Abstract
Abstract Thermodynamic parameters of four elementary steps of hydrolysis of TiCl4, viz. formation of (i) TiCl3(OH), (ii) TiCl2(OH)2, (iii) TiCl(OH)3, and (iv) Ti(OH)4 as well as condensation of the hydroxides giving rise to titanoxanes (Cl4âx(OH)xâ1TiâOâTiCl4âx(OH)xâ1 (x = 1â4)) have been studied using B3LYP/6-311++G(d,p) level of DFT. The first elementary step required the highest free energy of activation (ÎG# = 22.8 kcal molâ1) as well as the highest enthalpy of activation (ÎH# = 16.9 kcal molâ1), while subsequent steps showed a decrease in both ÎG# and ÎH#, reaching the lowest value of ÎG# = 20.4 kcal molâ1 and ÎH# = 11.9 kcal molâ1 for the fourth step. Condensation reactions were triggered by OâH···OâH hydrogen bonding in pre-reactant complexes. The ÎG# of the condensation of mono-, di-, tri-, and tetrahydroxides are 23.0, 17.1, 20.8, and 14.5 kcal molâ1, respectively. Thus gas phase hydrolysis of TiCl4 and subsequent condensation of TiCl4âx(OH)x are feasible at low temperature and higher order condensation would lead to the formation of TiO2. TiCl4 showed higher Lewis acid character to a water dimer than a water molecule as their respetive interaction energies were â4.8 and â14.2 kcal molâ1. Coordination of the water dimer to titanium has significant effect on lowering the activation bariers of the hydrolysis reactions and therefore the amount of water vapor in the gas phase reaction is critical to the overall rate of the reaction.
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