Decomposition of azocumene on silica surfaces

Section: Introductionmentioning

confidence: 93%

Surface photochemistry: the photolysis of α-methoxy acetophenones on silica gel

Mayo¹,

Ramnath²

1986

“…Operating conditions for the analysis of products from the photolysis of various substrates were as follows: 1, 5, 6,7: injector, 225°C; column, 170°C (1). 185°C (5,6), and 185°C for 15 min followed by 200°C for 25 min (7); detector, 250°C; 3, 13: injector, 190°C; column, 170°C for 20 min followed by 176°C for 25 min; detector, 250°C. Irradiations were I carried out with a 150 W or 1000 W XBO high pressure xenon lamp 1 in a Photochemical Research Associates lamp housing (with an infrared water filter) or in a Rayonet reactor equipped with either 254.7 or 300 nm lamps.…”

Section: Apparatusmentioning

confidence: 99%

“…More recently, limited translational motion on a silica gel surface has been shown to precede recombination of asinglet radical pair generated i n the photoFries rearrangement (4). Similarly, substantial surface mobility has been observed for radical pairs generated by photolysis of azocumene (5) and diacyl peroxides (6) on silica gel, although decomposition of the latter is reportedly complicated by the intervention of ionic processes. Evidence for restriction of the mobility of adsorbed radicals has been provided by the observation, on silica gel, of previously undetected reaction pathways in the photolysis of benzoin methyl ether (7).…”

mentioning

confidence: 95%

Surface photochemistry: generation of benzyl radical pairs on dry silica gel

Frederick¹,

Johnston²,

Mayo³

et al. 1984

. 62, 403 (1984).Singlet and triplet benzyl radical pairs have been generated on silica gel by photolysis of a benzyl phenylacetate, a dibenzyl ketone, and a dibenzyl sulfone. The extent of geminate radical recombination has been measured and requires that translational motion of radicals occur on the silica gel surface. This motion was affected by the radical pair multiplicity and the photolysis temperature, but was relatively insensitive to the state of hydration of the silica gel and the presence of coadsorbates. The presence of certain rearranged starting materials, which are not formed in solution, amongst the products from photolysis of both dibenzyl ketone and dibenzyl sulfone on silica gel indicates the restrictions on radical movement on the surface on the shorter tirnescale of the benzyl-phenylacetyl and benzyl -benzyl sulfonyl radical pairs.

“…The authors suggested that the synthetic monolayer surface was analogous to a micelle in providing an artificial "reflecting boundary" which led to an enhanced magnetic isotope effect. However, it appeared more likely that the above results were a reflection of the silica gel surface properties rather than the micelle-like properties of the synthetic monolayer surface, since a number of studies have indicated that radical mobility is restricted on Can silica surfaces (12)(13)(14)(15)(16). For example, limited translational motion has been shown to precede recombination of a singlet radical pair generated on silica gel by the photo-Fries rearrangement (12).…”

mentioning

confidence: 99%

Surface photochemistry: ¹³C enrichment by photolysis on silica gel

Johnston¹,

Wong²

1984

The enrichment of the 13C isotope by partial photolysis of dibenzyl ketone on silica gel has been demonstrated. The 13C enrichment is substantial and is parallel to the increase in the probability of geminate radical recombination on a silica surface as compared with that in solution. A substantial 13C enrichment was also observed for the rearranged starting material, 1-phenyl-4′-methylacetophenone. The single-stage isotope separation factors are different for the two ketones although both are isomers derived from the same benzyl–phenylacetyl radical pairs.