The influence of β-diketones on the induction times for hydrolysis of zirconium(IV) alkoxides

Abstract

The influence of low ligand/Zr mole ratios (ρ=0-0.1) of acetylacetone on the hydrolysis of Zr(OPr ⁿ ) ₄ has been examined by investigating its effect on the induction time (t _i ) before precipitation commences in the system. A remarkable feature of the data is the large increase in the induction time (reduction in hydrolysis/condensation rate) caused by addition of acetylacetone. This occurs even though only a maximum of one in eighty Zr-OR bonds have reacted with ligand and are no longer available for hydrolysis or further condensation. The effects on t _i of five other β-diketones having varying steric properties (trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, dibenzoylmethane and dipivaloylmethane) are compared with that of acetylacetone, under similar concentration conditions, with ρ=0.1. Each shows a greater effect than acetylacetone, the largest change being caused by dibenzoylmethane which, under the conditions used, increases the induction time by a factor of 26 relative to acetylacetone. A mechanism rationalising the origin of the effect is discussed.