Acide carbamique

Carbamic acid, which might also be called aminoformic acid or aminocarboxylic acid, is the chemical compound with the formula . It can be obtained by the reaction of ammonia and carbon dioxide at very low temperatures, which also yields ammonium carbamate . 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 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 , the salts of which can be relatively stable. Carbamate is also a term used for esters of carbamic acids, such as methyl carbamate . The carbamoyl functional group RR′N–C(=O)– (often denoted by Cbm) is the carbamic acid molecule minus the OH part of the carboxyl. Carbamic acid is a planar molecule. The group of carbamic acid, unlike that of most amines, cannot be protonated to an ammonium group . The zwitterionic form is very unstable and promptly decomposes into ammonia and carbon dioxide, yet there is a report of its detection in ices irradiated with high-energy protons. Carbamic acid is formally the parent compound of several important families of organic compounds: File:Carbamic-acid-group-2D-L.png|carbamic acids File:Carbamate-anion-generic-2D.png|carbamate anions File:Carbamate-group-2D.png|carbamate esters File:Carbamoyl-chloride-generic-2D.