adianadiadi1
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Nitration of aniline
When aniline is nitrated, para to ortho to meta ratio is 57:2:41. My question is why ortho nitroaniline is just 2%. Ortho position is also activated
as that of para.....? I dont think steric hindrance is the reason.
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Outer
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When you use unprotected aniline (and not acetanilide for example), in the presence of acids it is protonated, and this protonated cation (Ph-NH3+) is
actually nitrated. Active nitrating agent is NO2+, and because of electrostatic interactions, ortho-position is the least preferable.
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Sigmatropic
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Does anyone know why diazotizations work on anilines? The first step on paper involves the interaction of the nitrogen lone pair with nitrosonium. In
my mind I can't picture there being any nitrogen lone pair in conc. HCl (or even diluted HCl for that matter) because the aniline exists as the
ammonium salt in such conditions. But I can very much verify that these reactions occur. This discrepancy between practice and theory bothers me.
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Tsjerk
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Apperantly the NO2+ is such a good electrophile that, with amine/NO2+ reaction being irreversible, the reaction proceeds.
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Sigmatropic
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So it is such a good electrophile that it reacts with a N-H bond of an ammonium ion? Hmmm, seems feasible but unlikely although very similar to
protonated methane.
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Tsjerk
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Well, nitronium salts have to have a fully oxidized anion to be stable. I have a feeling that extreme electrophiles can do more stuff like this.
If azidozition works, I don't see why for example carboxylic acids couldn't be nucleophiles...
[Edited on 8-6-2018 by Tsjerk]
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Outer
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Quote: Originally posted by Sigmatropic  | | Does anyone know why diazotizations work on anilines? The first step on paper involves the interaction of the nitrogen lone pair with nitrosonium. In
my mind I can't picture there being any nitrogen lone pair in conc. HCl (or even diluted HCl for that matter) because the aniline exists as the
ammonium salt in such conditions. But I can very much verify that these reactions occur. This discrepancy between practice and theory bothers me.
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In this reaction PhNH3+ ion interacts with a neutral molecule of HNO2, giving an equilibrium of PhNH2 (aniline) and H2NO2+ (protonated HNO2). The
latter one after elimination of water gives NO+ (nitrosonium), which reacts with aniline.
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Tsjerk
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Do I understand you right when I understand you suggesting a weak nucleophile (NH3+) attacking a weak electrophile (HNO2) in a reaction requiring
dehydration of a molecule in a aqueous solution while there is an easier and more reasonable explanation for the reaction?
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Outer
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| Quote: Originally posted by Tsjerk | | a weak nucleophile (NH3+) attacking a weak electrophile (HNO2) in a reaction requiring dehydration of a molecule |
PhNH3+ is not a nucleophile, but after proton transfer (to HNO2) is gives PhNH2 (nucleophile) and H2NO2+ (good electrophile). They can react each with
other after dehydration of H2NO2+ (or maybe even without dehydration).
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Sigmatropic
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Wouldn't the proton for dehydration of nitrous come from the acid environment, instead of the ammonium ion? I very much doubt the abysmally small
amount of free base amine present in acidic solutions is able to give such a fast reaction (15 minutes at 0c). There must be something else at play
here.
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