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When succinic acid is treated with excess $\ce{NH3}$, what will the mechanism be? I feel both $\ce{COOH}$ groups should be converted to $\ce{CONH2}$, but this is not the product.

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    $\begingroup$ Did you actually mean to say $\ce{COONH2}$? Because that is about as wrong as it gets … $\endgroup$ – Jan Aug 16 '16 at 16:23
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    $\begingroup$ I actually think you mean $\ce{CONH2}$, the amide, but feel free to correct me if I'm wrong. $\endgroup$ – The_Vinz Aug 16 '16 at 17:55
  • $\begingroup$ Yup.. Its amide $\endgroup$ – Adarsh chaturvedi Aug 18 '16 at 10:42
  • $\begingroup$ @Jan It's not as simple as it seems... the ring actually closes. (Picture taken from here) $\endgroup$ – DHMO Jan 26 '17 at 16:05
  • $\begingroup$ @DHMO I knew. But OP suggested a peroxide product which was just badly wrong ;) (Actually, it is as simple as it seems because five-membered rings are kinetically favoured and intramolecular attacks are faster than intermolecular ones, etc. etc.) $\endgroup$ – Jan Jan 26 '17 at 20:20
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From Synthesis of Succinimide on Thomas' Chemistry:

Add 186 g of succinic acid to RBF, place the beaker in an ice bath and start adding 220 ml of 26% ammonia slowly. Assemble short path distillation without a condenser, add some boiling chips. Heat the mixture under a small flame to distil of all the water. When the temperature reaches over 100°C the mixture darkens. Switch the receiver and collect everything that comes off before yellow fumes temp 280-300°C. Cool down to room temperature and place the receiver into a freezer for 24h, recrystallize the crude succinimide in hot ethanol. Then filter the crystals and wash with 40 ml of cold ethanol.

(Note that RBF = round-bottom flask)

mechanism

The catch is that the amide can attack itself to close the ring, forming succinimide.

There are two rounds of amidification via a nucleophilic addition/elimination mechanism.

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