Reaction of 2-propanol with ozone in aqueous media

Abstract

This paper deals with reactions occurring in the aqueous system of 2-propanol/ozone. The considered reactions are discussed from thermodynamic and kinetic points of view. The major finding refers to the fact that 2-propanol reacts with O₃ mainly via hydride transfer: (HO)(H₃C)₂CH + O₃ → [(HO)(H₃C)₂C⁺ + HO₃^-]_cage → (HO)(H₃C)₂C⁺ + HO₃^- → (H₃C)₂CO + H₂O + O₂ Arguments supporting this proposed mechanism are: high exergonicity of reaction (ΔG = -234 kJ mol^-1 for the first two steps), low HO yield - (2.4 ± 0.5)% and high acetone yield - (87.2 ± 1.5)%. Other oxidation products detected within the system are acetaldehyde - (1.4 ± 0.1)%, formaldehyde - (4.0 ± 0.1)%, acetic acid - (2.8 ± 0.2)%, formic acid - (0.6 ± 0.2)% and hydrogen peroxide - (1.5 ± 0.1)%. The temperature dependence of the second order rate constant for the reaction 2-propanol + O₃ → products is ln k_II = 29.64-8500 × T^-1. The activation energy and pre-exponential factor derived from this relationship are (71 ± 3) kJ mol^-1 and (7.5 ± 6.4) × 10¹² M^-1 s^-1, respectively. At 23 °C, the second order rate constant is k_II = (2.7 ± 0.1) M^-1 s^-1. The low reaction rate can be explained by the transfer of one hydride ion from 2-propanol to electrophilic ozone.

Keywords: 2-Propanol; Activation energy; Hydride transfer; Ozone; Pre-exponential factor; Rate constant.