Aminyl radicals source

Figure 4.12. Second-order rate constants for reactions of hydrogen atom donors with various radical types at ambient temperature. Data sources group 14 (IV A) hydrides (15) aminyl radicals (69) amidyl radicals (70) alkyl radials with group 16 (VI A) hydrides (71) acyl radical with PhSeH (72).

The rate constant of this reaction was measured by flash photolysis with tetraphenyl-hydrazine as a source of diphenylaminyl radicals [64]. Peroxyl radicals were generated through the photodecay of bis(l,l-dimethylethyl) peroxide followed by the rapid reaction of formed alkoxyl radicals with cyclohexane used as a solvent the reaction conditions were chosen in such a way that [R02 ]o > [Ph2N ]0. Under these conditions, aminyl radicals were destroyed only in the reaction with peroxyl radicals and, hence, the concentration of peroxyl radicals during the measurement of the kinetics of Ph2N consumption varied insignificantly. The rate constant of the recombination of peroxyl and diphenylamine radicals was found to be equal to 6 x 108 L mol 1 s 1 (cyclohexane, 283-303 K). 

The use of /V-chloramines, in principle, allows the facile generation of aminyl radicals upon UV photolysis in neutral media. A radical chain can be envisioned for the formation of 2-chIoromethylpyrrolidines (Scheme 7). In practice, however, there is a slow step in this sequence, step A and/or B, such that other reaction pathways, disproportionation or H-abstraction from the solvent, compete. Surzur has studied the reaction in Scheme 7 in the alcoholic solvents MeOH and /-PrOH, which serve as hydrogen atom sources, and achieved acceptable ratios of cyclic products 25 and 26 to acyclic amine 27 (70TL3107). Other /V-chloroalkenylamines gave similar results (71TL903 80TL287). /8-chloro-substituted amine products such as 25 were the sole products when the reactions were carried out in acetic acid-water mixtures these reactions involve aminium cation radicals and are discussed further in Section III,B. 

Recombination of Aminyl Radicals. A convenient source of In is tetraphenylhydrazine, Inin. Diphenylamine and oligomeric semidienes were found to be the products of Inin decomposition at T > 400°K 0,4). The kinetics of their formation were studied by Varlamov (5). He found that InH and o-semidienes were primary stable products of... 

The reaction of TEMPO with ketenes (in particular Ph2C=C=0) proceeds to yield unstable species that upon reaction with O2 form a stable peroxide (60). Heating (60) at 100°C in toluene with added TEMPO leads to benzophenone, PhCH20TEMP0, and tetramethylpiperidine, indicating that the peroxide is a source of aminyl radicals (61) (Scheme 42). ° Kinetic studies of the reaction of TEMPO with ketenes in hydrocarbon solvents have also been reported. ... 

Huang, W.-W, Henry-Riyad, H., and Tidwell, T.T., Reactions of the Stable Nitroxyl Radical TEMPO with Ketenes Formation of a Unique Peroxidic Source of Aminyl Radicals, /. Am. Chem. Soc., 121, 3939, 1999. 

According to the classical definition. Barton esters are mixed anhydrides of carboxylic acids with thio-hydroxamic acid such as I (Scheme Ij. This class of compound was originally developed to allow the transformation of carboxylic acids to a convenient source of radicals for synthetic application. Even now, they are one of the most important entries to C-radicals. Over time, the scope of the reaction was broadened, allowing the generation of heteroatom-centered radicals, particularly oxyl-, aminyl-, and iminyl radicals of synthetic interest. For these transformations, carbonates and carbamates (II), acetates (IV), and ethers (V) were developed (Scheme 1). Finally, oxalates (III) were used for deoxygenation of secondary and tertiary alcohols. The radical fragmentation reaction of these compounds can be carried out either by irradiation or by thermal activation. Both methods are discussed here briefly. 

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