Hydrogen peroxide–urea
Template:Short description Template:Chembox Hydrogen peroxide–urea (also called Hyperol, artizone, urea hydrogen peroxide, and UHP) is a white crystalline solid chemical compound composed of equimolar amounts of hydrogen peroxide and urea. It 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. Often called carbamide peroxide in dentistry, it is used as a source of hydrogen peroxide when dissolved in water for bleaching, disinfection and oxidation.
Production
For the preparation of the complex, urea is dissolved in 30% hydrogen peroxide (molar ratio 2:3) at temperatures below Template:Convert. upon cooling this solution, hydrogen peroxide–urea precipitates out in the form of small platelets.<ref name="Giguère">Template:Cite journal</ref>
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.<ref name = Ullmann>Template:Ullmann</ref> The laboratory synthesis is analogous.<ref name="ReferenceA">Template:Cite journal</ref>
Structure and properties
The solid state structure of this adduct has been determined by neutron diffraction.<ref>Template:Cite journal</ref>
Hydrogen peroxide–urea is a readily water-soluble, odorless, crystalline solid, which is available as white powder or colorless needles or platelets.<ref name="Giguère" /> Upon dissolving in various solvents, the 1:1 complex dissociates back to urea and hydrogen peroxide. So just like hydrogen peroxide, the 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 safer substitute for the unstable aqueous solution of hydrogen peroxide. Because of the tendency for thermal decomposition, which accelerates at temperatures above Template:Convert,<ref name="e-EROS">Template:Cite book</ref> it should not be heated above Template:Convert, particularly in pure form.Template:Cn
Applications
Disinfectant and bleaching agent
Hydrogen peroxide–urea is mainly used as a disinfecting and bleaching agent in cosmetics and pharmaceuticals.<ref name = Ullmann/> As a drug, this compound is used in some preparations for the whitening of teeth.<ref name=Ullmann/><ref name="ADA-CP-HP">Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It is also used to relieve minor inflammation of gums, oral mucosal surfaces and lips including canker sores and dental irritation,<ref name="ummc">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and to emulsify and disperse earwax.<ref name="WebMDeardrops">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Carbamide peroxide is also suitable as a disinfectant, e.g. for germ reduction on contact lens surfaces or as an antiseptic for mouthwashes, ear drops or for superficial wounds and ulcers.
Reagent in organic synthesis
In the laboratory, it is used as a more easily handled replacement for hydrogen peroxide.<ref name="ReferenceA"/><ref name="Varma">Template:Cite journal</ref><ref name="e-EROS"/> 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<ref name="Karami">Template:Cite journal</ref> or inorganic catalysts such as sodium tungstate.<ref name="Lukasiewicz">Template:Cite conference</ref>
It converts thiols selectively to disulfides,<ref name="Karami" /> secondary alcohols to ketones,<ref name="Lukasiewicz" /> sulfides to sulfoxides and sulfones,<ref name="Varma"/> nitriles to amides,<ref name="Varma" /><ref>Template:Cite patent</ref> and N-heterocycles to amine oxides.<ref name="Varma" /><ref>Template:Cite journal</ref>
Hydroxybenzaldehydes are converted to dihydroxybenzenes (Dakin reaction)<ref name="Varma" /><ref name="Heaney">Template:Cite journal</ref> and give, under suitable conditions, the corresponding benzoic acids.<ref name="Heaney" />
It oxidizes ketones to esters, in particular cyclic ketones, such as substituted cyclohexanones or cyclobutanones to give lactones (Baeyer–Villiger oxidation).<ref name="Rios">Template:Cite journal</ref><ref>Template:Cite journal</ref>
The epoxidation of various alkenes in the presence of benzonitrile yields oxiranes in yields of 79 to 96%.<ref>Template:Cite journal</ref>
The oxygen atom transferred to the alkene originates from the peroxoimide acid formed intermediately from benzonitrile. The resulting imidic acid tautomerizes to the benzamide.
Safety
The compound acts as a strong oxidizing agent and can cause skin irritation and severe eye damage.<ref name="SigmaSDS"/>
Urea–hydrogen peroxide was also found to be an insensitive but moderately powerful secondary explosive.<ref name="PEP2022">Template:Cite journal</ref><ref>Template:Cite journal</ref>
See also
References
External links
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