Solid-solid catalysis by inorganic solid acids: Pinacol rearrangement over a heteropoly compound consisting of fine particles

Article abstract of DOI:10.1246/bcsj.71.2817

Solid-state pinacol rearrangement of 1,1,2-triphenyl-1,2-ethanediol was performed over various solid acids at room temperature. The reaction was initiated by grinding a mixture of the solid reactant and catalyst for 5 min at room temperature. Heteropoly compounds (Cs_2.5 H_0.5)PW₁₂O₄₀ and H₃PW₁₂O₄₀) and polymer resins (Amberlyst-15 and Nation/SiO₂), all which possess strong acidities, were active, whereas H-ZSM-5, SiO₂-Al₂O₃, and p-toluenesulfonic acid were inactive. Cs_2.5H_0.5PW₁₂O₄₀ showed the highest activity (per unit catalyst weight). The turnover number, which is defined as the number of molecules reacted divided by the number of protons on the surface, exceeded 20 for 9 h, indicating that the solid-solid reaction proceeded catalytically. This activity of Cs_2.5H_0.5PW₁₂O₄₀ was higher than that for the solid-liquid reaction carried out in chloroform at room temperature, demonstrating the superiority of the solid-solid catalysis. Powder X-ray diffraction measurements indicated that [he reactant crystals became nearly amorphous by grinding with Cs_2.5H_0.5PW₁₂O₄₀, while the crystallinity of Cs_2.5H_0.5PW₁₂O₄₀ was unchanged. The microstructure built up from fine particles of Cs_2.5H_.05PW₁₂ O₄₀ would be favorable to intimate contact of the reactant with the catalyst.