57-13-6 Usage
Uses
Used in Agriculture:
Urea is used as a nitrogen-release fertilizer for providing a concentrated source of fixed nitrogen to soils. It is highly soluble in water, making it suitable for use in fertilizer solutions and foliar feed fertilizers. Urea is also used in multi-component solid fertilizer formulations and as a supplement in livestock feeds to assist protein synthesis.
Used in Pharmaceutical Industry:
Urea reacts with malonic acid to form barbituric acid, which is used in the production of various acylureas and urethanes for use as sedatives and hypnotics.
Used in Chemical Industry:
Urea is a raw material for the manufacture of urea-formaldehyde resins and urea-melamine-formaldehyde used in marine plywood. It is also used to trap organic compounds in the form of clathrates, which can be used to separate mixtures, and has been used in the production of aviation fuel and lubricating oils, and in the separation of paraffin.
Used in Laboratory:
Urea, in concentrations up to 10 M, is a powerful protein denaturant that disrupts noncovalent bonds in proteins, increasing the solubility of some proteins. It can also serve as a hydrogen source for subsequent power generation in fuel cells and is used to make fixed brain tissue transparent to visible light while preserving fluorescent signals from labeled cells.
Used in Automobile Systems:
Urea is used in SNCR and SCR reactions to reduce NOx pollutants in exhaust gases from combustion sources, such as power plants and diesel engines. The BlueTec system, for example, injects a water-based urea solution into the exhaust system, where the ammonia produced by decomposition of the urea reacts with nitrogen oxide emissions and is converted into nitrogen and water within the catalytic converter.
Used in Others:
Urea has various other applications, including as a stabilizer in nitrocellulose explosives, a component of animal feed, a non-corroding alternative to rock salt for road de-icing, a flavor-enhancing additive for cigarettes, a main ingredient in hair removers, a browning agent in factory-produced pretzels, an ingredient in hair conditioners and skin care products, a reactant in ready-to-use cold compresses for first-aid use, a cloud seeding agent, a flame-proofing agent, an ingredient in tooth whitening products, an ingredient in dish soap, and a nutrient used in plankton nourishment experiments for geoengineering purposes.
Chemical structure
Lewis structure
Ball-and-stick diagram
Space-filling model
Urea, also known as carbamide, is an organic compound with chemical formula CO (NH2)2. This amide has two –NH2 groups joined by a carbonyl (C=O) functional group.
History
Pure urea was first isolated from urine in 1727 by the Dutch scientist Herman Boerhaave, and he extracted urea from urine by working with the concentated-by-boiling residue. But if only not considering the purity of urea, the discovery of urea should be attributed to the French chemist Hilaire Rouelle, and he prepared urea (or its addition compound with sodium chloride) from urine some time before 1727.
In 1828, just 55 years after its discovery, urea became the first organic compound to be synthetically formulated, this time by a German chemist named Friedrich W?hler, one of the pioneers of organic chemistry. It was found when Wohler attempted to synthesis ammonium cyanate, to continue a study of cyanates which he had been carrying out for several years. On treating silver cyanate with ammonium chloride solution he obtained a white crystalline material which proved identical to urea obtained from urine.
AgNCO + NH4Cl → (NH2)2CO + AgCl
Synthetic urea is created from synthetic ammonia and carbon dioxide and can be produced as a liquid or a solid. The process of dehydrating ammonium carbamate under conditions of high heat and pressure to produce urea was first implemented in 1870 and is still in use today. Uses of synthetic urea are numerous and therefore production is high. Approximately one million pounds of urea is manufactured in the United States alone each year, most of it used in fertilizers. Nitrogen in urea makes it water soluble, a highly desired property in this application.
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.
Productions
The primary raw material used to manufacture urea is natural gas, which ties the costs directly to gas prices. Consequently, new plants are only being built in areas with large natural gas reserves where prices are lower. Finished product is transported around the globe in large shipments of 30,000 metric tons. The market price for urea is directly related to the world price of natural gas and the demand for agricultural products. Prices can be very volatile, and at times, unpredictable. TCC is positioned to know the world markets and keep your prices competitive.
Annual production of sulfuric acid
▼▲
World
164 million tonnes
China
62 million tonnes
India
23 million tonnes
Middle East
20 million tonnes
Rest of Asia
18 million tonnes
FSU
12 million tonnes
North America
9.5 million tonnes
Europe
9.5 million tonnes
It is expected that the global annual production will increase to over 200 million tonnes by 2018.
