Reaction of 1-propanol with Ozone in Aqueous Media

Abstract

The main aim of this work is to substantiate the mechanism of 1-propanol oxidation by ozone in aqueous solution when the substrate is present in large excess. Further goals are assessment of the products, their formation yields as well as the kinetic parameters of the considered reaction. The reaction of ozone with 1-propanol in aqueous solution occurs via hydride transfer, H-abstraction and insertion. Of these three mechanisms, the largest share is for hydride transfer. This implies the extraction of an hydride ion from the activated C−H group by O3 according to reaction: (C2H5)(H)(HO)C−H + O3 → [(C2H5)(H)(HO)C+ + HO3−]cage → (C2H5)(H)(HO)C+ + HO3−. The experimentally determined products and their overall formation yields with respect to ozone are: propionaldehyde—(60 ± 3)%, propionic acid—(27.4 ± 1.0)%, acetaldehyde—(4.9 ± 0.3)%, acetic acid—(0.3 ± 0.1)%, formaldehyde—(1.0 ± 0.1)%, formic acid—(4.6 ± 0.3)%, hydrogen peroxide—(11.1 ± 0.3)% and hydroxyl radical—(9.8 ± 0.3)%. The reaction of ozone with 1-propanol in aqueous media follows a second order kinetics with a reaction rate constant of (0.64 ± 0.02) M−1·s−1 at pH = 7 and 23 °C. The dependence of the second order rate constant on temperature is described by the equation: l n   k I I = ( 27.17 ± 0.38 ) – ( 8180 ± 120 ) × T − 1 , which gives the activation energy, Ea = (68 ± 1) kJ mol−1 and pre-exponential factor, A = (6.3 ± 2.4) × 1011 M−1 s−1. The nature of products, their yields and the kinetic data can be used in water treatment. The fact that the hydride transfer is the main pathway in the 1-propanol/ozone system can probably be transferred on other systems in which the substrate is characterized by C−H active sites only.