Redox catalysts hydroxylamines

IV. HYDROXYLAMINES AND HYDROXAMIC ACIDS AS REDOX CATALYSTS A. Hydroxylamines... 

TEMPO and other organic nitroxyls have been used as catalysts in combination with numerous stoichiometric oxidants, such as sodium hypochlorite [24], PhI(OAc)2 [25], and sodium chlorite [26]. A number of recent studies have shown that NO -based redox cocatalysts enable these reactions to be conducted with O2 as the terminal oxidant [27]. The general catalytic cycle for these aerobic nitroxyl/NO -catalyzed alcohol oxidation reactions is depicted in Scheme 15.6a. A variation of this approach features halides as additives, in which the X2/HX redox couple is believed to mediate the NO2/NO and oxoammonium/hydroxylamine redox couples (Scheme 15.6b). 

Fez and coworkers developed amination of benzene and toluene with hydroxylamine in the presence of transition metal redox catalyst [86]. They found that Na4PWii039Fe(H20) shows its best performance in 85 % acetic acid. Pd/MoOa/ Si02 is an active heterogeneous catalyst in sulfuric acid/acetic acid (1 2). The protonated amino radical cation generated by reduction of NH2OH by transition metal redox species is considered as key species in this amination chemistry. 

Kuznetsova Nl, Kuznetsova LI, Detusheva LG, Likholobov VA, Pez GP, Cheng H (2000) Amination of benzene and toluene with hydroxylamine in the presence of tranistion metal redox catalysts. J Mol Catal A Chem 161 1-9... 

A variety of different metal complexes have been screened as catalysts for allylic amination using phenyl hydroxylamine 108 as the nitrogen fragment donor, and it was found that iron-complexes have better redox capacity compared to molybdenum [64]. With the iron compounds, higher yields and a lower amount of hydroxylamine-derived byproducts are obtained. These byproducts constitute one of the problems in this type of allylic amination reactions in general, as their formation is difficult to suppress. The allylic amination reaction of a-methyl styrene 112 with 108 can, e.g., be catalyzed by the molybdenum dioxo complex 107, iron phthalocyanine 114, or by the combination of the iron chlorides 115 [64,65]. It appears from the results in... 

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