Harnstoff Chemische Eigenschaften,Einsatz,Produktion Methoden
ERSCHEINUNGSBILD
WEISSE KRISTALLE MIT CHARAKTERISTISCHEM GERUCH.
CHEMISCHE GEFAHREN
Zersetzung beim Erhitzen über den Schmelzpunkt unter Bildung giftiger Gase. Reagiert sehr heftig mit starken Oxidationsmitteln, Nitriten, anorganischen Chloriden, Chloriten und Perchloraten unter Feuer- und Explosionsgefahr.
ARBEITSPLATZGRENZWERTE
TLV nicht festgelegt (ACGIH 2005).
MAK nicht festgelegt (DFG 2005).
AUFNAHMEWEGE
Aufnahme in den K?rper durch Inhalation des Aerosols und durch Verschlucken.
INHALATIONSGEFAHREN
Verdampfen bei 20°C vernachl?ssigbar; eine bel?stigende Partikelkonzentration in der Luft kann jedoch schnell erreicht werden, vor allem als Pulver.
WIRKUNGEN BEI KURZZEITEXPOSITION
WIRKUNGEN BEI KURZZEITEXPOSITION: Die Substanz reizt die Augen, die Haut und die Atemwege.
WIRKUNGEN NACH WIEDERHOLTER ODER LANGZEITEXPOSITION
Wiederholter oder andauernder Hautkontakt kann Dermatitis hervorrufen.
LECKAGE
Verschüttetes Material in Beh?ltern sammeln; falls erforderlich durch Anfeuchten Staubentwicklung verhindern. Reste mit viel Wasser wegspülen.
R-S?tze Betriebsanweisung:
R36/37/38:Reizt die Augen, die Atmungsorgane und die Haut.
R40:Verdacht auf krebserzeugende Wirkung.
S-S?tze Betriebsanweisung:
S26:Bei Berührung mit den Augen sofort gründlich mit Wasser abspülen und Arzt konsultieren.
S36:DE: Bei der Arbeit geeignete Schutzkleidung tragen.
S24/25:Berührung mit den Augen und der Haut vermeiden.
Beschreibung
Urea is a stable highly water-soluble compound
of high nitrogen content (47%), with good storage
properties that make it the most commonly used nitrogen
fertilizer. The synthesis process has remained essentially
unchanged since it was first developed by the BASF
Corporation in 1922. In this process, liquid ammonia
is reacted with carbon dioxide to produce ammonium
carbamate, which is then dehydrated to form urea. The
reactions are:
2NH3 + CO2 ===? NH2·CO2·NH4
NH2·CO2·NH4 ===? (NH2)2CO + H2O
Chemische Eigenschaften
Urea,CO(HN2)2, also known as carbamide, is a white crystalline powder that has a melting point of l32.7 °C (270 °F). It is a natural product of animal protein metabolism and is the chief nitrogen constituent of urine. Commercially, urea is produced by the reaction of ammonia and carbon dioxide. It is soluble in water, alcohol, and benzene.
Occurrence
The compound was discovered by Hilaire Rouelle in 1773 as a constituent of urine.
History
Urea has the distinction of being the first synthesized organic compound. Until the mid-18th century, scientists believed organic compounds came only from live plants and animals. The first serious blow to the theory of vitalism, which marked the beginning of modern organic chemistry, occurred when Friedrich W?hler (1800 1882) synthesized urea from the two inorganic substances, lead cyanate and ammonium hydroxide: Pb(OCN)2 + 2NH4OH→2(NH2)2CO + Pb(OH)2. W?hler's discoveries on urea occurred while he was studying cyanates; he was attempting to synthesize ammonium cyanate when he discovered crystals of urea in his samples. He first prepared urea in 1824, but he did not identify this product and report his findings until 1828. W?hler's synthesis of urea signaled the birth of organic chemistry.
Verwenden
Urea is a physiological regulator of nitrogen excretion in mammals; synthesized in the liver as an end-product of protein catabolism and excreted in urine. Also occurs normally in skin. Emollient; diu
retic.
Indications
Urea-containing preparations have a softening and moisturizing effect on the stratum
corneum and, at times, may provide good therapy for dry skin and the pruritus
associated with it. They appear to have an antipruritic effect apart from their hydrating
qualities. Urea compounds disrupt the normal hydrogen bonds of epidermal
proteins; therefore, their effect in dry hyperkeratotic diseases such as ichthyosis
vulgaris and psoriasis is not only to make the skin more pliable but also to help
remove adherent scales. Lactic acid also has a softening and moisturizing effect on
the stratum corneum.
Urea 40% ointment may be useful in removing hypertrophic or dystrophic
psoriatic nails. Subsequent topical therapy to the denuded nail bed and proximal
nail fold may result in regrowth of ‘‘normal’’ nails in half of those treated.
