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.