The Decomposition of Urea in Aqueous Media

Shaw, William H.; Bordeaux, John J.

doi:10.1021/ja01623a011

Cited by 332 publications

(254 citation statements)

References 4 publications

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“…Urea is a very stable molecule with a half-life (t ) of approximately 40 years at 25°C, and therefore, it is not spontaneously hydrolyzed (degraded) in solution (Callahan et al 2005;Shaw and Bordeaux 1955). However, the enzyme urease (EC 3.5.1.5) catalyzes a reaction in which one molecule of urea is hydrolyzed to form two molecules of ammonia (NH 3 ) and one carbonic acid (H 2 CO 3 ) via the formation of carbamic acid (H 3 CNO 2 ) according to the reaction shown in Fig.…”

Section: Enzymatic Degradation Of Ureamentioning

confidence: 99%

The molecular processes of urea hydrolysis in relation to ammonia emissions from agriculture

Sigurdarson

Svane

Karring

2018

Rev Environ Sci Biotechnol

243

129

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Ammonia emissions from the agricultural sector give rise to numerous environmental and societal concerns and represent an economic challenge in crop farming, causing a loss of fertilizer nitrogen. Ammonia emissions from agriculture originate from manure slurry (livestock housing, storage, and fertilization of fields) as well as urea-based mineral fertilizers. Consequently, political attention has been given to ammonia volatilization, and regulations of ammonia emissions have been implemented in several countries. The molecular cause of the emission is the enzyme urease, which catalyzes the hydrolysis of urea to ammonia and carbonic acid. Urease is present in many different organisms, encompassing bacteria, fungi, and plants. In agriculture, microorganisms found in animal fecal matter and soil are responsible for urea hydrolysis. One strategy to reduce ammonia emissions is the application of urease inhibitors as additives to urea-based synthetic fertilizers and manure slurry to block the formation of ammonia. However, treatment of the manure slurry with urease inhibitors is associated with increased livestock production costs and has not yet been commercialized. Thus, development of novel, environmentally friendly and cost-effective technologies for ammonia emission mitigation is important. This mini-review describes the challenges associated with the volatilization of ammonia in agriculture and provides an overview of the molecular processes of urea hydrolysis and ammonia emissions. Different technologies and strategies to reduce ammonia emissions are described with a special focus on the use of urease inhibitors. The mechanisms of action and efficiency of the most important urease inhibitors in relation to agriculture will be briefly discussed.

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Section: Enzymatic Degradation Of Ureamentioning

confidence: 99%

The molecular processes of urea hydrolysis in relation to ammonia emissions from agriculture

Sigurdarson

Svane

Karring

2018

Rev Environ Sci Biotechnol

243

129

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“…The process yields isocyanic acid, which has been experimentally observed as a product of urea decomposition. [1][2][3][4] A 2-D projection of the PDDG PES was obtained using two reaction coordinates, the length of the breaking C-N bond and a coordinate representing the hydrogen transfer (Figure 1a). The choice for the latter required some investigation.…”

Section: Intramolecular Eliminationmentioning

confidence: 99%

“…Cyanate ion further readily undergoes conversion to CO 2 and ammonia. [1][2][3][4] In contrast, when catalyzed by ureases, urea is generally believed to undergo hydrolysis rather than ammonia elimination. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The products of hydrolytic decomposition have been reported to be either HCO 3 − and NH 4 + or ammonium carbamate depending on the buffer system.…”

Section: Introductionmentioning

confidence: 99%

Why Urea Eliminates Ammonia Rather than Hydrolyzes in Aqueous Solution

Alexandrova

Jorgensen

2007

J. Phys. Chem. B

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A joint QM/MM and ab initio study on the decomposition of urea in the gas phase and in aqueous solution is reported. Numerous possible mechanisms of intramolecular decomposition and hydrolysis have been explored; intramolecular NH 3 -elimination assisted by a water molecule is found to have the lowest activation energy. The solvent effects were elucidated using the TIP4P explicit water model with free energy perturbation (FEP) calculations in conjunction with QM/ MM Monte Carlo simulations. The explicit representation of the solvent was found to be essential for detailed resolution of the mechanism, identification of the rate-determining step, and evaluation of the barrier. The assisting water molecule acts as a hydrogen shuttle for the first step of the elimination reaction. The forming zwitterionic intermediate, H 3 NCONH, participates in 8-9 hydrogen bonds with water molecules. Its decomposition is found to be the rate-limiting step, and the overall free energy of activation for the decomposition of urea in water is computed to be ca. 37 kcal/mol; the barrier for hydrolysis by an addition/elimination mechanism is found to be ca. 40 kcal/mol. The differences in the electronic structure of the transition states of the NH 3 -elimination and hydrolysis were examined via natural bond order analysis. Destruction of urea's resonance stabilization during hydrolysis via an addition/elimination mechanism, and its preservation in the rearrangement to the H 3 NCONH intermediate were identified as important factors in determining the preferred reaction route.

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“…The detailed sequence of chemical reactions describing the decomposition of urea in aqueous media has previously been documented. 47,56 The extremely small amounts of precipitates formed just at the precipitation-start point (i.e., pH 2.05, T ϭ 85°C) have been immediately recovered from the urea-containing solutions by quenching the beaker of that solution in an ice-water bath (0°C), followed by centrifugal filtration at 10000 rpm, and 2-propanol washing (5ϫ) and drying at 90°C. The unique morphologies of these precipitates are depicted by the FESEM micrographs given in Figs.…”

Section: (1) Homogeneous Decomposition Of Ureamentioning

confidence: 99%

Synthesis of Gallium Oxide Hydroxide Crystals in Aqueous Solutions with or without Urea and Their Calcination Behavior

Taş

Majewski

Aldinger

2002

Journal of the American Ceramic Society

163

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Gallium oxide hydroxide (GaOOH⅐xH 2 O) single crystals were synthesized in aqueous solutions by using two different precipitation techniques: homogeneous decomposition of urea and forced hydrolysis in pure water. Precipitation of crystals started at exactly the same pH value (i.e., 2.05 at 85°C) in both cases. The morphology of crystals turned out to be quite different (zeppelin-like with urea, rodlike without urea) in each of the above methods. Calcination of these gallium oxide hydroxide crystals in air at temperatures >500°C transformed them into Ga 2 O 3 . Characterization of the samples was performed by X-ray diffractometry, scanning electron microscopy, thermogravimetry/differential thermal analysis, Fourier transform infrared spectroscopy, and ICP, carbon, and nitrogen analyses.

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The Decomposition of Urea in Aqueous Media

Cited by 332 publications

References 4 publications

The molecular processes of urea hydrolysis in relation to ammonia emissions from agriculture

The molecular processes of urea hydrolysis in relation to ammonia emissions from agriculture

Why Urea Eliminates Ammonia Rather than Hydrolyzes in Aqueous Solution

Synthesis of Gallium Oxide Hydroxide Crystals in Aqueous Solutions with or without Urea and Their Calcination Behavior

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