Nature of the Colour-forming Species in Peroxy Titanium Sulphate

Abstract

ALTHOUGH titanium is determined colorimetrically in aqueous sulphuric acid medium in presence of excess of hydrogen peroxide, the nature of the colour-forming species is not known definitely. Schwarz¹ suggested that the colour was due to the peroxo–disulphato titanate anion [O₂Ti(SO₄)₂]²⁻. On the other hand, Jahr² and later Gastinger³ considered that the colour of the compound was due to the peroxy titanyl cation [TiO₂ aq.]²⁺, and suggested the following equilibrium in solution: Schaeppi and Treadwell⁴ attributed the colour bo O₂TiSO₄ or [O₂Ti(SO₄)₂]²⁻, whereas Babko and Volkova⁵ represented the coloured complex ion as [Ti(H₂O₂)]⁴⁺. Mori, Shibata, Kyuno and Ito⁶ regarded the coloured species as [TiO₂ aq.]²⁺ or [Ti(OH)₂ (H₂O)(H₂O₂)]²⁺, assuming the co-ordination number of titanium to be four. Thus, a variety of constitutions has been proposed to explain the colour-forming species of the titanium complex, based on the investigations carried out in dilute sulphuric acid medium, but the complex has not been isolated so far.