KHARASCH AND METALLOPORPHYRIN CATALYSIS IN THE FUNCTIONALIZATION OF ALKANES, ALKENES, AND ALKYLBENZENES BY T-BUOOH - FREE-RADICAL MECHANISMS, SOLVENT EFFECT, AND RELATIONSHIP WITH THE GIF REACTION

New results for the oxidation of alkanes, alkenes, and alkylbenzenes b y t-BuOOH according to the Kharasch reaction and Mn(III)- and Fe(III)- porphyrin catalysis are reported. Chemical and kinetic evidence show t he role of t-BuO(.) and t-BuOO(.) radicals in these oxidations and the strict relationship with the Gif reaction, for which recently a free- radical mechanism has been emphasized in contrast with the Barton inte rpretation. A key step appears to be the hydrogen abstraction from t-B uOOH by t-BuO(.), very fast in nonbasic solvents, but inhibited by sol vents which form hydrogen bonds with t-BuOOH. As a consequence, the ge nerally accepted Kochi mechanism of the Kharasch reaction must be modi fied, and the similar mechanistic features of the three types of catal ysis (Kharasch, metalloporphyrins, and Gif) are discussed.