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 b een studied in reaction with 2-methoxyethanol (moe), acetylacetone (ac ac) and water. Structural information has been obtained using FTIR and H-1, C-13 FT NMR spectroscopies. The number of interchanged alkoxy gr oups increased with increasing excess of 2-methoxyethanol and reaction temperature. The exchange reaction between Nb(OEt)(5) and 2-methoxyet hanol was the least effective. Reaction with acetylacetone proved to b e 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 mod es of acac added. The appearance of multiplets in NMR spectra due to C H, CO centers of acac ring in Zr monoacetylacetonate indicated non-sym metric bonding of the bidentate acac group and more than one magnetica lly non-equivalent species. Conversely, a modified Nb(OEt)(4) (acac) p recursor 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 f ollowed by very slow removal of the acac ring. Zirconium and niobium m odified precursors, respectively, were the least and the most suscepti ble to gelation. Addition of strong acid further increased the stabili ty of acetylacetonates against condensation.