Sciencemadness Discussion Board

Urea Synthesis

Oleum - 12-2-2005 at 09:56

I am interested in synthesizing Urea as it relates to the gold refining process (neutralizing aqua regia). I have read that it is made industrially by reacting CO2 and NH3, but requires very high temperatures and pressures, which I cannot reproduce. Does anybody know of a simpler way (other than just buying it) to make Urea?

BromicAcid - 12-2-2005 at 21:28

There's always urine ;)

Urea is of course incredibly soluble so it seems like it would always be the last constituent to drop out of solution, cheap and readily avalible although smelly, urine would be one OTC way to procure this useful reagent.

Esplosivo - 12-2-2005 at 23:32

It's not worth synthesizing urea. IIRC, chemoleo created a thread including a protocol for its extraction from urine, in which it is quite abundant, especially if you eat quite a lot of excess protein-containing food.

Anyways if you want to synthesis you can carry out the procedure created by Wohler to produce urea (he made the first organic compoun out of inorganic chemicals, where at those times it was thought that some 'special' force was required to synthesize 'the chemicals of life';). It basically requires a double displacement between potassium cyanate and lead (II) nitrate, reacting the resulting lead (II) cyanate with excess ammonia soln. The ammonium cyanate produced undergoes nearly immediate rearrangement to produce urea. Hope this helps. The attachment below includes some extra details about this reaction.

Attachment: Synthesis of urea _ Wohlers synth.pdf (365kB)
This file has been downloaded 1421 times

chemoleo - 13-2-2005 at 11:41

Re the purification of urea from urine, this is the thread in question. I should add that urea nitrate is barely soluble only if the solution is made acidic (i.e. excess) with HNO3.

THe Woehler synth. is of course the well-known one, but there are others.
It can be made by reacting ammonia with either phosgen OCCl2, chloroformic acid , urethanes H2N-CO-OR, and carbonic acid esters OC(OR)2.

What I found interesting is the ease with which urea derivatives are made.
I.e. N-alkylated urea derivatives are made, analogous to the Woehler synth, with primary or secondary amines with potassium cyanate.
Another Woehler type reaction is the production of semicarbazide (H2N-CO-NHNH2), which is done with KNCO and hydrazine sulphate (as opposed to ammonia or amines). An excess of the cyanate in the presence of acetic acid produces bis-urea, or 1,2 hydrazin dicarboxamide, (H2N-CO-NH)2.

IPN - 14-2-2005 at 11:03

Quote:

Another Woehler type reaction is the production of semicarbazide (H2N-CO-NHNH2), which is done with KNCO and hydrazine sulphate (as opposed to ammonia or amines).


That simple? Or will it require high pressures or something?
Potassium cyanate can be made with potassium carbonate and urea so that would make semicarbazide quite OTC. :)

CherrieBaby - 4-3-2005 at 11:18

I agree that it isn't worth synthesising urea. It is easy to buy OTC. It is used as a fertiliser and in photographic processing; so is available from suppliers of such chemicals. You can also buy it from suppliers who sell chemicals to individuals (even in the UK).

Rosco Bodine - 12-8-2006 at 11:17

Quote:
Originally posted by chemoleo
Another Woehler type reaction is the production of semicarbazide (H2N-CO-NHNH2), which is done with KNCO and hydrazine sulphate (as opposed to ammonia or amines). An excess of the cyanate in the presence of acetic acid produces bis-urea, or 1,2 hydrazin dicarboxamide, (H2N-CO-NH)2.


Is there more specific information or a lab synthesis describing this Wohler ( sp? ) reaction for semicarbazide from potassium cyanate and hydrazine sulfate ?

[Edited on 12-8-2006 by Rosco Bodine]

jim20/20 - 12-8-2006 at 12:15

Quote:
Originally posted by CherrieBaby
I agree that it isn't worth synthesising urea. It is easy to buy OTC. It is used as a fertiliser and in photographic processing; so is available from suppliers of such chemicals. You can also buy it from suppliers who sell chemicals to individuals (even in the UK).


http://www.boma.org/NR/rdonlyres/24B4C461-8B28-4B0B-BC12-1EB...

