Creation of a monomeric vanadate species in an apatite framework as an active heterogeneous base catalyst for Michael reactions in water

Vanadium-apatite containing the VO43− species was synthesized. Several characterization techniques such as XRD, TEM, XPS, ESR, UV–vis DRS, V K-edge XAFS, 51V MAS NMR, Raman spectroscopy, and CO2 TPD revealed that the vanadium-apatite was Ca9(VO4)5(HVO4)(OH), abbreviated to VAP, covered with calcium oxide. This surface-coated calcium oxide phase could be removed by washing with water and then, the monomeric V-OH species having the strong Brønsted basicity were generated on the surface of VAP. The strong basicity of the solid VAP-catalyzed efficient Michael reaction in water solvent. Furthermore, VAP was found to be applicable to the direct synthesis of pyrazolinone derivatives using aryl hydrazines and diethyl ethoxymethylenemalonate.