Raman Spectrometric Study of the Thermal Decomposition of Aqueous Tri-and Tetrathionate

The decomposition of 0.25 M trithionate and 0.5 M tetrathionate was followed at 20, 35, 50 and 70°C. During the reaction tri-and tetrathionate interconvert. Thiosulfate is observed as a prominent intermediate. The end products are elemental sulfur, sulfate, disulfite and bisulfite. The decomposition of trithionate follows a first order reaction with a rate constant of 1.4 × 10−1 at 70°C. In tetrathionate the reaction is preceded by an induction period and is second order, with a rate constant of 4 × 10−3 at 20°C. In both systems sulfate is formed in a first order reaction with a rate constant of 3.1 × 10−3 hrs−1 at 20°C. The decomposition mechanism in both systems involves the hydrolysis of trithionate.