Urea
Properties
| State | Solid at room temperature |
| Color | White crystalline solid |
| Solubility | Very soluble in water (108 g/100 mL at 20 °C) |
| Melting Point | 133 °C |
| Boiling Point | Decomposes before boiling |
About Urea
Urea occupies a unique place in the history of chemistry as the molecule that killed vitalism: in 1828 Friedrich Wohler accidentally synthesized urea by heating ammonium cyanate (NH4OCN -> CO(NH2)2), demonstrating that an organic compound previously thought to require a "vital force" could be made from simple inorganic salts. His letter to Berzelius — "I must tell you that I can prepare urea without requiring a kidney of an animal, either man or dog" — marks the conventional birthdate of organic chemistry as a discipline. Almost two centuries later, urea is the most-produced organic chemical on the planet by mass: global production runs around 200 million tonnes per year, almost all of it via the Bosch-Meiser process, which combines NH3 with CO2 at 200 bar and 180 °C to form ammonium carbamate, then dehydrates the carbamate to urea and water in the same reactor. The 46.7% nitrogen content by mass is the highest of any solid nitrogen fertilizer, and roughly 90% of urea production goes straight to crop fertilization, primarily for cereal grains in China, India, and the U.S. corn belt. Beyond agriculture, urea is the active ingredient in diesel exhaust fluid (DEF/AdBlue) where it hydrolyzes in hot exhaust to NH3 that reduces NOx over a vanadia-titania SCR catalyst — a reaction now standard on every diesel passenger car and truck sold in the EU and US. In the lab, 8 M urea is the canonical chaotrope for protein denaturation in SDS-PAGE sample buffers and gel filtration columns.
Where you'll encounter it
If you have ever filled the blue AdBlue tank on a modern diesel pickup or watched a center-pivot irrigation system spray fertilizer-laden water across an Iowa cornfield, you've handled urea. AdBlue is a 32.5 wt% aqueous urea solution dosed by an injector into the exhaust just upstream of the SCR catalyst — a 50,000 km tank lasts about a year for a typical passenger car. In a biochemistry lab, urea shows up two ways: as the chaotrope that unfolds proteins for analysis (8 M urea breaks the hydrogen bond network of secondary structure, with 6 M typically used to maintain enzyme activity for limited proteolysis), and as the analyte in BUN (blood urea nitrogen) testing where elevated levels above 20 mg/dL flag impaired renal clearance. The Berthelot reaction (urea + hypochlorite + phenol + nitroprusside -> blue indophenol) is still the basis of automated BUN measurement on Beckman and Roche clinical chemistry analyzers in essentially every hospital lab. In dermatology, prescription-strength 40% urea cream softens hyperkeratotic skin and removes thickened toenails — the keratolytic effect comes from urea breaking the disulfide and hydrogen bonds in keratin.
Common Uses
- Nitrogen fertilizer applied at 100-200 kg N/hectare for cereal grain and corn production worldwide
- Active ingredient in diesel exhaust fluid (DEF/AdBlue) for SCR NOx reduction in passenger and commercial diesel vehicles
- Chaotrope at 6-8 M for protein denaturation in SDS-PAGE sample prep and gel filtration unfolding studies
- Keratolytic agent at 10-40% in dermatology creams for psoriasis, ichthyosis, and onychomycosis treatment
- Feedstock for urea-formaldehyde resin production used in particleboard, MDF, and plywood adhesive systems
- Analyte in BUN (blood urea nitrogen) clinical chemistry assays for renal function assessment
- Carbon and nitrogen source in microbial fermentation media for industrial yeast and bacterial culture
- Cooling salt in instant cold packs (urea + ammonium nitrate dissolution is endothermic by about 10 kJ/mol)
Safety Information
Urea has very low acute and chronic toxicity. GHS classification: Eye Irritation Category 2A and Skin Irritation Category 2 for prolonged contact with the bulk solid; otherwise unclassified. The oral LD50 in rats is around 8,500 mg/kg, putting it in the category of "essentially harmless if ingested in small quantities," though the human kidney still has to clear it (which is why elevated BUN above 20 mg/dL is a marker of renal impairment, not urea toxicity). No OSHA PEL is established. Standard handling uses nitrile gloves and safety glasses; respiratory protection is needed only for dusty bag-handling operations. The fertilizer-grade prill and granule forms can support combustion if mixed with ammonium nitrate (CAN-urea blends are mildly explosive when contaminated with fuel oil), so storage at agricultural co-ops keeps urea separated from AN and from organic combustibles. Decomposition above 133 °C produces NH3, isocyanic acid, and biuret; ventilation is required when heating urea above its melting point.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.