维生素C氧化反应的研究——H2O2-Cu2+-磷酸体系中的反应动力学

Study of Ascorbic Acid Oxidation Reaction——Reaction Kinetics with the H2O2-Cu2+-Phosphoric Acid System

维生素C(抗坏血酸H2 A)的氧化反应与生理过程密切相关.在Cu2+离子催化下氧气氧化H2 A的反应动力学已有不少报道.一般认为在反应过程中会有H2 O2出现,因此H2 O2对H2 A的氧化作用就引起了人们的兴趣.Mario与Pispisa用生物学上酶催化模式对H2 O2氧化H2 A的反应进行了研究,而对其反应动力学方程和机理讨论得不多.Skurlatov在酸性条件下得到如下的反应速率方程.Υ=k[Cu2+][H2 A]1/2[H2 O2]1/2/[H+](1)并讨论了相应的反应机理.由于生物体的体液大多近于中性,我们在弱酸性条件下,对H2 O2-Cu2+-磷酸体系中H-2 A的氧化反应动力学进行研究,得到与式(1)不同的反应速率方程:Υ=k[Cu2+]1/2[H2 A][H2 O2]1/2[H+](2)对相应的反应机理亦进行了讨论.

The oxidation of ascorbic acid(H2A)by H2O2 in the presence of cupric ions hasbeen investigated.The reaction was followed by direct spectrophotometric measurementof the unchanged acid.The experimental data were treated with a PC-8001 microcomputer by means ofnonlinear optimum initiation method to obtain the rate equation,i.e.r=k[H2A][Cu2+]1/2[H2O2]1/2/[H+],at pH=5.40—6.00,[H2A]=5—8×10-5 mol·dm-3,[Ca2+]=0.25—1.5×10-6mol·dm-3,[H2O2]=0.5—2.5×10-3mol·dm-3.The Arrhenius activation energy of this reaction is 65.25 kJ.mol-1.A chain mechanism for catalytic oxidation of ascrobic acid with hydrogen peroxidein relation to our experimental condition is proposed as Shown in the Chinese Text.