Allophanic acid

Allophanic acid

Names
Preferred IUPAC name Carbamoylcarbamic acid
Identifiers
CAS Number	625-78-5
3D model (JSmol)	Interactive image
Beilstein Reference	1756623
ChEBI	CHEBI:9889
ChemSpider	132943
KEGG	C01010
PubChem CID	150833
UNII	0W5I7B2C2H
CompTox Dashboard (EPA)	DTXSID20211550
InChI InChI=1S/C2H4N2O3/c3-1(5)4-2(6)7/h(H,6,7)(H3,3,4,5) Key: AVWRKZWQTYIKIY-UHFFFAOYSA-N
SMILES C(=O)(N)NC(=O)O
Properties
Chemical formula	C2H4N2O3
Molar mass	104.065 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Allophanic acid is the organic compound with the formula H₂NC(O)NHCO₂H. It is a carbamic acid, the carboxylated derivative of urea. Biuret can be viewed as the amide of allophanic acid.

Treating urea with sodium bicarbonate is claimed to give allophanic acid: ^[1]

H₂NC(O)NH₂ + NaHCO₃ → H₂NC(O)NHCO₂H + NaOH

Although allophanic acid per se may not have been purified, its conjugate base, H₂NC(O)NHCO₂⁻, allophanate is well known. Salts of this anion have been characterized by X-ray crystallography. ^{[2] [3]} The allophanate anion is the substrate for the enzyme allophanate hydrolase.

Allophanate esters arise from the condensation of carbamates.

References

1. Karachinskii, S. V.; Dragalov, V. V.; Chimishkyan, A. L.; Tsvetkov, V. Yu. (1987). "Reaction of urea with alkali metal carbonates". Zhurnal Organicheskoi Khimii. 23: 93–6.  
2. Mak, Thomas C. W.; Yip, Wai Hing; Li, Qi (1995). "Novel Hydrogen-Bonded Host Lattices Built of Urea and the Elusive Allophanate Ion". Journal of the American Chemical Society. 117 (48): 11995–11996. doi:10.1021/ja00153a022.
3. Li, Qi; Mak, Thomas C. W. (1996). "A Novel Inclusion Compound Consolidated by Host-host and Host-guest Hydrogen Bonding: (2-hydro-xyethyl)trimethylammonium Ions Included in a Channel Host Lattice Built of Urea Molecules and Allophanate Ions". Supramolecular Chemistry. 8: 73–80. doi:10.1080/10610279608233970.