Ammonium carbamate is a chemical compound with the formula consisting of ammonium cation and carbamate anion . It is a white solid that is extremely soluble in water, less so in alcohol. Ammonium carbamate can be formed by the reaction of ammonia with carbon dioxide , and will slowly decompose to those gases at ordinary temperatures and pressures. It is an intermediate in the industrial synthesis of urea , an important fertilizer.
Properties Solid-gas equilibrium In a closed container solid ammonium carbamate is in equilibrium with carbon dioxide and ammonia R. N. Bennett, P. D. Ritchie, D. Roxburgh and J. Thomson (1953): "The system ammonia + carbon dioxide + ammonium carbamate. Part I. — The equilibrium of thermal dissociation of ammonium carbamate". Transactions of the Faraday Society, volume 49, pages 925-929.
Lower temperatures shift the equilibrium towards the carbamate.
At higher temperatures ammonium carbamate condenses into urea:
This reaction was first discovered in 1870 by Bassarov, by heating ammonium carbamate in sealed glass tubes at temperatures ranging from 130 to 140 °C.
Equilibrium in water At ordinary temperatures and pressures, ammonium carbamate exists in aqueous solutions as an equilibrium with ammonia and carbon dioxide, and the anions bicarbonate, , and carbonate, .George H. Burrows and Gilbert N. Lewis (1912): "The equilibrium between ammonium carbonate and ammonium carbamate in aqueous solution at 25°". Journal of the American Chemical Society, volume 34, issue 8, pages 993-995. Fabrizio Mani, Maurizio Peruzzini, and Piero Stoppioni (2006): " absorption by aqueous solutions: speciation of ammonium carbamate, bicarbonate and carbonate by a 13C NMR study". Green Chemistry, volume 8, issue 11, pages 995-1000. Indeed, solutions of ammonium carbonate or bicarbonate will contain some carbamate anions too.
Structure The structure of solid ammonium carbamate has been confirmed by X-ray crystallography. The oxygen centers form hydrogen bonds to the ammonium cation. There are two polymorphs, α and β, both in the orthorhombic crystal system but differing in their space group. The α polymorph is in space group Pbca (no. 61), whereas the β polymorph is in Ibam (no. 72). The α polymorph is more volatile.
Preparation From liquid ammonia and dry ice Ammonium carbamate is prepared by the direct reaction between liquid ammonia and dry ice (solid carbon dioxide):
From gaseous ammonia and carbon dioxide Ammonium carbamate can be prepared by reaction of the two gases at high temperature (175–225 °C) and high pressure (150–250 bar).
It can also be obtained by bubbling gaseous and in anhydrous ethanol, 1-propanol, or DMF at ambient pressure and 0 °C. The carbamate precipitates and can be separated by simple filtration, and the liquid containing the unreacted ammonia can be returned to the reactor. The absence of water prevents the formation of bicarbonate and carbonate, and no ammonia is lost.
Uses Urea synthesis Ammonium carbamate is an intermediate in the industrial production of urea. A typical industrial plant that makes urea can produce up to 4000 tons a day. in this reactor and can then be dehydrated to urea according to the following equation:
Pesticide formulations Ammonium carbamate is an inert ingredient in some formulations of the pesticide aluminium phosphide (AlP). Ammonium carbamate make the phosphine less flammable released by AlP by freeing ammonia and carbon dioxide to dilute the phosphine.United States Environmental Protection Agency. (2006). Inert Reassessment-Ammonium Carbamate [Data File]. Retrieved from
Laboratory Ammonium carbamate can be used as a ammoniating agent. It has been used to preparation substituted β-amino-α,β-unsaturated esters.Mladen Litvić, Mirela Filipan, Ivan Pogorelić and Ivica Cepanec (2005): "Ammonium carbamate; mild, selective and efficient ammonia source for preparation of β-amino-α,β-unsaturated esters at room temperature". Green Chemistry, volume 7, issue 11, pages 771-774.
Ammonium carbamate reacts with potassium chloride KCl in liquid ammonia to give potassium carbamate .Carl Theodor Thorssell and August Kristensson (1935): "Process for the production of potassium carbamate". US Patent 2002681, US31484228A Carbamates of other metals, such as calcium, can be produced similarly in anhydrous solvents such as methanol, ethanol, or formamide, even at room temperature.Erns Kuss and Emil Germann (1935): "Production of metal carbamates". US Patent US2023890A
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