1. Potash Corporation, 2013
2. International Fertilizer Industry Association, 2014
Production methods
Historical process
Urea was first noticed by Hermann Boerhaave in the early 18th century from evaporates of urine. In 1773, Hilaire Rouelle obtained crystals containing urea from human urine by evaporating it and treating it with alcohol in successive filtrations. This method was aided by Carl Wilhelm Scheele's discovery that urine treated by concentrated nitric acid precipitated crystals. Antoine Fran?ois, comte de Fourcroy and Louis Nicolas Vauquelin discovered in 1799 that the nitrated crystals were identical to Rouelle's substance and invented the term "urea." Berzelius made further improvements to its purificationand finally William Prout, in 1817, succeeded in obtaining and determining the chemical composition of the pure substance. In the evolved procedure, urea was precipitated as urea nitrate by adding strong nitric acid to urine. To purify the resulting crystals, they were dissolved in boiling water with charcoal and filtered. After cooling, pure crystals of urea nitrate form. To reconstitute the urea from the nitrate, the crystals are dissolved in warm water, and barium carbonate added. The water is then evaporated and anhydrous alcohol added to extract the urea. This solution is drained off and evaporated, leaving pure urea.
Industrial process
For use in industry, urea is produced from synthetic ammonia and carbon dioxide. As large quantities of carbon dioxide are produced during the ammonia manufacturing process as a byproduct from hydrocarbons (predominantly natural gas, less often petroleum derivatives), or occasionally from coal, urea production plants are almost always located adjacent to the site where the ammonia is manufactured.
Urea can be produced as prills, granules, pellets, crystals, and solutions. The prills are formed by spraying molten urea down a tower up which air is pumped. They are slightly smaller than urea sold as granules and are particularly useful when the fertilizer is being applied by hand. In admixture, the combined solubility of ammonium nitrate and urea is so much higher than that of either component alone that it is possible to obtain a stable solution (known as UAN) with a total nitrogen content (32%) approaching that of solid ammonium nitrate (33.5%), though not, of course, that of urea itself (46%).
Fig.3 Industrial process of urea
Fig.4 An aerial view of a large plant in Alberta, Canada, in which ammonia is synthesized and then converted to urea.( By kind permission of Agrium Inc.)
Fig.5 Prills(small spheres of urea)
Fig.6 UAN(admixture of urea and ammonium nitrate)
Laboratory process
Ureas in the more general sense can be accessed in the laboratory by reaction of phosgene with primary or secondary amines, proceeding through an isocyanate intermediate. Non-symmetric ureas can be accessed by reaction of primary or secondary amines with an isocyanate.
Also, urea is produced when phosgene reacts with ammonia:
COCl2 + 4 NH3 → (NH2)2CO + 2 NH4Cl
Urea is byproduct of converting alkyl halides to thiols via a S-alkylation of thiourea. Such reactions proceed via the intermediacy of isothiouronium salts:
RX + CS(NH2)2 → RSCX(NH2)2X
RSCX(NH2)2X + MOH → RSH + (NH2)2CO + MX
In this reaction R is alkyl group, X is halogen and M is alkali metal.
Hazards
Health hazards
Inhalation:?
Causes irritation to the respiratory tract. Symptoms may include coughing, shortness of breath. May be absorbed into the bloodstream with symptoms similar to ingestion.?
Ingestion:?
Causes irritation to the gastrointestinal tract. Symptoms may include nausea, vomiting and diarrhea. May also cause headache, confusion and electrolyte depletion.?
Skin Contact:?
Causes irritation to skin. Symptoms include redness, itching, and pain.?
Eye Contact:?
Causes irritation, redness, and pain.?
Chronic Exposure:?
A study of 67 workers in an environment with high airborne concentrations of urea found a high incidence of protein metabolism disturbances, moderate emphysema, and chronic weight loss.?
Aggravation of Pre-existing Conditions:?
Supersensitive individuals with skin or eye problems, kidney impairment or asthmatic condition should have physician's approval before exposure to urea dust.
Fire Hazards
Behavior in Fire: Melting and decomposing to generate ammonia.
Not combustible. Gives off irritating or toxic fumes (or gases) in a fire.
https://pubchem.ncbi.nlm.nih.gov/compound/urea#section=EPA-Safer-Chemical
Handling and Storage
Keep in a tightly closed container, stored in a cool, dry, ventilated area. Protect against physical damage. Isolate from incompatible substances. Containers of this material may be hazardous when empty since they retain product residues (dust, solids); observe all warnings and precautions listed for the product.
Reference
https://en.wikipedia.org/wiki/Urea#Explosives
https://www.lookchem.com/ProductChemicalPropertiesCB5853861_EN.htm
https://chemistry.stackexchange.com/questions/54387/extracting-urea-from-urine/60338#60338
http://www.chm.bris.ac.uk/motm/urea/urea.html?
https://thechemco.com/chemical/urea/ ?
file:///C:/Users/zl/Desktop/kurzer1956.pdf
https://www.britannica.com/science/urea?
http://www.expertsmind.com/topic/biochemistry/urea-cycle-96120.aspx
http://sesl.com.au/blog/what-is-urea/?
http://www.essentialchemicalindustry.org/chemicals/urea.html?
http://www.atmos.umd.edu/~russ/MSDS/urea.htm
Production Methods
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.
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.
Preparation
All current processes for the manufacture of urea are based on the reaction of
ammonia and carbon dioxide to form ammonium carbamate which is
simultaneously dehydrated to urea:
The dehydration of ammonium carbamate is appreciable only at temperatures
above the melting point (about 150°C) and this reaction can only
proceed if the combined partial pressure of ammonia and carbon dioxide
exceeds the dissociation pressure of the ammonium carbamate (about
10 MPa at 160°C and about 30 MPa at 200°C). Thus commercial processes
are operated in the liquid phase at 160-220°C and 18-35 MPa (180-350
atmospheres). Generally, a stoichiometric excess of ammonia is employed,
molar ratios of up to 6: 1 being used. The dehydration of ammonium
carbamate to urea proceeds to about 50-65% in most processes. The reactor
effluent therefore consists of urea, water, ammonium carbamate and the
excess of ammonia. Various techniques are used for separating the components.
In one process the effluent is let down in pressure and heated at about
155°C to decompose the carbamate into ammonia and carbon dioxide. The
gases are removed and cooled. All the carbon dioxide present reacts with the
stoichiometric amount of ammonia to re-form carbamate, which is then
dissolved in a small quantity of water and returned to the reactor. The
remaining ammonia is liquefied and recycled to the reactor. Fresh make-up
ammonia and carbon dioxide are also introduced into the reactor. Removal of
ammonium carbamate and ammonia from the reactor effluent leaves an
aqueous solution of urea. The solution is partially evaporated and then urea is
isolated by recrystallization. Ammonium carbamate is very corrosive and at one time it was necessary to use silver-lined equipment but now satisfactory
alloy steel plant is available.
Biological Functions
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.
Air & Water Reactions
Water soluble.
Reactivity Profile
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.
Fire Hazard
Behavior in Fire: Melts and decomposes, generating ammonia.
Trade name
PRESPERSION, 75 UREA?; SUPERCEL
3000?; UREAPHIL?; UREOPHIL?; UREVERT?;
VARIOFORM II?
Biochem/physiol Actions
Urea solution is primarily used for protein denaturation. It also increases solubility of hydrocarbons and reduce micelle formation. Urea solution at high concentration leads to the destabilization of amyloid β16?22 oligomers.
Safety Profile
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.
Potential Exposure
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.
Metabolism
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.
Purification Methods
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.]
Toxicity evaluation
The primary mechanism of toxicity appears to be inhibition of
the citric acid cycle. It leads to blockade of electron transport
and a decrease in energy production and cellular respiration,
which leads to convulsions.
Incompatibilities
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.
Check Digit Verification of cas no
The CAS Registry Mumber 57-13-6 includes 5 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 2 digits, 5 and 7 respectively; the second part has 2 digits, 1 and 3 respectively.
Calculate Digit Verification of CAS Registry Number 57-13:
(4*5)+(3*7)+(2*1)+(1*3)=46
46 % 10 = 6
So 57-13-6 is a valid CAS Registry Number.
InChI:InChI=1/CH4N2O/c2-1(3)4/h(H4,2,3,4)
57-13-6Relevant articles and documents
Real-Time in Vivo Detection of H2O2 Using Hyperpolarized 13C-Thiourea
Wibowo, Arif,Park, Jae Mo,Liu, Shie-Chau,Khosla, Chaitan,Spielman, Daniel M.
