Oxygen-centered radicals specificity

Table 3.8 Specificity Observed in the Reactions of Oxygen-Centered Radicals with Various Monomers at 60 °C...

Nitrogen- and oxygen-centered radicals offer some specific features. The rate constant of the reaction of dialkylaminyl radicals with (TMSlsSiFl is close to the analogous reaction of secondary alkyl radicals. In the reactions of... 

Another strategy involves decomposition of a peroxide or other initiator in the presence of a monomer. Conditions can be chosen such that only one unit of monomer is consumed. I hus, decomposition of UBPOX in S in the presence of DTBN provides 101 (Scheme 9.20). " The monomer initiator and/or combination should be chosen with care to obtain high yield of effective alkoxyamines. Many oxygen-centered radicals react with monomer by multiple pathways. Specificities shown by oxygen-centered radicals in their reaction with monomers have been studied extensively and are discussed in Section 3.4.2. Hydrogen abstraction, often by a source of f-butoxy radicals at low temperature [e.g. (/BuO)2/hv, DBPOX, " /BuOOH/Co(lI) "- j, in the presence of a nitroxide is another common method for generating benzylic and other alkoxyamines. 

Other methods, among which thermolysis or photolysis of tetrazene [59], photolysis of nitrosoamines in acidic solution [60], photolysis of nitrosoamides in neutral medium [61], anodic oxidation of lithium amides [62], tributylstannane-mediated homolysis of O-benzoyl hydroxamic derivatives [63, 64], and spontaneous homolysis of a transient hydroxamic acid sulfinate ester [65] could have specific advantages. The redox reaction of hydroxylamine with titanium trichloride in aqueous acidic solution results in the formation of the simplest protonated aminyl radical [66] similarly, oxaziridines react with various metals, notably iron and copper, to generate a nitrogen-centered radical/oxygen-centered anion pair [67, 68]. The development of thiocarbazone derivatives by Zard [5, 69] has provided complementary useful method able to sustain, under favorable conditions, a chain reaction where stannyl radicals act simply as initiators and allow transfer of a sulfur-containing... 

In that same pnblication, Chnrch and Pryor (746) stated that the vapor phase of cigarette smoke contains small oxygen-and carbon-centered radicals that are mnch more reactive than the particnlate-phase radicals. Althongh no vapor-phase radicals were specifically identihed, they stated that the vapor-phase radicals do not arise from the initial combustion of the tobacco, bnt are rather prodnced in a steady state by the oxidation of NO to NO2, which then reacts with reactive species already present in smoke, snch as isoprene. They suggested that these reactive vapor-phase free radicals and the metastable prodncts derived from the radical reactions may be responsible for the inactivation of al-proteinase inhibitor by fresh smoke. 

Abstract Boron-doped diamond (BDD) electrodes provide an unusually wide electrochemical window in protic media, since there exist large offset potentials for the evolution of molecular hydrogen and oxygen, respectively. At the anode, alcohols are specifically converted to alkoxyl radicals. These can be used for chemical synthesis. When the enormous reactivity of such intermediate spin centers is not controlled, mineralization or electrochemical incineration dominates. Efficient strategies include either high substrate concentrations or fluorinated alcohols which seem to stabilize the spin centers in the course of reaction. 

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