Urea, known as carbamide due to its composition as a diamide of carbonic acid, is an organic molecule represented by the chemical formula CO(NH2)2. This compound is an amide consisting of two amino groups (–NH2) connected by a carbonyl functional group (–C(=O)–). Therefore, it is the most basic form of carbamic acid amide.

Urea plays a crucial function in the metabolism of nitrogen-containing substances in animals and is the primary nitrogen-containing molecule found in mammalian urine. The term “urea” is derived from the Neo-Latin language, specifically from the French word “urée,” which may be traced back to the Ancient Greek word “οὖροv” (oûron), meaning “urine.” This Greek word, in turn, has its origins in the Proto-Indo-European language, namely from the word “*h₂worsom.”

The substance is a transparent, scentless material that easily dissolves in water and is virtually harmless (with a lethal dose of 15 g/kg for rats).The user’s text is “[6]”. When mixed with water, it has a neutral pH. The body utilizes it in numerous physiological functions, particularly in the elimination of nitrogen. In the urea cycle, the liver synthesizes it by chemically mixing two ammonia molecules (NH3) with a carbon dioxide (CO2) molecule. Urea is extensively utilized in fertilizers as a nitrogen (N) source and serves as a crucial raw element in the chemical sector.

In 1828, Friedrich Wöhler made the significant breakthrough of synthesizing urea from inorganic precursors, marking a crucial milestone in the field of chemistry. This experiment demonstrated, for the first time, that a substance previously recognized solely as a byproduct of living organisms could be artificially created in a laboratory without the use of biological materials. This finding challenges the widely accepted principle of vitalism, which asserts that only living organisms have the ability to generate the essential chemicals of life.

Analysis of the arrangement of molecules and the geometric arrangement of atoms in a crystal
In a solid crystal, the urea molecule exhibits planarity due to the sp2 hybridization of its nitrogen orbitals.[7][8] In the gas phase or in aqueous solution, it exhibits non-planar geometry with C2 symmetry. The bond angles C–N–H and H–N–H are midway between the trigonal planar angle of 120° and the tetrahedral angle of 109.5°. The oxygen core in solid urea forms two N–H–O hydrogen bonds. The dense and energetically favorable hydrogen-bond network that forms is likely achieved by sacrificing efficient molecule packing. The structure has a significant degree of openness, with the ribbons arranged in tunnels that possess a square cross-sectional shape. The carbon in urea is sp2 hybridized, resulting in C-N bonds with substantial double bond character. Additionally, the carbonyl oxygen in urea exhibits relatively high basicity. The great aqueous solubility of urea is a result of its capacity to form large hydrogen bonds with water.

Due to its propensity to create permeable structures, urea possesses the capacity to ensnare numerous chemical molecules. Within these structures known as clathrates, the organic “guest” molecules are confined within channels created by intertwined helices made up of hydrogen-bonded urea molecules.

Due to interconnection, all helices within a crystal must possess identical molecular handedness. The determination of this is contingent upon the nucleation of the crystal and can therefore be manipulated through the process of seeding. The obtained crystals have been employed for the purpose of isolating racemic mixtures.

Urea has a high pH and rapidly accepts protons. Additionally, it acts as a Lewis base by creating metal complexes with the structure [M(urea)6]n+.

The reaction between urea and malonic esters yields barbituric acids.

Decomposition refers to the process of breaking down complex substances into simpler components.
At approximately 152 °C, molten urea undergoes decomposition, resulting in the formation of ammonium cyanate. Above 160 °C, it further decomposes into ammonia and isocyanic acid.

The chemical equation CO(NH2)2 is transformed into the ions [NH4]+ and [OCN]−. Ammonia reacts with isocyanic acid.
When subjected to temperatures over 160 °C, a reaction occurs between the substance and isocyanic acid, resulting in the formation of biuret (NH2CONHCONH2) and triuret (NH2CONHCONHCONH2).

The reaction between CO(NH2)2 and HNCO yields NH2CONHCONH2.
The reaction between NH2CONHCONH2 and HNCO yields NH2CONHCONHCONH2.
At elevated temperatures, it undergoes a transformation into several condensation products, such as cyanuric acid (CNOH)3, guanidine HNC(NH2)2, and melamine.

Urea undergoes a gradual equilibration process with ammonium cyanate in a water-based solution. The process of hydrolysis simultaneously produces isocyanic acid, which has the ability to carbamylate proteins. This carbamylation mostly affects the N-terminal amino group, the amino group of lysine, and to a lesser extent, the side chains of arginine and cysteine. Every instance of carbamylation increases the protein’s mass by 43 daltons, a change that may be detected using protein mass spectrometry. To ensure the absence of cyanate (20 mM in 8 M urea), it is advisable to create and utilize fresh urea solutions, as older solutions may accumulate a notable concentration of cyanate.The user’s text is enclosed in tags. It is recommended to dissolve urea in ultrapure water, then remove ions (specifically cyanate) using a mixed-bed ion-exchange resin. The resulting solution should be stored at a temperature of 4 °C. Nevertheless, cyanate will accumulate to substantial amounts within a matter of days. In contrast, the inclusion of 25–50 mM ammonium chloride in a highly concentrated urea solution reduces the production of cyanate due to the influence of the common ion effect.

Urea may be accurately measured using various techniques, including the diacetyl monoxime colorimetric method and the Berthelot reaction, which involves converting urea to ammonia using urease. These approaches can be easily adapted for use with high throughput instruments, such as automated flow injection analyzers and 96-well micro-plate spectrophotometers.

Associated substances
Primary focus: ureas
Ureas are a group of chemical compounds characterized by the presence of a carbonyl group connected to two organic amine residues: R1R2N−C(=O)−NR3R4, where R1, R2, R3, and R4 can be hydrogen (–H), organyl, or other groups. Some examples comprise carbamide peroxide, allantoin, and hydantoin. Ureas exhibit structural similarities to biurets, as well as to amides, carbamates, carbodiimides, and thiocarbamides.