Carbamic acid

Carbamic acid, which might also be called aminoformic acid or aminocarboxylic acid, is the chemical compound with the formula H₂NCOOH. It can be obtained by the reaction of ammonia NH₃ and carbon dioxide CO₂ at very low temperatures, which also yields ammonium carbamate [NH₄]⁺[NH₂CO₂]⁻. The compound is stable only up to about 250 K (−23 °C); at higher temperatures it decomposes into those two gases. The solid apparently consists of dimers, with the two molecules connected by hydrogen bonds between the two carboxyl groups –COOH.

Carbamic acid could be seen as both an amine and carboxylic acid, and therefore an amino acid; however, the attachment of the carboxyl group –COOH directly to the nitrogen atom (without any intermediate carbon chain) makes it behave very differently from the amino acids with intermediate carbon chain. (Glycine NH₂CH₂COOH is generally considered to be the simplest amino acid.) The hydroxyl group –OH attached to the carbon also excludes it from the amide class.

The term "carbamic acid" is also used generically for any compounds of the form RR′NCOOH, where R and R′ are organic groups or hydrogen.

Deprotonation of a carbamic acid yields a carbamate anion RR′NCOO⁻, the salts of which can be relatively stable. Carbamate is also a term used for esters of carbamic acids, such as methyl carbamate H₂N−C(=O)−OCH₃. The carbamoyl functional group RR′N–C(=O)– (often denoted by Cbm) is the carbamic acid molecule minus the OH part of the carboxyl.