THE PHOTOINDUCED ALPHA-CLEAVAGE OF ALPHA-BROMOMETHYLBENZOIN - THE GENERATION AND BEHAVIOR OF BETA-BROMOKETYL RADICALS

The photodecomposition of alpha-bromomethylbenzoin was studied by elec tron spin resonance and by radical trapping using 1-dodecanethiol and a stable nitroxyl (TMPO) respectively. Photoinduced alpha-cleavage int o benzoyl and alpha-hydroxy-alpha-bromomethylbenzyl (beta-bromoketyl) radicals is observed. The beta-bromoketyl radicals are found to underg o an extremely fast elimination of hydrogen bromide to give benzoylmet hyl radicals. These beta-bromoketyl radicals are also generated by hyd rogen-abstraction from 2-bromo-1-phenyl-ethanol using triplet excited benzophenone. The only products observed are 'unchanged' benzophenone, acetophenone and hydrogen bromide. The same result is obtained on irr adiation of 2-bromoacetophenone in the presence of benzhydrol. Possibl e mechanisms and implications are discussed. (C) 1997 Published by Els evier Science S.A.