Peroxide, hydrogen cleavage

It is evident that some leeway is available in the substituents tolerable in the m-position. The bronchodilator sulfonterol (28) is descended from this observation. Chloromethylanisole (29) is reacted with methylmereaptan to give 30, and the newly introduced group is oxidized to the methyl-sulfonyl moiety of 31 with hydrogen peroxide. Ether cleavage, acetylation and Fries rearrangement of the phenolic acetate produces 32, which is next brominated with pyrrolidinone hydrobromide tribromide and then oxidized to the glyoxal (33) with dimethyl sulfoxide. 

Detection of HRP Activity. The substrate for HRP used in assays is H2O2 or sometimes other peroxides. The cleavage of H2O2 is coupled to the oxidation of a hydrogen donor (chromogen) and goes through several intermediary steps with different rate constants. 

An illustration of DNA strand cleavage mediated by hydroxyl radicals produced by the Fenton reaction (A) of Fe(EDTA) with hydrogen peroxide. The cleavage scheme (B) shows the products obtained as a result of initial C4 -Fl abstraction by the hydroxyl radicals. 

Under the influence of oxygen, polyamides preferably react on the methylene group adjacent to the amide bond. This reaction consists of hydrogen cleavage and subsequent formation of peroxide radicals. Under oxygen-poor conditions, cross-linking reactive compounds are formed that react further to high-molecular products [625]. 

Free-Radical Formation. Hydrogen peroxide can form free radicals by homolytic cleavage of either an O—H or the O—O bond. 

Oxidation. Ketones are oxidized with powerful oxidizing agents such as chromic or nitric acid. During oxidation, carbon—carbon bond cleavage occurs to produce carboxyHc acids. Ketone oxidation with hydrogen peroxide, or prolonged exposure to air and heat, can produce peroxides. Concentrated solutions of ketone peroxides (>30%) may explode, but dilute solutions are useful in curing unsaturated polyester resin mixtures (see... 

Ozonation ofAlkenes. The most common ozone reaction involves the cleavage of olefinic carbon—carbon double bonds. Electrophilic attack by ozone on carbon—carbon double bonds is concerted and stereospecific (54). The modified three-step Criegee mechanism involves a 1,3-dipolar cycloaddition of ozone to an olefinic double bond via a transitory TT-complex (3) to form an initial unstable ozonide, a 1,2,3-trioxolane or molozonide (4), where R is hydrogen or alkyl. The molozonide rearranges via a 1,3-cycloreversion to a carbonyl fragment (5) and a peroxidic dipolar ion or zwitterion (6). 

Substitution reactions on dialkyl peroxides without concurrent peroxide cleavage have been reported, eg, the nitration of dicumyl peroxide (44), and the chlorination of di-/ fZ-butyl peroxide (77). Bromination by nucleophilic displacement on a-chloro- or a-hydroxyalkyl peroxides with hydrogen bromide produces a-bromoalkyl peroxides (78). 

Thermal decomposition of dihydroperoxides results in initial homolysis of an oxygen—oxygen bond foUowed by carbon—oxygen and carbon—carbon bond cleavages to yield mixtures of carbonyl compounds (ketones, aldehydes), esters, carboxyHc acids, hydrocarbons, and hydrogen peroxide. 

Tetracyanoethylene oxide [3189-43-3] (8), oxiranetetracarbonitnle, is the most notable member of the class of oxacyanocarbons (57). It is made by treating TCNE with hydrogen peroxide in acetonitrile. In reactions unprecedented for olefin oxides, it adds to olefins to form 2,2,5,5-tetracyanotetrahydrofuran [3041-31-4] in the case of ethylene, acetylenes, and aromatic hydrocarbons via cleavage of the ring C—C bond. The benzene adduct (9) is 3t ,7t -dihydro-l,l,3,3-phthalantetracarbonitrile [3041-36-9], C22HgN O. 

Free radicals are initially generated whenever polymer chains are broken and carbon radicals are formed. These effects occur during manufacture and in service life. Many elastomers are observed to oxidize at relatively low temperature (about 60°C), where carbon-hydrogen and carbon-carbon bond cleavages are highly unlikely. It has been demonstrated [52] that traces of peroxides impurities in the rubber cause low-temperature oxidation of rubber. These initiating peroxides are present in even the most carefully prepared raw rubber polymer [53]. 

This excellent method of oxidative cleavage (/) of carbon-silicon bonds requires that the silane carry an electronegative substituent (2), such as alkoxy or fluoro. Either hydrogen peroxide or mcpba may be used as oxidant, and the alcohol is produced with retention of configuration (3). Fluoride ion is normally a mandatory additive in what is believed to be a fluoride ion-assisted rearrangement of a silyl peroxide, as shown below ... 

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