Vorbereitung Methode
Urea is an important industrial compound. The synthesis of urea was discovered in 1870.Commercial production of urea involves the reaction of carbon dioxide and ammonia at highpressure and temperature to produce ammonium carbamate. Ammonium carbamate is thendehydrated to produce urea (Figure 96.1). The reaction uses a molar ratio of ammonia tocarbon dioxide that is approximately 3:1 and is carried out at pressures of approximately 150atmospheres and temperatures of approximately 180°C.
Definition
A
white crystalline compound made from
ammonia and carbon dioxide. It is used in
the manufacture of urea–formaldehyde
(methanal) resins. Urea is the end product
of metabolism in many animals and is present in urine.
Biologische Funktion
The use of urea (Ureaphil, Urevert) has declined in
recent years owing both to its disagreeable taste and to
the increasing use of mannitol for the same purposes.
When used to reduce cerebrospinal fluid pressure, urea
is generally given by intravenous drip. Because of its potential
to expand the extracellular fluid volume, urea is
contraindicated in patients with severe impairment of
renal, hepatic, or cardiac function or active intracranial
bleeding.
Allgemeine Beschreibung
Solid odorless white crystals or pellets. Density 1.335 g /cc. Noncombustible.
Air & Water Reaktionen
Water soluble.
Reaktivit?t anzeigen
Urea is a weak base. Reacts with hypochlorites to form nitrogen trichloride which explodes spontaneously in air [J. Am. Chem. Soc. 63:3530-32]. Same is true for phosphorus pentachloride. Urea reacts with azo and diazo compounds to generate toxic gases. Reacts with strong reducing agents to form flammable gases (hydrogen). The heating of improper stoichiometric amounts of Urea and sodium nitrite lead to an explosion. Heated mixtures of oxalic acid and Urea yielded rapid evolution of gases, carbon dioxide, carbon monoxide and ammonia (if hot, can be explosive). Titanium tetrachloride and Urea slowly formed a complex during 6 weeks at 80°C., decomposed violently at 90°C., [Chem. Abs., 1966, 64, 9219b]. Urea ignites spontaneously on stirring with nitrosyl perchlorate, (due to the formation of the diazonium perchlorate). Oxalic acid and Urea react at high temperatures to form toxic and flammable ammonia and carbon monoxide gasses, and inert CO2 gas [Von Bentzinger, R. et al., Praxis Naturwiss. Chem., 1987, 36(8), 41-42].
Health Hazard
May irritate eyes.
Brandgefahr
Behavior in Fire: Melts and decomposes, generating ammonia.
Landwirtschaftliche Anwendung
Fertilizer, Fungicide: Used in fertilizers and animal feeds, as a fungicide,
in the manufacture of resins and plastics, as a stabilizer
in explosives and in medicines, and others. Urea is used
to protect against frost and is used in some pesticides as
an inert ingredient as a stabilizer, as an inhibitor and as an
intensifier for herbicides. Registered for use in EU countries
. Registered for use in the U.S.
Handelsname
PRESPERSION, 75 UREA®; SUPERCEL
3000®; UREAPHIL®; UREOPHIL®; UREVERT®;
VARIOFORM II®
Sicherheitsprofil
Moderately toxic by
intravenous and subcutaneous routes.
Human reproductive effects by
intraplacental route: ferthty effects.
Experimental reproductive effects. Human
mutation data reported. A human skin
irritant. Questionable carcinogen with
experimental carcinogenic and
neoplastigenic data. Reacts with sodium
hypochlorite or calcium hypochlorite to
form the explosive nitrogen trichloride.
Incompatible with NaNO2, P2Cl5, nitrosyl
perchlorate. Preparation of the 15N-labeled
urea is hazardous. When heated to
decomposition it emits toxic fumes of NOx.
m?gliche Exposition
Urea is used in ceramics, cosmetics,
paper processing; resins, adhesives, in animal feeds; in the
manufacture of isocyanurates; resins, and plastics; as a stabilizer
in explosives; in medicines; anticholelithogenic, and
others.
Environmental Fate
Terrestrial Fate
Urea is expected to have very high mobility in soil. Urea is not
expected to volatilize from dry soil surfaces based on its vapor
pressure. Various field and laboratory studies have demonstrated
that urea degrades rapidly in most soils. Urea is rapidly hydrolyzed
to ammonium ions through soil urease activity, which
produces volatile gases, that is, ammonia and carbon dioxide.
However, the rate of hydrolysis can be much slower, depending
on the soil type, moisture content, and urea formulation.
Aquatic Fate
Urea is not expected to adsorb to suspended solids and sediments.
Volatilization from water surfaces is not expected. Urea
is rapidly hydrolyzed to ammonia and carbon dioxide in
environmental systems by the extracellular enzyme urease,
which originates from microorganisms and plant roots.
