [NO2]+ (the positive charges repel each other).

Amides such as acetanilide (N-acetyl aniline) are much less basic so are not totally converted to unreactive cations by the acidic nitration mixture. They are also less easily oxidised.

A mixture containing AlBr3 is also highly acidic, so will not work with a simple aromatic amine.