The gas-phase oxidation of acetic acid by nitrogen dioxide

Abstract

This thesis presents the results of a preliminary investigation of the gas-phase oxidation of acetic acid by nitrogen dioxide and is an example of a chemical process in which nitration competes with destructive oxidation of an organic molecule. The products of the reaction are CO, CO ₂, CH₃NO₂, NO, H₂O and possibly small quantities of N₂O and N₂. Carbon and nitrogen balances within 95% were obtained, about as expected when the analytical errors are considered. Small quantities of other products cannot be excluded. An induction period of ~900 seconds was observed at low temperature (~190°C) but no induction period was observable at 253.5°C. The induction period at low temperature indicates a complicated reaction mechanism. The rate using CH₃COOD indicated that carboxyl hydrogen abstraction reactions were kinetically important. For the same initial pressure of acetic acid and NO₂ the total pressure rise is not greatly changed by adding NO, or by using D- acid as the reactant. The reaction is auto catalysed by NO. With the techniques used the reaction rate was found to depend on the CH₃COOH and NO₂ concentrations but accurate orders could not be determined. As will be seen in the result section the method used is not suitable due to concurrent decomposition of NO₂. Although a final complete mechanism cannot be written at this time, the partial one discussed in this thesis has been suggested because it explains the formation of products and stimulates further study.