# What is the reaction between NaOH and urea?

In this video it is mentioned that urea and sodium hydroxide will react to produce ammonia. However, I can't seem to find a clear explanation of the reaction and the other products generated.

One explanation I found says that the NaOH causes the urea to hydrolyze, yielding sodium carbamate, which will then further hydrolyze to sodium carbonate.

Another says that the urea tautomerizes to ammonium cyanate, which preforms a substitution with the NaOH to yield ammonium hydroxide and sodium cyanate.

Which of the two reactions occurs? Do they both occur? Neither?

Urea can be attacked by nucleophiles like any carbonyl. The immediate intermediate is a tetrahedral orthoacid which will break down to liberate ammonia once. The same process can be repeated a second time to liberate the second molecule of ammonia.

Technically, this is a hydrolysis catalysed by hydroxide. Hydroxide may be the reactive species but it is regenerated in the course of the reaction.

For urea to tautomerise to ammonium cyanate, a significant rearrangement and breaking a $\ce{C-N}$ bond would be required. Neither is likely in any way.

• Does the carbamic acid react further and we end up with carbonate ion + more ammonia? Sep 24 '17 at 15:53
• Carbamic acid is inherently unstable and will decompose to ammonia and carbon dioxide rapidly @OscarLanzi
– Jan
Sep 25 '17 at 8:19

Well, in practice adding sodium hydroxide granules to a concentrated urea solution at room temperature results in the rapid growth of needle crystals, most likely urea being pushed out of solution. Further heating does not result in $\ce{NH4+}$ or $\ce{NH3}$. However the melting of the dry reactants might produce a different result.

• There are a lot of possible experiments using urea and sodium hydroxide; you are presenting just one variety. Of course, given concentrated solutions of both, chances are that one of the two becomes over-concentrated and crystallises out but there are a lot more variables.
– Jan
Feb 7 '17 at 16:19
• Is heating compulsory for this reaction to take place, considering dilute solutions of both urea and sodium hydroxide? Jun 15 '20 at 5:16

When dissolved urea is heated in the presence of around an equal mass of dissolved sodium hydroxide I can say for sure the stench of ammonia is very present and bubbling is nearly instant upon heating, note this was performed in about 5 or 10 parts water. To generate large quantities a equal molar ratio of caustic soda and urea would likely be required as the carbamic acid byproduct can react to convert the sodium hydroxide to sodium carbonate, additional CO2 scribing should also be implemented as CO2 will likely leave the reaction mix and contaminate the ammonia gas

• "note this was performed in about 5 or 10 parts water" why in past tense? Apr 11 '20 at 22:06