Initiation of free radical reactions

The addition of halogenated aliphatics to carbon-carbon double bonds is the most useful type of carbon-carbon bond forming synthetic method for highly halogenated substrates Numerous synthetic procedures have been developed for these types of reactions, particularly for the addition of perfluoroalkyl iodides to alkenes using thermal or photolytic initiators of free radical reactions such as organic peroxides and azo compounds [/]... 

The initiation of free radical reactions by ozone in the gas phase at elevated temperatures occurs due to ozone monomolecular decomposition [131,132] ... 

AIBN is a very common initiator of free radical reactions. The radical derived from its fragmentation abstracts H from Ph3SnH to give Ph3Sn. ... 

Diaroyl peroxides and diacyl peroxides without a-branches are significantly more thermally stable than those with mono- or di-cr-substituents. Tlie primary use of most commercial diacyl peroxides (16. R1 = R2 = alkyl or aryl) is initiation of free-radical reactions. 

Diazo compounds (diazenes) are an important class of compounds typically used as initiators of free-radical reactions. Upon heating, diazenes undergo decomposition as illustrated in Scheme 4.3. The concerted pathway is important for symmetrical diazenes (R = R ), while unsymmetrical diazenes (R f R) decompose via the stepwise pathway, especially when R is more stable than R . 

Diacyl peroxides are another important source of free-radicals and, consequently, are also commonly used as initiators of free-radical reactions. There is a vast amount of data pertaining to the kinetics and mechanism of decomposition of these compounds in conventional solvents there are a number of side reactions, both radical and ionic in nature, that complicate the kinetics of their decomposition. Generally, these compounds decompose by initial 0-0 bond cleavage that generates carboxyl radicals (RC02 ), which subsequently decarboxylate yielding R (Scheme 4.7)... 

The features of initiation of free radical reactions in polymers by dimers of nitrogen dioxide are considered. The conversion of planar dimers into nitrosyl nitrate in the presence of amide groups of macromolecules has been revealed. Nitrosyl nitrate initiates radical reactions in oxidative primary process of electron transfer with formation of intermediate radical cations and nitric oxide. As a result of subsequent reactions, nitrogen-containing radicals are produced. The dimer conversion has been exhibited by estimation of the oxyaminoxyl radical yield in characteristic reaction of p-benzoquinone with nitrogen dioxide on addition of aromatic polyamide and polyvinylpyrrolidone to reacting system. The isomerisation of planar dimers is efficient in their complexes with amide groups, as confirmed by ab initio calculations. 

Manganese has a rich history within the field of organic synthesis (363, 364). For example, the permanganate anion has long been used as an oxidant to produce a variety of products (363). Manganese111 acetate also has been extensive explored over the years for the initiation of free radical reactions that lead to carbon-carbon bond formation. These topics have been reviewed and will not be presented further here (363, 364). Manganese chemistry, however, has made an impact in other areas as well, notably the asymmetric epoxidation of alkenes. 

Initiation step, 149, 153-154, 221, 246 Initiators of free-radical reactions, 220-221, 245-246, 415 16 Insulin, 1070, 1073-1074, 1080 Integration and NMR peak area measurement, 497... 

Nitric oxide is a low-activity free radical and can be used as a counter of radicals in gas and liquid phases. The reactions of alkyl radicals with NO lead to the formation of nitroso compounds, which are spin traps. Thus, the initiation of free-radical reactions in solid polymers in the presence of nitric oxide provides further information on their mechanism. It is well established that at room temperature NO is not able to remove allylic and tertiary hydrogen atoms and add to isolated double bonds [24-26]. There are discrepant opinions on the capability of NO to react with low molecular weight (low molar mass) dienes and polyenes. Some authors believe that NO is able to add to dienes and polyenes, for example, to substituted o-quinonedimethane, phorone and P-carotene, with the formation of free radicals [27-29]. Another way of looking at these reactions lies in the fact that they can be initiated by NO2 impurities [25, 26]. 

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