Diphenylpicrylhydrazyl preparation

Diphenylpicrylhydrazyl, which is prepared from MA -diphenyl-A -(2,4,6-trinitrophenyl)hydrazine by oxidation with lead dioxide [982], is used for the dehydrogenation of 1,4-dihydronaphthalene to naphthalene and of hydrazobenzene to azobenzene [983]. Simpler and cheaper compounds are, however, available for such purposes (equation 21). 

Dehydrooenation 1,4-Benzoquinone. Chloranil. o-Chloranil. Copper chromite. Copper-Chromium oxide. Diethyl azodicarboxylate. 2,3-Dichloro-3,6-dicyano-I,4-benzoquinone. DIphenylpIcrylhydrazyl, N-Lithioethylenediamlne. Mercuric acetate. Nickel catalyst. Oleic add, Palladium. Perbenmic acid. Potassium l-butoxide. Pyrldinium hydrobromide per-bramlda, Balinlum. Selenium dioxide. Sodium borohydride. Sulfdr (sm 1,2-Naphthalic anhydridli preparation). Tetracyanoethylene. Thionyl chloride. Trityl perchlorate. 

Products were characterized by a number of different spectroscopic methods. Infrared spectra were recorded on a Perkin-Hmer Model 298 or 580 B spectrophotometer. Samples were prepared as 1% dispersions in Csl or Nujol mulls. nmr spectra were recorded on a Varian Model FT-80 spectrometer solutions of 5 mg of complex in 0.6 mL CDCI3 were used,with tetramethylsilane as internal reference. Electronic absoiption spectra were recorded on a Perkin-Elmer Model 330 spectrometer, using 5 x lO mol/L dichloromethane solutions. Raman spectra were recorded on samples cooled by liquid nitrogen, on a DILOR Model RTI 30 spectrometer, using an excitation wavelength of 514.5 nm. ESR spectra of the powders in MgS04 were recorded at X-band frequency with a Varian Model E-4 spectrometer. Signal g values and intensities were calibrated with a standard diphenylpicrylhydrazyl (DPPH) sample (g = 2.0036). 

When steric effects are combined with stabilizing effects such as delocalization, radicals that are very "stable" can be prepared. For example, both galvinoxyl and diphenylpicrylhydrazyl (DPPH) are commercially available free radicals that can be handled with no special precautions (see margin). 

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