INFLUENCE OF MEDIUM pH AND SOME ADDITIVES ON KINETICS AND MECHANISM OF H2O2 DECOMPOSITION IN AQUEOUS SOLUTIONS

摘要

Taking into consideration the fact that H2O2 is a weak acid and NaOH - a strong base and the substitution of the more reactive HOO~2 by O_2~(2-) towards H2O2 at n=[H2O2]_0/ [NaOH]_0 < 0.5, a correct approach is used to establish the reaction rate law.It is shown that when n=2=const the absolute concentrations of both reagents practically do not act on medium pH. In such conditions the reaction is first order with respect to each component. In alkaline medium the reaction has maximum value at pH=11.3.The detailed study of EtOH + TEMPO mixture and acrylamide (AA) on the reaction rate showed that in both cases the oxygen evolvement continuously runs while TEMPO is being consumed and AA polymerises to a small degree.The general conclusion is: the reaction occurs by two parallel mechanisms: nonradical (= 84%) and with radical formation (≌ 16%). The E_a of both ways has the same value: 55±3 kJ/mol. It is assumed that the difference between both rates is conditioned by the difference in the activation entropy value. A mechanism is proposed.Taking into consideration literature data according to which DMSO easily reacts with HO~· free radicals in strong acidic medium, it has been studied DMSO action on H2O2 decomposition in alkaline medium. It is established that DMSO favours H2O2 decomposition catalysing its heterolysis.