, p. 1737 - 1742 (2017)
Reactive oxygen species (ROS) are essential cellular metabolites widely implicated in many diseases including cancer, inflammation, and cardiovascular and neurodegenerative disorders. Yet, ROS signaling remains poorly understood, and their measurements are a challenge due to high reactivity and instability. Here, we report the development of 13C-thiourea as a probe to detect and measure H2O2 dynamics with high sensitivity and spatiotemporal resolution using hyperpolarized 13C magnetic resonance spectroscopic imaging. In particular, we show 13C-thiourea to be highly polarizable and to possess a long spin-lattice relaxation time (T1), which enables real-time monitoring of ROS-mediated transformation. We also demonstrate that 13C-thiourea reacts readily with H2O2 to give chemically distinguishable products in vitro and validate their detection in vivo in a mouse liver. This study suggests that 13C-thiourea is a promising agent for noninvasive detection of H2O2 in vivo. More broadly, our findings outline a viable clinical application for H2O2 detection in patients with a range of diseases.
Oxidation of Thiourea by Aqueous Bromine: Autocatalysis by Bromide
Simoyi, Reuben H.,Epstein, Irving R.
, p. 5124 - 5128 (1987)
The reaction between thiourea and aqueous bromine was studied in the pH range 1.5-4.The reaction occurs in two stages: a very fast initial stage in which 1 mol of bromine is consumed for each mole of thiourea, followed by a slower second stage in which the rest of the bromine is consumed.The stoichiometry of the reaction at pH >/= 2 is 4Br2 + CS(NH2)2 + 5H2O -> 8Br- + CO(NH2)2 + SO42- + 10 H+.At pH 8Br- + 2NH4+ + SO42- + CO2 + 8H+.The second stage of the reaction is autocatalytic in bromide.At 25.0 +/- 0.1 deg C and ionic strength 0.2 M (NaClO4), the rate expression is -1/3d/dt = (k1 + k2->), with k1 = 27.8 +/- 0.5 M-1 s-1 and k2 = (3.17 +/- 0.3) x 1E3 M-2 s-1.This reaction is explained by successive electrophilic attacks on the sulfur center by bromine.
Fingering Patterns and Other Interesting Dynamics in the Chemical Waves Generated by the Chlorite-Thiourea Reaction
Chinake, Cordelia R.,Simoyi, Reuben H.
, p. 4012 - 4019 (1994)
The reaction between chlorite and thiourea is excitable and autocatalytic in HOCl.It produces a chemical wave of ClO2 when ClO2(-) is in stoichiometric excess over thiourea.The chemical wave has been studied in glass tubes of varying diameters.The dynamics of the front propagation have been studied as a function of convection, which is known to induce density gradients.The ClO2(-)-thiourea reaction is highly exothermic, and the chemical wave has a positive isothermal density change.In vertical tubes the effect of the exothermicity of the reaction opposes the effect of the isothermal density change, giving an asymmetric and unstable wave front in descending waves.Multicomponent convection and fingering patterns heve been observed in descending waves.Ascending waves propagate without structure and are generally slower than descending waves.In strach solutions fingering patterns are observed which propagate downward at greater than 10 times the normal front velocity.These fingers turn into rapidly-rising plumes after they reach the botton of the tube.Formation of rising plumes is due to the hot interior of the finger which is lighter than the unreacted solution, but when the reacted solution propagates upward into the cold unreacted region, the cooling effect makes the solution heavier, giving a symmetric "mushroom-shaped" plume.
Evidence for an inhibitory LIM domain in a rat brain agmatinase-like protein
Castro, Victor,Fuentealba, Pablo,Henriquez, Adolfo,Vallejos, Alejandro,Benitez, Jose,Lobos, Marcela,Diaz, Beatriz,Carvajal, Nelson,Uribe, Elena
, p. 107 - 110 (2011)
We recently cloned a rat brain agmatinase-like protein (ALP) whose amino acid sequence greatly differs from other agmatinases and exhibits a LIM-like domain close to its carboxyl terminus. The protein was immunohistochemically detected in the hypothalamic region and hippocampal astrocytes and neurons. We now show that truncated species, lacking the LIM-type domain, retains the dimeric structure of the wild-type protein but exhibits a 10-fold increased kcat, a 3-fold decreased Km value for agmatine and altered intrinsic tryptophan fluorescent properties. As expected for a LIM protein, zinc was detected only in the wild-type ALP (～2 Zn2+/monomer). Our proposal is that the LIM domain functions as an autoinhibitory entity and that inhibition is reversed by interaction of the domain with some yet undefined brain protein.
Aminoguanidinium hydrolysis effected by a hydroxo-bridged Dicobalt(II) complex as a functional model for arginase and catalyzed by mononuclear Cobalt(II) complexes
He, Chuan,Lippard, Stephen J.
