Photochemical Studies of the Esters of Aroylphosphonic Acids
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概要
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The photochemical behavior of several dialkyl benzoylphosphonates and <I>para</I>-substituted benzoylphosphonates in various solvents has been studied using product isolation, ultravioletspectral change, the electron spin resonance (ESR) technique, and quantum yield measurements. Upon irradiation to a degassed solution of these benzoylphosphonates through a Pyrex filter, the photo-pinacolization reaction was observed, except in the case of diethyl benzoylphosphonate; it was effectively quenched by 1,3-pentadiene or oxygen. On the other hand, the ESR spectra of photo-irradiated aroylphosphonates at 77°K have a large anisotropic doublet of 53–128 gauss separation; this separation is thought to be due to the interaction between an unpaired electron and the phosphorus nucleus. The structure of these radicals is also discussed. From these observations, it can be considered that the photochemical reaction proceeds <I>via</I> the ketyl radical formed by the hydrogen abstraction of the lowest excited triplet state of these aroylphosphonates. Irradiation to the diethyl benzoylphosphonate solutions in various solvents gave, not the pinacolized product, but 2,4,6-triphenyl-2,4,6-tris[diethylphosphoryl]-1,3,5-trioxane almost quantitatively. The quantum yields (Φ) of the disappearance of several <I>para</I>-substituted derivatives are highly sensitive to the electron-inductive abilities of the substituents; that is, Φ drops from 2.10 in the <I>p</I>-methoxybenzoylphosphonate derivative to 1.79 in the <I>p</I>-chloro derivative at room temperature. Such a substituent effect can be considered to result in the difference in the conformation between the carbonyl and phosphoryl groups. On the basis of these studies, the mechanism of the photochemical reaction of aroylphosphonates is described and discussed.
- 公益社団法人 日本化学会の論文
著者
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SAKURAI Hiroshi
The Institute of Scientific and Industrial Research, Osaka University
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Terauchi Ken-ichi
The Institute of Scientific and Industrial Research, Osaka University
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