Oxidation to radicals

In carboxylic acids with an aromatic group or a double bond the ii-systems can be oxidized to radical cations that react with the carboxyl group to lactones (Eqs. 7, 42) [142, 351]. 

The first structure type to be established for a hexadiene radical cation was one in which cleavage is achieved without bonding, i.e. a representative of the dissociative mechanism. Dicyclopentadiene and several derivatives can be oxidized to radical cations (137) in which one of the bonds linking the monomer units is cleaved. The unique spin density distribution of 137 is reflected in an unmistakable polarization pattern [386-389]. 

The supporting electrolyte is anodically oxidized to radicals, which abstract ohydrogen from the ether to form alkoxymethyl radicals that are subsequently oxidized to cations. An analogous route leads to alkenyl derivatives. 

Tetraphenylethylene cyclizes anodically to 9,10-diphenylphenanthrene analogously to its photooxidative cyclization. The attempted anodic cyclization of cis- or frans-stilbene to phenanthrene however failed due to electrophilic reaction of the intermediate radical cation with the solvent 37S Primary aromatic amines are oxidized to radical cations which, depending on the pH of the electrolyte couple to aminodiphenylamines (C-N coupling (84) in Eq. (172) ), yield benzidines (85) at low pH (C-C coupling) or dimerize to hydrazobenzene (86) (N-N coupling) which is subsequently oxidized to azobenzene (Eq. (172) ) 2 5,376,377)... 

As an illustration, the results of the application of the ESYCAD program to the oxidative coupling of methane are explained. For this reaction, methane may by activated at strong basic sites of the catalyst by hcterolytic chemisorption, resulting in methyl anions which may be oxidized to radicals. In the selective reaction, these radicals dimerize to ethane as the primary product. Acid sites or /j-conductivity should be avoided because they lead to total oxidation. Under reaction conditions the catalyst should be stable, i.e. not be oxidized or reduced or volatize, which can be checked by thermodynamics. 

Tetrakis(dimethylamino)ethylene (TKDE) is a strong electron donor which oxidizes to radical-cation and dication states similar to the well-known Wurster s radicals. Cyclic... 

Electrochemical oxidation of l,3-dithiol-2-one and -2-thione gave behavior consistent with the formation of dimers which were subsequently oxidized to radicals of uncertain structure. Chemical oxidation of the isoelectronic dithiafulvenes 151 (R = phenyl, 4-chlorophenyl, 4-tolyl, or anisyl) led to dimeric exocyclic C—C-coupled products, indicating the intermediacy of the radical 152. 5o... 

Suitable organic molecules may be reduced or oxidized to radicals by electron-donors and electron-acceptors, respectively. 

Compounds with enato 1,3-diaza chelate rings, e.g., (138) (cf. (37) and (38)), are oxidized to radical species which form 6,6 -C—C (139), and 6,6 -C=C linked bismacrocycles, which can be reduced to form 6,6 -biscyclams (140) (Scheme 33).177 [Ni(cyclam)]2+ and [Fe(cyclam)(MeCN)2]3+ are aerially oxidized to the 6-6 -ethylidene linked cations (141) which reduce to the 6,6 -biscyclam cations. Reaction of (138) with bifunctional o-phthaloyl dichloride gave bisacyl-linked macrocycles (142).178... 

Treatment of benzophenone with 153 in THF gave good yields of benzhydrol and imines 156 and 157 but no trace of cyclic products derived from 155 (formed via oxidation of 153 to give 154). The anion 153 does not cyclize under the reaction conditions. Cyclic products would be expected if 153 had been oxidized to radical 154 since 154 cyclizes 111). This and other experiments led to the conclusion that the reduction of benzophenone by dialkyl amides containing P-hydrogen atoms occurs via hydride and not via electron transfer. 

At the anode, anions can be oxidized to radicals (la), neutral substrates to radical cations that can either lose a proton or react with a nucleophile to form a radical (lb), and the radicals can be further oxidized to carbocations (Ic). At the cathode, the mirror image reactions occur. Carbocations formed either by dissociation (Id) or by protonation of a C=X double bond are reduced to radicals (Id), neutral substrates are reduced to radical anions that can expel a leaving group or can be pro-tonated to a radical (le,f), and the radicals can be further reduced to anions (Ig). 

Cavalieri and coworkers, following earlier investigators , have championed the hypothesis that the covalent binding of polycyclic aromatic hydrocarbons to DNA is due to radical cations formed from them by the action of cytochrome P450 and/or peroxidase enzymes . They have reported that polycyclic aromatic hydrocarbons with ionization potentials below 7.35 eV can be oxidized to radical cations by peroxidases . Furthermore, the formation of a benzo[a]pyrene-DNA adduct consistent with oxidation of the... 

Unsaturated fatty acid esters as obtained by Wittig reactions as well as saturated ones have been dimerized to gemini-diesters by deprotonation and subsequent oxidation to radicals (Scheme 2.3.4). 

With respect to halogen anions the enzymes possess little substrate specificity. They react with chloride as well as bromide and iodide ions. These halogen anions are probably first oxidized to radicals by means of hydroxyl radicals before substituting the substrate ... 

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