Study of Tetraethyllead Oxidation Pathways Using Density Functional Theory

The potential energy profiles in oxidizing tetraethyllead Pb(C 2H5)4 are calculated at the B3LYP levels of density functional theory (DFT) to elucidate its reaction mechanism. There are a number of possible pathways to oxidize the organic lead radicals after the first step of cleaving one ethyl group from Pb(C2H5) 4. Several pathways are calculated from the viewpoint of two basic types of reaction; the hydrogen scrambling from an ethyl group to an oxygen, and the oxygen insertion into a lead-carbon bond. A preference is predicted for those pathways involving the hydrogen scrambling reactions owing to their relatively lower reaction barriers. Among various reaction paths, the most important pathway is as follows: cleaving one ethyl from Pb(C2H 5)4, binding with O2, undertaking two consecutive β-hydrogen migrations from the rest of the ethyls to the oxygens, and yielding one lead dihydroxide, two ethylenes, and one ethyl radical. The pathway is facile since the radical combines with O2 right after it forms and the following energy barriers are less than 25 kcal/mol. The major barrier is the first step of breaking Pb-C2H 5, 54 kcal/mol. Other pathways involving oxygen insertion reactions are also calculated and compared, they are found to be less important energetically.