4-Oxo-TEMPO or TEMPONE is a remarkably stable free radical, related to the more well-known compounds 4-hydroxy-TEMPO and TEMPO.
Synthesis 4-Oxo-TEMPO was first prepared by Lebedev and co-workers in 1961, via the condensation of phorone with ammonia in alkaline aqueous solution at 100 °C, producing a triacetonamine-containing mixture, followed immediately by oxidation with hydrogen peroxide and sodium tungstate in the presence of tetrasodium EDTA at 50 °C.
It is also possible to use the same reagents to directly oxidize triacetonamine at room temperature, which yields a much easier-to-purify product.
Properties It is a yellowish-orange solid; it is storable for several months in solid form at temperatures of around -20 °C.
It dissolves in water and other polar solvents to form yellow solutions, and in ether, ethanol, and benzene to form ruby-red solutions.
It forms a series of adducts with n-alkanes from heptane onwards, each of which has a well-defined melting point, unlike the corresponding adducts formed by urea with n-alkanes.
Their formation is perhaps attributable to the twist-boat conformation adopted by 4-oxo-TEMPO, which differs from related aminoxyls, for example, 4-hydroxy-TEMPO, which adopts a boat confirmation.
Applications 4-Oxo-TEMPO has been used to investigate the generation of singlet oxygen by photoexcited titanium dioxide in ethanol by ESR spectroscopy. It can be used as a catalyst in various reactions. It can also be used as a polarizing agent in dynamic nuclear polarization NMR spectroscopy.
It may be used as a free radical scavenger.
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