Urea

Ball-and-stick Stick Space-filling

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8 atoms, 7 bonds.

IUPAC name: urea
Molar mass: 60.0560(58) g/mol
Atoms: 8
SMILES: C(=O)(N)N
InChIKey: XSQUKJJJFZCRTK-UHFFFAOYSA-N
PubChem CID: 1176

Made of

Structural formula of urea. Each unlabelled corner is a carbon atom. It shows which atoms are joined to which, not the shape. The model above shows the shape.

When the body breaks down protein, the nitrogen leaves in one small compound, urea. MeSH, the US National Library of Medicine’s subject vocabulary, calls it the principal end product of protein breakdown and about one half of the total solids in urine. Its formula is CO(NH₂)₂, built from carbon, oxygen, nitrogen and hydrogen. Its IUPAC name is simply urea, and a mole weighs 60.056 g.

Urea forms odourless white crystals or pellets that do not burn, according to CAMEO Chemicals. It has a cooling, salty taste and melts at 132.70 °C, in figures from the Hazardous Substances Data Bank (HSDB). It dissolves generously in water, 5.45 × 10⁵ mg in a litre at 25 °C by HSDB’s figure, about 545 g, yet hardly at all in benzene. Left in damp air, the solid may slowly pick up a faint smell of ammonia. Urea was also, in HSDB’s words, the first organic compound ever made by synthesis.

Structure and bonding

Urea’s carbon sits at the centre of three bonds. A double bond, drawn as two sticks, runs to the oxygen, and single bonds run to two nitrogens, each carrying two hydrogens. The Labels button marks one C, one O, two N and four H: eight atoms and seven bonds. ChEBI, a database of small biological molecules, reads this pattern as a carbonyl group flanked by two amine groups.

Turned edge-on, the model collapses to a thin line: PubChem’s computed conformer places all eight atoms in one plane. In the model the angles at the carbon are 123.7° for each O–C–N pair and 112.7° for N–C–N, adding up to 360°. That stays close to the 120° spacing that Chem1 gives three electron regions around one atom in a plane. Each NH₂ group lies flat in the model too.

The Stick view strips the atoms to their bonds and shows the same flat outline. In the Space-filling view the hydrogens nearly vanish into the two nitrogen spheres, and the oxygen caps one end. HSDB calls urea the diamide of carbonic acid, a name for its two NH₂ groups on one carbonyl carbon.

Where it turns up

Every human body makes urea. It is made in the liver, where ammonia produced from amino acids becomes the final product of protein breakdown, according to MeSH and the NCI Thesaurus. MedlinePlus describes the blood carrying this waste to the kidneys, which pass it out in urine. Once made, urea spreads through roughly the whole of the body’s water, according to HSDB.

Outside the body, urea turns up on food labels and bathroom shelves. JECFA, the food-additive committee run jointly by FAO and WHO, lists it as a chewing-gum base compound, a texturiser, a thickener and yeast food, and ChEBI adds flour treatment. The US Environmental Protection Agency (EPA) lists it as a humectant, a substance that holds moisture, among consumer uses. WHO’s drug classification files it under skin emollients and protectives. Dyers have used it as a mordant, a fixing agent for dye, according to Haz-Map. Urea from urine also reacts with chlorine to form chloramines, as HSDB records.

Why it matters

Fields took the largest share of urea in HSDB’s 1985 consumption figures. Solid fertiliser took 39 per cent, 32 per cent went to fertiliser solutions and 19 per cent to exports. The urea made from ammonia serves fertiliser, plastics and livestock feed, according to Los Alamos National Laboratory, and industry makes it from ammonia and carbon dioxide. Its commercial fertiliser grade is 46-0-0 in ChEBI’s record, the figures counting nitrogen, phosphorus as P₂O₅ and potassium as K₂O.

Another 6 per cent in the same figures became urea-formaldehyde resins and adhesives. Particle board, wood chips glued into sheets, is the main outlet for these resins, in Chem1’s account. They also give baked enamel coatings for kitchen appliances and finishes that help cotton and rayon resist wrinkles, water and stains. The resins come out paler and cheaper than phenolic ones, per Chem1, while melamine, with even more amino groups, reacts with formaldehyde to give harder, colourless solids.

Urea once served medicine as an oral diuretic, a drug that increases urine flow, until better agents replaced it, according to HSDB.

