Diphenylnitroxide

A similar case is the catalysis of Gomberg-Bachmann arylations by A,A-diphenyl-hydroxylamine, which was discovered by Cooper and Perkins (1969). As Scheme 8-46 shows, the covalent adduct cation 8.62 first loses a proton. This facilitates the homolytic dissociation, as a stable radical, A/,A-diphenylnitroxide (8.63), is formed. This... 

A- + RH —> AH + R 4-MeO-phenoxy + 9,10-dihydro-anthracene Phenoxy + Tetralin terf-Bu3-phenoxy + ethylbenzene (MeO)2-diphenylnitroxide + ethyl-... 

Because of the slow recombination of RO j there is a nearly constant RO concentration ( 6xl0 mole.l ). The rate constant of the reaction with Inj with R0 was estimated to be equal to the 6x10 l.mole s in the temperature range of 283-303 K in cyclohexane. The decomposition of Inin in the presence of cumylhydro-peroxide yielded diphenylamine, quinone imine, cumyl alcohol and acetophenone (8). Diphenylnitroxide was detected by EPR techniques. The comparison of the concentrations of decomposed ROOH and InH and ROH formed shows that ROOH is not the only donor of hydrogen atoms but a part of InH and ROH was formed in the reactions of In and RO" with labile intermediate products. The most probable products are labile quinone imines R0 C,H, C H anC (C H,.) NC H NC H,. w c 1 react with In and Ro forming InH and ROH. Quinone imine apparently is... 

Conflicting accounts of the dye-sensitized photo-oxidation of diphenylamine in alcohols have been published, with one group of workers152 reporting diphenylnitroxide as the product, and another group158 repeating their claim (see Vol. 6, p. 545) that iV-phenyl-p-benzoquinonimine is formed. The photo-oxidation of 2,4,6-triphenylpyridine TV-phenylimine may involve ozone production.154... 

It was reasoned that perchlorodiphenyl nitroxide radical (PDNO-) might be much more stable than diphenylnitroxide since, not only would the p-position be blocked, but the NO group would be protected by four flanking o-chlorines, much like t-butyl mesityl nitroxide radical (Forrester and Hepburn, 1970) and PDM- reviewed here. 

Diphenylamine (pKa = 23) can be used to determine the amount of strong base sites by measuring the amount of diphenylnitroxide radicals by ESR which are formed from diphenylamine in the presence of oxygen by an action of basic sites. 

Fig. 3.21 Amounts of diphenylnitroxide radicals (9) and COj molecules irreversibly adsorbed at 373 K (O) on Z1O2 pretreated at various temperatures.

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