, p. 105 - 113 (1998)
The dinuclear complex [Co2(μ-OH)(μ-XDK)(bpy)2(EtOH)](NO3), where XDK is the dinucleating dicarboxylate ligand m-xylylenediamine bis(Kemp's triacid imide) and bpy = 2,2'-bipyridine, was prepared as a functional model for arginase. The substrate aminoguanidinium nitrate was hydrolyzed to urea in ethanol by the complex but not by free hydroxide ion under the same conditions. The amino group of the substrate binds to cobalt, as demonstrated by W-vis spectroscopic studies. The syntheses of related dinuclear cobalt(II) complexes [Co2(μ-XDK)(NO3)2(CH3OH)2(H2O)], [Co2(μ-Cl)(μ-XDK)(bpy)2(EtOH)2](NO3), and [Co2(μ-XDK)-(py)3(NO3)2] are described. Mononuclear complexes [Co(XDK)(bpy)(H2O)] and [Zn(XDK)(bpy)(H2O)] were also prepared and characterized. The former catalytically hydrolyzes aminoguanidinium nitrate to urea in basic 1:1 methanol/water solutions, whereas the latter does not promote this reaction. Hydrolysis of aminoguanidinium ion is effected by [Co(CH3COO)2] and [Cu(CH3COO)2] in the presence of bpy, but not by [Zn(CH3COO))2], [Ni(CH3COO)2], or [Mn(CH3COO)2] in the presence of bpy in 1:1 methanol/water solution. In all cases, coordination of the amino group of the substrate to the metal center under the reaction conditions may activate the leaving group and orient the guanidinium moiety close to the attacking nucleophile, metal-bound hydroxide ion, to promote the hydrolysis reaction.
Photocatalytic synthesis of urea from in situ generated ammonia and carbon dioxide
Srinivas, Basavaraju,Kumari, Valluri Durga,Sadanandam, Gullapelli,Hymavathi, Chilumula,Subrahmanyam, MacHiraju,De, Bhudev Ranjan
, p. 233 - 241 (2012)
TiO2 and Fe-titanate (different wt%) supported on zeolite were prepared by sol-gel and solid-state dispersion methods. The photocatalysts prepared were characterized by X-ray diffraction, scanning electron microscopy and ultraviolet (UV)-visible diffuse reflectance spectroscopy techniques. Photocatalytic reduction of nitrate in water and isopropanol/oxalic acid as hole scavengers are investigated in a batch reactor under UV illumination. The yield of urea increased notably when the catalysts were supported on zeolite. The Fe-titanate supported catalyst promotes the charge separation that contributes to an increase in selective formation of urea. The product formation is because of the high adsorption of in situ generated CO2 and NH3 over shape-selective property of the zeolite in the composite photocatalyst. The maximum yield of urea is found to be 18 ppm while 1% isopropanol containing solution over 10 wt% Fe-titanate/HZSM-5 photocatalyst was used.
Oxyhalogen-sulfur chemistry: Kinetics and mechanism of oxidation of formamidine disulfide by acidic bromate
Madhiri, Nicholas,Olojo, Rotimi,Simoyi, Reuben H.
, p. 4149 - 4156 (2003)
The kinetics and mechanism of the oxidation of formamidine disulfide, FDS, a dimer and major metabolite of thiourea, by bromate have been studied in acidic media. In excess bromate conditions the reaction displays an induction period before formation of bromine. The stoichiometry of the reaction is: 7BrO3- + 3[(H2N(HN=)CS-]2 + 9H 2O → 6NH2CONH2 + 6SO4 2- + 7Br- + 12H- (A). In excess oxidant conditions, however, the bromide formed in reaction A reacts with bromate to give bromine and a final stoichiometry of: 14BrO3- + 5[(H2N(HN=)CS-]2 + 8H2O → 10NH 2CONH2 + 10SO42- + 7Br2 + 6H+ (B). The direct reaction of bromine and FDS was also studied and its stoichiometry is: 7Br2 + [(H2N(HN=)CS-] 2 + 10H2O → 2NH2CONH2 + 2SO42- + 14Br- + 18H+ (C). The overall rate of reaction A, as measured by the rate of consumption of FDS, is second order in acid concentrations, indicating the dominance of oxyhalogen kinetics which control the formation of the reactive species HBrO2 and HOBr. The reaction proceeds through an initial cleavage of the S-S bond to give the unstable sulfenic acids which are then rapidly oxidized through the sulfinic and sulfonic acids to give sulfate. The formation of bromine coincides with formation of sulfate because the cleavage of the C-S bond to give sulfate occurs at the sulfonic acid stage only. The mechanism derived is the same as that derived for the bromate-thiourea reaction, suggesting that FDS is an intermediate in the oxidation of thiourea to its oxo-acids as well as to sulfate.
