No, I am not kidding!
I have always been interested in the chemicals the body produces/excretes, and urea is one of them!
Of course, urea is mostly easily available, but not everywhere. So there are ways of obtaining it yourself, from a chemical synthesiser called your
own body
Urea is of course an ancient, well studied chemical, in fact it was discovered over 230 years ago, and Friedrich Woehler determined that urea could
also be synthesised from inorganic chemicals, i.e. by the reaction of potassium cyanate with ammonium sulfate (1828).
The original discovery of urea was by Hilaire Marin Rouelle in 1773, who obtained it by boiling urea dry and obtaining a white residue (which later
proved to be identical with Woehlers reaction products - disproving the idea that the chemistry of the living is radically different from inanimate
matter)
Unfortunately, simply boiling down urine doesnt quite satisfy anyone, as it still contains certain quantities of salt, creatine, ureic acid, proteins
etc.
Per day, about 1.5 - 2 litres are excreted, consisting of 95% of water. The rest (in grams per day consists of)
# 25 g urea
# 1 g uric acid (metabolic endproduct of purines from DNA)
# 1.5 g creatinine (derived from creatine phosphate, the muscle booster)
# 10 g of salts, mainly NaCl
# 3 g of phosphates, citric acid, oxalic acid,
# milligrams of proteins, and urochromen, which is the compound giving rise to the yellow colour of urine.
Now, looking at this information, what could be the best way of isolating urea from it?
How about this:
1. Collect urine for about a week, one should get about 10 litres. Needless to say, urine is STERILE to start off with. Preferably though, after each
urine addition, the solution should be simply boiled to keep it sterile. Otherwise, just literally pee into a sterile pot with lid, and keep it at 4
deg C for the rest of the week. I dont think bacterial contamination should be a problem then (unless your have a medical condition, where bacteria
are excreted through your urinary tracts)
2. AFter a week, boil down the urine, until a solid mass is obtained (from the above table, it should way about 300 grams. Do this outside, unless you
want 10 litres of water condensing on your windows
3. That's when things become interesting. You want to get rid of salts (primarily), and phosphates. At this point there is no easy way to get rid of
the creatinine, and the ureic acid. Proteins aren't much to worry about anyway, as conc. are very low.
So - I checked - urea is soluble in ethanol, at 50 g / l, @ 20 degC . Probably a lot more is soluble at higher temperatures. In water, it dissolves at
>1500 g/litre, so very highly soluble. I'd try to dissolve the urine residue in an excess of cheap industrial ethanol (doesnt matter if it contains
other things), which would mean, around 3 litres, if you heat the ethanol up a little (no open flames ok). All the inorganic stuff (salts etc) are
barely soluble in ehtanol, so they should remain precipitated.
4. Filter off the remainder, and boil of the ethanolic solution of urea (with a small amount of creatinine potentially) down to a few hundred ml's, or
even to dryness. If you distill, you can obviously recycle the ethanol, although it may prove to be a pain to recycle such large amounts, considering
that ethanol is cheap anyhow.
5. Alternatively, once you boiled down the ethanolic solution of urea to a few hundred ml, you could add HCl (conc) or H2SO4, and precipitate urea as
the respective salt (which is surely insoluble in ethanol). The salt can be turned back into urea with the appropriate amount of NaOH.
What do you think? Sure this is a very simple way of purifying urea, and of course if you had all the reagents, one could get extremely high purities.
At least, this way, one gets about 200 g of urea, straight from urine, with the only expense of 3 litres of industrial ethanol.
[Edited on 10-1-2010 by chemoleo] |