Can hydrogen be abstracted from urea?

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Discussion Overview

The discussion centers on the potential reactions of urea when dissolved in sodium hydroxide (NaOH), specifically exploring whether hydrogen can be abstracted from the amine groups of urea. The scope includes theoretical considerations and possible chemical reactions involving urea and various reagents.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant notes that urea reacts with acids to form uronium ions but questions the reactions with alkalis, specifically NaOH.
  • Another participant suggests that a strong base, such as metallic sodium, may be required to facilitate the reverse hydrolysis reaction of cyanamide to urea.
  • A different viewpoint emphasizes the need to determine the pKa of the protons in urea to identify a sufficiently strong base for hydrogen abstraction, indicating that this may not occur in water.
  • A later reply provides a specific pKa value for urea in DMSO and suggests that non-nucleophilic lithium bases like LDA or LHMDS could be effective for the abstraction process.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of hydrogen abstraction from urea in the presence of NaOH, with some suggesting that strong bases are necessary while others propose specific reagents that might work. The discussion remains unresolved regarding the exact conditions and reagents required for the reaction.

Contextual Notes

There are limitations regarding the assumptions about solvent effects, the strength of bases, and the specific conditions under which reactions may occur. The discussion does not resolve whether hydrogen abstraction is achievable or under what precise conditions.

Vickyl Simpl
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Homework Statement


Urea is known to react with an acid to form salt. The carbonyl oxygen of urea is protonated in the process to form uronium ion. But, I have not seen conclusive reaction of urea with an alkali. So, if urea is dissolved in NaOH, what are the possible reactions? Can hydrogen be abstracted from one or both NH2 group? What reagent can afford this abstraction if any.

Homework Equations


(NH2)2CO + HCl --> (NH2)2COH+ Cl-
(NH2)2CO + NaOH --> ?
(NH2)2CO + ? --> HNCONH2 ]-
(NH2)2CO + ? --> HNCONH ]2-

The Attempt at a Solution

 
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The reverse reaction, namely the hydrolysis of cyanamide is used in the preparation of urea. To reverse it, you will need a rather strong base. E.g. heating urea with metallic sodium.
 
You need to find pKa for these protons and then find a base strong enough. Definitely won't happen in water, and I doubt it will be possible to isolate such cations as salts, but organic chemists routinely use bases that should do the trick.

Edit: DrDu beat me.
 

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