Thermal Ion-Molecule Reactions in Oxygen-Containing Molecules. Condensation-Elimination Reactions in Dimethyl Ether-Trioxane Mixtures

Abstract

Abstract Thermal ion-molecule reactions in dimethyl ether - trioxane mixtures have been studied with a time-of-flight mass spectrometer. The appearance potentials and ionization efficiency curves of product and major fragment ions were measured by an RPD technique. The product ions, having a linear structure such as CH3OCH3(CH2O)n +, CH3OCH3(CH2O)nH+, CH3OCH2(CH2O)n +, and CH3OCH2(CH2O)nH+ (n = 1 - 3), are formed by condensation-elimination reactions of CH3OCH3 + and CH3OCH2 + with trioxane. The formation of the product ions involves the dissociation of an intermediate-complex, which has a linear structure. It was found that homo-elimination of neutral products occurs preferentially from the trioxane molecule site in the complex. Extensive scrambling does not take place. The rate constants for the ions formed in dimethyl ether (or dimethyl-d6 ether) - trioxane mixtures are obtained, and a small isotope effect is observed. The rate constants of the condensation-elimination reactions of CH3OCH2+ with trioxane are compared with those with dimethyl ether.