What is the chemical structure of urea


Chemical lexicon "H"

Other names: carbamide, carbonyl diamide, carbonic acid diamide, diamide of carbonic acid; French: Urée; eng .: urea; span .: urea; Italian: urea; lat .: carbamidum, urea (pura), ureum (lat. new)


Urea is the end product of protein metabolism. It is made in the liver and enters the urine via the blood and kidneys. Humans excrete around 30 g of urea with normal daily urine. Urea is also found in many plants, especially mushrooms.

Chemical and physical characteristics

Molecular formula: CH4N2O
Structural formula:

Molecular mass / F.W. 60.06 g / mol
Density / s.g. 1,335
Melting point / m.p. 132.7 ° C (melting range of the merchandise between 132 and 135 ° C)
Decomposition: Thermal decomposition from 132 ° C
Solubility in water: 1080 g / l (at 20 °C); in ethanol 96%: soluble in about 5 parts by volume


Urea forms colorless, odorless, nitric-tasting crystals (tetragonal prisms) that are easily soluble in water and ethyl alcohol. When heated to about 140 OC the substance decomposes with the formation of Biuret. This initially produces isocyanic acid, which reacts with further urea to form biuret:

H-N = C = O + H2N-CO-NH2



Isocyanic acid + urea


That became known Biuret-Reaction, as protein bodies can be detected with it (see section Chemical properties and reactions). The substance is sparingly soluble in ether or chloroform. On dissolving in water one observes a strong cooling. Urea is hygroscopic (attracts humidity). Chemically, it is the diamide of carbonic acid. In comparison, carbamic acid, the mono-amide of carbonic acid, is not stable, since carboxyl groups bound to nitrogen usually split off carbon dioxide immediately:

H2N - COOH    --------> CO2 ^ + NH3 ^

Carbamic acid decomposition


Urea was already in 1729 by BOERHAVE and again in 1773 by ROQUELLE (1718 to 1778), the Duke of Orleans' apothecary, discovered in human urine. In 1797 FOURCROY and VAUQUELIN conducted more detailed chemical investigations with him.

The first production of urea by F.R.. W.ÖHLER (1800-1882) in 1828 from the salt ammonium cyanate. The historical significance of this simple synthesis lies in the fact that it proved that no mystical "vis vitalis" is necessary for the creation of an organic substance. So a "product of life" was made outside of a living body. This reaction is still used technically today for the production of urea:

Another manufacturing option is the reaction of carbon dioxide with ammonia at 150 OC and high pressure (50 to 100 bar). The carbamic acid ammonium that forms in between breaks down into urea and water.


Urea is considered to be in approx. 2% preparations promotes granulation (Granulation tissue is the name given to the typical young, vascularized connective tissue that is formed during wound and ulcer healing or in chronic inflammation and that turns into scar tissue after a while). Nothing is known about the mechanism of action for this.

The dermatologist uses the in higher concentrations (5-10%) hygroscopic (water-attracting) effect of urea, e.g. in the treatment of ichthyosis ("fish scale disease"), psoriasis and neurodermatitis (atopic eczema). Hygroscopic Substances, primarily urea, act as natural moisturizing factors to retain moisture in the cornea. If the water content in the horny layer (caused by a lack of urea) falls below 15%, e.g. in atopic neurodermatitis, the skin becomes dry, brittle and cracked. Similar to atopic eczema, psoriasis also lacks urea in the epidermis. The result is severe drying of the affected skin areas.

Urea is used in cosmetic skin preparations as a substance that binds moisture in the skin (1 to 2%). A 10% aqueous solution of urea is bactericidal. Finally, urea has a keratolytic or keratoplastic (softening effect on the keratin of the skin) as well as relieves itching - which can be used in both pharmaceuticals and cosmetics. Due to its polar structure, it holds the water firmly in the skin and thus keeps it smoothness and suppleness.

RECIPE: Liposome lotion with urea (against blemished skin)


* 20 g Lipodermin concentrate from Hobbythek (from the tube)
* 1 measuring spoon (2.5 ml) of tea tree oil(only from Melaleuca alternifolia)
* 1 measuring spoon (as above) lavender oil (only from Lavandula officinalis)
Mix these three ingredients together thoroughly.


* 1.5 teaspoons (6-8 ml) HT cosmetic base water
* 1 pinch of xanthan gum
Mix the xanthan gum with the base water in a separate glass, then mix 1) give. Now you can add the other ingredients as follows:


* 1 g urea, dissolved in 30 ml of boiled water that has cooled down again
* 1 measuring spoon of D-Panthenol 75L
* 1 measuring spoon of Vitamin E-Fluid HT
* 1 measuring spoon of Vitamin A-Fluid HT to be added. This lotion is applied twice a day to the skin that has been previously cleaned with facial toner. Interestingly, the effect of the comfrey active ingredient allantoin is also based on urea, as this is split off from the allantoin.

