The absorption spectra in a large range of concentrations show that the reactions of iodate with iodine in 96% sulfuric acid produce (IO) HSO4, I-3(+) and I-5(+), just like in the pure 100% acid. We discovered that, in 96% H2SO4, these reactions also produce I2O which is not formed in the pure acid. I2O is an important intermediate of reactions in diluted sulfuric acid, including the Bray-Liebhafsky reaction, but it had never been observed directly because of its very high reactivity. The equilibrium constants of the reactions producing these four compounds were determined. (C) 2017 Elsevier B.V. All rights reserved.