Effect of water on the titanium complexes in methanolic solutions containing hydrogen chloride

Abstract

Publication costs assisted by the North American Rockwell Corp.The electrochemical behavior of the Ti(III) |Ti(IV) couple was investigated in methanol solutions containing 0.02-0.22 M chloride ion and 0.02-7.0 M water. The presence of two electrochemically distinct Ti(III) complexes was observed and the mechanism of the electrode processes was shown to consist of the reactions e-+ Ti(IV) ^Ti(IH)(a) (E1/2 ~-0.4 V); Ti(III)(a) + H20 ^Ti(III)(b) + C1"(K); Ti(III)(b)T i(IV) + e~( E1/2 ~0.1 V). The equilibrium constant K was evaluated from pulse polarographic and cyclic voltammetric data to be 0.029 ± 0.006. The reaction rates have been calculated from the kinetic contribution to the kinetic polarographic current, and the parameters ks and a of the first electron transfer reaction were estimated from pulse polarographic data. Combining these results with electron spin resonance measurements, the species Ti(III)(a) comprised [TiCl2(CH3OH)4]+ and [TiCl(CH3OH)5]2+. These two species equilibrate rapidly on an electrochemical time scale. Ti(III)(b) was assigned the structure [TiCl(CH3OH)4H20]2+. In addition, the Ti(IV) in methanol containing more than 0.3 M H20 contains at least one more water ligand than the Ti(III), based on the negative shift of the half-wave potential with the concentration of water.