Atmospheric Fate
According to a model of gas/particle partitioning of semivolatile
organic compounds in the atmosphere, urea, which has
a vapor pressure of 1.2×10
-5mm Hg at 251°C, will exist in
both the vapor and particulate phases in the ambient atmosphere.
Vapor-phase urea is degraded in the atmosphere by
reaction with photochemically produced hydroxyl radicals; the
half-life for this reaction in air is estimated to be 9.6 days.
Stoffwechsel
The high analysis and good handling properties of urea
have made it the leading nitrogen fertilizer, both as
a source of nitrogen alone or when compounded with
other materials in mixed fertilizers. Although an excellent
source of nitrogen, urea can present problems unless
properly managed; due to its rapid hydrolysis to ammonia,
significant volatilization loss of this may occur if prilled
or granular urea is applied to and left on the soil
surface without timely incorporation. Mixtures of urea
and ammonium nitrate for use in mixed fertilizers are also
more highly hygroscopic than ammonium nitrate itself.
l?uterung methode
Crystallise urea twice from conductivity water using centrifugal drainage and keeping the temperature below 60o. The crystals are dried under vacuum at 55o for 6hours. Levy and Margouls [J Am Chem Soc 84 1345 1962] prepared a 9M solution in conductivity water (keeping the temperature below 25o) and, after filtering through a medium-porosity glass sinter, added an equal volume of absolute EtOH. The mixture was set aside at -27o for 2-3 days and filtered cold. The precipitate was washed with a small amount of EtOH and dried in air. Crystallisation from 70% EtOH between 40o and -9o has also been used. Ionic impurities such as ammonium isocyanate have been removed by treating the concentrated aqueous solution at 50o with Amberlite MB-1 cation-and anion-exchange resin, and allowing it to crystallise on evaporation. [Benesch et al. J Biol Chem 216 663 1955.] It can also be crystallised from MeOH or EtOH, and is dried under vacuum at room temperature. [Beilstein 3 H 42, 3 I 19, 3 II 35, 3 III 80.]
Inkompatibilit?ten
Violent reaction with strong oxidizers,
chlorine, permanganates, dichromates, nitrites, inorganic
chlorides; chlorites, and perchlorates. Contact with hypochlorites
can result in the formation of explosive compounds.
Waste disposal
Controlled incineration in
equipment containing a scrubber or thermal unit to reduce
nitrogen oxide emissions.
Harnstoff Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
Reactive Black KN-BN
ureaformaldelyde resin UF
Ethyl-1,2,3,4-tetrahydro-2,4-dioxopyrimidin-5-carboxylat
2,4-DICHLOROTHIENO[3,2-D]PYRIMIDINE
5,6-Dihydro-5-methyluracil
5-Nitro-2-furfurolsemicarbazon
Tanning agent for white leather
synthetic carbamider ring tanning agent No.1
1-(2-Aminoethyl)imidazolidin-2-on
DIRECT FAST BLACK G
2-((Aminocarbonyl)oxy)-N,N,N-tri-methylethan-aminiumchlorid
Dihydrouracil
2-[(4-Methoxy-2-nitrophenyl)azo]-N-(2-methoxyphenyl)-3-oxobutyramid
6-Aminouracil
flame retardane ZR-01
2,4-Dichlorothieno[3,2-d]pyrimidine
2,6-Dichlor-4,8-dipiperidinopyrimido[5,4-d]pyrimidin
biodegrddable finishing agent for fabric
1,1-Hydrazoformamid
1-(1,3-DIHYDRO-1-OXOISOBENZOFURAN-3-YL)UREA
N,N''-(Isobutyliden)diharnstoff
N-Methyl-N-nitrosoharnstoff
4,5-Dihydroxy-1,3-bis(hydroxymethyl)imidazolidin-2-on
1,2-Dihydro-1-phenyl-3H-1,2,4-triazol-3-on
Dichlorisocyanurs?ure
2-Cyan-N-((ethylamino)carbonyl)-2-(methoxyimino)acetamid
1,5-Dihydropyrimido[5,4-d]pyrimidin-2,4,6,8(3H,7H)tetron
Hydrogenperoxid-Harnstoff
5-(sec-Pentyl)barbitursure
Amino moulding plastic
Tableware cleaner
synthetic tanning agent PNC
rubber latex 104T/C
Biuret
ETHYL 2-HYDROXYPYRIMIDINE-5-CARBOXYLATE
Phenicarbazid
Allylharnstoff
Water flush fertilizer
2-HYDROXY-4-PHENYLPYRIMIDINE-5-CARBOXYLIC ACID
2,4-DIHYDROXYTHIENO[3,2-D]PYRIMIDINE
