July 09, 2020, 12:44:05 AM
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Topic: Struggling with a reaction mechanism for the synthesis of a fluorescend compound  (Read 597 times)

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Offline basbear

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Hello

This is my first post and i'm struggling with uploading my reaction mechanism, hopefully u can still help me out here.

I'm having struggles with the reaction mechanism for the formation of 4-benzylamino-n-benzyl-1,8-naphthalimide out of 4-chloro-1,8-naphthalic anhydride and 2 benzylamine with the solvent N-methylpyrrolidone.

It's an fluorescend compound I had to synthesize for school.

I know the double bond of the carbon on the anhydride attacks the amine on the benzylamine. This way the ring opens up and its fairly obvious its an condensation reaction. so H2O leaves. Then with some electron pushing going on i think the Cl leaves leaving a carbon electrophile attacking another benzylamine.

I don't know how to send my reaction mechanism but i'm fairly certain its wrong. Really hope u can help me out here.

Thanks
« Last Edit: February 29, 2020, 12:34:55 PM by basbear »

Offline rolnor

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In the first step its usually written as the amine attacs one carbonyl of the anhydride, the second step is as in this link:

https://en.wikipedia.org/wiki/Nucleophilic_aromatic_substitution


Offline basbear

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Thank you!

That helped. Is this correct?

Offline rolnor

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It seems OK, the exact details for the ring-closure is maybe not 100% correct.

Offline kamiyu2550

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Let me be candid, the mechanism is very wrong. Your synthesis has two parts. First is substitution and the second is SNAr.

For the first part, mistake occurs at the third arrow.
For the second part where the first step is the addition of benzylamine to the aromatic ring. Please check, for example, the SNAr of hydroxide ion on 1-chloro-4-nitrobenzene. You should be able to get this part right then.

Offline rolnor

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Snar is also substitution?

Offline kamiyu2550

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Snar is also substitution?

Well, the first substitution I referred to is the substitution of oxygen by nitrogen. What class of reaction it is? it seems no particular name for it.

The second SNAr is nucleophilic aromatic substitution reaction and yes, it is also a substitution.

Note, there is no evidence on which step (O/N substitution and SNAr) occurs faster. We are referring first and second based on OP's drawing only..

Offline basbear

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Let me be candid, the mechanism is very wrong. Your synthesis has two parts. First is substitution and the second is SNAr.

For the first part, mistake occurs at the third arrow.
For the second part where the first step is the addition of benzylamine to the aromatic ring. Please check, for example, the SNAr of hydroxide ion on 1-chloro-4-nitrobenzene. You should be able to get this part right then.

Hello!

Thank you for your response. I honestly appreciate it very much.

I'm still not entirely sure what how the mechanism is wrong from the third arrow.

1. As the oxygen has a negative charge doesn't it want to steal protons from the nitrogen?

2. And if so, does the ring closes first before leaving of the watermolecule?

3. If it does closes first before the watermolecule leaving, could it be that the double bond on the carbonyl attacks the amine instead of the otherway around as i have it notated now?

4. As for the SNar, I did look at that mechanism. And tried to follow it for this case. Could you be so kind as to point out the mistake in my drawing?

Thank you very much! I had troubles finding help for this.

Offline rolnor

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Kamiyu, can you draw the mechanism and post it here?

Offline kamiyu2550

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I am wondering if the OP needs the mechanism for presentation or assignment, or he will lose marks for it. I strongly advise the OP to ask senior in person for discussion. It is hard for me to make it clear online. Best luck!

Offline wildfyr

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Nitrogen will attack the carbonyl of the carboxylic acid, then the OH of the acid will pick up a proton and be lost as water. the carbonyl never has a formal + charge and no substituent.

I'm fine with your SnAr mechanism for the second amine attacking the chlorobenzene.

Kamiyu, I feel like you are possibly a bit hung up because your google link has a carbanion on the beznene ring. I think OP is actually more correct to have the anion on the oxygen. It is much better stabilized there. OP, I think it is best not to draw your 6th step, basically the nitrogen attacks and all those double bonds shift all in the same step to generate structure 7. The term we use is "concerted." In this case it seems like a matter of semantics, but formally its a better representation.

I think the attack on the anhydride will be way faster than the SnAr. Anhydrides generally aren't even that water stable at RT, while chlorobenzenes are usually very water stable at RT. So his order is correct. I would call this reaction simply amidation of anhydride. Not very elegant, but we all know what this is.

Offline kamiyu2550

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Nitrogen will attack the carbonyl of the carboxylic acid, then the OH of the acid will pick up a proton and be lost as water. the carbonyl never has a formal + charge and no substituent.

I'm fine with your SnAr mechanism for the second amine attacking the chlorobenzene.

Kamiyu, I feel like you are possibly a bit hung up because your google link has a carbanion on the beznene ring. I think OP is actually more correct to have the anion on the oxygen. It is much better stabilized there. OP, I think it is best not to draw your 6th step, basically the nitrogen attacks and all those double bonds shift all in the same step to generate structure 7. The term we use is "concerted." In this case it seems like a matter of semantics, but formally its a better representation.

I think the attack on the anhydride will be way faster than the SnAr. Anhydrides generally aren't even that water stable at RT, while chlorobenzenes are usually very water stable at RT. So his order is correct. I would call this reaction simply amidation of anhydride. Not very elegant, but we all know what this is.

I agree with you on the first part.

It seems I never gave any Google link here. And yes, the OP SNAr mechanism where the carbonyl oxygen tooks the negative charge is also correct. What I meant is that a fundamental mistake is found in the mechanism, where there is a carbon with 5 bonds in the structure below.

Offline wildfyr

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Just saw this. Defifinitely a minor but real mistake on his part!

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