Walter Reppe Revival - Identification and Genesis of Copper Acetylides Cu2 C2 as Active Species in Ethynylation Reactions.

More than six decades after proposing copper acetylide, Cu2 C2 , as catalytically active species in ethynylation reactions by Walter Reppe, the explosive species have been experimentally identified and investigated during catalysis in detail now. Taking into account specific safety precautions, unequivocal qualitative characterization was achieved by Raman spectroscopy and X-ray powder diffraction of supported copper catalysts Cu/Bi/SiO2 during and after activation and catalysis in comparison to bulk Cu2 C2 materials. Quantification of Cu2 C2 succeeded by thermal analysis and Raman spectroscopy. Its formation in aqueous suspension is studied starting from copper(II) oxide catalysts including dissolution, reduction and precipitation steps. Copper acetylide formation can be correlated with catalytic performance in the ethynylation of formaldehyde to 1,4-butynediol.