16827-94-4

Upstream product

• 134-81-6 benzil 

Relevant academic research and scientific papers

Time-Resolved EPR Study on the Photochemical Reactions of Benzil

A time-resolved EPR (TREPR) study on the photochemical reactions of benzil in 2-propanol and benzene-triethylamine (TEA) mixed solvents is reported.The emissive signals observed in 2-propanol are assigned to the benzoyl and benzil ketyl radicals, and the absorptive one observed in benzene-TEA is assigned to the benzil anion radical.The reactions are considered to occur from higher excited triplet (Tn) states through two-photon processes in 2-propanol but from the lowest excited triplet state through a one-photon process in benzene-TEA.TREPR studies are supplemented by optical studies including measurements of transient absorptions, phosphorescence quenching, and fluorescence quenching, whose results support the conclusion drawn from the EPR results.Possible polarization mechanisms to produce emissive signals are considered in detail.It is shown that the direct T1 -> Tn excitation does not produce the inversion of the polarization regardless of the signs of the zero-field splitting of the T1 and Tn states.It is then concluded that the emissive signals are due to the reaction from Tn produced via the Sn -> Tn intersystem crossing process.It is also found that the rise of the chemically induced dynamic electron polarization signal of the ketyl radical in 2-propanol consists of fast and slow components.The time profile of the slow rise component strongly depends on the temperature, the concentration of benzil, the excitation laser power, and the oxygen addition.From the analysis of these dependences it is suggested that the free-pair radical-pair mechanism can account for the main features of the slow polarization.

Diffusion of electrically neutral radicals and anion radicals created by photochemical reactions

Diffusion processes of the intermediate radicals created by the photochemical reactions of ketones in alcoholic solvents are investigated by using the transient grating (TG) method. The electrically neutral radicals and the anion radicals of acetophenone, benzaldehyde, xanthone, benzophenone and benzil were created selectively by controlling the concentration of sodium hydroxide (NaOH) in alcoholic solvents. The translational diffusion constants (D) of the anion radicals, the neutral radicals, and the parent stable molecules can be successfully measured under the same conditions by this method. It is found that both the neutral and anion radicals diffuse slower than the parent molecules. Values of D of the anion radicals, the neutral radicals and the parent molecules are compared in detail in wide ranges of solvent viscosities, solute sizes and temperatures. Under any conditions, D values of the charged radicals are similar to those of the neutral radicals. A possible origin of such a similarity is discussed in term of the intermolecular charge polarizabilities of the radicals.

REACTIONS OF AROMATIC BIS-1,2-DIKETONES. V. REACTION OF BIS-1,2-DIKETONES WITH ALKALI. FORMATION OF SEMIDIONE RADICALS

The reaction of bis-1,2-diketones PhCOCOArCOCOPh with alkali (a benzilic rearrangement) gave dihydroxy dicarboxylic acids.It was found that 1,4-di(2-phenyl-1,2-dioxoethyl)benzene has anomalously high reactivity compared with benzil and other bis-1,2-diketones.It is characterized by successive reaction at each of the 1,2-dicarbonyl reaction centers; the products from this reaction were isolated and identified.The reactions are accompanied by the formation of radical particles, which were assigned by analysis of the hfs to radical-anions of the semidione type.