화학공학소재연구정보센터
Journal of Physical Chemistry, Vol.99, No.20, 8190-8195, 1995
Photochemical Generation of Radical-Anions of Photolabile Aryl Ketones
The radical anions of a series of substituted alpha-(aryloxy)acetophenones have been generated by trapping the solvated electron produced by 355-nm laser-induced photoionization of 4,4’-dimethoxystilbene in either acetonitrile or dimethylformamide (DMF). The radical anion of the parent ketone, alpha-phenoxyacetophenone, has lambda(max) at 500 nm and decays with a rate constant 7 x 10(5) s(-1). This rate constant reflects the rate of beta-cleavage to generate phenoxide ion and phenacyl radical. The rate constant for beta-cleavage decreases for ketones with electron donating substituents in the alpha-aryloxy ring. Substituent effects on the aceotphenone ring are in the opposite direction, and many of the 4-substituted (aryloxy)acetophenones have half-lives in excess of 10 mu s that reflect a combination of second order processes and are not limited by beta-cleavage. The generality of the photoionization/electron trapping method for the generation of radical anions of ketones with short-lived excited states that preclude direct excitation is illustrated by its application to other aryl ketones that undergo alpha-cleavage, beta-phenyl quenching, and intramolecular hydrogen abstraction reactions.