Carbon catalyzed organic reactions: racemization of 1,1′-binaphthyl by carbon surfaces

Abstract

Rotation around the bond joining the two naphthalene rings (i.e., racemization) in 1,1′-binaphthyl is very effectively catalyzed by carbon blacks and decolorizing carbons. In acetone at 20 °C where a small fraction of binaphthyl is reversibly absorbed, the activity of various carbons increases with surface area (relative catalytic rates are in the order Acetylene Black < Spheron 6 < Norit < Carbolac 1). The racemization is inhibited by structurally analogous compounds (naphthalene, anthracene) and poisoned by small concentrations (ca. 10−5 M) of larger polynuclear aromatics (pyrene, perylene). The barrier to inversion is lowered to ΔH≠ = 16 kcal/mol in acetone by Spheron 6 as catalyst (ΔH≠ = 22 kcal/mol for the uncatalyzed reaction). Although reaction via a relatively small number of specific active sites on the catalyst has not been eliminated, the kinetic data and inhibition effects also correlate with catalysis by more general adsorption of binaphthyl on the planar surfaces of the graphite-like lattice of active carbons.