KINETICS AND MECHANISM OF THE OXIDATION OF HEXAAQUAVANADIUM(II) IONS BY ALKYL RADICALS

The title reaction produces vanadium(III) ions and the corresponding hydrocarbons. The kinetics were studied by laser flash photolysis with the use of the paraquat radical ion as a kinetic probe. Results are reported for 11 radicals, consisting of primary alkyl radicals (substituted and unsubstituted) and secondary and aralkyl radicals. The rate constants are remarkably insensitive to the nature of the radical, lying in the range (1-6) x 10(5) L mol-1 s-1. The solvent kinetic isotope effects comparing V(H2O6(2+) in H2O with V(D2O)6(2+) in D2O was determined for .CH3,k(H)/k(D) = 3.0. Of several mechanisms considered, we prefer one in which the radical attacks at a trigonal face of V(H2O)6(2+). This leads to electron transfer and a transient (H2O)6VR2+ intermediates, the protonolysis of which yields the observed alkane.