RATE CONSTANTS AND ARRHENIUS PARAMETERS FOR THE REACTION OF ACYL RADICALS WITH BU(3)SNH AND (ME(3)SI)(3)SIH

The kinetics of hydrogen abstraction from Bu(3)SnH and (Me(3)Si)(3)SiH by a variety of acyl radicals have been studied in nonpolar solvents over a range of temperatures by using competing decarbonylation reacti ons. The relative preexponential factors are essentially independent o f the nature of the acyl radical and of the hydride; i.e. log(A(d)/A(M H)) congruent to 4.8. On the other hand, the relative activation energ ies, i.e. E(d) - E(MH), decrease by ca. 2 kcal mol(-1) on going from p rimary to secondary and also on going from secondary to tertiary subst ituents at the carbonyl moiety for a particular hydride. As one goes f rom Bu(3)SnH to (Me(3)Si)(3)SiH for a particular acyl radical, the E(d ) - E(MH) also decreases by ca. 2 kcal mol(-1). Combining our relative kinetic data with the gas-phase Arrhenius parameters for the propanoy l radical decarbonylation allows for the evaluation of the absolute Ar rhenius expressions for the reactions of acyl radicals with Bu(3)SnH a nd (Me(3)Si)(3)SiH and for the decarbonylation of secondary and tertia ry acyl radicals. Rate constants at 80 degrees C for the reactions of (Me(3)Si)(3)Si-. and Bu3Sn(.) radicals with acyl derivatives have also been estimated.