Kinetics and Mechanism of the Complex Oxidation of Aminoiminomethanesulfinic Acid by Iodate in Acidic Medium
Mambo, Elizabeth,Simoyi, Reuben H.
, p. 13662 - 13667 (1993)
The reaction between iodate and aminoiminomethanesulfinic acid, NH2(NH)CSO2H (AIMSA), has been studied in acidic medium.The stoichiometry of the reaction in excess AIMSA is 2IO3- + 3AIMSA + 3H2O -> 3SO42- + 3CO(NH2)2 + 2I- + 6H+ (eq 1), and the soichiometry of the reaction in excess iodate is 4IO3- + 5AIMSA + 3H2O -> 5SO42- + 5CO(NH2)2 + 2I2 + +6H+ (eq 2).In excess AIMSA and high acid concentrations the reaction shows an induction period and a transient formation of iodine, while in excess iodate concentrations iodine is produced and partially consumed, leaving a finite iodine concentration at the end of the reaction.The dynamics of the reaction is explained by a combination of three reactions: the first is the oxidation of AIMSA by iodate to give iodide, the second is the Dushman reaction which forms iodine from the iodate-iodide reaction, and the third is the reaction of iodine and AIMSA.The relative rates of these three reactions will determine the dynamics of the reaction.The oxidation of AIMSA with I2 and I3- was also investigated.The oxidation of AIMSA by I2 and I3- was found to be inhibited by acid because the oxidation of AIMSA by HOI is faster than that with molecular I2.The reaction is also autoinhibitory because the product of the reaction, I-, combines with unreacted I2 to form I3- which is relatively inert toward AIMSA.A computer simulation study is performed to enhance the proposed mechanism.
The kinetics of pentoxyl oxidation by hypochlorite ions
Kheidorov,Ershov,Zyabkina
, p. 353 - 356 (2006)
The kinetics of pentoxyl (I) oxidation in aqueous media under the action of hypochlorite ions was studied at pH 8.8 and 273-298 K. The order of the reaction with respect to both participants was found to be one. The temperature dependence of the reaction rate obeyed the Arrhenius law. The reaction activation parameters were found to be E a=11.08 kJ/mol, ΔH ≠=8.73 kJ/mol, ΔS ≠=-200.70 J/(mol K), and ΔG ≠=66.88 kJ/mol. Reaction stoichiometry was studied, the chemical characteristics of the process considered, and a mechanism of the oxidative transformation of I under the action of OCl- suggested. Pleiades Publishing, Inc., 2006.
Oxyhalogen-Sulfur Chemistry: The Bromate-(Amininoimino)methanesulfinic Acid Reaction in Acidic Medium
Chinake, Cordelia R.,Simoyi, Reuben H.,Jonnalagadda, Sreekantha B.
, p. 545 - 550 (1994)
The reaction between (amnoimino)methanesulfinic acid, HO2SC(NH)NH2(AIMSA), and bromate has been studied in acidic medium.In excess AIMSA the stoichiometry of the reaction is 2BrO3- + 3AIMSA + 3H2O -> 3SO42- + 3CO(NH2)2 + 2Br- + 6H+, and in excess bromate the stoichiometry is 4BrO3- + 5AIMSA + 3H2O -> 5SO42- + 5CO(NH2)2 + 2Br2 + 6H+.Br2 is produced only when BrO3- is in stoichiometric excess over AIMSA.It is produced from the reaction of the product, Br-, with excess BrO3- after all the AIMSA has been consumed.The reaction has an initial induction period followed by formation of bromine.Although AIMSA is oxidized to SO42-, no SO42- formation is observed until Br2 production commences.The reaction is autocatalyzed by bromide.The reactive oxidizing species in solution are HOBr and Br2.Bromide enhances their formation from bromate.A simple eight-reaction mechanism is used to describe the reaction.The reaction commences through a direct reaction between BrO3- and AIMSA: BrO3+ + HO2SC(NH)NH2 + H+ -> HBrO2 + HO3SC(NH)NH2 with k = 2.5E-2M-2s-1.The rate-determining step is the standard BrO3- - Br- reaction which forms the reactive species HOBr:BrO3- + Br- + 2H+ -> HBrO2 + HOBr.A computer simulation analysis of the proposed mechanism gave good fit to the data.
