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Dicarbonyl amides, that is carboxylic acid anhydrides with their single-bonded oxygen between their carbonyl groups replaced with an amide group, I'm curious as to whether they're stable in water or unstable like carboxylic acid anhydrides.

This is what I mean by a dicarbonyl amide:

enter image description here

where R1 and R2 are organic substituents/hydrogen.

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This functional group is an imide. Imides are stable to water and require significantly more effort to hydrolyze than anhydrides (from personal experience). The acyl nitrogen group is a better resonance donor and poorer leaving group than acyl oxygen groups.

From the wikipedia page:

Being highly polar, imides exhibit good solubility in polar media. The N-H center for imides derived from ammonia is acidic and can participate in hydrogen bonding. Unlike the structurally related acid anhydrides, they resist hydrolysis and some can even be recrystallized from boiling water.

As an example, succinimide, a cyclic imide has a solubility in water of 1 g for every 3 mL - if succinimide reacted with water, such a high solubility would not be possible.

The related N-bromosuccinimide (show below) is also water stable despite that unfriendly looking $\ce{N-Br}$ bond. It is prepared from succinimide in water and an be recrystallized from near-boiling water.

enter image description here

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Turns out that I knew of a dicarbonyl amide that's stable in water prior to asking this question but I just hadn't realised it: aniracetam. How I know it is stable in water is the fact that it is orally bioavailable in humans and since this would require them to be water-stable I consider it a safe assumption that it is water-stable. But I agree with F'x odds are most dicarbonyl amides are unstable in water and this dicarbonyl amide is probably only stable in water because its amide group is contained within a 5-membered cyclic ring.

This is the molecular structure of aniracetam:

enter image description here

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  • $\begingroup$ Imides are quite stable to water. Check out the Wikipedia articles I link in my answer. $\endgroup$ – Ben Norris Aug 31 '13 at 1:54
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The standard compound with your formula is diacetylamide:

   enter image description here

I expect it to be unstable in water, just like anhydrides. I cannot, however, find a definitive reference on that. The NIST page linked above has a value for the $\Delta_r H°$ of the hydrolysis reaction in gas phase, but no $\Delta_r G°$ or aqueous solution data.

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