Rosco Bodine - 12-8-2006 at 12:31

I found a citation on semicarbazide via potassium cyanate and hydrazine sulfate attributing a source other than Wohler .

Amidourea, or semicarbazide, NH2CONHNH2, is best prepared from hydrazine sulphate and potassium cyanate (J. Thiele and O. Stange, Ber., 1894, 27, p. 31)

The citation was found a bit more than halfway doen the following page
http://jcsm.org/StudyCenter/Encyclopedia_Britannica/TUM_VAN/...

Anybody have anything on that Berichte citation for Thiele ?

Rosco Bodine - 12-8-2006 at 15:59

Hmmmm...

Shouldn't this topic be in the * Organic * Chemistry
section ?

S.C. Wack - 12-8-2006 at 20:28

Problems with Gallica can generally be worked around by reloading the page, or starting acrobat, or in this case by downloading the first 45 pages. It always has been screwy but has gotten more so in a file location change. At least 3 members here have scanned books published between 1937 and 1982 containing semicarbazide via hydrazine/cyanate.

[Edited on 13-8-2006 by S.C. Wack]

Attachment: semicarbazid.pdf (195kB)
This file has been downloaded 936 times

not_important - 12-8-2006 at 20:38

Ah, that you S.C. Wack. I checked my archives and did not have that method in detail.

Another source for urea is supplies for the hobby/home fabric dyeing people;

http://www.halcyonyarn.com/dyeing.html

http://www.mendels.com/tiedye.html

Rosco Bodine - 13-8-2006 at 08:06

Quote:
Originally posted by S.C. Wack
At least 3 members here have scanned books published between 1937 and 1982 containing semicarbazide via hydrazine/cyanate.


Thanks for that Thiele article from Berichte .

About the other references you mentioned , do you recall
what books those were , can you point me to them ?

S.C. Wack - 13-8-2006 at 10:19

The 1937 (English) Gattermann, the (German) 1982 Gattermann, and Vogel 3rd.

PS: Vanino and Biltz also.

[Edited on 14-8-2006 by S.C. Wack]

Rosco Bodine - 13-8-2006 at 22:03

Here is the Gattermann reference .



[Edited on 14-8-2006 by Rosco Bodine]

Attachment: Semicarbazide via hydrazine sulfate and alkali cyanate gattermann.pdf (104kB)
This file has been downloaded 1332 times

Al Koholic - 2-3-2008 at 21:44

Digging the thread up as I've been doing some work on this.

90g NH4Cl was dissolved in 300ml H2O and 200ml of 91% isopropyl alcohol. This was heated to ~50C. Another solution of 100g NaOCN in 500ml H2O was prepared and heated to effect dissolution of NaOCN. The NaOCN solution was added to the stirred NH4Cl solution in a steady stream over about 1 minute. Immediately there was noted a large volume of precipitated NaCl and very light effervescence of gas from the solution. Ammonia smell was VERY intense and stirring was continued for 30 minutes with heating from 50-60C. The heat was stopped and the NaCl filtered from the warm solution.

The liquid was then boiled down until bumping could no longer be controlled and poured into a dish to evaporate under an air current. The solid mass of crystals now present was removed from the dish and dissolved in boiling ethanol, then filtered from impurities (more NaCl).

The ethanol, on cooling precipitates a large volume of crystals, but it was deemed sufficient to simply evaporate all the ethanol and precipitate everything.

I will add the final yield when everything is dry.

Thoughts:

- I assume I am smelling strong ammonia during the reaction because any ammonium cyanate intermediate is decomposing to NH3, CO2, via a reaction with water. That would seem to be reducing yields. I added the alcohol and heat according to the pdf linked above, but would keeping things cold and dilute be better?

- The choice of ethanol in nearly every recrystallization of urea I have read seems odd since NaCl, and NH4Cl for that matter are both slightly soluble in it. Acetone would seem to be a better choice but I don't know what sort of solubility, or issues, urea might have with it. I will try it out with a small amount of the product.

- Mostly I'm worried a lot of nitrogen is being wasted here due to the insane liberation of ammonia from the reaction.

LSD25 - 3-3-2008 at 06:08

Go to just about any farm supply in any country I can think of and you will find it, it comes in 1kg, 2kg...20kg,...1,000kg bags for absolutely fuck all. Interestingly, because of its affinity for water, one of the places it is made in the biggest quantities is Saudi Arabia (one of their only exports other than oil).

I have helped to unload trucks of this shit (around 10-15,000kg), stacking it 100ft high in stacks, with two excavators - one picking it up and passing it to the next (just putting it in front)... Looks for all the world like mechanical ballet when you have good operators.

As to wasting perfectly good acetone, ammonia, hydrochloric acid on making it - fuck that...

PS I am sorry, trying to synthesise reagents might be fun and even enjoyable to work out and do, nonetheless working this hard on making the worlds number one fertilizer, which is also quite probably the worlds cheapest fertilizer, from more expensive fertilizers, acids, solvents etc. is just dumb. You ain't even going to be noticed buying urea, shit - the more of this crap you buy the less notice anybody is gunna take of you.

smuv - 3-3-2008 at 06:51

Some people on this forum actually ENJOY chemistry! I understand how to many on this forum synthesizing the first organic molecule ever discovered would be really interesting.

This forum is devoted to amateur experimentation, not getting the most for the least cost. Also watch the way you talk to people, you are being really rude without provocation.

not_important - 3-3-2008 at 09:16

I must comment that I one lived in a district where for some reason urea could not be found for sale at the retail level. On the outskirts there was one farm goods supplier, but they only dealt with large quantities, think 50 kg sacks, and required the setting up of an account with them. Hardly useful to a home experimenter who needs 50 or 100 grams.

At the same time a friend some distance away could buy urea off the shelf, but could not find ammonium sulfate. They ended up making it from urea and the readily available sulfuric acid.

Yes, these can be purchased from laboratory supply houses, but for younger experimenters this may proved to be impossible; in other places it may involve so much effort as to make seeking DIY routes preferable.

JohnWW - 3-3-2008 at 09:24

In at least one farm supply shop in my town, urea is available in large sacks as a fertilizer, along with Ca(NO3)2, (NH4)2SO4, KNO3, (NH4)3PO4, etc., NH4MgPO4, along with "superphosphate" (rock phosphate acidified with H2SO4 to make it sparingly soluble), although I am not sure about NH4NO3.

Al Koholic - 3-3-2008 at 10:52

LSD25, I appreciate the comments, and the interesting tidbit of info about Saudi Arabia. However, as I'm sure you know, this is about actually studying this reaction and it's nuances. I CAN buy dirty, coated, impure, crap urea from Walmart, but that's not really the point here.

I agree with not_important on the point that certain chems are just NOT available in every region within a given country as well. Sometimes the point is just not to "not be noticed" but that you can't find it! For a long time in upstate NY, I was unable to find urea ANYWHERE (unless of course I went the 50kg sack route).

I must say, even though to some it might seem like a waste of chemicals to make something like urea, it also seems like a huge waste to me to have to buy 15 pounds or more at a time, when I KNOW I'm not going to need anywhere remotely near that amount. Plus the forum is lacking in detailed info on the Wohler-like methods...

LSD25 - 3-3-2008 at 13:06

Yeah, I appreciate you might have wanted information on the very first organic synthesis...

I applaud your move toward replicating it in that case... But what of the search engine? We have people advocating turning toothpaste to lime, so it is entirely conceivable that someone, now or in the future, could see that they need urea, use the search engine (its gotta happen one day) and find this thread.

I know it sounds overly simplistic, but the option needs to be provided...

PS As to a waste to buy large amounts, consider using it for semi and actual ionic liquids and room-temp solvents, there is a lot of work going into this at the moment. As to purchasing dirty, impure crap - I personally enjoy purifying chemicals from fertilizers, multiple recrysallisations, separation of the organics (nearly all of 'em are coated or covered in oils), etc.:P

woelen - 3-3-2008 at 14:07

The historic reaction of making urea wasn't that simply heating of solid ammonium cyanate? I might be wrong though and it might have been more involved, as described above by Al Koholic.
I have some ammonium thiocyanate, and that can be heated to make thiourea, so I was thinking that making urea could go through a similar route.

