Study of intermolecular interactions in an equilibrium system in the catalytic transesterification of esters 3. Interaction of tetrabutyl titanate with alcohols from ir and NMR spectroscopic data

The reactions of tetrabutyltitanate (TBT) with alcohols have been studied using IR, Raman, and NMR spectroscopy. It has been shown that TBT is associated and has a centrosymmetrical structure. In nonpolar solvents (CCl4, cyclohexane) the associates do not break down on dilution. In the presence of butanol breakdown of the associates occurs accompanied by a reduction in the number, and even the disappearance, of bridging alkoxy groups.13C NMR results show that in mixtures of TBT and alcohols two types of exchange reaction take place simultaneously: between terminal and bridging alkoxy groups, and between TBT and the alcohol. In the case of n-BuOH the first type of exchange is retarded as the temperature is reduced to 283 K but the second is unaffected right down to 213 K. IR results show that alcohols form complexes with TBT in which the alcohol is bonded by a H-bond to the oxygen of the alkoxy group of the TBT and by the oxygen atom to the Ti of a second molecule of TBT. For the exchange reaction between TBT radicals and n-C7H15OH in a binary mixture of 1∶1 composition at 293 K, IR spectroscopy showed the degree of conversion in terms of alcohol to be 65% and the equilibrium constant Ke= 3.4. For MeOH in CCl4 solution the conversion amounted to around 100%.