Oxidative dimerization, arylamines

Oxidative dimerization of arylamines. Azoxybenzenes are formed when the amines and hydrogen peroxide are heated under reflux in acetone in the presence of TS-1 zeolite. 

In 1994, Paul, Patt, and Hartwig showed that the Pd(0) catalyst in Kosugi s process was Pd[P(o-C6H4Me)312 (3), which underwent oxidative addition of aryl halides to give dimeric aryl halide complexes (4) [91]. These aryl halide complexes reacted directly with tin amides to form arylamine products (Eq. (3)). Thus, this chemistry could formally be viewed as being roughly parallel to Stille coupling. 

The one-electron oxidation of a secondary amine results in the formation of a secondary aminium ion which on deprotonation gives an aminyl radical (Scheme 1). The nature of the final products derived from these intermediates dqiends very much on the structure of the substrate and the reaction conditions. If the amine has a hydrogen atom on the a-carbon atom the major products usually result from deprotonation at this a-position. With aromatic secondary amines, products can result from coupling of the delocalized radicals at a ring carbon atom. The formal dimerization of aminyl radicals shown in Scheme 21 is therefore not often a useful method of preparation of hydrazines. Nickel peroxide has been used to oxidize diphenylamine to tetraphenylhydrazine in moderate yield, and other secondary arylamines also give... 

Oxidation of arylamines, nitroso compounds, and azobenzenes. Several 2,6-di-haloanllines have been oxidized successfully to the nitroso compounds with 30% hydrogen peroxide in acetic acid at room temperature. When a solution of the reactants is let stand for a time, crystals of the (dimeric) nitroso compound begin to... 

Secondary arylamines also form hydroxylamines initially, but these invariably oxidise further to the radicals Ar2N and ArgN (O) The diphenylimino radical (At2N) also results from oxidation by non-peroxidic reagents and it exists in equilibrium with its dimer, tetraphenylhydrazine (equation 80) Diaryl nitroxide radicals... 

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