GAS-PHASE STUDY OF THE REACTION SYSTEM ME3SII+HBR-REVERSIBLE-ME3SIBR+HI - EQUILIBRIUM AND THE BOND-DISSOCIATION ENERGY D(ME3SI-I)

The title reaction has been studied in the temperature range 290-390°C (but mainly at 321°C) by a UV spectrophotometric method. The reaction reaches a steady state, and experiments starting from both sides over a range of partial pressures of reactants indicate that equilibrium is reached. At 321°C the equilibrium constant is 12.2 ± 2.4. The third-law enthalpy change, ΔH°298.15, is -13.4 ± 1.2 kJ mol-1. From the literature value for ΔHf°(Me3SiBr) a value of ΔHf°298.2(Me3SiI(g)) = -218 ± 4 kJ mol-1 is derived. Additionally, from an estimate of ΔHf° (Me3Si·), the bond dissociation energy D(Me3Si-I) = ca. 322 kJ mol-1 (76.9 kcal mol-1) may be deduced. The kinetics of this system are discussed briefly. © 1979 American Chemical Society.