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. The compound can be prepared by treating urea with sodium bicarbonate:
 * H2NC(O)NH2 +  NaHCO3  →  H2NC(O)NHCO2H  +  NaOH

The anionicconjugate base, H2NC(O)NHCO2−, is called allophanate. Salts of this anion have been characterized by X-ray crystallography. The allophanate anion is the substrate for the enzyme allophanate hydrolase.

Allophanate esters arise from the condensation of carbamates.