Biuret

Biuret is a chemical compound with the chemical formula HN(CONH2)2. It is a white solid that is soluble in hot water. The term "biuret" also describes a family of organic compounds with the chemical formula R1R2N−C(=O)−N(R3)−C(=O)−NR4R5. Thus, dimethyl biuret is H(CH3)N−C(=O)−N(H)−C(=O)−N(CH3)H. A variety of organic derivatives are known. Also known as carbamylurea, it results from the condensation of two equivalents of urea. As such, it is an undesirable impurity in urea-based fertilizers. As biuret is toxic to plants, its percentage in fertilizers must be kept low.

Biuret
Names
Preferred IUPAC name
2-Imidodicarbonic diamide[1]
Other names
Biuret[1]
Allophanamide[2]
Carbamylurea[2]
Allophanic acid amide[2]
Allophanimidic acid[2]
N-Carbamoylaminomethanamide
Ureidoformamide[2]
Imidodicarbonic diamide
Diurea
Identifiers
3D model (JSmol)
3DMet
1703510
ChEBI
ChemSpider
ECHA InfoCard 100.003.236
EC Number
  • 203-559-0
49702
KEGG
MeSH Biuret
UNII
  • InChI=1S/C2H5N3O2/c3-1(6)5-2(4)7/h(H5,3,4,5,6,7) Y
    Key: OHJMTUPIZMNBFR-UHFFFAOYSA-N Y
  • NC(=O)NC(N)=O
Properties
HN(CONH2)2
Appearance White crystals
Odor Odourless
Density 1.467 g/cm3
Melting point 190 °C (decomposes)
Thermochemistry
131.3 J/(K·mol)
146.1 J/(K·mol)
(−565.8) – (−561.6) kJ/mol
(−940.1) – (−935.9) kJ/mol
Hazards
GHS labelling:
Warning
H315, H319, H335
P261, P305+P351+P338
Related compounds
Related compounds
 urea, triuret, cyanuric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Preparation and structure

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:[3]

2 CO(NH2)2 → HN(CONH2)2 + NH3

Under related conditions, pyrolysis of urea affords triuret O=C(−N(H)−C(=O)−NH2)2.[3] 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.[4]

Structure of biuret in the solid state (blue = N, red = O, gray = C, cyan = H).

Applications

Biuret is also used as a non-protein nitrogen source in ruminant feed,[5] where it is converted into protein by gut microorganisms.[6] It is less favored than urea, due to its higher cost and lower digestibility[7] but the latter characteristic also slows down its digestion and so decreases the risk of ammonia toxicity.[7][8]

Biuret test

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.

History

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.[9][10][11][12]

References
  1. Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 866. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
  2. Scifinder, version 2007.1; Chemical Abstracts Service: Columbus, OH; RN 108-19-0 (accessed June 15, 2012)
  3. Meessen, J. H.; Petersen, H. "Urea". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a27_333.
  4. E. W. Hughes, H. Yakel, H. C. Freeman (1961). "The Crystal Structure of Biuret Hydrate". Acta Crystallogr. 14 (4): 345–352. doi:10.1107/S0365110X61001194.{{cite journal}}: CS1 maint: uses authors parameter (link)
  5. Beef cattle feed, Encyclopædia Britannica Online
  6. Kunkle, B.; Fletcher, J.; Mayo, D. (2013). "Florida Cow-Calf Management, 2nd Edition - Feeding the Cow Herd". IFAS Extension, University of Florida. Publication #AN117.
  7. Oltjen, R. R.; Williams, E. E.; Slyter, L. L.; Richardson, G. V. (1969). "Urea versus biuret in a roughage diet for steers". Journal of Animal Science. 29 (5): 816–822. doi:10.2527/jas1969.295816x. PMID 5391979.
  8. Fonnesbeck, P. V.; Kearl, L. C.; Harris, L. E. (1975). "Feed Grade Biuret as a Protein Replacement for Ruminants. A Review". Journal of Animal Science. 40 (6): 1150–1184. doi:10.2527/jas1975.4061150x.
  9. Wiedemann, G. (1848). "Ueber ein neues Zersetzungsproduct des Harnstoffs" [On a new decomposition product of urea]. Annalen der Physik. 150 (5): 67–84. Bibcode:1848AnP...150...67W. doi:10.1002/andp.18491500508.
  10. Wiedemann, G. (1847). "Neues Zersetzungsproduct des Harnstoffs" [New decomposition product of urea]. Journal für Praktische Chemie. 42 (3–4): 255–256. doi:10.1002/prac.18470420134. This notice reports that biuret reacts with alkaline copper sulfate to produce a red solution -- the so-called "Biuret test"
  11. Wiedemann, G. (1848). "Ueber eine neue, aus dem Harnstoff entstehende Verbindung" [On a new compound arising from urea]. Journal für Praktische Chemie. 43 (5): 271–280. doi:10.1002/prac.18480430133.
  12. Wiedemann, G. (1848). "Biuret. Zersetzungsprodukt des Harnstoffs" [Biuret: decomposition product of urea]. Justus Liebig's Annalen der Chemie. 68 (3): 323–326. doi:10.1002/jlac.18480680318.
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