The chemical formula of urea is $\ce{CO(NH2)2}$ or is sometimes written as $\ce{CH4N2O}$. How would I decompose or precipitate the $\ce{CO}$ from urea to get ammonia? I know that in the olden days people used to make gunpowder (potassium nitrate) and ammonium nitrate from human urine, which was made by reacting ammonia and nitric acid, so it should be possible. (Just as a side note: this is for a high school chemistry project, I am not attempting to make explosives out of this).


Short answer: use crushed watermelon seeds (urease)

Combine urea in solution with urease, get some ammonia with carbamate intermediary, which rapidly decomposes to ammonia and carbon dioxide.

$$\ce{(NH2)2CO + H2O ->[urease] NH3 + H2NCOOH -> 2NH3(gas) + CO2(gas)}$$

Of course the ammonia gas dissolves in the water and increases the pH.



The following article (available freely under a creative commons license) outlines two different procedure to decompose urea to ammonia, one via thermal hydrolysis (THU), the other using a Ni catalyst under an applied electrochemical potential:

ECS Electrochem. Lett. 2015 volume 4, issue 10, E5-E7


doi: 10.1149/2.0041510eel

The following passage describes the THU process which is carried out at high temperature in water (references and more details can be found in the article):

Warner postulated that urea hydrolysis -THU summarized by reaction 1- consists of two steps. The first step is the decomposition of urea to ammonia and isocyanic ion (Eq. 6) which is irreversible at pH less than 5 and greater than 12. The second step is the hydrolysis of isocyanic ion to produce ammonia and CO2 (Eq. 7).

$\ce{ NH2CONH2 -> NH3 + H+ + CNO- ~~} $ [6]

$\ce{ CNO- + H+ + H2O -> NH3 + CO2 ~~~} $ [7]

  1. First hydrolyze the urea as follows to form ammonium carbonate. $$\ce{NH2CONH2 + H2O -> (NH4)2CO3}$$

  2. Next decompose this ammonium carbonate to yield our required product, $\ce{NH3}$. $$\ce{(NH4)2CO3 -> 2NH3 + H2O + CO2}$$

  • $\begingroup$ Please use MathJax to format the formulas. You'll see links to the right of your text box when you ask a new question. $\endgroup$ Feb 8 '18 at 5:14
  • 2
    $\begingroup$ This answer could use some more background information, like reaction conditions with explanations, instead of only reaction equations. $\endgroup$ Feb 8 '18 at 5:35
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    $\begingroup$ Does said ammonium carbonate decompose readily? Rather, does it decompose on its own, and if so, how quickly? Is a catalyst needed to speed up this process? $\endgroup$
    – john doe
    Feb 8 '18 at 8:20
  • 3
    $\begingroup$ How would I react the water and urea together? Urea and water already exist together in urine, and they don't react to form the above compound. $\endgroup$
    – john doe
    Feb 8 '18 at 8:54

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