Difference between revisions of "Urea"

Revision as of 01:51, 2 February 2016

Urea or carbamide, is an organic compound commonly used as a fertilizer. It has the chemical formula (NH₂)₂CO. Urea was the first organic chemical produced from inorganic chemicals, a breakthrough in chemistry, which proved organic substances can be produced from inorganic substances, disproving the notion of vitalism.

Properties

Chemical

Thermal decomposition of urea produces ammonium isocyanate, who in turn yields isocyanuric acid.

NH₂CONH₂ → NH₄NCO → HNCO + NH₃

Urea is a weak organic base. It forms salts with strong acids. Despite its two amino groups, it acts as a monoprotic base, only accepting one H+ cation. With diprotic acids such as sulfuric, urea forms two types of salts: monocarbamide dihydrosulfate (carbamonium bisulfate, analogous to inorganic bisulfates) and dicarbamide dihydrosulfate (carbamonium sulfate, analogous to inorganic sulfates).

Urea forms an adduct with hydrogen peroxide. In some countries, this adduct is sold in drugstores under names such as "Carbamide peroxide", "Percarbamide" or "Hydroperite". Urea can be separated from this adduct by dissolving it in water and adding manganese dioxide which catalyses the decomposition of hydrogen peroxide; this way you can obtain high grade urea, but the peroxide is lost. Separating the two compounds without losing either is more tricky; one method involves using calcium or barium hydroxides to precipitate peroxide, leaving urea dissolved, and, after filtering out the alkaline earth metal peroxide, recovering hydrogen peroxide from it with sulfuric acid. This, however, requires a very concentrated solution of the adduct, decanted or vacuum-filtered from a sludge of wet powdered percarbamide.

Physical

Urea is a white crystalline substance. Its melting point is between 133-135 °C. Urea is soluble in water (107.9 g/100 ml at 20 °C) and when dissolved, it is neutral on the pH scale. Urea is soluble in glycerol (500 g/L) and slightly less soluble in ethanol.

Availability

Urea is available as a fertilizer, either pure or mixed with other substances. It can be very cheaply purchased online, often at less than $5/kg.

ScienceCompany sells 500g of lab grade urea at 16.95 $.

Ebay has many listings for urea as a lab chemical and as fertilizer

Preparation

Urea was first synthesized by reacting silver cyanate with ammonium chloride.

AgNCO + NH₄Cl → (NH₂)₂CO + AgCl

Industrially it is produced by the thermal decomposition of ammonium carbamate.

It can also be produced from the reaction of phosgene and ammonia

COCl₂ + 4 NH₃ → (NH₂)₂CO + 2 NH₄Cl

Projects

• Urea nitrate synthesis
• Sodium azide synthesis
• Hydrazine sulfate(Hoffman Rearrangement)
• Separating the adduct of urea and hydrogen peroxide into its constituent substances

Handling

Safety

Urea is non-toxic, though is may cause irritations to sensitive tissues. It may corrode metallic surfaces, even the more resistant forms of stainless steel.

Storage

Urea doesn't require any special storage, and can be safely stored in glass, metal, plastic or ceramic containers.

Disposal

As urea is a good fertilizer, it can be safely dumped in the soil, although it's recommended to avoid dumping it in water reservoirs to prevent the growth on unwanted algae.

References

Relevant Sciencemadness threads

• Urea Synthesis