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Involvement of adsorption effects in the TiO 2 ‐sensitized photooxidation rate of benzylic derivatives in CH 3 CN
Author(s) -
Giacco Tiziana Del,
Rol Cesare,
Sebastiani Giovanni V.
Publication year - 2003
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.583
Subject(s) - chemistry , adsorption , steric effects , moiety , ring (chemistry) , medicinal chemistry , photochemistry , aromaticity , polar effect , organic chemistry , molecule
Competitive kinetic experiments in the TiO 2 ‐sensitized photooxidation of some series of differently ring‐substituted benzylic derivatives (ArCHROR′) in aerated and/or deaerated CH 3 CN and in the presence of Ag 2 SO 4 were carried out. From log k rel vs E p plots it was hypothesized that a changeover of the electron abstraction site occurs on going from electron‐donating to electron‐withdrawing groups on the ring, from the aromatic moiety to the OCH 3 group of benzyl methyl ethers, probably owing to the preferential adsorption of this group on TiO 2 with respect to the aromatic ring. This phenomenon is not observed with benzyltrimethylsilanes because the orbital resulting from the overlap between the C— Si bond and the aromatic π system is the only adsorption site. The steric hindrance of an α‐methyl group (in benzylic alcohols) or a tert ‐butyl group (in benzyl tert ‐butyl ethers) reduces the degree of adsorption but does not influence the shape of the plot because OR′ should still be the preferential adsorption group. This also provides useful information about the surface structure of TiO 2 suspended in CH 3 CN. Copyright © 2003 John Wiley & Sons, Ltd.