Sciencemadness Discussion Board - Hydrolysis of Urea

Hydrolysis of Urea

Waffles SS - 2-4-2012 at 22:16

What is product of urea hydrolysis
According to Morrison & Boyd (organic chemistry), 6th

Urea + (H+) ->(NH4+) + CO2
Urea + (-OH) ->NH3 + (-2CO3)
Urea + enzyme(urease) -> NH3 + CO2

I think this mean hydrolysis of urea by HCl make Ammonium chloride and carbon dioxide also hydrolysis by sodium hydroxide make Sodium carbonate and ammonia.am i wrong?
I havent seen this route so far.also i found below paper

THE KINETICS OF THE HYDROLYSIS OF UREA AND OF ARGININE

Attachment: J. Biol. Chem.-1942-Warner-705-23.pdf (831kB)
This file has been downloaded 2319 times

[Edited on 3-4-2012 by Waffles SS]

weiming1998 - 4-4-2012 at 04:20

The hydrolysis of urea in HCl or NaOH probably will work if a catalyst+a dilute solution is used. In a dilute solution, the affect is minimal. Thus you are right, for HCl, NH4Cl+CO2 and for NaOH, NH3+Na2CO3. For more concentrated solutions of NaOH, I see problems. The solution might reach a point where is is so deficient in H+ ions that it might not protonate the NH2-. Even if it does protonate, the reaction is going to be slower than normal. For concentrated HCl, I am not sure.

I first thought that because HCl will donate H+ far more easily than H2O, it will protonate the NH2- first, attaching a Cl- to the molecule. When two Cl- is attached, phosgene might form. But then I realized that phosgene slowly hydrolyzes to HCl and CO2, so the small amounts produced is immediately going to react with the water, producing the same products. Either way, whether the Cl- attaches or not, in an acidic condition, the hydrolysis is going to be significantly faster. There is also a chance that urea HCl forms instead, but I can't find any details about the production of urea HCl (whether you use gaseous HCl or aqueous solutions of it)

Of course, it is all what I have thought up, I don't have references (can't found them!)

francis - 6-4-2012 at 02:04

Quote: Originally posted by weiming1998

The hydrolysis of urea in HCl or NaOH probably will work if a catalyst+a dilute solution is used. In a dilute solution, the affect is minimal. Thus you are right, for HCl, NH4Cl+CO2 and for NaOH, NH3+Na2CO3. For more concentrated solutions of NaOH, I see problems. The solution might reach a point where is is so deficient in H+ ions that it might not protonate the NH2-. Even if it does protonate, the reaction is going to be slower than normal. For concentrated HCl, I am not sure.

I first thought that because HCl will donate H+ far more easily than H2O, it will protonate the NH2- first, attaching a Cl- to the molecule. When two Cl- is attached, phosgene might form.

Like most amides, the lone pair on either of the nitrogens is resonance-stabilised and thus much less basic than say, an amine nitrogen.

The lone pair electrons on the nitrogen will not be protonated in the first step of the reaction.

In fact the first step of this particular reaction is not a hydrolysis at all (see this paper: www.chem.ucla.edu/~ana/pdf/18.pdf)

In aqueous solution, water protonates and deprotonates the nitrogens to form a zwitterion:

The next step is the elimination of ammonia to form isocyanic acid. I have drawn the ammonia being protonated by the acid to form the cyanate anion and ammonium.

Then under acid conditions, acid-catalysd hydrolysis of isocyanic acid occurs to produce CO2 and NH4(+) (the exact nature of the species being dependent on the buffer system).

The conditions would need to be vigorous.

Probably moderate conditions give a mixture of addition-elimination products (bicarbonate and ammonium depending on the pH).

Basic conditions would give direct hydrolysis by addition-elimination with OH- as the nucleophile in the first step: and the products being the carbonate anion and ammonia.

The urease enzyme is predicted to work by catalysing the addition-elimination method.

francis - 6-4-2012 at 22:27

Quote: Originally posted by ellaharris

These reaction is executed successfully. Mechanisms of the hydrolysis of urea have been investigated using the MNDO and AM1 methods.

Right, as stated by Lee et al., in this paper: Theoretical studies on the hydrolysis of urea in acid solution

Quote:

Mechanisms of the hydrolysis of urea have been investigated using the MNDO and AMI methods....the results showed that: (i) The unimolecular decomposition process via the direct intramolecular proton transfer is preferred to both the A1 and the bimolecular nucleophilic attack by water

Waffles SS - 6-4-2012 at 23:13

If Really this is possible to make ammonium chloride by acid hydrolysis of urea,What PH ,catalyst and condition is needed?

[Edited on 7-4-2012 by Waffles SS]

weiming1998 - 6-4-2012 at 23:37

Catalyst: either the urease enzyme, or, as this reference describes (http://pubs.acs.org/doi/abs/10.1021/ic961500p), palladium (II) complexes.

Condition: In boiling hot HCl because urea hydrolyses in hot water faster than cold (which is the main problem in boiling down a urea solution to retrieve solid urea).

pH: Less than 0, as 1M HCl has a pH of 0.

But I suggest you to just distil solid urea and lead the gasses through water, then react with HCl. Faster and more convenient.

Waffles SS - 7-4-2012 at 00:36

Thanks but i think on heating urea also decompose to toxic Carbon Dioxide which make this method so dangerous
What about Sulfuric acid ?it will lead to ammonium sulfate or goes different route?

