CTAB对H_2O_2氧化抗坏血酸反应动力学的影响  

Kinetics of the Complex Reaction of Ascorbic Acid with Hydrogen Peroxide Catalyzed by CTAB

作　　者：孟祥光[1] 李建梅[1] 庞钦辉[1] 朱杰[1] 臧蓉蓉[1] 曾宪诚[1] 

机构地区：[1]四川大学化学学院,成都610064

出　　处：《物理化学学报》2005年第3期283-286,共4页Acta Physico-Chimica Sinica

基　　金：国家自然科学基金(20107004;20173038)资助项目~~

摘　　要：H2O2氧化抗坏血酸H2A的反应为一复杂过程,其过程可用下面可逆连续反应来描述:HA-+H2O2A—●→A,本文用热导式热量计研究了该复杂反应在25℃和pH=7的磷酸缓冲溶液(离子强度μ=0.1mol·L-1)以及在阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)存在下的反应动力学,获得了不同CTAB浓度下该复杂反应的表观动力学参数k1、k2和k-1.研究结果表明,表面活性剂CTAB单体分子对反应参数k-1影响不大,但却能催化第一步正向反应使k1变大,而使k2减小;在临界胶束浓度cmc附近k1达到最大值,随后又降低;低浓度胶束对k-1影响不大,而使k2增大;高浓度胶束则使k-1增大而使k2减小.低浓度CTAB胶束对A—●的活性影响不大,而高浓度CTAB胶束将较显著地促进A—●的歧化过程,减缓A—●的氧化过程.胶束的静电效应、疏水效应和局部浓聚效应是影响上述反应的重要因素.Kinetics of the reversible-consecutive reaction of ascorbic acid H(2)A with hydrogen peroxide was studied in phosphate buffer (mu = 0.1 mol center dot L-1) at pH 7 and 25 degrees C with conduction calorimeter. The apparent rate constants of this reaction, k(1), k(-1) and k(2), were measured at different concentrations of cetyltrimethylammonium bromide(CTAB). The results indicated that the apparent rate constants of the reaction, k(1), k(-1) and k(2), were remarkably affected by the cationic surfactant CTAB. ki initially increased, up to a maximum, and then fell off with increasing CTAB micellar concentration, while ki was hardly affected by CTAB of low concentrations( < 2 mmol center dot L-1) and increased when the CTAB concentration was more than 5 mmol center dot L-1; with the increasing concentration of CTAB, k(2) decreased before cmc, then increased up to a maximum, and at last fell off. CTAB micelles of low concentration had almost no influence on the activity of intermediate A(-.), but high concentrated micelles could promote the dismutation of A(-.) and inhibit its oxidation reaction. Electrostatic effect, hydrophobic effect, and local concentration effect of CTAB premicelles and micelles were the main factors influencing this reversible-consecutive reaction.

关 键 词：可逆连续反应 热动力学 抗坏血酸 胶束催化 自由基反应 

分 类 号：O643[理学—物理化学]