Interaction of carbonyl triplets with α-phenylethyl hydroperoxide in CCl 4

Abstract

Photochemical reactions of the triplets of benzophenone, 9,10-anthraquinone, anthrone, 1,4-naphthoquinone 1,2-benzanthracene with α-phenylethyl hydroperoxide in CCl 4 at 303 K have been investigated. Benzene was used as spin trap for ȮH radicals, producing phenol. The quantum yields (φ) of the formation of products have been measured. By exciting the carbonyl compounds (but not 1,2-benzanthracene) to their first triplet states at 366 nm in both the presence and the absence of C 6H 6 only methylphenyl carbinol (HROH) and acetophenone (RO) were formed as products with Φ HROH/ Φ RO=0.95±0.05 at [HROOH] 0=0.01–0.1 M. With excited 1,2-benzanthracene Φ HROH/ Φ ROH was 1.32±0.08 in CCl 4 and ca. 2.9 in C 6H 6. No phenol was detected in CCl 4. It can be assumed that the decomposition proceeds via sensitized O-O cleavage in the presence of 1,2-benzanthracene and via hydrogen abstraction in the presence of the other sensitizers. For systems in which hydrogen abstraction prevails, the ratios of the rate constants of physical quenching by HROOH to the rate constants of chemical reactions vary between 0.3 and 2.4 depending on the structure of the carbonyl compound.