[Edited on 7-4-2012 by Waffles SS]

weiming1998 - 7-4-2012 at 03:12

Quote: Originally posted by Waffles SS

Thanks but i think on heating urea also decompose to toxic Carbon Dioxide which make this method so dangerous
What about Sulfuric acid ?it will lead to ammonium sulfate or goes different route?

[Edited on 7-4-2012 by Waffles SS]

Carbon dioxide only slightly toxic. To kill you, 10% CO2, or 100 000ppm, is needed in the air. With proper ventilation (I don't even see the need for a fume-hood), there is no way you can die of CO2 poisoning from the reaction. The escaped ammonia from the solution is more to worry about than the CO2. So no, the method is not dangerous.

Yes, sulfuric acid will do the trick too, just use about 10% sulfuric acid instead of anything too concentrated. With an increase in boiling point because of the acid, the urea is going to hydrolyse even faster.

Waffles SS - 7-4-2012 at 10:30

Excuse me.
I mean Carbon Monoxide not Dioxide
I think pyrolysis of urea make Carbon monoxide.isnt it?

weiming1998 - 7-4-2012 at 17:34

Actually, it doesn't make CO. The main equation for the pyrolysis of urea is: CO(NH2)2===> NH3+HCNO. Don't be afraid of HNCO, or isocyanic acid, as it is nowhere as toxic as HCN. The HNCO hydrolyzes in water (catalyzed by low pH) to form: HNCO+H2O===>NH3+CO2. Some HCNO also trimerizes into C3H3N3O3, or cyanuric acid, and a variety of other solid products. The reaction isn't really dangerous, and all you need is proper ventilation.

[Edited on 8-4-2012 by weiming1998]

Waffles SS - 8-4-2012 at 00:28

Thanks my dear friend weiming1998 and another friends
I will try this method as soon as possible.i have access to hydrochloric acid gas and i want to use this gas directly in this reaction and make ammonium chloride.
I think best way is hydrolysis of urea for making ammonia gas an then reacting with Hydrochloric gas

weiming1998 - 8-4-2012 at 00:58

Quote: Originally posted by Waffles SS

Thanks my dear friend weiming1998 and another friends
I will try this method as soon as possible.i have access to hydrochloric acid gas and i want to use this gas directly in this reaction and make ammonium chloride.
I think best way is hydrolysis of urea for making ammonia gas an then reacting with Hydrochloric gas

Why do you need to react the ammonia produced with HCl(g)? Surely a one-flask setup of a boiling HCl solution of urea and catalyst will work. If you want purer anhydrous NH4Cl, you can always sublime it.

Waffles SS - 8-4-2012 at 01:45

Because the catalyst that you mentioned is expensive and is not suitable for large scale(i want to try this method on large scale)
Preparing HCl gas from Sulfuric acid and Sodium chloride is cheaper than buying 30% hydrochloric acid solution and also reacting Ammonia gas with HCl make solid ammonium chloride and there is no need for boiling any solution also this reaction is exothermic and we can use heat of this step for first step(Pyrolysis of urea)

[Edited on 8-4-2012 by Waffles SS]

weiming1998 - 8-4-2012 at 03:14

But the resulting NH4Cl smoke might be too hard to condense, so leading HCl gas through the formed NH4OH solution (from bubbling the gasses of the pyrolysis of urea in water) with a backflow prevention trap might be better

Waffles SS - 8-4-2012 at 04:55

Yes.your idea is better
I will be so happy if you or another member suggest better way for this purpose
You put reference 9 post ago and i dont have access to this paper,Do you know what palladium (II) complex it used?and how we can prepare it?

[Edited on 8-4-2012 by Waffles SS]

weiming1998 - 8-4-2012 at 05:10

The source did not specify which palladium complex, only this:[Pd(en)(H2O)2]2+(I don't have access to full text either, so I read the abstract one)
So I don't know.

Also, may I ask what you meant by suggesting better way for this purpose?

Waffles SS - 8-4-2012 at 08:23

Fir example one of my friend suggest me :
First i Hydrolysis urea by Sulfuric acid(because is cheaper and easier to work)and then react Ammonium Sulfate with calcium chloride(also calcium chloride is cheap)
There is no need for gaseous step by this route

[Edited on 8-4-2012 by Waffles SS]

weiming1998 - 8-4-2012 at 16:25

But H2SO4 isn't a catalyst for this reaction and if you do have a catalyst, then you can just react urea in dilute HCl with catalyst. There has to be a gaseous route for this without the catalyst, but the apparatuses for pyrolysing urea can be fashioned out of metal (for ammonia generation) and high melting plastic pipes, so it isn't really that difficult. If you don't have a glass setup for bubbling HCl gas through the solution, then I'm afraid you'll have to buy some bottles of HCl from your hardware store or pool shop.

Waffles SS - 9-4-2012 at 01:06

My bubbling device made of SS316 and HCl will attack it
I think this not mean if i dont have catalyst then reaction doesnt happen.I think reaction will happen but slowly(am i wrong?)

[Edited on 9-4-2012 by Waffles SS]

weiming1998 - 9-4-2012 at 01:12

Ok, then your previous method of reacting NH3 with H2SO4, then with CaCl2 works.

As for your question, it is true that the reaction will eventually occur, even if you had no catalyst, but it proceeds extremely slowly, in the orders of a few months at room temperature and possibly days if boiled. It simply isn't convenient enough.