Reaction Mechanism for the Hydrolysis of Titanium Alkoxide

Abstract

Metal alkoxides have strong reacitivities due to the difference of polarizabilities between metal and alkoxy groups. Hence, many kinds of metal alkoxides can be hydrolyzed with ease and transformed to metal oxide powder via a condensation-polymerization reaction of the hydrolyzed species. The hydrolysis reaction mechanisms of the metal alkoxides depend on the electron affinities, sizes and charges of metal ions and alkoxy groups.1-3 In the case of alkoxides that have the same metal ions, the sizes and numbers of alkoxy groups play an important role in the hydrolysis reaction. Examples are found in silicon alkoxide where the reaction rates of hydrolysis decrease with increasing size of the alkoxy groups through steric effects.4,5 Reaction rates or mechanisms of metal alkoxides can be also changed by the kinds of metal ions. Particularly, the transition metal ions, which have different oxidation states, have different electron affinities, sizes and coordination numbers, so careful investigation of the hydrolysis of transition metal alkoxides is required.2 The kinetic studies on the hydrolysis reactions of metal alkoxides, in general, have been carried out by spectroscopic methods6-8 such as NMR, Raman, Infrared, UV, etc. Extensive kinetic data for the silicon alkoxides9,10 have been obtained by the above methods, but very few kinetic results for the transition metal alkoxides have been reported. In this study, the hydrolysis reaction rate and mechanism of the titanium tetra ethoxide (Ti(OC2H5)4) were investigated by the use of the UV spectroscopic method and the results were compared with those of the other titanium alkoxides reported in our previous works.