Singlet oxygen with bromine

When l,6-imino-10-annulene (68) is oxidized with singlet oxygen and the product is thermolyzed, the homobenzene derivative 69 is formed. This, on treatment with nitrosyl chloride in the presence of triethylamine gives 25 in 5% yield.38 Also, annulene 70 on treatment with bromine gives the dibromoarene... 

The exact nature of the brominating species released by the enzyme is unknown. Hypobromous acid is known (35) to be in rapid equilibrium with molecular bromine and tribromide ions in aqueous solutions. Further, it is important to note that at neutral pH values a very fast reaction occurs between H2O2 and OBr to yield singlet oxygen (36). This rapid side reaction hampers direct observation of brominating species at neutral pH values and is why rapid-reaction kinetics had to be used by De Boer and Wever (33) to detect Bri formation. 

Another modification of a cyclopentene moiety was achieved by the cycloaddition reaction of the 1,3-dithiolane derivative 483 with singlet oxygen O2 to form the endoperoxide 484, which upon treatment with either triethyl-amine, triphenylphosphine, or bromine gave the corresponding hydroxy ketone 485, a mixture of the epoxide 486 and the enonc 487, or a mixture of isomeric adducts 488 and 489, respectively (Scheme 69) <1995JOC1333>. 

Conjugated dienes (and compounds that behave like conjugated dienes in the Diels-Alder reaction) react with singlet oxygen to form cyclic peroxides as if molecular oxygen acted as a dienophile. The yields of the peroxides, prepared by photochemical oxidation [13, 55] or by chemical oxidations with hydrogen peroxide and sodium hypochlorite, alkaline hydrogen peroxide and bromine, alkaline salts of peroxy acids [14, 26], or the ozonide of triphenyl phosphite [29], are comparable. 

The bromine/methanol (18.1.1.4) oxidation of furans to give 2,5-dialkoxy-2,5-dihydrofurans and the cycloaddition of singlet oxygen (18.7) are discussed elsewhere in this chapter. 2,5-Dialkoxy-2,5-dihydrofurans can also be obtained by electrochemical oxidation in alcohol solvents or conveniently by oxidation with magnesium monoperoxyphthalate in methanol. Reaction of furan with lead(IV) carboxylates produces... 

Singlet oxygen is also formed in the reaction of hydrogen peroxide with bromine [412]. McKeown and Waters [411, 412] found that peracids and nitriles evolve singlet oxygen in the presence of hydrogen peroxide. 

The reactive species in sensitized photo-oxidations appears to be molecular oxygen in an excited singlet state (3, 4, 5, 6). To test whether singlet oxygen reacts with benzene, it has been generated by the action of bromine on alkaline hydrogen peroxide (8). It is necessary to isolate the benzene from the aqueous peroxide since these react at 0°-I0°C. to give phenol and other products similar to those from the photo-oxidation. Initial qualitative results indicate that benzene is not readily oxidized by... 

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