Ebulliometric studies have been made 011 the hydrolysis of some zirconium alkoxides, Zr(OR)4 where R = E t , Prn, Bu" and Bun. The variation of the degree of polymerization of the zirconium oxide alkoxides so produced was determined as a function of the degree of hydrolysis. The results are interpreted in terms of structural models based on octahedrally 6-co-ordinated zirconium.
ABSTRXCTThe hydrolysis of zirconium a1l;oxides with secondary or tertiary allioxide groups Zr(OR)c, where I< = Pri, Bun, Bul, and XIII~, has been studied. The relatively low polymers formed by the ~iietal oxide alkoxides have been interpreted on the basis of s t r~~c t~~r a l models involving octahedrally 6-co-ordinated zirconium. IXTRODUCTIONPrevious work (1) on the hydrolysis of some primary alltoxides of zirconium showed that polymeric oxide alltoxides [Zr0z(OR)4-2z]n were formed. A satisfactory ii~terpretation of the number-average degree of polymerization as a function of degree of hydrolysis was developed on the basis of three structural models involving 6-co-ordinated zirconium and identical with those originally proposed for titanium (2, 3). Model I was based on the unsolvated trimeric alltoxide Zr3(OR)12 and gave rise to a series of co-ordination -condensation polymers having the general formula Zr3cz+1)04z(OR)4(z+3). The requirement of relatively low polynlers by this structural inodel was a consequence of the highly compact structures which are made possible by the sharing of common faces of octahedra. Even lower polymers are predicted by the solvated species Zr2(0R)8,(ROH)2 (model 11) and Zr(OR)4,(ROH)2 (model 111), where the zirconiuin achieves some or all (respectively) of its increase in co-ordination by bonding with alcohol molecules instead of by intermolecular bonding with allroxide groups. The degrees of polymerization of zirconium secondary alltoxides (4) i11 benzene are lower than for the normal alltoxides, whilst the tertiary allcoxides ( 5 ) are monomeric. This behavior was ascribed to the powerful steric effects of secondar)~ ancl, especially, tertiary alltoxide groups which prevent intermolecular coordination. The steric effect thus provides an entirely different process for the formation of low polymers and it was therefore iillportailt to study the polyrneric nature of zirconium oxide alltoxides involving secondary and tertiary allroxide groups. In this con~illunication we report results on the hydrolysis of zirconium isopropoxide, sec-butoxide, tert-butoxide, and tert-amyloxide under carefully controlled conditions. EXPERIMENTAL AYD RESULTS Zirconiz~m AlkoxidesThese were prepared and analyzed using previously described methods (4, 5). The secand tert-butoxides and the tert-amyloxide were redistilled in vaczlo prior to each experiment. The tetraisopropoxide was distilled in vaczlo and then crystallized froill isopropanol as the solvate Zr(OPri)4,Pr'OI-I. Ebz~lliometric StudiesThe variation of number-average degree of polymerization with degree of hydrolysis for the zirconium oxide alkoxides in their respective boiling alcohols was determined by
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