In the past, urea was used as a means to increase urine excretion (diuretic for cirrhosis of the liver and pleurisy). A special medical application is the use as an antidote (antidote) for poisoning with formaldehyde. Technically, the substance can be used as a fertilizer due to its high nitrogen content (46% N). Special types of fertilizer are also derived from urea, which release their nutrient content only slowly in appropriately distributed doses during the entire growth period of the plant. These depot fertilizers are of particular importance because the nitrogen is washed out of the main nutrients particularly strongly when there is excessive rainfall. Also used in agriculture as a protein supplement in feed for ruminants.

Urea is also used as a raw material for synthetic resins (aminoplasts), for glue resins, adhesives for the wood industry, paper auxiliaries, and dewaxing of petroleum fractions. The raw material used to be of particular importance as a component of sleeping pills of the so-called ureide class (Carbromal, Acecarbromal).

Chemical properties and reactions

Has urea basic Properties, which, however, are only weakly developed (pKB.= 13.9). Due to the particularly low-energy basic state of the end product, a stable, crystalline mononitrate is still obtained with concentrated nitric acid.

In the hydrolysis (Splitting with water absorption), which is catalyzed by alkalis or acids, either alkali carbonate and ammonia or carbon dioxide and ammonium salt are formed. Hydrolysis is very easy with the enzyme urease, which is found in soybeans. Urease can be used to identify urea, since the ammonia gas produced can easily be detected analytically.


Dissolve some urea in water and add about 5 to 10 drops of strong caustic soda. Boil and check the rising vapors for ammonia escaping. Acid the remaining alkaline solution with hydrochloric acid. Carbon dioxide escapes from the sodium carbonate (soda) present in the solution.

Heat 10 ml urine in an Erlenmeyer flask with barite water [Ba (OH)2]. A strip of moist red litmus paper held over the mouth is blued by the escaping ammonia. At the same time, the liquid becomes cloudy due to the excreted barium carbonate.

Add a little soybean powder to a neutral urea solution in water in a sealable flask. The jar is closed and left for half an hour at normal temperature. Then check for ammonia odor, alkaline reaction of the solution (ammonium carconate!) And add hydrochloric acid again, whereby carbon dioxide escapes.

The decomposition from urea to biuret has already been addressed above.

V.REQUEST (Biuret reaction):

In a test tube, 1 ml of 10% sodium hydroxide solution is added to about 2 ml of protein solution, then shaken and about 3 drops of a 3% copper sulfate solution are added. The liquid takes on a beautiful red-violet color. Solid protein substances, such as those found in sausage, bread, hair, feathers, etc., must be completely or at least partially dissolved by boiling with caustic soda before this reaction (after boiling wait until the solution has cooled down, otherwise black copper oxide will precipitate! ). The biuret reaction is triggered by the peptide bond -CO-NH-, which is characteristic of all protein bodies. This bond is also present with urea. In addition, the reaction is triggered if at least 2 of the following groups are present: -CS-NH2, -C (= NH) NH2, .CH2NH2

Urea can be understood as the diamide of carbonic acid. As such, it reacts with nitrous acid to form nitrogen:

H2N-CO-NH2 + 2 HONO ==> CO2 ^ + 2 N2 ^ + 3 H.2O

Here urea reacts in a similar way to ammonia, hydrazoic acid and sulfamic acid. This decomposition of nitrite is important in the analysis, since nitrates can only be detected when nitrite is absent. For this purpose, the acid extract or the neutral solution of the analysis substance is cold mixed with a urea solution and very weakly acidified. Nitrite then rapidly decomposes to form nitrogen.

Quantitative determination of urea

The various methods of determining the content are important for urine analyzes. Urea is usually subjected to the enzymatic hydrolysis by urease (described above) and the ammonia split off is determined titrimetrically. To VAN S.LYKE Alternatively, the nitrogen produced by the action of nitrous acid can be measured volumetrically.

Biochemical appendix

Excess amino acids, which are not used in the metabolism of the human organism for the construction of proteins and other biologically important molecules, cannot be stored in the body - unlike fatty acids and grape sugar. However, they are not excreted either, but are used for other metabolic processes.

Most of the nitrogen-bearing amino groups of these surplus amino acids are converted to urea, and their carbon structure is used to form fatty acids, ketone bodies and glucose. The breakdown of amino acids and urea synthesis takes place in mammals mainly in the liver.

Created on 01/04/1999 * Last change on 07/11/1999

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