The decomposition of hypochlorous acid in the neutral pH region was studied in 1.0 M NaClO4 from 15 to 50 °C. The pKa of HOCl was also determined under these conditions. Hypochlorous acid has a maximum decomposition rate at pH 6.89. The decomposition is a third-order process. The values of ΔH‡ and ΔS‡ are 64.0 ± 0.6 kJ/mol and -67 ± 2 J/mol K, respectively. A mechanism for the decomposition of HOCl is proposed involving C12O.H2O and C1O2- as intermediates. Rate constants for the rate-determining steps of the mechanism are presented. Above pH 6, the rate-determining step is proposed to be as follows: OC1− + C12O.H2O → HCl2O2- + HOCl. Below pH 6, this process is proposed to be in competition with a parallel pathway: HOC1 + C12O.H2O →H2C12O2 + HOCl. The proposed mechanism was tested by mathematical simulation of the experimental data using the GEAR algorithm. The simulation gives additional support for the proposed mechanism.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry