Abstract:

The oscillation reaction in itaconic acid-BrO_3~-Mn~(2+) investigated. This paper deals with the behavior of this oscillating reaction. The absorption of light at the two wavelengthe λ=310 nm and λ=475 nm oscillated in phase. A mechanism for this oscillating reaction was suggested. The mechanism is composed of three main processes:Process A: Consumption of bromide and formation of Br_2IA. Process B: Autocatalytic formation of bromous acid with a rapid oxidation of Mn~(2+) to Mn~(3+). Process C: Generation of bromide and reduction of Mn~(3+).
The time of initiation (τ_i) can be divided into two parts τ_(i1) and τ_(i2), is determined by the process A (i.e the rate of bromide consumption), as the consumption of BrO~-_3 and H_2SO_4 is increased, the rate of Br~- consumption is increased, τ_(i1) therefore, must be decreased. τ_(i2) is determined by process A, B and C. It is decreased by the acceleration of process B, C and increased by increased the rate of bromide consumption. As a result, at higher concentrations of H_2SO_4 and BrO~-_3, τ_(i2) will be increased, τ_(i2) will change in opposite direction by increase of the concentration of Mn~(2+). High [Br~-] can increase process C, then τ_(i2) decreases.
Based on the experiments, the following relationship can be obtained:
1/τ_(i1)=k_1[BrO~-_3]^(0.92)_0[H_2SO_4]~(1.63)_0[Br~-]~(-0.56)_0[IA]~(0.25)_0 exp(-E_(i1)/RT)
1/τ_(i2)=k_2[BrO~-_3]~(-0.53)_0[H_2SO_4]~(-0.50)_0[Br~-]~(3.28)_0[IA]~(0.25)_0[Mn~(2+)]~(0.78)_0 exp(-E_(i2)/RT)
E_(i1)=66.9 kJ.mol~(-1) E_(i2)=112 kJ.mol~(-1)
The oscillation period is mainly effected by H_2SO_4 and BrO~-_3. The polt of lnτ_p vs ln[H_2SO_4] is not a straight line.
1/τ_p=κ[BrO~-_3]~(0.44)f_(H_2SO_4)exp(-E_p/RT) E_p=100 kJ.mol~(-1)
It was also found that τ_(i2) and τ_p decrease with the increasing of concentration of glucose.