Methanesulfonyl Iodide

Methanesulfonyl iodide is produced in aqueous solutions from the reaction of triiodide with methanesulfinate. Dichroic crystals of (CH3SO2I)4·KI3·2I2 are formed from KI/I2 solutions with high concentrations of CH3SO2 –, while dichroic crystals of (CH3SO2I)2·RbI3 are formed from RbI/I2 solutions. X-ray crystallography of these two compounds shows that the CH3SO2I molecules coordinate through their oxygen atoms to the metal cations and that the S–I bond length is 2.44 Å. At low concentrations of CH3SO2 –, the solutions remain homogeneous and the sulfonyl iodide is formed in a rapid equilibrium: CH3SO2 – + I3 – ⇌ CH3SO2I + 2I–, K MSI = 1.07 ± 0.01 M at 25 °C (μ = 0.1 M, NaClO4). The sulfonyl iodide solutions display an absorbance maximum at 309 nm with a molar absorptivity of 667 M–1 cm–1. Stopped-flow studies reveal that the equilibrium is established within the dead time of the instrument (∼2 ms). Solutions of CH3SO2I decompose slowly to form the sulfonate: CH3SO2I + H2O → CH3SO3 – + I– + 2H+, k hyd. In dilute phosphate buffer, this decomposition occurs with k hyd = 2.0 × 10–4 s–1; the decomposition rate shows an inverse-squared dependence on [I–] because of the K MSI equilibrium.