The Mg(0001) surface in Grignard reagent formation.

摘要

The interaction of MgBr{dollar}sb2{dollar} and 1,2-dibromoethane with polycrystalline and single crystal Mg surfaces has been studied to simulate the activation of magnesium during the Grignard reagent formation. Experimental measurements were based upon low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS).; The study of the composition commercial (as-received) Mg metal indicates a surface covered by a film constituted predominantly by magnesium hydroxide and a small quantity of magnesium carbonate. These results lead to the study of the interaction of O{dollar}rmsb2, Hsb2Osb{lcub}(g){rcub}{dollar}, and CO{dollar}sb2{dollar} with Mg(0001) single-crystal surfaces. When Mg(0001) interacted with O{dollar}sb2{dollar} (up to 100 L), an ordered MgO overlayer was formed. The interaction of Mg(0001) with water vapor yielded a disordered oxide film that contained relatively large amounts of hydroxide species. A disordered oxide film consisting primarily of carbonates was formed when Mg(0001) was exposed to CO{dollar}sb2{dollar}. Reactions of Mg(0001)-MgO(100), as received and acid-etched Mg turnings with MgBr{dollar}sb2{dollar} and 1,2-dibromoethane (promoters) indicate that, the activation of the Mg surface during the Grignard reagent formation is achieved by the removal of the oxide film. Based upon these results, a flake-off model was proposed for the activation mechanism.