Biuret

The parent compound can be prepared by heating urea at 150 °C for ~6 hours until it gets slightly cloudy, then recrystallizing from water. After that, it can be recrystallized repeatedly from 2% sodium hydroxide solution and water to finally get base-free crystalline needles of the monohydrate which are free of cyanuric acid. While heating, a lot of ammonia is expelled:{{ Ullmann | author = Meessen, J. H. | author2 = Petersen, H. | title = Urea | doi = 10.1002/14356007.a27_333 }}

:{{chem2|2 CO(NH2)2 → HN(CONH2)2 + NH3}}

Under related conditions, pyrolysis of urea affords triuret {{chem2|O\dC(\sN(H)\sC(\dO)\sNH2)2}}.

In general, organic biurets (those with alkyl or aryl groups in place of one or more H atoms) are prepared by trimerization of isocyanates. For example, the trimer of 1,6-hexamethylene diisocyanate is also known as HDI-biuret.

In the anhydrous form, the molecule is planar and unsymmetrical in the solid state owing to intramolecular hydrogen bonding. The terminal C–N distances of 1.327 and 1.334 Å are shorter than the internal C–N distances of 1.379 and 1.391 Å. The C=O bond distances 1.247 and 1.237 Å. It crystallizes from water as the monohydrate.{{cite journal|journal=Acta Crystallogr.|year=1961|volume=14|issue=4|pages=345–352|doi=10.1107/S0365110X61001194

|title=The Crystal Structure of Biuret Hydrate |author=E. W. Hughes |author2=H. Yakel |author3=H. C. Freeman|doi-access=free}}

image:ZZZLQC01.png

Biuret is used as a non-protein nitrogen source in ruminant feed,[http://www.britannica.com/eb/article-67947/livestock-farming Beef cattle feed], Encyclopædia Britannica Online where it is converted into protein by gut microorganisms.{{cite web | url = http://edis.ifas.ufl.edu/AN117 | author1 = Kunkle, B. | author2 = Fletcher, J. | author3 = Mayo, D. | year = 2013 | title = Florida Cow-Calf Management, 2nd Edition - Feeding the Cow Herd | publisher = IFAS Extension, University of Florida | id = Publication #AN117 | access-date = 2008-01-15 | archive-date = 2019-05-13 | archive-url = https://web.archive.org/web/20190513085424/http://edis.ifas.ufl.edu/an117 | url-status = dead }} It is less favored than urea, due to its higher cost and lower digestibility{{cite journal | author1 = Oltjen, R. R. | author2 = Williams, E. E. | author3 = Slyter, L. L. | author4 = Richardson, G. V. | title = Urea versus biuret in a roughage diet for steers | journal = Journal of Animal Science | year = 1969 | volume = 29 | issue = 5 | pages = 816–822 | pmid = 5391979 | url = http://www.journalofanimalscience.org/content/29/5/816 | doi = 10.2527/jas1969.295816x | access-date = 2013-10-22 | archive-date = 2021-01-12 | archive-url = https://web.archive.org/web/20210112220628/https://www.asas.org/publications/jas/content/29/5/816 | url-status = dead | url-access = subscription }} but the latter characteristic also slows down its digestion and so decreases the risk of ammonia toxicity.{{cite journal | last1=Fonnesbeck | first1=Paul V. | last2=Kearl | first2=Leonard C. | last3=Harris | first3=Lorin E. | title=Feed Grade Biuret as a Protein Replacement for Ruminants. A Review | journal=Journal of Animal Science | publisher=Oxford University Press (OUP) | volume=40 | issue=6 | date=1975 | issn=0021-8812 | doi=10.2527/jas1975.4061150x | pages=1150–1184 | url=https://academic.oup.com/jas/article-abstract/40/6/1150/4699012| url-access=subscription }}

The biuret test is a chemical test for proteins and polypeptides. It is based on the biuret reagent, a blue solution that turns violet upon contact with proteins, or any substance with peptide bonds. The test and reagent do not actually contain biuret; they are so named because both biuret and proteins have the same response to the test.

Biuret was first prepared and studied by Gustav Heinrich Wiedemann (1826–1899) for his doctoral dissertation, which was submitted in 1847. His findings were reported in several articles.{{ cite journal | author = Wiedemann, G. | title = Ueber ein neues Zersetzungsproduct des Harnstoffs |trans-title=On a new decomposition product of urea | journal = Annalen der Physik | volume = 150 | issue = 5 | pages = 67–84 | year = 1848 | doi = 10.1002/andp.18491500508 | bibcode = 1848AnP...150...67W | url = https://zenodo.org/record/1423618 }}{{ cite journal | author = Wiedemann, G. | title = Neues Zersetzungsproduct des Harnstoffs |trans-title=New decomposition product of urea | journal = Journal für Praktische Chemie | year = 1847 | volume = 42 | issue = 3–4 | pages = 255–256 | url = https://books.google.com/books?id=WNQPAAAAQAAJ&pg=PA255 | doi = 10.1002/prac.18470420134 | url-access = subscription }} This notice reports that biuret reacts with alkaline copper sulfate to produce a red solution – the so-called "Biuret test"{{ cite journal | author = Wiedemann, G. | title = Ueber eine neue, aus dem Harnstoff entstehende Verbindung |trans-title=On a new compound arising from urea | journal = Journal für Praktische Chemie | year = 1848 | volume = 43 | issue = 5 | pages = 271–280 | doi = 10.1002/prac.18480430133 | url = https://books.google.com/books?id=hgYwAAAAIAAJ&pg=PA271 }}{{ cite journal | author = Wiedemann, G. | year = 1848 | title = Biuret. Zersetzungsprodukt des Harnstoffs |trans-title=Biuret: decomposition product of urea | journal = Justus Liebig's Annalen der Chemie | volume = 68 | issue = 3 | pages = 323–326 | doi = 10.1002/jlac.18480680318 }}

• Cyanuric acid
• Allophanic acid, the carboxylic acid derivative of biuret

{{reflist}}

Category:Ureas

Category:Functional groups