[beheada]

Here's the reaction. The major reactant is 6-aminohexanoic acid.

C6H13NO2(aq) + NaNO2 (aq) + HCl (aq) ------> NaCl (aq) + NO2 (g) + C6H10O2 (aq) + ?NH3 (g)?

Is this balanced correctly?
I'm under the assumption that this is a carboxylic acid being rearranged into its ester derivative. The NO2 comes off as gas, the halogen forms a salt.

1) What happens to the NH2 group?
2) What happens first, the deprotonation of the OH group or the protonation of the carbonyl group via H-Cl?
3) What are the intermediate steps? The example I'm using involving the intramolecular esterification is using a terminal alcohol instead of an amine which already naturally has a negative charge and attacks the carbocation formed by protonation via HCl. But is NH2 partially negative enough to perform the same function?

[alphahydroxy]

I'm under the assumption that this is a carboxylic acid being rearranged into its ester derivative.

Nope, this is loss of the amine function via diazotisation.

check out this link:


http://www.organic-chemistry.org/namedreactions/diazotisation.shtm

[beheada]

So once it gets to the dianozium salt intermediate, what exactly is happening to form the ring?
My book only covers arenediazonization and it has HSO4- reacting with any nucleophile to add the nucleophile.

BUT! my best guess is that the diazonium portion kicks itself off the molecule leaving electron pair on the terminal carbon and then the neg goes after the positive... in this case C6 going after C1 (after protonation of the carbonyl which results in a C1 carbocation)? and then it proceeds like a carboxylic acid to ester?

[Dan]

It looks like you're getting in a muddle. As I understand it, you are suggesting that the diazonium salt loses N₂ to form a carbanion at C6. Correct?

If so, look at it again, you have ⁺N₂-Chain-CO₂H

[beheada]

It looks like you're getting in a muddle. As I understand it, you are suggesting that the diazonium salt loses N₂ to form a carbanion at C6. Correct?

If so, look at it again, you have ⁺N₂-Chain-CO₂H

Naaaawwwww... I was saying that the N2 kicks itself off and is most stable as N2 itself. Then you have a carbanion at C6 which bonds with the partially positive C1 (due to all the oxygen substitutions), it bonds with the carbon C1 forming the ring (which is how the rxn is supposed to proceed)?

If not, I'm lost on how this creates a ring.

[Dan]

I was saying that the N2 kicks itself off and is most stable as N2 itself.

Fine

Then you have a carbanion at C6

I disagree.

You suggest:

⁺N₂-CH₂-CH₂-CH₂-CH₂-CH₂-COOH -----> N₂ + ^-CH₂-CH₂-CH₂-CH₂-CH₂-COOH

In this reaction that you have proposed, the charges do not balance, you have +1 on the left, and -1 on the right...

[beheada]

I see. I was condensing a step or two I suppose. My understanding is that when you put a carboxylic acid into aqueous solution it is automatically deprotonated at the terminal hydrogen. I also understand that the HCl is supposed to protonate the carbonyl oxygen. I understand that the reagents used are for a diazonization where N2 must form. What I'm missing is how it goes from: +N2-chain-COOH to a ring?

[Dan]

What I'm missing is how it goes from: +N2-chain-COOH to a ring?

You are vey close to the answer. The problem is your carbanion on C6. You do lose N₂, but this doesn't leave an anion. Draw the curly arrow from the N-C bond in ⁺N₂-CH₂.. to show where the electrons in that bond go when you lose nitrogen gas.

Do the electrons go to C, or the +N₂ group?
Given the movement of electrons, what charge would you expect on C6?
Which part of this molecule could now attack C6?

[beheada]

What I'm missing is how it goes from: +N2-chain-COOH to a ring?

You are vey close to the answer. The problem is your carbanion on C6. You do lose N₂, but this doesn't leave an anion. Draw the curly arrow from the N-C bond in ⁺N₂-CH₂.. to show where the electrons in that bond go when you lose nitrogen gas.

Do the electrons go to C, or the +N₂ group?
Given the movement of electrons, what charge would you expect on C6?
Which part of this molecule could now attack C6?

I'VE GOT IT NOW!!!

Okay, so first off the amine group undergoes diazonization and after an elongated process winds up as a terminal +N2. Then the N2 breaks off (TAKING ITS ELECTRONS WITH IT) and making C6 a carbocation! Now, since the oxygen is deprotonated in aqueous solution, the negative from the oxygen goes after the positive terminal carbocation and forms the ring!

Heh. I've been toiling over this for days.

Someone verify my answer?

EDIT: I also noticed when going over diazonization that the reaction has to take place at 0 degrees? What happens to the rxn if it isn't cooled? Why does it have to be cooled in the first place?
My best guess would be that the rxn proceeds too quickly if left to its own devices and the NO2 gas becomes a hazard.

[Dan]

Nice one! You got it.

The loss of nitrogen is highly entropically favourable, and forms the very stable N₂, so also (probably) has favourable enthalpy. So if you don't cool it you risk having an explosion caused by very rapid evolution of nitrogen gas.