Nitrogen oxides alkoxy radicals

Mn (IT) is readily oxidized to Mn (ITT) by just bubbling air through a solution in, eg, nonanoic acid at 95°C, even in the absence of added peroxide (186). Apparently traces of peroxide in the solvent produce some initial Mn (ITT) and alkoxy radicals. Alkoxy radicals can abstract hydrogen to produce R radicals and Mn (ITT) can react with acid to produce radicals. The R radicals can produce additional alkylperoxy radicals and hydroperoxides (reactions 2 and 3) which can produce more Mn (ITT). If the oxygen feed is replaced by nitrogen, the Mn (ITT) is rapidly reduced to Mn (IT). 

Organic nitrites display a weak long-wavelength absorption (n -> n ) involving excitation of a nonbonding electron on nitrogen. Photolysis has been found to result in photodissociation of the RO—NO bond to produce alkoxy radicals and nitric oxide ... 

Studies on the photolysis of simple aliphatic and alicyclic nitrites have confirmed the need for a six-membered transition state, which decides the point of attack on a carbon chain [ 18]. The photolysis of a nitrite (9) gives an active alkoxy radical and a molecule of nitric oxide, which is itself a stable free radical. These radicals must at first be confined within a solvent cage (lo), for no significant scrambling of isotopic nitrogen occurred when a mixture of the nitrite (14) and... 

Step 2 Reaction with Oxygen. The free radical reacts with a molecule of oxygen, forming a peroxy (alkoxy) radical. Presence of oxygen is absolutely necessary. This is why oil does not oxidize when it is stored under vacuum or saturated with nitrogen. 

Another possible reaction of peroxy radicals in the atmospheric environment, particularly when nitrogen oxide concentrations are low (as they are in very clean air), is a hydrogen abstraction from HOO to produce a hydroperoxide, ROOH. Since all the above reactions of ROO- have comparable rates, the relative concentrations of HOO and NO species will determine the extent of formation of hydroperoxides, alkoxy radicals, and pernitrate esters (McFarland et al., 1979 Hanst and Gay, 1983). 

Rose, M. (1979), Photolysis of alkyl nitrites and reactions of alkoxy radicals with nitrogen oxides, Ph.D. Thesis, Case-Western Reserve University. 

As Schaffer has found 2.4.6-triphenyl-X -phosphorin 22 and other 2.4.6-tri-substituted X -phosphorins react smoothly with aryl diazonium salts in benzene. Nitrogen develops and the aryl residue bonds with the phosphorus. In presence of alcohols as nucleophiles, l-alkoxy-l-aryl-2.4.6-triphenyl-X -phosphorins 100 can be isolated. The aryl diazonium-tetrafluoroborate without any nucleophile in DMOE yields l-aiyl-l-fluoro-2.4.6-triphenyl-X -phosphorin 70i. As with other oxidants like halogen or mercury-Il-acetate, we suppose that in the first step triphenyl-X -phosphorin radical cation is formed. This could be shown by ESR spectroscopy. The next step may be a radical-radical addition to the X -phosphorin cation or a nucleophileradical addition respectively ... 

Pyridylarenes undergo Cu(II)-catalysed diverse oxidative C-H functionalization reactions. The tolerance of alkene, alkoxy, and aldehyde functionality is a synthetically useful feature of this reaction. A radical-cation pathway (Scheme 4) has been postulated to explain the data from mechanistic studies. A single electron transfer (SET) from the aryl ring to the coordinated Cu(II) leading to the cation-radical intermediate is the rate-limiting step. The lack of reactivity of biphenyl led to the suggestion that the coordination of Cu(II) to the pyridine is necessary for the SET process. The observed ortho selectivity is explained by an intramolecular anion transfer from a nitrogen-bound Cu(I) complex.53... 

Tandem radical addition/cydization reactions have been performed using unsaturated tertiary amines (Scheme 9.11) [14,15]. Radical attack is highly stereoselective anti with respect to the 5-alkoxy substituent of 2-(5f-J)-furanones, which act as the electron-deficient alkenes. However, the configuration of the a position of the nitrogen cannot be controlled. Likewise, tandem addition cyclization reactions occur with aromatic tertiary amines (Scheme 9.12) in this case, acetone (mild oxidant) must be added to prevent the partial reduction of the unsaturated ketone [14]. 

Examples of the former take place when radical 234 is stabilized by a heteroatom. When Y is an alkoxy moiety, an oxonium is formed and trapped by several external nucleophiles [193]. When an amide was present on the starting material, as was the case with 235, amino sugars were obtained in good yields (68% for 238) [ 194]. Finally, when Y is an azide, oxidation to the a-azido cation delivers nitriles upon loss of nitrogen [195]. 

Some radical sources will, in the presence of oxidizing agents, or light or heat energy, initiate cationic polymerizations of monomers, like n-butyl vinyl ether. Those that are most readily oxidized are carbon atom centered radicals that have substituents like benzyl, allyl, alkoxy, or structures with nitrogen or sulfur. Also, radicals that are formed by addition of other radicals to alkyl vinyl ethers are particularly reactive. 

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