Mechanistic Studies in Tellurium Chemistry

Abstract

The reduction of p-ethoxyphenyltellurium trichloride by sodium sulphite and metabisulphite has been investigated. The reactions have stoichiometries of one mol of p-EtOPhTeCl₃ to 1.5 and 0.75 mol of SO₃²⁻ and S₂O5²⁻ respectively. The paths of the reaction mechanisms with both reducing agents are almost identical. The reductions are acid catalysed and proceed via a common two-electron process. Both systems obey a second-order rate law. The percentage of water in the mixed solvent used plays a role in deciding the rate-determining step of the reaction. A mechanism for the above reactions is suggested. The reduction of p-EtOPhTeCl₃ by chromous and vanadous ions was also investigated. The stoichiometric measurements show that one mol of p-EtOPhTeCl₃ is equivalent to three mols of Cr(II) or V(II). The rates of the overall reactions are second order. The catalysis by chloride ion of the reactions suggests that they are inner-sphere processes. The chloride group which acts as a bridge is brought in by the tellurium species. The interpretation is that tellurium in p-EtOPhTeCl₃ prefers an inner-sphere mechanism for its reactions. The solvolysis of p-EtOPhTeCl₃ in aqueous and non-aqueous media has been investigated. The study shows that the solvolysis is a reversible, acid catalysed reaction which is agreed to be associative. The number of chloride ligands on tellurium replaced depends upon the hydrogen and chloride ion concentrations in the solution, and also upon the size of the substituent. The rate of solvolysis in aqueous media is faster than in non-aqueous media and varies in the order of trichloride > tribromide > triiodide.