The development of mild and efficient processes for the selective oxygenation of organic compounds by molecular oxygen (O2) is key for the synthesis of oxygenates. This paper discloses an atom‐efficient synthesis protocol for the photo‐oxygenation of 9,10‐dihydroanthracene (DHA) by O2 to anthraquinone (AQ), which could achieve quantitative AQ yield (100 %) without any extra catalysts or additives under ambient temperature and pressure. A yield of 86.4 % AQ was obtained even in an air atmosphere. Furthermore, this protocol showed good compatibility for the photo‐oxidation of several other compounds with similar structures to DHA. From a series of control experiments, free‐radical quenching, and electron paramagnetic resonance spin‐trapping results, the photo‐oxygenation of DHA was probably initiated by its photoexcited state DHA*, and the latter could activate O2 to a superoxide anion radical (O2.−) through the transfer of its electron. Subsequently, this photo‐oxidation was gradually dominated by the oxygenated product AQ as an active photocatalyst obtained from the oxidation of DHA by O2.−, and was accelerated with the rapid accumulation of AQ. The present photo‐oxidation protocol is a good example of selective oxygenation based on the photoexcited substrate self‐activated O2, which complies well with green chemistry ideals.
This
paper discloses a simple and productive hybridizing engineering
(HE) strategy for the 3d transition-metal-ion (M
n+ = Fe3+, Fe2+, Co2+, Ni2+)-doped (nBu4N)4W10O32 (M
n+-TBADT) compounds
as highly efficient visible-light catalysts. Ultraviolet visible (UV–vis),
Fourier transform infrared (FT-IR) and photoluminescence (PL) spectra,
and cyclic voltammetry (CV) characterizations indicate that the synthetic
quality, redox capacity, and visible light harvesting efficiency of
TBADT, especially the separation efficiency of its photogenerated
electron–hole pairs, are regulated by the metal ion dopants
and gradually improved with a change of the dopant from Fe3+, Fe2+, and Co2+ to Ni2+, along
with a continuous and significant enhancement of its photocatalytic
efficiency in the visible-light-triggered selective oxidation of ethylbenzene
with dioxygens in acetonitrile. The best 0.5 mol % Ni2+-doped TBADT can achieve a ca. 55% conversion under optimal reaction
conditions and also exhibits much higher photocatalytic activity for
the photo-oxidation of toluene, cyclohexane, and benzyl alcohol compared
to pure TBADT. This HE strategy showcases great potential in improving
the photocatalysis performance of TBADT.
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