A Kinetic Study of High Pressure Aqueous Oxidations of Organic Compounds Using Elemental Oxygen

Abstract

The high pressure (< 136 atm) and high temperature (< 250°) reactions of elemental oxygen with aqueous solutions of selected soluble alcohols, ketones, and acids have been examined in detail for the first time. Saturated acids and methyl alcohol are not oxidized under the imposed conditions. The end product for the oxidation of ketones and primary alcohols is mainly carbon dioxide at 200 °C; however, appreciable yields of acids are obtained at 250 °C. tert-Butyl alcohol and secondary alcohols form the corresponding ketones which are then further oxidized. Those alcohols and ketones which were studied quantitatively all exhibited second-order kinetics, first order in organic compound and first order in oxygen. The compounds are listed below in the order of decreasing rate at 200°, ΔH≠ in kcal/mol and ΔS≠ in entropy units are noted in parentheses: 2-butanone (16.0, −25) > tert-butyl alcohol (24.2, −9) > cyclopentanone (12.4, −36) > isobutyl alcohol (21.5, −17) > sec-butyl alcohol (23.9, −15) > n-butyl alcohol > (21.3, −22) > acetone (15.1, −37). The alcohols have both higher entropies and enthalpies of activation than the ketones. Two non-chain mechanisms are proposed. (I) A ketone equilibrates with its enol which oxidizes to a metastable oxygenated intermediate. At 250° the intermediate decomposes to an acid or at 200° it is further oxidized to carbon dioxide. (II) Alcohols oxidize by an initial bimolecular mechanism to the corresponding ketone or aldehyde which may then be oxidized further.