Fourier-transform infrared study of the oxidative thermolysis of tetramethyltin in the temperature range 533–613 K

Abstract

The kinetics of the oxidative thermolysis of tetramethyltin have been investigated in the temperature range 533–613 K using Fourier-transform infrared spectroscopy. Even in the presence of a large molar excess of oxygen (molar ratio Me₄Sn : O₂≈ 1 : 9), the gaseous reaction products were methane (2.6 mol) and carbon dioxide (1.4 mol). Small amounts of transient methanol and formaldehyde were also observed in the gas phase. The disappearance of tetramethyltin follows zero-order kinetics, with rate constants varying from 1.19 × 10^–8 mol dm^–3 s^–1 at 533 K to 29.9 × 10^–8 mol dm^–3 s^–1 at 613 K. The activation energy is determined to be 116(6) kJ mol^–1. The data are interpreted in terms of a surface-mediated process. The rate-determining step is proposed to be the dissociative chemisorption of a tetramethyltin molecule at two adjacent surface oxygen sites, giving a surface trimethylstannyloxy, 1-OSnMe₃, species and surface methoxide. Subsequently, the predominant process is the stepwise electrophilic cleavage of the tin–carbon bonds of the surface trimethylstannyloxy species by surface hydroxyl groups producing methane. Carbon dioxide is produced by the oxidation of the surface methoxide.