Properties

Properties of urea Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 1176.
Property	Value	Unit	Source
Molecular formula (Hill order)	CH₄N₂O
Molar mass	60.0560(58) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	1
Oxygen atoms	1
Nitrogen atoms	2
Hydrogen atoms	4
Bonds	7
Single bonds	6
Double bonds	1
PubChem molecular weight	60.056 g/mol	g/mol	PubChem

Safety

In its everyday forms urea is essentially harmless. It meets no GHS hazard criteria in 96.1% (4430 of 4611) of reports to the European Chemicals Agency, and EPA’s Safer Choice programme lists it as of low concern. The PubChem Laboratory Chemical Safety Summary still lists irritation of the eyes, skin and airways, and dermatitis after repeated skin contact. Heated past its melting point, urea breaks down and releases toxic gases.

Questions

What is the shape of a urea molecule?

In PubChem's computed model every one of the eight atoms lies in a single plane. The carbon sits in the middle with three partners: an oxygen joined by a double bond and two nitrogens joined by single bonds. The model's O–C–N angles are about 124° and its N–C–N angle about 113°, close to the 120° spacing Chem1 gives three electron regions around one atom.

What does a BUN test measure?

BUN stands for blood urea nitrogen. MedlinePlus explains that the test reports how much urea nitrogen is in the blood, where the waste travels until the kidneys pass it into urine. A high result can point to kidneys that are not working well, but dehydration, burns, some medicines, a high-protein diet or a recent heart attack can raise it too.

Is urea-formaldehyde foam insulation still used in homes?

Rarely. The National Cancer Institute records that the foam went into many homes in the 1970s and that few houses are insulated with it now. The concern is formaldehyde released from urea resins. Pressed-wood products graded for outdoor use give off less formaldehyde, the institute notes, because they are bonded with phenol resins rather than urea resins.

What happens when urea is heated?

HSDB puts its melting point at 132.70 °C and says that further heating breaks it down to biuret, ammonia and cyanuric acid. Solid urea usually carries a trace of biuret already, 0.3 to 2.0 per cent by weight. Heated to full decomposition, it gives off toxic fumes of nitrogen oxides, in HSDB's words, and the PubChem safety summary lists toxic gases on heating alongside eye and skin irritation.

Made of the same elements

C₂H₅NO₂ Glycine 10 atoms, 9 bonds.
C₄H₄N₂O₂ Uracil 12 atoms, 12 bonds.
C₄H₅N₃O Cytosine 13 atoms, 13 bonds.
C₃H₇NO₂ Alanine 13 atoms, 12 bonds.
C₅H₆N₂O₂ Thymine 15 atoms, 15 bonds.
C₅H₅N₅O Guanine 16 atoms, 17 bonds.
C₅H₄N₄O₃ Uric acid 16 atoms, 17 bonds.
C₅H₉NO₄ Glutamic acid 19 atoms, 18 bonds.

All 25 compounds made of carbon, oxygen, nitrogen and hydrogen

C₈H₉NO₂ Acetaminophen 20 atoms, 20 bonds.
C₈H₁₀N₄O₂ Caffeine 24 atoms, 25 bonds.
C₈H₁₁NO₂ Dopamine 22 atoms, 22 bonds.
C₆H₁₃NO₂ Isoleucine 22 atoms, 21 bonds.
C₆H₁₃NO₂ Leucine 22 atoms, 21 bonds.
C₉H₁₁NO₂ Phenylalanine 23 atoms, 23 bonds.
C₁₀H₁₂N₂O Serotonin 25 atoms, 26 bonds.
C₉H₁₁NO₃ Tyrosine 24 atoms, 24 bonds.
C₁₁H₁₂N₂O₂ Tryptophan 27 atoms, 28 bonds.
C₉H₁₃NO₃ Epinephrine 26 atoms, 26 bonds.
C₁₂H₁₇NO DEET 31 atoms, 31 bonds.
C₁₃H₁₆N₂O₂ Melatonin 33 atoms, 34 bonds.
C₁₄H₁₈N₂O₅ Aspartame 39 atoms, 39 bonds.
C₁₄H₂₂N₂O Lidocaine 39 atoms, 39 bonds.
C₁₃H₂₁NO₃ Albuterol 38 atoms, 38 bonds.
C₁₇H₂₁NO Diphenhydramine 40 atoms, 41 bonds.
C₂₀H₂₄N₂O₂ Quinine 48 atoms, 51 bonds.