How does a primary amine react with phthalic anhydride to form an imide?

[Horseb0x]

I'm trying to figure out the mechanism for the reaction between phthalic anhydride and a primary amine, yielding an imide. Can't find it anywhere.

 

[sjb-2812]

What nucleophiles can you see in your pot? What electrophiles?

 

[Horseb0x]

The amino group is a nucleophile but I'm not too sure about phthalic anhydrides electrophilicity. The carbonyl carbons of the anhydride would be electrophilic enough I suppose. Heres my guess. The amino group attacks one of the carbonyl carbons of the anhydride which breaks the C=O pi bond and forms a tetrahedral intermediate. The quaternary ammonium salt then ejects a proton which protonates the alkoxy O.

The rest I don't understand. Someone drew a mechanism for me and the next step she drew was the carbonyl pi bond reforming and yielding a C=OH+ group. First time I've ever come across a C=OH+ group. Is that step correct?

 

[sjb-2812]

The amino group is a nucleophile but I'm not too sure about phthalic anhydrides electrophilicity. The carbonyl carbons of the anhydride would be electrophilic enough I suppose. Heres my guess. The amino group attacks one of the carbonyl carbons of the anhydride which breaks the C=O pi bond and forms a tetrahedral intermediate. The quaternary ammonium salt then ejects a proton which protonates the alkoxy O

Instead of ejection of the proton at the tetrahedral intermediate stage, how about the C=O pi bond reforms, kicking out the alkoxy oxygen as carboxylate (reasonably good LG), then proton transfer to a secondary amide / carboxylic acid hybrid. Whilst amides aren't usually that basic, perhaps the proximity of the amide to the acid means you can repeat the nucleophilic attack on the other carbonyl?

 

[LudusRex]

The reaction between phthalic anhydride and a primary amine to form an imide is a nucleophilic substitution reaction. The mechanism of this reaction involves the attack of the primary amine on the electrophilic carbonyl carbon of the phthalic anhydride, resulting in the formation of an intermediate amide. This intermediate then undergoes intramolecular cyclization to form the imide product.

The first step of the reaction is the nucleophilic attack of the primary amine on the carbonyl carbon of the phthalic anhydride, resulting in the formation of a tetrahedral intermediate. This intermediate is then protonated by the acidic conditions of the reaction, leading to the formation of an amide.

In the second step, the amide undergoes intramolecular cyclization, where the carbonyl oxygen of the amide attacks the carbonyl carbon of the phthalic anhydride. This results in the formation of a cyclic intermediate, which then undergoes a proton transfer to form the final imide product.

Overall, the reaction between phthalic anhydride and a primary amine to form an imide is a two-step process involving nucleophilic attack and intramolecular cyclization. This mechanism has been well-studied and is commonly used in organic synthesis to form imides.