@LSD25: As stated by others in this thread, I also ENJOY the chemistry behind many reactions. Even if I can buy reagent grade of a certain chemical for just a dime, then still I may be interested in the synthesis of such a chemical, just for the sake of understanding and scientific interest. I recently made some CO by means of electrolysis of chloroacetic acid, and in your eyes that may seem a tremendous waste of such a rare chemical. But sometimes, the process of getting an understanding of a certain reaction or a mechanism is of much more value than the chemical produced in the reaction.

LSD25 - 3-3-2008 at 14:37

Oh I enjoy making the damndest things as well, the thing is that while some members suggest buying 'EVERYTHING' even from chem supply, in preference to making shit, I only suggest buying as opposed to making where the purchase would be far easier, cheaper and a great deal more OTC than making whatever.

In this case, unless one actually wants to make urea from ammonia, it would be far better to buy it. I point this out, as this site (like many others) is currently suffering through an influx of new 'chemists' (couldn't be brand new college students could they? Finally got their very own internet connections?), most of whom seem to have some aversion to using search functions.

My concern, thus my post, is pointed toward ensuring that if such were to read this thread because they need urea for one reason or another, they understand that the purchase option is open.

By the way, for those who cannot access 'pure' urea from farm supply, buy a bag of mixed fert from the supermarket. The stuff you want is the larger, bright white prills (little balls), the smaller off-white balls are ammonium sulfate, the brown-green is either MAP/DAP or a mix of the two. To test for urea, put in a large covered bowl with a glass of water beside it, sit in sunlight to allow the humidity to increase. Urea will turn into a puddle in next to no time at 80% humidity.

Al Koholic - 3-3-2008 at 19:09

Well, I ended up getting 54 grams from the procedure I mentioned above.

Yield based on NaOCN should have been 93 grams which makes this a 58% yield. Also the material is somewhat (slight) moist still so it is likely a bit worse than that.

Now here are some concerns I have:

1) Drying the urea is difficult. Heating it very lightly with a current of air helps, but it always seems to hold onto some bit of moisture, even when drying from ethanol.

2) Basing this yield on NaOCN of uncertain purity (used straight from Na2CO3/Cyanuric acid heated until gas evolution stops) could mean that the yield is actually a bit higher if the NaOCN is far less than 100% pure.

Thinking about 2, makes me wonder if some of this ammonia I am smelling during the reaction is simply unreacted Na2CO3 liberating it from the NH4Cl. Anyone think neutralizing the NaOCN solution at the start would hurt anything? I think it has some Na2CO3 in it because of fizzing with HCl.



In a related note I dissolved a small amount of the urea into HCl then added a solution of KNO3 in an effort to precipitate urea nitrate. Is there a problem with this? I imagined the protonated urea would bind nitrate ions and precipitate leaving KCl in solution. Edit: This didn't work however.

Oh and woelen, the Wohler synthesis was the combination of ammonium salt and metal cyanate salt in aqueous solutions. Apparently ammonium cyanate does not technically exist as more than an intermediate in this reaction, being rearranged to urea.

[Edited on 4-3-2008 by Al Koholic]

not_important - 3-3-2008 at 19:23

Quote:
In a related note I dissolved a small amount of the urea into HCl then added a solution of KNO3 in an effort to precipitate urea nitrate. Is there a problem with this?

As HCl + nitrate, or nitric acid + chloride, is effectively aqua regia, you're going to have Cl2 and NOCl in it, neither of which are friends with urea. Using other acids may not be a solution, check the solubilities of the salts of those acids and urea vs urea nitrate.

Al Koholic - 3-3-2008 at 19:35

Good point not_important.

I will attempt this with sulfuric acid and acetic acid as both potassium salts should be very soluble in H2O.