Allophanic acid
Allophanic acid is the organic compound with the formula H2NCNHCO2H. 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:
Although allophanic acid per se may not have been purified, its conjugate base, H2NCNHCO2−, allophanate is well known. 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.