ChemInform Abstract: Kinetics of Hydrolysis of Iodine Monochloride Measured by the Pulsed-Accelerated-Flow Method (PAF).
Abstract
The hydrolysis of ICl in water to give HOI and Cl- is shown to be 5-6 orders of magnitude faster (k(H2O) = 2.4·106 s-1at 25 °C, μ = 0.50) than that of Cl2 and I2, a difference, which is attributed to the dipole moment and polarizability of ICl and to the ease of valence shell expansion of iodine.
ChemInform Abstract
The hydrolysis of ICl in water to give HOI and Cl- is shown to be 5-6 orders of magnitude faster (k(H2O) = 2.4·106 s-1at 25 °C, μ = 0.50) than that of Cl2 and I2, a difference, which is attributed to the dipole moment and polarizability of ICl and to the ease of valence shell expansion of iodine. Reaction rates of that order can be measured by the PAF method, which extends accessible first-order rate constants by a factor of 103 beyond the limit of stopped-flow methods. OH- accelerates the rate of hydrolysis (k(OH) = 4.5·109 M-1 s-1. An acceleration of the same order is also observed in the presence of buffers as H2PO4-/H2PO42- and HCO3-/CO32-. It is proposed that two reactive ICl(aq) species, H2OICl and ICl, are in rapid equilibria in aqueous solution. ICl is so reactive that it is unselective and reacts with the buffer species and OH- at the diffusion limit (7·109 M-1 s-1. H2OICl reacts with OH- (3.9·109 M-1 s-1 by proton transfer to form H2O and HOICl-. The HOICl- intermediate rapidly loses Cl- to give HOI.
