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: 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. The allophanate anion is the substrate for the enzyme allophanate hydrolase.
Allophanate esters arise from the condensation of carbamates.
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