Ammonium carbamate is an inorganic compound with the formula NH4[H2NCO2] consisting of ammonium NH+
4 and carbamate H
2. 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 intermediary in the industrial synthesis of urea, an important fertilizer.
ammonium amidocarbonate, azanium amidodioxidocarbonate, ammonium aminoformate, carbamic acid ammonium salt, carbamic acid monoammonium salt
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||78.071 g·mol−1|
|Appearance||Colorless, rhombic crystals|
|Density||1.38 g/cm3 (20 °C)|
|Melting point||60 °C (140 °F; 333 K) decomposes|
|Freely soluble in water|
|Solubility||Soluble in ethanol, methanol, liquid ammonia, formamide|
|log P||−0.47 in octanol/water|
|Vapor pressure||492 mmHg(51 °C)|
Std enthalpy of
|Main hazards||Harmful if ingested, harmful to aquatic life, harmful if inhaled, respiatory tract irritation, skin irritation, eye irritation|
|Safety data sheet||External MSDS|
|GHS Signal word||Warning|
|NFPA 704 (fire diamond)|
|Flash point||105.6 °C (222.1 °F; 378.8 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|1,470 mg/kg in a rat|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
- NH2CO2NH4 ⇌ 2NH3 + CO2
Lower temperatures shift the equilibrium towards the carbamate.
At higher temperatures ammonium carbamate condenses into urea:
- NH2CO2NH4 → (H
2C=O + H
Equilibrium in waterEdit
At ordinary temperatures and pressures, ammonium carbamate exists in aqueous solutions as an equilibrium with ammonia and carbon dioxide, and the anions bicarbonate HCO−
3 and CO3, Indeed, solutions of ammonium carbonate or bicarbonate will contain some carbamate anions too.
+ 2 H
2O ⇌ NH+
4 + HCO−
3 + HO−
- 2 H
+ 2 H
2O ⇌ 2 NH+
4 + CO2−
The structure of solid ammonium carbamate has been confirmed by X-ray crystallography. The oxygen centers form hydrogen bonds to the ammonium cation.
Ammonium carbamate serves a key role in the formation of carbamoyl phosphate, which is necessary for both the urea cycle and the production of pyrimidines. In this enzyme-catalyzed reaction, ATP and ammonium carbamate are converted to ADP and carbamoyl phosphate:
- ATP + NH2CO2NH4 → ADP + H2NC(O)OPO32−
From liquid ammonia and dry iceEdit
Ammonium carbamate is prepared by the direct reaction between liquid ammonia and dry ice (solid carbon dioxide):
- 2 NH3 + CO2 → H2NCOONH4
From gaseous ammonia and carbon dioxideEdit
Ammonium carbamate can also be obtained by bubbling gaseous CO
2 and NH
3 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.
Ammonium carbamate is an intermediate in the industrial production of urea. A typical industrial plant that makes urea can produce up to 1500 tons a day. in this reactor and can then be dehydrated to urea according to the following equation:
- NH2CO2NH4 → NH2CONH2 + H2O
Ammonium carbamate has also been approved by the Environmental Protection Agency as an inert ingredient present in aluminium phosphide pesticide formulations. This pesticide is commonly used for insect and rodent control in areas where agricultural products are stored. The reason for ammonium carbamate as an ingredient is to make the phosphine less flammable by freeing ammonia and carbon dioxide to dilute hydrogen phosphine formed by a hydrolysis reaction.
Ammonium carbamate can be used as a good ammoniating agent, though not nearly as strong as ammonia itself. For instance, it is an effective reagent for preparation of different substituted β-amino-α,β-unsaturated esters. The reaction can be carried out in methanol at room temperature and can be isolated in the absence of water, in high purity and yield.
Preparation of metal carbamatesEdit
Ammonium carbamate can be a starting reagent for the production of salts of other cations. For instance, by reacting it with solid potassium chloride KCl in liquid ammonia one can obtain potassium carbamate K+
. Carbamates of other metals, such as calcium, can be produced by reacting ammonium carbamate with a suitable salt of the desired cation, in an anhydrous solvent such as methanol, ethanol, or formamide, even at room temperature.
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