REACTIVITY OF TITANIUM ISOPROPOXIDE, ZIRCONIUM PROPOXIDE AND NIOBIUM ETHOXIDE IN THE SYSTEM OF 2-METHOXYETHANOL,2,4-PENTANEDIONE AND WATER

Titanium isopropoxide, zirconium propoxide and niobium ethoxide have been studied in reaction with 2-methoxyethanol (moe), acetylacetone (acac) and water. Structural information has been obtained using FTIR and H-1, C-13 FT NMR spectroscopies. The number of interchanged alkoxy groups increased with increasing excess of 2-methoxyethanol and reaction temperature. The exchange reaction between Nb(OEt)(5) and 2-methoxyethanol was the least effective. Reaction with acetylacetone proved to be very efficient, but dilution with an excess of solvent quenched this reaction. A solid phase of Zr(acac)(4) was formed for more than 2 modes of acac added. The appearance of multiplets in NMR spectra due to CH, CO centers of acac ring in Zr monoacetylacetonate indicated non-symmetric bonding of the bidentate acac group and more than one magnetically non-equivalent species. Conversely, a modified Nb(OEt)(4) (acac) precursor proved to be monomeric with a symmetrically bound acac group. During the interchange reaction the symmetry of the Nb(OEt)(x)(Omoe)(4-x) (acac) species was reduced. Alkoxy groups were first hydrolyzed followed by very slow removal of the acac ring. Zirconium and niobium modified precursors, respectively, were the least and the most susceptible to gelation. Addition of strong acid further increased the stability of acetylacetonates against condensation.