GA-KBrO3-H2SO4体系化学振荡的研究

研究了GA(没食子酸)-KBrO_3-H_2SO_4体系的诱导期τ、振荡周期T_2与反应物起始浓度的依赖关系, 302 K时的经验式为τ=22.8 c~(-2.23)_(H_2SO_4) c~(-2.17)_(KBrO_3) c~(0.795)_(GA) (mol.dm~(-3))~(4.25)·sT_2=0.84 c~(-2.28)_(H_2SO-4)c~(-1.97)_(KBrO_3) exp{(0.000147(mol.dm~(-3))~2/c~2_(GA)}(mol.dm~(-3))~(4.25)·sτ及T_2都随~CGA的增加而增长, 这与B-Z反应中关于有机物的结论不同。用循环伏安法研究该体系的结果表明, GA在诱导期结束时就基本上都被氧化为中间物, GA并不象前人所认为的是维持振荡的物种, 实际参与振荡的是由GA生成的物质。本文还研究了Fe(Phen)_3~(2+)对GA-KBrO_3-H_2SO_4体系振荡的影响, 发现Br~-振荡行为随Fe(Phen)_3~(2+)的浓度而变。低~CFe(phen)_3~(2+)时,Br~-的振荡行为与GA-KBrO_3-H_2SO_4体系的基本相似, 其特征是每个振荡周期内, Br~-振荡脉冲发生前是逐渐积累的。随着~CFe(phen)_3~(2+)的增大, Br~-出现另一特征的振荡行为, 在每个振荡周期内, Br~-振荡脉冲发生前是逐渐减小。我们认为, GA-KBrO_3-H_2SO_4-Fe(Phen)_3~(2+)体系的振荡不能单一地用OKN机理加以解释, 它可能是两套振荡机理耦合的振荡。

STUDY ON THE OSCILLATION OF GA-KBrO3-H2SO4 SYSTEM

The relations between preoscillatory period τ as well as oscillating period T_2 and each reactant initial concentration have been studied. The formula at 302K are:τ=22.8 c~(-2.23)_(H_2SO_4) c~(-2.17)_(KBrO_3) c~(0.795)_(GA) (mol.dm~(-3))~(4.25)·sT_2=0.84 c~(-2.28)_(H_2SO-4)c~(-1.97)_(KBrO_3) exp{(0.000147(mol.dm~(-3))~2/c~2_(GA)}(mol.dm~(-3))~(4.25)·sThe major conclusions are:(1): τ and T_2 decrease while increasing concentrations of KBrO_3 and H_2SO_4, which is similiar to classical BZ systems(1).(2):τ and T_2 increase with increasing the concentration of GA (Gallic Acid), which is contrary to the classical BZ systems. This implies that organic subtrate GA plays special rule in the oscillation of GA-KBrO_3-H_2SO_4 system.With the method of CV(Cyclic Voltammgrams) the effects of GA in this system have been studied. It has been found that when preoscillatory period ends GA is almost exhausted. In other word, It is impossible to hold oscillation of this system with GA subtrate. In fact, GA subtrate only supplies the substances that hold oscillation of this system. Therefore, The explanation of OKN mechanism~([4]) to this system is not available.It has been studied that the effects of Fe(Phen)~(2+)_3 on the oscillation of GA-KBrO_3-H_2SO_4 system. It has been found that the oscillating behavior of Br~- ion will change with the concentration of Fe(Phen)~(2+)_3, ie, at low concentration of Fe(Phen)~(2+)_3 the behavior of Br~- ion is similiar to that of GA-KBrO-H_2SO_4 system, at high concentration of Fe(Phen)~(2+)_3 the behavior of Br~- ion is contrary to that GA-KBrO_3-H_2SO_4 system. The significant differenc es are that before the oscillating pulse of Br~- ion during each oscillating period the former is gradual increase of Br~- ion concentration and the latter is gradual decrease of Br~- ion concentration. The kind of phenomenon in chemical oscillations is first discovered. This implies that the oscillation of GA-KBrO_3-H_2SO_4-Fe(phen)~(2+)_3 system cannot be explained with OKN mechanism. The oscillation is phenomenally couple of two different oscillations.