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Urea salts during heating
I was thinking for some time, urea often makes salts with acids like HCl and citric acid. If I read correctly, urea citrate is insoluble salt. But
now, what would happen if we heat those salts like urea hydrohloride, urea citrate, urea acetate..?
Maybe some cyclic compounds might form which could be useful.
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AndersHoveland
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I do not think anything very interesting would form. You might get something similar to this: http://en.wikipedia.org/wiki/Allantoin
When urea is heated with alcohol in sealed tubes, esters of carbamic acid are formed.
http://pubs.acs.org/doi/abs/10.1021/ja01275a011
Coincidentally, I had recently been thinking about what products would form from refluxing urea, ethyl carbamate, and hydrazine together.
Optimistically, some 3,5-diamino-1,2,4-triazole may form. Or substitute formamidine HC(=O)NH2 for the ethyl carbamate to possibly produce
3-amino-1,2,4-triazole. Similar condensations are well known (Einhorn-Brunner and Pellizzari reactions).
However, refluxing semicarbazide hydrochloride with formic acid is known to produce only 1,2,4 triazol-3-oxide. Semicarbazide can be made by reacting
hydrazine with urea*, and is therefore equivalent as a reactant to a mixture of urea and hydrazine, but with less ammonia. It is for this reason that
if one hoped to obtain aminotriazoles, the reaction conditions should be much more alkaline, with more ammonia.
*there has been some controversy on this forum about whether semicarbazide can be so easily produced, but it seems that it indeed can,
United States Patent 4482738
Rossel and Frank, Ber. 27, 56 (1894)
I also found a mention in another reputable piece of online literature: "...semicarbazide is best made from urea and hydrazine; using excess urea."
structure of 1,2,4-triazole-3-one can be seen here:
http://img1.guidechem.com/chem/e/dict/61/930-33-6.jpg
[Edited on 23-3-2011 by AndersHoveland]
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Nicodem
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What is the reference?
| Quote: | | If I read correctly, urea citrate is insoluble salt. |
Urea can not form true salts with carboxylic acids (check the corresponding pKa's!). It does however very readily form complexes and chelates with
many compounds of different types, including also carboxylic acids (complexes are commonly called "double compounds" in the older literature).
Particularly the chelates with fatty acids and straight chain alkanes are well known due to their usefulness in separation processes.
The urea-citric acid complexes, including the 1 : 1 ratio which corresponds to "urea citrate" and can be conditionally called as such provided you
know it is neither a salt nor ester, are known (see DOI: 10.1007/s11167-005-0579-2 for their synthesis and characterization). The 4 : 1 and 2 : 1
urea-citric acid complexes are also described, as well as the 1 : 2 urea-acetic acid, and the 2 : 1 and 1 : 2 urea-tartaric acid (see DOI:
10.1021/ja01284a001). The urea-oxalic acid is also known (see DOI: 10.1021/ja01318a010).
| Quote: | | But now, what would happen if we heat those salts like urea hydrohloride, urea citrate, urea acetate..? |
If you heat them, they decompose. The products depend on what you heat, at which temperature and whether it is heated in a closed system, solvent or
openly.
PS: You have been told a dozen times to open referenceless threads only in the Beginners section, so either start giving references or conform to this
simple rule. Do you think it is fun for those interested in answering your questions to do literature searches on their own when it is about your
interests?
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Random
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Sorry about those referenceless threads, this is the last thread I posted here without reference and it won't happen again.
I read on BromicAcid's page about urea oxalate and it's decomposition, before I also seen urea nitrate insoluble and explosive and fund urea citrate
also insoluble.
AndersHoveland, thanks for that carbamate ester info, I could maybe attempt it sometime. I also found something interesting about semicarbazide, but
now I forgot what it was..
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Nicodem
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Don't play with homebuilt autoclaves until you grow to know what you are doing!
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Random
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Thanks for the warning, though I think I found before some way of forming carbamate without autoclave, but I am not sure. I am not even thinking about
building them, that stuff is too dangerous.
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