Allophanic acid

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.

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

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.