RATE CONSTANTS FOR REACTIONS OF PERHALOALKYLPEROXYL RADICALS WITH ALKENES

Trichloro- and tribromomethylperoxyl radicals were produced by radioly tic reduction of CCl4 and CBr4 in various aerated solvents. Rate const ants for the reactions of these radicals with unsaturated organic comp ounds were determined in methanol solutions by competition kinetics, u sing mainly chlorpromazine as a reference. The rate constants were in the range k = 104-107 L mol-1 s-1, and a good correlation was obtained between log k and the Taft substituent constants sigma. Steric effec ts were also noticeable in some cases. The reactivities of the radical s were in the order CBr3O2. < CCl3O2. < C4F9O2., which is in contrast with the order observed in electron-transfer reactions. The rate const ants for reaction of CCl3O2. with 2,3-dimethyl-2-butene (DMB) and cycl ohexene (CH) were studied in 12 solvents. In all cases DMB is consider ably more reactive than CH, indicating that at least in the case of DM B the reaction is predominantly via addition. The rate constant for ad dition of CCl3O2. to DMB varies by a factor of 7 in the different solv ents. No correlation was found between these rate constants and thermo dynamic or polarity parameters of the solvents, although viscosity app ears to have an effect.