Heterogeneous photocatayltic deperoxidation with UV and visible light

Abstract

A physical-organic study is described on the photodecomposition of dicumyl peroxide co-adsorbed with the sensitizers 4,4′-dimethylbenzil or chlorin e 6 on fumed (nonporous) silica. Dicumyl peroxide was decomposed by the heterogeneous photosensitization and monitored by the desorption of products acetophenone, 2-phenylpropan-2-ol, and α-methylstyrene using proton nuclear magnetic resonance and gas chromatography-mass spectrometry. Dicumyl peroxide and sensitizer were co-adsorbed on silica in 1:4 up to 200:1 ratios, with high peroxide destabilization occurring in ratios of about 10:1. This increased photodecomposition corresponded to sensitizer-peroxide distances of 6 to 9 Å. A Dexter triplet energy transfer mechanism is proposed that explains the short sensitizer and peroxide separation distances for higher peroxide O-O bond homolysis efficiencies on silica. This biphasic (gas/ solid) system can thus serve both to destabilize and stabilize a peroxide, which may be of practical use for the delivery of alkoxy radicals for bacterial disinfection.

A fluorinated phosphite traps alkoxy radicals photogenerated at the air/solid interface of a nanoparticle

“…Despite relatively few reports, [ 49–51 ] the sensitized homolysis of an organic peroxide is used here to provide a facile source of alkoxy radicals. In our case, cumyloxy and ethoxy radicals are generated and react with ( p ‐F‐C 6 H 4 ‐O) 3 P and to a lesser extent ( p ‐Cl‐C 6 H 4 ‐O) 3 P suggesting that these alkoxy radicals do not efficiently acquire H‐atoms from surface SiOH groups or surface‐adsorbed water.…”

“…Compounds were adsorbed to native and fluorinated silica in a manner previously reported. [ 51,57 ] In subdued room light, 4,4′‐dimethylbenzil 1 (0.01 mmol), cumylethyl peroxide 2 (0.1 mmol), and triaryl phosphites 3a ‐ 3d (pairs of them each 0.1 mmol) were dissolved in 5 mL dichloromethane and stirred with 1.0 g of native silica or fluorinated silica particles for 1 h in a 25 mL round bottom flask. The dichloromethane was evaporated from the particles with a stream of N 2 gas and then by applying a vacuum.…”

Dark-Binding Process Relevant to Preventing Photosensitized Oxidation: Conformation-Dependent Light and Dark Mechanisms by a Dual-Functioning Diketone

“…The use of phosphite as alkoxy radical traps is reported in the literature. 17,18 Table 1 shows that the dione 1 sensitized dicumyl peroxide 3 decomposition as a function of the sensitizer to peroxide ratios. The ratios correspond to concentrations of 100 mM 1 and 0.5 to 100 mM 3 .…”

“…In addition to phosphite chelation to dione (path B), we show that phosphite can be used to indirectly monitor the photodecomposition of dicumyl peroxide by trapping the resultant cumyloxy radicals (light path A) (Table ). The use of phosphite as alkoxy radical traps is reported in the literature. , Table shows that the dione 1 sensitized dicumyl peroxide 3 decomposition as a function of the sensitizer to peroxide ratios. The ratios correspond to concentrations of 100 mM 1 and 0.5 to 100 mM 3 .…”

“…The preparation of 4,4′-dimethylbenzil 1 and dicumyl peroxide 3 coadsorbed onto fumed silica has been described previously. 17 Briefly, fumed silica was immersed in a dichloromethane solution of solvated 1 and 3 . After stirring, the dichloromethane was evaporated with a stream of N 2 gas, leaving reagents adsorbed on the silica.…”