Biuret


Biuret is a chemical compound with the chemical formula 2NH. It is a white solid that is soluble in hot water. The term "biuret" also describes a family of organic compounds with the functional group -2N-. Thus, dimethyl biuret is 2NH. 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.

Preparation and structure

The parent compound can be prepared by heating urea above the melting point at which temperature ammonia is expelled:
Under related conditions, pyrolysis of urea affords triuret.
In general, organic biurets are prepared by trimerization of isocyanates. For example, the trimer of 1,6-hexamethylene diisocyanate is also known as HDI-biuret.
In the anhydrous material, 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 hydrate.

Applications

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

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 for his doctoral dissertation, which was submitted in 1847. His findings were reported in several articles.

Related compounds