Hydrogen peroxide - urea
Urea peroxide, percarbamide, UHP
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||94.070 g·mol−1|
|Melting point||75 to 91.5 °C (167.0 to 196.7 °F; 348.1 to 364.6 K) (decomposes)|
|Safety data sheet||External MSDS|
|Flash point||60 °C (140 °F; 333 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Hydrogen peroxide - urea (also called Hyperol, artizone, urea hydrogen peroxide, and UHP) is a solid composed of equal amounts of hydrogen peroxide and urea. This compound is a white crystalline solid which dissolves in water to give free hydrogen peroxide. Often called carbamide peroxide in the dental office, it is used as a source of hydrogen peroxide for bleaching, disinfection, and oxidation. Hydrogen peroxide - urea contains solid and water-free hydrogen peroxide, which offers a higher stability and better controllability than liquid hydrogen peroxide when used as an oxidizing agent.
For the preparation of the compound, urea (which is stable to oxidizing agents such as hydrogen peroxide) is dissolved in 30% hydrogen peroxide (molar ratio 2:3) at temperatures below 60 °C. On cooling, hydrogen peroxide - urea precipitates in the form of small platelets.
Determination of the hydrogen peroxide content by titration with potassium permanganate solution gives a value of 35.4% which corresponds to 97.8% of the theoretical maximum value. The remaining impurity consists of urea.
The compound is considered a 1:1 complex and the dashed blue line in the above figure signifies a hydrogen bond. There are different possibilities for the numbers and types of hydrogen bonds in the complex but the two most stable structures appear to have carbonlyic hydrogen bonds involving the oxygen atoms and hydrogen atoms on the peroxide molecule attracted to, respectively, hydrogen and oxygen atoms on the urea molecule (the latter of which is not indicated in the simplified structural formula above) to form a "closed" monocyclic ring. In the three-dimensional solid phase, the individual rings are held together by packing forces, a large dipole moment, and additional hydrogen bonds.  The adduct can be stabilized by adding about 1% sodium pyrophosphate, sodium hexametaphosphate, dihydroxybutanedioic acid or EDTANa2, since these complex the catalytically active heavy metal ions.
Akin to water of crystallization, hydrogen peroxide cocrystallizes with urea with the stoichiometry of 1:1. The compound is simply produced (on a scale of several hundred tonnes a year) by the dissolution of urea in excess concentrated hydrogen peroxide solution, followed by crystallization. The laboratory synthesis is analogous.
Structure and properties
Hydrogen peroxide-urea is a readily water-soluble, odorless, crystalline solid, which is available as white powder or colorless needles or platelets. Upon dissolving in various solvents, the 1:1 complex dissociates back to urea and hydrogen peroxide. So just like hydrogen peroxide, the (erroneously) so-called adduct is an oxidizer but the release at room temperature in the presence of catalysts proceeds in a controlled manner, thus the compound is suitable as a safe substitute for the unstable aqueous solution of hydrogen peroxide. Because of the tendency for thermal decomposition, which accelerates at temperatures above 82 °C, it should not be heated above 60 °C, particularly in pure form.
Disinfectant and bleaching agent
Hydrogen peroxide - urea is mainly used as a disinfecting and bleaching agent in cosmetics and pharmaceuticals. As a drug, this compound is used in some preparations for the whitening of teeth. It is also used to relieve minor inflammation of gums, oral mucosal surfaces and lips including canker sores and dental irritation, and to emulsify and disperse earwax.
Reagent in organic synthesis
In the laboratory, it is used as a more easily handled replacement for hydrogen peroxide. It has proven to be a stable, easy-to-handle and effective oxidizing agent which is readily controllable by a suitable choice of the reaction conditions. It delivers oxidation products in an environmentally friendly manner and often in high yields especially in the presence of organic catalysts such as cis-butenedioic anhydride or inorganic catalysts such as sodium tungstate.
The epoxidation of various alkenes in the presence of benzonitrile yields oxiranes in yields of 79 to 96%.
The oxygen atom transferred to the alkene originates from the peroxoimide acid formed intermediately from benzonitrile. The resulting imidic acid tautomerizes to the benzamide.
The compound acts as a strong oxidizing agent and can cause skin irritation and severe eye damage.
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- Sigma-Aldrich specification sheet
- Chemicalland data sheet
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- US 0
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