How does reactions like these proceed? [closed]








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*I encountered this question in the chapter Amines and trust me I've gone through many textbooks but couldn't find the functioning of those reagents, well some of them.*


[![reaction](https://i.stack.imgur.com/pRcHo.png)](https://i.stack.imgur.com/pRcHo.png)


Firstly could you explain what does the 3 reagents under the same arrow signify? Also, can you explain the mechanism step by step?


I'd be greatful.




**Step 1**


1. Your starting material is *o*-phthalic acid.
2. Phosphorous pentoxide, $\ce{P4O10}$, is a strong dehydration agent.
3. The $\Delta$ symbol in your original image means that heat is applied


What happens here?



> 
>  The intramolecular reaction of the two $\ce{-COOH}$ groups yields [phthalic anhydride](https://en.wikipedia.org/wiki/Phthalic_anhydride).
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**Step 2**


1. Carboxylic acids can react with amines to form amides, but what happens here?



> 
>  Anhydrides react with amines to form imides.  
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>  Here, the reaction of phthalic anhydride with ammonia yields [phthalimide](https://en.wikipedia.org/wiki/Phthalimide).
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**Step 3**


1. The product of the previous reaction is first reacted with potassium hydroxide, which is a strong base. What could possible happen here?



> 
> The $\ce{N-H}$ proton of an [imide](https://en.wikipedia.org/wiki/Imide) can be removed easily. Draw some resonance structures of the anion to see why this is the case! 
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2. Chlorobenzene ($\ce{Ph-Cl}$) is added.



> 
>  This reaction will furnish *N*-phenyl phthalimide. Read about [nucleophilic aromatic substitutions](https://en.wikipedia.org/wiki/Nucleophilic_aromatic_substitution) to understand what is going on here.
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3. The product of the previous step is treated with aqueous potassium hydroxide.



> 
>  Read about the hydrolysis of esters, amides, and imides to understand what has happened.
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