Uses of urea

Because of its very high nitrogenous content urea is widely used as a fertilizer in combination with superphosphate. Its other uses are outlined in Table 3.11. 

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Urea can be considered the amide of carbamic acid, NH2COOH, or the diamide of carbonic acid, CO(OH)2. At room temperature, urea is colorless, odorless, and tasteless. Properties are shown ia Tables 1—4. Dissolved ia water, it hydrolyzes very slowly to ammonium carbamate (1) and eventually decomposes to ammonia and carbon dioxide (qv). This reaction is the basis for the use of urea as fertilizer (qv). 

G. Hoffmeister and G. H. Megar, "Use of Urea iu Bulk Blends," Proceedings of the 25th Finnual Meeting of the Fertiliser Industry Round Table, Washington, D.C., 1975, pp. 212-226. 

Obsolete uses of urea peroxohydrate, as a convenient source of aqueous hydrogen peroxide, include the chemical deburring of metals, as a topical disinfectant and mouth wash, and as a hairdresser s bleach. In the 1990s the compound has been studied as a laboratory oxidant in organic chemistry (99,100). It effects epoxidation, the Baeyer-Villiger reaction, oxidation of aromatic amines to nitro compounds, and the conversion of sodium and nitrogen compounds to S—O and N—O compounds. 

Trees and soils of forests act as sources of NH3 and oxides of nitrogen. Ammonia is formed in the soil by several types of bacteria and fungi. The volatilization of ammonia and its subsequent release to the atmosphere are dependent on temperature and the pH of the soil. Fertilizers are used as a tool in forest management. The volatilization of applied fertilizers may become a source of ammonia to the atmosphere, especially from the use of urea. 

Uses of Urea. The major use of urea is the fertilizer field, which accounts for approximately 80% of its production (about 16.2 billion pounds were produced during 1994 in U.S.). About 10% of urea is used for the production of adhesives and plastics (urea formaldehyde and melamine formaldehyde resins). Animal feed accounts for about 5% of the urea produced. 

Precipitation of calcium oxalate may also be made from homogeneous solution either by use of urea as reagent or by the use of dimethyl oxalate. Both procedures lead to satisfactory separations from magnesium. 

Presently the catalytic selective NOx reduction by ammonia is efficient and widespread through the world for stationary sources. The remarkable beneficial effect of 02 for the complete reduction of NO into nitrogen is usually observed between 200 and 400°C. However, such a technology is not applicable for mobile sources due to the toxicity of ammonia and vanadium, which composes the active phase in vanadia-titania-based catalysts. Main drawbacks related to storing and handling of ammonia as well as changes in the load composition with subsequent ammonia slip considerably affect the reliability of such a process. On the other hand, the use of urea for heavy-duty vehicles is of interest with the in situ formation of ammonia. 

Condensation reaction of thiourea with 1,3-dichloroacetone provides 2,7-diamino-l,6-dithio-3,8-diazaspiro[4.4]nonane-2,7-diene. The use of urea... 

Nitrite solution is added to an acidified urea solution. Use of urea for the removal of nitrous acid, e.g. in the preparation of ethyl nitrate (p. 148). 

The introduction of simple or substituted formamide radicles by the use of urea chlorides (cyanic add and cyanic esters + HC1). 

The use of urea triton gel electrophoresis (Zweidler and Cohen, 1972 Alfageme et al., 1974) has permitted the further resolution of histone fractions and the identification of histone variants. Microcomponents or variants of histone HI have been known for a long time (for references, see Cole, 1977). Recently, it has been shown that microcomponents or variants of histones H2B, H2A, and H3 occur in many systems (Marzluff et al., 1972 Laine et al., 1976 Garrard, 1976 Blankstein and Levy, 1976 Zweidler, 1976 Franklin and Zweidler, 1977). Furthermore, in sea urchin embryo the synthesis of new histone variants has been correlated with development (Cohen et al., 1975 Newrock et al., 1978 Von Holt et al., 1979). 

The use of urea must be approached with caution, because urea solutions often contain ammonium cyanate, the concentration of which increases with temperature and pH. This contaminant can react with the amino group of lysines and the amino terminus of the polypeptide chain, thus leading to artifact peaks. This effect is minimized by the presence of ampholytes, whose primary amines are cyanate scavengers, and by deionizing the urea solution with a mixed-bed resin prior to adding the ampholytes and detergent. 

Urea nitrate (UN), more properly called uronium nitrate, is an energetic salt, and as such would not be expected to have much vapour pressure however, it might be detectable due to evolved urea or nitrogen oxides. Detection of urea nitrate is essential because for over a decade it has been a frequent choice of terrorists. It was used in the bombing of the World Trade Center in New York City (Februaryl 993) and in many car bombings in Palestine. In 1992, the use of urea nitrate became so prevalent in bombings by the Shining Path that sales of urea were outlawed in Peru. 

Frankenberger WT Jr. 1988. Use of urea as a nitrogen fertilizer in bioreclamation of petroleum... 

The advances in the knowledge of fast SCR and in its implementation may also offer a challenging opportunity for the use of urea-ammonia SCR at low temperatures in some stationary applications. 

At the proper temperature, the injected reagent reacts selectively in the presence of oxygen to reduce the oxides of nitrogen (NOJ primarily to molecular nitrogen (Nj) and water (FI2O). Figure 17.4 shows the results of pilot-scale tests of the use of urea and ammonia in the SNCR performance. 

The use of urea (Ureaphil, Ur evert) 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. 

Another use of urea is for resins, which are used in numerous applications including plastics, adhesives, moldings, laminates, plywood, particleboard, textiles, and coatings. Resins are organic liquid substances exuded from plants that harden on exposure to air. The term now includes numerous synthetically produced resins. Urea resins are thermosetting, which means they harden when heated, often with the aid of a catalyst. The polymerization of urea and formaldehyde produces urea-formaldehyde resins, which is the second most abundant use of urea. Urea is dehydrated to melamine, which, when combined with formaldehyde, produces melamine-formaldehyde resins (Figure 96.2). Melamine resins tend to be harder and more heat-resistant than urea-formaldehyde resins. Melamine received widespread attention as the primary pet food and animal feed contaminant causing numerous cat and dog deaths in early... 

Other minor uses of urea are as rehydrating lotion, diuretics, deicers, and cold-compresses. 

AN prills (74), Na nitrate (2), w (16), urea (5.5), guar gum (0.4), Zn chromate (0.1), and naphthalene (2.0%). Francis (Refs 15 16) claims the use of urea primarily as a crystallization inhibitor for compns which when detonated in 2" and 3" diam schedule 40 steel pipe, using from 10 to 25g of 0-4 compn as the initiator, yielded deton velocities in the range of from 4663 to 6126m/sec. Typically, a mixt comprising urea (4), AN (21.3), guar gum (0.7),... 

Initially, the use of urea, dilute alkali, or anionic detergent was suggested415 for solubilization of the enzyme from S. aureus membrane. Nonionic detergents were effective for this purpose with the enzyme from the same micro-organism and from Micrococcus luteus.416,417 Repeated freezing and thawing of a membrane preparation was used in the case of Escherichia co/i.418... 

The analysis of the obtained data shows that the use of urea and vinyl acryl solutions fails to provide sufficiently strong granules (11 to 30% of the granules were disintegrated). For this reason, impact loads were applied to granules obtained by the use of water, polyethylene oxide, and several original preparations of agglomerating liquid. 

Urea, ranging from 5 to 9 M, is the most common choice of chaotropic agent, and disruption of hydrogen and hydrophobic bonding between proteins is the main mode of action. When used in conjunction with thiourea (from 0 to 2 M), the two can aid solubilization of poorly soluble samples. The use of urea or urea-thiourea mixtures in SD buffers has no effect on the charge of the proteins within the sample. This is ideal for use in separating proteins according to their p in the first... 

A better AE value (59wt%) is obtained with the coproduction of ethylene glycol from the methanolysis of ethylene carbonate (entry 2). The AE value is higher when water is coproduced (83 wt %, entries 4—5). The use of urea as a feedstock (entry 3) may also lead to AE = 83 wt%, by coupling the urea synthesis equation. The complete use of feedstock atoms (AE = 100 wl%) has been demonstrated commercially for cyclic carbonate synthesis, but as yet no real case has been reported for unstrained ethers (entry 6). 

It is important to realize that a thermosetting polymer reacted to high (but not full) conversion contains a small fraction of free monomers if the monomers are volatile, their emissions may produce forbidden contamination levels, particularly for indoor applications. The decline in the use of urea-formaldehyde resins in agglomerated wood panels resulted from contamination problems associated with formaldehyde emission. 

Recommendations on the synthesis of metal phthalocyanines. It is still difficult to evaluate real reaction mechanisms in each synthetic procedure applied. It is clear that the use of such polar protic solvents as alcohols contributes to higher yields of Pc from PN in the electrosynthesis conditions due to the ease of nucleophilic attack of the generated additional RO-. In the further steps of Pc formation from PN or 1,3-D, a solvent s nature has no significant importance. These data about the importance of, first of all, the initial stage correspond to those reported on UV irradiation [40] of PN solutions, where such a treatment is effective only at the beginning of the process. However, in the case of the use of urea and PA, a solvent must be completely inert (or be close to urea s nature) to carry out the one-step synthesis of metal phthalocyanines, in order to exclude any negative influence on the reaction course. The fact that the yields are almost always higher in the case of direct electrosynthesis could serve as an additional confirmation about the usefulness and necessity of this technique. 

Proteins were then dissolved in 20 mL of 0.125 M Tris-HCl, pH 7.4 containing 1% (m/v) CHAPS and the protease inhibitor cocktail, and treated with CPLL. With several variations from the standard treatments such as other complementary extractions from seeds, the use of urea-containing extraction buffer, and an additional peptide ligand library, the total number of detected gene products was quite large. Two hundred and thirty one unique proteins were found in the pulp (vs. 56 described previously) and 61 in the seeds (vs. only four reported by the literature). In the latter case, the presence of seed storage proteins, oleosins, and histones were detected in the pulp, a thaumatin-like protein, an allergenic protein also named Ole el3, was confirmed. 

The simultaneous use of urea, or thiourea [76] and DABCO catalyst was introduced by the Connon group for the addition of methyl acrylate and benzaldehyde [39]. The study revealed that, although both ureas and thioureas accelerated the reaction relative to the uncatalyzed process, urea was superior to thiourea in terms of stability and efficiency. Chiral thiourea derivatives may offer, however, superior enantioselectivity. It was postulated, that the catalysts operate mainly via a Zimmerman-Traxler-type transition state 69 for addition of the resulting enolate anion to the aldehyde (Scheme 5.15). 

Rattner, H. Use of urea in hand cream, Arch. Dermatol. Siph., 48, 47, 1943. 

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